A Simple Spreadsheet Model to Calculate Storm Water Runoff Storage Requirements.

Jay H. Niec


With the promulgation of the MS4 rules and regulations governing water quantity and water quality issues within municipal storm water collection systems, engineers and municipal officials alike are faced with many analytical methods to determine storm water storage requirements needed to minimize the volume of storm water runoff from new and /or re-development in urban and suburban areas. Increased urban and suburban development decreases pervious surfaces and subsequently increases the quantity of storm water runoff volume. The number of models and programs available to calculate the volume required to attenuate the increase in storm water runoff due to increased development or re-development can be confusing, and in many instances, may have a steep learning curve. A review of the models currently available to determine storm water runoff volume attenuation was conducted, and it was discovered that, in addition to certain complexities, most currently available models were lacking in the use of criteria such as soil permeability, stone bedding volume, pipe volume and rain garden capacity. Research was conducted on the typical run-off methodologies, and it was determined that for most practical day-to-day purposes, the rationale method would be a favorable technique. Specifically, the Chens method approach (Chen, C.L. FHWA, 1976), and the Rationale approach were selected to present an easy to understand volume calculation technique that can be adapted to most municipal storm water runoff situations. Therefore, the adaptation of Chens and the Rationale method through the use of a simple Excel spreadsheet model has resulted in an easy to use calculator. It will be shown how this simple spreadsheet calculator can be used to adjust storm water runoff storage requirements based on user input of site specific storm water data.

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