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runoff for drainage areas contributing flow to each storm sewer inlet. Drainage <br />boundaries were developed using LiDAR and verified by site investigation, aerial <br />photography. <br />Runoff coefficients were calculated for residential areas by selecting several sample lots <br />and measuring the percent of impervious cover verses ground cover. These calculations <br />include the area between side lot lines and from the back lot line to center line of <br />roadway. Runoff coefficients were determined for representative areas to be between <br />0.55 - 0.60, 0.55 is used in the runoff calculations. <br />Time of concentration for each inlet was calculated using the City of La forte nomagraph. <br />These inlet times were compared to the City of Houston method and are consistent. <br />Overland slope comparisons provided lower inlet time of concentrations and higher flows <br />getting to the storm sewer. Detailed analysis of the existing storm sewer is estimated and <br />should be verified during design using topographic survey and/or as -built record <br />drawings. A three-year storm event was used to calculate runoff and is about 180 cubic <br />feet per second (cfs) for 106.6-acre area using a runoff coefficient of 0.55. A five-year <br />storm even generates about 220 cfs for the same area. <br />2.3 Inlet Capacity Analysis <br />The City requires inlets and storm sewers to be designed for a minimum three-year <br />rainfall frequency. Two City of Houston Type-B or BB curb inlets collect drainage from <br />each residential street. From the City of Houston Design Manual, Type B or BB inlets <br />have a capacity of 5.0 cfs each. Accordingly, each street has a capacity to drain 10.0 cfs <br />of runoff based on inlet capacity alone. Eleven (11) streets intersect Fleetwood Drive <br />with forty-four (44) inlets for all residential streets and one (1) inlet on Fleetwood Drive, <br />total number of inlets is forty-five (45). Three-year runoff for most of the contributing <br />areas is about 5.0 cfs with the highest equal to 8.1 cfs and lowest equal to 2.2 cfs. <br />1-4 <br />Klotz Associates Project No. 0127.009.000 Fairmont Park East & Brookglen Drainage Study <br />May 2009 City of La Porte <br />