Channel centerline for the Tillamook, Trask, Wilson, Kilchis, and Miami Rivers, Oregon in 1939

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.

蒂拉穆克湾次级流域与内哈勒姆河流域分别覆盖俄勒冈州西北部1369与2207平方公里的区域，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与加里巴迪镇附近注入蒂拉穆克湾。威尔逊河与特拉斯克河流域为本次研究中面积最大的两个流域（分别为500与451平方公里）；蒂拉穆克河与基尔奇斯河流域面积相近（分别为156与169平方公里），迈阿密河流域则为面积最小的流域（94平方公里）。美国地质调查局（U.S. Geological Survey）与美国陆军工程兵团（U.S. Army Corps of Engineers）合作，对6个河系的主要冲积河段开展了河道状况与床沙输移的踏勘级评估，相关评估服务于河道内砾石开采的许可审批工作。涉及的河系包括：蒂拉穆克河下游14.1公里河段、特拉斯克河16.3公里河段、威尔逊河15.2公里河段、基尔奇斯河7.8公里河段、迈阿密河11.6公里河段以及内哈勒姆河31.4公里河段。为支撑上述评估分析，本项目制作了多期数字河道地图，用以展示蒂拉穆克湾次级流域与内哈勒姆河流域不同时期的河道与漫滩状况。本项目针对1939年、1967年、2005年与2009年四个时期，分别构建了研究区域内的过水河道、沙洲要素以及河道中心线的地理信息系统（Geographic Information System，GIS）图层。本项目中将"活动河道"定义为年度高水位期间通常会被淹没的区域，涵盖枯水河道、汊道、河心洲以及河道两侧的砾石沙洲。过水河道与沙洲要素数据集通过对航空影像进行数字化矢量化处理生成。本项目对1939年与1967年的航空影像进行了扫描、校正与拼接处理（各影像集的校正流程与数据集分辨率详情，请参见各数据集的元数据文件）。2005年与2009年的数字正射影像可公开获取。