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A quantitative study of sediment delivery and stream pollution from different forest road types
Author(s) -
Sheridan Gary J.,
Noske Philip J.
Publication year - 2006
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.6244
Subject(s) - forest road , environmental science , hydrology (agriculture) , sediment , surface runoff , sediment transport , bed load , traffic intensity , pollution , geology , geotechnical engineering , forestry , ecology , engineering , geography , paleontology , telecommunications , biology
The objective of this paper is to quantify, and enable the prediction of, sediment delivery and water pollution impacts from a spectrum of forest roads. Ten 100–200 m long sections of forest road were selected to incorporate a wide range of the key physical site factors that are likely to affect the rate of sediment generation. Each road section was permanently instrumented for 1 year to measure rainfall and runoff continuously. Suspended load, bedload, and traffic were integrated measurements over 2‐ to 3‐week site‐service intervals. Total annual sediment load (normalized for slope) varied about 25‐fold, from 216 mg m −2 per millimetre of rain for a high‐quality gravel surfaced road with minimal traffic to 5373 mg m −2 per millimetre of rain for an unsurfaced road on an erodible subsoil with moderate light‐vehicle traffic. For the seven gravel‐surfaced roads in this study, truck traffic (axles/week) explained 97% of the variation in annual sediment delivery (per unit of rainfall) from the road. Equations are proposed that allow annual sediment delivery rates to be estimated when net rainfall, road slope, road area, and truck traffic are known. Roads produce runoff rapidly and were found to deliver sediment for about the same duration as rainfall is falling, in this study varying between 5 and 10% of the time. The patterns of sediment delivery measured from the experimental roads (frequency, duration, and intensity) in this study are similar to levels that have been shown to alter the composition of in‐stream macroinvertebrate communities in small (e.g. <10 l s −1 ), clean, mountain streams. However, in larger well‐mixed streams (e.g. >500 l s −1 ), dilution is sufficient to prevent concentrations reaching critical levels that are likely to result in biological impacts. Copyright © 2006 John Wiley & Sons, Ltd.