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Sediment export and impacts associated with river delta channelization compound estuary vulnerability to sea-level rise, Skagit River Delta, Washington, USA
Marine Geology ( IF 2.9 ) Pub Date : 2020-09-06 , DOI: 10.1016/j.margeo.2020.106336
E.E. Grossman , A.W. Stevens , P. Dartnell , D. George , D. Finlayson

Improved understanding of the budget and retention of sediment in river deltas is becoming increasingly important to mitigate and plan for impacts expected with sea level rise. In this study, analyses of historical bathymetric change, sediment core stratigraphy, and modeling are used to evaluate the sediment budget and environmental response of the largest river delta in the U.S. Pacific Northwest to western land-use change beginning in ~1850. An estimated 142±28 M m3 of sediment accumulated offshore of the emergent Skagit River delta in Washington State between 1890 and 2014 and ~68% of which was found in sand deposits. The fraction of sediment retained in sand reservoirs represents 83% of the expected fluvial sand delivery over this time suggesting their potential utility to evaluate the relative contribution of different land uses to sediment runoff through time. A significantly higher ratio of sand retention to delivery during the period 1890–1939 coincided with extensive watershed denudation (clear-cut logging) and channel dredging, relative to the period 1940–2014, which was characterized by improved forest practices and sediment management to protect endangered species but also more extensive river channelization. Retention in the delta foreset of 78% of the sand delivered by the river between 1890 and 1939 was associated with extensive sediment bypassing and delta progradation that is shown to be 5–10x higher than rates over the Holocene. Comparable offshore sand retention over time and higher nearshore retention subsequent to 1940 after normalizing for the assumed reduction in sediment runoff with improved forest practices, suggests that channelization has continued to influence sediment export at a magnitude equivalent to the effects of early logging. Adverse impacts of the bypassing sediment regime to natural hazards risk and ecosystem management concerns are discussed, including the role of the lost sediment as a resource to mitigate subsiding coastal lands vulnerable to flood impacts. The sediment budget and coastal change analyses provide a framework for evaluating opportunities to achieve greater resilience across several sectors of coastal land use important in low-lying deltas worldwide.



中文翻译:

美国华盛顿州斯卡吉特河三角洲,泥沙出口以及与河三角洲渠道化相关的影响使河口易受海平面上升的影响

更好地了解三角洲的预算和沉积物保留对于减轻和计划海平面上升带来的预期影响变得越来越重要。在这项研究中,使用历史测深变化,沉积物岩心地层学和模型分析来评估美国太平洋西北部最大的三角洲对1850年以来对西部土地利用变化的沉积物收支和环境响应。估计142±28 M m 31890年至2014年间在华盛顿州新兴的斯卡吉特河三角洲近海沉积的沉积物,其中约68%是在砂矿中发现的。在这段时间内,保留在砂储层中的沉积物占预期河道输沙量的83%,这表明它们有潜力用于评估不同土地利用对沉积物径流的相对贡献。相对于1940-2014年,沙丘固留与输沙的比率显着较高,这与1940-2014年期间的大范围流域剥蚀(伐木伐木)和河道疏coincide相吻合,其特点是森林实践和沉积物管理得到改善濒危物种,但河道也更加广泛​​。1890年至1939年间,三角洲前缘保留的河水中有78%的沙子与广泛的泥沙绕过和三角洲的退化有关,这比全新世的沉积率高5-10倍。在假定的沉积物径流量减少和森林改良措施正常化之后,随着时间的推移,随着时间的推移,可比的海上沙粒滞留量和1940年之后更高的近海保留量表明,渠道化继续影响沉积物的出口,其幅度与早期伐木的影响相当。讨论了绕过沉积物制度对自然灾害风险和生态系统管理问题的不利影响,包括损失的沉积物作为缓解易受洪水影响的沿海土地沉降的资源的作用。

更新日期:2020-09-25
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