Research papers
Evaluation of Boundary Dam spillway using an Autonomous Sensor Fish Device

https://doi.org/10.1016/j.jher.2016.10.004Get rights and content

Highlights

  • Baffle blocks increased the number of severe acceleration events on the chute.

  • Baffle blocks reduced the number of severe acceleration events in the tailrace.

  • Baffle blocks fragmented discharge jet reducing plunge depth into tailrace.

Abstract

Fish passage conditions over spillways are important for the operations of hydroelectric dams because spillways are usually considered as a common alternative passage route to divert fish from the turbines. The objectives of this study were to determine the relative potential of fish injury during spillway passage both before and after the installation of baffle blocks at Boundary Dam, and to provide validation data for a model being used to predict total dissolved gas levels. Sensor Fish were deployed through a release system mounted on the face of the dam in the forebay. Three treatments, based on the lateral position on the spillway, were evaluated for both the baseline and post-modification evaluations: Left Middle, Right Middle, and Right. No significant acceleration events were detected in the forebay, gate, or transition regions for any release location; events were only observed on the chute and in the tailrace. Baseline acceleration events observed in the chute region were all classified as strikes, whereas post-modification events included strike and shear on the chute. While the addition of baffle blocks increased the number of severe events observed on the spillway chute, overall fewer events were observed in the tailrace post-modification. Analysis of lateral positioning of passage indicated that the Right Middle treatment was potentially less injurious to fish based on relative frequency of severe events at each location. The construction of baffle blocks on the spillway visibly changed the flow regime. Prior to installation the flow jet was relatively thin, impacting the tailrace as a coherent stream that plunged deeply, possibly contributing to total dissolved gas production. Following baffle block construction, the discharge jet was more fragmented, potentially disrupting the plunge depth and decreasing the time that bubbles would be at depth in the plunge pool. The results in this study support the expected performance of the modified spillway chute: the addition of the baffle blocks generally lessened the depth and impact of entry. This study provides information that can be used to help design and operate spillways for improving fish passage conditions.

Introduction

Hydropower is one of the largest renewable energy resources in the world, producing approximately 16.6% of global electricity and 72.8% of renewable electricity in 2014 (Ren21, 2015). While it is an established industry, it is still growing at a large scale compared to other renewable sources. Hydropower has a total global capacity of approximately 1055 GW from 150 countries with 37 GW capacity added in 2014 (Ren21, 2015). Although hydropower offers many economic and environmental advantages, hydropower dams have potential adverse ecological impacts to fish passage, water quality, and habitat (Cada, 2001).

Downstream migrating fish may be injured or killed by several possible mechanisms as they pass through turbine routes (Cada, 2001): rapid and extreme pressure changes, cavitation, shear stress, turbulence, strike, and/or grinding. Therefore, alternative passage routes have been installed to divert migrants over spillways or through bypass systems (Weber et al., 2006). A common method used to bypass fish at small to medium sized hydroelectric plants uses screens as barriers to prevent fish from entering turbines, guiding fish through adjacent passage routes during their migration (Larinier, 2008, Larinier and Travade, 1999). Some kelts and smolts have been observed to select spillways as their migration route rather than turbine passage (Arnekleiv et al., 2007).

Spill passage is usually regarded as the most benign downstream migration route for juvenile salmonids (Schilt, 2007). However, large spillway discharges have been known to produce high (supersaturated) levels of dissolved gases in downstream rivers (Schilt, 2007), which can stress or kill fish because of gas bubble disease (Lutz, 1995, Backman and Evans, 2002), reduce swimming performance (Sciewe, 1974) and resistance to pathogens (Weiland et al., 1999), and affect spawning (Geist et al., 2013). Efforts have been devoted to dam physical modifications to reduce dissolved gas generation requiring a quantitative understanding of the relationship between river hydrodynamic conditions and the dissolved gas levels encountered by fishes (Urban et al., 2008). In an effort to minimize the supersaturation of dissolved gases, spillway flow deflectors have been installed in several dams, and their impacts on the flow fields were investigated by an anisotropic two-phase flow model based on mechanistic principles (Politano et al., 2009). In addition, the flow fields upstream of a high dam in China under different intake and spillway operation patterns were investigated by using both numerical and experimental methods (Huang et al., 2015). Large-Scale Particle Image Velocimetry (LSPIV), as an extension of a quantitative imaging technique, was applied successfully to obtain surface flow velocities in the context of river and dam engineering projects (Kantoush et al., 2011). The Clean Water Act (33 U.S.C. § 1341 et seq.) and the Revised Code of Washington (RCW 90.48) require conformance with Washington State water quality standards and pollution prevention obligations. Water quality standards specify that Pend Oreille River total dissolved gas (TDG) concentrations shall not exceed 110 percent of saturation at any point of sample collection. TDG production at Boundary Dam, located on the Pend Oreille River, has been a concern to Seattle City Light since 1999. Research and field studies analyzing TDG abatement alternatives have been explored in efforts to mitigate any issues. Alternatives considered included throttle sluice gates, roughening sluice flow, and providing spillway flow splitters/aerators.

Baffle blocks have been designed for different engineering purposes. Reduced-scale evaluations have been conducted to evaluate the effects of semi-circular baffle blocks downstream of a Fayoum type weir (Abdelhaleem, 2013). Experimental investigations have also been conducted to optimize stilling basin influences using a shallow-water cushion for low Froude number energy dissipation (Li et al., 2015). Assessments involving computational fluid dynamics (CFD) and physical modeling contributed to Seattle City Light’s decision to add baffle blocks at the end of Boundary Dam Spillway 2. The baffle blocks were designed to break up the flow jet sufficiently to disrupt the depth of plunge and decrease the time that bubbles are at depth in the plunge pool, reducing TDG potential.

The objectives of this study were to determine the fish passage conditions of Boundary Dam Spillway 2 under both baseline (prior to modifications) and post-modification conditions and to provide validation data for a model being developed to predict total dissolved gas levels. Autonomous Sensor Fish were used to collect passage data to establish a baseline assessment in 2014 and to evaluate post-modification conditions in 2015 (after the installation of the baffle blocks). Significant acceleration events were identified and classified as strike or shear, based upon the acceleration magnitude impulse. The plunging depth of Sensor Fish in the tailrace was also calculated to assess the effect of the added baffle blocks on jet dispersion.

Section snippets

Study site

Boundary Dam, operated by Seattle City Light, is located at river kilometer 27 on the Pend Oreille River, about 16 km north of Metaline Falls, Washington, and just south of the US-Canada border (Fig. 1). It is a concrete arch gravity-type dam, 225 m long and 103 m high. Normal pool elevation is 607 m above mean sea level (MSL). It has six Francis turbines, with a total generating capacity of approximately 1040 MW, and two spillways, each 15 m wide with a 14 m long radial gate. Spillway No. 2 is on the

Passage examples

Fig. 5 shows the pressure, acceleration, and rotational data collected by a Sensor Fish from a typical passage during the baseline evaluation before the baffle block installation. The tailrace designation includes Sensor Fish entry into the plunge pool and passage in the tailrace. An example of Sensor Fish passage data from the post-modification evaluation after the installation of the baffle blocks is shown in Fig. 6. While similar to the baseline condition, there is a noticeable increase in

Discussion and conclusions

In efforts to reduce TDG production at Boundary Dam nine baffle blocks were added to the spillway chute. These baffle blocks contribute to the fragmentation of the flow jet, disrupting the depth of plunge which decreases the aeration at depth. The objective of this study was to describe and compare the baseline and post-modification passage conditions on Spillway 2 at Boundary Dam, contrasting conditions for three release locations and to determine the relative potential of fish injury due to

Acknowledgements

The study was conducted by Pacific Northwest National Laboratory (PNNL), operated by Battelle for the U.S. Department of Energy. The field data collection and data analysis was funded by Seattle City Light. Andrew Bearlin and James Lussman were the technical point of contacts. The Sensor Fish and related evaluation tools were funded by the U.S. Department of Energy Wind and Water Power Technologies Office. The Sensor Fish release pipe was designed by the engineering consulting company Hatch. We

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