Provided by Newron Consultants
• Planning for proposed reservoirs to accommodate storage volume for the intended use of water. Services include engineering geologic and civil engineering evaluations of proposed reservoir sites to determine feasibility of reservoir construction and to provide basis for storage permit applications. Newton also arranges and coordinates investigations for archeological and cultural resources that may be necessary.
• Assistance to owners of proposed reservoirs in preparing and submitting storage permit applications and related maps to the state water resources departments.
• Assistance to owners of proposed reservoirs in preparing and submitting Oregon Department of State Lands and Army Corps of Engineers permit applications that may be required.
• Preparation of engineering plans and specifications for construction of dams, reservoirs, primary outlet works and emergency spillways. These services include engineering geologic and civil engineering reports on site conditions, project feasibility, watershed conditions, design flood flows for spillway design, foundation preparation and suitability of on-site earth materials for dam construction.
• Conducting engineering and geologic inspections and oversight during dam and reservoir construction. This includes preparation and submittal of reports to regulatory agencies on construction and changes made to the project in response to field conditions or other purposes.
• Assisting owners in increasing storage capacity of existing reservoirs. Services include engineering geology and civil engineering to estimate and confirm existing storage volume, potential additional volume that can be achieved, improve existing infrastructure (dam, spillways, etc.) to accommodate increase in storage, and preparation, submittal and coordination with state regulatory agency on permit to authorize increase in storage.
• Design of repairs to existing dams for managing seepage through or beneath the dam structure, improve stability of the dam embankment slopes, or repair erosion in spillways.
Dams - Earth and Earth Dam Rehabilitation
Earth Dams, also called earthen, rolled-earth or simply earth-fill dams, are constructed of well compacted earth. A homogeneous rolled-earth dam is entirely constructed of one type of material but may contain a watertight concrete or clay core or upstream face, or sometimes with a hydraulic fill to produce a watertight core and a drain layer to collect seep water.
A zoned-earth dam has distinct parts or zones of dissimilar material, typically a locally plentiful shell with a watertight clay core. Modern zoned-earth embankments employ filter and drain zones to collect and remove seep water and preserve the integrity of the downstream shell zone. An outdated method of zoned earth dam construction utilized a hydraulic fill to produce a watertight core. Rolled-earth dams may also employ a watertight facing or core in the manner of a rock-fill dam. An interesting type of temporary earth dam occasionally used in high latitudes is the frozen-core dam, in which a coolant is circulated through pipes inside the dam to maintain a watertight region of permafrost within it.
Because earth dams can be constructed from materials found on-site or nearby, earth dams can be very cost-effective in regions where the cost of producing or bringing in concrete would be prohibitive.
Earth Dam Rehabilitation
All dams have some seepage as the impounded water seeks paths of least resistance through the dam and its foundation. Seepage must, however, be controlled in both velocity and quantity.
At most dams, some water will seep from the reservoir through the foundation. Where it is not intercepted by a subsurface drain, the seepage will emerge downstream from, or at the toe of the embankment. If the seepage forces are large enough, soil will be eroded from the foundation and be deposited in the shape of a cone around the outlet. If these "boils" appear, professional advice should be sought immediately. Seepage flow which is muddy and carrying soil particles may be evidence of "piping," and complete failure of the dam could occur within hours. Piping can occur along a spillway and other conduits through the embankment, and these areas should be closely inspected. Sinkholes that develop on the embankment are signs that piping has begun. A whirlpool in the lake surface may soon follow and then likely a rapid and complete failure of the dam. Emergency procedures, including downstream evacuation, must be implemented if this condition is noted.
A continuous or sudden drop in the normal lake level may be an indication that seepage is occurring. In this case, one or more locations of flowing water are usually noted downstream from the dam. This condition, in itself, may not be a serious problem, but will require frequent and close monitoring and professional assistance.
Controlling the content of the seepage or preventing seepage flow from removing soil particles is extremely important. Modern design practice incorporates this control into the embankment through the use of cutoffs, internal filters, and adequate drainage provisions. Control at points of seepage exit can be accomplished after construction by using weighted filters and providing proper drainage. The filter and drainage system should be designed to prevent migration of soil particles and still provide for passage of the seepage flow. The bottom layer of the weighted filter should be 6 to 12 inches of sand placed over the seepage area. The sand layer should be covered with a gravel layer of similar thickness. Larger rock should be placed next to complete the berm. This method will permit the seepage to drain freely, but prevent piping (removal) of soil particles. The weight of the berm will hold the filter in place and may also provide additional stability to the embankment and/or foundation.
The location of the seepage or wet area on the embankment or abutment is often a primary concern. Excessive seepage pressure or soil saturation can threaten the stability of the downstream slope of the dam or the abutment slopes. An abutment slide might block or damage the spillway outlet or other appurtenances. In these cases, not only must the seepage be controlled but the area must be dried out. This is sometimes accomplished by installing finger drains (lateral drains for specific locations). Seepage control systems must always be free-draining to be effective.
Regular surveillance and maintenance of internal embankment and foundation drainage outlets is also required. Normal maintenance consists of removing any soil or other material that obstructs flow. Internal repair is complicated and often impractical and should not be attempted without professional advice. The rate and content of flow emerging from these outlets should be monitored regularly.
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