A REVIEW OF STORMWATER MANAGEMENT IN KARST

Stormwater management can be a challenge in any environment, but it is especially difficult in karst terrane. The characteristic dissolution of bedrock creates depressions in topography as well as voids in the subsurface, resulting in problems such as collapse sinkhole development, groundwater contamination, and flooding. To better understand these issues and ways in which practitioners have addressed stormwater concerns, we conducted an extensive review of pertinent information. A focused bibliography was created using standard search methods as well as expert input. The following aspects were evaluated: stormwater and the hydrologic cycle, an overview of carbonate geology and hydrology, stormwater design risks and ranking systems, stormwater management practices, and case studies. Overburden thickness, existing sinkhole density, relationship to joint and fracture systems, and hydrogeologic conditions are the top four factors in collapse development, and are also likely related to water quality issues. Thinner overburden has a larger potential for suffosion/collapse sinkhole development and vice versa. The greater the number of sinkholes in a given area, the higher is the probability that future collapse/suffosion sinkholes will occur. Proximity to certain pre-existing geologic features such as faults and fractures has been found to increase subsidence events. The chance of subsidence decreases as distance from these features increases. Successful risk ranking systems have been designed based on these parameters, but each is unique to a specific carbonate environment. Some investigators have used regression and ANOVA to assign a risk rank, while other authors designed decision/flow charts that evaluate site susceptibility and applicability. Taking the main parameters into consideration, preferred practices for stormwater management in karst environments include: bioretention, rain tanks, green roofs, and dry swales. These practices are ideal in karst terrane due to their ability to increase or maintain water quality while decreasing the risk for sinkhole formation and subsidence. Existing databases such as USDA-NRCS’s Web Soil Survey have the potential to guide selection of practices, but site-specific investigation by qualified professionals is still beneficial.