Umpqua River Oregon Roseburg 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.乌姆普夸河（Umpqua River）流域面积达12103平方千米（4673平方英里），流经俄勒冈州西南部，最终在里德斯波特市附近的温彻斯特湾注入太平洋。本研究与美国陆军工程兵团（U.S. Army Corps of Engineers, USACE）波特兰分局合作开展，由美国地质调查局（USGS）对北乌姆普夸河、南乌姆普夸河的下游冲积河段以及整条乌姆普夸河干流的泥沙输移与砾石储积情况进行评估。评估范围涵盖北乌姆普夸河下游46.8千米（29.1英里）河段，以及南乌姆普夸河下游122.6千米（76.2英里）河段。 本次乌姆普夸河砾石输移研究包含多项分析内容，涵盖历史河道变迁模式追踪与泥沙收支预算估算。为支撑上述分析工作，研究团队制作了数字河道地图，用以呈现不同时期乌姆普夸河水系的河道与漫滩状态。 针对1939年、1967年、2005年三个时期，研究团队研发了乌姆普夸河水系主河道（active channel）的地理信息系统（GIS）图层。针对南乌姆普夸河，以及北乌姆普夸河与南乌姆普夸河汇流点下游19千米（12英里）的乌姆普夸河干流河段，研究团队还针对1994年、2000年、2009年三个时期研发了对应的GIS图层。 本项目中，主河道（active channel）被定义为年度高水位期间通常被淹没的区域，包含低流量河道、旁道、沙洲以及河道两侧的砾石滩。本次主河道数据集通过对航空影像进行数字化矢量化获取。研究团队对1939年与1967年的航空影像进行了扫描、几何校正与拼接处理。1994年、2000年、2005年及2009年的数字正射影像均已公开（可查阅各影像集的元数据，了解各数据集的校正流程与分辨率详情）。尽管本研究的覆盖范围包含乌姆普夸河及北、南乌姆普夸河下游河段，但各数据集的实际覆盖范围取决于所采用的原始航空影像：例如，1967年的影像仅延伸至漫滩7千米处，而1939年与2005年的数据集则延伸至乌姆普夸河注入太平洋的河口处。