Submitted to: Geomorphology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/31/2004
Publication Date: 6/15/2004
Citation: Ritchie, J.C., Finney, V.L., Oster, K.J. and Ritchie, C.A. 2004. Sediment deposition in the flood plain of Stemple Creek watershed, northern California. Geomorphology. 61:347-360. Interpretive Summary: This study shows that the floodplain area in the Stemple Creek in northern California is a significant sink for the soils being eroded from the upland area. Deposition rates of 1 to 2 cm/yr were measured for the period between 1954 and 2002. The deposition of the eroded soil material in the floodplain reduces the sediment delivery to the stream and subsequently to bay. Given the significance of the floodplain for trapping eroded material before it reaches the stream channel and the Bay, efforts need to be made to manage the floodplain area to insure that it remains a sink for eroded soil material and not become a source of eroded material. Such management would insure a reduced load of pollutants entering the stream and the Bay thus improving the aquatic habitat.
Technical Abstract: Over the past 150 years major land use changes have occurred in the Stemple Creek Watershed in northern California that have caused erosion to move soils from the upland to the floodplain, stream channels, and the bay. The purpose of this study is to document the recent sediment deposition (1954 to present) patterns in the floodplain area adjacent to Stemple Creek using the 137Cesium technique. Sediment deposition ranged from 0.26 to 1.84 cm/yr for the period from 1964 to 2002 with an average of 0.85 cm/yr. Sediment deposition rates were higher for the 1954 to 1964 period with a range of 0.31 to 3.50 cm/yr and an average of 1.29 cm/yr. These data indicate that sediment deposition in the floodplain has decreased since the middle 1950's probably related to reduction in row crop agriculture and an increase in pasture land in the uplands. This study shows that the floodplains in the Stemple Creek Watershed are a significant sink for the soils being eroded from the upland area. Given the significance of the floodplain for trapping eroded materials before they reach the stream channels or bay, efforts need to be made to manage these floodplain areas to insure that they do not change and become a source rather than a sink for eroded materials as improved management practices on the upland areas reduce sediment input to the floodplain.