Simulating Antecedent Moisture Conditions to Calibrate Rainfall Derived Inflow and Infiltration for Sanitary Systems

A pilot study was conducted from September through November 2011, and was aimed at simulating the monthly variation of the flow conditions in a sanitary system by calibrating the rainfall derived infiltration and inflow (RDII). The study was conducted on three different metersheds in the East Branch of the Mill Creek basin in Cincinnati, Ohio with different acreage and historic infiltration/inflow (I/I) percentages. United States Environmental Protection Agency's (U.S. EPA) Storm Water Management Model (SWMM) version 5.0.0.21 was used for these analyses. The goal of the study was to simulate the monthly variation of I/I into the sewer system and the variation of the I/I response in the sewer system for multiple events within the same month due to changing soil moisture conditions. The results of the study indicated that the process of using one representative RTK set for the entire year with monthly varying initial abstraction parameters worked well to simulate flow conditions within the Wastewater Planning Users Group (WaPUG) standards. The identified RTK set was representative of the events in the growth period of the year and drove the model towards those events. The initial abstraction values were calibrated for months in the dormant period to simulate flow conditions as recorded by the meter.