Two contrasting fall line watersheds in NW Delaware and SE Pennsylvania
Date
2023
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Publisher
University of Delaware
Abstract
Streamflow discharge in natural watersheds is typically considered a mixture of baseflow from groundwater discharge plus transient increases in discharge from precipitation events. In contrast, baseflow within urban watersheds is considered to be limited by decreased infiltration due to extensive impervious land cover, with a flashy response to runoff from precipitation events. ☐ We examined two contrasting fall line watersheds in NW Delaware and SE Pennsylvania (White Clay Creek, a designated Wild and Scenic Waterway, and Darby Creek, respectively). Hourly average data for discharge, water temperature, and specific conductance over a one-year period from the USGS streamflow monitoring stations #01478650 (White Clay Creek in Newark, DE) and #01475510 (Darby Creek near Darby, PA) were augmented with daily to bi-weekly grab sample measurements of stable isotope ratios of H and O in water. Watershed catchment areas above these USGS monitoring stations were 277 square km and 199 square km, respectively. ☐ The purpose of this study is to better understand the contrasting watershed characteristics that influence streamflow processes and water quality; and to analyze rural vs. urban stream response to storm events including, (1) overall shape and timing of the storm hydrograph, including peak flows and lag times (i.e., the time interval from maximum rainfall event to peak discharge) and (2) relative contributions and timing of baseflow and event water. ☐ The observed contrasts between these two watersheds are summarized as follows: The land cover percentages in the White Clay Creek watershed are roughly 37% developed, 33% agriculture, and 30% forested. The land cover within the Darby Creek watershed is 58% developed, and 20% forested, and the remaining 22% consists of grasslands, bare soil, and water. The White Clay Creek Watershed’s runoff curve number ranged from 55-89, while Darby Creek Watershed’s runoff curve number ranged from 69 to 98. Darby Creek experienced sporadic elevated specific conductance levels during cold winter months reaching a high of 1,992 µS/cm, White Clay Creek did not have this trend. Base flow varied throughout the year and averaged from 30-60 cubic feet per second for White Clay Creek and from 10-50 cubic feet per second for Darby Creek. The average lag time for White Clay Creek’s precipitation events was about 8 hours, while that for Darby Creek’s precipitation events was about 3 hours.
Description
Keywords
Streamflow, Watersheds, Discharge, Land cover, White Clay Creek, Runoff