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Nebraska Pond Management - Second Edition

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Ponds with large watersheds typically require a larger dam and therefore cost more to build. Ponds with very large watersheds, or very high watershed ratios for their part of the state, are often unsuitable for fish production. Major runoff events from heavy rains may cause flooding and erosion in the pond or spillway area. They may also bring in heavy sediment loads that fill in the pond and muddy the water. The added turbidity, or muddiness of the water, affects fish, their food organisms, and aquatic plants. Even runoff from normal rainfall can slow fish growth by causing temporary food shortages if most of the food items, particularly microscopic plants and animals, are flushed out. When possible, check dams, terraces, and vegetated buffer areas should be established in the watershed before a pond is built. These practices will slow runoff and allow suspended sediment to settle out before entering the pond, thus reducing sediment problems and prolonging the life of the pond. Terraces can also be used to divert excess water away from the pond. Another potential problem associated with major runoff events is fish movement. Fish may swim out of a pond or enter it from either the watershed or downstream areas during high water. Any undesirable fish in the pond's watershed should be eliminated, if feasible, prior to construction, or they may hamper fishery management efforts. Installation of an overflow structure (see pages 16-21) in the dam will prevent most fish movement into the pond from downstream. It is difficult to maintain good fish populations in ponds with small watersheds. Water levels may drop so low during prolonged hot and dry periods that all aquatic life could be jeopardized. The smaller the volume of water, the faster it warms and the less oxygen it can hold. Less water also means a reduction in the pounds of fish the pond can support. With decreased water levels, aquatic vegetation can become more abundant. If this vegetation dies, its decomposition can reduce oxygen levels and cause a fish kill. Terraces can be used to divert more water to a pond with a small watershed. An important aspect of site selection is the immediate topography (land elevations and slopes). Since earth moving is one of the biggest construction costs, select a pond site that requires the smallest dam to impound the largest amount of water and that has an adequate volume of soil for dam construction on site or close by. An ideal site would be a natural draw, or low area with a moderate slope, that narrows at the dam site. This would result in a pond that contains adequate amounts of deep and shallow water. Steep-sided sites should be avoided because they will not contain sufficient shallow water for fish spawning and nursery areas and may become unstable and slump into the pond once it fills. Sites that have extensive flat areas should also be avoided because they may result in high evaporation rates and excessive aquatic vegetation growth. To ensure your pond will hold water, it is very important to determine the water holding capacity of the soils present at your site prior to construction. This will help you avoid building a pond that doesn't hold water. Soils containing sand or gravel are typically not suitable for dam and spillway construction. Since soils can vary at surface and subsurface levels, a number of core samples must be collected within the site to depths deeper than the expected excavation depth. NRCS personnel should be contacted about soil suitability and testing. The best soils for a pond site are those that allow water to penetrate very slowly. These include clay, silty clay, loams, and sandy clay/loams. When compacted and moistened, particles in these soils swell and seal the bottom. If there isn't enough clay at the site to build a reliable dam, it may have to be imported from a nearby source. Keep in mind, some clay soils are easily suspended in water and do not readily See page 58 for additional information on effects of muddy water and ways to resolve turbidity problems. 10 • Nebraska Game and Parks Commission . . . . . . . . . . . . . . . . . . . . . . . .

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