Development and Application of Combined 1-D and 3-D Modeling System for TMDL Studies

A combined 3-D and 1-D modeling system was developed to include many streams, ponds and lakes that enter multiple receiving water bodies. The combined model will be used as a management tool for TMDL (Total Maximum Daily Load) studies in the Delaware's Inland Bays. The Inland Bays TMDL study region consist of 19 river networks with two to ten tributaries in each network, five ponds and three water bodies that were listed as impaired waters under section 303(d) of the Clean Water Act for nutrients, dissolved oxygen or bacteria. Both the hydrodynamic / transport and water quality models of the combined system were used for TMDL studies. The combined modeling system also uses HSPF (Hydrological Simulation Program-FORTRAN) watershed model outputs as time varying non-point source loadings in the rivers. The combined 3D and 1D modeling system was calibrated for the years 1998, 1999 and verified for the year 2000 using the available and synthesized input data. Delaware's Inland Bays have been sampled and measured frequently over the past decade. For the purposes of this model, data retrieval was concentrated upon the years 1998 to the present. Recalibration is being performed using the HSPF model outputs for the Inland Bays watershed regions. The calibrated and verified model with HSPF results will be applied to perform TMDL scenario studies in near future.