ALEXKOR RMC POOLING AND SHARING JV · ALEXKOR RMC POOLING AND SHARING JV ORANGE RIVER COMPONENT OF MARINE DIAMOND MINING LICENCE 554 MRC ENVIRONMENTAL DESCRIPTION AND ESTUARINE REHABILITATION

A L E X K O R R M C P O O L I N G A N D S H A R I N G J V

ORANGE RIVER COMPONENT OF MARINE DIAMOND MINING LICENCE 554 MRC

ENVIRONMENTAL DESCRIPTION AND ESTUARINE REHABILITATION MEASURES

Compiled by:

P.D. Morant

Placer Resource Management (Pty) Ltd.

33 Quarter Deck Road

Kalk Bay

7975

October 2017

ALEXKOR RMC POOLING AND SHARING JV

ORA NGE R I VER COMPONENT OF MA RINE DIAMOND MI NING L ICENCE 554 MRC ENVIRONMENTA L DESCRIPT ION A ND ESTUA RINE REHA BI L I TA T I ON MEA SURES

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EXPERTISE Mr Patrick Morant is an M.Sc. graduate in Environmental Studies from the University of Cape Town. He is a Registered Professional Natural Scientist (Registration No. 401514/83) of 34 years standing. He headed the CSIR's Estuarine and Coastal Research Unit and has been extensively involved in coastal environmental management and in environmental impact assessment in southern and western Africa.

DECLARATION OF INDEPENDENCE

I, Patrick Morant, certify that I have no financial or other material interest in the outcome of this study. I am an independent consultant and do not represent the interests of any party involved.

P.D. Morant

M.Sc., Pr.Sci.Nat.


ORA NGE R I VER COMPONENT OF MA RINE DIAMOND MI NING L ICENCE 554 MRC ENVIRONMENTA L DESCRIPT ION A ND ESTUA RINE REHA BI L I TA TI ON MEA SURES

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EXECUTIVE SUMMARY The Orange River mouth has been subject to anthropogenic impacts since the European settlement of South Africa. Since the early Twentieth Century, when diamond mining began on both sides of the Orange River mouth, attempts have been made to manage the system. These activities included breaching the mouth after natural closure, building structures in the flood plain, e.g. sewage oxidation ponds, berm walls to protect farm land and a golf course, and isolating approximately one third of the estuary from the active system by an embankment to manage a mosquito problem. This embankment also prevents the natural migration of the estuary mouth to its southern limit.

In parallel with these developments in and around the estuary, the flow regime of the Orange River has been substantially altered by the construction of 23 major impoundments and numerous smaller dams. The consequence has been that fewer smaller floods reach the estuary and the base flow in the dry season (winter) has become elevated as a result of hydroelectric power generation. The Orange River mouth has become more estuarine in nature as a result of these changes in flow. Historically, the estuary used to close naturally every two to three years, back-flood the saltmarshes with low-salinity water for a few weeks and then either breach naturally or the mouth would be opened artificially. This cycle of events maintained the saltmarshes in good health. Since 1993 the mouth has only closed very briefly on two occasions with the result that the salt marsh has undergone degradation.

Since designation as a Wetland of International Importance in terms of the Ramsar Convention in 1991 and 1995 by South Africa and Namibia respectively, the precipitous decline in bird populations and the desiccation of the southern saltmarsh has led to the Ramsar Site being placed on the Montreux Record. The Orange River Mouth Strategic Estuarine Management Plan has as one of its key objectives the restoration of the River Mouth Ramsar Site to meet the Ramsar Convention criteria that led to its original designation. The PSJV is committed to the restoration of the environment affected by both current and historic diamond mining operations. In so doing PSJV has to contribute to the restoration of the presently desiccated saltmarsh on the south side of the estuary as well as the system as a whole. The key remedial actions required to be undertaken by PSJV are:

Removal of historic scrap material from the beach berm at the Orange River Mouth which interferes with the natural migration of the mouth (yellow circle on Figure 1);

Removal of the road embankment which currently isolates approximately one third of the saltmarsh area from the active estuarine system (indicated in yellow on Figure 1);

Rehabilitate the area formerly occupied by the sewage oxidation ponds in the floodplain (yellow square on Figure 1);

Consider the removal of the dyke at Dunvlei and to re-open the river channel running along the south bank to facilitate river flow into the desiccated saltmarsh (red line on Figure 1); and

Control dust generated by the slimes dam within the mine. This dust smothers estuarine vegetation.

In addition PSJV should actively participate in the implementation of the Orange River Mouth Ramsar Site Strategic Estuarine Management Plan.



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Figure 1: Map indicating structures to be removed during remedial action by PSJV.



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Details of the remedial actions required to address the removal of the structures currently affecting the function of the saltmarsh are presented in Section 5 of this report.

Should the PSJV successfully implement the remedial actions required to remove the scrap machinery from the beach berm, remove the road embankment through the saltmarsh, and rehabilitate the former sewage oxidation pond site it will have made a significant contribution to the rehabilitation of the Orange River Mouth Ramsar Site. However, full recovery of the degraded areas depends on managing the estuary mouth closure regime such that closure occurs for a period of 4 – 6 weeks every 2 - 3 years. This latter is the responsibility of the authorities (e.g. DEA, DENC) charged with implementing the Orange River Mouth Estuarine Management Plan.

The combined effect of the PSJV’s remedial actions and the correct mouth closure/back-flooding regime could result in the recovery of the Orange River Estuary such that it is removed from the Montreux Record and restored to full Ramsar Site status.



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CONTENTS 1. INTRODUCTION 10

1.1 BACKGROUND 10

1.2 ORANGE RIVER MOUTH ESTUARINE MANAGEMENT PLAN 11

2. PHYSICAL COMPONENTS 14

2.1 GEOMORPHOLOGY 14

2.1.1 Riparian Zone 14 2.1.2 Estuarine zone 14 2.1.3 Estuary mouth 14 2.1.4 Sediments 20

2.2 HYDROLOGY 21

2.2.1 River inflows 21 2.2.2 Mouth closure 22 2.2.3 Tidal range 23 2.2.4 Salinity and circulation 25

3. BIOLOGICAL COMPONENTS 26

3.1 RIPARIAN VEGETATION 26

3.2 ESTUARINE VEGETATION 27

3.2.1 Overview 27 3.2.2 Habitat types and their ecological function 29 3.2.3 Desiccation of the supratidal saltmarsh 35

3.3 INVERTEBRATES 36

3.3.1 Zooplankton 37 3.3.2 Hyperbenthos 37 3.3.3 Macrozoobenthos 37

3.4 FISHES 37

3.4.1 Introduction 37 3.4.2 Fish fauna 38 3.4.3 Flow regime and mouth condition 41

3.4.3.1 Flow regime 41

3.4.3.2 Mouth condition 41

3.4.4 The Orange River and Estuary as fish habitat 42 3.4.5 Value of the Orange River Estuary-associated fishery 42

3.5 BIRDS 42

3.5.1 Introduction 42 3.5.2 Population size and structure 43 3.5.3 Habitat utilization 46 3.5.4 Conclusions 48

3.6 MAMMALS 48



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4. CONSERVATION STATUS 49

4.1 WETLAND OF INTERNATIONAL IMPORTANCE (RAMSAR SITE) 49

4.2 ESTUARINE MANAGEMENT PLAN 49

4.3 OWNERSHIP AND PROTECTION STATUS 50

5. REHABILITATION OF THE SALTMARSH 51

5.1 INTRODUCTION 51

5.2 RESTORING THE CONNECTION WITH THE ESTUARY BASIN 51

5.2.1 Present condition 51 5.2.2 Remedial action 54

5.2.2.1 Removal of scrap machinery from the beach berm at the Orange River Mouth 54

5.2.2.2 Removal of the road embankment 56

5.2.2.3 Rehabilitation of the location of the former sewage oxidation ponds 56

5.2.2.4 Back‐flooding 56

5.2.3 Impact Assessment 58 5.2.3.1 Scrap machinery in the beach berm at the Orange River Mouth 58

5.2.3.2 Removal of road embankment 59

5.2.3.3 Rehabilitation of former sewage oxidation ponds site 60

5.3 RESTORING THE UPSTREAM RIVER CONNECTION 62

5.3.1 Present situation 62 5.3.2 Remedial action 62

5.4 DUST CONTROL 63

5.4.1 Remedial action 63 5.5 CONCLUSION 64

6. REFERENCES 65

APPENDIX 1: METHOD FOR SIGNIFICANCE DETERMINATION 68



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Tables

Table 1.1: Management action plans for the restoration of the saltmarsh 13

Table 3.1: Changes in habitat cover of the Orange River Estuary 28

Table 3.2: Macrophyte species and associated habitats recorded in 2012 28

Table 3.3: Summary of events affecting the saltmarsh at the Orange River mouth. 35

Table 3.4: A list of all 36 species and 19 families recorded in the Orange / Gariep Estuary 40

Table 3.5: Classification of South African fish according to their dependence on estuaries 41

Table 3.6: Water bird species recorded at the Orange River Estuary, 2012 44

Figures

Figure 1.1: The Orange River component of Marine Diamond Licence 554 MRC running from Arrisdrif

to the sea. 10

Figure 1.2: Riverine habitat upstream of the Sir Ernest Oppenheimer Bridge proposed for inclusion in

the Ramsar Site. 11

Figure 2.1: The Orange River Estuary. The red line is the 5 m a.m.s.l. contour demarcating the

estuarine functional zone. 15

Figure 2.2: Orange River mouth on 19 June 1966 showing road embankments isolating the saltmarsh

on the southern (right) side of the system. 16

Figure 2.3: Flood protection works and Dunvlei cut‐off dykes 17

Figure 2.4: Extreme northward migration of the Orange River mouth to the Namibian bank on 2

November 1986 18

Figure 2.5: The Orange River mouth on 25 July 2017 19

Figure 2.6: Scrap machinery (“Detroit riprap”) used to anchor the seaward end of the road

embankment built in 1964. The scrap limits the southward migration of the estuary

mouth. 19

Figure 2.7: Building damaged by storm waves. June 2017. The beach in front of the building appears

to be sand‐deficient as a consequence of the coffer dams restricting the northward

movement of sand towards the Orange River Mouth. 20

Figure 2.8a and 2.8b: Extensive flooding of the estuarine basin during the prolonged mouth closure in

the spring of 1993. a) View from north bank with beach berm on right; b) view towards

Alexander Bay town (Photographs: P. Morant). 22

Figure 2.9a and 2.9b: Breaching of the estuary mouth after prolonged closure, Spring 1993. a)

Bulldozer preparing to cut channel opposite the road embankment (top photograph); b)

Sea overtopping breach in beach berm (bottom photograph). (Photographs: P. Morant). 24

Figure 3.1: Riparian thicket lining the river banks at Arrisdrif. 26

Figure 3.2a and 3.2b: Seasonally flooded sandbanks used as pasture near Brandkaros. 27



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Figure 3.3: The Sir Ernest Oppenheimer Bridge which approximately marks the boundary between the

riparian and estuarine vegetation. 27

Figure 3.4: Habitats and vegetation of the Orange River Estuary 30

Figure 3.5: Sedge‐lined channel near Dunvlei. The open water in the channel serves as habitat for

phytoplankton which can reach bloom densities at times. 31

Figure 3.6: Intertidal saltmarsh. 32

Figure 3.7: Desiccated saltmarsh. 32

Figure 3.8: Reed and sedge‐lined channel at Dunvlei. Note dyke protecting farm land from river

floods. 33

Figure 3.9: Accumulation of seepage containing ferrosilicate (red colour) at seaward end of the

desiccated saltmarsh, 2 November 1986. Note: Causeway preventing estuary water from

entering southern caution of saltmarsh. 34

Figure 3.10: Channel opened in 1997 to connect desiccated saltmarsh to the estuary. Note vehicle

parked at end of breached embankment. 36

Figure 3.11: Comparison of community structure between counts in 1980 and 2012 43

Figure 3.12: Water and seabirds at the Orange River Mouth, Spring 1993. a) Great White Pelicans and

Cape Cormorants roosting on an island; b) Palaearctic migrant terns roosting on the lee

side of the beach berm (Photographs: P. Morant) 46

Figure 3.13: Distribution of bird groups in the Orange River Estuary in relation to broad habitat types,

November 2012 (Anderson, 2013) 47

Figure 3.14: Flamingos feeding in re‐flooded portion of the saltmarsh. 47

Figure 5.1: The road embankment preventing ingress of water into the southern saltmarsh, 2

November 1986 52

Figure 5.2: Road embankment at Orange River mouth showing breach made in 1997 to permit the

flooding of the desiccated saltmarsh. 53

Figure 5.3: The Orange River mouth showing the saltmarshes connected to both the river and

estuary, May 1943. 54

Figure 5.4: Structures to be removed during remedial action by PSJV. 55

Figure 5.5: Inundation potential of saltmarsh 57

Figure 5.6: Dyke protecting Dunvlei Farm which prevents river flow to the saltmarsh on the south side

of the estuary. 63



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Glossary

BCLME Benguela Current Large Marine Ecosystem

DEA South African National Department of Environmental Affairs

DENC Northern Cape Provincial Department of Environmental Affairs and Nature Conservation

DMR South African National Department of Mineral Resources

DWS South African National Department of Water and Sanitation

EFR Environmental Flow Requirement

IBA Important Bird Area

MET Namibian Ministry of Environment and Tourism

Namdeb Nambeb Diamond Mining Company

NEM:PAA National Environmental Management: Protected Areas Act (South Africa)

ORASECOM Orange-Senqu River Commission

ORMEMP Orange River Mouth Estuarine Management Plan

PSJV Pooling and Sharing Joint Venture

SAD State Alluvial Diggings (South Africa)



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1. INTRODUCTION

1.1 Background Alexkor RMC Pooling and Sharing JV (PSJV) is the holder of Marine Diamond Mining Licence 554 MRC comprising six components one of which covers the lowermost reaches of the Orange River between Arrisdrif and the sea (Figure 1.1). More specifically this riverine-estuarine area extends from the centre line of the Orange River to the banks of the following properties:

a) Farm Corridor Wes No. 2 b) Portion 17 (a portion of Portion 8) c) Portion 16 (a portion of Portion 9) d) Portion 15 (a portion of Portion 10) e) Arrisdrif No. 616 f) Farm No. 1 g) Farm Brandkaros No. 517

Figure 1.1: The Orange River component of Marine Diamond Licence 554 MRC running from Arrisdrif to the

sea.

(Source: http://www.ramsar.org/wetland/south‐africa).



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At present the southern boundary of the Orange River Mouth Ramsar Site (Wetland of International Importance No. 526) only abuts Farm No. 1. However, there are plans to extend the Ramsar Site upstream of the Sir Ernest Oppenheimer Bridge to incorporate riverine habitats not represented below the bridge (Figure 1.2). Nevertheless, for this study the emphasis is on the role the PSJV is expected to play in the restoration and management of the Ramsar Site. Specifically the study is to identify “measures required to be implemented to manage the estuary in the light of the fact that it is the intention of the Department of Environmental Affairs (DEA) to declare this [the Ramsar Site] as a Protected Area under the NEM: Protected Areas Act”.

Figure 1.2: Riverine habitat upstream of the Sir Ernest Oppenheimer Bridge

proposed for inclusion in the Ramsar Site.

1.2 Orange River Mouth Estuarine Management Plan The Orange River Mouth Estuarine Management Plan (ORMEMP) was formally accepted by the Minister of Environmental Affairs on the 30th June 2017. The development and implementation of the Estuarine Management Plan is governed by Section 34 of the National Environmental Management: Integrated Coastal Management Act (Act No. 24 of 2008).

In Chapter 3 of the ORMEMP the Vision for, and the Mission of those responsible for its management are presented.



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Vision: A healthy estuary providing opportunities for all.

Mission: To restore, manage and maintain the estuary in order to enhance ecological values that qualify the Orange River Estuary as a Ramsar Site whilst providing opportunities through sustainable

socio-economic activities.

Chapter 4 of the ORMEMP presents a set of Strategic Goals and Objectives with their associated Management Objectives grouped into three Thematic Areas namely, Institutional, Ecological and Socio-Economic. While as a key stakeholder the PSJV will be involved in the activities, to a greater or lesser degree as appropriate, of all three Thematic Areas the focus of this study is on the role it should play in the Ecological Thematic Area.

The Strategic Goal of the Ecological Thematic Area is:

“To ensure ecological restoration, management and maintenance of the Orange River Mouth Ramsar Site so as to maximise its functional integrity (C+ Ecological Category). The Strategic Objective most relevant to the PSJV is:

“2.2: To implement directed management interventions to ensure recovery of the degraded saltmarsh area”.

In turn, there are four Management Objectives which should be addressed by the PSJV:

To manage the Orange River Mouth so as to facilitate recovery of the system and optimise fish nursery functions.

To improve flows into the degraded saltmarsh in order to promote rehabilitation of the degraded saltmarsh habitat.

Remove and rehabilitate oxidation ponds.

To limit impacts from adjacent mining operations through appropriate rehabilitation strategies.

Chapter 6 of the ORMEMP provides detailed management actions plans and identifies those activities in which The PSJV is expected to play a role either as a Leading Institution or a Supporting Institution. Those particularly relevant to the rehabilitation of the saltmarsh are presented on pages 64 and 65 of the ORMEMP (Table 1.1).



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Table 1.1: Management action plans for the restoration of the saltmarsh (Adapted from: Orange River Mouth Estuarine Management Plan, 2017)

ID Key Issue Management Objective

Management Activities Output / Outcome Leading Institution

Supporting Intuitions

Priority Duration Phasing Indicative budget

Possible funding sources

Strategic Objective 2.2: To implement directed management interventions to ensure recovery of the degraded salt march

E5 Careful management of the mouth is necessary to facilitate recovery of the salt marsh habitat and to optimise fish nursery fluctuations.

To manage the Orange River Mouth so as to facilitate the recovery of the system and optimise fish nursery functions.

Implement guidelines for mouth management regarding the timing, conditions and methods for artificially breaching and closing the estuary mouth

Mount management optimised in line with management objectives

DEA DENC

Alexkor (PSJV)

Medium Ongoing 2017 - 2021 - Operational budgets

E6 The causeway (berm) and other infrastructure needs to be removed / breached to facilitate recovery of the degraded salt marsh

To improve fresh water flows into the degrade salt marsh areas in order to promote rehabilitation of the degrade salt marsh habitat.

Refine rehabilitation plan based on learnings from prevision rehabilitation activities and the need to also address social concerns.

Revised rehabilitation plan to address barriers to flow

DEA DENC

Working for Wetlands Alexkor (PSJV) Working for Coast

High 3 months 2017 - 2018 R 100 000 Working for Wetlands

Obtain relevant authorisations to proceed with rehabilitation

Authorisation for proposed rehabilitation activities obtained

Alexkor (PSJV) DEA DWS

DENC Working for Wetlands

High 6 months 2017 - 2018 R 50 000 Alexkor (PSJV)

Implement rehabilitation actions to improve fresh water flows into the salt marsh area

Rehabilitation plan implemented

DEA DENC

Alexkor (PSJV) Working for Wetlands Working for Coast

High 1 year 2017 - 2019 R 22 million

DEA Alexkor (PSJV) / Working for Wetlands

E7 Existing oxidation ponds need to be removed and rehabilitated prior to breaching of the upper section of the causeway

Remove and rehabilitate oxidation ponds

Obtain authorisation for the proposed new sewage works and proposed rehabilitation of oxidation ponds

Authorisation for new sewage works obtained

Alexkor (PSJV)

DEA DENC

High 3 months Complete N/A Alexkor (PSJV) – legal requirement

Remove walls on oxidation ponds and flatten oxidation ponds to facilitate flow of water through the area

Area reshaped to facilitate more natural flows through the area

Alexkor (PSJV)

DEA DENC

High 3 months 2017 – 2018 N/A Alexkor (PSJV) – legal requirement

E8 Windblown sediments from mining operations and saline water from slimes dams needs to be addressed to facilitate the recovery of the degraded salt marsh area.

To limit impacts from adjacent mining operations through appropriate rehabilitation strategies

Identify specific action to problems of sand and salt inputs posed by mining activities on the salt marsh

EMP update to include specifications designed to address risk to the salt marsh

Alexkor (PSJV)

DENC Medium 6 months September 2017

R 50 000 Alexkor (PSJV)

Implement and monitor management actions to minimise the problem

Management actions successfully implemented and refined as necessary

Alexkor (PSJV)

DENC Medium 18 months September 2017 – 2018

R 100 000 Alexkor (PSJV)



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2. PHYSICAL COMPONENTS

2.1 Geomorphology

2.1.1 Riparian Zone

The Orange River between Arrisdrif and the Sir Ernest Oppenheimer Bridge is confined between its banks which are bordered by alluvial terraces which may be over-topped during major floods. Within the channel these sand and mudbanks which are exposed under low flow conditions are often vegetated and quite stable but may be re-shaped during major floods.

2.1.2 Estuarine zone

The estuary below the Sir Ernest Oppenheimer Bridge is an elongated fan in shape with numerous channels and islands. Most of the islands are vegetated and exhibit a high degree of morphological stability. Only some small islands close to the mouth are ephemeral in nature in response to the location of the estuary mouth (Figure 2.1).

Part of the estuary has been isolated from the active system by a road embankment (Figure 2.2). The seaward end of this embankment has been breached in an attempt to re-activate the saltmarsh in the area. The Dunvlei channel which fed river flow along the southern side of the estuary was closed by a dyke in 1974 (Figure 2.3). This has contributed significantly to the degradation of the saltmarsh. It will require extensive earthmoving activities to re-activate the Dunvlei channel.

2.1.3 Estuary mouth

The estuary mouth may migrate between the end of the causeway in the south to the extreme north of the beach berm on the Namibian side of the estuary (Figure 2.4). The location of the mouth is a result of a combination of sea state and river flow conditions (Figure 2.5). However the position of the mouth may depend upon which of the two operations, PSJV and Namdeb, undertook the breaching of the berm after a period of mouth closure. Consequently the mouth is closer to the north bank if the breaching was undertaken by Namdeb and closer to the south bank if done by PSJV. The migration of the mouth to the south is limited by scrap machinery (“Detroit riprap”) used to anchor the end of the road embankment on the beach berm (Figure 2.6). Removal of this material would enable the mouth to move further south which could be of benefit to the presently desiccated saltmarsh on the south bank.



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Figure 2.1: The Orange River Estuary. The red line is the 5 m a.m.s.l. contour demarcating the estuarine functional zone.



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Figure 2.2: Orange River mouth on 19 June 1966 showing road embankments isolating the saltmarsh on the southern (right) side of the system.



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Figure 2.3: Flood protection works and Dunvlei cut‐off dykes

(Adapted from CSIR, 1994).


ORA NGE R I VER COMPONENT OF MA RINE DIAMOND MI NING L ICENCE 554 MRC ENVI RONMENTA L DESCRIPT I ON AND ESTUA RI NE REHA BI L I TAT I ON MEASURES

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Figure 2.4: Extreme northward migration of the Orange River mouth to the Namibian bank on 2 November 1986

(Source: State Alluvial Diggings)



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Figure 2.5: The Orange River mouth on 25 July 2017

Figure 2.6: Scrap machinery (“Detroit riprap”) used to anchor the seaward end of the road embankment

built in 1964. The scrap limits the southward migration of the estuary mouth.

(Photo: S. Lamberth, August 2013).



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A recent development is coffer dam mining for diamonds on the coast south of the Orange River Estuary. The rock-walled coffer dams extend into the sea for 200 m and act as barriers to northwards longshore transport of sediment. During the site visit in July 2017 it was noted that the beach immediately to the north of the northernmost coffer dam wall appeared to be starved of sand. At the top of the beach was a building badly damaged by storm waves in June 2017. It is probable that the effect of the waves was exacerbated by the sand-deficient beach in front of it (Figure 2.7). Whether the sand-starvation of the beach will extend further northwards and affect the beach berm across the mouth of the Orange Estuary is not clear but the situation should be monitored.

Figure 2.7: Building damaged by storm waves. June 2017. The beach in front of the building appears to be

sand‐deficient as a consequence of the coffer dams restricting the northward movement of sand towards the

Orange River Mouth.

The current operation by Namdeb to prograde a section of the coast north of the Orange River Estuary by up to a kilometre seawards to mine diamonds in the inter- and sub-tidal zones is very unlikely to have any effect on the Orange River Estuary since the predominant sediment transport is northwards (G.G. Smith, WSP Ltd, pers. comm.).

2.1.4 Sediments

The sediments in the estuary and along its banks are almost entirely of fluvial origin. The sediments originating from the Orange River catchment have a distinctly different mineralogy from those derived from the Fish River catchment in Namibia (Bremner et al., 1990). The majority of the sediments are fine-grained consisting of silts and muds, including clays. During the 1988 flood a large proportion of the sediments carried down by the floodwaters were deposited in a lobe-shaped delta which



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extended seawards up to 400 m from the normal coastline. Over the succeeding months this deposit was eroded by wave action and transported northwards in the longshore drift.

The large dams in the upper catchment trap a considerable proportion of the eroded sediments from the area. Erosion, primarily, due to overgrazing in the lower catchment, may to some extent offset this reduction in sediment load (ORASECOM, 2012). However the proposed Lower Orange River Dam upstream from Vioolsdrif will trap this sediment. Similarly, the Neckartal Dam being constructed on the Fish River will trap much of the sediment from that system. Consequently, in future far less sediment will reach the Orange River Estuary than at present.

The reduction in smaller floods (see Section 2.2.1 below) has resulted in the meandering channels in the upper estuary becoming more stable and shallower than hitherto. The reduction in the variability of the river flow has led to the more permanent exposure of the sandbanks, and therefore they have become more vegetated. This stabilisation of the sandbanks by vegetation suggests that much larger floods are required to remove them.

2.2 Hydrology

2.2.1 River inflows

River inflow is the main driving force shaping the nature of an estuary. The Orange River catchment is approximately 1,000,000 km2 in extent (DWA, 1990), and the natural mean annual runoff (MAR) is estimated to be 11,306 million cubic metres. The entire Orange River system is highly regulated and the catchment contains twenty three major impoundments besides a myriad of smaller dams on the tributaries. Water is drawn for the industries and metropolitan areas of the Witwatersrand as well as for agriculture along almost its entire length to the sea. The consequence of this is that by 1989 the MAR had been reduced to approximately 50% of the natural level (DWA, 1990) and at present to 40% of MAR.

Besides this significant reduction in flow volume, the variability of the flow has also been greatly reduced as a result of the dams in the catchment and the regulated releases from them. As a result low flows (dry season) are elevated and flood peaks reduced (captured by the dams). The consequences for the Orange River Estuary of these changes in the flow regime are summarised below:

Large floods: the frequency of occurrence and magnitude of large floods has been reduced. Orange River floods normally occur during the summer;

Small floods: the frequency of occurrence and magnitude of smaller floods with return periods of 1:1 to 1:10 years have been greatly reduced. These floods normally occur in the summer. This decrease in flood frequency has resulted in a considerable reduction in the flooding of the saltmarsh at the estuary mouth. The duration of these floods generally would have been a few weeks;

Low flow periods: almost continuous releases from the dams for electricity generation and irrigation have resulted in an elevated baseflow. Consequently the occurrence of periods of



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very low flow in the winter, causing estuary mouth closure and back-flooding of the supratidal saltmarsh, has been reduced significantly.

2.2.2 Mouth closure

Since the 1988 Orange River flood there have been only three documented mouth closure events (CSIR, 2004). These were the prolonged period of closure in the spring of 1993 (Figures 2.8a and 2.8b) and two brief periods in December 1994 and December 1995. The latter were recorded by the permanent water level recorder (D8H012) near Alexander Bay. There are no measured water level data for 1993 thus the precise river flow rate at which the estuary closed is unknown. However flows of less than 5 m3/s occurred for 148 consecutive days between 6 August and 31 December 1993.

Figure 2.8a and 2.8b: Extensive flooding of the estuarine basin during the prolonged mouth closure in the

spring of 1993. a) View from north bank with beach berm on right; b) view towards Alexander Bay town

(Photographs: P. Morant).

a

b



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The exact flow conditions giving rise to mouth closure have not been established (Van Niekerk, 2013), although mouth closure does occur at flows of 5 m3/s or less. However under certain conditions the mouth may close at higher river flows (10 – 20 m3/s). A gauging station capable of recording low flows accurately needs to be established close to the head of the estuary by the Department of Water and Sanitation (DWS).

When mouth closure occurs at low flows (< 5 m3/s) the water level in the estuary will rise until it stabilises as a result of seepage through the berm and evaporation. Under these conditions the mouth would remain closed until the river flow increases, the berm is overtopped and a new mouth established. In 1993 the mouth was closed for four months before it was finally breached artificially in December 1993 to prevent flooding of low lying infrastructure and the golf course on the north bank (Figure 2.9a and 2.9b).

Ideally the duration of mouth closure should not exceed 4 – 6 weeks. Extended periods of inundation of the supratidal saltmarsh leads to degradation (rotting) of the plants.

If closure occurs at flows higher than 5 m3/sec the water level in the estuary rises rapidly leading to natural breaching of the berm. In December 1994 the mouth closed for three days prior to which the median flow for a 45-day period was 15 m3/s (min. 3 m3/s and max. 25 m3/s).

2.2.3 Tidal range

The mean tidal range at the mouth of the Orange River is approximately 0.4 m and can reach 1.0 m during spring tides. This pattern extends to 6 km upstream from the mouth. Upstream of this point tidal influence is very limited and at low river flow and spring tide the range at the Sir Ernest Oppenheimer Bridge is 20 mm or less.

Tidal penetration into the saltmarsh area to the south of the road embankment depends upon the connectivity with the main water body. The inability of the mouth to migrate south of the road embankment which was “anchored” to the beach berm by old heavy machinery (see Figure 2.6) probably prevents the development of a more permanent tidal inflow into the saltmarsh area.



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Figure 2.9a and 2.9b: Breaching of the estuary mouth after prolonged closure, Spring 1993. a) Bulldozer

preparing to cut channel opposite the road embankment (top photograph); b) Sea overtopping breach in

beach berm (bottom photograph). (Photographs: P. Morant).



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2.2.4 Salinity and circulation

The salinity regime in the Orange River Estuary is dynamic and results from interaction between the variability in river flow, the position of the estuary mouth and the constantly changing distribution of braided channels.

At low flows (< 20 m3/s) the estuary is relatively well mixed becoming highly stratified under high flow conditions (> 50 m3/s). During river flows of 20 – 50 m3/s the estuary is relatively well mixed on the flood tide and stratified on the ebb when the fresh river water runs over the denser, underlying salt water.

The location of the mouth has a major influence on the salinity of the water reaching the saltmarsh and the re-opened long-shore channel on the southern bank. When the mouth is at its southern-most position the amount of seawater entering the saltmarsh and long-shore channel area at spring tides is considerable. However, if the mouth is adjacent to the northern bank (see Figure 2.4) the water entering the saltmarsh area is of much lower salinity being diluted with river water.

Broadly the salinity regime of the Orange River Estuary can be summarised as follows:

High river flow (> 50 m3/s): salinity will be low throughout the system with limited intrusion of seawater, mainly at spring high tide.

Intermediate river flow (20 – 50 m3/s): the estuary is open to the sea with regular tidal penetration. Vertical stratification in the deeper basin in the lower reaches occurs with bottom water salinity of > 20 ppt and surface water salinity of 0 – 10 ppt. Approximately 6 km upstream from the mouth the water is fresh.

Low river flow (5 – 20 m3/s): vertical stratification still occurs near the mouth with the salinity close to that of seawater. There is a general salinity gradient upstream to 7 – 8 km from the mouth where the water becomes fresh.



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3. BIOLOGICAL COMPONENTS

3.1 Riparian vegetation The Orange River between Arrisdrif and the Sir Ernest Oppenheimer Bridge is quite tightly confined between its banks. The vegetation comprises Lower Gariep Alluvial Vegetation (AZa 3) as described by Mucina and Rutherford (2006). The flat alluvial terraces and riverine islands support riparian thickets dominated by Ziziphus mucronata, Euclea pseudebenus and Tamarix usneoides (Figure 3.1). The reed Phragmites australis lines much of the channel and the seasonally-flooded sandbanks and lower alluvial terraces are covered with grasslands and herblands supporting graminoid species such as Cynodon dactylon, Eragrostis echinochloa and Stipagrostis namaquensis and herbs such as Amaranthus praetermissus and Coronopus integrifolius. (Figures 3.2a and 3.2b.)

Figure 3.1: Riparian thicket lining the river banks at Arrisdrif.

Alien invasive species such as Prosopis spp., Nicotiana glauca and Argemone ochroleuca can invade the alluvial soils particularly after disturbance for agricultural or mining purposes.

Approximately 50% of the Lower Gariep Alluvial Vegetation type (AZa 3) has been transformed by farming and diamond mining. Currently only 6% of this vegetation type is formally conserved (Mucina and Rutherford, 2006).



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Figure 3.2a and 3.2b: Seasonally flooded sandbanks used as pasture near Brandkaros.

3.2 Estuarine vegetation

3.2.1 Overview

The Sir Ernest Oppenheimer Bridge is considered to be the head of the Orange River Estuary: tidal variation is just detectable and measureable marine-derived salinity is present (Figure 3.3). The estuarine area is some 2709 ha in extent and responds dynamically to the river flow regime. Major floods “prune” the aerial components of macrophytes and re-shape sand- and mud-banks (Morant and O’Callaghan, 1990). Veldkornet and Adams (2013) mapped the habitat types (Figure 3.4) within the estuary and compared the situation in 2012 with the Reference Condition used to benchmark changes within the system (Table 3.1). The 5 m a.m.s.l. topographical contour was used as the boundary to delineate the estuarine functional zone (see Figure 2.1).

Figure 3.3: The Sir Ernest Oppenheimer Bridge which approximately marks the boundary between the

riparian and estuarine vegetation.



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Table 3.1: Changes in habitat cover of the Orange River Estuary (from: Veldkornet and Adams 2013).

Habitat type Reference Condition (ha) Status in 2012 (ha) Channel 630 609

Sand/mudbanks 101 144

Reeds and sedges 300 316

Submerged macrophytes 0 <1

Supratidal saltmarsh 1,144 602

Macroalgae 0.5 1

Intertidal saltmarsh 134 144

Desiccated saltmarsh 0 511

Terrestrial vegetation 399.5 383

TOTAL 2,709 2,709

The most notable change has been the loss of approximately 50% of the saltmarsh (ca. 300 ha) to desiccation, as a result of anthropogenic activities. This desiccation of the saltmarsh is discussed in detail in Section 2.2.4 below.

The Orange River Estuary has a unique diversity of macrophyte species. A list of the macrophyte species recorded during the August 2012 survey is presented in Table 3.2.

Table 3.2: Macrophyte species and associated habitats recorded in 2012

(from: Veldkornet and Adams, 2013)

Species Habitat

Apium graveolens L. Intertidal saltmarsh

Beta vulgarus subsp. maritima (L.) Arcang. Intertidal saltmarsh

Cotula coronopifolia L. Intertidal saltmarsh

Juncus kraussii Hochst. Intertidal saltmarsh

Plantago lanceolata L. Intertidal saltmarsh

Samolus porosus (L.f.) Thunb. Intertidal saltmarsh

Sarcocornia decumbens (Toelken) A.J. Scott Intertidal saltmarsh

Sarcocornia natalensis (Bunge ex. Ung‐Sternb.) A.J.Scott Intertidal saltmarsh

Sarcocornia tegetaria S. Steffen, Mucina & G. Kadereit Intertidal saltmarsh

Spergularia media (L.) C.Presl ex Griseb Intertidal saltmarsh

Tetragonia decumbens Mill. Intertidal saltmarsh

Triglochin bulbosa L. Intertidal saltmarsh

Polysiphonia incompta Harvey Macroalgae

Ulva capensis J.E. Areschoug Macroalgae

Ulva intestinalis L. Macroalgae

Bolboschoenus maritimus (L.) Palla Reeds and Sedges

Ficinia lateralis (Vahl) Kunth Reeds and Sedges



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Species Habitat

Phragmites australis (Cav.) Steud. Reeds and Sedges

Schoenoplectus scirpoides (Schrad.) Browning Reeds and Sedges

Stuckenia pectinata (L.) Boerner Submerged macrophtytes

Atriplex vestita (Thunb.) Aellen Supratidal saltmarsh

Atriplex semibaccata R.Br. Supratidal saltmarsh

Cynodon dactylon (L.) Pers. Supratidal saltmarsh

Lagurus ovatus L. Supratidal saltmarsh

Psilocaulon dinteri Schwantes Supratidal saltmarsh

Salsola aphylla Spreng. Supratidal saltmarsh

Sarcocornia pillansii (Moss) A.J.Scott Supratidal saltmarsh

Sporobolus virginicus (L.) Kunth. Supratidal saltmarsh

Suaeda fruticosa (L.) Forssk. Supratidal saltmarsh

Aspalathus sp Terrestrial Fringe

Datura stramonium L. Terrestrial Fringe

Gomphocarpus fruticosus (L.) Aiton f. Terrestrial Fringe

Sporobolus africanus (Poir.) Robyns & Tournay Terrestrial Fringe

3.2.2 Habitat types and their ecological function

Open water/channels

The open water areas near the mouth and the channels further upstream serve as habitat for both marine-derived and fluvial phytoplankton (Figure 3.5). Their distribution is controlled primarily by their salinity tolerance. The structure and distribution of the phytoplankton community responds dynamically to the tidal and fluvial regimes. No long-term studies of the phytoplankton of the Orange River Estuary have been undertaken. The most detailed study was undertaken by Snow (2013) during August 2012 when 10 sites were sampled for phytoplankton. Phytoplankton chlorophyll a was used to determine the most productive areas of the estuary: it was lowest at the mouth of the estuary (1.5 µg/litre) and highest 1 km upstream (27.6 ± 7.1 µg/litre). A surprising find, given the high turbidity of the estuary, was the highest biomass was found in 2 m deep saline water in the middle to lower reaches. Flagellates were the dominant group at these sites whereas further upstream, 3.5 km from the mouth, diatoms and chlorophytes in bloom densities (> 10 000 cells/ml) were present, most probably introduced into the estuary by the river. The high phytoplankton biomass and cell density indicate that the Orange River Estuary was eutrophic at the time of sampling.



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Figure 3.4: Habitats and vegetation of the Orange River Estuary

(Source: Veldkornet and Adams, 2013)



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Figure 3.5: Sedge‐lined channel near Dunvlei. The open water in the channel serves as habitat for

phytoplankton which can reach bloom densities at times.

Intertidal sand and mud flats.

The distribution of the channels and associated mud and sand flats in the estuary responds to river flow and the location of the estuary mouth. Temporary islands may form which are used as roosts by cormorants, pelicans and gulls. In 2012 the area covered by intertidal sand and mud flats was 50% greater than under Reference Conditions (Table 2.1).

Submerged macrophytes

The strong flow regime and high turbidity of the Orange River Estuary provides little opportunity for submerged macrophytes to become established on a significant scale. During the August 2012 survey the rooted submerged macrophyte Stuckenia pectinata (pond weed) was found in the upper reaches of small channels where the salinity was low (below 10 ppt).

Macroalgae

In 2012 abundant growths of the green algae Ulva capensis and Ulva intestinalis and the red alga Polysiphonia sp. were present along the west bank. This is the first record of such species in the Orange River Estuary indicating the system has become more marine-dominated than hitherto.



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Intertidal saltmarsh

There are two areas of intertidal saltmarsh (Figure 3.6) on either side of the main channel in the lower reaches of the estuary (see Figure 3.4) comprising a diversity of Sarcocornia species including an ecomorphotype of Sarcocornia pillansii (Moss) that displays a unique morphology characterised by corky, swollen internodes (Steffen et al., 2010). Cotula coronopifolia grows in intertidal saltmarsh areas where the salinity does not exceed 20 ppt.

Figure 3.6: Intertidal saltmarsh.

Supratidal saltmarsh

The dominant species in the supratidal saltmarsh is the salt and drought-tolerant Sarcocornia pillansii. However, approximately 50% (ca. 300 hectares) of the supratidal saltmarsh areas has been lost to desiccation as a result of a number of human interventions (Figure 3.7).

Figure 3.7: Desiccated saltmarsh.



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Reeds and sedges

Dense stands of Phragmites australis are present along the channels where the salinity does not exceed 15 ppt. The reedbeds provide an important habitat for invertebrates, fish and birds (Figure 3.8). In some areas the sedge Schoenoplectus scirpoides dominates the channel banks.

Figure 3.8: Reed and sedge‐lined channel at Dunvlei. Note dyke protecting farm land from river floods.

On the PSJV side of the river the construction of a road embankment in the 1960s isolated approximately a third of the estuary (see Figure 2.2), and in the 1970s dykes were built to protect the Dunvlei Farm (see Figure 2.3). The dykes and the sewage treatment ponds blocked the southernmost channel feeding the saltmarsh in the southwestern corner of the estuary. Starved of freshwater the supratidal saltmarsh began to die, a situation compounded by dust from the slimes dams to the south smothering the stressed plants. The sewage treatment ponds have been removed and new ones constructed outside the estuary. However the river channel against the south bank has not yet been rehabilitated.

During the major 1988 Orange River flood the entire estuary was flooded which provided an opportunity to leach accumulated salt from the supratidal saltmarsh and permit the germination of new seeds. A breach was cut through the beach berm to drain the marsh after the flood had peaked. It was expected that the breach would close rapidly as a result of longshore drift (Swart et al., 1990). Unfortunately this closure did not occur for some considerable time and permitted the ingress of seawater and most of the benefits of the leaching were lost.



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In the period prior to the 1988 flood a considerable amount of seepage containing ferrosilicate from the HMS diamond processing plant entered the southernmost portion of the desiccated saltmarsh (Figure 3.9). During the 1988 flood the ferrosilicate was washed out to sea through an artificial breach cut through the beach berm. Ferrosilicate seepage no longer occurs since the HMS plant is no longer in production.

Figure 3.9: Accumulation of seepage containing ferrosilicate (red colour) at seaward end of the desiccated

saltmarsh, 2 November 1986. Note: Causeway preventing estuary water

from entering southern caution of saltmarsh.

(Source: State Alluvial Diggings).



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3.2.3 Desiccation of the supratidal saltmarsh

Significant interventions in the management of the Orange River mouth began at the time mining commenced in the late 1920s (Table 3.3). Initially the interventions were local, however by the late 1960s the major impoundments, e.g. the Gariep and Van der Kloof Dams, in the catchment of the Orange River began to have a significant impact on the function of the Orange River mouth. In particular the large dams captured the smaller annual floods and, as a result of hydro-electric power generation, raised the dry season base flow.

Table 3.3: Summary of events affecting the saltmarsh at the Orange River mouth.

1929 Mining commenced. Estuary mouth kept open reducing back‐flooding.

1960s Road embankment isolating approximately one third of the saltmarsh. (See Figures 2.2 and 3.9)

1974 Diversion of Dunvlei channel to extend agricultural land.

1980 Disposal of mine waste water contributing to increased salinity of floodplain.

1980s Increased input wind‐blown dust originating from the slimes dam.

1988 Orange River flood: saltmarsh flooded, some silt deposition and areas of standing water led to die‐back of saltmarsh. Ingress of seawater increased salinity.

1993 Prolonged period of mouth closure and back‐flooding resulted in saltmarsh die‐back.

1994 & 1995 Short period of mouth closure

1997 Causeway breached close to beach berm. Water entered dead saltmarsh area.

1998 ‐ present Mouth of estuary open. No back‐flooding occurred. No recovery of saltmarsh.

In 1997 the seaward end of the causeway was breached with the objective of allowing water to enter the desiccated saltmarsh (Figure 3.10). This was partially successful but the breach was too small to permit large volumes of water to enter the saltmarsh. Also the failure to remove the scrap machinery, which had been used to “anchor” the seaward end of the causeway onto the beach berm, prevented the estuary mouth from migrating southwards. This also restricted the water exchange to the saltmarsh.



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Figure 3.10: Channel opened in 1997 to connect desiccated saltmarsh to the estuary. Note vehicle parked at

end of breached embankment.

Since 1995 the estuary mouth has remained open continuously thus limiting the opportunity for back-flooding the saltmarsh and enabling its recovery.

Mouth closure is dependent on river flow which needs to fall below 5 m3/sec for this to occur. Water releases from the Van der Kloof Dam to supply the lower Orange River are governed by agricultural requirements and the need to generate electricity in the winter months when demand is high. The result, particularly of the latter, is an elevated baseflow which prevents the Orange River mouth from closing. If the objective of restoring the saltmarsh is to be achieved river flow management is necessary to ensure mouth closure at least every two to three years. The optimum period of closure is 4 – 6 weeks. Extended closure, and thus inundation of the saltmarsh, results in die-back of the saltmarsh plants (Bornman et al, 2004).

3.3 Invertebrates There is little published information on the invertebrate fauna of the Orange River Estuary. Brown (1959) described the estuarine fauna of lower reaches of the Orange River near the mouth as “extremely poor” attributing this to the extremes of salinity between summer and winter. Brown (1959), Day (1981) and Whitfield (2000) concluded that the Orange River does not have a “real estuary” i.e. it does not have an established, temporally stable estuarine mixing zone.

The study undertaken by Wooldridge (2013) is the first attempt to provide a systematic quantified analysis of the invertebrate fauna of the Orange River Estuary.



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3.3.1 Zooplankton

The species richness of the zooplankton is strongly related to the salinity regime. Up to 25 species were present when the salinity was relatively high. Neritic copepod species, e.g. Centropagids, Clausocalanids and Clytemnestrids, dominate the plankton. Species richness was low when the salinity was low with only few neritic species were present near the mouth.

There are two broad categories of mesozooplankton in the Orange River Estuary whose distribution is primarily linked to the volume of freshwater entering the system at the time. A typical euryhaline zooplanktonic community is not well developed and is represented by a few species occurring in low numbers. A freshwater-associated community is present in the upper reaches and its extent depends on the strength of the flow.

3.3.2 Hyperbenthos

The mysid shrimp Mesopodopsis wooldridgei numerically dominated the hyperbenthic community. In comparison with the zooplankton mysid abundance was relatively high in the hyperbenthos. Mysids are relatively mobile moving into the estuary from the nearshore when conditions become favourable. M. major is a transient species entering the estuary with the high tide and returning to sea on the ebb.

3.3.3 Macrozoobenthos

The macrozoobenthic community is poorly represented with only seven species recorded in three surveys. Polychaete worms were the dominant group with Ceratonereis keiskama and Desdemona ornata dominating the community numerically and being widely distributed throughout the estuary.

The invertebrate fauna of the Orange River Estuary is species-poor and atypical of tidal estuaries along the west coast of South Africa. The species resident in the estuary are tolerant of a highly variable physico-chemical environment although the populations fluctuate in response to the fluvial flow regime. The invertebrate groups with the highest biomass are linked either to the benthos or hyperbenthos. The euryhaline zooplankton community is particularly poor and species that often dominate euryhaline mesozooplankton communities are absent (e.g. Acartia longipatella) or present in very low numbers (e.g. Pseudodiaptomus hessei).

3.4 Fishes

3.4.1 Introduction

Fish in estuaries benefit from high productivity, low predation, salinity gradients, and refuge from adverse conditions in the marine environment such as low temperatures or oxygen levels – thus improving body condition, growth and/or survival. The degree to which fish utilise or are dependent



38

on estuaries varies amongst species and between populations in different biogeographical regions. In South Africa over 90% of the landed catch biomass of small-scale fisheries and recreational anglers comprises estuary-dependent fish.

The Orange River Estuary is one of only three predominantly open estuaries in the cool-temperate region on the west coast. The estuary falls within the winter rainfall zone but most of the Orange catchment falls within the summer rainfall zone with a MAR of 10 833 X 106 m3 or 83 % of total Mean Annual Runoff (MAR) reaching the sea from all catchments on the west coast.

Open-water estuarine fish nursery habitat in the Orange River Estuary is more than 1 200 ha stretching from the mouth to Brandkaros and Arrisdrif, 35 km upstream. This represents 40 % of the total estuarine nursery habitat for fish on the west coast.

3.4.2 Fish fauna

Thirty-six species of fish representing 19 families have been recorded from the Orange River Estuary (Brown, 1959; Day, 1981; Cambray, 1984; DWAF, 1986; Morant and O’Callaghan, 1990; Harrison, 1997; Seaman and van As, 1998; Lamberth (2013), (Table 3.4). Six of these, the estuarine round herring Gilchristella aestuaria, Cape silverside Atherina breviceps, barehead goby Caffrogobius nudiceps, commafin goby Caffrogobius saldhana, klipvis Clinus superciliosus and pipefish Syngnathus temminckii live and breed in estuaries. With the exception of G. aestuaria, these fish also have marine breeding populations. Three species, white steenbras Lithognathus lithognathus, leervis Lichia amia and the facultative catadromous flathead mullet Mugil cephalus are dependent on estuaries for at least their first year of life whereas another two, elf Pomatomus saltatrix and harder Liza richardsonii are partially estuarine dependent. Eight species such as west coast steenbras Lithognathus aureti and silver kob Argyrosomus inodorus are marine species that occasionally venture into estuaries whereas 15, such as largemouth yellowfish Labeobarbus kimberleyensis, river sardine Mesobola brevianalis and the introduced carp Cyprinus carpio are euryhaline freshwater species whose penetration into the estuary is determined by salinity tolerance. One catadromous species the longfin eel Anguilla mossambica has been recorded from the Orange River near Kakamas and it is assumed that recruitment occurred through the estuary notwithstanding the (more likely) possibility that it entered the system through one of the inter-basin transfer schemes that connect the catchment with rivers on the east coast of South Africa. Overall, 31% of the fish species recorded from the Orange River Estuary are either partially or completely dependent on estuaries for their survival, 22% are marine and 47% freshwater in origin.

Two species of kob, silver kob Argyrosomus inodorus and Angolan kob A. coronus are known from the Orange River Estuary, the latter only been caught by anglers in the mouth region. Interestingly, on the east coast of South Africa dusky kob A. japonicus are dependent on estuarine nursery areas whereas A. inodorus seldom if ever ventures into estuaries. On the west coast however, A. inodorus frequently (& predictably) occurs in the Berg, Olifants and Orange Estuaries whereas A. coronus is predominantly caught on the beaches immediately adjacent to their mouths only having been recorded in estuaries during low oxygen conditions in the sea (Lamberth et al., 2008, Lamberth et al



39

2010). Therefore, A. inodorus may show some degree of estuarine dependence on the west coast of South Africa. All three of the kob species mentioned prefer turbid waters such as that in the Orange River Estuary. Further, towards the edge of the range of A. inodorus, A. coronus becomes the dominant kob species in the Kunene River Estuary over 1, 500 km to the north. Silver and dusky kob both increase in abundance immediately adjacent to the mouth during the summer months which is most likely a response to avoid cool upwelled waters in the nearshore. Large aggregations of both species predictably occur up to two weeks before and during flood events, a circumstance that anglers take advantage of and plan their trips around. This contributes disproportionately towards the effort directed at these species.

Comparisons with other estuaries and biogeographical regions are difficult because the data collected in the Orange River Estuary, and consequently the relative contribution of each estuarine-dependence category, varies according to the gear used in each study and the distance sampled from the mouth. Overall, species that breed in estuaries and / or estuarine residents comprise 10–22% of the Orange River Estuary fish fauna as compared to 26–27% for the Berg and Olifants estuaries (400 – 500 km to the south) and 4–25% for estuaries on the south, east and KwaZulu-Natal coasts (Bennett, 1994; Lamberth and Whitfield, 1997). Entirely estuarine dependent species comprise 24–33% of the Orange River Estuary fish fauna comparing well with the 26, 25–54, 22 and 9% recorded for the west, south, east and KwaZulu-Natal coasts respectively (Bennett, 1994; Lamberth and Whitfield, 1997; Harrison, 1997, 1999). Partially estuarine dependent species comprise 7– 22% of the Orange fish fauna, which is lower than the 29–40% for the Berg and Olifants and 18–27% for estuaries from Cape Point to KwaZulu-Natal (Bennett, 1994; Lamberth and Whitfield, 1997; Lamberth et al., 2008). Non estuarine dependent marine species comprise 21% of the species recorded but at least two of these, A. inodorus and L. aureti, occur predictably according to season and weather conditions as opposed to being vagrants that occur randomly.

Table 3.4/...



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Table 3.4: A list of all 36 species and 19 families recorded in the Orange / Gariep Estuary

by (a) Harrison, 1997; (b) Day, 1981; (c) Seaman and Van As, 1998; (d) Cambray, 1984; (e) Brown, 1959; (f)

DWAF, 1986; (g) Morant and O’ Callaghan, 1990; and (h) this study. The species are classified into five major

categories of estuarine‐dependence as suggested by Whitfield, 1994, Table 3.5.

Species recorded caught by anglers marked with an asterisk *.

Family Species Common name Dependence category

(see Table 3.5)

Recorded by % Samples reported

Anguillidae Anguilla mossambica Longfin eel Va f * 14

Atherinidae Atherina breviceps Cape silverside Ib h 7

Austroglanididae Austroglanis sclateri Rock catfish IVa d 14

Carangidae Lichia amia Leervis IIa c,h 14

Cichlidae Oreochromis mossambicus Mozambique tilapia IVa a,c,d,g,h 57

Pseudocrenilabris philander Southern mouthbrooder IVa a,c,d,h 43

Tilapia sparrmanii Banded tilapia IVa d,h 14

Clariidae Clarias gariepinus Sharptooth catfish IVa c,d,g,h 43

Clinidae Clinus sp. Klipvis Ib f 14

Clinus superciliosus Super klipvis Ib h 1

Clupeidae Gilchristella aestuaria Estuarine round‐herring Ia a,c,h 29

Sardinops sagax Sardine III a,h 14

Cynoglossidae Cynoglossus capensis Sand tonguefish III h 1

Cyprinidae Barbus hospes Namaqua barb IVa d,h 14

Barbus paludinosus Straightfin barb IVa c,d,h 29

Barbus trimaculatus Threespot barb IVa d,h 14

Cyprinus carpio Carp IVc c,h 29

Labeo capensis Orange River mudfish IVa c,d,h 29

Labeo umbratus Moggel IVa g,h 14

Labeobarbus aeneus Smallmouth yellowfish IVa a,b,c,d,g,h 71

Labeobarbus kimberleyensis Largemouth yellowish IVa c,d,h 43

Mesobola brevianalis River sardine IVa c,d,h 29

Gobiidae Caffrogobius nudiceps Barehead goby Ib a,h 14

Caffrogobius saldhana Commafin goby Ib a,h 3

Mugilidae Liza richardsonii Southern mullet / harder IIc a,b,c,d,e,f,g,h 100

Mugil cephalus Flathead mullet IIa a,b,c,e,h 57

Poecillidae Gambusia affinnis Mosquito fish IVc h

Pomatomidae Pomatomus saltatrix Elf IIc c,h 14

Rajidae Raja spp. Skates III g 14

Sciaenidae Argyrosomus coronus West coast dusky kob III *

Argyrosomus inodorus Silver kob III a,b,c,g,h 57

Sparidae Diplodus cervinus Wildeperd / zebra III c 14

Lithognathus aureti West coast steenbras III *,h 1

Lithognathus lithognathus White steenbras IIa b,c,g 43

Syngnathidae Syngnathus temminckii. Longsnout pipefish Ib h 1

Triglidae Chelidonichthys capensis Cape gurnard III h 1



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Table 3.5: Classification of South African fish according to their dependence on estuaries

(Adapted from: Whitfield, 1994)

Category Description I Truly estuarine species, which breed in southern African estuaries; subdivided as follows:

Ia Resident species which have not been recorded breeding in the freshwater or marine environment

Ib Resident species which have marine or freshwater breeding populations

II Euryhaline marine species which usually breed at sea with the juveniles showing varying degrees of dependence on southern African estuaries; subdivided as follows:

IIa a. Juveniles dependant of estuaries as nursery areas

IIb b. Juveniles occur mainly in estuaries, but are also found at sea

IIc c. Juveniles occur in estuaries but are more abundant at sea

III Marine species which occur in estuaries in small numbers but are not dependant on these systems

IV Euryhaline freshwater species that can penetrate estuaries depending on salinity tolerance. Includes some species which may breed in both freshwater and estuarine systems. Includes the following subcategories:

a. Indigenous

b. Translocated from within southern Africa

c. Alien

V Obligate catadromous species which use estuaries as transit routes between the marine and freshwater environments

3.4.3 Flow regime and mouth condition

3.4.3.1 Flowregime

During floods and high flows fish tend to find refuge in the shallow marginal areas on the floodplain and / or amongst saltmarsh and reedbeds. In the Orange River Estuary, flow velocities are higher during the summer months. High flow velocities generate numerous eddies that provide refuge and concentrate prey as well as standing waves, small and large, that fish use to recruit into the estuary or move upstream. Most estuary associated fish are adapted to take advantage of both high and low flow velocities. If reduced flow velocities translate into increased phytoplankton, zooplankton and benthic algae production, fish will benefit from this abundant prey.

3.4.3.2 Mouthcondition

During the summer months, open mouth conditions maintain a substantial warm, turbid plume that provides a refuge from cool up-welled water in the nearshore and cues for fish attempting to recruit into the estuary. Predominantly summer recruitment of fish into the Orange coincides with that of the Olifants, Berg and temporarily open / closed estuaries to the south even though it experiences high-flow as opposed to summer low-flow of other west coast systems. Elevated flow may actually enhance recruitment above that of the other systems. Under closed mouth conditions increased phytoplankton and zooplankton production will favour growth of all species and spawning success, survival and population size of estuary breeders will increase. Populations of most of the latter will crash once breaching occurs. Whilst closed, inundated floodplain and saltmarsh areas will increase



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available foraging habitat. Prolonged mouth closure will likely see salinity levels decrease and freshwater species moving into the lower reaches of the estuary.

3.4.4 The Orange River and Estuary as fish habitat

Over the past eighty years, mining activities mouth manipulation, construction of road embankments, dykes, bridges, a golf course and roads have either isolated or greatly reduced the spatial and temporal availability of fish habitat in the estuary. Nevertheless the Orange River Estuary still plays a critical role in the maintenance of west coast fish resources.

The lower and upper reaches of the estuary-proper to the Sir Ernest Oppenheimer Bridge comprise 280 ha and 100 ha of water surface-area respectively. However, from the bridge to Brandkaros 20 km upstream there’s a further 650 ha of water extensively used as an adult and nursery habitat by estuary-associated fish. Therefore, total effective estuary habitat available to fish is at least 1,030 ha. Persistent low or zero flows coupled with obstructions presented by the present and past bridge site may see the upstream reaches and associated habitat become inaccessible to fish. This said, the dominant species in the system L. richardsonii is an opportunistic species tolerant of both hypo- and hyper-salinity and able to remain isolated from the sea or within disconnected river reaches for extended periods. Consequently, changes in the salinity regime are unlikely to see noticeable changes in abundance or biomass of fish in the estuary but will see a drop in diversity with the loss of species that have more narrow salinity tolerances or preferences.

3.4.5 Value of the Orange River Estuary-associated fishery

Until recently, legal and illicit commercial, small-scale and recreational fishing in the Orange River Estuary has been well controlled (Lamberth, 2013). Potential catches in the estuary are in the region of 140 t per annum with a landed catch value of R2.8 M but the real value lies in the contribution of the Orange River Estuary to recruitment in marine fisheries. A conservative estimate of the value of fisheries production is R38 500/ha/annum. Thus, the current contribution of the Orange River Estuary to the value of marine fisheries is in the region of R46 Million per annum.

3.5 Birds

3.5.1 Introduction

The Orange River Estuary was designated as a Wetland of International Importance in terms of the Ramsar Convention on 28th June 1991. The factors leading to the designation include:

The Orange River Estuary is one of only nine perennial coastal wetlands on the predominantly arid west coast of southern Africa;

The estuary supports more than 20 000 waterbirds of more than 60 species; The estuary supporting an assemblage of rare and endangered waterbird species;



43

It supports more than 1% of the world and southern African populations of several species of waterbirds.

The estuary has been recognised as one of the most important in South Africa in terms of its waterbird populations (Turpie et al., 2002; Turpie and Clark, 2007). It has also been designated as an Important Bird Area (Barnes and Anderson, 1998).

Despite the exact location of the South African-Namibian border in the estuary being a subject of dispute between the two countries Namibia designated the Orange River Estuary as a Ramsar Site on 23 August 1995 thereby creating a transboundary Ramsar Site in the Orange River Estuary. Regrettably shortly thereafter, (September 1995), the Orange River Transboundary Ramsar Site was placed on the Montreux Record1 primarily because of the dramatic decline in bird numbers but also because of the desiccation of large areas of saltmarsh on the southern side.

3.5.2 Population size and structure

During the 1980s the bird population was considerably greater than at present: numbers exceeded 20 000 individuals. Twenty years later (2000 – 2005) the numbers had declined to approximately 6500 both in summer and winter. In contrast, the number of species of waterbirds recorded at the estuary has been fairly constant during the past 25 years. The average number of species recorded per count is 52 (Anderson, 2006 and Table 3.6). There has been dramatic decline in the members of cormorants, waders and terns from 1980 to 2012 (Figure 3.11).

Figure 3.11: Comparison of community structure between counts in 1980 and 2012

1 The Montreux Record is a mechanism whereby a state responsible for a Ramsar Site which fails to meet the criteria under which it was originally proclaimed is served notice to undertake remedial action.

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1980

2012



44

Table 3.6: Water bird species recorded at the Orange River Estuary, 2012 (Anderson, 2013)

Name Upper

estuary

Lower

estuary

Salt

Marsh Mouth Total

Avocet, Pied (Recurvirostra avosetta) 3 30 6 39

Coot, Red‐knobbed (Fulica cristata) 72 72

Cormorant, Cape (Phalacrocorax capensis) 4 11 172 187

Cormorant, Reed (Phalacrocorax africanus) 7 1 8

Cormorant, White‐breasted (Phalacrocorax carbo) 26 2 36 64

Curlew, Eurasian (Numenius arquata) 1 1

Duck, Yellow‐billed (Anas undulata) 7 8 15

Egret, Cattle (Bubulcus ibis) 1 1

Egret, Little (Egretta garzetta) 9 26 35

Egret, Yellow‐billed (Egretta intermedia) 2 2

Fish‐Eagle, African (Haliaeetus vocifer) 7 7

Flamingo, Greater (Phoenicopterus ruber) 15 5 111 4 135

Flamingo, Lesser (Phoeniconaias minor) 137 15 152

Goose, Egyptian (Alopochen aegyptiacus) 134 121 11 266

Goose, Spur‐winged (Plectropterus gambensis) 4 4

Grebe, Little (Tachybaptus ruficollis) 4 1 5

Greenshank, Common (Tringa nebularia) 4 3 1 3 11

Gull, Hartlaub's (Larus hartlaubii) 40 4 43 87

Gull, Kelp (Larus dominicanus) 2 56 16 4 78

Heron, Grey (Ardea cinerea) 2 6 2 10

Ibis, African Sacred (Threskiornis aethiopicus) 1 1

Kingfisher, Malachite (Alcedo cristata) 1 1

Kingfisher, Pied (Ceryle rudis) 6 30 3 39

Lapwing, Blacksmith (Vanellus armatus) 21 21

Night‐Heron, Black‐crowned (Nycticorax nycticorax) 27 27

Oystercatcher, African Black (Haematopus moquini) 1 1

Pelican, Great White (Pelecanus onocrotalus) 19 1 50 70

Plover, Chestnut‐banded (Charadrius pallidus) 82 82

Plover, Common Ringed (Charadrius hiaticula) 9 29 2 1 41

Plover, Grey (Pluvialis squatarola) 1 1 1 3

Plover, Kittlitz's (Charadrius pecuarius) 23 4 1 2 30

Plover, Three‐banded (Charadrius tricollaris) 8 8

Plover, White‐fronted (Charadrius marginatus) 15 1 4 20

Pochard, Southern (Netta erythrophthalma) 5 5

Sandpiper, Common (Actitis hypoleucos) 5 2 7

Sandpiper, Curlew (Calidris ferruginea) 36 61 25 3 125

Sandpiper, Marsh (Tringa stagnatilis) 4 4

Shelduck, South African (Tadorna cana) 16 20 32 68

Shoveler, Cape (Anas smithii) 1 1

Spoonbill, African (Platalea alba) 1 42 43



45

Name Upper

estuary

Lower

estuary

Salt

Marsh Mouth Total

Stilt, Black‐winged (Himantopus himantopus) 2 2

Stint, Little (Calidris minuta) 79 33 106 1 219

Swamphen, African Purple (Porphyrio madagascariensis) 1 1

Teal, Cape (Anas capensis) 2 7 5 14

Teal, Red‐billed (Anas erythrorhyncha) 2 5 7

Tern, Caspian (Sterna caspia) 1 9 14 11

Tern, Common (Sterna hirundo) 7 4 24 16

Tern, Sandwich (Sterna sandvicensis) 10 420 287

Tern, Swift (Sterna bergii) 8 11 1 81 46

Wagtail, Cape (Motacilla capensis) 19 7 7 3 36

Harrier, African Marsh 1 1

Whimbrel, Common (Numenius phaeopus) 1 1

TOTAL No. 468 705 583 891 2,417

TOTAL No. of SPECIES 21 46 27 22 52

The decline in numbers of Cape Cormorants at the Orange River Estuary is almost certainly a reflection of the precipitous decline in the overall Cape Cormorant population primarily due to the decline in omega-3-rich fish species (anchovies and pilchards) as a result of over-fishing. Other factors affecting the number of Cape Cormorants at the Orange River Estuary include the lack of suitable islands for breeding and roosting and human disturbance.

Since the 1980s the number of waders has also declined dramatically, even more than might be expected in relation to general global population declines.

Terns have also declined significantly in number (Figure 3.11). Anderson et al., (2003) suggest that the change in the geomorphological form of the estuary mouth and islands may have made it less suitable for roosting terms. They also suggest that other large nearby wetlands in Namibia currently may be more suitable and attract birds that formerly used the Orange River Estuary. An indication of the previously large bird populations at the Orange River Mouth is shown in Figure 3.12.



46

Figure 3.12: Water and seabirds at the Orange River Mouth, Spring 1993. a) Great White Pelicans and Cape

Cormorants roosting on an island; b) Palaearctic migrant terns roosting on the lee side of the beach berm

(Photographs: P. Morant)

3.5.3 Habitat utilization

Anderson (2013) divided the Orange River Estuary into four main areas for the purpose of the survey made in 2012 (Figure 3.13). The “Upper Section” was generally freshwater dominated, the “Lower Section” was more typically saline/estuarine, “Salt Marsh” primarily on the south side of the estuary and “River Mouth” which included the landward side of the beach berm and the longshore channel leading to the southernmost part of the saltmarsh (Figure 3.14).

a

b



47

Figure 3.13: Distribution of bird groups in the Orange River Estuary in relation to broad habitat types,

November 2012 (Anderson, 2013)

Figure 3.14: Flamingos feeding in re‐flooded portion of the saltmarsh.

As discussed above changes in the size and form of islands in the estuary near the mouth may have played a role in the decline in the number of Cape Cormorants utilizing the estuary. However, this is likely to be a minor factor when set against the massive decline in the population, as a result of over fishing, to the point where the species is considered to be Endangered.

0

100

200

300

400

500

600

700

800

900

1000

Upper section Lower Section Salt Marsh River Mouth

Other

Kingfishers

Wading birds

Waterfowl

Gulls & terns

Flamingos

Waders

Cormorants



48

Wader numbers have declined more than the global rate which suggests that the Orange River Estuary has become less attractive to waders as a result of a loss of intertidal and shallow water habitat. The degradation of the saltmarsh may have played a role as this habitat is ideal for waders (Anderson et al, 2003). However other species, e.g. Lesser Flamingo and Curlew Sandpiper, which use saltmarsh habitat for foraging, have not declined in numbers significantly (Anderson et al., 2003). The reduction in saltmarsh habitat may have been offset by the system being tidally dominated as a result of the mouth being almost permanently open. This has permitted the maintenance of extensive areas of intertidal mudflats which serve as foraging areas for wading birds that feed on benthic organisms.

The numbers of waterfowl have also declined since the early surveys when the Orange River mouth was freshwater-dominated. The upper reaches of the estuary may also serve as a dry-season refuge for waterfowl that opportunistically use ephemeral wetlands in the region.

The Black-necked Grebe was numerous in early counts but has become rare in recent surveys. However, these birds are known to use the mining polders to the north of the estuary in large flocks (P. Morant, pers. obs).

3.5.4 Conclusions

While the Orange River mouth has become more estuarine in character over the past two decades with the result that it has become less attractive to freshwater-loving bird species, e.g. waterfowl, there is considerable scope for restoration of the desiccated saltmarsh habitat. This alone should increase the attractiveness of the estuary to waders.

3.6 Mammals The wetlands of the lower reaches of the Orange River and its estuary serve as an oasis in an otherwise arid region. Gemsbok Oryx gazella and springbok Antidorcas marsupialis graze on the vegetated islands in the estuary and upstream of the Oppenheimer Bridge. The Cape clawless otter Aonyx capensis and the water mongoose Atilax paludinosus are present particularly in the channels on the southern side of the estuary. It is not known what impact the increasingly estuarine nature of the system has on the otter population.

Cape fur seals Arctocephalus pusillus may enter the estuary mouth area on occasion.

In the past the Orange River Estuary enjoyed a de facto nature reserve statue as a result of the diamond mine security. However, at present, there appears to be little control over the area. During the July 2017 site visit hunters with dogs were encountered near Dunvlei and cattle and sheep were seen grazing in the wetland.



49

4. CONSERVATION STATUS

4.1 Wetland of International Importance (Ramsar Site) The Orange River Estuary was designated as a Wetland of International Importance in terms of the Ramsar Convention on the 28th June 1991. Key attributes leading to the designation of the Orange River mouth as a Ramsar Site included:

The Orange River Estuary is one of only nine perennial coastal wetlands on the predominantly arid west coast of southern Africa;

The estuary supports more than 20 000 waterbirds of more than 60 species;

The estuary supports an assemblage of rare and endangered waterbird species;

The estuary supports more than 1% of the world and southern African populations of several species of waterbirds including the Black-necked grebe, Lesser flamingo, Chestnut-banded Plover, Curlew Sandpiper Swift Tern and Caspian Tern.

Additional attributes associated with the Orange River mouth Ramsar Site include:

The estuary supports a high diversity and abundance of estuarine-dependent and marine fish species and is believed to play an important role in linking fish populations in South Africa, Namibia and Angola.

The flood plain is an important source of grazing for wild animals in an extremely arid environment.

The estuary has been recognised as one of the most important in South Africa in terms of its waterbird populations (Turpie et al., 2002; Turpie and Clark, 2007). It has also been designated as an Important Bird Area (Barnes and Anderson, 1998).

Despite the location of the border between South Africa and Namibia in the estuary not having been resolved, Namibia designated the Orange River Estuary as a Ramsar Site on 23 August 1995 thereby creating a transboundary Ramsar Site. Subsequent to this (September 1995) the Orange River Transboundary Ramsar Site was placed on the Montreux Record principally because of the dramatic decline in bird numbers but also because of the desiccation of large areas of saltmarsh on the southern (South African) side.

4.2 Estuarine Management Plan In terms of the National Estuarine Management Protocol where an estuary straddles an international boundary, DEA in collaboration with the responsible authority of the affected neighbouring state must develop an Estuarine Management Plan in consultation with the relevant government departments of the affected states. In addition, section 34(1)(b)(i & ii) of the National Environmental Management: Integrated Coastal Management Act (Act 24 of 2008) states that the Estuary Management Plan must be consistent with the National Estuarine Management Protocol and the National Coastal Management



50

Plan (NCMP). The NCMP requires DEA to develop Estuarine Management Plans for all estuaries assigned to national government. The Orange River Estuary is one such estuary.

The Estuarine Management Plan is intended to be a strategic five-year document providing direction for the management of the Orange River Mouth Ramsar Site. The purpose of the Plan is to:

Facilitate co-operative management of the Ramsar Site through the development of a shared vision and strategic objectives for the management of the site;

Provide for the formal establishment of a governance structure that will oversee the implementation of the plan;

Provide the primary strategic tool for management of the Orange River Mouth Ramsar Site, informing the need for specific programmes and operational procedures;

Enable stakeholders to manage and use the Orange River Mouth Ramsar Site in such a way that its values and purpose for which it was declared are protected;

Provide a basis for integrating site management into broad-scale landscape and ecosystem planning;

Provide motivations for budgets and future funding and providing indicators that available funds are spent correctly;

Build accountability into the management of the Orange River Mouth Ramsar Site; and

Provide for capacity building, future thinking and continuity of management.

The effectiveness of the Plan depends upon it being integrated into international, national, regional and local plans. At the international level the Orange-Senqu River Commission’s (ORASEDOM) Orange River Integrated Water Resources Management Plan is of critical important to the Orange River Estuary as it ultimately governs the flow pattern and quantity of water reaching the estuary.

4.3 Ownership and protection status The wetland on the Namibian side of the Ramsar site forms part of the Sperrgebiet National Park and is managed by the Namibian Ministry of Environment and Tourism.

When the Orange River Mouth Ramsar Site was proclaimed by South Africa it was not given any formal conservation status probably as a result of the de facto protection provided by the security required by the diamond mining operations both in South Africa and Namibia. Alexander Bay and Oranjemund were both closed “company” towns with controlled access.

It is the intention of the South African DEA to declare the Ramsar Site as a Protected Area under the National Environmental Management: Protected Areas Act. In the meantime the Orange River Mouth Estuarine Management Plan is being implemented under the leadership of DEA and the Northern Cape Department of Environment and Nature Conservation (DENC).



51

5. REHABILITATION OF THE SALTMARSH

5.1 Introduction The Orange River Estuary is the end-user of water derived from the approximately one million square kilometre catchment of the Orange River. The changes in the flow regime as a result of the demands placed on the river have had a significant effect on the Orange River mouth. In 1959 Brown (1959) described the system as a “river mouth” as it was dominated by fluvial flow. The present situation is that the Orange River mouth has become increasingly estuarine in character. Except for two brief periods of a few days each the mouth has been consistently open since December 1993. A major consequence of this is the further degradation of the desiccated saltmarsh on the south side of the estuary. The management of river flow falls within the ambit of ORASECOM which will have to respond to the needs of the Orange River Mouth Estuarine Management Plan to which The PSJV contributed. The PSJV alone, however, cannot be expected to mitigate the changes in flow. Nevertheless the PSJV can contribute by enabling the free connection of the degraded saltmarsh with the estuary basin and to facilitate inflow of freshwater to the saltmarsh when the river is in flood.

5.2 Restoring the connection with the estuary basin

5.2.1 Present condition

The road embankment built by State Alluvial Diggings in the 1960s ostensibly to control a “mosquito problem” isolated approximately a third of the vegetated estuarine area (approximately 300 ha) from the system (Figure 5.1). Since that time the isolated saltmarsh has followed a trajectory of increasing degradation despite the major 1988 flood and other smaller floods, and the breaching of the seaward end of the embankment in 1997 to permit water from the estuary to enter the southernmost extremity of the degraded saltmarsh (Figure 5.2).

The seaward end of the embankment was “anchored” or pinned” in position by means of scrap machinery (“Detroit riprap”) being embedded in the beach berm at the Orange River Mouth (see Figure 2.6). The scrap machinery has prevented the mouth from migrating southwards to its fullest possible extent and thus limited the ingress of seawater into the saltmarsh.



52

Figure 5.1: The road embankment preventing ingress of water into the southern saltmarsh, 2 November 1986

(Source: State Alluvial Diggings)



53

Figure 5.2: Road embankment at Orange River mouth showing breach made in 1997 to permit the flooding of the desiccated saltmarsh.



54

5.2.2 Remedial action

The remedial action required is the complete removal of the scrap machinery from the beach berm at the Orange River Mouth, the portion of the embankment remaining after the 1997 breaching, and the embankment on the upstream side of the channel created by the 1997 breaching. The overall objective is to return the topography of the lower estuary to as near a pre-1960 condition as possible (Figure 5.3).

Figure 5.3: The Orange River mouth showing the saltmarshes connected to

both the river and estuary, May 1943.

5.2.2.1 RemovalofscrapmachineryfromthebeachbermattheOrangeRiverMouth

The volume of, and area containing, the scrap machinery needs to be determined by a geomagnetic

survey in order to define accurately the work to be done. The approximate area containing the

scrap material is indicated by the circle in Figure 5.4.



55

Figure 5.4: Structures to be removed during remedial action by PSJV.



56

Removal of the scrap machinery will be dependent on tidal and sea-state conditions and may have to be spread over some time (months or even 1 – 2 years). All equipment required to undertake the excavation and removal of the scrap material will have to be brought to site along the beach. While it may be considered simpler and more convenient to temporarily fill the 1997 breach in the embankment to provide access to the beach, the probable need to maintain the access for up to two years will be unacceptable. Such a closure of the longshore channel is almost certain to cause further degradation of the saltmarsh.

5.2.2.2 Removaloftheroadembankment

The objective of removing the approximately 3 km – long road embankment (see Figure 5.4) is to eliminate a major obstruction to the ingress of water from the river and estuary basin into the saltmarsh during periods of high water levels.

The embankment must be surveyed to determine the amount of material to be removed to restore the saltmarsh area to its natural geomorphological state. A suitable site for the disposal of the removed embankment material must be located within the PSJV mine property. Under no circumstances should any embankment material be disposed of within the estuary or on the beach. The removal of the road embankment should also include re-opening the flood channel inlet (see Figure 5.5) immediately downstream of the former sewage oxidation pond site.

5.2.2.3 Rehabilitationofthelocationoftheformersewageoxidationponds

The former sewage oxidation ponds (see Figure 5.4), which occupied part of the southern most river channel downstream from Dunvlei, still have to be removed and the river channel re-established. Should Dunvlei Farm be retained (see Section 5.2.2.4 below) consideration should be given to facilitating river flow from the flood channel inlet (see Figure 5.5) into the oxidation pond channel. It should be noted that prior to being drained the sewage oxidation ponds supported a diversity of waterfowl and water-associated bird species.

5.2.2.4 Back‐flooding

River flow will have to be reduced to ca. 5 m3/sec to permit the estuary mouth to close. This requires the cooperation of ORASECOM, DEA and DENC. After mouth closure the water level in the system should be allowed to rise and back-flood the saltmarsh areas. The inundation potential of the presently desiccated saltmarsh is shown in Figure 5.5. A back-flood level of > 1.5 m will inundate more than 70% of the saltmarsh area.



57

Figure 5.5: Inundation potential of saltmarsh

(Adapted from CSIR, 1994).



58

5.2.3 Impact Assessment

In this section the assessment of the impact of the various interventions contributing to the present condition of the Orange River Estuary and its wetlands and saltmarshes is compared with the projected impact resulting from the implementation by the PSJV of the remedial measures discussed above. An assessment of the effect of back-flooding after the implementation of the remedial action by the PSJV is also provided. It should be noted, however, that estuary mouth management and the associated back-flooding is the responsibility of the authorities (DEA, DENC) charged with implementing the ORMEMP. The assessment criteria are listed in Appendix 1.

5.2.3.1 ScrapmachineryinthebeachbermattheOrangeRiverMouth

Removal of the scrap machinery from the beach berm at the Orange River Mouth will permit the estuary mouth to migrate to its fullest extent southwards thereby allowing water to enter the intertidal marshes.

The present impact of the scrap machinery is negative, high at the local level for the inter- and supra-tidal saltmarsh, regional for the fish nursery function of the estuary, and international for the migrant birds using the system. After removal of the scrap machinery to permit the migration of the estuary mouth to its fullest extent the impact will be positive, medium, for the saltmarsh, positive high for fishes and positive high for birds.

However the full benefit of the removal of the scrap material will only be realised when the back flooding regime is implemented in terms of the ORMEMP. If a closure and back-flooding regime of 2 - 3 year intervals is achieved the assessment would be positive, high for the saltmarsh, fish and birds.

Assessment of the impact of the removal of the scrap machinery on:

Saltmarsh

CRITERIA WITHOUT MITIGATION (status quo)

WITH MITIGATION AFTER BACK‐FLOODING

Extent Local Local Local

Duration Long‐term Long‐term Long‐term

Intensity High Medium High

Probability Definite Probable Probable

Confidence High High High

Significance VERY HIGH (‐ve) MEDIUM (+ve) HIGH (+ve)



59

Fishes



Extent Regional Regional Regional


Intensity High Medium Medium ‐ High



Significance VERY HIGH (‐ve) HIGH (+ve) HIGH (+ve)

Birds



Extent International International International


Intensity High Medium Medium ‐ Low




5.2.3.2 Removalofroadembankment

The removal of the road embankment from within the saltmarsh will permit greater ingress of water from the estuary basin both under tidal conditions when the estuary mouth is open and under back-flooding conditions when the estuary mouth is closed.

The present impact of the road embankment is negative, very high at the local level for the inter- and supra-tidal saltmarsh, negative, high at the regional level for the fish nursery function of the estuary, and negative, high at the international level for the migrant birds using the system. After removal of the embankment to permit free ingress of water to the saltmarsh the impact will be positive, medium.

However the full benefit of the removal of the road embankment will only be realised when the back flooding regime is implemented in terms of the ORMEMP. If a closure and back-flooding regime of 2 - 3 year intervals is achieved the assessment would be positive, high for the saltmarsh, fish and birds. If a closure and back-flooding regime of 2 - 3 year intervals is achieved the assessment would be positive, high for the saltmarsh, fish and birds.



60

Assessment of the impact of the removal of the road embankment on:

Saltmarsh





Intensity High Medium Medium‐High




Fishes








Significance HIGH (‐ve) MEDIUM (+ve) HIGH (+ve)

Birds



Extent International International International


Intensity High Medium Medium




5.2.3.3 Rehabilitationofformersewageoxidationpondssite

While in operation the former sewage oxidation ponds supported a wide range of waterfowl and water-associated bird species many of which have been present in the river channel habitat replaced by the sewage oxidation ponds. Reconnecting this area to the main river/estuary basin should assist in re-establishing this aquatic habitat attractive to birds as well as providing more habitat for fishes, other aquatic organisms, and aquatic vegetation (reedbeds).



61

The present impact of the former sewage oxidation ponds is negative, very high, at the local level for aquatic vegetation and aquatic organisms (invertebrates), high, negative at the regional level for fishes and high, negative at the regional/international level for aquatic birds using the area. After rehabilitation to re-establish the channel occupied by the now-disused sewage oxidation ponds the impact will be positive, high for aquatic vegetation and aquatic organisms (invertebrates) and positive, medium for fishes and aquatic birds.

However the full benefit of the rehabilitation of the sewage oxidation pond site will only be realised when the back flooding regime is implemented in terms of the ORMEMP. If a closure and back-flooding regime of 2 - 3 year intervals is achieved the assessment would be positive, high for the aquatic vegetation and aquatic organisms (invertebrates), fish and birds.

Assessment of the impact of rehabilitating the former sewage oxidation pond site on:

Aquatic vegetation





Intensity High Medium Medium‐ High




Aquatic organisms (invertebrates)





Intensity High Medium Medium‐ High






62

Fishes









Aquatic and water-associated birds

CRITERIA WITHOUT MITIGATION(status quo)


Extent Regional/International Regional/International Regional/International


Intensity High Medium Medium




5.3 Restoring the upstream river connection

5.3.1 Present situation

The flood channel from Dunvlei Farm to the saltmarsh has been closed off by dykes (see Figure 5.6) built to protect the farmlands from flood waters. Consequently, no fresh water can enter the saltmarsh along this channel thereby limiting the potential for leaching accumulated salt from the soil. This, in turn, reduces the germination potential of the seeds of saltmarsh plants. The sewage oxidation ponds have been relocated from the flood channel to a site within the PSJV property but the old ponds have not been rehabilitated such that river flow from Dunvlei should it be re-established could move down the channel to the saltmarsh.


In order to restore the estuarine wetlands to their pre-1960 condition (see Figure 5.3) consideration should be given to the removal of the protective dyke around Dunvlei Farm and to re-open the river channel running along the south bank. This action will require both a separate feasibility study and consultation with the community to determine whether Dunvlei Farm should be restored to full agricultural production or whether it should be decommissioned and the original wetland restored to full functionality. The feasibility study must include the environmentally acceptable disposal of the dyke and other excavated material within the PSJV mine property.



63

Figure 5.6: Dyke protecting Dunvlei Farm which prevents river flow to the saltmarsh on the south side of the

estuary.

5.4 Dust control Wind-blown dust originating within the mine has been implicated in smothering plants in the desiccated saltmarsh area; however a considerable proportion of the dust is also generated within the desiccated saltmarsh itself.


Within the saltmarsh dust control will be achieved by re-establishing the links with the main estuarine basin (see Sections 5.2.2.1, 5.2.2.2 and 5.2.2.3). Once the saltmarsh has been returned to a healthy condition plant cover will have increased thus preventing wind-mobilisation of the soil. Therefore no specific dust abatement measures will be required within the saltmarsh. Control of dust arising from activities in the mine should be managed in terms of the PSJV’s EMP for its onshore operations.



64

5.5 Conclusion Should the PSJV successfully implement the remedial actions required to remove the scrap machinery from the beach berm at the Orange River Mouth, remove the road embankment through the saltmarsh, and rehabilitate the former sewage oxidation pond site it will have made a significant contribution to the rehabilitation of the Orange River Mouth Ramsar Site. However, full recovery of the degraded areas depends on managing the estuary mouth closure regime such that closure occurs for a period of 4 – 6 weeks every 2 - 3 years. This latter is the responsibility of the authorities (e.g. DEA, DENC) charged with implementing the Orange River Mouth Estuarine Management Plan.

The combined effect of the PSJV’s remedial actions and the correct mouth closure/back-flooding regime could result in the recovery of the Orange River Estuary such that it is removed from the Montreux Record and restored to full Ramsar Site status.



65

6. REFERENCES

Anderson, M.D., Kolberg, H., Anderson, P.C., Dini, J. & Abrahams, A. (2003). Waterbird populations at the Orange River mouth from 1980-2001: a reassessment of its Ramsar status. Ostrich 74(3&4): 159-172.

Barnes, K.N. and Anderson, M.D. (1998) Important bird areas of the Northern Cape. In: Barnes KN (ed) The Important Bird Areas of Southern Africa. pp 103-122. BirdLife South Africa, Johannesburg, South Africa.

Bennett, B.A. (1994). The fish community of the Berg River Estuary and an assessment of the likely effects of reduced freshwater inflows. South African Journal of Zoology, 29(2): 118-125.

Bornman, T.G, Adams, J.B. and Nix, C. (2004). Adaptations of salt marsh to semi-arid environments and management implications for the Orange River mouth: anthropogenic effects on arid systems. Transactions of the Royal Society of South Africa: Proceedings of a colloquium on adaptations in desert fauna and flora 59: 125-131.

Bremner J.M., Roger J. & Willis,. J.P. (1990). Sedimentological aspects of the 1988 Orange River floods. Transactions of the Royal Society of South Africa 47: 247-94.

Brown, A.C. (1959). The ecology of South African estuaries Part IX: Notes on the estuary of the Orange River. Transactions of the Royal Society of South Africa, 35: 463-473.

Cambray, J. (1984). Fish populations in the middle and lower Orange River, with special reference to the effect on stream regulation. Journal of the Limnological Society of South Africa, 10 (2):, 32-49.

CSIR, (1994). Alexkor Environmental Management Programme: Specialist Study Report. Volume 2. Stellenbosch, CSIR Report EMAS-C 94047(2).

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Day, J.H. (1981). Chapter 14. Summaries of current knowledge of 43 estuaries in southern Africa. In: Day J.H. (ed), Estuarine Ecology with particular reference to southern Africa. A.A. Balkema, Cape Town. pp. 251-329.

Harrison, T.D. (1997). A preliminary survey of coastal river systems on the South African west coast, Orange River – Groot Berg, with particular reference to the fish fauna. Transactions of the Royal Society of South Africa, 52 (2): 277-321.

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Lamberth, S.J. & A.K. Whitfield (1997). The likely effects of altered freshwater flows on the fish of the Olifants River Estuary. Unpublished report to CSIR.

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APPENDIX 1: METHOD FOR SIGNIFICANCE DETERMINATION

In assigning significance ratings to potential impacts before and after mitigation the approach presented below is followed.

1. Determine the impact consequence rating: This is a function of the “intensity (or severity)”, “extent” and “duration” of the impact (see Section 1). The consequence ratings for combinations of these three criteria are given in Section 2.

2. Determine impact significance rating: The significance of an impact is a function of the consequence of the impact occurring and the probability of occurrence (see Section 1). Significance is determined using the table in Section 3.

3. Modify significance rating (if necessary): Significance ratings are based on largely professional judgement and transparent defined criteria. In some instances, therefore, whilst the significance rating of potential impacts might be “low”, the importance of these impacts to local communities or individuals might be extremely high. The importance/value which interested and affected parties attach to impacts will be highlighted, and recommendations should be made as to ways of avoiding or minimising these perceived negative impacts through project design, selection of appropriate alternatives and / or management.

4. Determine degree of confidence of the significance assessment (see Section 1): Once the significance of the impact has been determined, the degree of confidence in the assessment will be qualified. Confidence in the prediction is associated with any uncertainties, for example, where information is insufficient to assess the impact.

1. Criteria for Impact Assessment

The criteria for impact assessment are provided below.

Criteria Rating Description

Criteria for

ranking of the

INTENSITY

(SEVERITY) of

environmental

impacts

ZERO TO VERY

LOW

Negligible change, disturbance or nuisance. The impact affects the

environment in such a way that natural functions and processes are not

affected. People / communities are able to adapt with relative ease and

maintain pre‐impact livelihoods.

LOW

Minor (Slight) change, disturbance or nuisance. The impact on the

environment is not detectable or there is no perceptible change to people’s

livelihood.

MEDIUM

Moderate change, disturbance or discomfort. Where the affected

environment is altered, but natural functions and processes continue, albeit in

a modified way. People/communities are able to adapt with some difficulty

and maintain pre‐impact livelihoods but only with a degree of support.

HIGH

Prominent change, disturbance or degradation. Where natural functions or

processes are altered to the extent that they will temporarily or permanently

cease. Affected people/communities will not be able to adapt to changes or

continue to maintain‐pre impact livelihoods.

Criteria for

ranking the

DURATION of

impacts

SHORT TERM < 5 years.

MEDIUM TERM 5 to < 15 years.

LONG TERM > 15 years, but where the impact will eventually cease either because of

natural processes or by human intervention.



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Criteria Rating Description

PERMANENT

Where mitigation either by natural processes or by human intervention will not

occur in such a way or in such time span that the impact can be considered

transient.

Criteria for

ranking the

EXTENT / SPATIAL

SCALE of impacts

LOCAL Impact is confined to project or study area or part thereof, e.g. limited to the

area of interest and its immediate surroundings.

REGIONAL Impact is confined to the region, e.g. coast, basin, catchment, municipal region,

etc.

NATIONAL Impact is confined to the country as a whole, e.g. South Africa, Namibia, etc.

INTERNATIONAL Impact extends beyond the national scale.

Criteria for

determining the

PROBABILITY of

impacts

IMPROBABLE Where the possibility of the impact to materialise is very low either because of

design or historic experience, i.e. ≤ 30% chance of occurring.

POSSIBLE Where there is a distinct possibility that the impact would occur, i.e. > 30 to ≤

60% chance of occurring.

PROBABLE Where it is most likely that the impact would occur, i.e. > 60 to ≤ 80% chance

of occurring.

DEFINITE Where the impact would occur regardless of any prevention measures, i.e. >

80% chance of occurring.

Criteria for

determining the

DEGREE OF

CONFIDENCE of

the assessment

LOW ≤ 35% sure of impact prediction.

MEDIUM > 35% and ≤ 70% sure of impact prediction.

HIGH > 70% sure of impact prediction.

2. Determining Consequence

Consequence attempts to evaluate the importance of a particular impact, and in doing so incorporates extent, duration and intensity. The ratings and description for deterring consequence are provided below.

Rating Description

VERY HIGH

Impacts could be EITHER:

of high intensity at a regional level and endure in the long term;

OR of high intensity at a national level in the medium term;

OR of medium intensity at a national level in the long term.

HIGH


of high intensity at a regional level and endure in the medium term;

OR of high intensity at a national level in the short term;

OR of medium intensity at a national level in the medium term;

OR of low intensity at a national level in the long term;

OR of high intensity at a local level in the long term;

OR of medium intensity at a regional level in the long term.

MEDIUM


of high intensity at a local level and endure in the medium term;

OR of medium intensity at a regional level in the medium term;



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Rating Description

OR of high intensity at a regional level in the short term;

OR of medium intensity at a national level in the short term;

OR of medium intensity at a local level in the long term;

OR of low intensity at a national level in the medium term;

OR of low intensity at a regional level in the long term.

LOW

Impacts could be EITHER

of low intensity at a regional level and endure in the medium term;

OR of low intensity at a national level in the short term;

OR of high intensity at a local level and endure in the short term;

OR of medium intensity at a regional level in the short term;

OR of low intensity at a local level in the long term;

OR of medium intensity at a local level and endure in the medium term.

VERY LOW

Impacts could be EITHER

of low intensity at a local level and endure in the medium term;

OR of low intensity at a regional level and endure in the short term;

OR of low to medium intensity at a local level and endure in the short term.

OR Zero to very low intensity with any combination of extent and duration.

3. Determining Significance

The consequence rating is considered together with the probability of occurrence in order to determine the overall significance using the table below.

PROBABILITY

IMPROBABLE POSSIBLE PROBABLE DEFINITE

CONSEQUEN

CE

VERY LOW INSIGNIFICANT INSIGNIFICANT VERY LOW VERY LOW

LOW VERY LOW VERY LOW LOW LOW

MEDIUM LOW LOW MEDIUM MEDIUM

HIGH MEDIUM MEDIUM HIGH HIGH

VERY HIGH HIGH HIGH VERY HIGH VERY HIGH

In certain cases it may not be possible to determine the significance of an impact. In these instances the

significance is UNKNOWN.

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