The most cost effective sites for pond construction often have gently sloping topography. Ideally, this would be in a low area, safe from flooding, with roughly ten feet of elevation difference between the sides and the bottom. This greatly reduces the volume of material to excavate. For instance, a one acre pond that averages ten feet deep will have a volume of 16,133 cubic yards. If you only need to excavate one-tenth of this to build a low dam, your excavation expense could drop. Note that building a dam is more expensive per volume than simply excavating a basin.
Once the site is excavated, the new basin must be sealed unless the site is dug into a tight clay formation. Most sites require at least compacting existing clay soils, or if clay is not present then we need to augment the soil by importing quality clays or other sealants.