Channel centerline for the Nehalem River, Oregon in 1967

The Tillamook Bay subbasins and Nehalem River basins encompass 1,369 and 2,207 respective square kilometers of northwestern Oregon and drain to the Pacific Ocean. The Tillamook, Trask, Wilson, Kilchis, and Miami Rivers flow into Tillamook Bay near the towns of Tillamook and Garibaldi. The Wilson and Trask River basins cover the largest areas (500 and 451 square kilometers, respectively) whereas the Tillamook and Kilchis Rivers encompass similar sized areas (156 and 169 square kilometers, respectively) and the Miami River the smallest area (94 square kilometers). In cooperation with the U.S. Army Corps of Engineers, the U.S. Geological Survey completed a reconnaissance-level assessment of channel condition and bed-material transport relevant to the permitting of in-stream gravel extraction along the the major alluvial portions of six river systems, including the lowermost 14.1 km of the Tillamook River, 16.3 km of the Trask River, 15.2 km of the Wilson River, 7.8 km of the Kilchis River, 11.6 km of the Miami River, and 31.4 km of the Nehalem River. To support these analyses, digital channel maps were produced to depict channel and floodplain conditions in the Tillamook Bay sub-basins and Nehalem River basin from different time periods. GIS layers defining the wetted channel and bar features and channel centerline in the study area were developed for four time periods: 1939, 1967, 2005, 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 wetted channel and bar feature datasets were developed by digitizing from aerial photographs. Aerial photographs from 1939 and 1967 were scanned, rectified, and mosaicked for this project (See metadata for each photograph set for more information on the rectification process and resolution of each dataset). Digital orthophotographs from 2005 and 2009 are publicly available.蒂拉穆克湾子流域与内哈勒姆河（Nehalem River）流域分别覆盖俄勒冈州西北部1369平方千米与2207平方千米的区域，最终注入太平洋。蒂拉穆克河、特拉斯克河、威尔逊河、基尔奇斯河与迈阿密河均在蒂拉穆克镇与加里波第镇附近汇入蒂拉穆克湾。其中，威尔逊河与特拉斯克河流域面积最大，分别为500平方千米与451平方千米；蒂拉穆克河与基尔奇斯河流域面积相近，分别为156平方千米与169平方千米；迈阿密河流域面积最小，仅94平方千米。本研究与美国陆军工程兵团（U.S. Army Corps of Engineers）合作，由美国地质调查局（U.S. Geological Survey）针对6个河流系统的主要冲积河段开展了踏勘级航道状况与推移质输运评估，相关工作服务于河道内砾石开采的许可审批，涉及河段包括：蒂拉穆克河下游14.1千米、特拉斯克河16.3千米、威尔逊河15.2千米、基尔奇斯河7.8千米、迈阿密河11.6千米以及内哈勒姆河31.4千米。为支撑上述分析工作，研究团队生成了数字化航道地图，用于展示蒂拉穆克湾子流域与内哈勒姆河流域不同时期的航道与河漫滩状况。针对研究区域内的过水航道、沙洲特征以及航道中心线，研究人员开发了对应4个时期的地理信息系统（GIS）图层，分别为1939年、1967年、2005年与2009年。本项目中将有效河道（active channel）定义为年度高水位期间通常被淹没的区域，包含枯水航道、分流河道、江心洲以及河道两侧的砾石滩。过水航道与沙洲特征数据集通过对航空影像进行数字化矢量化得到：1939年与1967年的航空影像已完成扫描、几何校正与影像拼接，有关影像校正流程与各数据集分辨率的详细信息，请参阅各影像集的元数据；2005年与2009年的数字正射影像为公开可用数据。