Standard 350

NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD ARIZONA

SEDIMENT BASIN (No.)

CODE 350

DEFINITION  Where the Hazard Class of the dam is Low.  Where site conditions shall be such that A basin constructed with an engineered outlet, runoff from the design storm can be safely formed by an embankment or excavation or a passed through (1) a natural or constructed combination of the two. auxiliary spillway, (2) the combination of a principal spillway and auxiliary spillway, or (3) PURPOSE a principal spillway.

To capture and detain sediment laden runoff, or This practice is also serves to: other debris for a sufficient length of time to  Preserve the capacity of reservoirs, wetlands, allow it to settle out in the basin. ditches, canals, diversion, waterways, and streams CONDITIONS WHERE PRACTICE  Prevent undesirable deposition on bottom APPLIES lands and developed areas or trap sediment originating from construction sites or other This practice applies to urban land, construction disturbed areas sites, agricultural land, and other disturbed  Reduce or abate pollution by providing lands: basins for deposition and storage of silt, sand,  Where physical conditions or land ownership gravel, stone, agricultural waste solids, and preclude treatment of a sediment source by the other detritus installation of -control measures to keep soil and other material in place or where a CRITERIA sediment basin offers the most practical solution to the problem. Sediment Basins shall be designed on an  Where failure of the basin will not result in individual basis to meet site conditions and loss of life, damage to homes, commercial or functional requirements. They shall be part of an industrial buildings, main highways or railroads; approved and overall engineering plan for or in the interruption, service or use of public irrigation, drainage, wildlife, recreation, utilities. channel improvement, or similar purposes.  Where the product of the storage times the effective height of the dam or embankment is Design and implementation of subsidiary less than 3,000. Storage is the volume, in acre- components and/or structures shall meet all feet, in the reservoir below the elevation of the applicable Natural Resource Conservation crest of the auxiliary spillway. Service (NRCS) conservation practice  Where the effective height of the dam is 35 standards. The criteria for the design of any feet or less. The effective height of the dam is components not specifically addressed in NRCS the difference in elevation, in feet, between the practice standards or specifications shall be auxiliary spillway crest and the lowest point in consistent with sound engineering principles the cross section taken along the centerline of and/or manufacturer recommendations. the dam. If there is no auxiliary spillway, the top of the embankment is the upper limit.

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 1 of 14 October 2010

Standard 350

All pertinent safety codes (OSHA, ADOSH) and Location. Sediment basins are the last line of manufacturer’s recommendations shall be defense for capturing sediment when erosion has followed in the installation and operation of the already occurred. When possible construct equipment. basins prior to soil disturbance in the watershed. Choose the location of the sediment basin so that Laws and Regulations. Sediment basin design, it intercepts as much of the runoff as possible installation, and construction must comply with from the disturbed area of the watershed. all applicable federal, state, Tribal and local Choose a location that minimizes the number of laws, rules, and regulations. Laws and entry points for runoff into the basin and regulations of particular concern include those interference with construction or farming involving water rights, land use, pollution activities. Do not locate sediment basins in control, property easements, wetlands, perennial streams. preservation of cultural resources, and endangered species. Basin Capacity. The sediment basin must have sediment storage capacity, detention storage and The owner is responsible for securing necessary temporary flood storage capacities. For permits and water rights, complying with all maximum sediment retention, design the basin laws and regulations, and meeting legal so that the detention storage remains full of requirements applicable to the installation, water between storm events. However, if site operation, and maintenance of this practice and conditions, safety concerns, or local laws associated structures. preclude a permanent pool of water, design all or a portion of the detention and sediment storages Cultural Resources and Wildlife to be dewatered between storm events. If it is Habitat. Impact to cultural resources, wetlands determined that periodic removal of sediment and Federal and state protected species shall be will be practicable, the capacity may be evaluated and avoided or minimized to the proportionately reduced. extent practicable during planning, design and implementation of this conservation practice in Design the sediment storage for a minimum of accordance with established National policy, 900 ft3/acre of disturbed area. The sediment General Manual (GM) Title 420-Part 401; Title storage volume is calculated from the bottom of 450-Part 401, Title 190-Parts 410.22 and the basin. Design the detention storage for a 410.26, National Planning Procedures minimum of 3,600 ft3/acre of drainage area. The Handbook (NPPH), National Cultural detention volume is calculated from the top of Resources Procedures Handbook (NCRPH), the sediment storage to the crest of the principal National Food Security Act Manual (NFSAM), spillway. and the National Environmental Compliance Handbook (NECH). Sediment yield shall be computed and the sediment basin sized using one or more of the General Criteria Applicable to All Purposes following references: National Engineering The design of dams, spillways, and drainage Handbook, Section 3 – Sedimentation; facilities shall be according to Arizona Engineering Field Manual, Chapter 10 – Gully Conservation Practice Standard 378 (), Treatment; Engineering Field Manual, Chapter Conservation Practice Standard 410 (Grade 15 – Irrigation; Actual field studies; or other Stabilization Structure) or according to the approved NRCS references. requirements in NRCS TR-60 (Earth Dams and Reservoirs), as appropriate, for the class and Where field data for sediment bulk density is not kind of structure being considered. available, the designer may assume that one ton of sediment occupies one cubic yard.

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 2 of 14 October 2010

Standard 350

Flood storage is based on the required design An auxiliary spillway must be provided for each storm for the auxiliary spillways. Flood storage embankment, unless the principal spillway is is calculated between the crest of the principal large enough to pass the peak discharge from spillway and the crest of the auxiliary spillway. the routed design hydrograph and anticipated A minimum of 1 foot in elevation is required trash without over topping the embankment. between the principal and auxiliary spillways. The minimum criteria for a closed conduit principal spillway without an auxiliary spillway Required Sediment Basin Storage Capacities are a conduit with a cross-sectional area of 3 ft2 or more, an inlet that will not clog, and an Flood Storage Auxiliary Spillway Based on aux. spwy. elbow designed to facilitate the passage of trash. flow reqmt. 1.0' min. The minimum capacity of a natural or

Detention Principal Spillway constructed auxiliary spillway shall be that Storage 3600 cu. ft./acre required to pass the peak flow expected from a Sediment Storage 900 cu. ft./acre design storm of the frequency and duration shown in the following tables, less any reduction creditable to conduit discharge and detention Principal and Auxiliary Spillway Design storage. Minimum Spillway Capacity for Design the principal spillway to carry Drainage Area of 20 acres or less (discharge) long-duration, continuous, or Effective Storage Minimum Design frequent flows without discharge through the Height of Storm auxiliary spillway. The diameter of the principal Embankment spillway pipe must be 6 inches or greater. (feet) (acre-feet) 10 or less Less than 9.2 10-year, 24-hour The principal spillway can be designed to 10 or less More than 9.2 25-year, 24-hour remove only water from the temporary flood More than 10 Less than 9.2 50-year, 24-hour storage or it can be designed to dewater all or part of the detention storage. Design the Minimum Spillway Capacity for principal spillway to drawdown the temporary Drainage Area of 20 acres or greater Height of Storage Minimum flood storage within 24 hours. Drawdown times Embankment1 Design Storm2 for the detention storage can be longer to (feet) (acre-feet) improve sediment trapping. 10 or less Less than 9.2 25-year, 24-hour 10 or less More than 9.2 50-year, 24-hour When design discharge of the principal spillway More than 10 Less than 9.2 100-year, 24-hour is considered in calculating peak outflow 1 As defined under criteria through the auxiliary spillway, the crest 2 Select rain distribution based on climatological elevation of the inlet shall be such that the full region flow will be generated in the conduit before there is discharge through the auxiliary The minimum capacity of a closed auxiliary spillway. The inlets and outlets shall be designed spillway shall be sufficient to pass the peak flow to function satisfactorily for the full range of expected from a 100-year 24-hour frequency flow and hydraulic head anticipated. storm, less any reduction credited to principal spillways or detention storage. Design the auxiliary spillway to pass large storms without damage to the basin. Refer to Constructed auxiliary spillways are open Arizona Conservation Practice Standard 378, channels that usually consist of an inlet channel, for the required design storm and design a control section, and an exit channel. They criteria for the auxiliary spillways. shall be trapezoidal and shall be located in undisturbed or compacted earth. The side slopes shall be stable for the material in which the

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 3 of 14 October 2010

Standard 350 spillway is to be constructed. For embankments shall not be less than that necessary to support having an effective height exceeding 20 feet, the the design load with a maximum of 5 percent emergency spillway shall have a bottom width of deflection. not less than 10 feet. Upstream from the control  The inlets and outlets shall be structurally section, the inlet channel shall be level for the sound and made of materials compatible with distance needed to protect and maintain the those of the pipe. crest elevation of the spillway. The inlet channel  No valve shall be installed when the conduit may be curved to fit existing topography. The serves the single purpose of carrying flow from grade of the exit channel of a constructed a trickle tube riser. For secondary discharge auxiliary spillway shall fall within the range systems, control valves shall be installed on the established by discharge requirements and upstream end unless otherwise approved by the permissible velocities. State Conservation Engineer.  To prevent clogging of the conduit, an Where there are embankments in series (NEM, appropriate trash guard shall be installed at the 520.24(a)(1), the design of the downstream inlet or riser. structure shall address what will happen should  All pipe joints shall be made watertight by the upstream structure fail. Some precautions the use of couplings, gaskets, caulking, or by that could be considered are: welding. 1. Adding additional freeboard to the embankment. For embankments 20 feet or less in effective 2. Larger capacity auxiliary spillway. height, acceptable pipe materials are cast-iron, 3. Address how overtopping will affect the steel, corrugated steel or aluminum, asbestos- structure being designed. cement, concrete, plastic, vitrified clay with rubber gaskets, and cast-in-place reinforced The outlet of the principal and auxiliary concrete. Asbestos-cement, concrete, and spillway must be stable for anticipated design vitrified clay pipe shall be installed on concrete flow conditions. bedding. Plastic pipe that will be exposed to direct sunlight shall be made of ultraviolet- Structural Emergency Spillways. If chutes or resistant materials and protected by coating or drops are used for principal spillways or shielding, or provisions for replacement should principal emergency or emergency spillways, be made as necessary. they shall be designed according to the principles set forth in the Engineering Field For embankments more than 20 feet in effective Manual for Conservation Practices and the height, conduits shall be plastic, reinforced National Engineering Handbook-Section 5, concrete, cast-in-place reinforced concrete, Hydraulics; Section 11, Drop Spillways; and corrugated steel or aluminum, or welded steel Section 14, Chute Spillways. pipe. The maximum height of fill over any principal spillway steel or aluminum pipe must Pipe or Conduits through Embankments. A not exceed 25 feet. All pipes shall have concrete pipe conduit, with needed appurtenances, shall bedding or a concrete cradle. Cantilever outlet be placed under or through the embankment sections, if used, shall be designed to withstand where required for safety, for proper operation the cantilever load. Pipe supports shall be of the reservoir and spillway, or for water rights provided when needed. Other suitable devices requirements. such as a Saint Anthony Falls stilling basin or an impact basin may be used to provide a safe Pipe conduits under or through the embankment outlet. shall meet the following requirements:  The pipe and connections shall be capable of Protective coatings of asbestos-bonded, asphalt withstanding external loading without yielding, coated, or vinyl coating on galvanized buckling, or cracking. Flexible pipe strength corrugated metal pipe, or coal tar enamel on

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 4 of 14 October 2010

Standard 350 welded steel pipe should be provided in areas Basin Shape. Design basins with a length to that have a history of pipe corrosion, or where width ratio of 2 to 1 or greater. Baffles to divert the saturated soil resistivity is less than 4,000 the flow in the basin can be used to lengthen the ohms/cm, or where soil pH is lower than 5. flow path of incoming water to achieve the required length to width ratio. Pipe diameter, pipe rating and embankment depth criteria for polyvinyl chloride (PVC), The basin length shall be at least 4 times the steel, and aluminum pipe shall be as follows: average width, unless calculations show that the proposed length is adequate to trap at least 65- Polyvinyl Chloride – PVC 1120 or PVC 1220, percent of the suspended particles. Length is conforming to ASTM D1785 or ASTM D2241 defined as the shortest distance from where Nominal Schedule or Maximum particles enter the pond area to the outlet Pipe Size Standard Depth of fill leaving the pond. Sediment basins must be Dimension Ratio over pipe designed to allow for sediment removal using (inch) (SDR) (feet) available equipment. 4 or smaller Schedule 40 15

Schedule 80 20 SDR 26 10 Embankment and Side Slopes. If the sediment 6, 8, 10, 12 Schedule 40 10 basin includes an embankment, it must be Schedule 80 15 constructed of well compacted soil with stable SDR 26 10 side slopes. Refer to NRCS Conservation Practice Standard 378, Pond for design Steel & Aluminum – Minimum gage or thickness for requirements for the embankment. The 2 1 corrugated metal pipe ( /3” x ½” corrugations) combined upstream and downstream side slopes Fill Steel pipe with Aluminum Pipe2 of the settled embankments shall not be less than Height diameter (inch) of… with diameter 5 horizontal to 1 vertical. All slopes must be (inch) of… designed to be stable, even if flatter side slopes (feet) <21 24 30 36 42 48 <21 24 30 36 are required. Above the permanent water line, 1 – 15 16 16 16 14 12 10 .06 .075 .075 .075 the side slopes of the pool area must be 3 15 – 20 16 16 16 14 12 10 .06 .075 .075 .105 horizontal to 1 vertical or flatter. Side slopes 20 – 25 16 16 16 14 12 10 .06 .105 .135 n/a 1 1 below the permanent water line can be as steep Pipe with 6-, 8-, and 10-in diameters has 1- /2 in x 1 as 2 horizontal to 1 vertical. /4 in corrugations 2 Riveted or helical fabrication If the embankment top is to be used as a public Cathodic Protection. Cathodic protection is to road, the minimum width shall be 16 feet for be provided for coated welded steel and one-way traffic and 26 feet for two-way traffic. galvanized corrugated metal pipe where soil and Guardrails or other safety measures shall be resistivity studies indicate that the pipe needs a used where necessary and shall meet the protective coating, and where the need and requirements of the responsible road authority. importance of the structure warrant additional Unless otherwise specified, the minimum top protection and longevity. If cathodic protection width for all embankments is as follows: is not provided for in the original design and Total Height of Top Width installation, electrical continuity in the form of Embankment joint-bridging straps should be considered on (feet) (feet) pipes that have protective coatings. Cathodic 10 of less 8 10 – 20 10 protection should be added later if monitoring 20 – 25 12 indicates the need. When cathodic protection is 25 – 35 14 needed, the procedures of Design Note 12, Control of Underground Corrosion, shall be The design height of the embankment shall be used. increased by the amount needed to insure that after settlement the height of the embankment

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 5 of 14 October 2010

Standard 350 equals or exceeds the design height. This  Be located immediately downstream of the increase shall not be less than 5 percent, except cutoff trench, approximately parallel to the where detailed soil testing and laboratory centerline of the embankment. analyses show that a lesser amount is adequate.  Outlet at the embankment downstream toe, The borrow operation shall not be permitted preferably using a drain backfill envelope closer than 50 feet from the upstream toe of the continuously along the pipe to where it exits the embankment except where the cutoff trench embankment. extends into firm impervious material for its entire length. Freeboard. The minimum difference in elevation between the crest of the emergency spillway and Foundation Cutoff. A cutoff of relatively the settled top of embankment shall be either impervious material shall be provided under the depth of design flow plus 1 foot or 3 feet embankment if necessary. The cutoff shall be whichever is greater. located at or upstream from the centerline of the embankment. It shall extend up the abutments as When drainage areas are less than 20 acres, the required and be deep enough to extend into a minimum depth of an open emergency spillway relatively impervious layer or provide for a will be the depth of flow plus 1.5 feet, but never stable embankment when combined with seepage less than 2 feet. The minimum bottom width control. The cutoff trench shall have a bottom shall be 5 feet. width adequate to accommodate the equipment used for excavation, backfill, and compaction For concrete chute spillways the minimum operations. Side slopes shall not be steeper than difference in elevation between the crest of the one horizontal to one vertical. emergency spillway and the settled top of embankment shall be either the depth of flow Seepage Control. Seepage control is to be plus 0.5 feet or 2.0 feet whichever is greater. included if (1) previous layers are not intercepted by the cutoff, (2) seepage creates Other Criteria. Closed conduit spillways swamping downstream, (3) such control is designed for pressure flow must have adequate needed to insure a stable embankment, or (4) anti-vortex devices. special problems require drainage for a stable embankment. A pipe with a suitable valve shall be provided to drain the pool area if needed for proper Seepage may be controlled by (1) foundation, sediment basin management or if required by abutment or embankment drains; (2) reservoir State law. The principal spillway conduit may be blanketing; or (3) a filter or drainage used as a sediment basin drain if it is located diaphragm. where it can perform this function.

The filter or drainage diaphragm shall: Supply pipes through the embankment to  Consist of sand, meeting fine concrete watering troughs and other appurtenances shall aggregate requirements (at least 15% passing have an inside diameter of not less than 1-1/4 in. the No. 40 sieve but no more than 10% passing the No. 100 sieve). If unusual soil conditions Vegetation. Establish vegetation on all exist, a special design analysis shall be made. disturbed areas, including the embankment and  Be a minimum of 2 ft thick and extend side slopes of the basin and pool area, vertically upward and horizontally at least three immediately after construction ends to control times the pipe diameter, and vertically erosion and prevent excess sediment from downward at least 18 in. beneath the conduit leaving the site. Refer to NRCS Conservation invert. Practice Standard 342, Critical Area Planting for criteria for the establishment of vegetation, seedbed preparation, seeding, and fertilization.

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 6 of 14 October 2010

Standard 350

If construction takes place during a time period Design Capacity. Sediment basins for that is not conducive to establishing vegetation precipitation runoff shall be designed to trap at or if soil or climatic conditions preclude the use least 65-percent of the sediment from a 10-year of vegetation, protect the embankment by 24-hour storm over the contributing area. mulching, gravel or other methods. Refer to Erosion may be estimated using the Universal NRCS Conservation Practice Standard 484, Soil Loss Equation (USLE) or the Revised Mulching for mulching criteria. Universal Soil Loss Equation (RUSLE) as appropriate when field measurements are not If arid climatic conditions do not allow for the available. establishment of vegetation other means of reducing erosion may be used. If needed to Additional Criteria for Sediment Basins protect the slopes of the embankment, special included in Animal Waste Management measures, such as berms, rock riprap, sand- Systems gravel, soil cement, or special vegetation, shall Structures designed under this standard may be be provided (Technical Releases 56 and 69). used to separate agricultural waste solids from liquids as a component of an agricultural waste Safety. Sediment basins are often installed in management system (AWMS). developing areas and can be an attractive nuisance and safety hazard to the public. Design Sediment basin embankments, foundations, and with the safety of the public in mind. Where fabricated structures (concrete, metal, wood) appropriate, include safety features such as must meet structural requirements outlined in fencing to limit access to the pool area and the Arizona Conservation Practice 313, Waste embankment, signs to warn of danger and a Storage Facility. safety ledge below the water level 6 feet wide and 4 horizontal to 1 vertical (4:1) or flatter Liquids and solids removed or discharged from around the edge of the permanent pool. the sediment basin must be delivered to a waste Provisions shall be made for dewatering storage facility, waste treatment lagoon, or sediment pools if necessary for safety and vector other appropriate component of the AWMS. control. Solids removed from the sediment basin must be applied in accordance with the Arizona Additional Criteria for Sediment Basins for Conservation Practice 590, Nutrient Irrigated Cropland and Vegetated Treatment Management. Areas An auxiliary spillway is not required in the Design Storage Volume. Specific design storage design if the combination of storage volume and volume criteria, which includes both solids and mechanical spillway discharge will safely liquid storage is listed below. Sediment basins handle the design storm. that are a component of AWMS must provide the minimum solids capacity as determined by the Standard flood routing procedures may be used following equation: to determine pipe size and storage requirements. 0.5 Design Storage Volume. Sediment basins controlling sediment from irrigated cropland Where, shall be designed to store at least one year’s VS = Volume of Solids accumulation of sediment from the contributing A = No. 1000-lb Animals area. Provisions must be included in the CD = Confinement Days operation and maintenance plan for periodic SF = Slope Factor (3% or less = 0.25, 3% removal of the sediment. to 6% = 0.50, 6% to 10% = 0.75, and over 10% = 1.00)

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 7 of 14 October 2010

Standard 350

Sediment basin drainage structures (screen with Design Capacity. Where water will be 1 inch maximum opening size, perforated riser, impounded adjacent to the embankment to a slatted wall, v-notch weir etc.,) or filtered depth exceeding 3 feet, the embankment must not pumping systems must be provided to remove be overtopped by runoff from a 10-year liquids from sediment basins within 72 hours or frequency, 24-hour duration storm. less of runoff events. Investigations, Surveys and Design Design Capacity. The NRCS Curve Number Criteria. Documentation requirements will be (CN) or other approved method may be used in as outlined below, in additional to the computing runoff from feedlot surfaces and documentation requirements of the practice other contributing runoff areas. The soil cover components used in the system. complex number used in computing runoff from feedlot surfaces shall not be lower than 97 for Make a preliminary site assessment or paved lots and 90 for unpaved lots. reconnaissance to determine the complexity of the problem, availability of land and/or The required design storm event for animal watershed for selecting the applicable system feeding operations that involve waste from component which will best meet the needs of the swine, poultry, or veal shall be the 100-year owner. Determine if a stable outlet is available frequency, 24-hour duration storm event. or can be made. 1. Review of soil borings or geological site The required design storage volume must be one investigation, depending on existing site of the following: conditions or scope and complexity, to 1. The entire runoff volume from the design determine site feasibility and/or foundation storm event with the design solids volume materials and characteristics. Documentation contained in the sediment basin. shall include the following, at a minimum: 2. Flood routing the design storm event through a. Classification by the Unified Soil the sediment basin with the design solids Classification System (SM, CL, etc.) and volume contained in the sediment basin. The texture (silty sand, lean clay, etc.). maximum liquid elevation during the flood b. Soil physical and chemical properties and routing is considered the top of the design limitations. storage volume. c. Depth to ground water and seasonal high water table; Additional Criteria for Temporary Sediment d. Estimate of soil permeability or each Basins layer; Temporary sediment basins are used at e. Determination of foundation materials construction and other sites where the basin will and borrow source or disposal area. be used for periods of 2 years or less, the 2. Verify appropriate state or local laws for drainage area is 10 acres or less, and where permitting and approval requirements and failure of the embankment (if any) would not notify landowner of his/her responsibilities. cause loss of life or damage to high value 3. Verification or certification of used materials property. Maximum design height of the (if any). embankment must be 10 feet or less measured from natural ground at centerline of the To adequately plan and layout this practice, a embankment. detailed topographic survey is required, that adequately details: At the end of the period of need for the structure, 1. Site topography, as needed to show the the structure should be removed and the area physical features of the site, including graded and seeded as appropriate. existing features/practices, ground elevations, location of any utilities or markers, etc. Where applicable, USGS 7.5-

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 8 of 14 October 2010

Standard 350

minute topographic Quadrangles may be vegetative components, geotextile and used, provided design analysis verifies fabrics, or other minimum criteria are meet at all locations. appurtenances. 2. Survey the embankment centerline profile the full length of the structure extending above Installation and Basis of Acceptance. For the expected elevation of the dam and beyond construction that does not meet State, OSHA, or the location of the auxiliary spillway. Record Tribal criteria or requirements where deficient readings at all grade breaks and at intervals construction materials were used, NRCS may no greater than 50 feet. consider a waiver request for approval of 3. Survey a sufficient number of cross sections construction after it has received a signed and to accurately compute earth work quantities. sealed construction and/or material exemption 4. Set reference stakes and a permanent from a licensed engineer. Required exemption benchmark(s). Preferably, the elevations and shall be for installation of materials that do not coordinates should be based on a local meet minimum quality criteria as found in (assumed) or coordinate system (State or applicable Standards, Specifications, ASTM’s, grid) and clearly stated on the plan. Datum AWWA standards, etc. may be in the form of Northing and Easting coordinates, or Longitude and Latitude. Contractors performing work under this practice shall abide by all Federal, State or The design of a practice is the application of Tribal laws or criteria, and must be licensed by Field Office Technical Guide practice the state board of technical registers where the standards, and using experience and judgment work is being implemented. in the development of a solution to the problem or the objective. All computations and decisions CONSIDERATIONS made during the design of a practice are to be checked by another qualified individual and A large sediment basin may have an effect on appropriate notations made. Design the peak discharge rate from a watershed. computations, calculations or analysis shall Planners should consider this, and take steps to meet the following criteria: mitigate any potential negative effects this may 1. Record drainage areas, grades, dimensions, have on riparian habitat downstream from the site conditions and related hydraulic design structure. data. 2. Record computations for hydrology, sediment In many cases the use of a sediment basin alone yield, spillways, and basin size. may not provide sufficient protection for offsite 3. Hydraulic analysis and determinations sedimentation problems. To work most (capacity of ditch, channel or structure), for effectively, the sediment basin should be the last pipe structures, check hydraulics for all flow practice in a series of erosion control and conditions (pipe, weir, and orifice). sediment capturing practices installed in the 4. Structural analysis (concrete and steel disturbed area. This incremental approach will reinforcement requirements), stability, reduce the load on the basin and improve buoyancy, for any inlet or outlet works. effectiveness of the overall effort to prevent 5. Subsidiary and applicable components shall offsite sedimentation problems. be designed in accordance with applicable conservation practice standards (i.e., The efficiency of sediment removal in a basin is structures shall meet the requirements of affected by the detention time of runoff, the type Conservation Practice 587, Structure for of dewatering device, the presence of a Water Control, etc.). permanent pool in the basin, a decrease in 6. Prepare cost and material estimates turbulence in the basin and soil particle size. (material volume computations), includes The uses of the following techniques are estimates of earthwork, pipe, concrete, rock,

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 9 of 14 October 2010

Standard 350 particularly effective if there is a need to remove the design storm for the auxiliary spillway of the clay and other fine grained particles. basin.  Detention time can be increased by increasing the storage volume in the basin. The use of forebays that are separate from the Increased storage along with a properly designed main basin and easily accessible for cleanout dewatering device can significantly improve the will reduce turbulence and will allow larger efficiency of sediment capture. particles to settle out of the runoff before it  Dewatering should be done in a manner enters the main basin. which removes the cleaner water above the sediment storage, without removing the Because the sediment storage capacity of a basin sediment laden water found deeper in the basin. is finite, choose a location that will allow access One dewatering device that has been very for sediment removal when the storage capacity successful is a skimming device that floats on is full. the surface of the water and rises and falls with the water level in the basin. Use of this type of Visual aesthetics may be a concern, especially in dewatering device should improve the quality of urban or suburban areas. To address these the water leaving the basin. Details for this type concerns, design the basin to blend with the of dewatering device can be found in the North surrounding topography, or use plantings to Carolina Erosion and screen the view from surrounding homes or Planning and Design Manual. buildings.  Maintaining a permanent pool also improves sediment trapping by reducing the re-suspension In some situations, after they have served the of sediment in the basin. This can be sediment capture function, sediment basins may accomplished by only dewatering the temporary remain in place to function as storm water flood storage or only a portion of the detention detention or wildlife ponds. This will require storage. Removal of sediment from the basin appropriate planning during the design phase to before it reaches the sediment storage elevation ensure that the basin can function for a different will maintain the pool volume and improve use. In addition, significant modifications to trapping efficiency. outlet structures may need to be made as well as  Turbulence in the basin can be reduced by removal of accumulated sediment to convert it to constructing porous baffles that extend across a new use. the entire basin. The baffles slow down flows and force water to spread across the entire width If the basin will be used by wildlife, the use of of the basin. A thorough discussion and design native species is recommended to provide food criteria for porous baffles can be found in the and habitat diversity. Also, consider wildlife use North Carolina Erosion and Sediment Control of the basin when scheduling maintenance Planning and Design Manual. activities that may disrupt wildlife life cycles or  For very fine grained sediments, flocculants negatively impact pollinators. can be added to the runoff before it enters the basin. One commonly used flocculent is anionic In highly visible public areas and those polyacrylamide (PAM). Do not use cationic associated with recreation, careful polyacrylamide because it can be toxic to considerations should be given to landscape aquatic life. resources. Landforms, structural materials, water elements, and plant materials should Since the sediment basin must be designed to visually and functionally complement their handle all of the contributing drainage whether it surroundings. Excavated material and cut slopes is from disturbed areas or not, diverting runoff should be shaped to blend with the natural from undisturbed areas away from the basin will topography. Shorelines can be shaped and improve the function of the basin. The design islands created to add visual interest and storm for diversion measures should be equal to valuable wildlife habitat. Exposed concrete

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 10 of 14 October 2010

Standard 350 surfaces may be formed to add texture or Consider sediment basins that have concrete finished to reduce reflection and to alter color bottoms with curbs or walls (for machine contrast. Site selection can be used to reduce buckets to push against while loading) which adverse impacts or create desirable focal points. will allow sediment removal in less than ideal weather. Design alternatives presented to the client should address economics, ecological concerns Consider exclusion of livestock from the and acceptable level of risk for design criteria sediment basin to reduce the chance of damage as it relates to hazards to life or property. to the embankments and outlet/drainage structures. Excavated Material. The material excavated from the sediment basin shall be placed so that If earth basins are used, consider including two its weight will not endanger the stability of the basins so one can dry out for cleaning while the sediment basin side slopes and so that it will not other is being used to settle solids. be washed back into the sediment basin by rainfall. It shall be disposed of in one of the Sediment basins for agricultural waste require following ways: continuing management and maintenance. They 1. Uniformly spread to a height that does not should have solids removed frequently to exceed 3 ft, with the top graded to a function properly. continuous slope away from the sediment basin. PLANS AND SPECIFICATIONS 2. Uniformly placed or shaped reasonably well, with side slopes assuming a natural angle of Use Arizona standard drawings to the extent repose. The excavated material will be possible. These may be supplemented by placed at a distance equal to the depth of the additional drawings or specification notes on sediment basin but not less than 12 ft from the drawings to provide full installation the edge of the sediment basin. instructions. 3. Shaped to a designed form that blends visually with the landscape. Construction plans shall include all components 4. Used for low embankment and leveling. needed for the safe operation of the proposed 5. Hauled away. improvements such as railing, fencing, or warning signs as appropriate. The plans shall Flow Measurement. A water measurement address operations near existing utilities, trench device or structure (flow meter, ramp flume, excavations and any other items related to weir, etc.) may be installed to manage water construction of the structure that may pose a applications and for on-going evaluation of safety risk to those involved. system performance. Manufacturer’s recommendations or sound engineering Development and preparation of plans and guidance must be followed regarding size, specifications for sediment basins shall be site placement, orientation, etc. specific, guided by the National Engineering Handbook, (NEH) Part 641 “Drafting and Considerations for Waste Management Drawings” and Part 642 “Specifications for Where possible, the sediment basin surface area Construction Contracts”, and shall be in should be at least five percent of the size of the keeping with this standard and shall describe the sediment contributing area for effective removal requirements for applying the practice according of light weight sediment from liquids. Sediment to this standard. basin bottoms should be relatively flat with positive slope toward the sediment basin outlet The plans and specifications shall include all where possible, to facilitate sediment removal. details, material requirements, quantities, construction requirements, equipment

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 11 of 14 October 2010

Standard 350 requirements, and all other documents control, pipe cradle, and joints; cut/fill sections necessary for construction and completion of and shoulder side slopes; and earthfill this practice. Construction plans shall include compaction methods; all components needed for the safe operation of  Details of the inlet and outlet system, the proposed improvements such as railing, showing dimensions and reinforcement details; fencing, or warning signs as appropriate. The system components and appurtenances, as plans shall address operations near existing required; utilities, trench excavations and any other items  Location, size, type, length and invert related to construction of the structure that may elevations of all water control facilities or pose a safety risk to those involved. Include as a drainage features, if applicable, for proper minimum, the following in the plans and system functionality; specifications:  Site specific construction, notes, details or  Project location map, including section, specifications that describe in writing (if township and range, North arrow, necessary) site specific installation requirements cooperator/owner acknowledgement and of the sediment basin, drainage structures, certification signature blocks, engineering job culverts, headwalls, geotextile, rock, etc.; class (cover sheet);  Use Arizona Construction and Material  References that the owner/cooperator are Specifications for each item of work and responsible for all permits, rights-of-way, material, as applicable and available. easements and the contact, coordination and Additional specifications may need to be written location determination of any existing utilities or to provide full material and installation clearances (buried utility disclaimer); instructions. Fill in blanks and add or delete  If applicable, a map showing the location of items from the specifications to make them fit the the practice(s) or system in reference to a known job as needed. or established benchmark or reference point with the location, description and elevation All designs completed by non-NRCS personal clearly shown. Topographical features and/or shall meet minimum State licensing board and controls shall be shown, showing tie in with regulatory requirements and NRCS existing or other planned practices; requirements and criteria as outlined in the  Field surveys and notes, soil investigations or General Manual, the National Engineering geologic soil boring locations and soil Manual (including Arizona Supplements), and classifications, earthwork or material the National Engineering Handbook. estimates/quantities (foundation or subgrade preparation and requirements); ONCE ALL PARTIES HAVE ACCEPTED AND  A plan view of the location and layout of the SIGNED THE PLANS AND SPECIFICATIONS, sediment basin. (i.e., alignment, stationing, NO CHANGES SHALL BE MADE TO THE topographical features, and reference to existing DRAWINGS OR SPECIFICATIONS WITHOUT or proposed features or facilities; original PRIOR APPROVAL OF NRCS. ground elevations and planned or design elevation; applicable erosion controls for inlets OPERATION AND MAINTENANCE or outlets; requirements for diverting water, dewatering the site, and sediment disposal; Prepare an operation and maintenance (O&M) seeding requirements, if needed; plan that is specific to the site and/or facilities construction/installation criteria, State and installed for use by the landowner, cooperator Federal [OSHA] safety requirements; borrow or operator responsible for operation and areas location and dimensions; maintenance and shall be commensurate with  Profile view and typical cross section of the the size and complexity of the project. The plan basin, excavations, embankments and/or shall contain the operational requirements for spillways; details for pipe conduits, including emptying the sediment basin if its capacity is invert elevations, size, type of material, seepage exceeded during its design life.

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 12 of 14 October 2010

Standard 350

liner or the operations need to include the The following actions shall be carried out to necessary liner repairs. ensure the practice functions as intended  For AWMSs, the plan must include the design throughout its expected life. These actions schedule of required sediment basin sediment include normal repetitive activities in the removal operations, and lot cleanings. application and use of the practice (operation),  Eradicate or otherwise remove all rodents or repair, and upkeep. The minimum requirements burrowing animals that have or may potentially to be addressed in the operation and damage any part of the delivery or application maintenance plan are: facilities. Immediately repair any damage  Periodic inspections and maintenance of the caused by their activity. embankment, principal and auxiliary spillways  Immediately repair any damage resulting and dewatering device especially following from vandalism, vehicles, or livestock. significant runoff events.  Install and maintain fences to prevent  Periodic checks and removal of debris, livestock access where excessive trampling of foreign material obstructions, or blockage as banks or ditch may occur, and do not allow necessary from trash racks, ditch/pipe inlets, livestock near equipment during operation. outlets and structures to assure proper operation. REFERENCES  Periodic cleaning and re-grading of collection facilities (fields, ditches, pipes,  California Quality Association. structures) to maintain proper flow lines and 2003. California Stormwater BMP Handbook, functionality Construction. Menlo Park, CA.  Prompt repair or replacement of damaged  Center for Watershed Protection. 2000. components. Improving the Trapping Efficiency of Sediment  Prompt removal of sediment when it reaches Basins, Article 58, The Practice of Watershed pre-determined storage elevations. Sediment Protection: Techniques for Protecting and removed from the basin will be placed and Restoring Urban Watersheds. Ellicott City, MD. spread to prevent re-entry to the basin and  Department of Conservation and Recreation, streams. Commonwealth of Virginia. 1992. Virginia  Periodic removal of sediment from traps Erosion and Sediment Control Handbook, 3rd and/or storage facilities to maintain design Edition, Richmond, VA capacity and efficiency.  Jarrett, A. R. August 1998. Controlling the  Periodic mowing of vegetation to control of Dewatering of Sedimentation Basins, trees, brush and invasive species and to prevent Agricultural and Biological Engineering, the establishment of undesirable species. Pennsylvania State University, University Park,  Maintain vigorous growth of vegetative PA. coverings, this may include re-seeding,  North Carolina Department of Environmental fertilization, and application or herbicides. and Natural Resources, Division of Land Specify rates of seed, mulch, and fertilizer, Resources. 2006. North Carolina Erosion and appropriate planting dates, and method(s) of Sediment Control Planning and Design Manual. establishment. Raleigh, NC.  Periodic inspection of safety components and  Tennessee Erosion and Sediment Control immediate repair if necessary. Handbook . 2002. Tennessee Department of  Cleaning of pipe outlets, removal of sediment Environment and Conservation. Nashville, TN from basin, repair or filling of rills and eroded  USDA Natural Resources Conservation embankment fills, repair of any erosion in Service & Illinois Environmental Protection emergency spillway. Agency. 2002. Illinois Urban Manual.  In sediment basins with liners, cleaning Champaign, IL. operations will need to avoid damage to the

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 13 of 14 October 2010

Standard 350

 USDA Natural Resources Conservation Service. 1983. National Engineering Handbook, Section 3 – Sedimentation. Washington, DC  USDA-NRCS, Engineering Technical Release (TR)-12, Procedure – Sediment Storage Requirements for Reservoirs; TR-60, Earth Dams and Reservoirs; TR-62 Engineering Layout, Notes, Staking and Calculations  USDA-NRCS, eFOTG, Arizona Conservation Practice Standard and Specification 378, Pond  National Engineering Handbook - Part 650, Engineering Field Handbook, Chapter 1 – Engineering Surveys; Chapter 2 – Hydrology; Chapter 3 – Hydraulics; Chapter 4 – Elementary Soils Engineering; Chapter 5 – Preparation of Engineering Plans; Chapter 6 – Structures; Chapter 11 – Ponds and Reservoirs; and Chapter 17 – Construction & Construction Materials  National Engineering Handbook (NEH) Part 531 – Geology 531.31; Part 630 – Hydrologic Engineering; Part 634 – Hydraulic Engineering; Part 636 – Structural Engineering; Part 639 – Erosion Control Engineering; Part 652 – Irrigation Guide; USDA, Natural Resources Conservation Service  National Environmental Compliance Handbook  General Manual, Title 420-Part 401, Title 450-Part 401, Title 190-Parts 410.22 and 410.26  National Planning Procedures Handbook  USDA NRCS, Engineering Design Standards – Far West States  National Cultural Resources Handbook  USDA-NRCS, National Engineering Manual (NEM), 2nd Edition  NRCS Construction Specification 32, Structure Concrete

NRCS Field Office Tech Guide, Section IV NRCS-AZ Page 14 of 14 October 2010