Abstract
Numerous damages at structures and failures of dams can be ascribed to solution processes and attendant subsidence. Leaching in gypsum-bearing layers of the Middle Triassic has induced subsidence underneath the structure of the weir Hessigheim, River Neckar. The goals of this study were to gain a better understanding of the prevailing groundwater flow processes as well as the interaction between surface water and groundwater in the area of the weir lock and to verify the success of former remediation measures. In order to attain these objectives a combined groundwater and surface water tracer test in combination with hydraulic borehole tests were performed. In addition, a study of the dissolved sulfate distribution was carried out using sampling data from 1987 to 2013. Based on the results of these methods a strongly heterogeneous aquifer with main runoff occurring in few major flow paths could be characterized. Former remediation measures showed to be successful.
Highlights
Dissolvable bedrock often poses significant challenges to planners of hydraulic structures
Prior to the hydrogeochemical investigations and the time-consuming tracer tests,first information concerning the hydraulic situation was gained by performing hydraulic tests in 12 wells in the investigation area
Progressive leaching in the lower aquifer permanently changes hydraulic characteristics of the aquifer and results in strongly heterogeneous geohydraulic conditions
Summary
Dissolvable bedrock often poses significant challenges to planners of hydraulic structures. Due to the relatively high solubility of sulfates and carbonates, compared to other minerals, topography changes, such as subsurface erosion or subsidence in karst areas, are not uncommon (Cooper 1986). These kinds of transformations occur in, geologically speaking, very short periods of time (Jeschke 2002) and are sometimes intensified by human intervention in natural geohydraulic conditions. Caused by the higher solubility of sulfate in water, compared to carbonate minerals, solution processes often occur more rapidly in sulfate rocks (Dreybrodt et al 2002). The subject of this study, the weir lock Hessigheim at Neckar River, is situated in a sulfate-bearing geological environment
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