Dissolved Gas Abatement Study

Phase II 60% Draft Report

This report is presented in numerous different pdf files, all contained on a CD-ROM that may be available upon request from the DGAS Study Team. This website only reproduces selected summaries of the report.

TABLE OF CONTENTS

MAIN REPORT

• Executive Summary
• Section 1 Introduction
• Section 2 Alternatives
• Section 3 Project-specific Alternative Ratings
• Section 4 Bonneville
• Section 5 The Dalles
• Section 6 John Day
• Section 7 McNary
• Section 8 Ice Harbor
• Section 9 Lower Monumental
• Section 10 Little Goose
• Section 11 Lower Granite
• Section 12 Biological Research
• Section 13 TDG Field Research
• Section 14 Numerical Model Development
• Section 15 System-wide Alternative Analysis
• Section 16 Summary and Conclusions

APPENDICES

• General Information & Reports
• Points Of Contact
• Alternative Design & Cost Estimate Reports
• Physical Hydraulic Model Study Reports
• Gas Production & Transport Field Research Reports
• Gas Production Estimates
• Biological Research Reports
• Numerical Model Development

EXECUTIVE SUMMARY

The Dissolved Gas Abatement Study (DGAS) is a part of the Columbia River Fish Mitigation Program. The goal of the DGAS is, in response to the 1995 NMFS Biological Opinion on Operation of the Federal Columbia River Power System, to identify means to reduce TDG at the eight Corps projects on the Lower Snake and Columbia Rivers to the extent economically, technically, and biologically feasible. To date, gas abatement alternatives have been identified and evaluated for potential application at the eight study projects. Additionally, numerical modeling tools have been developed to help evaluate the complex issues related to gas abatement through more than 300 miles of river. This report documents the status of the gas abatement program and the information collected to date. The next step for this study is to evaluate the alternatives and potential implementation scenarios using the numerical modeling tools.

The Dissolved Gas Abatement Study includes two parts, a Phase I reconnaissance level report and a Phase II feasibility level report. The Phase I reconnaissance level report was completed in April 1996 and included the following.

• Background information on existing project features on the eight Corp’s dams.
• Information on the TDG production of existing dams.
• Summary of the causal mechanisms of TDG production.
• Historical background of TDG and related effects on fish.
• Evaluation and recommendations of improvements to the existing TDG fixed monitoring system.
• Recommendation of operational measures that could be accomplished quickly and easily to reduce TDG production immediately.
• Identification of numerous structural alternatives which held potential for reducing TDG production.
• Evaluation and recommendation of several alternatives for a further more detailed evaluation.
• Recommendation to develop an analytical decision tool (physical and biological numerical models) for use in assessing project specific and system-wide effects of alternatives.
• Identification of missing biological information and recommended a program for obtaining the information.
• Study plan for a more detailed Phase II feasibility level investigation.

The Phase II Report will present and document the results of the DGAS Phase II feasibility-level investigations. This 60% draft report presents the status of major components of the DGAS as of December 1998. Most of the background information surrounding dissolved gas issues are discussed in the April 1996 DGAS Phase I Technical Report. This document continues where the Phase I report ended and will be finalized when the study is complete in 2000. To facilitate dissemination of the extensive amount of information developed through this study, this report is being distributed electronically on compact disc. Supporting documentation and technical reports prepared for this phase of DGAS are included on the compact disc in pdf files (portable document format). This format is readable with Adobe Acrobat Reader, which is free software. An Adobe Acrobat Reader installation file is included on the compact disc.

The Phase II gas abatement effort includes a complex system-wide evaluation of alternatives and can be broken into five main tasks: alternative investigations, prototype construction, numerical modeling, biological research, and water quality research. Alternative investigations include the design and localized evaluation of alternatives. Prototype construction includes the construction and testing of an alternative to validate assumptions and estimates developed in the alternative investigations. Numerical modeling includes the development and use of numerical modeling tools to evaluate biological and water quality benefits of gas abatement alternatives throughout the river system. Biological research includes field and laboratory research required to validate assumptions made in the design of alternatives and to calibrate and validate the numerical modeling tools. Water quality research includes field research required to investigate gas production of the existing structures and the alternatives and to investigate transport and mixing characteristics of the river system as needed to develop the numerical modeling tools. Some parts of this study have been discontinued. Summaries of the objectives and status of these five main tasks follow. Additionally, the program’s review by the Independent Scientific Advisory Board, is also summarized, as this review played a significant role in changing the scope of this study.

Alternative Investigations. The gas abatement alternative investigation efforts are nearly complete. This task includes the design and localized evaluation of alternatives. The five main objectives of this task included:

1. Establishment of Design Criteria. This objective has been completed. The following design guidelines were established: Alternatives should reduce the production of TDG; provide adequate energy dissipation; provide safe fish passage; and be reasonable to construct, operate and maintain.
2. Identification of Alternatives. This objective has been completed. Over forty alternatives were initially identified and evaluated for gas-abating characteristics.
3. Feasibility Evaluation of the Identified Alternatives. This objective is 90 percent complete. The alternatives that showed promise for abatement of dissolved gas were evaluated on a site-specific basis for their applicability at each dam. Preliminary site-specific designs were developed for the alternatives found to be most applicable at each dam. Some alternatives were evaluated in physical hydraulic models to ensure feasibility. The physical hydraulic modeling effort within this task is not yet complete; a few alternatives (i.e. the Bonneville submerged gate and raised tailrace) are still being evaluated in physical hydraulic models to resolve feasibility issues.
4. Development of Estimated Construction Costs and Implementation Schedules. This objective is 80 percent complete. The cost and required implementation time have been estimated for the most promising site-specific designs. Table ES-1 summarizes the most promising structural alternatives at the Columbia River and Snake River projects. Cost and required implementation time estimates are included in the report and summarized in Section 16. The estimates will be reviewed over the next year and revised as necessary.
5. Development of Estimated TDG Performance of Alternatives. This objective is 95 percent complete. TDG production estimates have been prepared based on the site-specific designs. All of the alternatives reduce TDG to different degrees below the existing spillways’ performance. However, none of the alternatives appear to meet all of the design criteria and meet the water quality criteria developed under the Clean Water Act. The TDG performance of the alternatives is highly dependent on a variety of factors including the assumed project operations and incoming TDG supersaturation. Because of the large range of variable assumptions, the TDG performance is impossible to describe with numbers in a summary table. Spreadsheet models of each alternative at each project have been developed and are included in this report in Microsoft Excel files. These estimates will be reviewed over the next few months and revised as necessary. Prototype structures will need to be constructed and tested outside of this study in order to confirm the gas production estimates.

Table ES-1. Summary of the Most-promising Gas Abatement Alternatives

Prototype Construction. This task has been discontinued. This task was intended to provide validation to the estimates and assumptions made within the alternative investigations. One specific alternative, the raised tailrace with deflectors, was recommended for expedited investigation of potential prototype construction and testing at Ice Harbor. This alternative involves filling in the tailrace channel, or essentially raising the tailrace channel bottom, in order to make the river shallower downstream of the stilling basin. The original basis for this recommendation included:

1. validation of the alternative’s gas production estimates,
2. collection of information transferable to other projects,
3. reduction of gas production at Ice Harbor, and
4. relatively low cost of construction at Ice Harbor.

However, further investigation raised concern that the rock-filled tailrace may require a concrete cap in order to reduce juvenile fish injury and potential predator habitat. If a concrete cap is required, the construction costs of a raised tailrace at Ice Harbor will be significantly higher than shown in Table ES-1. Additionally, the gas production at Ice Harbor has been reduced significantly with the installation of deflectors and is very low compared to other projects. Therefore, the recommendation to prototype test the raised tailrace at Ice Harbor has been withdrawn. Testing the raised tailrace alternative at a project that is more in need of gas reduction might be a better investment if an expensive concrete cap is required. Prototype testing will still be recommended prior to full-scale implementation of any of the gas abatement alternatives. However, prototype construction and testing of alternatives will not be included within this study.

Physical Field Research. The TDG data collection effort in support of the gas transport/mixing portion of the numerical model has been completed. In addition to the pool sampling studies, near-field studies were performed in the tailraces of every dam except Lower Granite. The near-field tailrace research provided invaluable information for understanding gas production and for developing the gas production estimates for each project and the alternatives. A significant database of water quality and hydraulic data has been developed and will be available over the Internet and through a separate technical report currently being published by the Corps’ Waterways Experiment Station.

Biological Research. Analyses conducted in DGAS Phase I identified two areas for biological study required to enable biological analysis of DGAS alternatives and potential implementation scenarios. These two areas included the direct physical injury to fish during spill passage and the physiological response of salmonids to exposure to total dissolved gas supersaturation conditions. The necessity of performing these biological analyses was questioned during regional review of the DGAS Phase II plan of study. The biological studies were placed on hold pending review by the Independent Scientific Advisory Board (ISAB). Congress had requested that the ISAB, a committee formed by NMFS and the Northwest Power Planning Council, review the overall Columbia River Fish Mitigation Program. In 1998 the DGAS Phase II program was reviewed by the ISAB. The reviewers concluded that the Corps should continue the gas abatement program to reduce TDG as low as practicable with a modified set of short- and long-term objectives. Additionally, the reviewers concluded that the biological studies to enumerate TDG exposure and risk to migrants were not necessary. (This is the Corps’ interpretation of the ISAB recommendations; the actual recommendations are quoted in Section 12 of this report.) Consequently, all biological studies were discontinued in FY98 with the exception of those investigating direct physical injury to fish during spill passage. The study will be completed in accordance with the ISAB recommendations and regional funding priorities.

In FY98, all studies supporting the biological analyses of incremental gas reductions resulting from DGAS alternative implementation were discontinued pending the ISAB review. In accordance with the ISAB recommendations, the studies of juvenile salmonid migratory behavior and the response of juvenile salmonids to TDG supersaturation exposure will not be continued. Closure of these studies and removal of biological benefit analysis from the DGAS program will leave unresolved questions about the biological efficacy of DGAS alternatives and implementation scenarios.

Biological analysis of potential physical injury associated with the DGAS alternatives will be reinitiated in FY99 following guidelines provided by ISAB and regional prioritization of biological issues. In FY99 the physical injury component of DGAS will focus on the relationship between mortality rates and physical processes in the spillway stilling basin that can be quantified at physical model and prototype scales. This phase of physical injury assessment is designed to permit direct linkage between the design of spill structures and their operation for safer passage of migrants.

Numerical Modeling. The numerical modeling effort includes the development and use of computer models which will allow for analysis of the complex gas-related issues for numerous potential implementation scenarios of gas abatement structures. The interrelated numerical modeling tasks have reached significant milestones, and some tasks have been discontinued as summarized below.

1. TDG transport and mixing. This task is 95 percent complete. The two-dimensional flow and transport models for each of the lower Snake and Columbia River projects have been developed, calibrated, and validated. The separate project/pool models will linked together to form one model of the Lower Snake and Columbia River system.
2. Juvenile salmonid migratory behavior. This task has been discontinued in accordance with the ISAB recommendations and regional funding priorities. The juvenile salmonid migratory behavior model has been coded, but very little data exists for calibration and validation of the model.
3. Biological analysis of alternatives. This task has been discontinued in accordance with the ISAB recommendations and regional funding priorities. The analysis model for simulating biological impacts from numerous implementation scenarios of gas abatement alternatives has been coded and partially calibrated. No further efforts will be made on this task.
4. Water quality analysis of alternatives. This task will begin in FY99. Numerous system-wide alternative implementation scenarios will be identified. Gas production estimates and operational description of these alternative implementation scenarios will be input to the two-dimensional transport and mixing models. The output from those model simulations will be analyzed to compare the water quality benefits (primarily reductions of gas supersaturation) of the alternative implementation scenarios. This information will be included in the next DGAS report scheduled for release in FY00. v

Summary and Conclusions. A great deal of progress has been made in evaluating the alternatives for gas production benefits, addressing engineering concerns, and developing the numerical model capability to simulate the TDG supersaturation of different implementation scenarios of gas abatement alternatives. All biological analyses except the physical injury analysis of alternatives has been discontinued in this study in accordance with regional funding priorities and as recommended by the ISAB.

Numerous conclusions can be drawn at this point of the investigation. The following are some of the more significant conclusions:

0. None of the alternatives presented appear to meet all the design criteria and the 110 percent water quality standard up to the 7-day 10-year discharge events. Those structures that approach the 110 percent gas standard are likely to be harmful to juvenile fish during passage through the structure. The gas production estimates presented in this report are for a point located about 1000 feet downstream of the spillway. Evaluation of the alternatives in the system numerical model is required to estimate resulting gas at a location representative of the Fixed Monitoring Stations.
1. Uncertainties remain in the gas production estimates for some alternatives. Prototype construction and testing will be required to validate the gas production estimates of some alternatives, especially those that are significantly different than existing project structures.
2. Incremental reductions in TDG, beyond those achievable with deflectors and operational changes, will be very expensive. Flow deflectors have proven to significantly reduce gas supersaturation and for a relatively low cost. However, implementation of the other gas abatement alternatives will be very costly in comparison to flow deflectors.
3. An assessment of biological risk is important to evaluate the relative differences between alternatives. Two major elements of risk have been identified: physical injury and effects of exposure to TDG through the system. These two elements of risk need to be assessed in order to assess the biological benefits of different alternatives. However, all aspects of evaluating biological effects of TDG have been discontinued within this study in accordance with the ISAB’s recommendations and regional funding priorities.
4. The region is currently proceeding with the assumption that fish survival through spill is very high. Considerable uncertainty exists on estimating the extent of physical injury to fish passing through spill and the gas abatement alternative structures. The parameters that will likely cause injury to fish have been identified. However, little information is available to evaluate potential physical injury for the gas abatement alternatives. This makes the task of estimating physical injury purely based on professional judgement. Prototype structures will be required prior to implementation of the gas abatement alternatives in order to minimize the uncertainty related to physical injury.
5. A numerical model to evaluate direct cumulative GBT mortality resulting from a wide variety of dissolved gas and temperature exposure scenarios under realistic fish migratory behavior and TDG production, transport, and mixing conditions was completed. This effort has resulted in a new understanding of GBT mortality for migrating juvenile salmonids. However, due to the lack of calibration data and the discontinuation of biological research within this study, the model will not be used within this study.
6. Recommendations regarding implementation of specific gas abatement alternatives will not be made until the system numerical model analysis is completed over the next 1-2 years.

Upcoming Tasks. Most of the concerns regarding the consequences of exposure to TDG supersaturation, the potential for physical injury to juveniles passing through spillway structures, and the uncertainty of gas estimates will not be resolved within this study. This study will proceed with the system analysis of water quality effects from numerous of alternative implementation scenarios using the numerical model developed for that purpose. The tasks to be completed next include:

• Complete physical hydraulic modeling to resolve feasibility issues of a few alternatives
• Complete review of estimated cost, required implementation time, and gas production for the most promising structural alternatives
• Link the separate project/pool numerical models of gas transport and mixing together to form one numerical model of the Lower Snake and Lower Columbia River system.
• Identify alternative implementation scenarios.
• Exercise the transport and mixing model and compare the water quality benefits of the alternative implementation scenarios.
• Complete the physical injury assessment of gas abatement alternatives.

Meanwhile, a new Fast-track Program, or Spill Optimization Program, spun off from the Dissolved Gas Abatement Study in an effort to expedite the implementation of some of the gas abatement alternatives. As recommended by the ISAB, this new effort will be a short-term gas abatement effort while the DGAS Phase II effort continues with more of a long-term evaluation. The Spill Optimization Program will primarily focus on the deflector-related alternatives that can be constructed much quicker than other alternatives. The Spill Optimization Program will also include: development of spill patterns, further evaluation of the risk of physical injury associated with the alternatives, and evaluation of spillway survival and effectiveness under a range of spillway operations.

POINTS OF CONTACT

• John Kranda Project Manager, Portland District (503) 808-4709
• Rock Peters Biological Studies Technical Manager, Portland District (503) 808-4777
• Rick Emmert Technical Manager, Walla Walla District (509) 527-7536
• Tom Carlson Fisheries Biologist, Waterways Experiment Station (503) 808-4770

Return to Corps Water Quality Program Main Page