University of Glasgow, Glasgow G12 8QQ, United Kingdom.
Utah State University, Logan, 84322, UT, United States of America; Anabranch Solutions LLC, Logan, 84327, UT, United States of America.
Sci Total Environ. 2020 May 1;715:136817. doi: 10.1016/j.scitotenv.2020.136817. Epub 2020 Jan 21.
River restoration practice frequently employs conservative designs that create and maintain prescribed, static morphology. Such approaches ignore an emerging understanding of resilient river systems that typically adjust their morphology in response to hydrologic, vegetative and sediment supply changes. As such, using increased dynamism as a restoration design objective will arguably yield more diverse and productive habitats, better managed expectations, and more self-sustaining outcomes. Here, we answer the following question: does restoring lateral migration in a channelised river that was once a wandering gravel-bed river, result in more diverse in-channel geomorphology? We acquired pre- and post-restoration topographic surveys on a segment of the Allt Lorgy, Scotland to quantify morphodynamics and systematically map geomorphic units, using Geomorphic Unit Tool (GUT) software. GUT implements topographic definitions to discriminate between a taxonomy of fluvial landforms that have been developed from an extension of the River Styles framework, using 3-tiered hierarchy: (1) differentiation based on stage or elevation relative to channel; (2) classification of form based on shape (mound, bowl, trough, saddle, plane, wall); and (3) mapping geomorphic units based on attributes (e.g., position and orientation). Results showed restoration increased geomorphic unit diversity, with the Shannon Diversity Index increasing from 1.40 pre-restoration (2012) to 2.04 (2014) and 2.05 (2016) after restoration. Channel widening, due to bank erosion, caused aerial coverage of in-channel geomorphic units to increase 23% after restoration and 6% further in the two-years following restoration. Once bank protection was removed, allowing bank erosion yieled a local supply of sediment to enable the formation and maintenance of lateral and point bars, riffles and diagonal bar complexes, and instream wood created structurally-forced pools and riffles. The methodology used systematically quantifies how geomorphic unit diversity increases when a river is given back its freedom space. The framework allows for testing restoration design hypotheses in post-project appraisal.
河流修复实践常常采用保守设计，创造和维持规定的静态形态。这种方法忽略了一个新兴的弹性河流系统的理解，即这些系统通常会根据水文、植被和泥沙供应的变化来调整其形态。因此，将增加动态性作为修复设计目标，将产生更多多样化和多产的栖息地，更好地管理预期，并取得更可持续的结果。在这里，我们回答了以下问题：在曾经是游荡砾石河床的河道中恢复侧向迁移，是否会导致河道内形态更加多样化？我们在苏格兰的 Allt Lorgy 河段获取了修复前后的地形测量数据，使用地形单元工具（GUT）软件来量化形态动力学并系统地绘制地形单元。GUT 使用地形定义来区分从河流形态框架扩展而来的河流地貌分类法，使用三级层次结构：（1）基于相对于河道的阶段或高程的差异；（2）基于形状（土丘、碗形、槽形、鞍形、平面、壁面）的形态分类；（3）基于属性（例如位置和方位）的地貌单元映射。结果表明，修复增加了地貌单元的多样性，Shannon 多样性指数从修复前的 1.40（2012 年）增加到修复后的 2.04（2014 年）和 2.05（2016 年）。由于岸坡侵蚀，河道扩宽导致修复后河道内地貌单元的航空覆盖面积增加了 23%，修复后两年又增加了 6%。一旦拆除了护岸，允许岸坡侵蚀，就会产生当地的泥沙供应，从而形成和维持侧向和点滩、浅滩和对角滩复合体以及河道内木材形成的结构强制池和浅滩。该方法系统地量化了河流获得自由空间时地貌单元多样性如何增加。该框架允许在项目后评估中测试修复设计假设。
