Interpretation of Sidescan-sonar Imagery in the John Day Reservoir

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约翰·代水库（John Day Reservoir）开展了为期两周的野外作业，旨在对库底进行成像，测量蓄水后沉积物的分布与厚度，并通过水下视频摄影与底泥采样对所得地球物理数据进行验证。本次野外项目由美国地质调查局（USGS）地质调查部海岸与海洋地质团队，以及美国地质调查局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日在“埃斯特罗号”（R/V ESTERO）研究船上完成。

针对该水库的沉积物堆积问题，本次研究的关注焦点分为两方面：其一，该水库作为沉积物捕集阱的实际效能尚不明确——若未被水库拦截，沉积物本应顺流输送至河口并最终进入海洋。近期华盛顿州沿岸海滩的侵蚀现象，被归因于河流筑坝导致哥伦比亚河向沿岸系统输入的沉积物量减少。其二，有研究指出哥伦比亚河沿岸水库库底的沉积物堆积正在缩减鲑鱼产卵场范围，但约翰·代水坝建成以来的栖息地变化程度尚未得到记录。为同时解答这两个问题，亟需获取适配二者的通用数据集，因此本研究开展了本次地球物理探测与采样工作。