Storm Water Design Principles

1. Total Site Area (TSA) of any zoned lot will consist of development, vegetated areas and on-site storm water management facilities.
2. Vegetated Areas (VA) or design components of the landscape code become micro storm water management facilities.

3. Design Storms of one inch of rainfall will require detention of a minimum 576 square feet (12’ x 48’) in size per acre of the TSA to capture and infiltrate the water volume. (TSA x 1.3 or 1.3% of TSA).

4. Street Yard Buffers (SYB) and Side Buffers (SB) for storm water management, planting and screening comprise 30% of the Total Site Area. (TSA x .30)

5. Street Yard Buffers shall be a minimum of 78% of the required front setback width. (FSB/.78=25’)

6. Side Buffer width to meet zoning standards of a minimum of 6% of property width (PW). (PW x .06 

7. A Permeability Ratio (PA) between TSA and permeable open space shall be a minimum of 54.3 %. (TSA x .543)

8. Vehicular Use Areas Parking Lots (VUAP) used for car storage, planting and storm water management shall contain a minimum of 12.3% permeable planted area. (PA x .123)

9. VUA Parking Lot Detentions should be 1/12 the area of the VUA or 8.3% 

10. Street Wall Planting areas sized for building façade enhancement and roof top run-off collection shall be a minimum width of 20% of the building height (BH). (BH x .20)

11. Stream Bank Buffers or Water Front Yards of a minimum depth of 50% of stream width (SW). (SW x .50)

12. Storm water BMP’s recommended by the EPA/LDEQ consist of bio-swales, planted buffers, grassed swales, sand filters, micro-detentions, parking lot detentions, infiltration trenches, irrigation cisterns, storm water chambers, porous paving, preserved forest floor, protected wetlands and constructed wetlands.

13. Coefficient of Runoff For Building Lots known as c value for dense city residential and business areas shall be no more than 40% of the rain falling on the development site adjusted for soil type. (Seelye 1945). This suggests that 60% of all rainfall must be retained on site. This is roughly the amount of water falling on rooftops and parking areas.

14. Site Design based upon these principles is imperative to achieve the proper relationship between development, vegetated areas and on-site storm water management facilities.

15. On-site storm water BMPs must replicate natural methods of treating and cleaning storm water.

16. Site Design based upon these principles is imperative to achieve the proper relationship between development, vegetated areas and on-site storm water management facilities. 

17. Standard Horticultural Design Principles include:

1. Trees, shrubs and other woody vegetation is not allowed on any water retention more than 36” in depth.
2. Plant trees, shrubs and other woody vegetation at least 15’ away from the toe slope of a dam.25’ from perforated pipe, 25’ away from spillway structures and low flow regulators.

1. Stablize emergency spillways with plant material with strong fibrous root systems that will take strong water loads.
2. Temporarily divert storm water flow from seeded areas until plant materials are well rooted.
3. Check water tolerances of all plant materials to be used in storm water design plans.
4. Stablize aquatic and safety ledges with emergent wetland plants or wet seed mixes.
5. Do not block maintenance access to storm water facility with large trees or shrubs.
6. Conduct soil tests at each storm water facility site to check of ph, percolation rate, chemical balance,
7. Native plants including seed should be specified over foreign species due to preadaptability.
8. Decrease the use of manicured grass area, use field grasses, wildflower mixes and wet area grass miPreferred for Louisiana are Bermuda grass, Big Bluestem, Green Sprangletop, Prairie Wildrye, Eastern Gamma Grass, Bushy Bluestem, Cereal Rye Grain, Giant Cut Grass, Black Rush, Pickerelweed, Lizard’s Tail, Elephant’s Ear, Louisiana Iris, Spider Lily, Seaside Goldenrod, Duckpotato, Delta Duckpotato, Bulltongue, Joint Grass, Roseau Cane, Panicum species, Carex species, Spikerush, Soft Rush, Cyperus, Alligatorweed. (no Typha latifolia)

1. Reduce thermal warming to water detentions, southern exposures and inflow points by selective shading.
2. Avoid plantings that require chemical applications
3. Plant stream and water edge buffers to reduce back scour.
4. Maintain and frame desirable views to wetland facilities.
5. Use barrier plants to discourage pedestrian circulation particularly to steep slopes and deep banks.
6. Provide signage on public properties to educate the public about storm water and water quality.
7. Consider short term, and long term plant material maintenance needs.
8. Approved Sources for native wetland vegetation

• Classic Ground Covers, Athens, Georgia
• Emerald Coast Growers, Pensacola, Florida
• Live Oak Garden Nursery, New Iberia, Louisiana
• Native American Seed, Junction, Texas
• Wildlife Nurseries, Inc. Oshkosh, Wisconsin
• Association of Florida Native Nurseries, www.afnn.org/home
• Web Farms, Amite, Louisiana
• Baker Environmental Nursery,  Hoschton, Georgia
• Environmental Concern, St. Michael’s, Maryland

Click here to discover more about Storm Water BMPs

Click here to discover more about the 5 classes of BMPs

Click here to discover more about methods for Controlling Storm Water Flow

Click here to discover more about Storm Water Performance Standards