January 31, 2013

The foundation of the Instream Flow Study (IFS) analyses rests with the development of the Susitna River Mainstem Flow Routing Models (HEC-RAS and Ice Processes Model) that will provide hourly flow and water surface elevation data at numerous locations longitudinally distributed throughout the length of the river downstream of the proposed dam site. The robust performance and flexibility of HEC-RAS make this model an appropriate choice for routing stage fluctuations downstream from the proposed Project dam under open-water conditions (i.e., summer, ice-free).

The goal of this study was to determine the composition and frequency of mainstem aquatic habitats and delineate the proportion of habitat in the middle Susitna River from aerial imagery or videography. The objective was to measure, using geo-rectified imagery, river habitat in the middle Susitna River. A spatial database of the length and composition of habitat would be developed by drawing the beginning and end point of each specific habitat unit (i.e. remotely habitat map). The study is intended to provide baseline data for supporting the selection of representative focus areas for instream flow studies and the approach for fish distribution site selection.

The implementation plan will include: (1) a summary of relevant fisheries studies in the Susitna River, (2) an overview of the life-history needs for fish species known to occur in the Susitna River, (3) a review of the preliminary results of habitat characterization and mapping efforts, (4) a description of site selection and sampling protocols, (5) development of field data collection forms, and (6) development of database templates that comply with 2012 AEA QA/QC procedures. The implementation plan will include the level of detail sufficient to instruct field crews in data collection efforts. In addition, the plan will include protocols and a guide to the decision making process in the form of a chart or decision tree that will be used in the field, specific of sampling locations, details about the choice and use of sampling techniques and apparatuses, and a list of field equipment needed. The implementation plan will address how sampling events will be randomized to evaluate precision by habitat and gear type. The implementation plan will also help ensure that fish collection efforts occur in a consistent and repeatable fashion across field crews and river segments.

The overarching goal of the River Productivity study is to collect baseline data to assist in evaluating the potential Project-induced changes in flow and effects on environmental factors (e.g., temperature, substrate, water quality), and benthic macroinvertebrate and algal communities in the middle and upper Susitna River.

Specific objectives of this technical memorandum include: (1) review the general approach to stratification and the study site selection process used in the Instream Flow Study Revised Study Plan; (2) identify the 10 Focus Areas that were initially described in the Revised Study Plan and the criteria that were used in their selection; (3) describe and summarize the statistical analysis completed on the habitat mapping results of the middle river segment with respect to the 10 Focus Areas and their habitat units; (4) describe the implications of the habitat analysis and any modifications to the study site selection process, including refinements in Focus Areas, and the need to identify supplemental sites or areas; (5) list all proposed Focus Areas and study sites outside of the Focus Areas for all Instream Flow Study related studies to be implemented in the middle river segment of the Susitna River.