Vegetated Ditch

Technical Standards for Rain Gardens

1. Select sites that are nearly level along the edge of parking lots, roadways, walkway, open spaces  or athletic fields. Planting areas must receive full sun. 

2. Slopes shall not exceed two (2) percent slope.

3. Ditch gardens shall be planted with a minimum of three different plant types must be included in the design. They shall be of different heights and composed of grasses, sedges, rushes or evergreen broad leaved herbaceous material.  Suggested wetland species include iris, elephant ear, black rush, pickerel weed, alligator weed, delta duck potato, cutgrass or switch grass. Colonies of plants are preferred over spot planted vegetation so no more than five (5) species of plants shall be used per one hundred (100) linear feet of swale. In widened parts of the ditch or adjacent to the ditch small to medium sized trees can be planted but must be planted on the North exposure only. Suggest tree species include pond cypress, black willow, tupelo, Drummond red maple, Buttonbush, pumpkin ash, bitter pecan, overcup oak, swamp privet.

5. Maximum depth of flow for the 1-inch, 6-hour storm event is 4inches.

6. Ditch gardens shall have a trapezoidal cross-sectional shape with slide slopes flatter than 3:1 (h:v) and a minimum bottom width of six (6) feet  to pass the calculated design flow from an articulated drainage basin not to exceed 5000 sf.  Wide areas of the storm water facility can be periodically cleaned.   

7. Ditch gardens must be designed to pass the 10-yr, 25-yr and 100-yr storm event without causing erosion or flood damage problems.

8. Maximum ponding duration is unlimited. Weirs may be provided to allow for increased settling and infiltration time as well as to establish a permanent water level less than twelve (12) inches. 

9. The slope of the swale must be 2% or less with an under drain. Check dams may be used to produce an effective slope of 2% or less.

10. Drainage area must be a maximum of one (1) acre with no dry weather flow. Minimum area shall be five thousand (5000) sf.  

11. The minimum length in the direction of flow must be 100 feet.  Alignment may be straight but curvilinear is preferred to control slope and flow rate. Wide spots in the ditch shall occur a minimum of every two hundred (200) linear feet for special plantings and extra interest.