HR: 1340h
AN: H53C-1266    [Abstracts]
TI: Sediment Production from Forest Roads During Different Rainfall Conditions
AU: Kunz, M J
EM: mankunz@student.ethz.ch
AF: Dept. of Environmental Sciences, Swiss Federal Institute of Technology Zurich (ETH Zurich), Zwischenbaechen 91, Zurich, ZH CH-8092 Switzerland
AU: Sullivan, K
EM: ksullivan@scopac.com
AF: Scotia Pacific Company LLC, 125 main Street, Scotia, CA 95565 United States
AU: * Dhakal, A S
EM: adhakal@scopac.com
AF: Scotia Pacific Company LLC, 125 main Street, Scotia, CA 95565 United States
AB: Sediment productions from storm-proofed forest roads were investigated at four locations in the managed forested land of Northwestern California (annual rainfall @1000 mm), where rocks have been characterized as Wildcat group consisting of mudstone, siltstone, claystone, and minor conglomerate. Rocked road (storm-proofed road) constitutes a part of the effective road management practices in the study area where other management practices include disconnection of roads from watercourses, reduction in distance between culverts, frequent road maintenance, and seasonal (or during rainfall) restrictions of log traffic. Specifically, this study examines the influence of rainstorm and road characteristics on sediment production from storm-proofed road in the context of varieties of road management practices in place. Continuous ditch flow during the rainstorm events was monitored using an UNIDATA float device and data logger. An ISCO sampler collected suspended sediment at temporal resolution of 2-h during the rainstorm events, and collected sediment samples were analyzed for turbidity and suspended sediment concentration in the laboratory. Sediment samples were also collected for particle size distribution analysis. Two tipping bucket rain gages located in the vicinity of road sites collected rainfall. Using an electronic total station, road surface was surveyed in detail, and a road Digital Elevation Model (DEM) was generated. Thus produced DEM was processed to delineate the road surface area contributing to ditch flow. The analysis of collected data for rainstorm events of hydrological year 2003/2004 reveals that the suspended sediment concentration conforms closely to rainfall hyetograph and ditch flow hydrograph with rapid flushing of road sediments for about 15-h following the onset of rainstorm. In general, ditch flow and suspended sediment concentration relation illustrates that the sediment transport is evidently "supply limited". For this reason, suspended sediment concentration decreases to a low level after about 15-h of onset of rainstorm even when ditch flow as well as rainfall are considerably high. In addition to rainstorm characteristics, road characteristics such as slope gradient, and road use (traffic volume) caused differences in the short-term sediment concentration and total sediment yield among road segments during rainstorm events. Temporal distribution of suspended sediment concentration and short-term peak suspended sediment concentration dependent on the traffic volume prior to the onset of rainstorm event since truck traffic was ceased during rainstorms. During the same storm, road segments with high traffic volume produced peak suspended sediment concentration of up to 30-fold compared to road segments with low traffic volume; however, the total sediment yield during the rainstorm did not vary that much among road segments.
DE: 1800 HYDROLOGY
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting