Umpqua River Oregon North Umpqua PhotoMosaic 1939

The Umpqua River drains 12,103 square kilometers (4,673 square miles) in southwest Oregon before flowing into the Pacific Ocean at Winchester Bay near the city of Reedsport. In cooperation with the Portland District of the U.S. Army Corps of Engineers (USACE), the USGS evaluated sediment transport and gravel storage along the downstream alluvial reaches of the North and South Umpqua Rivers and the entire mainstem Umpqua River. This includes the lower 46.8 kilometers (29.1 miles) of the North Umpqua River and the lower 122.6 kilometers (76.2 miles) of the South Umpqua River.

The Umpqua River gravel transport study involved multiple analyses, including tracking patterns of historical channel change and estimation of a sediment budget. To support these analyses, digital channel maps were produced to depict channel and floodplain conditions along the Umpqua River system from different time periods.

GIS layers defining the active channel of the Umpqua River system were developed for three time periods: 1939, 1967, and 2005. For the South Umpqua River and the 19 kilometers (12 miles) of the mainstem Umpqua River downstream from the confluence of the North and South Umpqua Rivers, GIS layers were also developed for the time periods 1994, 2000, and 2009.

For this project, the active channel was defined as area typically inundated during annual high flows, and includes the low-flow channel as well as side channels, islands, and channel-flanking gravel bars. The active channel datasets were developed by digitizing from aerial photographs. Aerial photographs from 1939 and 1967 were scanned, rectified, and mosaiced for this project. Digital orthophotographs from 1994, 2000, 2005, and 2009 are publicly available (See metadata for each photograph set for more information on the rectification process and resolution of each dataset). Although our study area encompasses the Umpqua River and lower reaches of the North and South Umpqua Rivers, the extent of each dataset depended upon the underlying aerial photographs; for example, the 1967 photographs extend only as far downstream as floodplain kilometer 7, whereas the 1939 and 2005 datasets extend to the mouth of the Umpqua River at the Pacific Ocean.

Umpqua河（Umpqua River）流经俄勒冈州西南部12103平方公里（合4673平方英里）的流域，最终在里德斯波特（Reedsport）市附近的温彻斯特湾（Winchester Bay）注入太平洋。本研究与美国陆军工程兵团波特兰分局（Portland District of the U.S. Army Corps of Engineers, USACE）合作，由美国地质调查局（United States Geological Survey, USGS）对北Umpqua河、南Umpqua河下游冲积河段以及整条Umpqua干流的泥沙输运与砾石储量开展评估，评估范围涵盖北Umpqua河下游46.8公里（合29.1英里）河段，以及南Umpqua河下游122.6公里（合76.2英里）河段。

Umpqua河砾石输运研究包含多项分析内容，包括追踪历史河道变迁模式与估算泥沙收支。为支撑上述分析工作，研究团队制作了数字河道地图，用于呈现不同时期Umpqua河水系的河道与漫滩状态。

研究团队为1939年、1967年、2005年三个时期构建了Umpqua河水系主河道的GIS图层（GIS layer）。针对南Umpqua河，以及北、南Umpqua河汇流点下游19公里（合12英里）的Umpqua干流河段，团队还额外构建了1994年、2000年、2009年三个时期的GIS图层。

本项目中，主河道被定义为年度高水位期间通常会被淹没的区域，包含低流量河道、旁道、沙洲以及河道两侧的砾石滩。主河道数据集通过航拍照片（aerial photograph）数字化生成：本次研究对1939年与1967年的航拍照片进行了扫描、校正与拼接；1994年、2000年、2005年及2009年的数字正射影像（digital orthophotograph）均为公开可用数据，详见各影像集的元数据（metadata）以了解校正流程与各数据集的分辨率细节。尽管本研究的覆盖范围涵盖Umpqua河及北、南Umpqua河下游河段，但各数据集的实际范围取决于可用的航拍照片：例如，1967年的航拍照片仅延伸至漫滩7公里处，而1939年与2005年的数据集则覆盖至Umpqua河注入太平洋的河口区域。