Good morning, I have a proposed su 4

[Civilsurvey601]

Good morning,
I have a proposed subdivision design that is basically flat as a pancake. The outfall of the detention pond is at 98.20 feet. The end of the pipe run's invert is 98.88 feet. the run is a total of 677.65 feet long. Curb and gutter is required, as is subsurface drainage. I use Hydrology Studios to help with the stormsewer design. The most slope I can get on the stormsewer pipe is a measly 0.10%. The program sizes the pipes correctly but the HGL and EGL are plotting up above the ground level. What do you guys do in super flat areas like florida. I know it is the small scope, as I remodeled the run using 2.00 % slopes and the HGL remined in the pipe as it should. Any advice would be appreciated.

 

[swazimatt]

depends on the size of the pipes / catchment but have found open swales to be better in these situations, however they take up a lot of real-estate, but at flat grades the pipes get very big and if you need to discharge to a pond you run out of cover. swales also provide SW quality treatment
If it is flat enough the swale could form part of the pond (long skinny pond)

 

[Ekenny_G]

The long skinny open channel ponds are an option for such a flat area.
However, for the storm sewer have you considered large elliptical pipes (double barrel) and also check that you're not overestimating the loss in the system.