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6.0 Analysis of Project Effects on Sediment Transport and River Geomorphology

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6.0 ANALYSIS OF PROJECT EFFECTS ON SEDIMENT TRANSPORT AND RIVER GEOMORPHOLOGY 6.1 DESCRIPTION AND PURPOSE The purpose of this study is to characterize sediment transport and geomorphic conditions and controlling factors in the Project area, including understanding the potential effects of Project operations. As one component of this study, PacifiCorp assesses fluvial geomorphic processes and conditions in various river reaches by evaluating the range and trends of bed material size and channel form, estimating flows required to mobilize the riverbed material, and identifying bed armoring and channel change. As another component of this study, PacifiCorp assesses the character and quantity of sediments being retained in Project reservoirs. The results from this study will enable PacifiCorp to identify distinct geomorphic reaches, determine the important factors that control geomorphic processes and conditions in these reaches, assess potential sediment sources and transport through these reaches, and describe potential Project effects on these geomorphic processes and conditions. Specific reaches or segments of the Klamath River in the Project area contain different Project facilities and operations. River geomorphology in these reaches varies, with distinct River flows through Lake Ewauna and Keno reservoir (approximately RM 254 to RM 233), which is a relatively low gradient, wide, and slow-moving section of the river. By contrast, the reach from J.C. Boyle dam to Copco No. 1 reservoir extends about 20 miles (RM 225 to RM 204) in a confined canyon with a relatively high gradient channel composed predominantly of a step-pool or riffle-pool morphology, with minor alluvial reaches. Downstream of its confluence with Cottonwood Creek, the Klamath River leaves the predominantly volcanic Cascade province and traverses the Klamath Mountains within a valley of more diverse local geology and lithology. 6.2 OBJECTIVES The objectives and key questions addressed by the analysis described in this report are as follows: • How do the environmental features of the Project area relate to fluvial geomorphology? • Classify general geomorphic characteristics for reaches of the Klamath River within the Project area and downstream to Seiad Valley. • How do the Project facilities and the operation of those facilities affect fluvial geomorphic processes? • What are the potential measures or actions that can be taken to meet resource management objectives related to potential Project effects on sediment transport and river geomorphology? 6.3 RELICENSING RELEVANCE AND USE IN DECISIONMAKING This study helps PacifiCorp address resources issues related to Project effects on river geomorphology and sediment transport. The results of this task, together with the results of the © February 2004 PacifiCorp Water Resources FTR.DOC Water Resources FTR Page 6-1 PacifiCorp Klamath Hydroelectric Project FERC No. 2082 study of hydrology effects, are used to assess channel morphology and sediment transport characteristics in the Project area. It also helps determine the effects of Project operations on sediment transport and geomorphic processes. Relicensing of the Project requires Section 401 certifications from relevant state agencies and compliance with requirements of the federal Clean Water Act. This task helps PacifiCorp assess channel morphology and sediment transport effects as they relate to water quality objectives and standards as promulgated by these agencies. Water quality can be affected by channel morphology and sediment transport conditions, such as by sediment accumulation or channel changes that can occur within and downstream of reservoirs (Ligon et al. 1995). Therefore, the tasks described in this study provide information for the assessment of water quality as well as geomorphic conditions. Relicensing of the Project also requires PacifiCorp to assess channel morphology and sediment transport effects as they relate to other key aquatic resources issues, such as fisheries resources and riparian habitats. For example, salmon and steelhead below Iron Gate dam require sediment sources and sizes that are sufficient to support spawning. As another example, channel morphology and sediment transport conditions are important factors in the establishment and maintenance of riparian vegetation (Ligon et al. 1995). Therefore, the tasks described in this study provide information for the assessment of aquatic resources as well as geomorphic conditions. 6.4 METHODS AND GEOGRAPHIC SCOPE 6.4.1 Geographic Scope The geographic scope of this study generally extends from Link River dam (RM 254.3) to Seiad Valley (RM 128.5) in the Klamath River. However, the reaches within the Project area from Link River dam to Iron Gate dam (RM 190), and downstream to the confluence of the Shasta River (RM 176.7), are the primary focus of field surveys and data collection and analysis. It is within this area that PacifiCorp operations have the most potential to significantly affect hydrology, geomorphology, and sediment transport. Given the rapid downstream increase in flow and sediment from Klamath tributaries, it is expected that the principal Project influence will extend downstream to the confluence of the Shasta River. This expectation was reinforced by results of geomorphic investigations at Seiad Valley sites in 2002. In addition, the study area extends upstream along tributaries and onto slopes as needed to assess sources of sediment and sediment yield from various geologic units and land use types. Review of existing data and information on Klamath River geomorphology, together with examination of current and historical aerial photographs of the river channel, includes the Klamath River from Link River dam (RM 253.7) continuously to the confluence of the Scott River (RM 143). USFS geologic and sediment yield information was assessed for reaches downstream of Iron Gate dam. Spot observations of channel conditions at sites downstream to Seiad Valley (including Seiad Valley, important tributary confluences, and sites for which good historical aerial photographs were available) provided further information on sediment sources and yields. Project geomorphologists estimate that this area is adequate to establish the current and historical basin-level geomorphic setting for this study. © February 2004 PacifiCorp Water Resources FTR Page 6-2 Water Resources FTR.DOC PacifiCorp Klamath Hydroelectric Project FERC No. 2082 The geographic scope of this study generally extends from Link River dam (RM 254.3) to Seiad Valley (RM 128.5) in the Klamath River. However, the reaches within the Project area from Link River dam to Iron Gate dam (RM 190), and downstream to the confluence of the Shasta River (RM 176.7), are the primary focus of field surveys and data collection and analysis. It is within this area that PacifiCorp operations have the most potential to significantly affect hydrology, geomorphology, and sediment transport. Given the rapid downstream increase in flow and sediment from Klamath tributaries, PacifiCorp’s Project geomorphologists estimate that this area is adequate to establish the current and historical basin-level geomorphic setting for this study. 6.4.2 Reservoir Sedimentation Study 6.4.2.1 Bathymetry and Calculation of Sediment Accumulation in Project Reservoirs PacifiCorp collected bathymetric data from Keno, J.C. Boyle, Copco, and Iron Gate reservoirs in the fall of 2001 using SONAR/DGPS equipment with a positional accuracy of approximately 6 centimeters (cm). Additional survey work was concluded in Keno reservoir in August 2003. The positional accuracy was verified against available registered benchmarks for the area. The acoustic data were generated at a frequency of every second along transects from 50 to 100 meters (m), depending on the size of the domain being mapped. Sediment cores were collected in specific locations of each reservoir to determine the size distribution of materials transported to the reservoir. These data were edited and entered into a geographic coordinate system (e.g., NAD83), consistent with PacifiCorp’s GIS system for the Project area. The edge of shoreline was generated using a recent satellite image that has been rectified and has suitable pixel size for the application (e.g., 1 m). For each reservoir or lake, the following products were produced: • Digital and paper copies of the impoundment bathymetry • Topographic representation of the Project sites prior to impoundment (assuming the original topographic maps can be located) • Hypsographic curves of the Project reservoirs, with detailed information on lake surface area, maximum depth, mean depth, and volume • Calculations of estimated accumulated sediment volume in each reservoir Sediment accumulation in the reservoirs was calculated by comparing reservoir volume differences between the new bathymetry and previous reservoir volumes as derived from available information (such as City of Klamath Falls, 1986; Johnson et al. 1985) and calculated from original topographic maps. Classification of Sediments in Project Reservoirs The sediment classification for the Project reservoirs consisted of a multistep approach involving preclassification of the sediments using hydroacoustics, stratified sediment sampling, and postclassification using the sediment data. Each step is described as follows. © February 2004 PacifiCorp Water Resources FTR.DOC Water Resources FTR Page 6-3 PacifiCorp Klamath Hydroelectric Project FERC No. 2082 Step 1. Hydroacoustic Pre-Classification The hydroacoustic
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