Section 10.14 - Design and Construction Criteria for New and Existing Dams(1)General. Design and construction of dams shall comply with 302 CMR 10.14. Design and construction standards that are not included in 302 CMR 10.14, shall conform to design procedures established by: The U.S Army Corps of Engineers, the U.S. Bureau of Reclamation, the U.S. Natural Resources Conservation Service and other generally accepted engineering practices and principles. Where specific site conditions may exist which warrant appropriate changes in the following design and construction criteria, the Commissioner shall review and approve the design.(2)Foundations and Abutments. The foundations and abutments investigation shall consist of borings, test pits, and other subsurface exploration necessary to assess the soil, rock, and groundwater conditions.(3)Construction Materials. Specifications for construction materials shall establish minimum acceptance criteria so that anticipated design properties are achieved. If the use of onsite borrow materials is specified, exploration, testing, and calculations shall be performed to indicate that there are sufficient quantities of material available that meet the design criteria.(4)Surveys. Surveys shall be made with sufficient accuracy and scale to locate the proposed construction and to define the volume of the storage in the reservoir. The downstream area shall be investigated in order to delineate the area of potential damage in case of failure. Locations of centerlines, and other horizontal and vertical control points, shall be shown on a map of the site.(5)Hydrologic Investigation. The drainage area shall be determined. Present land use shall be considered in determining the runoff characteristics of the drainage area. All hydrologic assumptions and design calculations shall be included in the report.(6)Spillway Design. (a) The spillway system shall have a capacity to pass a flow resulting from a design storm, as indicated in the following table, unless the applicant provides calculations, designs and plans to show that the design flow can be stored, passed through, or passed over the dam without failure occurring. SPILLWAY DESIGN FLOOD DESIGN STORM
Hazard Potential | Size | Existing Dams | New Dams |
Low | small | 50 year | 100 year |
intermediate | 50 year | 100 year |
large | 100 year | 100 year |
Significant | small | 100 year | 500 year |
intermediate | 100 year | 500 year |
large | 500 year | 1/2 PMF |
High | small | 500 year | PMF |
intermediate | 1/2 PMF | PMF |
large | 1/2 PMF | PMF |
(b) Vegetated earth or unlined emergency spillway(s) will be approved when computations indicate that it will pass the design flood without jeopardizing the safety of the structure. The risk of recurring storms, excessive erosion, and inadequate vegetative cover will be considered acceptable in such a spillway when its average frequency of use is predicted to be no more than indicated in the following table. EMERGENCY SPILLWAY FREQUENCY TABLE
Hazard Potential | Size | Existing Dams | New Dams |
Low | small | 25 years | 25 years |
intermediate | 25 years | 25 years |
large | 25 years | 25 years |
Significant | small | 25 years | 50 years |
intermediate | 25 years | 50 years |
large | 50 years | 50 years |
High | small | 50 years | 100 years |
intermediate | 50 years | 100 years |
large | 100 years | 100 years |
(c) The Department recognizes that the relationships between valley slope and width, total reservoir storage, drainage area, and other hydrologic factors have a critical bearing on determining the safe spillway design flood. Rational selection of a safe spillway design flood for specific site conditions based on quantitative and relative impact analysis is acceptable. The spillway may be sized so that the increased downstream damage resulting from an overtopping failure of the dam (i.e., the selected spillway design capacity has been exceeded) would not be significant when as compared with the damage caused by the flood in the absence of dam overtopping failure. In lieu of quantitative and relative impact analysis, the preceding table shall be used as spillway design criteria.(d)Lined Spillways and Channels. The design report shall include design data criteria for open channel, drop, ogee, and chute spillways and other spillway types that include crest structures, walls, channel linings, and miscellaneous details. All masonry or concrete structures shall have joints that are relatively water tight and shall be placed on foundations capable of sustaining applied loads without undue deformation. Provisions must be made for handling leakage from the channel or under seepage from the foundation which might cause saturation of underlying materials or uplift against the undersurfaces.(7)Conduits. A gate or controlled conduit shall be provided to drain each reservoir.(a) Any new and/or existing conduit design shall include the computation of the minimum time required to drain the reservoir.(b) All pipe conduits shall convey water at the design velocity without damage to the interior surface.(c) Protection shall be provided to prohibit unsafe seepage along conduits through the dam, abutments, and foundations. The specific design for seepage protection along conduits shall be shown in the drawings and specifications.(d) Adequate allowances shall be incorporated in the design to compensate for differential settlement and possible elongation of the pipe conduit.(e) Trash racks shall be installed at the intake of conduits to prevent clogging the conduit.(f)Pipe Conduit Materials.1. Pipe conduits shall be designed to support the total external loads in addition to the total internal hydraulic pressure without leakage.2.Reinforced or Prestressed Concrete Pipe Conduits.a. All conduits shall be designed and constructed to remain watertight under maximum anticipated hydraulic pressure and maximum probable joint opening, including the effects of joint rotation and extensibility.b. Provisions for safe movement of the barrel shall be provided at each joint in the barrel and at the junction of the barrel and riser or inlet. Cradles shall be articulated if constructed on a yielding foundation.c. The owner's engineer shall submit the final design details of the proposed pipe to be used for all significant and high hazard potential dams.3.Corrugated Metal Pipe Conduits.a. Corrugated metal pipe shall not be used in any dam, except for special cases where the design engineer can adequately demonstrate satisfactory performance. Any exemption which allows their use must be issued in writing by the Commissioner.4.Dissipating Devices. All gates, valves, conduits and concrete channel outlets shall be provided with an energy dissipater designed and constructed to control erosion and prevent damage to the embankment or the downstream outlet or channel.(g) In the case when an alternative method(s) of drawdown is requested, the proponent shall submit with the permit application reasons why a waiver should be granted (i.e., contaminated sediment, funding issues, complexity of construction). The request for waiver shall demonstrate that the water in storage can be moved out of the reservoir by mechanical means. The project design report shall include a detailed description of the pumps, siphons, etc. that would be necessary to remove the stored water in a reasonable period of time and maintain the reservoir in a dry state if necessary. A detailed drawdown plan must be included in the design, that identifies the volume of water in storage, the rate of inflow under average inflow conditions, identification of pump equipment, or other means necessary to remove stored water and maintain a drawdown condition, the time it will take to lower the water level, etc. The alternative drawdown plan shall be included in the required Operation and Maintenance Manual (O&MM) and in the Emergency Action Plan (EAP), if required.(h) In the case where an existing conduit is in poor condition (i.e., severely deteriorated, structurally compromised, leaky) and the condition could compromise the structural stability of the existing dam, the design report shall address the compromised conduit condition (relining, slip lining, grouting or other feasible means) and bring the existing conduit to safe and good condition.(8)Seepage Control. (a) All dams shall be designed and constructed to prevent the development of instability due to excessive seepage forces, uplift forces, or loss of materials in the embankment, abutments, spillway areas, or foundation. Seepage analyses for design shall identify areas having high internal uplift or exit gradients.(b) The design shall include an embankment internal drainage system, a zoned embankment, a foundation cut-off, an upstream blanket, a sufficiently wide homogeneous section, or other methods to protect against instability from excessive seepage forces or high hydraulic gradients.(c) For high hazard potential dams, a flow net analysis shall be made to determine the location of the phreatic surface, flow lines, and equipotential lines within the embankment and its foundation. These analyses may be based on graphical construction, electrical or liquid analogs, soil prototype methods, or other generally accepted methods. The flow net and stability analysis shall be the maximum water storage elevation. Possible fluctuations in tail water elevation shall be included in the analysis. The flow net and seepage analysis shall be included in the final design report.(d) Piezometers for confirming the location of the phreatic surface assumed for seepage and slope stability analyses shall be considered by the design engineer for low and significant hazard potential dams and shall be required for high hazard potential dams. Where piezometers are required, their design, depths and locations shall be provided in the final design report.(9)Structural Stability and Slope Protection.(a) Design and construction of dams to assure structural stability shall be consistent with accepted engineering practice. The scope and degree of precision that will be required for a specific project will depend on the conditions of the site and the damage potential of the proposed structure. Consideration in design for structural stability shall include, but are not necessarily limited to, the following:1. The hazard potential of the dam under present downstream conditions and under conditions which would likely develop during the life of the reservoir;2. Foundation bearing capacity, compressibility, and permeability; the extent and reliability of the site investigation; and the predictability of the site and foundation conditions;3. The reliability of construction materials, such as borrow soils, in terms of sufficient volume to complete construction without unanticipated interruption and in terms of predictability of physical properties such as strength, permeability, and compressibility;4. Durability of construction materials;5. Construction conditions at the site;6. The degree of quality control to be exercised during construction;7. Pore pressure build-up during construction;8. The rate of filling the reservoir and the rate of possible reservoir drawdown;9. Tailwater conditions and the impact of drawdown;10. Possible effects of landslides and subsurface solution activity on the structural stability of the dam and spillway structures; and11. The extent of the proposed use of piezometers and other devices which will be used to monitor the completed dam and the means of access for inspections.(b) Slope stability analysis shall be considered by the design engineer for all embankment dams, or as required by the Commissioner, and is required for high hazard potential dams. Where slope stability analysis is required, documentation in the final design report, such analysis shall include the design cross section(s) showing the soil parameters assumed for analysis, the location of the phreatic surface assumed for analysis, stability computations, and the location and computed safety factor(s) for the most critical circle(s) or failure wedge(s).(c) Minimum factors of safety are listed in the following table. Final accepted factors of safety may depend upon the degree of confidence in the engineering data available. In selecting a minimum acceptable factor of safety, an evaluation should be made on both the degree of conservatism with which assumptions were made in choosing soil strength parameters and pore water pressures, and the influence of the method of analysis used.1.302 CMR 10.14(8)(c) shall not be applicable to embankments on clay shale foundations, soft sensitive clays, or materials with large strength loss under stresses.2. For embankments over 50 ft. high on relatively weak foundations, a minimum factor of safety of 1.4 shall be used. SLOPE STABILITY ANALYSIS MINIMUM FACTORS OF SAFETY
Loading Conditions | Minimum Factor of Safety Analyzed | Slope to be |
End of construction condition | 1.3 | upstream and downstream |
Sudden drawdown from maximum pool | >1.1* | upstream |
Sudden drawdown from spillway crest or top of gates | 1.2 | upstream |
Steady seepage with maximum storage pool | 1.5 | upstream and downstream |
Steady seepage with surcharge pool | 1.4 | downstream |
Earthquake (for steady seepage conditions with seismic loading using seismic coefficient method) | >1.0 | upstream and downstream |
* The factor of safety shall not be less than 1.5 when drawdown rate and pore water pressures developed from flow nets are used in the stability analyses and where rapid drawdown is a normal operating condition as with pumped storage reservoir.
(d) Foundation bearing capacity and sliding base analysis shall be considered for all dams and are required for high hazard potential dams. Where bearing capacity or sliding base analysis is required, documentation of assumptions, computations, and safety factors shall be included in the final design report.(e) Resistance of appurtenant structures against flotation uplift shall be provided for all dams. If the structures are anchored by dead weight alone, the buoyant weight shall be used for analysis. If the structures are anchored to soil or rock, the minimum factor of safety for that portion of the resistance provided by soil or rock anchorage shall be 2.0 unless the design engineer provides a thoroughly documented basis for using a lower safety factor.(f) For concrete, masonry, or other similar dams of relatively narrow cross section, resistance against overturning and sliding under maximum design loading conditions shall be considered; overturning and sliding stability computations shall be required for significant and high hazard potential dams.(g) The anticipated reservoir and tailwater drawdown conditions shall be considered in all stability computations and shall be included in the design documents provided in the final design report.(h) The slopes shall be protected against erosion by wave action, and the crest and downstream slope shall be protected against erosion due to wind and rain. Riprap and other erosion protection shall be provided over the full range in stages between the lowest drawdown elevation and at least two feet above maximum water storage elevation. Exemptions for specific site conditions such as special use slowly rising reservoirs or waste storage facilities may be approved in writing by the Commissioner upon written request by the Applicant.(i) All significant and high hazard potential dams shall be designed to withstand seismic accelerations of the following intensities: Zone 1 = 0.025 g., Zone 2 = 0.05 g., Zone 3 = 0.15. Zones refer to "Geologic Hazard Maps".(j)Loading Combinations. The following conditions and requirements are suitable in general for gravity dams of intermediate size. Loads which are not indicated such as wave action or any unusual loadings should be considered where applicable. Case I: Usual Loading Combination-Normal Operating Condition. The reservoir elevation is at the normal pool, as governed by the crest elevation of an overflow structure or the top of the closed spillway gates, whichever is greater. Normal tailwater is used. If applicable, horizontal silt pressure should also be considered.
Case II: Unusual Loading Combination-Flood Discharge. The projected inflow design flood up to and including the Probable Maximum Flood, if appropriate, that results in reservoir and tailwater elevations that exert the greatest head differential and uplift pressure upon the structure shall be used. However, unusual conditions, such as high tailwater, shall be examined on a case by case basis as it is possible that the worst case loading condition exists under other than extreme floods.
Case IIA: Unusual Loading Combination-Ice Case. I loading plus ice pressure, if applicable. Generally ice pressure will not be a factor in the stability analyses, but may affect the operation, or structural integrity of flash boards and spillway gates.
Case III: Extreme Loading Combination-Normal Operating with Earthquake. Case I loading except that the inertial force due to the earthquake acceleration of the dam, and the increased hydrostatic forces due to the reservoir reaction on the dam are added.
(k)Stability Criteria. Specific stability criteria for a particular loading combination shall be dependent upon the type of analysis being done (i.e. foundation or concrete analysis), the degree of understanding of the foundation-structure interaction and site geology, and, to some extent, on the method of analysis.1. For new dams, preliminary analyses shall be based upon more conservative criteria than final designs. As the design process progresses, the designer has available more sophisticated and detailed foundation information and material testing results. Therefore, when the unknowns associated with the preliminary designs are reduced by the final design stage, lower safety factors may be acceptable.2. For existing dams, assumptions used in the analysis shall be based upon construction records and the performance of the structures under historical flood loadings. In the absence of available design data and records, site investigations shall be conducted to verify all assumptions.3. Recommended safety factors shall apply to the calculations of stress and the shear-friction factor of safety within the structure, at the rock/concrete interface and in the foundation. Safety factors shall be determined using the gravity method of analysis. RECOMMENDED FACTORS OF SAFETY Dams having a high or significant hazard potential. |
Loading Condition | Factor of Safety |
Usual | 3.0 |
Unusual | 2.0 |
Extreme | >1.0 |
Dams having a low hazard potential. |
Loading Condition | Factor of Safety |
Usual | 20 |
Unusual | 1.25 |
Extreme | >1.0 |
(10)Design Life of a Dam. The selection of materials and equipment to be used in a dam and all of its appurtenant features shall either be based on sufficient quality and durability to function satisfactorily throughout the design life or to provide for safe and economical replacement within the design life span. The design life of a dam shall be the period of time the dam can be expected to perform effectively as planned. The design life of a dam shall be determined by the following:(a) The time required to fill the reservoir with sediment from the contributing watershed;(b) The durability of appurtenances and materials used to construct the dam; and(c) The time required to perform the specific function for which the dam was designed.(11)Additional Design Requirements.(a) All elements of the dam shall conform to good and generally accepted engineering practice. The safety factors, design standards, and design references that are used shall be included in the final design report.(b) Monitoring or inspection devices may be required by the Commissioner for use by the inspectors or owners during construction and filling and after completion of construction. The Commissioner may also require that such monitoring or inspection devices, existing or installed by requirement, be read and documented at specified intervals and copies of such be forwarded to his or her office.(12)Construction Schedule. The applicant shall submit a construction schedule that includes:(a) Suggested techniques and work force to be used to demonstrate that the dam will be constructed according to the plans and specifications;(b) An estimated time to complete the construction activities;(c) Techniques to be used to divert the stream flow to prevent interference with construction; and(d) The extent and method of quality control.(e) A determination of the likelihood of seasonal or winter shut down and any provisions or requirements to ensure safe dam operations during shut down period.(13)Proposed Changes In Design. The owner shall notify the Commissioner in writing of any proposed changes in design, plans, and specifications that will affect the stability of the dam. Rationale and analysis supporting the proposed changes must be provided. Approval shall be in the form of a written addendum to the Chapter 253 Permit and must be obtained prior to installation.(14)As-built Plans. Two complete sets of as-built plans shall be submitted to the Commissioner within 30 days of completion of the project.(15)Engineer's Certification. The registered professional civil engineer who has inspected the construction of the dam, shall submit a written statement bearing his or her professional seal that the dam and all appurtenances have been built, repaired, altered, or removed in conformance with the plans, specifications, and drawings approved by the Commissioner and that the dam is in compliance with 302 CMR 10.00. For repairs accomplished, the certification shall be for the repairs only.(16)Acceptable Design: Procedures and Technical References. The following represent acceptable design procedures and references:(a) The design procedures, manuals and criteria used by the United States Army Corps of Engineers;(b) The procedures, manuals, and criteria used by the United States Natural Resources Conservation Service (formerly US Soil Conservation Service);(c) The procedures, manuals, and criteria used by the US Bureau of Reclamation; and(d) Other procedures that are approved by the Commissioner.(17)Granting of Final Approval. Unless the Commissioner has reason to believe that the dam, on completion, is unsafe or not in compliance with any applicable requirement, regulation, or law, or of any condition or specification contained within the Permit, upon completion of construction and upon receipt of the engineer's statement, the Commissioner shall issue a final Certificate of Compliance certifying that the work has been completed in conformance with plans, specifications, drawings and conditions of the permit, subject to such terms as deemed necessary for the protection of life and property.Amended by Mass Register Issue 1332, eff. 2/10/2017.