Streamflow Alteration from Impervious Cover: Are All Watersheds Created Equal?

Abstract

Very small amounts of impervious cover can impact streamflows. In the Potomac basin, for example, significant streamflow alteration associated with watershed impervious cover >0.5%–2.0% have been found. Since these impacts were found with considerably lower amounts of impervious cover than previously documented in the literature, typically 10%–20%, this study evaluated whether certain watershed characteristics (e.g., watershed area, karst geology, precipitation, soil characteristics, physiographic province, and slope) make a stream reach more susceptible to the impacts of impervious cover than others. The results of this study indicate there are differences in streamflow sensitivity to impervious cover given certain landscape characteristics. The relationships of watershed characteristics with streamflow alteration in flashiness, high flow duration, and low pulse duration were evaluated. Flashiness alteration was positively correlated with impervious cover and influenced by watershed slope and area. High flow duration alteration was negatively correlated with impervious cover and influenced by mean annual precipitation and slope. Low pulse duration was poorly correlated with the watershed characteristics under consideration. These differences may assist in land management efforts and heighten awareness of the environmental impacts of impervious cover.

Urbanization in Arid Central Arizona Watersheds Results in Decreased Stream Flashiness

“…For each watershed, we calculated various hydrologic metrics related to flow magnitude or flashiness (Table 2). We used the Indicators of Hydrologic Alteration software (The Nature Conservancy, 2009) to generate metrics based on daily flow data, since this is a software that has been commonly used to evaluate flow regime and ecological flow metrics (e.g., McDaniel & O'Donnell, 2019;Moltz et al, 2018;Schoonover et al, 2006;The Nature Conservancy, 2006). Both Indicators of Hydrologic Alteration and another increasingly used similar software-the USGS's EflowStats package for R-only calculate metrics for daily flow data (US Geological Survey, 2017).…”

“…Evaluation of watersheds in major metropolitan areas across the United States found that lower slopes and higher soil permeability in urban watersheds reduced high flow events and flashiness but increased high flow durations (Hopkins et al, 2015). Modeling scenarios in the Potomac River basin found strong interactions between presence of karst geology, slope, precipitation, and watershed area with imperviousness impacts on streamflow regimes (Moltz et al, 2018); for example, small, flatter watersheds were most susceptible to increases in flashiness due to imperviousness, presumably because more sloped watersheds are already flashier. In our study, we observed interactions between precipitation and mean annual area-weighted flowrate with imperviousness; for example, decreased flashiness and zero-flow days and increased POTs were observed with higher imperviousness and higher precipitation or average flowrates (Tables 3 and 4).…”

“…The "urban stream syndrome" (Booth et al, 2015;Walsh, Roy, et al, 2005) associates higher peak flows, lower baseflows, and greater flashiness or variability with land development and impervious surfaces. However, responses of streams to urbanization can vary across climate and biophysical context at local to continental scales (Booth et al, 2015;Hale, Scoggins, et al, 2015;Hopkins et al, 2015;Moltz et al, 2018). It is critical that we understand these nuances as we design and plan storm water management strategies in our cities.…”

Integrating Sustainable Water Resource Management and Land Use Decision-Making

“…The result is a reduced negative impact on water and environmental resources from human activities. The impacts of urbanization on stream water quantity and quality has been well documented in the literature [4,9,[102][103][104].…”

“…The impacts of land management on the quality and quantity of sustainable water resources are well documented in the literature [2][3][4][5]. Each land use type (e.g., urban, agriculture, and forest) has specific, scale-dependent effects [6,7] on surface-and ground-water ecology, availability, demands, and quality [8][9][10][11][12][13]. The successful management of one (land or water resources) should by default involve the consideration of the other [14]; however, this is rarely the case.…”