To develop siltation TMDLs for the impaired reaches in the Wissahickon Creek basin, a 'reference watershed approach' was utilized. Once the impaired and reference watersheds were matched, a watershed model was used to simulate the sediment loads attributed to runoff from various landuses in the watershed and streambank erosion. The modeling framework used in this study consisted of a modified application of the Generalized Watershed Loading Function (GWLF) watershed model, including a special module for simulation of streambank erosion. The TMDLs are presented in the 'Nutrient and Siltation TMDL Development for Wissahickon Creek, Pennsylvania' report (USEPA 2003) (referred to as 'TMDL Report' for the remainder of this document). This modeling report is intended to accompany the TMDL Report and provide a more detailed discussion on the model used for the siltation analysis, including parameter descriptions and references.