Sediment Transport in an Urbanizing Karst Aquifer-Watershed

地下水在岩溶含水层中的湍流有效地将沉积物和胶体输送到地下，并可能为有机污染物的快速输送提供一条途径。相比之下，岩溶含水层中的沉积物储存可以在很长一段时间内隔离污染物，同时改变含水层的流动特性。岩溶含水层中泥沙的可获得性和运移反过来又受到土地利用变化以及相关的径流和河流流量变化的深刻影响。虽然人们对地表水中泥沙运移的水动力学进行了广泛的研究，但对岩溶水动力学知之甚少，对地表和地下区域之间的联系知之甚少，对岩溶含水层中泥沙运移的动力学几乎一无所知。这项拟议的研究将调查德克萨斯州中部爱德华兹含水层分水岭城市化巴顿河段的泥沙输送情况。将在巴顿溪通过奥斯汀西南部的主要补给区，进入含水层，并在分水岭唯一的排污点巴顿和冷泉进行泥沙特征、泥沙输送和沉积物化学研究。该项目的目标是：1)确定补给点河流中泥沙的化学特征，并将其与排出的泥沙进行比较；2)利用天然示踪剂和引入的示踪剂，量化通过这段含水层的泥沙输运；3)量化不同流态下城市化和农业流域的泥沙收支。我们将利用补给点和排泄点之间的几个监测井，描述巴顿河径流在基流和暴雨流阶段、巴顿和冷泉排放点以及直接在含水层中的泥沙特征。通过比较进入含水层的泥沙“补给”和泉水中的泥沙排放，可以建立泥沙质量平衡。样本将在基流和暴雨条件下采集，以检查泥沙负荷、粒度分布和矿物学随流量的变化。将与奥斯汀市合作，使用荧光染料追踪水流，并使用天然和引进的沉积物示踪剂来描述岩溶含水层中的沉积物运移情况。一种使用DNA标记粘土的新型沉积物示踪剂将被用来量化从含水层的补给特征和沉积物到储存的损失的运输时间。悬浮泥沙的污染物运移潜力将通过分析表面积沉积物有机碳来表征，污染物负荷将通过分析选定沉积物样本上的总石油烃来表征。该项目将提供对进入和通过岩溶含水层的泥沙运移过程、泥沙和泥沙结合污染物的移动性以及城市和农村流域中可移动泥沙的来源的基本见解。

0001197BennettThe turbulent flow of groundwater through karst-aquifers effectively transports sediment and colloids through the subsurface and may provide a pathway for the rapid transport of organic contaminants. Sediment storage in karst aquifers, in contrast, may sequester contaminants for long time periods while altering the flow properties of the aquifer. The availability and transport of sediment in a karst aquifer are in turn profoundly influenced by changes in land-use and the associated changes in runoff and stream discharge. While there has been extensive research into the hydrodynamics of sediment transport in surface water, little is known about karst hydrodynamics, less about the connection between the surface and subsurface domains, and almost nothing about the dynamics of sediment transport in karst aquifers. The proposed study will investigate the transport of sediment in the urbanizing Barton Creek segment of the Edwards aquifer watershed of central Texas. Sediment characteristics, sediment transport, and sediment chemistry will be examined in Barton Creek across the primary recharge area in SW Austin, into the aquifer, and out at the watershed's only discharge points at Barton and Cold Springs. The goals of this project are to 1) Characterize the sediment chemistry in the stream at the recharge point and compare that to the discharged sediment; 2) quantify the transport of sediment through this section of the aquifer using natural and introduced tracers; and 3) quantify the sediment budget in urbanizing and agricultural watersheds under different flow regimes.We will characterize the sediment in the Barton Creek runoff at base and stormflow stages, at the Barton and Cold Springs discharge points, and directly in the aquifer using several monitoring wells between the recharge and discharge points. A sediment mass-balance will be developed by comparing sediment 'recharge' into the aquifer to sediment discharge at the springs. Samples will be collected during baseflow and stormflow conditions to examine sediment loading, size distribution, and mineralogy as a function of discharge. Tracing of water flow using fluorescent dyes in cooperation with the City of Austin, and both natural and introduced sediment tracers, will be used to characterize sediment transport in the karst aquifer. A novel sediment tracer using DNA-labeled clay will be used to quantify transport time from the recharge feature and the loss of sediment to storage in the aquifer. The potential for contaminant transport by suspended sediment will be characterized by analyzing surface area sediment organic carbon, and contaminant loading will be characterized by analysis of total petroleum hydrocarbons on selected sediment samples.This project will provide fundamental insight into sediment transport processes into and through karst aquifers, the mobility of sediment and sediment-bound contaminants, and the sources of mobile sediment in urban and rural watersheds.