Intermountain Center for River Rehabilitation and Restoration, Department of Watershed Sciences, Utah State University, 5210 Old Main Hill, Logan, UT 84322-5210, USA.
J Environ Manage. 2012 Oct 30;109:154-63. doi: 10.1016/j.jenvman.2012.05.013. Epub 2012 Jun 21.
We used pre- and post-restoration channel surveys of the Donner und Blitzen River, Oregon, to evaluate the effects of grade-control structures on channel morphology and baseflow habitat conditions for native redband trout and other aquatic biota. Six years after installation, we found that the channel had a smaller proportion of riffles and pools and less gravel substrate, combined with an increase in the proportion of flat waters and consolidated clay on the bed surface. Both local scour downstream from weirs and backwater effects upstream from weirs appear to have caused the general flattening and fining of the channel. A direct-step backwater calculation indicates that backwaters extended to the upstream weir at both low and high flows, creating long sections of flat water separated by short, steep drops. Despite backwater effects, a comparison of longitudinal profiles before and six years after weir installation showed bed erosion downstream of nearly all weirs, likely a consequence of the cohesive clay material that dominates the channel bed and banks. A deep inner channel reflects the cohesive nature of the clay and the mechanisms of abrasion, and indicates that sediment load is low relative to the transport capacity of the flow. Unfortunately, weirs were problematic in this system because of the cohesive clay substrate, limited sediment supply, and low channel gradient. Although deeper flows due to backwaters might be more favorable for resident trout, less gravel and fewer riffles are likely to negatively impact trout spawning habitat, macroinvertebrate communities, and biofilm productivity. Our results demonstrate the potential limitations of a single-feature approach to restoration that may be ineffective for a given geomorphic context and may overlook other aspects of the ecosystem. We highlight the need to incorporate geomorphic characteristics of a system into project design and predictions of system response.
我们使用唐纳和布莱森河（俄勒冈州）修复前后的河道调查来评估控流结构对原生红大麻哈鱼和其他水生物种的河道形态和基流生境条件的影响。安装六年后，我们发现河道中急流和缓流区的比例减小，砾石底质减少，同时水面比例增加，床面固结粘土增多。堰下游的局部冲刷和堰上游的回水效应似乎导致了河道的整体变平变细。直接法回水计算表明，在低流量和高流量时，回水区都延伸到上游的堰，形成了几段长而平缓的水面，其间有短而陡峭的下降。尽管有回水效应，但堰安装前后的纵向剖面比较表明，几乎所有堰的下游都有河床侵蚀，这可能是由于主导河道床和岸坡的粘性粘土材料造成的。深的内部河道反映了粘土的粘性和磨损机制，并表明与水流的输送能力相比，泥沙负荷较低。不幸的是，堰在这个系统中存在问题，原因是粘性粘土基底、有限的泥沙供应和低的河道坡度。尽管由于回水导致较深的水流可能更有利于本地大麻哈鱼，但砾石较少和急流区减少可能会对大麻哈鱼的产卵生境、大型无脊椎动物群落和生物膜生产力产生负面影响。我们的研究结果表明，单一特征方法的修复可能在特定的地貌背景下无效，并可能忽略生态系统的其他方面，具有潜在的局限性。我们强调需要将系统的地貌特征纳入项目设计和系统响应预测中。
