Aerial photo mosaic of 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（Tillamook Bay subbasins）与尼黑利姆河流域（Nehalem River basins）位于俄勒冈州西北部，流域面积分别为1369平方千米与2207平方千米，最终均注入太平洋。蒂拉穆克河（Tillamook River）、特拉斯克河（Trask River）、威尔逊河（Wilson River）、基尔奇斯河（Kilchis River）与迈阿密河（Miami River）均在蒂拉穆克与加里瓦尔迪镇附近注入蒂拉穆克湾。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。
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，针对6个河系的主要冲积段开展了河道状况与推移质输沙的踏勘级评估，相关评估服务于河道内砾石开采的许可审批工作。涉及的6个河系包括：蒂拉穆克河下游14.1千米河段、特拉斯克河16.3千米河段、威尔逊河15.2千米河段、基尔奇斯河7.8千米河段、迈阿密河11.6千米河段，以及尼黑利姆河31.4千米河段。
为支撑上述分析，研究团队制作了多期数字河道地图，用以展示蒂拉穆克湾子流域与尼黑利姆河流域不同时期的河道与漫滩状况。研究针对1939年、1967年、2005年与2009年四个时期，分别构建了研究区内过水河道、滩地特征以及河道中心线的GIS图层（GIS layers）。本项目中，“活动河道”被定义为年度高水位期间通常会被淹没的区域，包含枯水河道、支汊、江心洲以及河道两侧的砾石滩。
过水河道与滩地特征数据集通过航空影像数字化处理生成。本项目对1939年与1967年的航空影像进行了扫描、几何纠正与拼接处理（各影像集的纠正流程与数据集分辨率详情，请参见各数据集的元数据）。2005年与2009年的数字正射影像为公开可获取数据。