Environmental Analysis
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3.0 ENVIRONMENTAL ANALYSIS The project is located in north central Washington approximately 7 miles north of the city of Wenatchee on the Columbia River in Chelan County. The dam is 215 river miles south of the Canadian border and 474 river miles above the mouth of the Columbia at Astoria, Oregon. The project reservoir extends upriver 43 miles and has a surface area of approximately 8,235 acres. The project’s drainage area at the dam is about 87,800 square miles. The watershed lies east of the Cascade Mountains and west of the Rocky Mountains, in parts of Washington, Idaho, Montana, and British Columbia. The normal maximum headwater elevation is 707 feet, and the average tailwater is at elevation 617.6 feet. The Columbia River System is primarily fed by snowmelt and upstream storage projects. The river at the project location is essentially a gorge interrupted by confluences with a number of tributary valleys. The two most significant tributaries within the project area are the Entiat and Chelan rivers, which enter the Columbia River at approximately RMs 483 and 503, respectively. The project lies between two significantly different physiographic areas. It is located in a valley that is north-south trending, with the North Cascades Mountains to the west and the Columbia plateau to the east. The rugged peaks in the Cascades average about 5,000 feet and reach elevations of over 10,000 feet. The climate in the vicinity of the project is semi-arid, which is typical of eastern Washington. The seasonal range of temperatures in the area is from a winter average of about 25ºF (degrees Fahrenheit) to a summer average of about 75ºF. Spring and fall temperatures average 50ºF. Extreme temperatures can approach –30ºF in winter and 110ºF in summer. Precipitation is generally low, with an annual average of approximately 10 inches, the bulk of which falls between October and March. There are usually no more than 8 to 15 inches of snow on the ground. Vegetative cover adjacent to the project reflects the low level of precipitation in the area and the definitive shoreline edge of the reservoir. Riparian vegetation occurs intermittently along the margins of the reservoir. Riparian grasses/forbs, riparian shrubs, and riparian deciduous trees are representative of vegetation within this typically narrow zone. Riparian vegetative types represent about 40 percent of the shoreline. Grassland, shrub steppe, and open conifer/shrub vegetation occur along the upland margins of the shoreline. Exposed rock of both fluvial and glacial origin is often mixed into the landscape. Narrow wetlands occur intermittently within the shoreline margins of the reservoir and are also found where depressions occur beside the highways that parallel much of both sides of the river. 29 3.1 Cumulative Effects According to the Council on Environmental Quality regulations for implementing NEPA 40 CFR 1508.7, cumulative effects are defined as the impact on the environment that results from the incremental impact of the action when added to other past, present, and reasonable foreseeable future actions, regardless of what agency or person undertakes such other actions. Cumulative effects can result from individually minor but collectively significant actions taking place over a period of time, including hydropower and other land and water development activities. Within the project, we have identified water quality, anadromous salmonids, Pacific lamprey, and white sturgeon as having the potential to be cumulatively affected by this project in combination with other hydroelectric project operations and other activities on the Columbia River. 3.1.1 Geographic Scope The geographic scope of the cumulative effects analysis defines the physical limits or boundaries of the proposed action's effects on the identified cumulatively affected resources. Analysis of the cumulative effects at the project is limited to the Columbia River watershed, as bounded by the project from the tailrace of the upstream Wells Hydroelectric Project (FERC No. 2149) downstream to the beginning of the Rock Island Hydroelectric Project (FERC No. 943) reservoir. 3.1.2 Temporal Scope The temporal scope of analysis includes a consideration of past, present, and future actions and their effects on cumulatively affected resources. Based on the likely term of a new license, we projected 30 to 50 years into the future, concentrating on the effects on the resources from reasonably foreseeable future actions. The historical discussion is limited, by necessity, to the amount of information available for each resource. We identify the current resource conditions based on the license application, comprehensive plans, and scoping comments received from various agencies and other stakeholders. 3.2 GEOLOGICAL AND SOIL RESOURCES 3.2.1 Affected Environment Columbia Plateau lava flows and repeated failure of glacial ice dams during the continental glaciation of the Pleistocene epoch influenced the position of the Columbia River at the project site. Repeated uplifts have caused the river to be entrenched into its position at the edge of the lava flows. Glacial activity also has greatly enlarged the river 30 valley and shifted the river channel in some locations. The resulting glacial dam failures and floods were often catastrophic, resulting in a large flow of ice- and dirt-filled water that would rush down the Columbia River drainage scouring the canyon in some areas and depositing sediment in others. Steep, rocky upper slopes currently characterize both sides of this part of the river valley. In a few places, bedrock slopes extend to the reservoir level. In most areas, bedrock on the lower slopes is covered by talus or other soil deposits. The valley is geologically young, and the Columbia River was still actively down- cutting at the time of project development. The river in the project area is commonly incised into alluvial fans, terrace deposits, eolian13 deposits, and some deposits of lacustrine14 sediments, many of which are remnants of glacial processes in the area. Where the river passes through terraces, eolian deposits, or lacustrine deposits, the shoreline is characterized by steep banks typical of youthful river valleys. These banks are the remaining erosion faces from downcutting by the river and have relatively flat slopes above them. Alluvial fans more commonly exhibit moderate to gentle slopes that extend to, or nearly to, the water surface. Both terrace and alluvial deposits are composed of sandy gravel with varying percentages of cobbles. The eolian and lacustrine deposits are typically composed mostly of sand-sized and finer materials. Based upon a flow of 220,000 cfs, a 1999 study conducted by Duke Engineering Services (DES) for Chelan PUD (DES, 2001a) found that silt was the most abundant substrate type in the river itself (25.6 percent), followed by large cobbles (17.7 percent) and sand (17.4 percent). 3.2.1.1 Existing Geologic Hazards There are no seismic hazards related to the project, and no geologic hazards of significance have been identified. The project is periodically assessed for seismic and other geologic hazards through the required Part 12 inspections under the Commission’s authority. 3.2.1.2 Sediment Supply, Transport, and Storage in Reservoir The project is a run-of-river project with a generally narrow reservoir and a noticeable current flowing through the reservoir. Storage projects farther upriver, including the Wells Project immediately above the Rocky Reach Project, have reduced the sediment supply to the project reservoir. 13 Eolian deposits are sediments transported by the wind. 14 Lacustrine deposits are sediments associated with deposition in or directly adjacent to a lake. 31 The reservoir created by the Rocky Reach dam (known as Lake Entiat) is essentially a backwater effect. As such, it slows river velocities in the reservoir and raises the water level. Since the first generating units were placed in operation in November 1961, the project has regulated the water level in the reservoir to maintain water levels at the dam between 703 feet and 707 feet msl. The water level at the dam is generally between 706 and 707 feet msl, with a 20-year average of 706.53 feet. During flood flows in the river, the reservoir can be raised as high as 710 feet at the direction of the Corps to minimize the downstream flooding effects. The water surface elevation is not constant throughout the reservoir, instead increasing measurably from the project dam to the upstream Wells Project dam and varying with the volume of flow. For example, with a headwater elevation at the Rocky Reach dam of 707 feet and a flow of 100,000 cfs, the reservoir water surface elevation at Wells dam is approximately 4 feet higher, or 711 feet msl. Generally, depths increase in the reservoir from upstream to downstream. The shallowest, most riverine portion of the reservoir is found near the Wells Project tailrace, with depths increasing downstream to the Rocky Reach forebay. As a result of project development, the typical range of flows and water levels experienced by the shoreline has changed. The annual range of flows has decreased as a result of water storage at upstream projects. These upstream projects store water when natural flows are high and release water during times of lower natural river flows, thus moderating the extremes of flow volume during the water year. Despite this tempering of seasonal variation, the daily range of changes in flow and water level may have increased as a result of regulation of the river. This effect results from the operation of projects upstream of the project and the project’s need to pass incoming flows. Water depths are relatively unchanged from that of the pre-project river in the upper part of the reservoir (i.e., immediately downstream of Wells dam). Immediately upstream of Rocky Reach dam, water depths exceed 100 feet, substantially more than prior to construction of the project.