Flood dynamics in low-relief landscapes control the lateral exchange of water and sediment between a river and its floodplain. Locations where these exchanges occur for any given river discharge depend on local bank elevations, which in turn depend on the type of landform present immediately adjacent to the river channel. Our analysis separated landforms bordering a river into six categories: levee, scroll bar, counter point bar, channel-bend cutoff, erosional surface, and inactive surface. Each landform is associated with a different range of elevations. Levees are the highest, and counter point bars and cutoffs are the lowest. Using a combination of lidar-derived measurements of topography and water-surface profiles derived from U.S. Geological Survey gauge data, we show that landforms at the margins of the river change with downstream position on the coastal reach of the Trinity River in the southern United States. The fractions of counter point bars and cutoffs decrease downstream, while the fraction and continuity of levees increase to nearly 100%. This spatial change correlates with downstream reductions in channel-bend migration and deformation, and the measured range in river stage. As a result, the greatest range in bank elevations occurs upstream where variation in river stage is also highest. Meanwhile, the smallest range in bank elevation and river stage exists in the coastal backwater zone. Our analysis indicates that essentially all levees within the backwater zone are overtopped by flow associated with a single river discharge. Moving upriver, the discharge associated with levee-overtopping flow systematically increases. This study highlights the morphodynamic control on coastal river flooding.

中文翻译：

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自然堤坝在回水区的流行率增加：美国德克萨斯州三一河沿岸

低地势景观中的洪水动态控制河流与其洪泛区之间水和沉积物的横向交换。对于任何给定的河流排放，这些交换发生的位置取决于当地的河岸高度，而这又取决于紧邻河道的地形类型。我们的分析将与河流接壤的地形分为六类：堤坝、滚动条、对位条、河道弯截断面、侵蚀面和非活动面。每个地形都与不同的海拔范围相关联。堤坝是最高的，反点条和截止点是最低的。使用激光雷达衍生的地形测量和美国地质调查局测量数据衍生的水面剖面的组合，我们展示了河流边缘的地貌随着美国南部三一河沿岸下游位置的变化而变化。下游的对位坝和截流的比例降低，而堤坝的比例和连续性增加到接近 100%。这种空间变化与下游河道弯曲迁移和变形的减少以及河流阶段的测量范围有关。因此，河岸高程的最大范围出现在上游，河流水位的变化也最大。同时，滨海回水带的河岸标高和河位范围最小。我们的分析表明，基本上回水区内的所有堤坝都被与单一河流排放相关的流量所淹没。逆流而上，与堤坝溢流相关的流量系统性地增加。本研究强调了对沿海河流洪水的形态动力学控制。