Pond Boss Forums POND CONSTRUCTION Building a dam Silly newb question

We just bought 90 acres and are looking to build a pond. Been reading up a lot and had a question. If a 1/2 acre pond is built on flat ground, what is the purpose of the dam? And does it only go on one side?

Not sure I understand. If it’s on flat ground, how will it fill?

Dave he's probably referring to some tanks you see on a farm that are in a nearly flat pasture that don't really have a dam per se

A hole dug out of flat ground would not necessarily have a dam. Many ponds that are dug on flat ground would be ground water ponds and fill up because of the high water table, and these ponds are often bermmed all the way around with he soil that is dug out of the hole just to have a convinient place to put it. This would resemble a dam, but is really a berm. These particular ponds are also ususlly lined with a liner and filled by a pump and well or nearby water source.

A dam by definition is meant to stop the flow of water and create a pool...that can not be done on perfectly flat ground without it becoming a full perimeter berm and then it would only collect rain water.

That makes sense. Watching videos and stuff of what looks like somewhat flat ground they always put a dam in it seemed. Our land is pretty much all flat within a half foot of each based on survey, so getting any runoff would be difficult. We were thinking either dig a well to fill it or hope it’s close enough where water table fills it. Any thoughts or guidance?

Either a well or water table

Some ponds are referred to as "dug" ponds, where the majority of the pond containment is a hole in the ground. That is opposed to damming up a ravine with a dam where the purpose of digging the hole is as much for obtaining dam material to construct the dam as it is to make the pond deeper. In a dug pond, what appears to be a dam may be just a place to pile the excess dirt from the hole.

When you say your ground is flat with only a half foot rise, that does not mean the pond will not fill with runoff. As long as the terrain has any slope at all, water is going to run somewhere if it rains more than what can soak into the soil. You can actually have lots of runoff on fairly flat ground but that is going to be more dependent on the type of soil (if it is sandy most rain will simply sink into the soil) and the size of rain events.

If you have flat ground with good water percolation and rarely get significant rain events you will not have much runoff. On the other hand, if 2-6" rain events are common, ground that is fairly flat can be prone to flooding.

Are there any indication of wash out areas? This would indicate water flow.

Your local NRCS office will have information on the suitability of runoff and the size of rain events with some guidelines for the watershed area to support a pond. That is if you have ponds in your area. If there are no other ponds around, there may be good reason for it. Then you might be looking at a well and a pond liner to get it done.

Firstly you want to determine the type of subsoil and see how much compactable clay is present. If there is good clay within 4 to 6ft of the surface then the pond will not be a water table pond. Loose sandy soil usually results in a water table pond where the water level goes up and down during the seasons; high when wet and low when dry. I've seen water level in water table ponds in NW Ohio go up and down 5-7ft (2m).

A lot of ponds in Ohio are dug ponds on fairly flat clay based ground. A good dug pond is not just a dug hole. The topsoil is removed 8 ft wider than the final size until good clay is reached. Then the pond bottom basin is dug out and compacted with sheepfoot rollers, not by bull dozers because bull dozers are not good soil compactors. Then the deep dug out clay is layered in 4"-6" "lifts" around the 8 ft wide rim as a band around the outside edge and compacted with the sheepsfoot roller. Excess dirt from creating a deep pond can be use to create a sloping watershed to help fill the pond during wet periods. This creates a well sealed all clay lined pond basin that if done correctly will have minimal leakage. Once the pond fills there is enough rain to keep the pond filled year round with water evaporation loss and seepage of 12"-20" each year. If runoff from building roofs is run into the pond the pond stays full. Annual precipitation in northern US and eastern Canada is usually more than 2ft.

For a water table pond just a simple hole is dug out in the porous ground and ground water seepage determines the water level.

A pond in Canada should be at least 16 to 22 ft deep to minimize winter fish kills due to extended snow cover that usually kills the fish in shallow 8 to 12 ft deep northern ponds.