Differentiation of transport for particulate and dissolved water chemistry load indices in rainfall–runoff from urban source area watersheds

SummaryControl of coupled hydrology and pollutant transport from urban areas generally specify a runoff (or rainfall) depth for treatment. Incarnations of such coupled transport and control include the “first flush” and recent, albeit similar, “water quality volume” (WQV) concepts. For a century the first flush, a mass limited behavior, has been held as the singular transport phenomena for urban areas. In contrast, this study hypothesizes that load transport can have two classifications; mass or flow limited for pollutant phases (dissolved and particulate). Recognition, quantification, and differentiation of two limiting behaviors and phases, is less common. Differentiation is defined physically (exponential or linear); and examined statistically (logistical regression, discriminant analysis); deriving load transport rules using only calibrated hydrologic parameters. The study is supported by 28 Baton Rouge and 14 Cincinnati events; both urban, paved source areas. Once calibrated with pollutant data, statistical approaches for such rules provide promise for transport differentiation based on more economical hydrologic data. Results demonstrate load transport from source areas can be differentiated into mass or flow limited behavior. Results also indicate that within a given event, pollutant phases exhibit differing transport. With hydrologic and chemical pollutant phase transport data, calibrated event-based differentiation rules can be combined with continuous simulations in tools such as SWMM. Such a combination allows time series differentiation of load transport behavior and unit operation volumetric requirements for urban source areas.