A Detailed Procedure for Separating RDII Stages and Generating a Single Set of RTK Hydrographs for Continuous Simulation
This chapter presents a step-by-step procedure for performing continuous calibration of the rain dependent inflow and infiltration (RDII) process using the RTK method in SWMM. The procedure starts with the separation of the observed RDII hydrograph into its three distinct stages; inflow, delayed inflow and groundwater infiltration. The separation approach relies on identifying the distinct difference in the time frame of each RDII stage. The discontinuities in the slope of the flow hydrograph reveal the peak and terminal recession times for each of the three stages. These stages are then simulated in SWMM using the RTK unit hydrograph method. A single set of RTK parameters for each RDII stage is calculated using rainfall volume, duration and start and peak times, and the time for flow routing through the collection system network. A combination of precipitation, depression storage recovery rate, and the calculated single set of the RTK parameters can then be used to calculate RDII response in continuous simulation of hydrology and hydraulics models.
This chapter details a secondary, but essential, step towards calculating a single set of RDII parameters for continuous calibration. The primary step (Gheith, 2010) was a procedure for calculating the total R value that is only a function of the internal factors affecting the RDII process.
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