Dam Removal and Other Fish Population Restoration Strategies in the ColumbiaRiver Basin
Prepared by:
Sara Powell
Kyle Palmer
Andy White
Executive Summary
The fish populations are declining in the Lower Snake River largely due to four major dams (Ice Harbor Dam, Lower Monumental Dam, Little Goose Dam, and Lower Granite Dam) located along this diverse waterway. The goal is to identify the most viable management strategy for restoring the natural balance of anadromous fish populations in the Lower Snake River. To do this, the widespread impacts of damming rivers on the ecosystem were determined andthe costs and benefits of dam removal as a management strategy for the Lower Snake Riverwere assessed. Also, we determined the potential positive effects that fish ladder installation, fish trapping and transportation, turbine diversion screen installation, and fish stocking will have on the recovery of the anadromous fish population in the region. Finally, we recommend an integrated restoration strategy that implements a combination of these previously mentioned techniques.
Table of Contents
The Problem………………………………………………………………………………2
Background……………………………………………………………………………….2
Goal Statement…………………………………………………………………………....3
Objectives………………………………………………………………………………...3
Approach…………………………………………………………………………………3
Findings…………………………………………………………………………………..3
Figures…………………………………………………………………………………..12
Works Cited…………………………………………………………………………….15
The Problem:
Fish populations in the ColumbiaRiver Basin are declining, in large part due to the vast network of hydroelectric dams located along this diverse waterway.
Background:
Anadromous fish, specifically steelhead and salmon, have been a large part of life in the ColumbiaRiver Basin since the time of the Native Americans. According to the Northwest Power Planning Council, these fish historically existed in annual runs of over 16 million fish and provided a basis for trade and economic expansion(Foster Wheeler et. Al, 1999) However, western expansion brought many changes to the region and greatly reduced the capacity for the Columbia River Basin and the Lower Snake River to sustain anadromous fish populations. This decrease in fish population is the result of several factors, including habitat alterations, ocean conditions, harvesting methods, and, most importantly, the construction of hydrodams.(Foster Wheeler et. Al, 1999) Migratory fish require different habitats for the four main stages of their life cycle: reproduction, production of juveniles, growth, and sexual maturation.(Larinier, 2000) As a result, anything that impedes their ability to travel to different regions in time to undergo these life changes can have a dangerous impact on a fish population. Dams represent a large challenge for migratory fish, as they act as a physical barrier to a fish’s migration up or downstream, as well as altering the discharge of the river, its water temperature, sedimentation and flood regimes, and availability of viable fish habitats. Furthermore, losses of fish over spillways and through turbines are significant. (Larinier, 2000) In recent years, these stressors on the fish population have been taking a serious toll, to the point that the extinction of several species has become a possibility.
As a result, a strategy is needed to restore the fish population to healthy, sustainable levels. Since many different people rely on the river and the fish within for a variety of reasons, economic and otherwise, care must be taken in deciding which restoration strategy is the most appropriate. Commercial fishermen rely heavily on the presence of large fish runs for their livelihood, and farmers in the region need water diverted from the river for crop irrigation. Electric power generated by the dams is used by people and businesses all over the area. The fish are also important to many outdoor enthusiasts that travel to the Snake River for recreational fishing. Environmentalists see the intrinsic value in the mere existence of the fish, and Native Americans have strong ties to the presence of the fish for economic, social, and religious reasons. As a result of all of these concerned parties, we are examining several different strategies for restoration that will have different levels of impact on the stakeholders. These are the implementation of fish ladders or elevators, screen diversion strategies, fish capture and transportation, stocking, and the removal or retention of dams.
Goal Statement:
The goal is to determine the most viable management strategy for restoring the natural balance of anadromous fish populations in the Lower Snake River.
Objectives:
There are several objectives to be addressed in this report. First, identify the widespread impacts of dam construction on the ecosystem. Next, weigh the costs and benefits of dam removal as a management strategy for fish restoration in the Lower Snake River. Evaluate the effectiveness of fish ladder installation at restoring migratory fish populations. Evaluate trapping and transportation of anadromous fish as a viable recovery strategy for migratory fish populations. Also, determine if turbine diversion screens are effective at protecting fish from turbine-caused mortality. Further, evaluate the usefulness of stocking in returning anadromous fish populations to acceptable levels. Finally, develop a comprehensive restoration plan that will help return the salmon and steelhead populations to acceptable levels for commercial fisheries to be successful and the ecosystem to remain healthy.
Approach:
We reviewed the pertinent literature using reliable and recent sources to make management recommendations pertaining to the problem of declining anadromous fish populations in the lower Snake River.
Findings:
The ColumbiaRiver Basin and its tributaries form the dominant water system in the Pacific Northwest Region. This complex network of rivers supports many wildlife species especially fish species, most importantly anadromous fish species that use this network of rivers to spawn. The fish populations are declining in the ColumbiaRiver Basin largely due to the vast network of hydroelectric dams located along this diverse waterway. There are currently two species of fish on the endangered species list from the basin, the Snake River Sockeye salmon and the Willamette steelhead. Only 13% of the Columbia River salmon habitat and 58% of the Snake River salmon habitat remain, contributing to the sever declines in the wild salmon runs in this region of North America (Dauble, DD, et al, 2003). The ecological impacts are immense. Most of the riverine habitat is found in the upper Snake River which unfortunately is upstream of the Hells Canyon Dam which does not allow for any fish passage (Dauble, DD, et al, 2003). In a study conducted by Dauble, et al (2003), they determined that approximately 661 and 805 km of the Columbia and Snake rivers were once used by fall Chinook salmon (Oncoryhnchus tshawytscha) for spawning.They also determined that currently this species only uses about 85 km of the main- stem Columbia River and 163 km of the main stem Snake River for their spawning activities (Dauble, DD, et al, 2003). While other dams do allow some fish passage turbines, predation in reservoirs, and other alterations in the ecosystem effect migration as well as increase salmon mortality. Looking at these impacts the benefits of the dams needs to be weighed against the cost to these important migratory species (Kareiva and Marvier, 2000). Historically, there were annual returns of 10 to 16 million anadromous adult salmon and rainbow trout Oncoryhnchus sp., but present adult runs consist of approximately 2.5 million fish (Williams, JG. 1998).
The IceHarbor, Lower Monumental, Little Goose, and the Lower Granite Dams are located on the lower Snake River, a small section of the larger ColumbiaRiver Basin. These dams were completed between 1962 and 1975 in order to provide shipping lanes for barges, as well as, for the production of power. The economic benefits of these dams must be weighed against their vast ecological costs. These costs are widespread, but the focus in the Snake River is on the decline of anadromous fish populations such as salmon and steelhead, which are important to the region both ecologically and economically. The ecological and even economical costs associated with the upkeep of these dams outweigh the benefits they provide. For this reason the removal of the four dams on the lower Snake River is being considered. Dam removal must, however, be viewed as a tradeoff, as some of the results may be considered beneficial, while others are ecologically and economically costly. It is important, then, to understand both the positive and negative impacts associated with these four dams, as well as, with their removal.
Rivers are ecologically complex systems that rely on natural cycles of disturbance in the form of heavy rainfall and droughts. This variation produces flow patterns known as a river’s flow regime. “By blocking flow, dams raise water heights, inundate surrounding terrestrial habitats, and slow the velocity of flowing water in rivers” (Stanley & Boyle 2002). Moreover, human demands for water supply, navigation, power production, and recreation often drive the timing of dam releases not taking into account the needs of the stream’s aquatic organisms. These unnatural fluctuations in flow have the potential to limit an aquatic community to a few generalist species that are able to withstand significant changes in flow dynamics (American Rivers 2002).
Dams cause the formation of reservoirs in fast flowing rivers. These reservoirs have lake-like habitats that differ greatly from fast moving river habitats. The increased surface area and depth in reservoirs creates temperature stratification, a process where several layers of water with varying temperatures are formed (American Rivers 2002). This stratification allows for reservoirs to support fish species more commonly found in lakes. Many of these species are predators of migratory fishes such as salmon and steelhead, further decimating anadromous fish populations. Many fish species, including anadromous fishes such as salmon, rely on cool water temperatures. It is possible for dams to increase river temperatures to a point where they create a thermal block for migrating fishes. This prevents these fish from making it to their spawning waters, and further exacerbates the problems dams cause to anadromous fish populations.
One of the greatest problems associated with dams is the accumulation of sediment in the reservoir close to the dam. This filling process greatly decreases the functional lifespan of a reservoir (Palmieri et al. 2001) and increases the likelihood of eventual dam failure (Evans et al. 2000). Furthermore, sediment and larger organic debris and rocks are prevented from moving downstream. This causes the water that flows through the dam to have very low nutrient levels. Releases of this type are known as “clear-water releases.” “Downstream of a dam, sediment-starved rivers often regain sediments lost behind a dam by eroding deeper into the river channel and away at the stream banks (Kondolf 1997).” These effects are known as stream-bank erosion and channel incision, and have the potential to eliminate many organisms or even communities from river habitats.
The connectivity of rivers is greatly compromised by dams. This connectivity is the most important factor when considering the impacts of dams on anadromous species. Anadromous fish species, such as salmon and steelhead, are those that live most of their lives in salt water, but travel upstream to spawn in freshwater rivers and streams. This upstream travel is necessary for anadromous fish to complete their life cycle. Therefore, the adverse effects that dams have on anadromous fish species are directly associated with reproductive success. It is not surprising, then, that salmon and steelhead are declining not only in the Snake River, but in the entire ColumbiaRiver Basin, which contains over 450 large dams.
The removal of the aforementioned dams is being considered as a viable option for restoring anadromous fish populations in the lower Snake River. Removal of these dams would return the flow regime of the lower Snake River back to its natural pattern (American rivers 2002). This would most likely cause biodiversity and population densities of native aquatic organisms to increase. In Florida, the removal of the DeadLakeDam on the ChipolaRiver increased natural fluctuations in the flow of the river, and the diversity of species nearly doubled from 34 to 61 aquatic species (Hill et al. 1993). It is important to note that many lake species may decline due to the loss of their lake-like reservoir habitats. Fish populations preferring cold water habitats, such as salmon and trout, often replace species that prefer warm water habitats. This is a desirable consequence in the lower Snake River.
Removal of the dams would also allow for sediment to be redistributed throughout the lower portion of the river. Following the removal of the Woolen Mills Dam on the Milwaukee River in Wisconsin, the percent of rocky substrate compared to silt and mud found in the former impoundment significantly increased (Kanehl et al. 1997). Native fish such as smallmouth bass increased as well. These positive trends can be attributed to the reintroduction of larger and more course sediments to the river habitat (Hayes & Klomp). Sand and silt deposits wash downstream re-exposing hard substrates such as cobble and stone. These substrates are very important, as they provide habitats for macroinvertebrates and spawning grounds for fish.
Not all the consequences of dam removal are positive, however. Dam removal may cause a process known as “supersaturation,” which is characterized by increases in velocity and air pressure above natural conditions (American Rivers 2002). This may cause many fish and aquatic insects to perish due to gas-bubble disease, a condition similar to the “bends” that divers experience when surfacing too quickly. Supersaturation occurred downstream of the Little Goose Dam in 1992 after it was drawn down. As a result, many fish and aquatic insects were killed. “Fortunately, fish losses associated with this draw down were short-term with minimal impacts on overall populations” (Wik 1995). In order to lessen the negative impacts of supersaturation dams should be drawn down slowly.
The sudden increase in suspended free-floating sediment due to the increase in turbidity after dam removal can also have adverse effects on organisms, especially if the removal occurs during the spawning season for migratory fish species. The influx of suspended sediments can have negative impacts on water, habitat, and food quality (Newcombe& MacDonald 1991). These impacts are short-term making the timing of dam removal of the utmost importance. Along with the gradual draw-downs, sediment trapping via screens and channel dredging are useful techniques that can be used to reduce the short-term impacts that sediments have on downstream habitats. (American Society of Civil Engineers 1997).
When considering dam removal it is necessary to determine not only the ecological costs and benefits, but also the economical costs and benefits. An extensive study was conducted by the Army Corps of Engineers to determine these costs and benefits. It is mandated by the federal government that steps are made to recover salmon and steelhead populations, as well as, to prevent extinction (Revenue Stream 2006). It is important to note that Federal law requires the federal government not only to prevent extinction, but also to take steps to recover salmon and steelhead to a point where they no longer need federal protections. This means that if the dams are not removed, other strategies must be implemented that may be just as costly over time as dam removal.
The costs of keeping the four dams in place are extensive. The Federal Columbia and Snake River Salmon Plan for restoring salmon populations was rejected, and was projected to cost $6 billion over a ten year period or $600 million per year. Using this as an estimate for a restoration strategy would be conservative, as costs will likely increase to allow the plan to become legal policy. The costs to operate the dams were also considered, as well as, maintenance costs. At the moment Lower Granite Dam has a serious problem with sedimentation build up. As of 2002, the designated 5 feet of levee protection had been reduced to only 2 feet (Revenue Stream 2006). This problem needs to be addressed or the risk of dam failure and subsequent injuries or deaths to citizens of Lewiston, Idaho will increase along with the sedimentation. It is projected to cost between $7.84 and $9.09 billion over the next ten years to keep the dams in place.
There are many things to consider when weighing the costs and benefits of dam removal. The Federal Columbia and Snake River Salmon Plan would drop from $6 billion over ten years to somewhere between $3.1 and $4.5 billion of the next ten years (Revenue Stream 2006). The Army Corps of Engineers estimates a one time cost of $790.5 million to remove the dams and restore the river. Not only must the costs of dam removal be taken into account, but the restoration of the benefits provided by the dams must also be considered. These include a small percentage of power provided to the Pacific Northwest (between 2 and 5% depending on season), the ability for barges to use the river for grain transportation to and from Lewiston, Idaho, and irrigation provided to farms from the Ice Harbor Dam. Switching to wind power mixed with energy efficiency would increase individual energy bills by about 65 cents to $2 per month over the next twenty years. Using the rail system to transport grains rather than river barges is estimated to cost between $65 and $230 billion. The large range in this estimate reflects varying assumptions about the ability of existing rail-served grain elevators to handle higher volumes of grain after the lower Snake dams are removed (Revenue Stream 2006). A plan put forth by the Army Corps of Engineers would cost a one time fee of $421 million to implement an irrigation system allowing the thirteen affected farms to continue using Snake River water. Although the initial costs of dam removal seem to be high, it was determined that it would actually be more economically costly to leave the dams in place while attempting to control salmon and steelhead populations (figure 1) (Revenue Stream 2006).