Umpqua River Oregon Days Creek 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）的流域面积达12103平方公里（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（United States Army Corps of Engineers, USACE）波特兰分局合作，由美国地质调查局（United States Geological Survey, USGS）对北乌姆普夸河、南乌姆普夸河下游冲积河段以及乌姆普夸河整条干流的泥沙输移与砾石储量开展评估。评估范围涵盖北乌姆普夸河下游46.8公里（29.1英里）河段，以及南乌姆普夸河下游122.6公里（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工作，包括历史河道变迁格局追踪与泥沙收支估算。为支撑上述分析，研究团队制作了数字化河道地图，用以呈现不同历史时期乌姆普夸河水系的河道与漫滩状态。 研究团队针对1939年、1967年、2005年三个时期，构建了用于表征乌姆普夸河水系活跃河道（active channel）的地理信息系统（Geographic Information System, GIS）图层。针对南乌姆普夸河，以及北、南乌姆普夸河汇流点下游19公里（12英里）的乌姆普夸河干流段，研究团队额外构建了1994年、2000年、2009年三个时期的GIS图层。 本项目中，活跃河道被定义为年度高水位期间通常会被淹没的区域，涵盖低流量河道、支汊、江心洲以及河道两侧的砾石滩。本数据集通过航拍照片数字化解译生成。研究团队对1939年与1967年的航拍照片进行了扫描、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（Digital Orthophotograph）均为公开可用数据（各影像集的元数据中包含了校正流程与各数据集分辨率的详细信息）。尽管本研究的覆盖范围涵盖乌姆普夸河以及北、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可用的航拍照片源数据：例如，1967年的航拍照片仅覆盖至下游7公里处的漫滩区域，而1939年与2005年的数据集则覆盖至乌姆普夸河注入太平洋的河口区域。