French drain 1

[Quake]

Found lots of help from recent french drain posting, but my problem is slightly different. Original grading effectively channeled hillside water flow to left and right of house. Slightly soggy in spring but not too bad. Construction activities last year apparently changed contour just enough that I get a standing water build up after prolonged rainfall. Want to french drain a 100 foot crescent, but overall the land will drop about 3-4 feet, a 0.4 inches per foot average. I am concerned that this will allow too much velocity at the discharge end of the drain and cause erosion. I can discharge onto a driveway parking area, but this also has it's downside for people trying to get to their cars. Any suggestions?

 

[gibfrog]

Some options
1) Drain to a 4'x4' concrete splash pad, set 1" below grade, with concrete tapered to grade.
2) Drain to an endwall structure with a velocity breaker - a small 4"-6" wall that has a 4"-6" opening at one end and splash pad.
3) Drain to a bubbler - a ADS plastic catch basin that will function the opposite of normal. This will be a recurring maintenance item. It should have an internal sump and be set atleast 1"-2" below adjacent grade.
4) Calculate your velocities and and determine what erosion protection is actually needed, if any
5) Do nothing, just repair (possibly excavate an additional 12" in all horozontal directions, except at the pipe end) the erosion with a minimum of 4" deep of fibermesh concrete, set a minimum of 1/2" below adjacent grade. Remember, when repairing erosion, the water must be blocked from channeling under the concrete repair.

Best of Luck.......
Clifford H Laubstein
FL Certified PE #58662