Forest activities and Water Quality What can we confidently say after 30 years of research?

Forest activities and Water Forest activities and Water QualityQuality

What can we confidently say after 30 years of What can we confidently say after 30 years of research?research?

DOES LOGGING IMPACT DOES LOGGING IMPACT UPON WATER QUALITY?UPON WATER QUALITY?

• $64,000 question that largely remains $64,000 question that largely remains unansweredunanswered

• The question itself is not The question itself is not CONSTRUCTIVECONSTRUCTIVE - it offers no - it offers no solution and no practical help to the solution and no practical help to the industryindustry

TRADITIONAL APPROACHTRADITIONAL APPROACH

• Paired catchmentPaired catchment monitored before monitored before and after the period of major and after the period of major disturbance.disturbance.

• Estimates of suspended solidsEstimates of suspended solids or or turbidity are used to infer increased turbidity are used to infer increased sediment delivery to streamssediment delivery to streams

IMPORTANT LIMITATIONSIMPORTANT LIMITATIONS

• Black-BoxBlack-Box ie you can NOT relate the ie you can NOT relate the increase in suspended load at the increase in suspended load at the catchment outlet to activities on the catchment outlet to activities on the slopesslopes

• Tells us nothing about where the Tells us nothing about where the sediment comes from and hence how sediment comes from and hence how to manage itto manage it

NEW APPROACH- NEW APPROACH- OPEN UP THE BLACK BOXOPEN UP THE BLACK BOX

For water pollution to occur, you need For water pollution to occur, you need 3 3 key ingredientskey ingredients;;

• a source of sediment, a source of sediment,

• delivered directly to the streamdelivered directly to the stream

• complete failure of any sediment complete failure of any sediment control strategies or BMP’scontrol strategies or BMP’s

CAN WE BE CONFIDENT?CAN WE BE CONFIDENT?

• BROAD GENERALISATIONSBROAD GENERALISATIONS

• WELL ESTABLISHEDWELL ESTABLISHED

• LIMITED EVIDENCELIMITED EVIDENCE

• SPECULATIVESPECULATIVE

SEDIMENT AND NUTRIENT SEDIMENT AND NUTRIENT SOURCESSOURCES

Well EstablishedWell Established Unsealed forest roads are the major sources Unsealed forest roads are the major sources

of sediment in managed forests. of sediment in managed forests.

Road usage is a critical factor in explaining Road usage is a critical factor in explaining sediment production rates on roads.sediment production rates on roads.

(Reid and Dunne 1984)

1010 100 1000 10000

100

1000

10000

100000

Culvert discharge (mL/s)

Abandoned

Feeder AccessSecondary Access

Dump Access5 yr snig track

Se

dim

ent

co

nc

en

trat

ion

(mg

/L)

Heavy use

Temporary use

0.001

0.01

0.1

1

10

100

0 500 1000 1500 2000 2500

Time (secs)

Sed

imen

t F

lux

(g/m

/s) Road

Snig Track

Hillslope

SEDIMENT SOURCESSEDIMENT SOURCES


Sediment production rates on roads and Sediment production rates on roads and tracks decline within the time frame of 2- tracks decline within the time frame of 2- to 5 yearsto 5 years

Sediment yeilds from managed forests are Sediment yeilds from managed forests are lower than those from other landuses lower than those from other landuses primarily agricultureprimarily agriculture

0.00

0.01

0.02

0.03

0.5 1 2 3 4 5 6

0.04

Age (years)

Yie

ld (

kg/m

2 )

Hillslope

0.00

0.40

0.80

1.20

0.5 1 2 3 4 5 6

Age (years)

Yie

ld (

kg/

m2 )

Snig Track

Metasediment

Red Granite

Light Granite

RECOVERY OVER TIMERECOVERY OVER TIME


Nutrient concentrations in streams draining Nutrient concentrations in streams draining forested catchments are considerably lower forested catchments are considerably lower than those reported for other landuses, than those reported for other landuses, primarily agriculture.primarily agriculture.

• The dominant cause of increased nutrients in The dominant cause of increased nutrients in streams if observed, is due to the effects of streams if observed, is due to the effects of prescribed burning and wildfire.prescribed burning and wildfire.

Limited EvidenceLimited Evidence The GHA is not a significant source The GHA is not a significant source

of sediment due to limited of sediment due to limited sediment availability, high sediment availability, high retention of vegetation cover and retention of vegetation cover and spatially variable infiltration rates.spatially variable infiltration rates.



Metasediment soil

2.31t/ha

0.26

0.69

0.35 t/ha

GHA Snig

xbank

Red granite soil

11.08t/ha

0.25

1.62

0.05 t/ha

GHA Snig

SEDIMENT DELIVERY SEDIMENT DELIVERY PATHWAYSPATHWAYS

• The degree to which the The degree to which the source source is is connectedconnected or or linkedlinked to the to the receiving watersreceiving waters

Direct linkage

No channellinkage

InfiltrationFull channel

linkage

Partial channellinkage

Bridge

DELIVERY PATHWAYSDELIVERY PATHWAYS

Well EstablishedWell Established Channelised pathways forming at road Channelised pathways forming at road

drainage outlets form the most efficient drainage outlets form the most efficient conduit for sediment and nutrient delivery to conduit for sediment and nutrient delivery to streams.streams.

Sediment delivery ratios are closely Sediment delivery ratios are closely associated with the size composition of the in-associated with the size composition of the in-situ and eroded soil.situ and eroded soil.

Full Channel

Partial Channel

MITRE DRAINMITRE DRAIN

CULVERTCULVERT

Mitres Push OutsCulverts

Per

cen

tag

e

0

10

20

30

40

50

60

70

80

90

100

Follow the Red LineFollow the Red Line

N

2km

Major area of ImpactMajor area of Impact

The impact can be widespreadThe impact can be widespread

• The impact of channelised pathways The impact of channelised pathways extends beyond a single point or extends beyond a single point or particular road drain and can be particular road drain and can be catchment-widecatchment-wide

• They also become They also become permanent permanent features of the landscapefeatures of the landscape

DELIVERY PATHWAYSDELIVERY PATHWAYS

Well EstablishedWell Established Channelised pathways forming at road Channelised pathways forming at road

drainage outlets form the most efficient drainage outlets form the most efficient conduit for sediment and nutrient delivery to conduit for sediment and nutrient delivery to streams.streams.

Sediment delivery ratios are closely Sediment delivery ratios are closely associated with the size composition of the in-associated with the size composition of the in-situ and eroded soil.situ and eroded soil.

Full Channel

Partial Channel

MITRE DRAINMITRE DRAIN

CULVERTCULVERT

Mitres Push OutsCulverts

Per

cen

tag

e

0

10

20

30

40

50

60

70

80

90

100

Follow the Red LineFollow the Red Line

N

2km

Major area of ImpactMajor area of Impact

The impact can be widespreadThe impact can be widespread

• The impact of channelised pathways The impact of channelised pathways extends beyond a single point or extends beyond a single point or particular road drain and can be particular road drain and can be catchment-widecatchment-wide

• They also become They also become permanent permanent features of the landscapefeatures of the landscape

Maximum contributing length95m

for road gradient of5 degrees

and DHG 7.5

Maximum contributing length95m

for road gradient of5 degrees

and DHG 7.5

Drain discharge hillslope gradient

90909090909090807065605550454040

0123456789101112131415

-15515515012510090807065605550454040

11011011011011010090807065605550454040

9595959595

90807065605550454040

85858585858585807065605550454040

80808080808080807065605550454040

75757575757575757065605550454040

102.5 5.0 7.5 15 20 25 45

75757575757575757065605550454040

95

Ro

ad t

rave

lway

gra

die

nt

200

Inter-bank length (m)5 6 8 20 30 405060 80 20010 100

568

20

3040506080

10

100

2 year event for T = 30mins



EFFECTS OF BEST EFFECTS OF BEST MANAGEMENT PRACTICESMANAGEMENT PRACTICES

Well established BMP’s play a significant role in the BMP’s play a significant role in the

reduction of adverse effects in forested reduction of adverse effects in forested catchments.catchments.

Forest buffer strips are an effective Forest buffer strips are an effective measure in reducing the volume of measure in reducing the volume of surface water and sediment/nutrients surface water and sediment/nutrients delivered to a stream.delivered to a stream.

EFFECTS OF BEST EFFECTS OF BEST MANAGEMENT PRACTICESMANAGEMENT PRACTICES

Limited EvidenceLimited Evidence The best location and design of The best location and design of

buffer strips in forested catchments buffer strips in forested catchments of varying topography and landuse.of varying topography and landuse.

The specific role and effectiveness The specific role and effectiveness of BMP’s on the hillslope compared of BMP’s on the hillslope compared with those in the near-stream area.with those in the near-stream area.

CONCLUDING REMARKSCONCLUDING REMARKS

• The Most Dramatic Impacts On Water The Most Dramatic Impacts On Water Quality Will Come About In Response To Quality Will Come About In Response To The Most Dramatic Landuse Impact- The Most Dramatic Landuse Impact-

• Broad Scale Slash And Burn- Large Scale Broad Scale Slash And Burn- Large Scale Conversion To PastureConversion To Pasture

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Forest activities and Water Quality What can we confidently say after 30 years of research?