SSOAP — A USEPA Toolbox for SSO Analysis and Control Planning

Rainfall Derived Inflow and Infiltration Modeling Approaches

“…In SWMM versions 4 and 5, RDII can be represented using either the RTK method or an RDII time series (Vallabhaneni et al, 2008). When using RDII time series as an input, the time series is pre-processed information and therefore must be updated whenever the rainfall input is altered.…”

“…Bishop et al (1987) claimed that inflows represent less than 10% peak flow while Vallabhaneni et al (2008) stated that inflows are the major contribution of RDII to peak flow. It is possible that in some systems with more direct connections inflow is more significant, and in other systems, where roof leaders and foundation drains are not connected to sanitary sewers, inflow is less significant.…”

“…In design, RDII estimation tools should provide appropriate estimates for sanitary sewer design allowance for inflow and infiltration, but this allowance is frequently exceeded by extraneous flows (Vallabhaneni et al, 2008). The ten state standards presented by Lai (2008) could shed some light on this.…”

“…It is common for GWI to be set equal to 90% of average minimum daily flow. GWI is treated as relatively constant during each season (Vallabhaneni et al, 2008). Once groundwater infiltration is set then the average DWF pattern can be determined from the monitored flow data.…”

“…It uses the RTK synthetic unit hydrograph method developed by CDM staff to characterize RDII (Vallabhaneni et al, 2008). Other estimation methods can be added to the program in the future.…”