Grassed Swale

Grassed Swale

Grassed swales are designed conveyance devices used to transport water over the surface of the ground to a point of disposal that may be a catch basin, ditch, or water body or a storm water BMP that will filter, infiltrate, evaporate and clean the water of TSS, solid waste and other pollutants. Swales collect the water from areas that must be drained and move it to some other location. Swales are often used along property lines, public streets and around buildings.

Calculations

Watershed Area

The one (1) inch design storm watershed area includes swale, proposed N/S drive, and parking area south of the parking island 17333 Square Feet multiply by 1/12 = Cubic Feet= 1444.5 Cubic Feet divide by 27 = Cubic Yards= 53.5 Cubic Yards

multiply by 202 = Gallons= 10806 GALLONS

SWALE CAPACITY

5050 Square Feet

multiply by 4/12' depth= Cubic Feet= 1683.3 Cubic Feet

divide by 27 = Cubic Yards+ 62.3 Cubic Yards

multiply by 202 = Gallons= 12584.5 GALLONS

divide by total GAL of rainfall

in rainshed

116% BMP CAPACITY FOR 1" DESIGN STORM

1" BMP watershed design storm GAL divided by

1" total property design storm GAL= 10806 GAL / 40736 GAL=

26.5% BMP MANAGEMENT FACTOR

General Design Standards for Grassed Swales

A well designed grass swale will be of moderate slope, as broad as practical and not very deep. Its slope must be shallow to prevent the erosive force of running water and to allow for the grass to survive. The best grassed swales are seldom noticed. Swales that are constructed over sandy soils not only transport rain water but will allow much of the run off to infiltrate into the ground as it slowly moves toward the point of disposal. A well designed and built grassed swales can be a wonderful storm water management facility if creatively designed and planted to blend into the landscape of a residential, commercial or institutional property.

Click Here for more Technical Standards

Buck Abbey

309 Design Building

Baton Rouge, LA 70803

(O) 225.578.1475

(F) 225.578.1445

LSUGreenLaws@aol.com