The size of the watershed, or the amount of the area that drains into a pond, is important to the success of the pond. Without special construction considerations, damming an area that carries too much water may cause erosion problems within the pond while too little water may allow the pond to go dry. The minimum area needed in the watershed for each acre of pond surface varies from 1,000 acres in western Kansas to 10 acres in eastern Kansas. Central Kansas ponds usually require a ratio of approximately 30 acres of drainage to 1 acre of pond surface. The best ratio for any specific location depends on the soils, type of vegetation in the watershed, the intended uses of the pond, drainage pattern, springs and slope of the watershed.
Land use in the watershed above the pond should be considered when selecting a site because the quality of the fish community in the impoundment will reflect the quality of the watershed. Active erosion may fill a pond with sediment in relatively few years. Land with grass cover generally has less erosion and is desirable. Land with row crops can produce erosion and sedimentation problems if soil conservation practices are not applied and if a grass buffer area is not developed. Cropland can also contribute toxic materials such as pesticides and excessive nutrients in the form of fertilizer, which can lead to fish kills and aquatic vegetation problems.
A site with suitable topography can save money during construction and avoid problems in operation. A natural draw or low area with a moderate slope which narrows at the dam site involves less earth moving and still provides adequate amounts of deep water. Extensive flat areas usually provide too much shallow water, which encourages the growth of aquatic vegetation and results in excessive evaporation losses. Extremely steep sides often contain too little shallow water for fish spawning to occur and may be unstable and slump into the pond. Major drainages should be avoided as pond sites because large amounts of runoff are difficult to retain. Damming a stream usually required an extensive spillway and modified dam to handle the volume of the flow. Streams also commonly carry high silt loads and provide access to the pond for undesirable fish species.
It is important to determine soil type at the proposed site before construction begins. Soils in the area to be impounded must hold water with a minimum of seepage. Soils for an embankment pond must also be suitable for dam and spillway construction. Clay and silty clay are good soils for impounded areas, but some clay soils stay in suspension, causing water to remain muddy. Sandy clay is generally suitable, while sand, gravel and sand-gravel mixtures are unsuitable. Outcrops of shale, limestone, sandstone or other bedded materials should be avoided. These may contain crevices or channels that can cause excessive water loss or seepage from the pond. Detailed information on the suitability of various soils for pond construction is available from the Natural Resources Conservation Service.
Intended pond uses and the question of whether to stock fish should be determined before a site is selected and the pond is designed. While it is sometimes best to design a pond for its primary use, multi-purpose ponds can be constructed for a variety of uses if all uses are considered in the design stage. While not normally compatible with fish production, even livestock can be accommodated through proper pond design.