Hill ponds east of town
MSU Extension says a Mississippi watershed pond should have about 5 to 10 acres of drainage area for each acre of water. Too little and it will not stay full. Too much and the spillway has to handle a lot of storm water. The dam's waterside slope should be no steeper than 3 to 1 and the back no steeper than 4 to 1 so it can be mowed. Dams under 12 feet high need an 8-foot top, or 16 feet if it will carry a road.
The hills around Yazoo City are silty loess, and MSU notes that in many parts of the state dams must be cored with clay to stop seepage. A pond also needs at least 20 percent clay in the soil to hold water. Soil borings across the site answer that before you build.
Bottom ponds west of town
On the Delta side, the land is flat and the ground is usually heavy clay that holds water well. Ponds there are dug out, with the spoil banked around the edge or hauled off. Water comes from rain, runoff routed to the pond, and sometimes a well. Low land near the Yazoo River can be wet, so wetlands and flood zones are worth checking before you pick a spot.
For either kind of pond, MSU Extension recommends an average depth of about 5 to 6 feet, no more than 10 to 12 feet at the deepest, and about 20 percent of the bottom at least 6 feet deep. Banks should drop fast to about 3 feet. And the dirt from the dig can build a pad, fill low ground or go on the truck.
MDEQ dam rules and other permits
Hill ponds bring MDEQ dam safety into play. MDEQ requires written authorization to build a dam unless it is 8 feet high or less, holds 25 acre-feet or less at maximum storage, or does not impound a watercourse with continuous flow. Exempt projects still must notify MDEQ before construction, and a surface water impoundment permit may be required. An acre or more of disturbed land brings stormwater permit conditions.
Damming any stream may also need a Corps of Engineers Section 404 permit, so check before you start. NRCS Practice Standard 378 covers embankment and excavated ponds, and the local NRCS office can help with drainage area and soils. Mississippi law requires an 811 locate request at least two working days before digging.
