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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Dissolution in a variably confined carbonate platform: Effects of allogenic runoff, hydraulic damming of groundwater inputs, and surface-groundwater exchange at the basin scale
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Dissolution in a variably confined carbonate platform: Effects of allogenic runoff, hydraulic damming of groundwater inputs, and surface-groundwater exchange at the basin scale

机译：在可变受限的碳酸盐岩平台中的溶解：同位径流，地下水输入的水力筑坝以及流域规模的地表-地下水交换的影响

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摘要

In variably confined carbonate platforms, impermeable confining units collect rainfall over large areas and deliver runoff to rivers or conduits in unconfined portions of platforms. Runoff can increase river stage or conduit heads in unconfined portions of platforms faster than local infiltration of rainfall can increase groundwater heads, causing hydraulic gradients between rivers, conduits and the aquifer to reverse. Gradient reversals cause flood waters to flow from rivers and conduits into the aquifer where they can dissolve limestone. Previous work on impacts of gradient reversals on dissolution has primarily emphasized individual caves and little research has been conducted at basin scales. To address this gap in knowledge, we used legacy data to assess how a gradient of aquifer confinement across the Suwannee River Basin, north-central Florida affected locations, magnitudes and processes of dissolution during 2005-2007, a period with extreme ranges of discharge. During intense rain events, runoff from the confining unit increased river stage above groundwater heads in unconfined portions of the platform, hydraulically damming inputs of groundwater along a 200 km reach of river. Hydraulic damming allowed allogenic runoff with SI_(CAL)<-4 to fill the entire river channel and flow into the aquifer via reversing springs. Storage of runoff in the aquifer decreased peak river discharges downstream and contributed to dissolution within the aquifer. Temporary storage of allogenic runoff in karst aquifers represents hyporheic exchange at a scale that is larger than found in streams flowing over non-karst aquifers because conduits in karst aquifers extend the area available for exchange beyond river beds deep into aquifers. Post-depositional porosity in variably confined carbonate platforms should thus be enhanced along rivers that originate on confining units. This distribution should be considered in models of porosity distribution used to manage water and hydrocarbon resources in carbonate rocks.
机译：在可变密闭的碳酸盐台地中，不可渗透的密闭单元收集大面积的降雨，并将径流输送至平台无限制部分的河流或管道。径流可以增加平台的无限制部分的河段或导管头，而降雨的局部渗透可以增加地下水头，从而导致河流，导管和含水层之间的水力梯度反转。梯度逆转会导致洪水从河流和导管流到含水层，在这里它们可以溶解石灰石。以前关于梯度逆转对溶蚀影响的研究主要着重于单个溶洞，在盆地尺度上很少进行研究。为了解决这一知识鸿沟，我们使用遗留数据评估了Suwannee流域，佛罗里达州中北部的含水层封闭梯度如何影响2005-2007年（排放量极高的时期）的位置，大小和溶解过程。在强降雨期间，封闭单元的径流增加了平台无限制部分中地下水头上方的河流水位，沿河段200 km的水力压入了地下水。水力筑坝使SI_（CAL）<-4的异源径流充满整个河道，并通过换向弹簧流入含水层。含水层中的径流存储减少了下游的高峰河流量，并导致了含水层内的溶出。岩溶含水层中的异源径流的临时存储代表了流变交换，其规模大于非岩溶含水层上流的水流，因为岩溶含水层中的导管将可交换的区域扩展到了河床深处到含水层之外。因此，应在沿约束单元发源的河流上增加在受约束的碳酸盐岩台地中沉积后的孔隙度。在用于管理碳酸盐岩中水和碳氢化合物资源的孔隙度分布模型中应考虑这种分布。

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