5.1C – Stream Channel Modification – Dams and Levees, Operation and Maintenance
- Develop and implement a program to manage the operation and release of surface water from dams so that aquatic habitat and water quality meet objectives required to maintain or restore designated beneficial use(s).
- Develop and implement a program to manage maintenance activities that limit the application, generation, and migration of chemicals (including herbicides/pesticides and nutrients) and ensures the proper storage and disposal of toxic chemicals.
- Develop and implement a dam or levee safety program that includes regular safety inspection of the infrastructure; as well as operation and maintenance activities.
The construction of dams and levees has a high potential for adversely impacting the hydrology and quality of surface waters in rivers and streams as well as bordering riparian habitats. For the purposes of this management measure, dams are defined as constructed impoundments that are either (1) 25 feet or more in height and greater than 15 acre-feet in capacity, or (2) 6 feet or more in height and greater than 50 acre-feet in capacity. Levees are embankments or shaped mounds constructed for flood control or hurricane protection (USACE, 1981). Floodwalls or slurry-walls are longitudinal structures used to reduce flooding. Setback levees are levees set back a distance from the banks of a river or stream, these flood control structures can be constructed without disturbing the adjacent natural channel vegetation (riparian habitat), and cross section of the stream or river channel. Levees act like small earthen dams but are typically not subject to constant hydrostatic forces that dams are built to withstand. This is due, in part, to the changing hydraulic head behind levees, especially in California’s Mediterranean climate. Channelized rivers are typically contained between levees. Reservoirs or impoundments of water behind dams are often used for recreational boating activities. Boat wakes are waves caused by vessel acceleration and the shape of the vessel hull. Waves impact shorelines or streambanks causing erosion.
Dams’ affect to water quality upstream depends on the size of the impoundment or reservoir behind the dam. Dams capture sediment and organic materials, when this organic material accumulates – biological activity increases which can decrease the amount of dissolved oxygen in reservoir waters. Large and deep reservoirs tend to make surface water temperatures cooler and stratified, whereas smaller and shallow reservoirs increase surface water temperatures. Cooler water temperatures reduce the amount of dissolved oxygen absorption into the water column, thus reducing the amount available to aquatic life. Warmer waters increase biological activity, thus reducing the amount of dissolved oxygen available to aquatic life. Other potential water quality issues related to the operation and maintenance of dams include sedimentation from shoreline or streambank erosion caused by adjacent roads and/or recreational boating activities.
Recommended structures to improve dissolved oxygen levels in dam impoundments, tailwaters and/or reservoirs include the following:
- Gated conduits. These are hydraulic structures that divert the flow of water under the dam. They are designed to create turbulent mixing to enhance oxygen transfer.
- Spillway modifications. Spillways can be modified by cutting a notch to prevent water from plunging directly into the stilling basin.
- Reregulation weirs. This type of weir has been constructed from stone, wood, and aggregate. In addition to increasing the levels of dissolved oxygen in the tailwaters, reregulation weirs result in constant rate of flow farther downstream during periods when turbines are not in operation.
- Labyrinth weirs. This type of weir has extended crest length and is usually W-shaped. These weirs spread the flow out to prevent dangerous undertows in the plunge pool.
Recommended practices to improve dissolved oxygen levels in dam impoundments, tailwaters and/or reservoirs include the following:
- Pumping and injection systems. Water pumps have been used to move surface water containing higher concentrations of dissolved oxygen downward to mix with deeper waters as the two strata are entering the turbine. Oxygen injection systems use pure oxygen to increase levels of dissolved oxygen in reservoirs.
- Selective withdrawal. Multilevel intake devices in storage reservoirs allow for selective withdrawal of water based on temperature and dissolved oxygen levels.
- Turbine operation. Implementation of changes in the turbine start-up procedures can enlarge the zone of withdrawal to include more of the epilimnetic waters in downstream releases.
- Turbine venting. This is the practice of injecting air into water as it passes through a turbine.
Recommended practices for maintaining minimum flows downstream of dams include the following:
- Turbine Pulsing. Turbine pulsing is the operation of one turbine at a hydropower dam for a short duration at a regular time interval.
- Small Turbine Units: Install and maintain a separate, small turbine unit to maintain minimum flows and generate a constant supply of hydroelectric energy.
- Spilling, Sluicing, and/or Siphoning: Flows that bypass turbines also have the added benefit of improving dissolved oxygen. However, managing reservoir releases by spilling, sluicing, and/or siphoning can cause cavitation and vibration to dam structure.
- Refer to MM 5.2B, Flow and Temperature Maintenance for more information on how to determine the minimum flows necessary to maintain and/or restore beneficial uses.
Recommended practices for managing temperature downstream of dams includes the following:
- Shift strategic hydroelectric power plant operations from peak use to base load use. This can theoretically reduce power plant outputs of warmer water during peak use times (which is coincidentally when air conditioner use is at its peak and temperatures are highest) - to more predictable times when releases can be scheduled in advance.
- Manage flow releases to take advantage of thermal stratification in reservoirs during the summer months. Release water from the spillway to eliminate warm water in reservoir. Release water from river outlets at the bottom of the dam to release cold water into the stream.
Practices to restore or maintain aquatic and riparian habitat include the following:
- Flow augmentation, see MM 5.2B, Flow and Temperature Maintenance for more information.
- Use watershed protection practices to reduce the amount of nonpoint source pollution from entering reservoir and streams. Management practices include: reducing sediment and nutrient loading in the watershed; planting and maintaining riparian vegetation; eliminating barriers to fish migration; and providing greater aquatic and riparian habitat diversity (see MM 6, Wetlands, Riparian Areas, and Vegetated Treatment Systems and MM 3.1A, Urban Watershed Protection).
Practices to maintain fish passage include the following:
- Behavioral barriers. Such barriers use fish responses to external stimuli to keep fish away from the intakes or to attract them to a bypass.
- Physical barriers. These include barrier nets and stationary screens to prevent the entry of fish and other aquatic organisms into the intakes at a hydroelectric generating facility.
- Collection systems. These are used to capture fish by screening and/or netting, followed by transport by truck or barge to a downstream location.
- Diversion systems and fish ladders (or fish lifts) lead or force fish to bypasses that transport them to the natural water body below or above the dam. These structures enable upstream and downstream passage of mature fish; however they can cause fish mortality due to elevated stress (Larinier 2000).
- Maintain a spill and water budget. Water release through spillways provides minimum flows necessary for fish passage and is less dangerous than passage through turbines. The spill and water budget is the mechanism for increasing flows through dams during the out-migration of anadromous fish species.
- Transfer of fish runs. Transfer involves inducing anadromous fish species to use different spawning grounds in the vicinity of the impoundment.
- Constructed spawning beds. When the adverse effects of a dam on the aquatic habitat of an anadromous fish species are severe, one option may be to construct suitable replacement spawning beds.
Develop and implement a dam and levee safety program that includes regular safety inspection of the dam or levee infrastructure; and operation and maintenance activities.
The primary areas of structural failure are:
- loss of clay soils used as berms or other earthen structures;
- underseepage through course-grained soils from buried stream channels;
- leakage (underseepage) at the base of dams or levees;
- seepage along pipes or other buried conduits;
- erosion (including wave action) along spillways and shorelines or streambanks;
- cracking and movement of structural components;
- defects in structure; and
- improperly managed vegetation.
Practices to control chemical pollution from dam and levee operation and maintenance activities include the following:
- Develop and implement a spill prevention program. Spill procedure information should be posted, and persons trained in spill handling should be onsite or on call at all times. Materials for cleaning up spills should be kept onsite and easily available. Spills should be cleaned up immediately and the contaminated material properly disposed of.
- Prevent pollutant runoff that comes in contact with equipment by housing equipment on impervious surfaces with rain covers, i.e. garages or buildings.
- Establish regular vehicle inspections and maintain vehicles to prevent leaks. Provide a garage area to perform inspections and dispose of any used oil at your local hazardous waste site.
- Mix, transport, load, and apply pesticides, and dispose of their containers in accordance with the label. Fertilizers should be handled and applied properly; refer to MM 1D – Agriculture, Pest and Weed Management for more information.
Recommended practices to mitigate damage caused by shoreline and streambank erosion caused by adjacent roads and/or recreational boating:
- Use vegetative armor preferably over hard armor to protect stream-side of levee profile and reservoir shorelines from incision and erosion. Refer to MM 5.2A, Streambank and Shoreline Erosion Control for applicable management practices.
- Service roads adjacent to dams or levees can be a signification source of fine-grained sediment, for more information refer to MM 3.2A – Construction, Structural and Permanent.
- Refer to MM 4.2F - Marinas and Recreational Boating, Boat Operation for more information on how to manage stream bank and shoreline erosion caused by boat-generated waves.
- Federal Energy Regulatory Commission (FERC) through the Federal Water Power Act (FPA) regulates the licensing of dam construction and re-licensing of large dams used for hydropower. The FERC re-licensing process (18 CFR Parts 2, 4, 5, 9, 16, 375, and 385) allows for the equal consideration of beneficial uses which may have not been considered when the dam was originally constructed (before the Clean Water Act, Endangered Species Act, and other environmental laws were passed). In fact, under FPA section 4(e) FERC must give equal consideration to energy conservation; the protection and enhancement of fish and wildlife habitat, the protection of recreational opportunities, and the preservation of other aspects of environmental quality including water quality under SWRCBs Clean Water Act Section 401. FERC must operate and maintain a dam so that the best mix of beneficial uses are considered and managed.
- Bureau of Reclamation’s Dam Safety Program must ensure that dams are operated and maintained in a safe manner through inspections for safety deficiencies, analyses using current technologies and designs, and corrective actions, if needed, based on current engineering practices. In addition, future evaluations should include assessments of benefits forgone with the loss of a dam.
- California Department of Water Resources Fish Passage Improvement Program staff meet with local, State, and federal agencies and stakeholder partners to plan and implement projects to remove barriers that impede migration and spawning of anadromous fish species. This program’s Web site has a link to a table of dams removed in California.
- California Resources Agency, Department of Water Resources (DWR), Division of Safety of Dams conducts investigations of selected dams, which include a comprehensive review of all pertinent material contained in the Division’s files, a visual project inspection, technical studies when necessary, and preparation of a comprehensive report.
- Department of Homeland Security, Federal Emergency Management Agency, National Dam Safety Program (NDSP) is a partnership of the states, federal agencies, and other stakeholders to encourage individual and community responsibility for dam safety. Established by the Water Resources and Development Act of 1996, three components include grant assistance to States, and Dam Safety research and training.
- DWR, Delta Levees Program is responsible for improving the flood protection and ecosystem resources of the Delta Levee System. DWR sponsors locals, who undertake various improvement projects to achieve these ends for the benefit of Delta landowners, State Water Project contractors, and the ecological communities which depend on vital natural habitats. DWR manages these projects in cooperation with the Department of Fish and Game, the Reclamation Board, and other federal, State, and local agencies. The Delta Levees Program is an active participant in the CALFED process.
- DWR, FloodSAFE is a sustainable integrated flood management and emergency response system throughout California that improves public safety, protects and enhances environmental and cultural resources, and supports economic growth by reducing the probability of destructive floods, promoting beneficial floodplain processes, and lowering the damages caused by flooding.
- DWR, Levee Repair web pages provide a wide range of information on California's levee system and the efforts the State is undertaking to evaluate the stability of the system and implement critically needed repairs designed to protect our communities, farmlands, and infrastructure.
- NRCS, USDA Service Centers provides the address of a USDA Service Center and other Agency offices serving your area along with information on how to contact them. The local NRCS staff can provide technical assistance to small dam owners for operator and maintenance activities.
- DPR Fate Reviews contains environmental fate reviews for many herbicides that are used.
- Association of Dam Safety Officials (ASDSO) is a non-profit organization of state and federal dam safety regulators, dam owners/operators, dam designers, manufacturers/suppliers, academia, contractors and others interested in dam safety. Their mission is to advance and improve the safety of dams by supporting the dam safety community and state dam safety programs, raising awareness, facilitating cooperation, providing a forum for the exchange of information, representing dam safety interests before governments, providing outreach programs, and creating a unified community of dam safety advocates.
- California Salmonid Stream Habitat Restoration Manual explains and describes the DFG ground level approach to restoration of fishery resources, and standardizes the DFG’s descriptive terminology and technical methods. Principal emphasis is on salmon, steelhead, and trout; therefore, this manual is principally intended to be used to assist in restoration efforts for those species in California.
- USEPA, Spill Prevention Planning this fact sheet outlines key programmatic components to establishing spill prevention plans.
- California Department of Water Resources Fish Passage Improvement Program, Bibliography provides several references on fish species biology, dam removal, geomorphology, fish passage structures, riparian and aquatic habitat restoration, road crossings, and riparian vegetation.
- FAO, Fisheries Technical Paper 419. Dams, fish and fisheries: Opportunities, challenges and conflict resolution. Habitat loss or alteration, discharge modifications, changes in water quality and temperature, increased predation pressure, as well as delays in migration caused by dams, are discussed. Various technical solutions are suggested and critical points, that have to be considered in fishpass construction, are stressed. A non-exhaustive review of the current status of the use of fish facilities at dams throughout the world is presented, with the main target species considered from North America, Europe, Latin America, Africa, Australia, New Zealand, Japan and Asia.
- USACE, WQ Technical Note MS-01. 1995. Improvement of Reservoir Releases by Aeration. Provides background and calculation procedures for using a spreadsheet, AERATE.
- USFWS, Fish Passage Decision Support System (FPDSS) is an online application funded by the U.S. FWS Fish Passage Program. The FPDSS makes information about barriers to fish passage in the U.S. available to policy makers and the public.
Larinier, M. 2000. Dams and Fish Migration. Institute de Mecanique des Fluides, Toulouse, France.
USACE. 1981. Low-cost shore protection, final report on the shoreline erosion control demonstration program (Section 54). U.S. Army Corps of Engineers. Washington, DC.
USEPA. 2007. National Management Measures Guidance to Control Nonpoint Source Pollution from Hydromodification. EPA 841-B-07-002. U.S. Environmental Protection Agency, Washington, DC.