12/2/2023 0 Comments Q in peak wet weather calculator![]() The discontinuities in this slope reveal the peak and terminal recession time for each of the three stages. This is accomplished by first splitting the RDII hydrograph into the three stages based on the rate of change of the flow response, which is visually represented as the slope of the flow hydrograph. This paper presents a logical approach to defining RDII stages and developing an accurate and reliable hydraulic and hydrology model by developing a single set of RTK parameters that are based on the physical features of the system. This inherent limitation could lead to flawed improvement recommendations. To take it one step further, these models are often used to evaluate potential system responses to improvements such as rehabilitation and/or replacement. The ability of hydrology and hydraulic models using this method of RTK development to accurately simulate the collection system response in a continuous simulation becomes unpredictable. In these practices, it is possible to generate an unlimited number of RTK sets since the RDII stages were not first split logically and the selected set of RTK parameters was based on reducing an error function (peak flow or volume). In some practices, several RTK sets are calculated from several monitored storms for a sewershed and a median or average set is then accepted as the representative set for that particular system. The RTK set of parameters are then manipulated to minimize the collective errors in peak RDII flow and/or volume. The set is then tested in several storm events. A best fit RTK set for one monitored RDII event is first calculated. One commonly accepted practice for splitting the RDII stages and determining the RTK parameters for continuous calibration is accomplished through trial and error. The three parameters for each unit hydrograph are R, percentage of runoff, T,time to peak, and K, multiple T, used to define the recession time of the triangle. These stages can be simulated in SWMM using the RTK unit hydrograph method. The third stage of the RDII is the infiltration of the rising groundwater surrounding the collection system as it enters through damaged joints and cracked pipes. lateral connections), damaged manhole castings, or leaks from storm pipe trenches near sanitary pipes. Delayed inflow enters the system within a few hours time frame through near-surface damaged pipes (e.g. ![]() Inflow ceases within minutes after the storm event. Inflow enters the system in minutes through illicit direct storm pipe connections, foundation drains, downspout connections and displaced or perforated sanitary manhole lids. ![]() The splitting approach relies on the distinct difference in the time frame of each RDII stage. The procedure starts with splitting the three distinct stages of the RDII hydrograph inflow, delayed inflow, and groundwater infiltration, from a flow meter record. This paper presents a step by step procedure for educated continuous calibration of the Rain Dependent Inflow and Infiltration (RDII) using the RTK method in SWMM.
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