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NATURAL CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD

IRRIGATION (Ac.-Ft.)

CODE 436

DEFINITION capacity requirements for storage . Storage reservoirs shall be planned An irrigation storage structure made by and located to serve as an integral part of an constructing a , embankment, pit, or tank. irrigation system. PURPOSE This practice applies to reservoirs created by embankment structures or excavated pits to This practice may be applied as part of a store diverted , , or management system to achieve one irrigation system for later use, or or more of the following purposes: reuse. • Store water to provide a reliable irrigation The practice also applies to reservoirs created or regulate available irrigation by embankment structures or excavated pits flows. and tanks constructed of concrete, steel, or • Improve water use efficiency on irrigated other suitable materials used to collect and . regulate available irrigation water supplies to accomplish the intended purpose. • Provide storage for tailwater recovery and reuse. CRITERIA • Provide irrigation runoff retention time to General Criteria Applicable to All Purposes increase breakdown of chemical Structure type selection (excavated pit, contaminants. embankment, or tank) shall be based on a site specific assessment involving hydrologic • Reduce use. studies, and geologic • Develop systems (i.e., investigations, available construction materials, ). and natural storage. Storage Capacity. Design capacity CONDITIONS WHERE PRACTICE APPLIES computations shall be based on planned inflow This practice applies to irrigation volumes and rates over the storage period, structures that meet one or more of the and outflow volumes and rates required to following criteria: meet planned irrigation system needs. • The existing available water supply is Structure storage capacity must provide insufficient to meet irrigation requirements sufficient volume to meet variations in water during all or part of the irrigation season. demand within the irrigation period. • Water is available for storage from surface Compute demand flow rates based on the runoff, stream flow, irrigation , or a consumptive use-time relationship using subsurface source. anticipated irrigation efficiencies, conveyance losses, and other uses such as , frost • A suitable site is available for construction control, seepage, and evaporation. of a storage reservoir. Irrigation storage reservoirs planned primarily This practice applies to planning and functional to regulate irrigation flows shall have adequate design of storage capacity, and inflow/outflow NRCS, CA Conservation practice standards are reviewed periodically and updated if needed. To obtain the current version of this standard, contact your Natural Resources Conservation Service October 2011 State Office or visit the Field Office Technical Guide. 436 - 2

capacity to provide design irrigation application • safe emergency bypass areas cannot be flow rates. provided, or Structure capacity shall provide adequate • tailwater discharges violate local or state storage for inflow while maintaining sufficient regulations, water levels to insure proper operation of outlet works and provide uniform outflow rate during Tailwater storage requirements shall, as a planned irrigation events. minimum, include a volume adequate to store all tailwater runoff from a single irrigation set. Provide additional capacity as needed for sediment storage. Additional Criteria Applicable to Irrigation Runoff Retention Time to Increase Foundation, Embankment, and Spillways. Breakdown of Chemical Contaminants Earthen , embankments, pits, associated Capacity. Where additional storage or flow spillways, and appurtenant structures shall be regulation are required to provide adequate designed to meet criteria in the applicable retention time for breakdown of chemicals in NRCS Conservation Practice Standards, runoff , storage facilities shall be sized (378), or Dam (402). accordingly. Allowable retention times shall be Seepage. Prevent excessive seepage losses site specific to the particular chemical of by use of an appropriate method of sealing or concern. lining. Additional Criteria Applicable to Reduce Overflow Protection. Overflow protection Energy Use shall be provided if overflow of the irrigation storage reservoir is possible. Provide analysis to demonstrate reduction of energy use from practice implementation. Inlet and Outlet Works. Design conduit and Reduction of energy use is calculated as open spillways according to guidelines in average annual or seasonal energy reduction appropriate chapters of the NRCS National compared to previous operating conditions. Engineering Handbook. Additional Criteria Applicable to Develop Provide inlet works when needed to prevent Renewable Energy Systems erosion or control flows into the irrigation storage reservoir. Inlet works may consist of a Renewable energy systems shall meet direct pumping system, conduit, grassed applicable design criteria in NRCS and/or channel, lined channel, chute, head gates, standards, and shall be in accordance , or other appurtenances necessary to with manufacturer’s recommendations. safely convey and control water entering the Hydropower systems shall be designed, structure. operated, and maintained in accordance with the Microhydropower Handbook, Sections 4 Outlet works shall be provided for controlled and 5, as appropriate. withdrawal, transfer, or release of irrigation water. Outlet works may consist of a direct CONSIDERATIONS pumping system or a conduit from the storage reservoir to an area of use. The capacity of When planning this practice, the following the outlet works shall be adequate to provide items should be considered where applicable: the outflow rate needed to meet irrigation • Potential energy savings resulting from system demands. regulation of irrigation flows, tailwater Design and install specialized inlet or outlet reuse, improved pumping efficiency, works when needed to avoid entraining or or management changes. impinging aquatic organisms. • Planting of critical areas at the completion Additional Criteria Applicable to Storage for of construction to protect the structure and Tailwater Recovery and Reuse borrow areas, and prevent erosion. Capacity. When energy sources for tailwater • Effects of physical and chemical back systems are subject to interruption properties, as as potential soil and limitations, relating to embankment NRCS, CA October 2011 436 - 3

construction, compaction, stability, bearing • Opportunities to include variety in strength, pool area seepage, and soil vegetation for embankment stabilization or corrosivity. Refer to soil survey data as a maintenance, that would preliminary planning for assessment of provide pollinator forage from early pool and borrow areas, and conduct to late fall. • On-site soil investigations during the final PLANS AND SPECIFICATIONS planning stage. Plans and specifications for constructing • Perimeter fences to prevent and irrigation storage reservoirs shall be in keeping animal access, and emergency escape with this standard and shall describe the facilities to minimize human safety requirements for applying the practice to hazards. achieve its intended purposes. • Construction-related effects on air quality Plans and specifications for constructing and on of downstream water earthen irrigation storage reservoirs shall be courses. based on criteria found in NRCS Conservation • Potential for earth moving construction to Practice Standards, Pond (378), or Dam (402). uncover or redistribute toxic materials or Plans and specifications for tanks constructed on-site invasive species. of non earthen materials shall be based on • Development of water budgets, to quantify construction and materials specifications for sources of inflow (precipitation and NRCS Conservation Practice Standard, withdrawals), and outflow Watering Facility (614). ( and losses). OPERATION AND MAINTENANCE • Impacts on downstream flows or that could affect other water uses or users. An Operation and Maintenance plan shall be prepared for landowner or operator use. The • Impacts on the quantity of downstream plan shall provide specific instructions for flows, which could have undesirable operating and maintaining facilities to ensure environmental, social, or economic effects. they function properly. The plan shall include • Impacts of erosion, sediment, soluble the following provisions: contaminants, seeds or vegetative • Periodic cleaning and regrading of water materials of invasive species, and storage facilities to maintain functionality. contaminants attached to sediment in runoff. • Periodic inspection, removal of debris, and repair if needed of trash racks and inlet • The movement of dissolved substances to and outlet structures to assure proper ground water. operation. • Effects of water temperature changes on • Routine maintenance of mechanical aquatic and communities. components in accordance with • Timing of vegetation-disturbing manufacturer recommendations. maintenance activities, to avoid grassland • Periodic inspection and maintenance of bird nesting seasons. embankments and earth spillways to repair • Impacts on or water-related damage or control erosion and undesirable wildlife habitats. vegetation. • Impacts on the visual quality of water • Periodic removal of sediment from traps or resources and the . storage facilities to maintain design capacity and efficiency. • Impacts on cultural resources. • Periodic Inspection or testing of all • Performing periodic water quality analysis pipelines and pumping plant components to evaluate , , pesticides, and appurtenances, as applicable. and pathogens.

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REFERENCES U.S.Department of Energy, Operations Office. McKinney, J.D., et al. Microhydropower Handbook, IDO-10107, Volumes 1 & 2.

NRCS, CA October 2011