Stormwater Management Plan Template Prepared by: BROWN+DANOS landdesign, inc. February 11, 2008 BROWN + DANOS landdesign, inc. Stormwater Managment Plan - Template Contents Table of Contents A. Introduction.........................................................................................4 B. Existing Conditions...............................................................................5 C. Proposed Conditions..........................................................................6 D. Conclusion...........................................................................................8 BROWN + DANOS landdesign, inc. Introduction The site for Woman’s Hospital sits on 97 acres located in Tract E, Township 7 South, Range 2 East and Section 5, Township 8 South, Range 2 East, Greensburg Land District, East Baton Rouge Parish, Louisiana. The site is bounded by Clay Cut Bayou to the north, L. Lamber and McCall Anderson Properties to the east, Airline Highway to the South, and Pecue Lane to the west. Parish location Source: EBR Online GIS database Stormwater Managment Plan - Template Site Location Source: EBR Online GIS database Existing Conditions Currently, the entire site drains in to Clay Cut Bayou to the north. The site is broken up in to four subwatersheds, with nine subwatersheds off-site that drain through the site towards Clay Cut Bayou. Existing Site Watershed Map Source: ABMB Engineers, Inc. BROWN + DANOS landdesign, inc. Proposed Conditions Previously a golf course, the site will be redeveloped to accomodate a 1.1 million square foot hospital complex, along with hard surfacing parking and drives. The site will continue to drain into Clay Cut Bayou. The site will be divided up in to 11 watersheds and further into 32 subwatersheds. y ilit Ut Ba y ou Watersheds and Sub-Watersheds cu t C 4 t en m se la y Ea 2 11 1 5 3 Re sid en tia la nd Co m m 9 9 er cia lD ev elo pm 10 en 7 t 9 6 8 11 Airline Highway Proposed Watesheds Proposed Site Watershed Map Watersheds and Sub-Watersheds yc ut T la C Q U t en G m J se I Ea H y E ilit Ba P Ut yo u F D HH C Re sid R K L M B en tia la nd Co m A m er cia lD ev elo pm V GG en t N W S Y Z X O GG CC BB FF HH Proposed Sub-Watesheds Proposed Site Subwatershed Map Stormwater Managment Plan - Template Airline Highway EE DD AA Twenty acres of the site will become impervious surfacing consisting of rooftops, parking, sidewalks, and roadways. 5.22 acres of bioswales will be constructed in parking medians and will channel the water towards the wetlands and lake while also treating the water. The total area of bioswales provided is 5.22 acres. The existing lake will be enlarged from 3.2 acre-feet to approximately 70 acre-feet. The static water surface will be lowered from 24 feet to 22 feet. The lake will discharge into the ditch behind behind the lots along Pecue Lane. Half acre wetland forebays will be constructed at the bioswale outfalls to further treat and slow the water. Off-site watersheds will continue to function normally and will drain into the lake or Clay Cut Bayou through sub-surface systems. y la yc ilit Ut ut Ba y ou Schematic Water Quality Treatment Plan t en m se C Ea Re sid en tia la nd Co m m er cia lD ev elo pm en t Drainage Patterns Open / Green Space Bioswales Buildings Impervious Parking Wetland Forebay Lake Airline Highway Land Cover Map Land Cover Map The developed site will yield a runoff of 25.53 cubic feet per second (cfs) for a 1 hour 10 year design storm. This is slighly higher than the 19.08 cfs before development, however the enlarged lake will mitigate the remaining runoff. The post-construction detention volume required for the first hour rainfall is .94 acre-feet, while the total detention volume provided by the BMPs is 70 acrefeet. The lake will also accomodate drainage and flood control needs and the excavation of the lake will more than mitigate the amount of fill needed for construction. As the water drains across the site it will run through a series of BMP trains that will treat the water for various pollutants. With this design, the stormwater will see a 90% -99% reduction in pollutants. The remaining pollutants will be detained in the lake and settle to the bottom. BROWN + DANOS landdesign, inc. Conclusion BMPs will treat the first flush of stormwater before it leaves the site, and while peak discharge will be increased, the enlarged lake will provide adequate on-site storage. In addition, the development will increase the storage volume within the 100-year floodplain. Proper maintenance of BMPs will be imperative for effective operation and will minimize future costs. Maintenance actions include keeping the site free of litter and debris as well as regular cleaning of structures and surfaces to remove oil and grease. Execute and recorded “Private Water Quality Maintenance Covenants” (PWQMC) will be required for all BMPs onsite prior to construction approval. BMPs will have to be detailed in construction plans for approval. Stormwater Managment Plan - Template