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NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD

DAM, DIVERSION (No. or Ft.)

CODE 348

DEFINITION CRITERIA A structure built to divert all or part of the water The installation and operation of this practice from a waterway or a stream. shall comply with all federal, state and local laws, rules, and regulations. PURPOSE Environmental Impacts - The impact of a proposed dam on water quality, fish and To divert all or part of the water from a wildlife habitat, forest, and visual resources waterway in such a manner that it can be shall be evaluated and the techniques and controlled and used beneficially or to divert measures necessary to overcome the periodic damaging flows from one watercourse undesirable effects shall be identified and to another watercourse thereby reducing the addressed. damage potential of the flows. Materials - All materials to be used in constructing the diversion dam and CONDITIONS WHERE PRACTICE APPLIES appurtenances shall have the strength, This standard applies to structures of a durability, and workability required to meet the permanent nature, constructed of materials installation and service conditions of the site. having an expected life span consistent with Structural design – Appurtenant structures the purpose for which the structure is shall be designed to withstand all anticipated designed. It does not apply where Diversion loads. (362), Floodwater Diversion (400), Floodwater Retarding Dam (402), or Grade Stabilization Outlet works - If part of the flow is to be Structure (410) would be used. diverted, the outlet works must provide for positive control of both maximum and This practice applies where: minimum flow rates consistent with the A diversion dam is needed as an integral purpose for which the diversion is made. The part of an irrigation system or a water- outlet works must provide for safe diversion of spreading system designed to facilitate the all expected flows, considering such hazards conservation use of soil and water as the potential for erosion, cavitation, and resources, reduction in flow capacity due to the buildup of debris and sediment. Diversion of water from an unstable watercourse to a stable watercourse is Bypass works - The bypass works must be desirable, capable of passing all flows needed to satisfy downstream priorities and all flows in excess The water supply available is adequate for of diversion requirements, including expected the purpose for which it is to be diverted, flood flows. This may require a combination of Adverse environmental impacts resulting orifices, weirs, and gates designed to meet the from the installation of the practice can be requirements of the site. The bypass works overcome. must provide for safe bypass of all expected flows, considering such hazards as the

Conservation practice standards are reviewed periodically, and updated if needed. To obtain the current version of this standard, contact the Natural Resources Conservation Service. NRCS, NHCP May 2002 348 - 2 potential for erosion, cavitation, and reduction Effects on erosion and the movement of in flow capacity due to the buildup of debris. sediment, pathogens, and soluble and sediment-attached substances carried by Special-purpose works - If debris, bed load runoff, materials, or sediments are present under flow conditions subject to diversion, provision shall Potential temperature changes in be made to bypass or remove materials that downstream waters resulting from may be detrimental to the functioning of the differences in bank shading in different outlet works, to other parts of the works, or to watercourses, areas to which diversion is made. This may Potential changes in the amount of soluble require the use of settling basins, debris traps, substances infiltrating and available for trash guards, or sluiceways, depending on site ground water recharge as well as the conditions. potential for salt pick-up, Vegetation - Disturbed areas, not otherwise Potential for introducing new plant or covered or protected, shall be vegetated as animal species to either the upstream or soon as practicable after construction. If soil downstream waters, or climatic conditions preclude the use of vegetation, and protection is needed, non- Effects on the natural migration of fish. vegetative materials, such as mulches, gravel, and rock riprap may be used. As a minimum, PLANS AND SPECIFICATIONS seedbed preparation, seeding, fertilizing, and mulching shall comply with instructions in local Plans and specifications for installing diversion technical guides. The vegetation shall be dams shall be in keeping with this standard maintained and undesirable species and shall describe the requirements for controlled. applying the practice to achieve its intended purpose. CONSIDERATIONS OPERATION AND MAINTENANCE The effects of this practice on water quantity, water quality, and the environment should be Provisions shall be made for operation and considered during the planning process. maintenance requirements and, for larger Effects to be considered are: more complex diversion dams, may include a formal plan. Typical maintenance may include Effects on the water budget, on volume the removal of accumulated trash and debris and rate of runoff, infiltration, evaporation, from the structure and the repair of gates, transpiration, deep percolation, and screens, and other appurtenances. ground water recharge, Effects of the use of diverted waters for irrigation, Effects on the original watercourse, on the newly constructed watercourse, and on the area where the water is being diverted to and from,

NRCS, NHCP May 2002