Current through Register Vol. XLI, No. 24, June 14, 2024
Section 47-34-7 - Design Requirements7.1. Hydrologic Considerations. 7.1.a. General Hydrologic Requirements. 7.1.a.1. Hydrologic Investigation. 7.1.a.1.A. A survey shall be conducted to evaluate soil types, land use, land slope, watershed area, runoff curve number, and any other factors needed to establish watershed characteristics. A summary of all hydrologic and hydraulic data compiled in the initial site investigation and used in the analysis shall be included in table or figure form in the plan package.7.1.a.1.B. A stream flow analysis shall be conducted to evaluate stream flow quantity and quality as it affects the dam and its appurtenances.7.1.a.2. Design Storm Requirements - The design storm and any incremental reduction of the design storm proposed by the applicant is subject to approval by the Secretary. All dams shall be designed to meet the following minimum hydrologic criteria based upon hazard classification:7.1.a.2.A. Class 1 Dams - Class 1 dams shall be designed for the probable maximum precipitation of six (6) hours in duration. The design precipitation for a Class 1 dam may be reduced based on Risk Assessment (subdivision 3.5.d.), but in no case to less than seventy percent (70%) of the probable maximum precipitation.7.1.a.2.B. Class 2 Dams - Class 2 dams shall be designed for fifty percent (50%) of a probable maximum precipitation of six (6) hours duration. The design precipitation for a Class 2 dam may be reduced based on Risk Assessment (subdivision 3.5.d.), but in no case to less than twenty-five percent (25%) of the probable maximum precipitation.7.1.a.2.C. Class 3 Dams - Class 3 dams shall be designed for twenty-five percent (25%) of a probable maximum precipitation of six (6) hours in duration. The design precipitation for a Class 3 dam may be reduced based on Risk Assessment (subdivision 3.5.d.), but in no case to less than a P100 rainfall of six (6) hours in duration.7.1.a.2.D. Class 4 Dams - Class 4 dams shall be designed for a P100 rainfall of six (6) hours in duration.7.1.a.3. Antecedent Moisture Conditions - Where applicable to the development of a hydrograph, Antecedent Moisture Condition II (AMC II) may be used unless a different condition class is required by the Secretary.7.1.a.4. Flood Routings - An analysis shall be performed for the reservoir and spillways which includes inflow hydrographs, stage storage curves, stage discharge curves, and routings. The spillways must be able to safely discharge that portion of the design storm that is not stored in the reservoir. If a computer analysis is used, the input data and output results must be clearly labeled and identified. Trial calculations or intermediate results not relevant to the final results may be omitted from the plan package.7.1.b. Specific Hydrologic Requirements.7.1.b.1. Embankment Dams.7.1.b.1.A. Storage and Discharge.7.1.b.1.A.1. Class 1 dams designed with either an open channel spillway only or with an emergency spillway and a principal spillway together must be capable of discharging that portion of the design storm that cannot be safely stored in the impoundment. Class 1 dams designed with a decant or principal spillway only must be capable of storing the volume of water generated by a PMP rainfall event of six (6) hours in duration. The design of a Class 1 dam must assure that ninety percent (90%) of the stored volume of the design storm will be discharged within ten (10) days after the storm event.7.1.b.1.A.2. Class 2 dams must be designed with either an open channel spillway only or a combination of principal and emergency spillways. A Class 2 dam shall be capable of passing that portion of the design storm that cannot be safely stored in the impoundment. The design of a Class 2 dam must assure that ninety percent (90%) of the stored volume of the design storm will be discharged within ten (10) days after the storm event.7.1.b.1.A.3. Class 3 dams must be designed with either an open channel spillway only or a combination of principal and emergency spillways. A Class 3 dam shall be capable of passing that portion of the design storm that cannot be safely stored in the impoundment. The design of a Class 3 dam must assure that ninety percent (90%) of the stored volume of the design storm will be discharged within ten (10) days after the storm event.7.1.b.1.B. Surface Drainage Control - Surface drainage control devices (e.g., vegetated slopes, benches, groin ditches, and collection channels) shall be provided as necessary to protect the dam and its appurtenances from the effects of erosion. Riprap or other erosion protection measures shall be included where excessive velocity is anticipated or experienced. All surface drainage control devices must be designed to exit safely beyond the downstream toe of an embankment in a natural drainway capable of carrying the design flow without excessive erosion. The 50-year, 6-hour rainfall event shall be used as the design storm for surface drainage systems.7.1.b.1.C. Spillway Frequency of Operation - Outlet works that incorporate vegetated earth or unlined earth emergency spillways shall be designed so that the average frequency of operation is no greater than the following recurrence schedule, based upon a 6-hour rainfall event:7.1.b.1.C.1. Class 1 Dams - Once in one hundred (100) years.7.1.b.1.C.2. Class 2 Dams - Once in fifty (50) years.7.1.b.1.C.3. Class 3 and Class 4 Dams - Once in twenty-five (25) years.7.1.b.1.D. Overtopping Embankments - Regardless of their hazard classification, dams designed to overtop in accordance with the provisions of subparagraph 7.4.b.1.E. shall not overtop more frequently than once in one hundred (100) years, based upon a 6-hour rainfall event.7.1.b.2. Gravity Dams - Gravity dams may be designed in the same manner as the corresponding hazard classes of embankment type dams in subparagraph 7.1.b.1.A. except that designed overtopping of the dam may be substituted for the emergency spillway requirements.7.1.b.3. Waste Disposal Dams. 7.1.b.3.A. Storage and Discharge - The following storage and discharge systems may be used in design of waste disposal dams:7.1.b.3.A.1. Open Channel Only or Emergency Spillway with Principal Spillway - A dam designed with either an open channel spillway only or with an emergency spillway and a principal spillway together shall be capable of discharging that portion of the design storm that cannot be safely stored in the impoundment. This type of design must assure that ninety percent (90%) of the stored volume of the design storm will be discharged within ten (10) days after the storm event. Slurry impoundments shall be provided with a means of removing water to maintain the lowest practical water level.7.1.b.3.A.2. Principal Spillway or Decant Only - A dam designed with a decant or principal spillway only shall be capable of storing the volume equivalent to a minimum of one (1) design storm. Risk assessment shall not be applied to dams with principal spillway or decant only. This type of design must assure that ninety percent (90%) of the stored volume of the design storm will be discharged within ten (10) days after the storm event. Slurry impoundments shall be provided with a means of removing water to maintain the lowest practical water level.7.1.b.3.A.3. No Outlet Works - A dam designed without discharge structures shall be capable of storing the volume equal to a minimum of two (2) design storms. Risk assessment shall not be applied to dams with no outlet works. Water shall be removed from the impoundment to its lowest practical level by pumping or other means if storm water reduces the storage capacity to one (1) design storm or less.7.2. Hydraulic Considerations. 7.2.a. General Hydraulic Requirements. 7.2.a.1. Hydraulic Analysis - Using standard engineering practices, a hydraulic analysis shall be performed for the spillways and surface drainage system. Typical cross-section design techniques may be used where constant slopes are encountered. All hydraulic structures shall be designed to safely control the velocity of water in order to prevent excessive erosion. Accepted engineering practices shall be used to design riprap, non-flexible channel linings, bedding, and energy dissipators.7.2.b. Specific Hydraulic Requirements.7.2.b.1. Open Channels - Open channels, including open channel spillways, shall be analyzed for flow depth, velocity, nonuniform flow conditions, super-elevation, and hydraulic jumps.7.2.b.1.A. Stage Discharge - Where an open channel is used as a spillway, a stage discharge rating shall be developed using standard engineering practices for the type and shape of the spillway. In developing the rating, increase in upstream water depth due to change in velocity head must be considered.7.2.b.1.B. Water Surface Profiles - Where channel slopes or cross-sections vary and nonuniform flow conditions result, a water surface profile may be necessary in order to analyze the channel flow depths and the location of hydraulic jumps.7.2.b.1.C. Hydraulic Jumps - Where hydraulic jumps will occur, channel sidewall height shall be sufficient to contain the jump. The channel lining shall be designed to withstand the hydraulic jump without damage.7.2.b.1.D. Critical Flows - Channels shall be designed so that water will not flow at critical depth for extended distances. In channels of varying slope or cross-section where nonuniform flow occurs, the transition through critical flow shall be as rapid as possible.7.2.b.1.E. Super-elevation - Channel walls shall be designed to contain super-elevated flows in curves. Where curves occur in spillway channels, the Secretary may approve super-elevation wall height based upon one-half of the design flow, but not less than the P100 design flow, provided the excess overflow will impinge on natural ground and will not endanger the dam, human life, or property.7.2.b.2. Closed Conduit Systems - Closed conduit systems including principal spillways, risers, and pipes shall be analyzed to determine the controlling limits of weir, orifice, and pipe flows.7.2.b.2.A. Risers and Drop Inlets - Risers shall be protected with a designed trash rack and anti-vortex device. The drop inlet shall be sized to provide a rapid transition from partial to full pipe flow conditions.7.2.b.2.B. Stage Discharge - When a closed conduit system is used as a principal system, a stage discharge rating shall be developed using standard engineering practices for weir, orifice, and pipe flow calculations.7.2.b.2.C. Slug Flow - Conduit systems shall be designed to avoid formation of alternating partial and full pipe flow conditions through proper selection of pipe slope and headwater or tailwater conditions.7.3. Geotechnical Considerations. 7.3.a. Geotechnical Investigation - A geotechnical investigation shall be performed. The quantity, location, and depth of borings, test pits, or trenches must be adequate for the evaluation of the bearing capacity and subsurface conditions for the proposed structure and may vary based upon the height, impoundment volume, and hazard classification of the dam. Factors to be considered include depth of soil, characteristics of bedrock, and determination of groundwater location. Results of in-situ testing and soil sampling shall be reported in the plan package. Soil profiles shall be utilized for critical foundation locations of the structure, spillways, and other pertinent locations which affect the safety of the structure. A geological study shall also be conducted to evaluate stratigraphy, landslides, bedrock discontinuities such as soft seams, joints, joint systems, bedding planes, and fault zones which may adversely affect the structure's performance. Past and future mining including thickness of coal seams, depth and type of rock above the coal seam, and previous or expected subsidence problems shall be considered where subsidence may affect the safety of the structure. 7.3.a.1. Project Area Survey - A project area survey shall be conducted to establish baselines and elevations of the dam embankments, reservoir and borrow areas, and appurtenant structures. The survey shall locate all test pits, borings, gas wells, oil wells, water wells, mine openings, landslides, and areas of natural seepage.7.3.a.2. Borrow Areas - Borrow areas shall be evaluated for appropriate construction materials and required volume. Borrow areas and excavation materials shall be tested to determine the suitability of material for use in embankments or drains.7.3.b. Laboratory Testing - Laboratory tests shall be conducted on a sufficient number of samples of foundation and embankment materials to provide an accurate representation of soil conditions. Tests shall include, but not be limited to, a complete soil classification including grain size, sieve, hydrometer analysis, Atterberg limits, density, water content, compaction tests, shear strength, consolidation, and permeability where applicable. Compaction and proctor curves shall be developed for all fill materials as appropriate.7.3.c. Geotechnical Evaluation - A summary of all geotechnical data determined in the initial site geotechnical investigation and used in the analysis shall be included in table or figure form in the plan package.7.3.c.1. Seepage Analysis - An analysis of seepage and its detrimental effects on structural integrity shall be made. The analysis shall include consideration of potential piping in the embankment, foundations, and abutments. Seepage control measures shall be specified as necessary in order to enhance the stability of the embankment and adjacent area. Drainage systems shall be designed and constructed using a material approved by the Secretary and shall be protected by a properly designed filter zone using standard geotechnical engineering design practices. The design shall specify methods for sealing or controlling seepage encountered in foundation zones during construction. 7.3.c.1.A. Foundation Treatment - If analysis indicates a highly fractured foundation, the engineer shall specify necessary treatment of the foundation zone including, but not limited to, foundation grout curtains, dental concrete treatment of fractures or overhangs, and detailed methods of foundation zone cleaning. Material used in grouts shall be specified in accordance with the provisions of subparagraph 7.4.a.1.B.7.3.c.2. Foundation Stability - The foundation must be designed to have adequate bearing capacity to support the embankment and any appurtenant works. Potential subsidence and settlement and their consequences shall be considered using standard engineering practices. Special attention shall be given to differential settlement which would lead to cracking of the dam. Spillway pipes on compressible foundations shall be protected from damage due to settlement.7.3.c.3. Landslides - The potential for landslides, as determined in the initial project area investigation, shall be evaluated by the engineer. If landslides noted in the project area could cause instability of the dam or appurtenant structures, blockage of spillways and other critical drainage structures, or overtopping of the dam by displacement of water in the reservoir area, such conditions shall be corrected to a minimum static safety factor of 1.5.7.4. Structural Considerations. 7.4.a. General Structural Requirements - All structures shall be designed to perform as intended for the design life of the dam with proper maintenance or replacement. 7.4.a.1. Structural Materials - Materials selected for use in the dam shall be of adequate quality and durability for the intended purpose of the structure. All structures shall be designed to have sufficient strength plus an adequate safety factor against failure during maximum anticipated loading conditions. 7.4.a.1.A. Earth Materials - Earth materials selected for use in dam construction shall be free from roots, brush, organic materials, construction waste, and other debris. Where rock or rock fill is specified, the rock shall be durable and not subject to slaking or breakdown. Size gradations of the earth materials shall be specified to perform as planned. Compaction requirements for earth materials shall be specified in the plan package.7.4.a.1.B. Concrete Design - Concrete shall be designed in accordance with standard engineering practices. Concrete design specifications shall include materials, proportioning, form-work, reinforcement, joints and embedded items, production, placing, repair of surface defects, finishing, curing and protection, testing, evaluation and acceptance, and allowable tolerances for acceptance. 7.4.a.1.B.1. Concrete Specifications - The engineer shall specify the nature of concrete to be used with sufficient detail for on-site quality control. The concrete may be specified by specific mix, aggregate, water content, additives, compressive strength, slump, and air entrainment or by reference to specific standards of concrete quality. If published standard specifications are referenced, a copy of the standard or pertinent sections of the standard shall be included in the plan package.7.4.a.1.B.2. Concrete Placement - The engineer shall specify methods and limits of placement of the concrete including foundation preparation, maximum lift height, maximum time allowed between mixing and placement, methods of working into forms and corners, methods of consolidation and use of vibrating devices, and allowable ambient air temperatures and concrete temperatures.7.4.a.1.B.3. Concrete Curing - The engineer shall specify the method of curing the concrete including moist curing or membrane curing, wetting, types of covering, acceptable curing temperature range of the concrete, any anticipated cold weather curing specifications or methods such as protection from freezing and insulation methods, hot weather placement methods and limitations, and curing time.7.4.a.1.B.4. Concrete Finishing - The engineer shall specify the type of finishing to be applied to the concrete and the acceptable temperature range.7.4.b. Specific Structural Requirements. 7.4.b.1. Embankment Dams. 7.4.b.1.A. Selection of Materials - Material selected for construction of embankments shall be select earth material that is free from roots, brush, organic matter, construction waste, and other debris. The material must not be subject to breakdown or chemical reaction. Unless otherwise approved by the Secretary, the selected material must be thoroughly tested for density, shear strength, liquid and plastic limits, and optimum moisture content. The source of the material and available quantities shall be identified and adequate sampling performed in order to attain consistent quality and soil characteristics.7.4.b.1.B. Seepage and Piping Control - The Secretary may require installation of a properly designed filter drain system to prevent embankment failure due to seepage and/or internal erosion of any dam which can cause loss of human life or major damage to dwellings, or commercial or industrial buildings, important public utilities, or where a high risk highway may be affected.7.4.b.1.C. Zoned Embankments.7.4.b.1.C.1. Filter Drains - Filter drains shall be used in embankment zones where necessary to intercept seepage, reduce phreatic level, and reduce potential for internal erosion. Drain outlets shall be visible, not submerged under normal conditions, unobstructed, and protected with an animal guard where conduits are utilized. 7.4.b.1.C.1(a). Gradations - The gradations of the filter material shall be sized to prevent or resist the migration of embankment material into the voids of the filter. The filter shall be permeable relative to the surrounding embankment material.7.4.b.1.C.1(b). Size - The filter drain shall be capable of passing the maximum anticipated seepage flows without excessive pore pressure. The combination of filter permeability and area shall be considered in sizing the drain.7.4.b.1.C.1(c). Durability - The material used in the filter shall be hard, durable material that is not subject to slaking, breakdown, or chemical reaction.7.4.b.1.C.1(d). Conduits - Perforated pipes may be used in the filter drain to increase capacity. Perforations shall be compatible with the filter gradations so that filter material will not enter the pipe. The pipe shall be capable of supporting the fill load and shall be of a material which will last for the design life of the structure. Corrugated metal pipe shall not be used in critical areas of the embankment or in any areas where the pipe is not reasonably accessible for replacement.7.4.b.1.C.1(e). Filter Cloth - Filter cloth shall not be used in critical areas of the embankment or in any areas where the cloth is not reasonably accessible for replacement. 7.4.b.1.C.2. Diaphragm Cutoff Walls - When concrete cutoff walls are used as an impermeable barrier, the concrete wall shall be placed upon an adequate foundation and be constructed of reinforced concrete. Where pipes pass through the concrete wall, adequate support for the pipe shall be provided to prevent differential settlement and pipe shearing.7.4.b.1.D. Embankment Stability -The following stability requirements apply to Class 1 through Class 3 dams. The Secretary may approve lower safety factors for Class 4 dams, based on engineering recommendations. 7.4.b.1.D.1. Embankment Safety Factors - Slope stability shall be analyzed to show that the embankment design achieves the following factors of safety under the conditions listed. Unless otherwise indicated, factors of safety requirements apply to both upstream and downstream slopes of the embankment:7.4.b.1.D.1(a) A safety factor of 1.5 for the embankment loading conditions specified in part 7.4.b.1.D.3.;7.4.b.1.D.1(b) An end of construction safety factor of 1.3;7.4.b.1.D.1(c) An upstream slope rapid drawdown safety factor of 1.2; and7.4.b.1.D.1(d) An earthquake safety factor under steady-state seepage conditions of 1.2 using seismic loading appropriate to the geological site conditions. 7.4.b.1.D.2. Appurtenance Structural Stability - Embankments constructed as part of an appurtenant structure where failure will lead to a dangerous condition in the dam shall achieve a static safety factor of 1.5.7.4.b.1.D.3. Embankment Loading Conditions - Loading conditions shall assume a long-term steady-state condition with the phreatic surface originating at the elevation of the emergency spillway crest for embankment dams with emergency spillways or at a maximum design pool elevation for embankment dams without spillways.7.4.b.1.D.4. Stability Analyses - All slope stability analyses shall be performed using standard engineering practices. Exceptions to this requirement will be allowed by the Secretary only where there is sufficient evidence to indicate that slope failures will not occur.7.4.b.1.D.4(a) Critical cross-sections of the dam using equal X and Y axes scales shall be provided in the plan package. The cross-sections shall show the embankment limits, foundation zones, soil zones, phreatic line, assumed reservoir elevation, stability arcs or failure planes through the dam, and resulting safety factors for each critical arc or failure plane shown.7.4.b.1.D.4(b) A listing of soil zone unit weights, angles of internal friction, and cohesion values for each soil shown on the cross-section shall be provided in the plan package. If an alternative analysis is utilized, assumed soil values of the analysis shall be shown.7.4.b.1.E. Overtopping Embankments. 7.4.b.1.E.1. Rock-Covered Embankments - Rock-covered embankments shall be designed so that the rocks selected will be sized to withstand the maximum depth and velocity of the overtopping flow and be individually placed to maximize the interlocking effect. A minimum of two (2) layers of boulders is required. Boulders shall cover the crest, downstream face, and necessary areas of the upstream face of the dam and extend beyond the dam abutments to the extent necessary to contain the overtopping flow depth. Graded smaller rock shall fill the voids where the boulders contact the embankment to prevent erosion due to flow through the voids. The rock cover may be covered with soil and vegetated, provided that the equipment used to place the soil will not break the rock.7.4.b.1.E.2. Roller-Compacted Concrete Embankments. Roller-compacted concrete lift thickness and width shall be sized to withstand the maximum anticipated loading and uplift forces. Filter drains and weep holes shall be provided to relieve hydrostatic pressure behind roller-compacted concrete facings. The roller-compacted concrete may be covered with soil and vegetated.7.4.b.2. Gravity Dams. The following stability requirements apply to Class 1 through Class 3 dams. The Secretary may approve lower safety factors for Class 4 dams, based on engineering recommendations.7.4.b.2.A. Stability Loading Conditions - Loading conditions for the stability analysis shall assume maximum overflow head from the design storm.7.4.b.2.B. Gravity Dam Stability. 7.4.b.2.B.1. Overturning - The reaction of all forces must act within the middle one-third of the base. This requirement may be modified by the Secretary if detailed computations prove that overturning will not occur.7.4.b.2.B.2. Sliding - The dam shall have a factor of safety against sliding of at least 3.0 for normal loading conditions and 1.5 for maximum loading conditions. The sliding factor of safety may be reduced to no less than 2.0 for normal loading conditions where intimate knowledge of subsurface conditions has resulted from a state-of-the-art subsurface investigation, testing program and design analysis. The subsurface investigation and testing necessary to reduce the factor of safety should include, but not be limited to: sampling and testing of weak zones such as discontinuities, joints, joint fill material, fracture zones, bedding planes, and faults and; determination of peak, ultimate and residual strengths of foundation materials. Design analyses should include, but not be limited to: three dimensional analyses of foundation strength resulting from the subsurface investigation. The adequacy of subsurface investigations, testing, and design analyses necessary to reduce the factor of safety is subject to approval by the Secretary.7.4.b.2.B.3. Bearing - The factor of safety against bearing failure shall be at least 1.5 for maximum stress at the downstream toe.7.4.b.3. Waste Disposal Dams - The potential for liquefaction must be considered and the design shall include safeguards against the development of this condition.7.4.b.4. Spillways - All spillways shall be designed to discharge an adequate distance beyond the downstream toe of the dam in a natural drainway to prevent erosion of the downstream toe or other detrimental effects to the dam structure. 7.4.b.4.A. Conduit Spillways - Inlets shall be protected by a designed trash rack and riser type spillways shall be designed to prevent detrimental vortexing. Risers shall have adequate weight to be non-buoyant and shall be of sufficient strength to withstand maximum dynamic water and ice forces. Foundations for risers shall be designed to support the riser without serious movement or deformation. 7.4.b.4.A.1. Conduits - Pipe conduits shall be placed on a designed foundation and bedding of sufficient strength to minimize settlement and other detrimental effects to the conduit. Anti-seep or anti-piping mechanisms shall be provided for all conduits passing through the dam, foundation, or abutments to control seepage along the pipe. Design allowances shall be made to compensate for differential settlement, elongation, and movement of the pipe conduit if the cradle is placed on a yielding foundation. Pipe conduits shall be of sufficient strength to support the maximum external loads and the maximum internal hydraulic pressure without leaking, and shall resist uplift pressures. The pipe conduit shall be constructed of material which will not deteriorate during the design life of the structure.7.4.b.4.A.1(a) Use of Corrugated Metal Pipes - Corrugated metal pipes, whether coated or uncoated, shall not be used in new Class 2 or new Class 1 dams. Corrugated metal pipes in existing dams must be either replaced with new pipe or retrofitted with an appropriate liner if the Secretary determines that the existing pipe constitutes a hazard to the proper operation of the dam because the pipe has developed leaks, has deteriorated, or has otherwise ceased to function properly. 7.4.b.4.A.2. Outlets - Pipe conduits shall be designed to outlet in a natural drainway or a designed channel leading to a natural drainway. An energy dissipator shall be provided to eliminate erosion at the pipe outlet and be designed for maximum pipe flow. If pipe blockage by animals may occur, the pipe outlet shall be protected by an animal guard.7.4.b.4.A.3. Gated Drain Pipe Required for New Freshwater Dams - All new freshwater dams shall have a gated drainpipe for draining the impoundment. The gate or valve shall be located in the reservoir or in the saturated zone upstream of the cutoff wall or impermeable barrier. If the gate is located within the embankment or structure, a service well shall be provided. The elevation of the gate system shall be such that the reservoir will be drained completely to original stream level. The drain system shall be designed to drain ninety percent (90%) of the volume of stored water at normal pool in ten (10) days including normal base flow and have a minimum capacity of three (3) times the normal base flow for the watershed with a headwater-to-diameter (HW/D) ratio of 1.5, unless otherwise approved by the Secretary. The drain conduit shall meet the requirements for conduits set forth in part 7.4.b.4.A.1. A designed trash rack shall be provided at the inlet of the drain. The controls to operate the drain gate shall be accessible without the use of specialized equipment or of divers. The drawdown rate for reservoir storage volumes in excess of two thousand (2000) acre-feet may be established by the Secretary.7.4.b.4.A.4. Existing Dams with Gated Drain Pipes - All existing dams currently equipped with a gated drain pipe must meet the design requirements of part 7.4.b.4.A.3. and continue to be operated and maintained with the gated drain pipe. If such a gate or valve was not previously installed, a gate or valve shall be installed in the reservoir or in the saturated zone upstream of the cutoff wall or impermeable barrier. The Secretary may approve reduced drawdown time and flow quantity requirements for existing drains. Drain systems not meeting the design requirements of part 7.4.b.4.A.3. or dams with leaking or inoperative drain systems must be repaired or modified to maintain the greatest practical capacity of the drain system. If installation of the upstream gate or valve is impractical without draining of the reservoir and reservoir drainage will cause major economic loss to the owner, the Secretary may approve delay of the upstream gate or valve installation until the next necessary draining of the reservoir, provided that the existing drain system is functioning properly and is not leaking in a manner that would create a serious problem. If the existing drain system develops a serious problem, the Secretary may order immediate remedial action. The Secretary may grant an exemption to this subpart when investigation of the existing drain system determines to the Secretary's satisfaction that installation of an upstream drain gate or valve is not feasible.7.4.b.4.A.5. The term "gate" or "valve" as used in this rule is a general term referring to a device used for controlling water flow.7.4.b.4.B. Open Spillways - Unless specifically excluded, spillways of this type include the various designs of open type spillways including open channel, side channel, chute, labyrinth, and ogee. 7.4.b.4.B.1. Earth Spillways - Spillways that are constructed of or in earth material shall be designed to pass the maximum design flow without excessive erosion. Earth spillways shall not be constructed over dam embankment fill material. 7.4.b.4.B.1(a) Flexible Linings - Vegetation, rock riprap, soil reinforcement, or other flexible linings may be used to increase flow quantities and velocities in earth spillways within design limits.7.4.b.4.B.2. Concrete Spillways.7.4.b.4.B.2(a) Concrete - The engineer shall specify the grade and strength of concrete to be used in the spillway construction. The concrete structure shall be of sufficient strength to withstand the maximum design applied load.7.4.b.4.B.2(b) Foundation - Concrete shall be placed on a prepared foundation and bedding capable of sustaining the applied loads without excessive deformation.7.4.b.4.B.2(c) Drains - Designed filter drains and water pressure relief devices shall be provided under concrete slabs and walls to collect and safely convey water from seepage or leakage of construction joints and to relieve uplift pressure from seepage conditions.7.4.b.4.B.2(d) Joints - Construction joints shall be made watertight by use of a sealant material. Sliding joints shall be supported by a slab to maintain alignment.7.4.b.4.B.2(e) Cutoff Barriers - Cutoff barriers keyed into the foundation shall be provided to prevent or reduce seepage flow under the spillway.7.4.b.4.B.2(f) Energy Dissipators - An energy dissipator shall be provided to reduce the hydraulic energy at the end of the spillway. The dissipator shall be designed to function properly for flows of at least one-half of the design spillway flow. Flows in excess of the design capacity of the energy dissipator shall not endanger the dam or its appurtenances and may result only in erosion. 7.4.b.4.B.3. Nonstandard Spillway Design - The Secretary may reject any spillway design if such design is of a nonstandard or untested nature and it is not possible to analytically predict the performance of the spillway or the detrimental effects of cross-waves, eddies, vortices, super-elevation, or hydraulic jumps within the spillway system.7.4.b.5. Water Supply Pipes - Water supply pipes through a dam shall be constructed of a long-life, high-strength material. Welded joints or mechanical joints with sealing rings, or an alternative sealing method approved by the Secretary, shall be utilized. Pipes shall be properly bedded to reduce differential settling or elongation. Anti-seep mechanisms or filter drains shall be provided to prevent piping along the exterior of the pipe. If the pipe is enclosed in or passes through concrete, the relative coefficients of expansion shall be considered. Anti-corrosive measures shall be employed if soil tests indicate corrosion may be a problem. An upstream shutoff valve shall be installed on all new dams or when upgrading existing dams where reservoirs are to be drained as part of the upgrading. The section of the pipe through the dam shall be capable of withstanding a minimum pressure of twice the maximum reservoir head. The pipe shall be pressure-tested for leaks at maximum reservoir head pressure prior to the final covering of the pipe installation.7.5. Miscellaneous Considerations. 7.5.a. Erosion and Sediment Control - Erosion and sediment control measures sufficient to comply with the provisions of paragraph 8.1.m. shall be included in the project design where the disturbed area within the site is less than NPDES limits. If the disturbed area within the site exceeds NPDES limits, a letter documenting submission of a NPDES permit application must be submitted in accordance with subparagraph 6.4.f.1.7.5.b. Waste Disposal Areas - The engineer shall delineate locations in the project area which are to be used as waste disposal areas.7.5.c. Instrumentation - The engineer shall recommend instrumentation as necessary to monitor and measure performance of new dams or modifications to existing dams. The engineer shall specify the types and purpose of the recommended instrumentation. 7.5.c.1. Piezometers or Observation Wells - Piezometers or observation wells may be required by the Secretary on embankment type dams to monitor phreatic level and water pressures in critical areas of the embankment and, if necessary, the foundation or abutments. All piezometer or well heads shall be anchored in concrete and protected from vandalism with a locking metal cylinder surrounding the piezometer or well pipe.7.5.c.2. Survey Monuments - Survey monuments may be required by the Secretary on embankment and gravity dams to monitor displacement, settlement, rotation, and deformation. Survey monuments on earth dams shall be sufficiently embedded into the structure to prevent localized movement of the monument. Protective casings shall be installed if necessary to prevent damage or forced movement of the survey point.7.5.d. Staged Construction - Waste disposal dams designed in stages of construction shall be capable of storing or passing the design storm specified in paragraph 7.1.a.2. and subparagraph 7.1.b.1.A. during all stages of construction except during the initial start-up period, unless otherwise approved by the Secretary. During the initial start-up period, the dam shall be capable of storing or passing the P100 rainfall event as soon as possible. Construction shall increase storm capacity, reaching the full design storm capacity within two (2) years.