Effect of Rain Gage Density on Runoff Simulation Modeling.pdf

EFF ECT OF RAINGAGE DENSI TY ON RUNOFF SIMULATION MODELING by Ken MacKenzie, P.E., M.ASCE 1 , Ben Urbonas, P.E., D.WRE, L.ASCE 2 , Michael Jansekok 3 , James C.Y. Guo, PhD, P.E., M.ASCE 4 ABSTRACT Rainfall and runoff data for a 3.08 square mile urban watershed in Denver, Colorado was used to investigate the effects of raingage density and hyetograph compositing on urban stormwater runoff simula tion. This water shed has rainfall data from five ra ingages and flow data fro m two gages, all in 5-minute time inc rements. The data were used to calibra te the EPA Storm Water Management Model (EPA SWMM, version 5.0), and the Urban Drainage and Flood Control District’s ve rsion of an earlie r EPA SWM model (UDSWMM). This calib rated model se rved two purpose s; first, to examine the eff ects on runoff calculations using a single composi te hyetograph for each of the recorded storm rainfall and runoff events modeled and second, to determine the effects of raingage density on volume of runoff and peak flow simulations. The effects of raingage density were investigate d by processing rainfa ll data from each raingage usin g several diffe rent combi nati ons of rain gag e dens itie s. The data were used to driv e the calibrated SWMM model and the results compared against recorded runoff volumes and flow rates for the recorded storms. It was demonstr ated that raingage density doe s affect the accuracy and the scatter of simulated results. The effects of compositing recorded rainfall data at several raingages into a single rainfall hye togr aph were als o investi gat ed. Two type s of composi ting wer e perfor med. One met hod simply used area weighted averag ing of rainfall recor ded at each time increme nt. This method was defined as straig ht across compos iting. In the second metho d, each hyetograp hs at the five gages was examined and all values were time shifted to line up the most intense five-minute rainfall values of the storms. The simulation results were then compared to the recorded flows. This pa per de scr ibe s the fin din gs of thi s stu dy and dis cusses the ir imp lic at ion s for urb an stormwater runoff modeling. It presents a summary the collaborative work and findings by the authors over the last 17 years. INTRODUCTION This report is based on a draft MSCE Thesis prepared by Mike Jansekok in 1990 (an abbreviated summary of which was presented at the International Conference on Computer Applications in Water Resources, Tamsui, Taiwan, July 1991), and on the author’s analyses of new rainfall and runoff data collected during the 15 years since. Two questions arise with hydr olog ic compute r mod elin g. The first is whether that model ing appropriately accounts for the temporal and spatial variations in rainfall patterns that occur in 1 Sr. Project Engineer, Master Planning Program, Urban Drainage & Flood Control District, Denver, CO. 2 Manager, Master Planning Program, Urban Drainage & Flood Control District, Denver, CO. 3 Programmer/Analyst s, Oppenheimer Funds, Inc., Centennial, CO. 4 Professor, University of Colorado at Denver, Denver, CO. World Environment al and Water Resources Congress 20 07: Restoring Our Natural Habi tat © 2007 ASCE Copyright ASCE 2 7 World Environmental and Water Resources Congress 2 7 opyright ASCE 2 7 World Environmental and Water Resources Congress 2 7 Downloaded 24 Oct 2009 to 132.194.84.58. Redistribution subject to ASCE license or copyright; see http://www.ascelibrary.org

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Effect of Rain Gage Density on Runoff Simulation Modeling.pdf