How to Read the GeoSWMM Status Report in Terms of Water Quality

The simulation of water quality generates added information in GeoSWMM’s Status Report. This information can be broken into four general sections (A, B, C and D). These additions to the status report are discussed below using Tutorial_05_EMC.gdb with the 0.1 inch precipitation event as an example.

Part A shows the runoff-quality continuity balance over the entire study area. The “input” loads include (a) Initial Buildup before the start of the simulation, (b) Surface Buildup during all dry weather periods, and (c) Wet Deposition (from pollutant in the rainfall). The “output” loads include (1) Sweeping Removal (not simulated), (2) Infiltration Loss for any direct rainfall or runon from other subcatchments (simulated automatically), (3) removal associated with BMP Removal (not simulated in this tutorial), and (4) pollutant load in the Surface Runoff (which includes the portion of buildup that is washed off as well as any loads produced by direct deposition and runon). Finally, the continuity report indicates the Remaining Buildup.

Part B shows the quality-routing continuity balance. In this tutorial, only runoff loads are routed through the conveyance system. No dry weather, groundwater, RDII, or user-supplied external inflows, nor is any treatment or decay considered. Therefore, the only three variables represented in this summary are the Wet Weather Inflow, the External Outflow and the Final Stored Mass. Note that the Wet Weather Inflow in Part B is equal to the Surface Runoff in Part A.

Part C provides a summary of the load of pollutant washed off from each subcatchment. Subcatchments S7 and S3 generate the lowest loads of TSS. S7 does not generate any load because it does not produce any runoff while S3 produces a smaller load due to a large amount of pervious surface in the subcatchment.

Part D shows the total loads leaving the system through its outfalls.