FINE SEDIMENT PRODUCTION FROM TRUCK TRAFFIC, QUEEN CHARLOTTE FOREST, MARLBOROUGH SOUNDS, NEW ZEALAND

• Published in: Journal of hydrology, New Zealand New Zealand, 1993-01, Vol.31 (1), p.56-64
• Main Authors: Coker, R.J., Fahey, B.D., Payne, J.J.
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Forest roads; Forest soils; Hydrology; Hydrology. Hydrogeology; Marine and continental quaternary; Rain; Schist; Sediment yield; Sediments; Storms; Stormwater; Surface courses; Surficial geology; Trucking
• ISSN: 0022-1708; 2463-3933

Fine sediment mobilised by 30-min simulated rainfall events on 10-by-4 m sections of forest road before, during, and after trucking was measured at two sites in Queen Charlotte Forest. One was on strongly weathered schist at 70 m elevation and the other was on moderately weathered schist at 460 m elevation. At the lower site, suspended sediment concentration from the fresh road surface reached 10 g L⁻¹ of runoff, but fell to 3 g L⁻¹ by the end of the test run. With simulated rainfall during trucking (20 passes), concentration peaked at 130 g L⁻¹ but declined to about 12 g L⁻¹ once trucking ceased. When the simulator was run immediately after 20 truck passes the maximum concentration was 21 g L⁻¹. This quickly fell to 6 g L⁻¹. At the higher site the sediment response was lower overall. Extrapolating this information to a 1-km length of road on strongly weathered schist with a 9-hour simulated storm, total suspended sediment production from a typical road surface without truck movements is estimated at 1.8 t. During trucking it rises to 10 t and after trucking it is only marginally higher (2 t). On moderately weathered schist at higher elevations suspended sediment production is only about half these amounts.