Effects of restricted recharge in an urban karst system |
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| Authors: | Email author" target="_blank">Laura?ToranEmail author Kathleen?Gross Youa?Yang |
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| Institution: | (1) Department of Geology, Temple University, Philadelphia, PA 19122, USA |
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| Abstract: | Urban karst systems are typically considered more vulnerable to contamination and excess storm discharge because of potential
source areas, increased sediment loading, and focusing of water from impervious surfaces. However, urban hydrology can lead
to unexpected patterns, such as pirating of recharge into man-made storm systems. Valley Creek Basin in southeastern Pennsylvania,
presents such an urban karst system. Four springs were monitored for suspended sediment, water chemistry, and storm response
for an 18-month period. The baseflow suspended sediment concentrations were low, less than 4.0 mg/l. Furthermore, trace metal
analysis of baseflow water samples and spring mouth sediment showed only low concentrations. The response to storms within
the system was rapid, on the order of 1–3 h. The maximum water stage increases at the urban springs were typically less than
15 cm, with springs from more commercialized areas showing <2 cm increase. A nearby retention basin, in contrast, had water
level rises of 100 cm, suggesting that pirating of recharge into stormwater systems occurs. Thus, the concept of an urban
karst system as a contaminant conduit is not the only one that applies. In Valley Creek Basin, reduced infiltration due to
paving led to smaller storm response and less contaminant input, and the smaller capture area due to diversion of stormwater
led to short flow paths and rapid storm response. Although contaminant levels have not increased due to urbanization, the
springs may be at risk for future contamination. Short flow paths may reduce flushing, which means that the system will not
cleanse itself if contamination occurs. |
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| Keywords: | Karst Urbanization Springs Geochemistry Data loggers |
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