Current through Register Vol. XLI, No. 44, November 1, 2024
Section 38-14-4 - Engineering Report RequirementsThe engineering report required to accompany the application for a certificate of approval shall contain the following information in the order listed:
4.1 Project Narrative - A general narrative and discussion of the project shall be submitted to include as required by the design concept a discussion of existing site conditions, local geology the design life of the facility, subsidence potential, design methodology backed up with design computations and data, method of construction to include clearing and grubbing, topsoil stockpiles, construction of surface and subsurface drainage facilities, phases of construction, routine inspection and maintenance, and timetable of construction, A description of the duties, responsibilities and lines of communication between those persons responsible for the design, construction and operation of the dam shall be included.4.2 Emergency Warning Systems - All owners of dams posing a hazard to human life shall include an emergency notification and evacuation procedure and shall include a list of appropriate agencies to be contacted in the event a dangerous condition develops. These agencies shall include as a minimum the Division of Oil and Gas of the Department of Energy, Office of Emergency Services and state and local law enforcement agencies.4.3 Hazard Classification - The hazard potential shall be determined by the applicant based on the potential loss that would result due to a failure and the classification determined as listed below: 4.3.1 Class A - Dams located in rural or agricultural areas where failure may damage farm buildings, agricultural land, or secondary highways. Failure of the structure would cause only loss of the structure and loss of property use such as related roads, but with little additional damage to adjacent property. Any impoundment exceeding 25 feet in height or 200 acre-feet storage volume or having a watershed exceeding 500 acres shall not be a Class A structure.4.3.2 Class B - Dams located in predominately rural agricultural areas where failure may damage isolated homes, primary highways or minor railroads or cause interruption of relatively important public utilities. Failure of the structure may cause great damage to property and project operations.4.3.3 Class C - Dams located where failure may cause loss of human life, serious damage to homes, industrial and commercial buildings, important public utilities, primary highways, or main railroads. This classification must be used if failure would cause possible loss of human life.4.4 Initial Site Investigation 4.4.1 Site Selection 4.4.1.1 Hazard Classification Evaluation 4.4.1.1.1 A complete upstream and downstream hazard evaluation shall be conducted based on Section 4.3. No dam shall be constructed so that upstream dwellings will be flooded during maximum pool conditions unless otherwise approved by the Director of the Division of Oil and Gas of the Department of Energy based on specific site conditions.4.4.1.1.2 A downstream, breach routing of the dam must be performed to justify a hazard classification of A or B if dwellings are located downstream.4.4.1.2 Site Survey - A site survey must be conducted to establish baselines and elevations of the dam embankments, reservoir and borrow areas, and appurtenant structures. The survey must locate all test pits, borings, mine openings, land-slides, etc.4.4.1.3 Borrow Areas - Suitable borrow areas shall be evaluated for appropriate construction materials and required volume.4.4.2 Geotechnical Investigation4.4.2.1 A geotechnical investigation shall be performed. The quantity, location and depth of borings, test pits or trenches shall be adequate for 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. Soil profiles may be required for critical locations in the structure, spillways and other pertinent locations which affect the safety of the structure. A geological study shall also be conducted to evaluate 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 to include thickness of seam, depth and type of rock above the seam, and previous or expected subsidence problems shall be considered where subsidence may affect the safety of the structure.4.4.2.2 Laboratory Investigation - Laboratory tests shall be conducted on foundation and embankment materials to include complete soil classification: grain size, sieve, and hydrometer analysis, Atterburg limits, density, water content, compaction tests, shear strength, consolidation and permeability where applicable. Compaction curves shall be developed for all fill materials as appropriate.4.4.3 Hydrologic Investigation4.4.3.1 A survey shall be conducted to determine soil types, land use, land slope, watershed area, runoff curve number, and any other factors needed to establish watershed characteristics.4.4.3.2 Stream flow analysis shall be conducted to determine stream flow quantity and quality as it affects the dam and its appurtenances.4.4.3.3 All necessary parameters to determine stream channel hydraulics shall be measured.4.5 Hydrology and Hydraulics 4.5.1 Design Data Required - A summary of all hydrologic and hydraulic data determined in the initial site investigation and used in the analysis (Section 4.4) shall be included in table or figure form.4.5.2 Design Requirements 4.5.2.1 Design Storm - All dams shall be designed to meet the following minimum hydrologic criteria based on hazard classification:4.5.2.1.1 Class A dams shall be designed for a minimum of P100+0.12(PMP-P100) inches of rainfall in six (6) hours plus three (3) feet of freeboard. If the storage X effective height is less than 3,000 (acre-feet X feet) then Soil Conservation Pond Standard 378 may be substituted.4.5.2.1.2 Class B dams shall be designed for a minimum of P100+0.40 (PMP-P100 inches of rainfall in six (6) hours plus three (3) feet of freeboard.4.5.2.1.3 Class C dams shall be designed for the probable maximum precipitation, or for 80 percent of the probable maximum precipitation plus three (3) feet of freeboard provided the watershed is less than ten (10) square miles in area.4.5.2.2 Storage and Discharge 4.5.2.2.1 Class A dams shall be designed with either an open channel spillway only, or a combination of principal and emergency spillways. The dam must be capable of passing that portion of the design storm that cannot be safely stored in the impoundment. Ninety (90) percent of the stored portion of the design storm shall be discharged within ten (10) days after the storm event.4.5.2.2.2 Class B dams shall be designed with either an open channel spillway only, or a combination of principal and emergency spillways. The dam must be capable of passing that portion of the design storm that cannot be safely stored in the impoundment. Ninety (90) percent of the stored portion of the design storm shall 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.4.5.2.2.3 Class C dams may be designed in one of three ways:4.5.2.2.3.1 A dam designed without discharge structures shall be capable of storing a minimum of two (2) probable maximum, 6 hour duration storms. 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) probable maximum storm or less.4.5.2.2.3.2 A dam designed with a decant or principal spillway only shall be capable of storing one (1) probable maximum, 6 hour duration storm. Ninety (90) percent of the stored portion of the storm shall 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.4.5.2.2.3.3 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 probable maximum storm that cannot be safely stored in the impoundment. Ninety (90) percent of the stored portion of the storm shall 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.4.5.2.3 Surface Drainage A diversion system shall be designed to protect the entire front slope of the dam from excessive erosion. All diversion systems shall exit safely beyond the toe of an embankment in a natural drainway capable of carrying the design flow without excessive erosion. The design storm for diversion systems shall be the 100 year, 6 hour duration storm event.
4.5.2.4 Spillways 4.5.2.4.1 All spillways shall exit in adequate distance beyond the toe of the embankment in a natural drainway to prevent erosion of the toe.4.5.2.4.2 Conduit spillway inlets must be protected by a designed trash rack and riser type spillways must be designed to prevent detrimental vortexing. An adequate foundation and bedding shall be designed for all conduits and risers. Anti-seep mechanisms shall be designed for all conduits. Conduits spillways shall be of sufficient strength to withstand the maximum load of fill above them and of suitable material to resist deterioration for the design life of the structure. Conduit spillways must also be designed to resist uplift pressures. The outlet of all conduits, where blockage by animals can occur, must be protected by an animal guard.4.5.2.4.3 All new freshwater dams must be designed with a gated drain pipe for draining the impoundment.4.5.2.5 Landslide Potential When locating all hydraulic structures the potential for landslides or slope failures as determined in the initial site investigation shall be evaluated according to Sections 4.6.4.3 and 4.6.5.
4.5.3 Hydrologic Analysis The hydrologic analysis shall be performed for the spillway and/or surface drainage system. This should include inflow hydrographs, stage storage curves, stage discharge curves and routings. The spillways shall safely discharge that portion of the design storm that is not stored in the reservoir. If a computer analysis is used, only the results of the analysis shall be included.
4.5.4 Hydraulic Analysis Using accepted engineering practices, a hydraulic analysis must be performed for the spillways and surface drainage system. Typical cross-section design techniques can be used where constant slopes are encountered. All hydraulic structures shall be designed to safely control the velocity to prevent excessive erosion. Accepted engineering practices shall be used to design rip-rap, non-flexible channel linings, bedding and energy dissipators.
4.6 Geotechnical Evaluation4.6.1 Design Data -- A summary of all geotechnical data determined in the initial site investigation (Section 4.4,2) and used in the analysis shall be included in table or figure form,4.6.2 Seepage Analyses - An analysis of seepage and its detrimental effects on structural integrity and on the environment shall be made. The analysis shall include consideration of potential piping in the embankment, foundation, and abutments. Seepage control will be required to insure stability of the embankment and adjacent areas. Drainage systems shall be designed and constructed of an approved material and protected by a properly designed filter zone using accepted geotechnical engineering design practices.4.6.3 Foundation Stability When locating dams, the potential for landslides as determined in the initial site investigation shall be evaluated according to Sections 4.6.4.3 and 4.6.5. Potential subsidence and settlement and their consequences must be considered using accepted engineering technology. Special attention should be given to differential settlement which could lead to cracking of the dam. Spillway pipes on compressible foundations must be protected from damage due to settlement. The foundation must have or must be treated to have adequate bearing capacity to support the embankment and any appurtenant works.
4.6.4 Stability Requirements4.6.4.1 Embankment stability Slope stability analyses will be required for construction and long term steady state conditions to achieve the following minimum factors of safety:
| Safety Factor |
Normal and Maximum Pool Conditions | 1.5 |
End of Construction | 1.3 |
Rapid Drawdown | 1.2 |
Seismic | 1.2 |
4.6.4.2 Appurtenance Structural Stability Embankments constructed as part of an appurtenant structure must achieve a static factor of safety of 1.5 where failure will lead to a dangerous condition in the dam.
4.6.4.3 Landslides If landslides noted in the dam site or reservoir areas will 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 landslides shall be corrected to a minimum static factor of safety of 1.5.
4.6.4.4 Special Considerations -- Gravity Structures4.6.4.4.1 Overturning -- The reaction of all forces must act within the middle one third of the base. Variation to this requirement may be given if detailed computations prove that overturning will not occur.4.6.4.4.2 Sliding - The dam must have a factor of safety against sliding of at least 4.0 for normal loading conditions and 1.5 for maximum loading conditions.4.6.4.4.3 Bearing - The factor of safety against bearing failure shall be at least 1.5 for maximum stress at the toe.4.6.5 Stability Analyses All slope stability analyses shall be performed using accepted engineering techniques. Exceptions to this requirement will be made only where there is sufficient evidence to indicate that slope failures will not occur.
4.6.6 Liquefaction The potential for liquefaction must be considered. Safeguards against the development of this condition shall be required.
4.7 Instrumentation Considerations for installation of instrumentation such as piezometer, settlement markers, slope indicators, and similar monitoring devices shall be included in the plan to monitor present conditions, construction conditions, and to verify design assumptions. A plan for installation, monitoring and maintaining these devices shall also be provided.
4.8 Specifications - Specifications for site development shall be provided to include as a minimum: clearing and grubbing; soil stockpiles; subdrain construction; slopes; grades; details of surface drainage facilities; spreading and compaction requirements to include lift thicknesses, moisture content and degree of compaction with appropriate compaction curves; material and/or gradation requirements for sub-drainage structures; pipes; concrete; anti-seep mechanisms; channel and slope protection (riprap, etc); installation and reading of monitoring devices; inspection and maintenance; revegetation; blasting safety; construction erosion and sediment control; and cutoff trenches.4.9 Maps and Drawings 4.9.1 Maps and plans shall be provided showing the site in relation to major highways, county seats, and major drainage. County highway maps may be used for this purpose.4.9.2 A map showing the limits of the watershed with respect to the site shall be provided. The minimum mapping requirement shall be a 71/2 minute USGS map with the site plotted on it.4.9.3 A plan view of the site shall be provided showing detailed contour intervals (5' maximum) including all disturbed and reservoir areas. Location of springs, seeps, underground mines, mine drainage and/or openings, the subdrain system, project stationing, cross-sections, borings and test pits, instrumentation, reference points and other pertinent data shall be included in the plan view.4.9.4 Cross-sections of the dam transversely and longitudinally shall be provided showing original ground, sub-drain locations, elevations, benches, spillways, and other pertinent features of the site. A cross-section shall be provided for stability computations showing the site at critical areas with subsurface data plotted.4.9.5 Cross-section and profiles of major drainage facilities shall be provided. Additional cross-sections shall be taken in all critical areas such as curves and weak areas.4.9.6 Construction drawings shall be provided for subdrains, spillways, anti-seep mechanisms, and other pertinent structures.4.10 Removal/Elimination Removal of a dam shall consist of the total elimination of its impounding capabilities in a safe and approved manner by one of the following methods:
4.10.1 Removal of the Embankment The embankment shall be completely removed to approximate original contour. A plan and timetable for removal shall be submitted.
4.10.2 Elimination of Impoundment The reservoir area shall be completely filled with suitable material in such a manner that will create a fill with a minimum long term static factor of safety of 1.5 unless otherwise approved by the Director. A plan and timetable for the modification shall be submitted.
4.10.3 Breaching 4.10.3.1 The embankment shall be breached with a design channel having the capacity to carry the peak runoff from the design storm corresponding to the dam's hazard classification. Channel protection shall be provided at least to a flow depth equal to the 100 year, 6 hour duration storm.4.10.3.2 Plans for removal shall be submitted which include a schedule for implementation.