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CRC PUBLICATIONS |
Surface Runoff and Sediment Movement on Logged Hillslopes in the Eden Management Area of SE NSW
Jacky Croke,
Peter Hairsine,
Peter Fogarty,
Simon Mockler,
Jim Brophy
Publication Type:
Technical Report
This is a publication of the initial CRC for Catchment Hydrology
CRC Program:
Forest Hydrology (Previous CRC)
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Publication Keywords:
Forest Cutting (N.B. Logging in Streamline is used for water data loggers)
Erosion
Sediment/Water System
Rainfall/Runoff Relationship
Roads and Streets
Catchment Areas
Water Quality (Natural Waters)
Modelling (Hydrological)
Water Pollution Control
Soil (Types of)
Rainfall Simulation
Compaction
Infiltration
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Abstract / Summary:
ABSTRACT
Timber harvesting activities can affect soil erosion and related water quality through the disturbance of catchment vegetation and soil. The basic parameters required to construct erosion hazard models, including relative erosion rates for different soil types, vegetation cover, and the degree of disturbance, are not available for most Australian catchments, particularly for forestry environments. This report investigates sediment and runoff generation on forested hillslopes within the Eden Management Area (EMA) of south eastern NSW using large scale rainfall simulator experiments. The experiments investigated a combined snig track and general harvest area system, where cross banks redirected runoff from the snig track into the general harvest area. Relative volumes of surface water and sediment from snig tracks and general harvesting areas are compared for three storm intensities, three soil types and three recovery periods since logging. The nature and extent of runoff and sediment re-distribution are also investigated.
These experiments confirm the importance of disturbed, compacted surfaces, such as snig tracks, as major sources of sediment and runoff in logged catchments. Snig tracks on recently logged sites generate, on average, seven times as much surface flow per unit area as general harvesting areas and, about 20 times more sediment, with maximum sediment yields in the order of 11 t/ha for a 1 in 100 year storm of 30 minute duration. General harvesting areas yield relatively small volumes of sediment and high infiltration rates predominate, with resultant patchy overland flow.
Highest on-site erosion rates were recorded on snig tracks developed on the granitic soils around Bombala in the west of the EMA, whilst those on the coastal Ordovician sediments produced relatively low erosion rates. However, these coastal sites actually delivered slightly higher sediment loads from the combined snig track and general harvest area. This is attributed primarily to their finer-grained texture and the sediments propensity to be transported further distances. Surface runoff and sediment yields decline over time so that within five years of logging, all three soil types behave similarly and yield little sediment. Cross banks were found to be effective measures to reduce sediment delivery rates to the general harvesting area, with between 40 and 90% of the eroded sediment being deposited at the base of the bank.
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Centre Office:
CRC for Catchment Hydrology
Dept of Civil Engineering
Building 60
Monash University Vic 3800
Tel: +61 3 9905 2704
Fax: +61 3 9905 5033
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