The James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, UK.
The James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, UK.
Sci Total Environ. 2021 May 20;770:144626. doi: 10.1016/j.scitotenv.2020.144626. Epub 2021 Jan 12.
Floodplain reconnection can potentially improve the hydrogeomorphology of river corridors and attenuate flood peaks. However, empirical evidence of its effectiveness - needed to inform future restoration - is limited. A 70 m long flood embankment was lowered on the upper River Dee, a medium sized gravel bed river in north-east Scotland to reconnect a backwater and floodplain. Comparison of two years pre- and three years of post-restoration hydro-geomorphic monitoring, shows the lowering and subsequent adjustment, assisted by several floods including a <1% annual exceedance probability event, have altered the morphology and hydrological dynamics. Channel aggradation of up to 1 m occurred. Erosion of the bank by up to 0.41 m in depth and deposition of gravel or sand within the backwater and the floodplain were the dominant geomorphic responses elsewhere. The channel adjustment, unexpected in the restoration design, improved hydrological connectivity with the floodplain; annual median water table levels were on average 0.037-0.089 m higher post-restoration although the correlation between river discharge and floodplain water levels did not change. Based on 1D modelling, the threshold river discharge for backwater connection decreased by 55% from 93 m s (discharge exceedance percentile: Q) to 42 m s (Q). Thus, overspill frequency increased. For a given peak discharge, floodplain water levels were higher on average by 0.25 m with a statistically significant difference (Mann Whitney U test: p < 0.05), due to improved hydrological connectivity. The monitoring demonstrates that localised but significant improvement of channel to floodplain hydro-geomorphic connectivity can result from targeted embankment lowering. Such actions could enhance future catchment resilience by improving water storage and biogeochemical processing.
漫滩连通可以改善河道走廊的水文地貌形态，并削减洪峰。然而，为了提供未来修复的依据，我们需要了解其有效性的经验证据，而这方面的证据却十分有限。在苏格兰东北部的中砾石床河——迪河的上游，一段长 70 米的防洪堤被降低，以重新连接回水区和漫滩。对修复前两年和修复后三年的水文地貌监测结果进行比较后发现，降低防洪堤的高度并在随后的调整过程中，在多次洪水的协助下，包括一次重现期小于 1%的洪水事件，改变了河道的形态和水文动态。河道出现了高达 1 米的淤积。河岸的侵蚀深度达到了 0.41 米，而回水区和漫滩内则出现了砾石或沙子的沉积，这些都是河道调整的主要地貌响应，这种调整超出了修复设计的预期。这种河道调整改善了与漫滩的水文连通性，使每年的中位地下水位平均高出 0.037-0.089 米，尽管河川流量与漫滩水位之间的相关性并未改变。基于一维模型，回水区连通的河流流量阈值从 93 立方米每秒（流量超过百分位：Q）降低到 42 立方米每秒（Q），降低了 55%。因此，溢洪的频率增加了。在给定的洪峰流量下，由于水文连通性的改善，漫滩水位平均高出 0.25 米，且具有统计学意义（Mann-Whitney U 检验：p < 0.05）。监测结果表明，通过有针对性地降低防洪堤，可以实现局部但显著改善河道与漫滩的水文地貌连通性。这种做法可以通过提高储水能力和生物地球化学处理来增强未来集水区的恢复能力。
