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Laboratory Flume and Numerical Modeling Experiments Show Log Jams and Branching Channels Increase Hyporheic Exchange
Water Resources Research ( IF 5.4 ) Pub Date : 2021-09-13 , DOI: 10.1029/2021wr030299
K. Wilhelmsen 1 , A.H. Sawyer 1 , A. Marshall 2 , S. McFadden 3 , K. Singha 3 , E. Wohl 2
Affiliation  

Log jams alter gradients in hydraulic head, increase the area available for hyporheic exchange by creating backwater areas, and lead to the formation of multiple channel branches and bars that drive additional exchange. Here, we numerically simulated stream-groundwater interactions for two constructed flume systems—one without jams and one with a series of three jams—to quantify the effects of interacting jam structures and channel branches on hyporheic exchange at three stream flow rates. In simulations without jams, average hyporheic exchange rates ranged from 2.1 × 10−4 to 2.9 × 10−4 m/s for various stream discharge scenarios, but with jams, exchange rates increased to a range of 1.3 × 10−3–3.5 × 10−3 m/s. Largely due to these increased hyporheic exchange rates, jams increased stream-groundwater connectivity or decreased the turnover length that stream water travels before interacting with the hyporheic zone, by an order of magnitude, and drove long flow paths that connected multiple jams and channel threads. Decreased turnover lengths corresponded with greater reaction significance per km, a measure of the potential for the hyporheic zone to influence stream water chemistry. For low-flow conditions, log jams increased reaction significance per km five-fold, from 0.07 to 0.35. Jams with larger volumes led to longer hyporheic residence times and path lengths that exhibited multiple scales of exchange. Additionally, the longest flow paths connecting multiple jams occurred in the reach with multiple channel branches. These findings suggest that large gains in hydrologic connectivity can be achieved by promoting in-stream wood accumulation and the natural formation of both jams and branching channels.

中文翻译:

实验室水槽和数值模拟实验表明日志堵塞和分支通道增加了低流交换

原木堵塞改变了水头的梯度,通过产生回水区来增加可用于下流交换的区域,并导致形成多个通道分支和水坝,从而驱动额外的交换。在这里,我们数值模拟了两个构建的水槽系统的河流-地下水相互作用——一个没有堵塞,一个有一系列三个堵塞——以量化相互作用的堵塞结构和通道分支对三种河流流速下的下流交换的影响。在没有堵塞的模拟中, 对于各种河流排放场景,平均下流交换率范围从 2.1 × 10 -4到 2.9 × 10 -4 m/s,但在发生堵塞时,交换率增加到 1.3 × 10 -3 –3.5 × 10 -3 多发性硬化症。很大程度上由于这些增加的下流交换率,堵塞增加了溪流-地下水的连通性或将溪水在与下流带相互作用之前的周转长度减少了一个数量级,并驱动了连接多个堵塞和通道线的长流动路径。减少的周转长度与每公里更大的反应显着性相对应,这是衡量下流带影响河流水化学潜力的指标。对于低流量条件,日志堵塞将每公里的反应显着性增加了五倍,从 0.07 增加到 0.35。较大体积的堵塞导致较长的低流滞留时间和路径长度,表现出多种交换尺度。此外,连接多个堵塞的最长流路出现在具有多个通道分支的河段。
更新日期:2021-09-23
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