Journal of Hydraulic Engineering

Since the early 1900s, virtually the only water screen used for power‐plant cooling water systems in the United States has been the “through‐flow” type of travelling screen. Trash bars and rakes upstream of the screens have been similarly restricted in design. Other industrialized countries of the world have gone their own separate ways in power plant water screening, having considerable confidence that they have the best. Serious and costly clogging and carryover of debris have plagued many U.S. installations over the years, but apparently not enough to push users to look at these other successful technologies. This paper explores the common alternatives to through‐flow screens, with comments on the pros and cons of performance, maintenance and cost. Some recent improvements to common U.S. screens will be discussed. Alternative trash rake designs will be similarly reviewed. Finally, this paper will discuss variations in the total water‐cleaning train.

A new angled‐screen intake was constructed in 1984 at the Brayton Point Generating Station Unit 4 to protect fish and larvae and to allow the use of a once‐through cooling system. The intake features low approach velocity, 1‐mm fine‐mesh screens, flush angled screens with fish buckets, and low‐pressure sprays. The intake functioned successfully, both hydraulically and environmentally.

Biofouling of water intakes can affect condenser performance and availability. Five biofouling control technologies are presented: thermal backwash; antifouling toxic coatings; nontoxic coatings; chlorination; and cathodic protection. Thermal backwash is currently used in power plants on the West Coast and on Long Island Sound. Toxic coatings, although effective, are currently restricted because of environmental concerns. Nontoxic coatings are currently being evaluated nationwide. Continuous low‐level chlorination can be effective if it is distributed uniformly on intake surfaces. Cathodic protection proves to be ineffective.

The Unit 6 intake system at Niagara Mohawk Power Corporation's Oswego Steam Station Unit 6 is designed to mitigate periodic losses of Lake Ontario fish by bypassing and returning to the lake those fish that enter the offshore intake. Fish are diverted along four traveling water screens installed in a chevron arrangement angled with respect to the flow. Jet pumps provide bypass flow necessary for fish return to the lake. Three years of information on the operational and biological effectiveness of the angled‐screen fish diversion system are presented and discussed. System components are discussed in terms of maintenance requirements and operation relative to an adjacent conventional intake system (Unit 5). Hydraulic measurements are also presented. Biological effectiveness of this system is compared with that of a once‐through system with conventional vertical traveling screens. Evaluation of fish survival up to 96 hrs after diversion indicates seasonal and species‐specific survival.

A three‐year study sponsored by the Empire State Electric Energy Research Corporation was conducted to determine the diversion efficiency and survival of adult and larval fish at a full‐scale angled screen demonstration facility located on the Hudson River estuary. A total of 59,309 fish were collected during the three‐year study, 99.4% from the diversion flow. Initial survival was 90.2%. Extended survival following a 96‐hr observation period was 35.3%. The angled‐screen system efficiency was 31.6%, increasing to 84.3% when corrected for collection and handling mortality. Ichthyoplankton diversion efficiency of 16.3% was inversely related to angled screen approach velocity and directly related to the size of the organism. Angled‐screen system efficiency for ichthyoplankton was 1.7%. The angled‐screen was judged to be successful for mitigating fish impingement. Ichthyoplankton study results indicate low diversion and high mortality, suggesting that angled screens are not effective for mitigating entrainment.

This paper presents a brief overview of factors to be considered in the design of hydropower penstock intakes. The paper notes areas of design concern including hydraulic losses, size and complexity of the intake with its associated gates and accessory equipment, the potential for air‐entraining vortex formation, release water quality control through selective withdrawal, gate design, stoplog design, trashrack design, fish diversion and passage, ice control and exclusion, and sediment control and exclusion. Alternative design approaches with recommended design criteria are given. Quality, application‐oriented references which supply substantial design guidance and support are cited. Specific examples that illustrate successful and unsuccessful designs are discussed and referenced. Specific concerns or deviations associated with high head, and pumped storage intakes are noted. It is intended that through use of the initial guidance given by this paper and the more detailed investigations generated, an appropriate, well‐conceived intake design can be achieved.

The Jeffrey Energy Center draws its cooling water makeup from the Kansas River, a shallow sand‐bed river of constantly changing bottom geometry. To accommodate this withdrawal, the water intake system was designed to be capable of maintaining intake capacity at all river stages. A set of river training devices keeps the deepest part of the river near the intake. Water is withdrawn from the river through three cylindrical wedge‐wire intake screens, passed to a sedimentation basin, and then pumped to the plant site. A reinforced‐concrete trough installed along the face of the screen structure protects the intake screens from potentially damaging debris. The trough diverts debris from the intake screen and also reduces sedimentation in this region. Water jets periodically clean the trough. Before construction of the facility, the trough and water jets systems were modeled to confirm and refine this portion of the design. The intake is environmentally acceptable and requires little maintenance.

Increasing fuel and construction costs of new power plants have emphasized the need to achieve cost‐effective, highly reliable circulating water intake designs that can improve power plant availability and performance while meeting environmental requirements. Additional concerns are to reduce maintenance, improve hydraulic conditions, and control fouling, siltation, and ice. The present paper discusses an Electric Power Research Institute (EPRI)‐sponsored study to assess the status of available intake technologies for fish protection and to develop a research program to evaluate and compare the operation, performance, cost, and reliability of selected fish protection systems. The initial assessment of all available behavioral barriers, physical barriers, collection and removal systems, and diversion systems identified for further study 11 of the most promising technologies. These 11 technologies were ranked as to the importance of various levels of specific design criteria and the importance among these criteria. The technologies were then matched with potential test sites. Biological and engineering test methodologies were developed, together with design schemes for behavioral barriers at each test site. As a result of the study, EPRI is testing behavioral barriers at several sites. EPRI also is collecting data from several existing intake facilities where angled screens, modified fish screens, and wedge‐wire screens are being evaluated.