Department of Urban and Regional Planning   
University of Illinois at Urbana-Champaign   

UP 503: Site and Physical Planning

6c. Site Engineering Analysis - Stormwater Runoff

Objective: Use the Hydro.xls model to estimate the change in runoff on your site during a rain event and explore how development decisions impact site level stormwater management issues.

Stormwater runoff - the rainwater that simply rolls off and away from pavement and buildings rather than seeping into the ground below - has become a major concern for physical planners and site designers. Development decisions directly impact the amount of precipitation that is not absorbed by the soil. Storm sewers should only be provided where natural channels and features cannot handle the quantity of runoff generated. As a result, planners need to understand the tools used to estimate the amount of water generated by development and the strategies availble to mitigate the impact of new development. Use the Hydro.xls model to test at least 4 stormwater runoff scenarios on your site and comment on the variation in results:

A. Pre-Development - conditions on your site as they may have been before human settlement
B. Greenfield - conditions on your site if it was being used for agricultural uses
C. Conventional - conditions on your site per your proposed land use mix
D. “Green” – an alternative scenario that uses stormwater management BMPs to conserve and slow down flows:

Prior to running the model you will need to gather data about the soil and slope conditions on your site. This information can be found in the shapefiles used to complete your region-wide suitability analysis. Determine the soil types on your site according to the given classifications, and estimate the percentage of each use located on top of the 4 soil types. Use site slope characteristics to analyze how water moves across the site. Based on your analysis, estimate the greatest distance (the hydaulic length) water will traverse on your site before leaving the area. Input these values in the model for each scenario. For the "Green" scenario, modify numbers in the hydrological model to approximate implementation of BMPs. This can be done by changing the percentage of the site allocated to different uses. For example, replacing impervious surfaces like pavement and roofs with permeable pavers and green roofs. Analyze the impact of BMPs, and compare unit hydrograph discharge rates to estimate percent reduction in stormwater generated by the site.

Report your results in a brief 'memo' format. We will discuss your work in the next lab session. This document named by 6c_[Last Name].pdf is to be uploaded to the Assignment Dropbox folder before start of class on Thurs, Nov 7.

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