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A proposed scheme for the enhancement of the Blackwater cross over of the River Medina, Isle of WightIntroductionRiver rehabilitation and restoration is a relatively new concept and procedure, having emerged from the sustainable development paradigm (Wheaton, Darby and Sear, n.d cited in Darby and Sear, 2008). In recent years, river restoration has been given another, new impetus through the European Union Water Framework Direction (EU WFD) and national government targets for both water quality and biodiversity conservation (Biodiversity Action Plans (BAPs) (iwight.com, 2003). Restoration schemes, focused on ecology (Shields Jr, Copeland et al, 2003; Pretty, Harrison et al, 2003), are increasingly incorporating in more boarder requirements such as recreation and accessibility (Woolsey, Capelli et al, 2007). One of the first to be carried out in the UK was the restoration of the Rivers Skerne and Cole, Swindon (Aberg and Tapsell, n.d. cited in Boon and Raven, 2012). This scheme has been successful in improving access to the river and geomorphological processes despite increasing sediment load and phosphorous during construction (Kronvang, Svendsen et al, 1998). Yet it was considered unsuccessful in improving biodiversity (Biggs, Corfield et al, 1998) which Palmer, Bernhardt et al (2005) suggest restoration isn’t always ecologically successful.

A variety of different approaches have been adapted to enhance or to rehabilitate a river, depending on the level of instability in the river (Downs and Gregory, 2004; Knighton, 1998). These approaches range from wholescale morphological reconstruction used at sites such as Ewan Water (Gilvear and Bradley, 1997), the Skerne and Cole (Biggs, Corfield et al, 1998), Deep and Whitemarsh Run, Maryland (Soar and Thorne, 2001; Smith and Prestegaard, 2005) to more subtle changes including low flow sinuosity (The Medina, Shide tributary (Hector, 2013), riparian corridors (Larsen n.d cited in Petts and Calow, 1996) and artificial step-pools/riffle-pool sequences (Knighton, 1998; Downs and Gregory, 2004). All these measures have been proven to have varying degrees of success (Palmer, Bernhard et al, 2005; Radspinner, Diplas, Lightbody and Sotiropoulos, 2010). Towards the future, the fate of the UK’s rivers and commitments to the EU WFD are uncertain given the BREXIT referendum. This report will discuss a proposed scheme for the enhancement of the Blackwater crossing of the Medina.

Aims and objectivesAim

To enhance the aesthics of the Medina cross over at Blackwater to improve local habitat and geomorphological diversity.

Objectives

1. To ‘soften’ the appearance of pre-existing concrete structures at the cross-over to blend it into the landscape.

2. To reactive the old channel course to provide a backwater shelter for fish.3. To improve bed diversity by introducing riffles.4. To reduce the channel’s wide through replanting bankside vegetation to encourage low flow

sinuosity and increase habitat diversity.

Study siteThe River Medina is the only river in the UK which flows directly north, from its source at Chale before then flowing directly north (Hector, 2013) to Cowes where it discharges into the Solent

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(figures 1 and 2). Its total length is 17 km, draining a 17 km2 catchment. It passes through two major towns in the centre of the island – Blackwater and Newport. Historically, the river has been modified significantly. First by the Victorians who constructed a railway which ran directly between Newport and St Catherine’s Point, South Downs. More recently, however, this railway has been removed and during the 1960s it was channelised and straightened further to create a flood alleviation scheme. As the river flows towards the sea, from Newport to Cowes and the Solent, it is an enclosed estuary consisting of industry, a navigable channel, and a large inland harbour (Islandrivers.org, 2015).

Since 2011, the river has undergone restoration and enhancement works with a view of improving ecological diversity, because the river is home to migratory Brown (Sea) trout and European Eels. The scheme was awarded £90,000 from the Sita Trust and carried out by the Newport Rivers Group, Natural Enterprise and the Island 2000 Trust and Environment Agency, to improve ecological diversity for the fish species (Hector, 2013). Divided into three phases, the scheme implemented a variety of different in-stream measures ranging from planted berms (figure 3), artificial islands and riffles (figure 4) to removing bankside trees to ‘lighten’ the ambiance of the river (Hector, 2013).

Figure 1: overview of the river medina as it passes through Newport to the estuary at Cowes. Image taken from Google Maps, accessed 11.12.2016, retrieved from https://www.google.co.uk/maps/place/Newport/@50.6900713,-1.2940365,14z/data=!4m5!3m4!1s0x48746214000d10c5:0xb93bd2652373300a!8m2!3d50.700803!4d-1.291633?hl=en&hl=en

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Figure 2: a zoomed in picture of the River Medina, stretching from Blackwater to Newport which is the study area. Images taken from Google Maps, accessed 11.12.2016 retrieved from https://www.google.co.uk/maps/place/Newport/@50.6900713,-1.2940365,14z/data=!4m5!3m4!1s0x48746214000d10c5:0xb93bd2652373300a!8m2!3d50.700803!4d-1.291633?hl=en&hl=en

Figure 3: the Shide tributary following construction of vegetated berms.

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Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

At this point is the Shide tributary, a concrete lined channel, subject to recent work to enhance the geomorphic and ecological diversity. Also, to a lesser, extent to ‘soften’ the aesthics of the river at this point.

Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

Here is the Medina as it flows towards Newport, from Blackwater. Notice how it splits into two channels. At this point, the Blackwater cross over, the railway runs directly through the middle of the old channel course.

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Figure 4: riffle close to St George's Road bridge. This is one of a variety of different in-stream measures implemented during the works.

Appraisal of existing measures implemented in the River Medina restorationWhen the scheme was constructed, a variety of in-stream and bankside measures were implemented to improve the ambiance, ecology and ‘naturalness’ of the river. These include artificial riffles (figure 4), vegetative and log berms and large woody debris. These measures have had some successes including the re-instatement of low flow sinuosity and the re-creation of, a more ‘natural’ looking and sounding river. But some of the measures implemented have either started to fail or failed to restore longitudinal, ecological connectivity.

Figure 5 shows evidence that some in-stream measures such as larch-spilling are beginning to fail. In figure 5, you can see the home owner has tried to re-enforce the failing bank line. Buchanan, Nagle, and Walter (2013) suggest failure along this bank line is related to the combined effects of high shear stress, associated with depth and velocity increases here. Thus, it may be suggested using willow spillings, without building in some form of geo-textile to secure the sediment has contributed to failure here. Another issue with this scheme is the absence of fish passages and Elver weirs which have been removed during the original works (figure 6). Lack of Elver passes may mean scheme is not ecologically successful because it has failed to improve longitudinal habitat diversity and connectivity (Lepori, Palm, Brannas and Malmqvist, 2005).

Similarly, an island installed, two years, has since disappeared. This island was envisaged, by the designers, to act like a flow deflector and promote scour either side of it. It failed, in part, because of high flow events and a lack of vegetation at this site. Another possible reason it failed was there was not active post-project monitoring, which could have otherwise avoided the complete wash out of the island (Downs and Kondolf, 2002). At other sites, such as the Shide tributary have been successful in re-creating low flow sinuosity, despite the inability to retain artificially coarse bed material.

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Figure 5: site 3, upstream of St Georges Road Bridge crossing. This photo shows clear evidence of bank undermining, perhaps, by high winter flows.

Figure 6: weir at site 2, St Georges Road Bridge. Towards the left-hand side, nearest the inner bank, there is a small notch. Here was where a fish pass was once installed, now it has been removed. The black circle indicates where the former fish pass once was.

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Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

Here the bank line is beginning to failure due to recent high winter flows. Previously this had been filled with sediment to support riparian vegetation but has since been washed out. As you can see, the home owner has tried to sure the bank line up which is likely to continue to fail without immediate structural re-enforcement.

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Figure 7: The Shide tributary, river Medina, Shide. Here you can see evidence of low flow sinuosity structures, vegetated meander bends. Towards the top of the image, you can see where there is a low-level weir-type structure which has been introduced for the purposes of catching coarse bed material and introduced some flow diversity.

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Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Figure 8: Zoomed in image of the head of the right hand vegetated berm. This structure shows evidence of scour, possibility related to secondary circulation.

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

Flow heading north

Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Velocity changes at this point, as the water flows over a rock weir. Also, the flow up and till this point is largely steady, uniform.

To the left hand-side, cylix (Willow) is starting to colonise the bend. This, however, was not planted.

Flow heading northFlow heading northFlow heading northFlow heading northFlow heading northFlow heading northFlow heading north

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

Zoomed in photo of the right-hand meander bend, looking from the bridge. This close-up shows evidence of scour at the head of the bend.

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Summary table of the current restoration measures in taken in the river MedinaSite along the

riverMeasure taken Advantages Disadvantages

Site 1: River Medina, centre of Newport

Vegetated berms to restore low flow sinuosity and removal of a weir just upstream.

Recreate low flow sinuosity, reduce fine sediment load, and improve water quality (ref).

Site 2: upstream of St Georges

Road Bridge crossing

Re-vegetate the bank line to improve habitat diversity and reduce channel width.

Re-create lateral connectivity, low flow sinuosity and improve habitat diversity.

Prone to failure as a result of secondary circulation and high, bank full flows (Buchanan, Nagle, and Walter, 2013).

Site 3: Shide tributary

Vegetated berms, bend way weirs and artificial gravel. Designed to create low flow sinuosity and slow the flow passing through this reach.

Improved aesthical value of the concrete lined channel, mimics natural bankside vegetation and provides refugia for macro-invertebrates

Scour at the head of the right hand-side berm (figure 8). Geotextile can be stripped from an area if vegetation has not been immediately planted following construction of the berm (Morris and Moses, 1999).

Site 4: Blackwater

reach, above Shide

Artificial riffle creation. Create low flow habitats through ponding in the upstream side of the riffle (Downs and Gregory, 2004). Re-oxygenate a reach and restore geomorphic diversity and improve the aesthics of a river (Pasternack et al, 2007).

Pasternack et al (2007) reveal riffles are prone to failure through “the “reverse domino” mechanism” (p. 25), whereby increases in the downslope water surface elevation increase the shear stress on the riffle’s crest. Resulting in a cascade of riffle re-organisation.

Site 5: Blackwater cross over

Concrete berm with vegetation planted behind it. Log berms along the outer bank of the meander bend to protect the bank toe. Instream grade control structures to capture coarse material (ref).

Log berms need to be selected so that they don’t move during high flows and are often designed to be longer than the bankfull channel width, in small streams (Kail, Hering et al, 2007)

Log berms can provide little in the way of ecological and morphological diversity, if they are not designed to the appropriate bankfull and flow conditions (Kail, Hering et al, 2007)

Table 1: summary table of existing rehabilitation measures along the 2-km target reach of the river Medina.

Design procedureThere is scope for further improvement in this reach, despite it being heavy concreted and situated close to a piece of high value infrastructure, a foot bridge. This scheme sets out to use a combination of the existing structures and introduce new ones as well.

For example, around the meander bend, figure 10, there is scope for re-introducing vegetation provided it is properly protected and secured. Similarly, pre-existing grade control structures could be removed and replaced with meander bend way berms to increase the hydraulic roughness. Although this may compromise the concrete walls. As the river joins the main channel, two or three artificial riffles could be introduced to create habitat diversity and improve the aesthical value of this reach. Aside from this, figures 13, 14 and 15 and Table 2 provides more detailed breakdowns of these measures.

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Summary table of the proposed measures to enhance the Blackwater cross-overMeasures to

be implemented

Design considerations

Merits Potential problems

Reed beds and wall coverings

Need to withstand high shear stresses and flow velocities within the meander bend.

Improved aesthical value, low velocity habitat and sediment trapping (Osbourne and Kovacic, 1993). Help to recreate a low flow, meandering thalweg (Downs and Gregory, 2004). Coir matting has been shown to be effective at both retaining and capturing fine sediment, further helping vegetation to establish (Vishnudas, Savenije et al, 2006) and are cost-effective, typically costing less than £1 per metre square.

Washed out at high discharges, scoured by secondary circulation. The success of this measure is also dependent upon the ability of other plant species to colonise the berms, particularly, if the neighbouring banks contain a viable seed bank (Rohde, Schutz, Kienast and Englmaier, 2005). Rominger, Lightbody et al (2010) reveal vegetation can displace the secondary circulation cell towards the outer bank, hereby increasing scour towards the pool and outer, cut bank and enhanced erosion of the point bar tip.

Artificial Riffles

Material to be designed to with-stand flows with a return interval of 100-years (Chin, Gelwick et al, 2010). Velocity over riffle crest should 40 cm/s with a maximum depth of 25 cm, for it to behaviour like a natural riffle at low flow stages.Sediment may need to be designed to suit the local ecology and to prevent vertical winnowing, if fine sediment is introduced to the river from upstream (Downs and Gregory, 2004).

Known to improve local, macro-invertebrate diversity as well as fish spawning grounds (Ebrahimnezhad and Harper, 1997; Chin, Gelwick et al, 2010). Hydrological diversity is also improved as well (Brown and Pasternack, 2008).

Can fail through the “‘reverse domino mechanism’” resulting in re-organisation of the riffle sequence (Pasternack et al, 2007, p. 25). Also, they can be prone to armouring and winnowing of fine sediments, during medium to high flows, leading to a degradation of spawning ground (Pasternack et al, 2007).

Restoring lateral

connectivity

Slows down the overall flow velocity and allows over-bank flooding to occurring during high flow stages.

Floodplain scallops provide “breeding and/or stepping stones” (Chovanec, Straif et al, 2005, p. 220) for migratory and resident species. Creation fo artificial side-channels have been shown to can support many fish from different species (Morley, Garcia et al, 2005).

Full lateral connectivity may not be attainable at this site because of the footpath running through the middle of the river. If it is not designed properly then it can become overly wide due to bank erosion and flow velocity can increase (Eder and Mestl, 2012), defeating the objective of creating a backwater habitat.

Table 2: summary table of the enhancement measures to be implemented in the Blackwater cross-over.

Discussion of the proposed re-imaging the Blackwater cross-overBy reviewing both the site and the literature, three different measures have been identified, each with their own merits and problems.

1. Reed bank construction:

Replanting riparian vegetation either by using reeds or resulting Willow (Salix type) has been shown to improve water quality, visual aesthetics, and geomorphic diversity of the bed (e.g. Downs and Gregory, 2004; Moses, and Morris, 2005; Francis and Hoggart, 2016.) Although, it must be used with

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caution to avoid enhanced erosion of the cut bank (Rominger, Lightbody and Nepf, 2010) or wash out at high flows which influences the ability of neighbouring vegetation to colonise the berm (Rohde, Schutz, Kienast and Englmaier, 2005). For them to be most effective, it is recommended that they are both be scaled to half to a third of the channel width to avoid full closure of the channel – and coir geotextile has been shown to be the best way of securing the subtract, allowing the vegetation to colonise it (Vishnudas, Savenije et al, 2006). From an ecological point of view, Chin, Gelwick et al (2010) imply increased faunal plant coverage, reduced cross-sectional area and velocity, associated with re-vegetation, improves macro-invertebrate diversity, a scenario greatly enhanced by the geomorphic changes associated with replanting of vegetation (Kail, Hering et al, 2007).

Rominger, Lightbody and Nepf (2010) highlight a significant problem with using vegetated berms in meander berm ways. They argue vegetation can initiate a positive feedback system associated with displacement of the helical flow onto the outer, cut bank whilst the vegetation captures fine sediment. Eventually cutting off sediment supply from the channel to the bar. Consequently, it can create a new problem associated with bank erosion and scour of the point bar tail. Francis and Hoggart (2016) exemplify using vegetation features, besides reed beds, not only improve habitat and geomorphic diversity but also can be used to soften the aesthetics of concrete-lined, urban channels such as Deptford Creek.

Figure 9: proposed site for the installation of artificial riffles and reed beds at the Blackwater cross-over.

Kenwick, Shammin and Sullivan (2009) disclose 80% and 89% of urban planners indicated they would include tree buffers into existing and proposed urban areas. Shammin and Sullivan (2009) evidence reflects why it may be important to re-instate vegetation along this reach has been shown to create a more ‘naturalised’ appearance. Despite strong support for riparian tree planting, planting trees in the immediate vicinity of the channel is not practical because of the potential risk of structural undermining by tree roots.

2. Artificial riffles:

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Use of artificial riffles has produced mixed ecological and geomorphic changes (Ebrahimnezhad and Harper, 1997), evident in their study of Harper’s brook, Northamptonshire. This, they reveal, is related to construction of the riffle chiefly the height of the crest, flow velocity and pool depth. It should be, therefore, noted the riffles planned for this scheme, need to be designed bankfull conditions and the substrate should be designed to withstand a 100-year flood event (Chin, Gelwick et al, 2010). Although, artificial riffles don’t always lead to significant changes in geomorphic activity. Thompson (2002) points out that low-flow deflectors and artificial riffles can attain a sustainable minimum depth but often create shallower pools than those associated with natural features. Consequently, low flow habitat is poor in quality and quantity.

Pasternack, Bounrisavong and Parikh (n.d, in press) highlight another potential problem with artificial riffles which is failure through the “reverse domino mechanism” (p. 25) associated with changes in the downstream water surface elevation (WSE). The net result is a wave of high velocity flow, passing upstream which destabilises one riffles and eventually triggers a systematic collapse. This is likely to be either caused by the at-a-station hydraulic geometry which induces a change in flow hydraulics or through structural failure in any riffle (Maytas, Korpak and Maczalowski, 2015).

3. Reconnecting the existing channel to its old course:

Reconnecting secondary to main channels has been shown to have had some mixed results (e.g. Coops, Tockner et al, n.d cited in Verhoeven, Beltman, Bobbink and Whigham (eds), 2002; Buijse, Coops et al, 2002; Lyon, Stuart, Ramsey and O’Mahony, 2010). Lyon, Stuart, Ramsey and O’Mahony (2010) suggest reconnecting primary to secondary channels is integral to either sustaining or rejuvenating floodplain ecosystems. They point out secondary channels provide refugia not only from either flood flows or fast water velocities but also opportunities to shelter from changes in water temperature in the main river. It can, therefore, be argued reconnecting the old channel course, figures 10 and 11, is an appropriate measure to help further enhance the ‘naturalness’ of the cross-over by providing a refugia for either young fish or species which require low-velocity spawning habitats.

Despite the ecological potential of reconnecting primary to secondary channels (Lyon, Stuart, Ramsey and O’Mahony, 2010), there are problems associated with this measure. Schropp and Jans (2000) who studied the Dutch Rhine (River Waal) found artificial secondary channels were susceptible to sedimentation, depending upon local conditions. They reported there are a variety of measures to prevent sedimentation from occurring including bottom vanes placed near the entire to the channel to trap migrating bedload waves or installing an upstream sediment trap. Installing an upstream sediment trap may not be practical given the channel is very narrow, but a modified and carefully sited bottom vane may help prevent aggradation through bedload migration. Geerling, Kater et al (2008) who also studied the River Waal discovered over-bank flows lead to aggradation which allowed vegetation colonisation and natural levee formation. The implication of this is a decrease in flood retention capacity within the catchment and a decrease in mean-flow velocities. To avoid this, coppicing may well help to suppress the succession of floodplain vegetation into structure-rich forest.

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Figure 10: contemporary Medina at Blackwater cross-over. Image taken from Edina Digimap, retrieved from http://digimap.edina.ac.uk/roam/historic, accessed December 2016

Aside from some of the problems associated with reconnecting side channels, Eder and Mestl (2012) disclose a side channel in the Upper Hamburg Bend, Missouri River, is largely stable. But has undergone some modifications associated with high flows. They found aggradation is beginning in some areas of the channel leading to a loss of low flow and shallow habitats, driven by a lack of frequent high flow events. Instead it has gradually been modified by high and low flows leading to depth and velocity changes. Consequently, completely re-opening the channel may make it more susceptible to over-widening and velocity changes. In view of Eder and Mestl (2012) experiences, pre-existing concrete bank line should be maintained on one side to provide some structural support.

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Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

Seen here, in this image, is the now diverted Medina. It has two very narrow channels running parallel to the footpath. Reconnecting one or both channels is likely to have some ecological and geomorphic benefit in this scheme. Although care must be taken to ensure high flow events don’t erode the bank lines and damage the footpath.

To avoid this, leaving one of the existing concrete channel walls in place may provide further structural support. Whilst maintaining some of the existing tree coverage may further provide bankside stability.

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Figure 11: The River Medina at the Blackwater Cross-over during the 1970s. Image retrieved from Edina Digimap, http://digimap.edina.ac.uk/roam/historic, accessed December 2016

Figure 12: The old course of the River Medina which is to be re-connected to create a backwater, low-flow habitat.

Future directions: where do we go from here?1. Following the announcement, during 2016, that Britain is to leave the European Union (EU)

this may complicate restoration work in the Medina and elsewhere. It may mean we are no longer obliged to following the EU WFD’s guidance on water and ecological quality. Although

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this may only occur, if a more hawkess, conservative government is elected. It may mean there is less funding made available to carry out such projects.

2. The past failings of this and other projects have provided a useful insight into what works and doesn’t work in terms of rehabilitation. Since there seems to be consensus from the literature, there is no ‘one-size or type-fits-all’ response to river restoration. Instead, past uses and modifications to a river and its ecological value. Once these measures have been implemented, carry monitoring and appraisal over a course of several years is recommended. But this is likely to be determined by the availability of people to carry out such monitoring, for example (Tunstall, Penning-Rowsell, Tapsell and Eden, 2000). Typically, monitoring could be carried out at 6 months to a year (post-completion) then 2-3 years then 5 to 10 years after. This is designed not only to assess the effectiveness of the scheme but also to assess whether there has been any significant losses or gains in terms of geomorphic and ecological diversity.

Conclusions The scheme sets out to use a combination of reed beds, side channel connectivity and

artificial riffles to restore geomorphic and ecological processes to improve the aesthics and ‘naturalness’ of this reach.

Several potential problems and merits have been identified, from the literature, including sedimentation, vegetation succession and riffle collapse which could present new challenges at this site.

Considering these problems, the combined measures are considered appropriate to use to restore and enhance geomorphic and ecological value of the cross-over.

Once these measures have been implemented, monitoring and post-project appraisal will be useful to assess the success of these measures and inform any future schemes.

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Appendix

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Figure 13: a schematic of the proposed side channel connection.

Figure 14: schematic drawing of the left hand-side of the cross over, based upon initial observations.

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Figure 15: the right hand-side of the cross-over, when viewed from the bridge. Again based upon initial field observations.

Figure 16: finalised schematic diagram following a literature search of the left hand-side of the cross-over.

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