Dam decommissioning and return of river Rivers are connected systems - - PowerPoint PPT Presentation

Lesson 8

Dam decommissioning and return of river

Rivers are connected systems, and barriers such as dams, culverts and floodgates disconnect one

area from another. They prevent species from migrating – isolating previously connected populations.

Human impact on river ecosystems are: pollution, flow modifications, exotic species, harvesting.

Pollution is the result of human infrastructure around a river. Pollution enters the river, sometimes in small amounts, at many different locations along the length of the river. The clearing of forests to produce farmland has led to on-going erosion, with large quantities of sediment deposited into rivers. Agricultural intensification (substantial increases in fertiliser application and increased stock numbers) has resulted in nutrient and chemical loss to nearby streams and rivers. Elevated nutrient concentrations (nitrogen and phosphorus – key components of fertilisers) can result in the eutrophication of slow-moving waterways. Pollution can lower the pH of the water, affecting all organisms from algae to vertebrates. Biodiversity decreases with decreasing pH.

Flow modifications

• Dams affect river systems by disconnecting different areas.
• Water taken from rivers for irrigation can lower river flows
• Dams alter the flow, temperature and sediment in river systems. Reduced flow alters aquatic habitats –

reducing or removing populations of fish, invertebrates and plants that depend on the flow to bring food.

• Reduced flow also decreases tributary stream flow, changing habitats and altering the water table in the

stream aquifer. Consequently, riverside vegetation may be affected and decline in numbers. This may affect animal biodiversity, for example, bird species may leave the area if their habitat is lost or altered.

• Changes in water temperature due to flow modification can affect insect development by not allowing them

to complete their life cycle.

• Exotic species have been introduced to river systems sometimes intentionally (for example, for fishing

purposes or as food for other species) and sometimes unintentionally (for example, species come in on the bottom of boats or on fishing gear or they escape from pond areas during flooding, such as koi carp).

Urban areas add to this pollution when contaminants (PAHs and heavy metals) are washed off hard surfaces such as roads and drain into water systems. Sulfur dioxide and nitrous oxide emitted from factories and power stations enter river systems through acid

• rain. Sewage and effluent are discharged into rivers in some areas.

Excessive fishing in river ecosystems can drastically reduce numbers of species. Ecological impacts of dam and diversion channels construction, channelization and changes in the river cross-section geometry, may be synthesized as follows:

• Significant reduction of habitats diversity, since hydraulic works interfere with the natural continuity
• f the river physical borders, and make more homogeneous both the river bed and the flooded areas.
• Reduction in the native species diversity, caused by the disappearance of the species that de-

pend on seasonal flow differences, and spatial habitat variations to survive. Simultaneously, the exotic species gain a competitive advantage due to the before mentioned alterations.

River training’ refers to the structural measures which are taken to improve a river and its banks.

It is an important component in the prevention and mitigation of flash floods and flood control, as well as ensures safe passage of a flood. It reduces sediment transportation and minimize bed and bank erosion. River training structures are implemented with bioengineering techniques to lessen the negative effects on environment and landscape Check dams are used along river courses to control erosion. Gabions, concrete, logs, bamboo, and many

• ther materials are used. They decrease the morphological gradient of the torrent bed and reduce the

water velocity during a flood event by increasing the time of concentration and reducing the flood peak and solid transportation capacity of the river. Spur, spur dyke, or groyne is a structure made to project flow from a river bank into a stream or river with the aim of deflecting the flow away from the side. They are placed in series along straight or convex bank lines where the flow lines are roughly parallel to the bank

Screen dams and beam dams are sediment retention structures, designed to trap medium to large size debris and boulders carried downstream in flood events. This type of dam is often installed in alluvial fans, along stretches with a steep slope, in wooded areas, in areas with frequent mass movements, and along narrow channel beds at the end of a valley just before the stream or river enters an alluvial fan or plains area. Porcupines like structure is used as a pro-siltation protection device for a natural river bank. They are flexible, which ensures stability against extreme water forces and even earthquakes. Porcupines reduce the flow velocity, intercept and break eddies formed by floodwater, and fill up scour holes with silt. Levees or earth fill embankments are dam-like earthen structures constructed along a river in order to protect the surrounding countryside from flooding and/or to confine the course of a river to provide higher and faster water flow. They are usually constructed for long stretches along a river in low lying areas with an extended floodplain

Guide banks are constructed to:

• Confine the flow to a single channel
• Improve the distribution of discharge across the width of a river thus controlling the angle of attack by a flash

flood, protect weirs, barrages, or other hydraulic structures constructed in the river such as intakes from flash floods

• Control the meander pattern of a river
• Control overtopping of natural embankments in a flash flood and protect adjacent land from flooding, reduce

erosion of banks by the water current, prevent sliding of soil as a result of the draw down effect of the flood water level, facilitate smooth transportation of water, and prevent piping of water through the banks. Channel lining is a protective layer used to protect the banks and bed of a watercourse against erosion. Channel lining can help increase the velocity of flow to ensure easy transport of sediment and reduce deposition in the channel bed. It is recommended in catchments highly prone to erosion, particularly in urban and alluvial fan reaches. Bamboo can be used in the form of piles to strengthen a foundation or stabilize a flood embankment or river bed. The rows of bamboo piles should be firmly fixed with a rope or iron wire. Piling in wet soil is very easy but may

• therwise require more strength. It may be necessary to excavate small holes in boulder covered parts of the

river bed. Two parallel rows of piles can be prepared and the space between them filled with boulders and pebbles as a toe protection measure for flood embankments (

Reservoirs are meant to absorb a part of flood water and the excess is discharged through a spillway. It is also essential to

study the relation between flood discharge, reservoirs capacity and spillway size in order to propose an economic solution to the whole project. Two main categories: (a) Impounding reservoirs into which a river flows naturally, and (b) Service or balancing reservoirs receiving supplies that are pumped or channelled into them artificially.

Multi Purpose reservoirs

• Human consumption and/or industrial use:
• Irrigation: usually to supplement insufficient rainfall.
• Hydropower: to generate power and energy whenever water is available or to provide reliable supplies of power and

energy at all times when needed to meet demand.

• Pumped storage hydropower schemes: water flows from an upper to a lower reservoir for generating power at times of

high demand through turbines. Water is pumped back to the upper reservoir when surplus energy is available. The cycle is usually daily or twice a day to meet peak demands.

• Flood control: storage capacity is required to be maintained to absorb foreseeable flood inflows to the reservoirs, so far

as they would cause excess of acceptable discharge spillway opening. Storage allows future use of the flood water retained.

• Amenity use: this may include provision for boating, water sports, fishing, sight seeing.

Types of reservoirs:

• Auxiliary or Compensatory Reservoir which supplements and absorbed the spill of a main reservoir.
• Balancing Reservoirs: A reservoir downstream of the main reservoir for holding water let down from the main

reservoir in excess of that required for irrigation, power generation or other purposes.

• Conservation Reservoir impounding water for useful purposes, such as irrigation, power generation,

recreation, domestic, industrial and municipal supply etc.

• Detention Reservoir where in water is stored for a relatively brief period of time. Such reservoirs usually

have outlets without control gates and are used for flood regulation. They are also called as the Flood Control Reservoir or Retarding Reservoir

• Distribution Reservoir - connected with distribution system a water supply project, used primarily to care for

fluctuations in demand which occur over short periods and as local storage in case of emergency such as a break in a main supply line failure of a pumping plant.

• Impounding or Storage Reservoir with gate-controlled outlets wherein surface water may be retained for a

considerable period of time and released for use at a time when the normal flow of the stream is in sufficient to satisfy requirements.

• Multipurpose Reservoir constructed and equipped to provide storage and release of water for two or more

purposes such as irrigation, flood control, power generation, navigation, pollution abatement, domestic and industrial water supply, fish culture, recreation, etc.

• Feasible Service Time: the period or notional period for which a reservoir is expected to provide a part of the

planned benefit in respect of storage in the reservoirs being impaired by sedimentation. it is estimated as the time after which the new zero elevation of the reservoir would equal the sill of the outlet relevant for the purpose.

• New Zero Elevation: The level up to which all the available capacity of the reservoir is expected to be lost due

to progressive sedimentation of the reservoir up to the specified time. The specified time should be any length of time such as Full Service Time, Feasible Service time, etc.

• Full Service Time: For a specified purpose, the period or notional period for which the reservoir provided is expected

to provide, a part of the full planned benefit inspite of sedimentation.

• Life of reservoir denotes the period during which whole or a specified fraction of its total or active capacity is lost.

The progressive changes in trap efficiency towards the end of the period are commonly not considered.

Reservoir storage broadly classified into:

• 1. Inactive storage including dead storage
• 2. Active or conservation storage
• 3. Flood and surcharge storage

Capacity of a reservoir depends:

• Precipitation, run-off and silt records available in the region
• Erodibility of catchment upstream of reservoir for estimating sediment yield
• Area capacity curves at the proposed location
• Trap efficiency
• Losses in the reservoir
• Water demand from the reservoir for different uses
• Committed and future upstream uses
• Criteria for assessing the success of the project
• Density current aspects and location of outlets
• Data required for economic analysis
• Data on engineering and geological aspects.

Precipitation, Run-Off and Silt Record - network of precipitation and discharge measuring stations in the

upstream and near the project location, to assess the capacity on spatial and temporal precipitation and stream flows.

Estimation of average Sediment Yield from the catchment area to reservoir: river sediment observation

data or more commonly from the experience of sedimentation of existing reservoirs with similar characteristics.

Elevation Area Capacity Curves: Topographic survey of the reservoir area for these curves, as they the plots of

elevation of the reservoir versus surface area and elevation of the reservoir versus volume.

Trap efficiency of reservoir, over a period, is the ratio of total deposited sediment to the total sediment inflow.

Calculation of trap efficiency highlight relationship between sedimentation index of the reservoir.

Losses in Reservoir - evaporation and seepage are reflected in the stream flow records used for estimating water

• yield. Estimation of these losses may be based on measurements at existing reservoirs and canals. Various methods

like water budget method, energy budget method, etc. , Evaporation from reservoir is estimated by using data from pan-evaporimeters or pans exposed to atmosphere with or without meshing in or near the reservoir site and suitably adjusted.

Demand, Supply and Storage The demand should be compared with supplies available year by year. If the demand is limited and less than the available run-off, storage may be fixed to cater to that particular demand which is in excess of the run-off. Committed and future upstream uses: The reservoir to be planned should serve not only the present day requirements but also the anticipated future needs. The social, economic and technological developments may bring in considerable difference in the future needs/growth rate as compared to the present day need/growth rate. Criteria for assessing the success of the project designed for achieving specified success. Irrigation projects are to be successful for 75% period, power projects and water supply projects are to be successful for 90 % and nearly 100 %t period of simulation respectively. Density Current aspects and location of outlets: Density current is defined as the gravitational flow of

• ne fluid under another having slightly different density. The water stored in reservoir is generally free from silt

but the inflow during floods is generally muddy. Thus two layers having different densities resulting in the formation of density currents. T

Economic Analysis indicate the economic desirability of the project. Benefit cost ratio, Net benefit,

Internal Rate of Return are the parameters. It is desirable to have the benefit cost ratio in the case of irrigation projects and flood mitigation projects to be above 1.5 and 1.1 respectively. Benefit functions for reservoir and water utilisation for irrigation, power, water supply etc., are also to be determined

• judiciously. Cost benefit functions are obtained as continuous functions using variable cost/benefit

against reservoir storage/net utilisation of water and from benefit functions the benefit from unit utilisation of water can be determined.

Geological exploration for reservoir sites

• Water tightness of the basins
• Stability of the reservoir rim
• Availability of construction material in the reservoir area
• Silting
• Direct and indirect submergence of economic mineral wealth
• Seismo-tectonics

Conveyance and distribution efficiency ratios: is the measured outflow over measured inflow to evaluate every element of the water balances. It is assessed annually for each water resource, and each distribution system. The differences are attributed between inflows and outflows, and the rate of evolution of these differences. It is used in improving accuracy and reliability of measurement devices, and helps to identify the losses which are worth while to reduce. Water delivery performance: considers the actual volume delivered volume/intended delivered volume. “Dependability of supply”, “regularity of deliveries“ are normally always equal to 1, This is true as long as the conveyance and distribution system are able to provide the total instantaneous flow and pressure requested by the user. It is necessary to measure the margin between actual demand and the capacity of the system: after years, even during the peak hour of the peak day of a very dry season. Line utilisation factor: This saturation ratio indicator is calculated annually to monitor the actual ability of the 70 main production lines (pumping stations, main feeders and associated reservoirs) to transfer the water resource necessary to feed the networks. Network utilisation index: this saturation ratio indicator is used to monitor the actual ability of the networks to deliver water to every customer, with the contracted pressure and flow for each of the 170 networks of SCP scheme

Water Reservoir Performance Assessment

Reservoir system analysis models support

• reservoir storage capacities and establishing operating policies during preconstruction planning of new projects,
• evaluation of the operating plans of existing reservoir systems,
• administration of water allocation systems involving water rights and agreements between water suppliers and

users,

• peration planning for developing management strategies for the next year or season,
• real time operations.

Reservoir management for managing the sediments coming into it from upstream catchments. The catchments contributing to the reservoir need to be monitored and managed for their soil erosion and sediment deposition, and water storage aspects. Soil conservation and reforestation in the upper catchments can help in substantially reducing sedimentation. Reservoir sedimentation reduces water into reservoir and more rainfall (because of increased forest) increases water into reservoir. This has a bearing on reservoir operations

Reservoir Water Management

Reservoir water needs to be appropriately managed with costs of operations involved to cater to multi- purpose needs of the water users. Reservoir level-area-capacity curves at 1 meter elevation are generated by topographic surveying in the initial construction stages of the Dam. Sediment deposited reservoirs are resurveyed periodically once in five years (3 to 10 years in average) depending on rates of sedimentation. Two methods of re-capacity surveys are in vogue. Water Resources Utilization water utilization analysis in watersheds, catchments, sub-basins and basins is carried out for small single purpose water reservoir / tank systems. Economic evaluation of multipurpose systems is derived by combining the marginal benefits of different purposes and the costs. Water stored in minor tanks and reservoirs in watersheds/ sub systems need to be assessed for their timely reliable water access to resolve water conflicts and generate efficient reservoir

• peration policies.

Reservoir operation It includes a set of rules or guidelines to store and release water depending on the purposes it is required to serve. The operating rule provides guidance to the water managers taking decisions

• f actual releases.

Parameters for Reservoir Water Management in a multi-purpose project. rainfall, temperature , number of degree days in a crop season, water vapour, soil moisture, humidity , surface water storage and ground water storage; type of crops , soil-water-plant relationships, crop evaporation, leaching , seepage Scheduling of irrigation is (i) scheduling for sole crops (based on ratio of irrigation water and cumulative pan evaporation) ( ii) scheduling of irrigation for intercropping and other cropping systems.

• planning irrigation from the reservoir of water (irrigation source) :
• water supply demands for domestic purposes ( as sanctioned in project ),
• upstream use demands ,
• irrigation demands (type of crop , growth stages , soil moisture , temperature , ground water status etc),
• hydropower demands,
• lower riparian uses ,
• existing reservoir storage,
• current rainfall .

Water distribution

• as per shares according to landholding,
• methods of rotation and allocation,
• partial demand system,
• supply demand,
• farmer managed water storage,
• farmer organization of warabandi etc.

Structured and Unstructured Decisions - Reservoir operations

Structured Unstructured Stable context Volatile context Common Place Atypical unique Recurrent Discrete Programmable Intuitive, Creative Easily accessible information Problematic access to information Decision Criterion understood Decision Criterion unclear Focused decision strategy Multiple decision strategies

Daily water recording of the Reservoir Rainfall (mm) , Date 30 Oct 2008

• A. RESERVOIR

1.Yesterday (Level, Area , Capacity) 2.Today (Level, Area , Capacity) 3.Net (a) depletion (b) filling 4.Evaporation Losses 5.Gross depletion = (3a-4) Filling (3a+4)

• B. DRAWALS

WORKING TABLE ACTUAL (LEFT BANK) M.Cum , M.Cusecs M.Cum. M. Cusecs

• 1. PH 2. IS 3. HLC
• C. DRAWALS

(RIGHT BANK)

• 1. PH
• 2. River Sluice
• 3. RB Channel
• 4. HLC
• D. TOTAL DRAWALS

E . RIVER DISCHARGE AT DAM 1.Spilling on Dam 2.ROFS ( Left) & (Right) F . Miscellaneous a. Head PH- Power House , M-Million , IS-Irrigation Sluice , HLC-High Level Canal, RB-Right Bank, RB-Right Bank, , ROFS-Reservoir Over Flow Spillway, LLC-Low Level Canal, FRL-Full Reservoir Level

Performance assessment of irrigation management

• perational performance evaluation help irrigation management
• Water supply indicators

Annual irrigation water delivery per unit irrigated cropped area Annual relative water supply - ratio of total annual water supplied (irrigation plus rainfall) to the annual crop water demand. Annual relative irrigation supply - ratio of annual irrigation supply to annual irrigation demand. Irrigation water is a scarce resource in many irrigation schemes and may be a major constraint for production. Output per unit irrigated cropped (harvested) area

• Output per unit irrigation water supply
• Output per unit water supply
• Irrigation ratio is the ratio of currently irrigated area to irrigable command (nominal) area. It tells the degree of utilization
• f the available command area for irrigated agriculture at a particular time. S
• Sustainability of irrigated area is the ratio of currently irrigated area to initially irrigated area when designed. It is a useful

indicator for assessing the sustainability of irrigated agriculture.

Strategic performance. Operational

• Evaluating the hydraulic and agricultural performance to make strategic decision for improving the

performance level.

• Evaluating Water User Association’s performance to address the issues for its better performance and

sustainability.

• Formulating a multi-objective optimization routine to determine the optimal size of the proposed

secondary storage reservoir and the optimal cropping pattern for the dry season.

• Assessing the improved performance of the project with the provision of secondary storage reservoir

and comparing it with the existing project performance i.e., without secondary reservoir.

• Evaluating the economic feasibility of the proposed secondary storage reservoir and collecting

information about existing water bodies in the command which can be used as secondary reservoirs with suitable modifications.

• Understanding the Water Users Association’s role in the operation and maintenance of secondary

reservoir and suggesting measures for creation, operation, maintenance of such intervention.

Hydraulic performance evaluation indicators assess the performance of the irrigation water delivery, the hydraulic performance indicators such as adequacy, equity, relative water supply and relative irrigation supply Agricultural performance evaluation indicators highlight the provision of irrigation, the agricultural scenario, such as production, productivity and cropping intensity will improve. irrigation intensity, cropping intensity, standardized gross value of production (SGVP), output per cropped area,

• utput per unit command, and output per irrigation supply were considered as the agricultural performance

indicators. Economic feasibility test indicators use techniques such as Net Present Value (NPV), Benefit Cost ratio (B/C ratio) and Internal Rate of Return (IRR) were used here for the economic analysis of the secondary storage reservoir. Institutional performance assessment Institutional intervention has taken place through formation of water user association (WUA) and handing over the irrigation system to WUA for operation and management of the system

Performance Enhancement of a Minor Irrigation System

Dams are characterized as follows:

Small: reservoir storage of 1 – 100 acre-feet Medium: reservoir storage of 100 – 10,000 acre-feet Large: reservoir storage of 10,000 – 1,000,000 acre-feet Very large: reservoir storage of more than 1,000,000 acre-feet ‘International Rivers report’ Estimates reveal that [in India] around 100 large dams are more than 100 years old and more than 400 large dams between 50 and 100 years.’ The Central Water Commission (CWC) and the Central Electricity Authority (CEA) are of the opinion that a dam is a permanent structure that does not need to be decommissioned, even though many old dams have developed leaks and fissures.’

Worst dam bursts took place in Gujarat in 1979 when the four-km long Machhu Dam II on the Machhu River collapsed. Deluge in the industrial city of Morbi located five km downstream as well as surrounding rural areas destroying thousands of homes and lives. India - Over forty dam bursts have taken place. Machhu Dam gave way in 1979 killing 2000 people. Kaddam (1957), Panshet (1961), Khadakwasla (1961), Chikkhole (1962) and Nanak Sagar (1967). The failure of the Malpasset Dam in France in 1959 killed 421 people and the Buffalo Creek dam in USA in 1972 claimed 125 lives. earthquake hazard continues to be a serious threat to dams. The long term safety of a dam depends upon the degradation of its materials, weakening

• f foundation and seismology issues to name a few.

Mullaperiyar dam, Dumbur dam over the Gumti River in Tripura and Jaikawadi Dam in Maharashtra in different contexts by civil society groups and independent experts

Dam is removed to undo the multiple detrimental impacts on the environment and biodiversity.

• Divert water from rivers for power, reducing the supply of water available to keep downstream ecosystems

healthy.

• Obstruct the migration of fish and wildlife; 91% of the migratory fish habitat is blocked by dams.
• Prevent nutrient rich sediments and woody debris needed for habitats from flowing downstream.
• Slow down the flow of rivers, which allows sediment to collect on the river bottom and bury spawning
• habitat. The slowed flow also disorients fish species whose lifecycles evolved to take advantage of the

swiftness and natural seasonal variations of a river’s flow.

• Warmer temperature of reservoir water sitting behind a dam may discourage cool-water fish species from

reaching their upstream spawning habitat.

• Water that is released from the bottom of the reservoir is much colder and contains less oxygen than river
• water. Oxygen less water can affect the reproductive processes of some fish species and can kill fish.
• Creation of reservoir lakes favours species better suited to lake-like conditions that harm native fish species.
• Sediment and silt trapped by dams can accumulate heavy metals and pollutants.

Dam removal may, however, stir up sediments as they are carried down a free flowing river and this resuspension can damage spawning grounds and habitat, and affect water quality, especially if the sediments contain toxins and pollutants.

Dams were never meant to last forever and, over time many suffer from sediment infilling or concrete deterioration while others outlive their usefulness or provide only marginal benefit. Dam removal is the process of removing dated, dangerous, or ecologically damaging dams from river systems.

• It is a one-time cost that restores river processes and permanently eliminates the public safety risk caused

by the dam. Removing dams can be quite challenging.

• Concerns are from the neighbouring community, lack of capacity, and high costs regularly deter dam
• wners from removing dams on their property.
• Communities often want dams to remain to preserve the history of an area, to maintain the

impoundments that people use for fishing and recreation.

• Managing a dam removal project is beyond the ability of most owners. It needs a management team to

meet with regulators, conduct outreach, oversee engineering and design, file permits, and raise funds.

• Obtaining permits and designing dam removal projects can be challenging, especially when sediments

behind the dam are contaminated with pollution from past industry in the area.

• Regulations that are not designed for habitat restoration, but still govern dam removal work, can lead to a

long, challenging, and costly permitting process.

• Dam removal projects aren’t cheap—the design, construction, and project management costs can range

from tens of thousands of dollars up to the millions.

Reasons for dam removal

• Economic obsolescence
• Structural obsolescence
• Safety considerations
• Legal and financial liability
• Dam site restoration
• Ecosystem and watershed restoration
• Restoration of habitat for riparian or aquatic species
• Unregulated flow recreation
• Water quality or quantity

Key Indicators for Dam Removal Decisions

Physical River network segmentation Watershed fragmentation Downstream hydrology Downstream sediment system Downstream channel geomorphology Floodplain geomorphology Reservoir geomorphology Upstream geomorphology Chemical Water quality Sediment quality (reservoir area and downstream) Air quality Ecological Aquatic ecosystems Riparian ecosystems Fishes Birds Terrestrial animals Economic Dam-Site economics Economic values, river reach Regional economic values Social Safety and security Aesthetic and cultural values Non-majority considerations

Environmental Issues associated with removing the existing structure.

• Will removal of the structure help to enhance the recovery of threatened or endangered

species?

• Will removal of the structure lead to changes in unwanted invasive species or perhaps restore

native species?

• Are there likely to be problems associated with contaminated sediments currently contained

behind the dam if the dam is removed?

• Will removing the dam cause sediment to help build beaches?
• Will dam removal lead to a net gain or loss in wetland area?
• Have so many other changes occurred in addition to the dam that removal of the dam

will not achieve the desired ecosystem restoration goals?

• What is the relationship of the dam and its removal to other parts of the watershed?
• How will drinking water supplies be affected?
• How will groundwater tables be affected?

Safety and Security Issues

• Is there a significant potential for loss of life, injury, and property damage if the dam should

fail or be removed?

• Is the dam vulnerable to failure because of either aging or inadequate maintenance?
• Is the dam vulnerable to acts of terrorism?

Management Issues

• How does the existing structure fit into the overall management plan for the river system? Is

it a critical element to meeting any legal agreements and providing a service to the local economy such as flood control, water supply, power production, irrigation,fire protection, or recreation?

• Do the operations fit into a broader context of river basin control?
• What is the source of funding for removal or restoration efforts?

ultimate decision to remove a dam is likely to balance concerns:

• Safety, security, and water management requirements
• Economics of maintaining the dam versus dam removal or other alternatives (i.e., alteration
• f the dam, change in operations)
• Ecological need and potential gains
• Societal considerations
• Legal relationships
• Public support and concerns
• Local, regional, and possibly national and international interests

Social Impact Assessment Variables for Dam Removal

Project Stage Variables Problem Identification Small or medium-sized dams Planning/Policy Safety issues, environmental issues, public attitudes towards the project Implementation Relocation of families, influx of workers, change in recreation, change in wildlife habitat Maintenance Safety problems, insurance liabilities, flood protection fish passage issues, native Vs non-native values, sediment removal Removal Changes in employment, potential change in property value, restoration of natural environment, hydropower replacement, native fish return, introduced fish species leave, flood protection needed for houses near river, sediment flows to beaches, sediment quality and removal

Social Issues

• Are there changes in the types of, and access to, recreational opportunities?
• Are there effects on local and regional populations in terms of economic stability (or lack thereof ),

displacement, water supply, and loss of access to traditional use areas?

• Are there direct and indirect effects on the cultural relationships of the peoples to the landscape?
• Are there impacts related to changing regional and local economics?
• Are there direct and indirect impacts related to any necessary service that was provided by the dam, and how

will this service be replaced?

• How will dam removal affect aesthetic property values in the area?

Economic Issues

• What is the cost of maintaining the dam versus the cost of other alternatives?
• Who is financially responsible for the dam and for any damage that might occur if the dam were breached?
• What are the potential costs (estimate) of any repair and annual maintenance of theexisting facility?
• What is the status of the repayment on the debt for the project?
• Has it met the financial criteria defined in its authorization language?
• Are there financial criteria that must be met or maintained if the project is funded with international or public funds?
• Is the dam providing a service that will need to be replaced by some alternative, and what is its cost?
• What are the costs of alternative measures to mitigate for project impacts?
• What are the costs to provide additional security measures?
• How will property values be affected?

Measuring the Benefits of Dam Removal

Cost-Effectiveness of Maintenance Versus Removal - Dams require maintenance to remove accumulating sediment, make small repairs, and upgrade safety systems. When older dams are no longer used for their original purpose, dam owners may defer maintenance to the point where the dams pose a threat to public safety. In some cases, it is less expensive to remove the dam than to make the necessary repairs. Vulnerable Species and Other Environmental Benefits - Dams interfere with the life cycle of migratory fish by blocking the migration of adults to upstream spawning grounds, as well as limiting the passage of sediment and large woody debris necessary to maintain suitable spawning areas downstream. Species quickly return to upstream spawning habitat, even when the river has been blocked for 100 years. Cultural Values - In addition to subsistence and commercial fish harvests, many Native American tribes have deep cultural, spiritual, and historical connections to specific free flowing rivers, features along those rivers, and the animal and plant species they support. Recreational and Commercial Fisheries - Benefits to commercial fisheries are measured in terms of increased revenue from improved catch rates while benefits to recreational anglers are measured in terms of improved experiences and in terms of additional jobs and income supported by more visiting anglers. River Recreation and Other Tourism - Removing dams and returning rivers to a free-flowing state provide new boating opportunities, white water rafting, canoeing, and kayaking.

Non-Market Values - People value seemingly unquantifiable outdoor amenities like free-flowing rivers, endangered species, and recreational opportunities. Apply statistical methods to measure how much people value selected environmental qualities and then translate that value into dollars. They can be incorporated into cost-benefit analyses. Environmental changes associated with removing dams:

• existence of a free-flowing river that individuals can see now or will be available for their children to visit;
• Knowledge that endangered species are present in a river and their population is recovering;
• Improved catch rates for recreational anglers;
• Improved experiences for white water boaters.

Non-market benefits are distinct from the additional spending that anglers and tourists bring to an area. Because the benefits are experienced by people close to the dam as well as those who live far away, total non-market benefits can be quite large and therefore influential in dam relicensing decisions. Cost-Effectiveness of Energy Production - Many older hydroelectric dams were built to support nearby mills, factories, and communities, and have relatively small generating capacity. U.S. power grid has shifted to more regional rather than local production. Economic Impact of Removal Projects - Dam removal and river restoration can be substantial, multi-year projects, employing local residents, providing personal income, and contributing to the local economy. Jobs associated with these removal projects often are relatively short-term, but nonetheless valuable particularly in smaller communities. Property Values - small dams with small upstream impoundments, can create an unpleasant feature that drives down property values due to lower water quality or flooding risk.

Primary analytical principles

Benefits as well as costs - Removing or keeping a dam would generate economic benefits as well as economic costs. Consider the full effect on the value of the goods and services derived from streams, forests, and other resources. Positive as well as negative impacts on jobs - Dealing with a dam would have both positive and negative effects on job

• pportunities. Consider them both to understand the full effect on workers, their families, and their communities.

Secondary analytical principles

Distribution of consequences and fairness- Those who enjoy the benefits or jobs of a decision on a dam would not necessarily be the same as those who would bear the costs or job losses. Consider the full distribution of economic consequences to understand who wins, who loses, and the fairness of the distribution. Rights and responsibilities - With any decision on a dam, property owners and resource users behave differently than they

• therwise would. Consider whether these changes represent infringement of their rights or enforcement of their responsibilities.

Uncertainty and sustainability - Any decision on a dam would rely unavoidably on information insufficient to guarantee the

• utcome. Consider fully the potentially high costs from decisions yielding undesirable outcomes that are irreversible or

extremely difficult to reverse. More than just salmon conservation - Removing or keeping a dam would have a variety of ecological and economic effects, such as changes in the quality of stream water used for other purposes, that may seem peripheral. But consider all the effects.

Decommissioning of dams

Every structure of each dam will age at a different rate in a different way. Some dams may remain safe for a thousand years, others may start to crack and leak after less than a decade. Around the world, some 5,000 large dams are now more than 50 years old, and the number and size of the dams reaching their half century is rapidly increasing. Biophysical Effects of Dam Decommissioning Positive Impacts Negative Impacts Lower water temperatures Lower water temperatures Increased nutrient transport Elevated nutrient transport and loading Increased sediment transport Elevated sediment transport, loading and sediment deposition Increased mobility of heavy metals or other sediment related contaminants Increased dissolved oxygen level Supersaturation of oxygen levels Return to natural channel flow levels Loss of ability to control flows for downstream fish spawning Decrease low flows downstream for other uses(fish, assimilation flows, water supply) Removal of a barrier to fish migration Increased access of predator species due to barrier removal

Decommissioning Process

• Detailed engineering design, preparation of tender specifications, construction management.
• Regulatory permits, environmental approvals and authorizations.
• Site access roads, construction staging and lay down areas and property requirements.
• Relocation and/or stabilization of roads, bridges, water and sewer main, buildings.
• Extension or relocation of water intakes or wells, sewage outfalls, boat docks and ramps.
• Reservoir/head pond lowering and dewatering including diversion implementation or acquisition
• f floating barges for construction.
• Dam demolition and removal of debris (full or partial removals).
• Dam construction and modification works (partial removal).
• Material testing for safe disposal and disposal locations (on- and off-site).
• Channel improvement works including natural channel design (bioengineering techniques).
• Flood plain stabilization and habitat creation works.

River Returns

• Sediment trapped behind the dams has washed downstream,
• rebuilding riverbanks and gravel bars in and around the river's mouth,
• creating some 70 acres of new beach and riverside estuary habitat

American Rivers reports that in the United States, nearly 850 dams have been removed in the last 20 years, with more than a hundred removed in 2012 and 2013 alone.

• Over time some dams become less economically viable.
• As sediment accumulates behind a dam, the reservoir cannot hold as much water;
• sediment can block water going to the turbines, or hamper a flood control dam’s ability to capture floodwaters

efficiently.

• The cost of regular maintenance, upgrading machinery to meet regulatory requirements, or liability risk may not

make economic sense.

• dam removal is often less expensive than trying to maintain or repair an older dam.
• decision to remove a dam is usually made by its owner; many dams are privately owned, with the rest owned by

the federal, local or state government, or public utilities.

• Dam removal is paid for by the dam’s owners, federal, state or local governments, or multiple stakeholders.

Thank you