Modeling LID Treatment Train Impacts on Runoff, Sediment, and Water Quality in US Urban Areas Using IDEAL: Part 1 — Model Description

Part 1 of this two part series is an overview of IDEAL, an object based program developed in Microsoft® Visual Studio.Net to predict the runoff and pollutant loadings in urban post construction watersheds. IDEAL has the capability of predicting distributed source area generation of runoff, sediment, nutrients, and pathogens in post construction watersheds and route those through channels and structural BMPs. Procedures are also available to apply the model to the urban fringe with construction and agricultural source areas as well. The user interface uses a graphic user interface (GUI) with drop and drag capability to generate large numbers of subwatershed source areas, conveyances, and BMPs arranged in treatment trains. The limit on numbers and sizes of subwatersheds that can be used is primarily computational time and appropriateness of the conveyance objects. BMPs are modeled with process based algorithms that take into account mass continuity and the processes of infiltration, settling, and sorption for chemicals and pathogens as well as mortality and growth for pathogens. Deposition of human and wildlife source pathogens on BMPs is also calculated. Using probabilities of rainfall amounts, seasons, and infiltration characteristics, annual averages are computed for loadings at any point on the watershed. Interarrival time of storms is also used as a factor. An example model computation is given.