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Impingement Mortality and Entrainment (IM&E) Reduction Guidance Document for Existing Seawater Intakes

Project: 10-04
Type: Report
Year Released: 2014

Program: Principal
Funding Partners: Bureau of Reclamation, California Department of Water Resources
Total Investment: $197,031.54 (Cash: $150,000, In-Kind: $47,031.54)

Principal Investigator: Timothy W. Hogan, Alden Research Laboratory, Inc.


Human population projections indicate that the demand for potable water will increase over time. This demand can be responsibly met through a diversified water supply portfolio, a component of which is desalinated water. Therefore, it is important to be mindful of the potential environmental impacts posed by desalination operations and prepare in advance to minimize these impacts.

The operation of intake structures designed to supply feed water to the desalination treatment processes creates potential environmental impacts. In particular, the withdrawal of water poses a risk of IM&E of aquatic organisms residing in the source water body. Careful consideration of these potential environmental impacts is also critical because they can significantly affect facility economics by dictating intake type, size, location, and operational requirements as well as the type and magnitude of mitigation required to offset the impacts.

Goals and Objectives

The project provides guidance on the intake technologies and modifications that have potential for mitigating IM&E of marine organisms at existing seawater intake structures. If existing intakes can be modified for desalination use, the seawater desalination industry can realize reduced capital costs associated with constructing new intakes.

The specific objectives of this project are to:

  • synthesize the available literature on intake technologies and their ability to reduce IM&E
  • present case studies of sites where intakes have been modified to reduce IM&E
  • provide guidance on how to evaluate intake technologies for reducing IM&E at existing intakes
  • describe the methods for measuring IM&E reductions
  • determine the costs associated with modifying intakes
  • describe the likely permitting requirements for modifying intakes

Research Approach

This project was comprised of:

  • A comprehensive literature review for papers associated with intake technologies and IM&E as well as state and federal intake-related regulations
  • A detailed review of the intake technologies available for reducing IM&E,
  • Guidance on how to improve the biological performance of existing intakes,
  • Presentation of hypothetical intake modification designs (with estimated costs),
  • A review of techniques to measure IM&E reductions,
  • Presentation of case studies of facilities that have undergone modification of existing intakes to reduce IM&E, and
  • Recommendations on how to navigate the intake permitting process.

Findings and Conclusions

More than 375 references pertaining to intake technologies and/or IM&E were identified and compiled into an annotated bibliography. Four groups of intake technologies offer potential for minimizing IM&E: behavioral systems, exclusion systems, collection systems, and diversion systems. While the federal Clean Water Act Section 316(b) describes the biological standard to which an intake will be held, there is more variation among states. The core tenets of 316(b) drive the intake technology selection process when considering modification of an existing seawater intake. These include the location, design, construction, and capacity of the intake.

Many intakes undergo modification to reduce IM&E – both the Tampa Bay Electric Company’s Big Bend Station and the Brunswick Steam Electric Power Plant are two examples. Each facility achieved reductions in IM&E after the modifications were made. In cases where no existing data are available to estimate the biological performance of an intake modification, the potential efficacy (i.e., exclusion and survival) can be estimated using the morphological and physiological characteristics of the target organisms. Costs for intake modifications can vary depending on: 1) the size, location, configuration, and operational status of the existing intake and, 2) the scenario under which the desalination intake is installed. In the ten scenarios developed, intake modification costs ranged between $2.1 and $6.6 million.

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