Seasonal variation in cascade‐driven hyporheic exchange, northern Honduras
Seasonal variation in cascade‐driven hyporheic exchange, northern Honduras
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洪都拉斯北部级联驱动的潜流交换的季节变化
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发表时间：
2011
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通讯作者：
L. Lautz
中科院分区：
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作者：
M. Fabian;T. Endreny;A. Bottacin‐Busolin;L. Lautz
在洪都拉斯北部的一级瀑布Prieta Creek中，研究了干湿季节基流的潜流交换特征，以及部分脱水排放。该梯级的流量为1 ~ 15 l s−1，平均坡度为12%，池间距为3 m，基材为浅砂和砾石。示踪剂测试在15米的亚河段进行，根据DaI测试（交换和运输过程的比率），该长度被认为对实验来说是足够的。在三次测试中，有9%至18%的示踪剂未被回收，可能是由于流经下游监测位置下方的流道夹带。对示踪剂数据进行了一维流入和储存输运（OTIS）瞬态存储模型（TSM）分析，得出标准交换参数，并通过河流溶质输运（STIR）模型检验了潜停留时间分布（rtd）。采用结合两个指数rtd的STIR模型拟合示踪剂突破曲线，得到了最佳的拟合结果。随着流量的增加，OTIS模型预测库区交换通量和交换系数增加，库区面积和瞬态存储时间减少，这一趋势得到了河岸和河床测压水头数据的支持。在旱季到雨季的过渡期间，河岸水位上升，这可能会收缩潜储区。19个河床气压计中有13个记录了水力梯度和通量方向的季节性变化，在高流量期间上升流区较少但较强。MODFLOW模式遗漏了观测到的季节变化，可能是由于水面剖面季节变化的微妙变化。与雨季交换相比，部分脱水的旱季交换以较小的压力梯度开始和结束，并且在不同的河床位置，体积更小，停留时间更长，并且可能与更深更长的流动路径相连。版权所有©2010 John Wiley & Sons， Ltd
A characterization of hyporheic exchange for dry and wet season baseflow, as well as partially dewatered discharge, was done in Prieta Creek, a first‐order cascade in northern Honduras. The cascade had discharges from 1 to 15 l s−1, had average slopes of 12%, pool spacing of 3 m, and shallow substrate of sand and gravel. Tracer tests were conducted in a 15‐m sub‐reach, a length considered to be adequate for the experiment based on the DaI test, a ratio of exchange and transport processes. In the three tests, between 9 and 18% of tracer was not recovered, possibly due to entrainment in flowpaths passing beneath the downstream monitoring location. Tracer data were analysed by the one‐dimensional transport with inflow and storage (OTIS) transient storage model (TSM) to derive standard exchange parameters, and by the solute transport in rivers (STIR) model to examine hyporheic residence time distributions (RTDs). The best fit of the observed tracer breakthrough curves was obtained by using the STIR model with a combination of two exponential RTDs to represent hyporheic retention. With increasing discharge, the OTIS model predicted increasing storage exchange fluxes and exchange coefficients and decreasing storage zone areas and transient storage times, which are trends supported by riparian and streambed piezometric head data. Riparian water levels rose during the transition from the dry to wet season, which could constrict the hyporheic storage zone. Thirteen of the 19 streambed piezometers recorded seasonal changes in hydraulic gradients and flux direction, with fewer yet stronger upwelling zones during higher discharges. The MODFLOW model missed the observed seasonal changes, possibly due to subtle changes in the seasonal change in water surface profiles. We conclude that partially dewatered dry season exchange, compared to wet season exchange, was initiated and terminated with smaller pressure gradients and, in different streambed locations, was smaller in volume, had longer residence times, and may connect with deeper and longer flow paths. Copyright © 2010 John Wiley & Sons, Ltd.