John Day Reservoir SeaBOSS video tracklines collected in 2000

A two-week field operation was conducted in the John Day Reservoir on the Columbia River to image the floor of the pool, to measure the distribution and thickness of post-impoundment sediment, and to verify these geophysical data with video photography and bottom sediment samples. The field program was a cooperative effort between the USGS Coastal and Marine Geology Team of the Geologic Division and the USGS Columbia River Research Laboratory of the Biological Resources Division. The data collection was completed aboard the R/V ESTERO during September 13-27, 2000.
The interest in sediment accumulation in the reservoir was two-fold. First, it was unknown how effective this reservoir was as a sediment trap to material that otherwise would have been transported down-river to the estuary and eventually to the ocean. The recent erosion of beaches along the Washington coast has been attributed to a decreased contribution of sediment from the Columbia River to the coastal system due to the damming of the river. Second, sediment accumulation on the floors of reservoirs along the Columbia River has been suggested to be diminishing salmon spawning grounds. The extent of changes in habitat since construction of the John Day Dam, however, had not been documented. Common data sets were needed to address both of these questions, and for these reasons this geophysical and sampling program was undertaken.

本研究于哥伦比亚河（Columbia River）约翰·代水库（John Day Reservoir）开展了为期两周的野外作业，旨在对库区水底进行成像勘测，测量蓄水后沉积物的分布与厚度，并通过摄像与底沉积物采样验证所获地球物理数据（geophysical data）。本次野外作业由美国地质调查局（USGS）地质部海岸与海洋地质研究组与美国地质调查局（USGS）生物资源部哥伦比亚河研究实验室合作完成，数据采集工作于2000年9月13日至27日期间在埃斯特罗号科考船（R/V ESTERO）上顺利完成。
针对该库区沉积物堆积情况的研究关注源于双重动因。其一，该水库作为沉积物捕集器（sediment trap），可拦截原本将顺流输送至河口并最终入海的沉积物，但其实际拦截效率尚未明确。此前华盛顿海岸沿线海滩的侵蚀现象，被归因于哥伦比亚河筑坝后向海岸系统输入的沉积物通量减少。其二，有研究指出哥伦比亚河沿岸水库库底的沉积物堆积已挤占三文鱼产卵场栖息地，但约翰·代大坝（John Day Dam）建成以来库区栖息地变化的范围尚未得到系统性记录。为解答上述两个核心科学问题，亟需统一的数据集支撑相关研究，因此本项地球物理勘探与采样作业得以实施。