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NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD

OPEN CHANNEL (Ft.)

CODE 582

DEFINITION cause significant erosion, flooding, or sedimentation. Constructing or improving a channel either natural or artificial in which water flows with a free surface. CRITERIA General Criteria Applicable to All Purposes PURPOSE Laws, rules, and regulations. This practice To provide discharge capacity required for flood shall conform to all federal, state, and local laws, prevention, drainage, other authorized water rules, and regulations. Laws, rules, and management purposes, or any combination of regulations of particular concern include those these purposes. involving water rights, land use, pollution control, property easements, wetlands, preservation of cultural resources, and endangered species. CONDITIONS WHERE PRACTICE APPLIES Plan. Channel construction or modification shall This standard applies to construction of open be according to an approved plan prepared for channels or modifications of existing streams or the site. Technical Release No. 25 (TR-25), ditches. Design of Open Channels, shall be used in This standard applies to Conservation Practice surveys, planning, and site investigations for Standard 608, Surface Drainage, Main or channel work. Design criteria in TR-25 shall be Lateral, where there is a drainage area in excess followed, using the procedure best adapted to of 1 square mile. site conditions. It does not apply to Conservation Practice In selecting the location and design of channels, Standards 362, Diversions; 412, Grassed careful consideration shall be given to Waterways; 388, Irrigation Field Ditches; 607 minimizing water pollution and damage to fish Surface Drainage, Field Ditches; or 320, and wildlife habitat and to protecting forest Irrigation Canal or Lateral. resources and the quality of the landscape. In considering requirements for construction and It also applies where stability requirements can operation and maintenance, selected woody be met; where the impact of the proposed plants must be preserved. The overall construction on water quality, fish and wildlife landscape character, prominent views, and fish habitat, forest resources, and quality of the and wildlife habitat requirements must be landscape is evaluated and the techniques and considered. measures necessary to overcome the undesirable effects are made part of any Planned measures necessary to mitigate planned work; where an adequate outlet for the unavoidable losses to fish or wildlife habitat shall modified channel reach is available for discharge be included in the project. The quality of the by gravity flow or pumping; and where landscape shall be maintained by both the excavation or other channel work does not location of channel works and plantings, as appropriate.

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, KS June 2002 582 - 2

The alignment of channels undergoing result in a stable channel that can be maintained modifications shall not be changed to the extent at reasonable cost. Vegetation, riprap, that the stability of the channel or laterals thereto revetments, linings, structures, or other is endangered. measures shall be used if necessary to ensure stability. Capacity. The capacity for open channels shall be determined according to procedures Select the method to use for the stability design applicable to the purposes to be served. The from Chapter 6 in TR-25. The method water surface profile or hydraulic gradeline for applicable to the site conditions shall be used in design flow shall be determined according to determining the stability of the proposed channel guidelines for hydraulic design in TR-25. When improvements. Manning's equation is used, the roughness Bankfull flow is the flow in a channel that creates coefficient "n" value for aged channels shall be a water surface at or near the normal ground based on the expected vegetation, along with elevation or the tops of dikes or continuous spoil other retardance factors, considering the level of banks that confine the flow for a significant maintenance prescribed in the operation and length of a channel reach. maintenance plan prepared with the owners or sponsors. The required capacity may be Channels must be stable under conditions established by considering volume-duration existing immediately after construction (as-built removal rates, peak flow, or a combination of the condition) and under conditions existing during two (as determined by the topography, purpose the effective design life (aged condition). of the channel, desired level of protection, and Channel stability shall be determined for economic feasibility). discharges under these conditions as follows: Cross section. The required channel cross 1. As-built condition  Bankfull flow, design section and grade shall be determined by the discharge, or 10-year frequency flow, plan objectives, the design capacity, the whichever is smallest, but not less than materials in which the channel is to be 50 percent of design discharge. constructed, the vegetative establishment The allowable as-built velocity (regardless of program, and the requirements for operation and type of stability analysis) in the newly maintenance. A minimum depth may be constructed channel may be increased by a required to provide adequate outlets for maximum of 20 percent if: subsurface drains, tributary ditches, or streams. Urban and other high-value developments  The soil and site in which the channel is through which the channel is to be constructed to be constructed are suitable for rapid must be considered in the design of the channel establishment and support of erosion- section. controlling vegetation, Channel stability. Characteristics of a stable channel are:  Species of erosion-controlling vegetation adapted to the area and proven 1. The channel neither aggrades nor methods of establishment are known, degrades beyond tolerable limits. and 2. The channel banks do not erode to the extent that the channel cross section is  The channel design includes detailed changed appreciably. plans for establishing vegetation on the channel side slopes. 3. Excessive sediment bars do not develop. 2. Aged condition  Bankfull flow or design 4. Gullies do not form or enlarge because discharge, whichever is larger, except of the entry of uncontrolled surface flow that it is not necessary to check stability to the channel. for discharge greater than the 100-year frequency. All channel construction and modification (including clearing and snagging) shall be according to a design that can be expected to

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Stability checks that are flow-related are not 2. Provide for the free flow of water between required if the velocity is 2 feet per second or the channel and flood plain unless the valley less. routing and water surface profile are based on continuous dikes being installed. For newly constructed channels in fine-grained soils and sands, the "n" values shall be 3. Not hinder the development of travelways determined according to procedures in Chapter for maintenance. 6 in TR-25 and shall not exceed 0.025. The n value for channels to be modified by clearing 4. Leave the right-of-way in the best condition and snagging only shall be determined by feasible, consistent with the project reaches according to the expected channel purposes and adjacent land uses. condition upon completion of the work. Appurtenant structures. The channel design 5. Direct water accumulating on or behind spoil shall include all structures required for proper areas to protected outlets. functioning of the channel and its laterals, as well as travelways for operation and 6. Maintain or improve the visual quality of the maintenance. Inlets and structures needed for site to the extent feasible. entry of surface and subsurface flow into channels without significant erosion or Vegetation of channel. Vegetation shall be degradation shall be included in the channel established on all channel slopes, berms, spoils, design. The design also shall provide for and other disturbed areas according to the necessary flood gates, water-level-control Conservation Practice Standard 342, Critical devices, bays used in connection with pumping Area Planting. plants, and any other appurtenances essential to the functioning of channels and contributing to CONSIDERATIONS attainment of the purposes for which they are built. If needed, protective structures or Water quantity concerns include the effects on treatment shall be used at junctions between components of the water budget, especially on channels to ensure stability at these critical volumes and rates of runoff and infiltration. locations. Water quality concerns include the following: The effect of channel work on existing culverts, 1. Effects of erosion and the movement of bridges, buried cables, pipelines, irrigation sediment and soluble and sediment- flumes, and inlet structures for surface and attached substances in runoff during and subsurface drainage on the channel and laterals immediately after construction thereto shall be evaluated to determine the need for modification or replacement. 2. Effects of the use of chemicals during vegetation control Culverts and bridges that are modified or added as part of channel projects shall meet 3. Effects of changes in channel vegetation on reasonable standards for the type of structure downstream water temperature and shall have a minimum capacity equal to the 4. Potential for temporary and long-term effects design discharge of state agency design on the visual quality of downstream waters requirements, whichever is greater. Capacity of some culverts and bridges may need to be Maintenance access. Travelways for increased above the design discharge. maintenance generally should be provided as part of all channel work. Disposition of spoil. Spoil material from clearing, grubbing, and channel excavation shall A travelway should be provided on each side of be disposed of in a manner that will: large channels if necessary for use of maintenance equipment. Travelways should be 1. Not confine or direct flows so as to cause adequate for movement and operation of instability when the discharge is greater than equipment required for maintenance of the the bankfull flow. channel. The travelway may be located adjacent to the channel on a berm or on 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, Kansas March 2002 582 - 4 spread spoil. In some places, the channel itself OPERATION AND MAINTENANCE may be used as the travelway. The travelway, An operation and maintenance plan shall be including access points, should blend into the developed and reviewed with the landowner or topography, the landscape, and adjacent land individual responsible for operation and uses. maintenance. Minimum requirements for Safety. Open channels can create a safety operation, maintenance, and replacement shall hazard. Appropriate safety features and devices be consistent with the design objectives. This should be installed to protect people and includes consideration of fish and wildlife habitat, animals from accidents such as falling or quality of the landscape, water quality, mitigation drowning. features, methods, equipment, costs, stability, function for design life, frequency, and time of year for accomplishing the work. Detailed PLANS AND SPECIFICATIONS provisions for operation and maintenance must Plans and specifications for constructing open be made if complex features such as water- channels shall be in keeping with this standard level-control structures and pumping plants are and shall describe the requirements for properly required. installing the practice to achieve its intended purpose.

NRCS, KS June 2002