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


DOES LOGGING IMPACT UPON WATER QUALITY?: DOES LOGGING IMPACT UPON WATER QUALITY? $64,000 question that largely remains unanswered The question itself is not CONSTRUCTIVE - it offers no solution and no practical help to the industry


TRADITIONAL APPROACH: TRADITIONAL APPROACH Paired catchment monitored before and after the period of major disturbance. Estimates of suspended solids or turbidity are used to infer increased sediment delivery to streams


IMPORTANT LIMITATIONS: IMPORTANT LIMITATIONS Black-Box ie you can NOT relate the increase in suspended load at the catchment outlet to activities on the slopes Tells us nothing about where the sediment comes from and hence how to manage it


NEW APPROACH- OPEN UP THE BLACK BOX: NEW APPROACH- OPEN UP THE BLACK BOX For water pollution to occur, you need 3 key ingredients; a source of sediment, delivered directly to the stream complete failure of any sediment control strategies or BMP’s


CAN WE BE CONFIDENT?: CAN WE BE CONFIDENT? BROAD GENERALISATIONS WELL ESTABLISHED LIMITED EVIDENCE SPECULATIVE


SEDIMENT AND NUTRIENT SOURCES: SEDIMENT AND NUTRIENT SOURCES Well Established Unsealed forest roads are the major sources of sediment in managed forests. Road usage is a critical factor in explaining sediment production rates on roads.


SEDIMENT SOURCES: Time (secs) Sediment Flux (g/m/s) SEDIMENT SOURCES


SEDIMENT AND NUTRIENT SOURCES: SEDIMENT AND NUTRIENT SOURCES Sediment production rates on roads and tracks decline within the time frame of 2- to 5 years Sediment yeilds from managed forests are lower than those from other landuses primarily agriculture


Slide11: 0.00 0.01 0.02 0.03 0.04 Age (years) Yield (kg/m2) Hillslope Age (years) Yield (kg/ m2) Snig Track RECOVERY OVER TIME


SEDIMENT AND NUTRIENT SOURCES: SEDIMENT AND NUTRIENT SOURCES Nutrient concentrations in streams draining forested catchments are considerably lower than those reported for other landuses, primarily agriculture. The dominant cause of increased nutrients in streams if observed, is due to the effects of prescribed burning and wildfire.


SEDIMENT AND NUTRIENT SOURCES: Limited Evidence The GHA is not a significant source of sediment due to limited sediment availability, high retention of vegetation cover and spatially variable infiltration rates. SEDIMENT AND NUTRIENT SOURCES


SEDIMENT DELIVERY PATHWAYS: SEDIMENT DELIVERY PATHWAYS The degree to which the source is connected or linked to the receiving waters


Slide16: Direct linkage No channel linkage Infiltration Full channel linkage Partial channel linkage Bridge


DELIVERY PATHWAYS: DELIVERY PATHWAYS Well Established Channelised pathways forming at road drainage outlets form the most efficient conduit for sediment and nutrient delivery to streams. Sediment delivery ratios are closely associated with the size composition of the in-situ and eroded soil.


Slide18: MITRE DRAIN CULVERT


Slide19: Follow the Red Line Major area of Impact


The impact can be widespread: The impact can be widespread The impact of channelised pathways extends beyond a single point or particular road drain and can be catchment-wide They also become permanent features of the landscape


DELIVERY PATHWAYS: DELIVERY PATHWAYS Well Established Channelised pathways forming at road drainage outlets form the most efficient conduit for sediment and nutrient delivery to streams. Sediment delivery ratios are closely associated with the size composition of the in-situ and eroded soil.


Slide22: MITRE DRAIN CULVERT


Slide23: Follow the Red Line Major area of Impact


The impact can be widespread: The impact can be widespread The impact of channelised pathways extends beyond a single point or particular road drain and can be catchment-wide They also become permanent features of the landscape


Slide25: Drain discharge hillslope gradient 90 90 90 90 90 90 90 80 70 65 60 55 50 45 40 40 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 - 155 155 150 125 100 90 80 70 65 60 55 50 45 40 40 110 110 110 110 110 100 90 80 70 65 60 55 50 45 40 40 95 95 95 95 95 90 80 70 65 60 55 50 45 40 40 85 85 85 85 85 85 85 80 70 65 60 55 50 45 40 40 80 80 80 80 80 80 80 80 70 65 60 55 50 45 40 40 75 75 75 75 75 75 75 75 70 65 60 55 50 45 40 40 10 2.5 5.0 7.5 15 20 25 45 75 75 75 75 75 75 75 75 70 65 60 55 50 45 40 40 95 Road travelway gradient


Slide26: 200 Inter-bank length (m) 5 6 8 20 30 40 50 60 80 200 10 100 5 6 8 20 30 40 50 60 80 10 100 10 year event for T = 30mins 100 year event for T = 30mins


EFFECTS OF BEST MANAGEMENT PRACTICES: EFFECTS OF BEST MANAGEMENT PRACTICES Well established BMP’s play a significant role in the reduction of adverse effects in forested catchments. Forest buffer strips are an effective measure in reducing the volume of surface water and sediment/nutrients delivered to a stream.


EFFECTS OF BEST MANAGEMENT PRACTICES: EFFECTS OF BEST MANAGEMENT PRACTICES Limited Evidence The best location and design of buffer strips in forested catchments of varying topography and landuse. The specific role and effectiveness of BMP’s on the hillslope compared with those in the near-stream area.


CONCLUDING REMARKS: CONCLUDING REMARKS The Most Dramatic Impacts On Water Quality Will Come About In Response To The Most Dramatic Landuse Impact- Broad Scale Slash And Burn- Large Scale Conversion To Pasture