Erosion and deposition for Fanno Creek, Oregon 2012

In 2010, the U.S. Geological Survey (USGS) began investigating the sources and sinks of organic matter in Fanno Creek, a tributary of the Tualatin River, Oregon. Organic matter, more specifically organic carbon, is abundant in Fanno Creek and has been tied to a variety of water-quality concerns. Since organic carbon is commonly found in the fine-grained, organic-rich sediment covering much of the watershed, developing a better understanding of sediment transport dynamics should greatly improve the quality of restoration efforts underway. To address this, a geomorphic approach was adopted, including mapping fine sediment erosion and deposition and measuring changes in sediment. Erosion and deposition mapping within the geomorphic floodplain in the summer of 2012 was used to identify specific sources and sinks of fine sediment and other features that might potentially contribute to the sediment cycle. The distribution of mapped features along Fanno Creek varies by reach. Areas having a high potential for erosion were greatest in the uppermost basin although other middle and lower basin reaches had relatively large areas subject to erosion. Areal deposition is largest in wide, low gradient wetland reaches such as in the middle basin.