Abstract A number of large rivers across the world are dredged for navigation. Dredging removes sediment from the channel, creates spoil mounds in the adjoining floodplain, and disposes sediment along the channel margin on a bar, or in open water. Retrospective studies that examine the placement and fate of this disposed material can provide guidance for other localities where dredging is practiced, and better elucidate the impacts associated with disposal at different types of sites. Many studies exist for impacts and benefits of dredging in the coastal environment, particularly to ecosystems and water quality. Few studies have examined disposal site selection and the fate of dredge spoil placed along a river corridor from a geomorphic and retrospective perspective. The Apalachicola River in Florida was dredged from the 1950s for several decades, with disposal on sand bars, in open water on the channel margins, and on the floodplain. Numerous large and small floodplain dredge-spoil mounds are a legacy from this navigation project. One of the larger mounds, disposal site 40 (DS 40), which locals call “Sand Mountain,” stands ~22 m high and extends ~10 ha in area. This disposal site originated in an artificial cutoff created in 1968–69 and grew to hold >625,000 m3 of sediment. Because this section of river was a problem for navigation when dredging was being conducted, detailed historical survey sheets with topographic and bathymetric data exist. The purpose of this paper was to analyze the local floodplain and channel geospatially, coupled with dredging and disposal data, to interpret the geomorphic changes of DS 40 and the adjoining river. Poor placement has resulted in this and other dredge spoil mounds returning sediment to the river through lateral erosion and mass wasting. Intermittent sediment pulses have altered channel morphology adjacent to the spoil mound with the channel becoming wider and shallower than originally, mean bed and thalweg elevations increasing by ~1.5 to 2 m, and width-depth ratio increasing three-fold. Although dredging of this river has not been conducted for nearly two decades, study of historical dredge spoil mounds in this reach suggest poor placement of spoil can continue to stress and alter a river in the decades that follow. Based on our findings, dredging downstream of distributaries will have poor outcomes. Dredge spoil placement in cut-off channels close to the river can be problematic because the river will regain sinuosity. Further, sites on the outer bend of meanders are more subject to erosion, and sites immediately upstream of problem or shallow areas will feed sediment to the problem reach. Findings of this study have implications to other settings, such as intensively mined rivers where unused unconsolidated material is often left on floodplains.

中文翻译：

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从侵蚀的疏浚弃土丘影响通道形态的地貌见解

摘要 世界上许多大河都被疏浚通航。疏浚从河道中清除沉积物，在相邻的洪泛区形成弃土丘，并沿河道边缘的栅栏或开阔水域处理沉积物。检查这种处置材料的放置和归宿的回顾性研究可以为其他进行疏浚的地方提供指导，并更好地阐明与在不同类型场地处置相关的影响。许多关于在沿海环境中进行疏浚的影响和益处的研究，特别是对生态系统和水质的影响。很少有研究从地貌和回顾性的角度研究处置地点的选择和沿河流走廊放置的疏浚弃土的命运。佛罗里达州的阿巴拉契科拉河从 1950 年代被疏浚了几十年，在沙洲、河道边缘的开阔水域和洪泛区处置。许多大大小小的洪泛区疏浚土丘都是这个导航项目的遗产。较大的土丘之一，处置场 40 (DS 40)，当地人称之为“沙山”，高约 22 m，面积约 10 公顷。该处置场起源于 1968-69 年间创建的人工截流区，后来发展到可容纳 >625,000 立方米的沉积物。由于这一段河流在进行疏浚时是航行的一个问题，因此存在包含地形和水深数据的详细历史调查表。本文的目的是从地理空间分析当地洪泛区和河道，结合疏浚和处置数据，解释 DS 40 和毗邻河流的地貌变化。放置不当导致这个和其他疏浚弃土堆通过侧向侵蚀和大量浪费将沉积物返回河流。断续的沉积物脉冲改变了弃土丘附近的河道形态，河道变得比原来更宽和更浅，平均河床和 thalweg 海拔增加了约 1.5 到 2 m，宽深比增加了三倍。虽然这条河的疏浚工作已经有近 20 年没有进行了，但对该河段历史疏浚弃土丘的研究表明，弃土放置不当会在接下来的几十年中继续对河流造成压力和改变。根据我们的研究结果，在支流下游疏浚的结果很差。在靠近河流的截止通道中疏浚弃土可能会出现问题，因为河流将恢复曲折。更多，位于曲流外弯的场地更容易受到侵蚀，紧邻问题上游或浅水区域的场地会将沉积物输送到问题区域。这项研究的结果对其他环境有影响，例如密集开采的河流，在这些河流中，未使用的未固结材料经常留在洪泛区。