A TALE OF TWO CREEKS: INVESTIGATING HYDROLOGIC RESPONSE TO URBANIZATION IN CARBONATE WATERSHEDS

The Little Lehigh and Monocacy Creek watersheds are in close proximity to each other in the Lehigh Valley and are part of the greater Lehigh River basin. On the watershed-wide scale, there appear to be a number of similarities such as growth in population density, land use, and amount of carbonate bedrock. The two streams have been noted as having similar baseflow characteristics as well. Despite these similarities, the two watersheds have shown a remarkably different response to urbanization. Analyses of annual runoff volume ratio, the annual peak flow, and the annual “flashiness index” have shown statistically significant increasing trends in the Little Lehigh Creek, but not in the Monocacy Creek. Analysis of gage data also shows that the Little Lehigh Creek watershed generates more runoff per unit area than the Monocacy Creek watershed. The cause of this disparity in hydrologic response was investigated by analyzing geomorphic characteristics, bedrock geology, and the spatial distribution of land use. Preliminary results show that response in the Little Lehigh Creek watershed is heightened by large, connected impervious areas on relatively flat land underlain by carbonate bedrock in the upper watershed. In addition to this, the orientation of higher-elevation areas underlain by less permeable bedrock compared to the Monocacy Creek watershed inhibit moderation of runoff peaks through underflow. Furthermore, stream flow readings along the Monocacy Creek show losing reaches upstream may have a “buffering” effect on smaller, more frequent storms. Further work will confirm these theories through statistical analysis of gage data, runoff modeling using GIS, and continuation of flow measurements.