Since the majority of road drainage points in western Washington and Oregon enter small, often ephemeral streams rather than large, fish‐bearing waters, impact of road‐surface sediment on biota in permanent streams depends, to a large extent, on transport through these small watercourses. A series of experimental additions of road‐surface sediment was made to two ephemeral streams to examine the downstream transport of this material as a function of discharge and channel characteristics. These small streams were found to store large amounts of sediment washed from road surface. In no instance did either stream transport more than 45 percent of the added material to their mouths, distances of 95 and 125 m. Larger‐sized sediment particles were delivered at a lower rate than finer material. Added sediment <0.063 mm in size was transported efficiently through the systems at all but the lowest flows tested. Material between 0.5 and 0.063 mm and from 2.0 to 0.5 mm in size were retained at progressively higher rates, with sediment in the coarser size category never exceeding a delivery of 10 percent of the added material. There were significant differences in the transport of sediment in the two larger size categories between the two streams. These differences were due to a much greater amount of woody debris in the stream with the lower delivery rates, which acted to trap and hold sediment, as well as a slightly longer and less steep channel.

A 30 x 0.9 cm piece of steel rod bent in the shape of an “L” and attached by hose clamps to a 15 x 3.2 cm section of plastic pipe sliding on an 86 x 1.9 cm steel shaft was tested for use in measuring scour and fill of salmon spawning riffles. Installed along channel cross‐sections, results of tests at four sites on two hydraulically different streams showed the device to be useful in monitoring event specific scour and fill. Measurement error was estimated to be ± 10 mm.

Studies conducted in southwestern Washington, examining the generation of sediment on gravel road surfaces, its transport to small streams and its fate after entering flowing waters, are reviewed. The amount of sediment produced on an hourly basis from a road segment was related to traffic rate. Accumulated material flushed rapidly from the road surface with precipitation, leading to a decrease in sediment concentration in the ditch with time during a storm. Depth of road ballast and type of surfacing material also influenced sediment generation. The majority of the sediment produced by these roads was finer than 0.004 mm. Steeper roads produced a higher proportion of coarser particles. Approximately 34% of surveyed road drainage points entered streams, mainly first- or second-order channels. Thus, the delivery of road sediment to larger streams often depended on its transport through these smaller channels. Small streams temporarily retained a high proportion of road sediment input to them. Coarser particles were retained at a higher rate than finer material. Due to the fine particle size of road sediment delivered to streams, little effect of this material on the composition of streambed gravel could be discerned. The results of these studies provide guidelines for management of those roads where sediment has the highest potential to impact aquatic resources. For. Sci 35(2):453-468.