DUSTING OFF THE ARCHIVES: WHAT ARCHIVES CAN TELL US ABOUT CHANGES IN WATER STORAGE AND STREAMFLOW DUE TO URBAN DEVELOPMENT

Urbanization contributes to increased and persistent flash flooding. The urbanization of a watershed radically impacts flooding characteristics and developed land is strongly associated with flood recurrence intervals. Although urbanization’s effects on floods, droughts, and water supply have been explored in recent decades through land-use modeling, hydrological modeling, remote sensing and empirical approaches, clarification of these effects remains a challenge due to limited availability and accessibility of useful data. Streamflow records for Abers Creek in Allegheny County, Pennsylvania provide a unique opportunity to study the influence of urbanization on watershed function. The discharge record (1948-1993) spans the complete residential development of the watershed. Build-out of the watershed was reconstructed from property records to provide the timing and intensity of watershed development (1955-1970). Coupling the streamflow and development records allows direct comparison of hydrologic changes with spatial patterns of land use change. Recession analysis was used to evaluate altered hydrologic response, particularly relationships between watershed storage and streamflow that may occur during urbanization. Sub-daily USGS discharge records from archival records were used to estimate hourly streamflow in Abers Creek and hydrograph recession analysis and sensitivity in parameter estimation conducted on this unique streamflow record. Recession approaches use variable time steps to estimate the time derivative of streamflow (dQ/dt) to avoid known issues in parameter estimation of a noisy time series. Preliminary results link spatial patterns in build out to changes in hydrograph patterns identified with recession methods. Analysis of sub-daily streamflow records across the entire process of urbanization reveals groundwater-surface water interactions driven by urbanization, previously only observed over relatively shorter time periods. These findings can inform implementation of sustainable design of stormwater management and, future city development. Refined connections between development history and changes in hydrology allow improved mitigation of stream impacts in urban areas.