Application of the experimental watershed approach to advance urban watershed precipitation/discharge understanding

Reliable methods are required to provide the detailed hydrologic information necessary to improve management of water resources and aquatic ecosystems in developing/urbanizing watersheds. A case study was implemented in a representative 230 km² mixed-use, urbanizing watershed to advance precipitation/discharge understanding. Precipitation and streamflow were monitored in five sub-watersheds (nested-scale experimental watershed study design), partitioned by dominant land use type. Data were collected at 30-min intervals through the 2009 to 2015 water years. Individual sub-watershed area-normalized flow and runoff coefficients differed by as much as 400%. Two high density, urban sub-watersheds displayed large runoff coefficients indicating disproportionately high flow response to precipitation inputs. Regression analyses of sub-watershed land use characteristics and flow metrics showed strong (i.e. R² > 0.9) statistically significant (p < 0.05) linear relationships for percentage developed, forest, and agriculture land cover. Observed relationships between land use and flow metrics illustrate the complexity of contrasting and intermingled land use types in urbanizing, mixed-land-use watersheds. Results highlight the variable hydrologic impacts of land use and suggest the potential for vegetation management as a tool for streamflow mediation in urban settings. The work is one of the first to utilize the experimental watershed method to isolate and quantify land use impacts in the context of a contemporary mixed-land-use watershed. Collectively, results emphasize the utility of the method for land and water resource managers seeking science-based information to guide management decisions and more effectively target remediation efforts in contemporary multiple-land-use watersheds.