Rivers provide important sediment inputs to many littoral cells, thereby replenishing sand and gravel of beaches around the world. However, there is limited information about the patterns and processes of littoral-grade sediment transfer from rivers into coastal systems. Here I address these information gaps by examining topographic and bathymetric data of river mouths and constructing sediment budgets to characterize time-dependent patterns of onshore, offshore, and alongshore transport. Two river deltas, which differ in their morphology, were used in this study: the Elwha River, Washington, which builds a mixed sediment Gilbert-style delta, and the Santa Clara River, California, which builds a cross-shore dispersed sand delta from hyperpycnal flows. During and after sediment discharge events, both systems exhibited a similar evolution composed of three phases: (i) submarine delta growth during offshore transport of river sediment, (ii) onshore-dominated transport from the submarine delta to a subaerial river mouth berm, and (iii) longshore-dominated transport away from the river mouth following subaerial berm development. Although stage (ii) occurred within days to weeks for the systems studied and was associated with the greatest rates of net erosion and deposition, onshore transport of sediment from submarine deposit to the beach persisted for years following the river discharge event. These morphodynamics were similar to simple equilibrium profile concepts that were modified with an onshore-dominated cross-shore transport rule. Additionally, both study sites revealed that littoral-grade sediment was initially exported to depths beyond the active littoral cell (i.e., below the depth of closure) during the stage (i). Following several years of reworking by coastal processes, bathymetric surveys suggested that 14 and 46% of the original volume of littoral-grade sediment discharged by the Santa Clara and Elwha Rivers, respectively, continued to be below the depth of closure. Combined, this suggests that integration of river sediment into a littoral cell can be a multi-year process and that the full volume of littoral-grade sediment discharged by small rivers may not be integrated into littoral cells because of sand and gravel “losses” to the continental shelf.

河流为许多滨海单元提供了重要的沉积物输入，从而补充了世界各地海滩的沙子和砾石。但是，关于沿河级沉积物从河流转移到沿海系统的模式和过程的信息有限。在这里，我将通过检查河口的地形和测深数据，并构建沉积物预算来表征陆上，近海和沿海运输的时变模式，从而解决这些信息空白。这项研究使用了两种形态各异的河流三角洲：华盛顿的Elwha河，建立了吉尔伯特风格的混合沉积物三角洲；加利福尼亚州的圣克拉拉河，建立了跨海岸的分散沙洲。肥大血流。在沉积物排放事件期间和之后，两种系统都显示出由三个阶段组成的相似演变：（i）河底沉积物近海运输过程中海底三角洲的增长；（ii）从海底三角洲到陆上河口护岸的陆上主导运输；以及（iii）长岸主导的运输远离地下堤坝发育的河口。尽管对于所研究的系统，阶段（ii）发生在几天至几周内，并且与最大的净侵蚀和沉积速率有关，但是在河流排放事件之后，从海底沉积物到海滩的沉积物在陆上的运输持续了数年。这些形态动力学与简单的平衡剖面概念相似，后者已通过陆上主导的跨岸运输规则进行了修改。另外，这两个研究地点都表明，在阶段（i）中，沿岸沉积物最初出口到活跃的沿岸单元以外的深度（即低于封闭深度）。经过几年的沿海工程改造，水深测量表明，圣塔克拉拉河和Elwha河分别排放的沿海级沉积物原始体积的14％和46％仍低于封闭深度。综合起来，这表明将河流沉积物整合到沿海单元中可能是一个多年的过程，并且由于沙子和砾石的“损失”，小河排放的沿海级沉积物的全部体积可能不会整合到沿海单元中。大陆架。经过几年的沿海工程改造，水深测量表明，圣塔克拉拉河和Elwha河分别排放的沿海级沉积物原始体积的14％和46％仍低于封闭深度。综合起来，这表明将河流沉积物整合到沿海单元中可能是一个多年的过程，并且由于沙子和砾石的“损失”，小河排放的沿海级沉积物的全部体积可能不会整合到沿海单元中。大陆架。经过数年的沿海工程改造，水深测量表明，圣塔克拉拉河和Elwha河分别排放的滨海级沉积物原始体积的14％和46％仍低于封闭深度。综合起来，这表明将河流沉积物整合到沿海单元中可能是一个多年的过程，并且由于沙子和砾石的“损失”，小河排放的沿海级沉积物的全部体积可能不会整合到沿海单元中。大陆架。