|The Spokane River now looks much the way it did before the river channels were altered to divert water, thanks to the installation of weirs designed to look like bedrock.|
To enhance views of the Spokane River in Riverfront Park, Avista Corp. installed weirs that look like the natural bedrock and spread water more evenly through the two river channels. The utility is now able to decrease flow while providing an aesthetically pleasing view.
By Speed Fitzhugh
Speed Fitzhugh is Spokane River License Manager with Avista Corp.
Avista Corp. restored two channels downstream of its Upper Falls Development on the Spokane River to look much the way it did long ago, before the channels were altered to divert water to numerous flour and lumber mills, as well as for hydropower generation. The channel restoration, using weirs shaped and colored to look like the bedrock throughout the river, spread water more evenly through the two channels and has now functioned successfully through two entire spill seasons. Combined, they produce an aesthetically pleasing flow over the falls that viewers can enjoy throughout the year.
For hundreds of years, the Spokane River and falls served as the gathering place for Native American tribes including the Spokane, Coeur d’Alene, Confederated Colville, and Kalispel. Today, the falls are at the center of the 100-acre Riverfront Park in the heart of downtown Spokane, Wash. Avista owns five hydroelectric developments on the Spokane River, collectively known as the Spokane River Project with a combined capacity of approximately 160 MW.
The Upper Falls Hydroelectric Development is located within Riverfront Park and has a licensed capacity of 10 MW. The development includes two dams on either side of Havermale Island in the Spokane River. The north channel dam and control works structure creates the bypass reach that includes the upper falls, while the south channel contains a dam and head gate structure that leads to the powerhouse. The north channel bypass reach splits into the north and south channels that flow around Canada Island. Although the development is operated as run-of-river, the two dams control the release of water to downstream areas of the Spokane River that are frequently viewed by the public.
The river channel at Spokane Falls has been heavily impacted by human activity since the late 1800s. Until recently, water flow slowed to a trickle (less than 30 cubic feet per second or cfs) in both channels during the summer months, with all of the water flowing through the south channel. The lack of water exposed barren riverbanks and rocks within the river. Aesthetic qualities including flow and sound were largely absent when water ceased to flow through the dams and downstream channels.
During the Federal Energy Regulatory Commission relicensing process for the project in the early 2000s, stakeholders requested an aesthetics study for the Upper Falls development. The study focused on identifying the desirable viewing times and river flow attributes that appealed to the public. At the same time, Avista staff offered an innovative and creative idea: modifying river channels to change the appearance of the flowing water and balance the amount of water in each channel. The stakeholder groups were open to the concept but were unsure that it would prove successful. Some stakeholders were persistent in requesting that Avista simply increase the amount and duration of aesthetic flows year-round, rather than modifying the channel.
Following extensive negotiations, stakeholders agreed with the proposal to evaluate channel modifications to determine if Avista could produce acceptable aesthetic spills with 300 cfs released from the dam, and if not the company would release minimum aesthetic spills of at least 500 cfs on a year-round basis. Avista would also release 100 cfs during nighttime hours to help maintain and enhance the redband rainbow trout habitat in the river.
Subsequently, in 2009, FERC issued a new 50-year operating license for the Spokane River Project, including the Washington State Department of Ecology’s 401 Water Quality Certification. The certification included a specific requirement for a year-round aesthetic spill at the Upper Falls development that was based on stakeholder recommendations. The Department of Ecology later modified the certification in accordance with a settlement agreement between Avista, the Sierra Club and the Center for Environmental Law and Policy. The certification also required development of a long-term aesthetics spill plan, a pilot study to determine the effectiveness of possible channel modifications, and analysis of the modifications with regard to any ecological impacts of modification (such as fish entrainment, stranding or trapping). Ultimately, stakeholders were required to mutually agree on the success of the project.
As Avista began to implement these efforts, it became apparent that as we theorized, not only would channel modifications balance flows between river channels, but with proper planning, less water (300 cfs) could provide the same or better visual and audible effects than more water (500 cfs) could. The additional water could be run through the powerhouse rather than spilled and would increase generation at Upper Falls, to the benefit of the utility and its customers. The overall scale of the project was intimidating, and gaining stakeholder buy-in would prove challenging. Rather than hypothesize or model what impact channel modifications might have on flows, Avista initiated a real-life pilot test in the river channel. Stakeholders were enlisted in the pilot test to evaluate the location, size and impact of the various weir structures on the aesthetic appeal of the river as 300 cfs was released into the bypass reach.
|One of nine weirs, basically engineered “rocks” used to modify the channel and redirect the water flow, was installed in this location.|
The pilot test process was designed to assess the effectiveness of potential channel modifications on the visual and audible effects of flows in the river. The goal was for the visual and audible effects to be similar to or better than those achieved by a spill of 500 cfs through the bypass reach without channel modifications. Over a period of months, Avista worked to identify possible locations for various weirs, basically engineered “rocks” used to modify the channel and redirect the water flow. Streambed surveys, aerial photos and reconnaissance visits were critical in determining the proposed location and size of the prospective weirs. Test weirs were constructed of a mix of materials, including 1-cubic-yard bags of pea gravel placed next to each other, smaller bags filled with sand, and ecology blocks (large concrete blocks) by local landscaping firm and lead construction contractor Land Expressions. FERC approved the test plan in June 2010.
The pilot test consisted of several components in addition to the temporary river channel modifications, including a viewer preference survey, assessing results and obtaining data for use in construction of the permanent structures. Stakeholders were invited to join the evaluation team. The team included a diverse range of parties and organizations that had a keen interest in the aesthetic condition of the Upper Falls. Participating organizations included the Sierra Club, Spokane City Parks and Recreation, the Department of Ecology, Friends of the Falls, the Center for Environmental Law and Policy, and the Spokane Canoe and Kayak Club. In addition to these groups, representatives from Avista worked on the pilot test and participated as evaluation team members, as did consultants agreed upon by Avista and other parties. Subject-matter experts served as evaluation team members and were present during the pilot test to answer technical questions.
After each evaluation team review, suggestions were made regarding changes in the distribution of water between the two channels and “fine tuning” changes within each channel to improve aesthetic flow characteristics. Suggestions that were agreed upon resulted in manipulating weirs or adding new ones. Testing various weir configurations required Avista to shut off flows from Upper Falls Dam into the river channels, waiting several hours for the flows in the channel to be low enough to allow safe access. Land Expressions, the primary construction contractor, then made the requested changes, Avista opened the spill gates to release 300 cfs back into the river, and then all parties had to wait several hours for the 300 cfs flows to stabilize in the river channels before the evaluation team could again make observations. After the conclusion of the pilot test, all of the materials were removed from the river channels.
Avista also had numerous meetings with Washington Department of Fish and Wildlife (WDFW) and the Department of Ecology, in which downstream connectivity and potential entrainment were the focus of discussions. Consultation continued through the tests, and any stranded fish, as the channels were emptied for the pilot-test, were hand captured and relocated downstream.
All parties concluded that the structures used during the pilot test maintained and appeared to enhance fishery connectivity. This led the team to work with WDFW during the design phase to ensure effective connectivity concerns were incorporated into the weir designs.. As a result, three of the nine weirs were modified during construction to allow fish to move downstream and to reduce the probability of stranding fish at night when the flows are reduced from 300 cfs to 100 cfs.
The project was truly a win-win for everyone involved. With a goal of not only evening out and enhancing the flows in the two channels but also modifying the channels in a way that blended with the existing environment, Avista hired two specialty firms to develop detailed designs for the weirs to modify the channels. The two firms normally work on landscape architecture and creation of artificial rock structures for water features and exhibits.
Reshaping the Spokane River was a water structure challenge of a different scale altogether. The riverbed at the location of the falls includes various basalt rock formations, textures and colors. Avista and its consultants worked closely with representatives from WDFW and the Department of Ecology as they designed the nine weirs in the two river channels. It was extremely important that the shapes and colors were consistent throughout each weir structure to ensure that the natural look was maintained even if the weir structures were damaged over time. This presented additional challenges, as the basalt formations where the concrete weirs were located varied from very smooth surfaces to those that resembled fractured rocks. In essence, Avista and its contractors took a new and creative approach to restoring the falls to a more natural state by matching the color, shape and texture of the weirs to that of the bedrock to produce seamless, natural looking river flows. Construction of the weirs took three months during the low-flow season in 2011.
Avista observed the weir structures through an entire spill season, declaring the project complete in the fall of 2012. Photo evidence shows that post-construction, with 300 cfs flowing through the channels, the Spokane Falls actually appear similar to the way they previously appeared with a 1,500 to 1,600 cfs of flow. Informal surveys showed visitors lingering on bridges over the falls throughout the summer months, which virtually never happened when the two channels were dry. With 300 cfs flowing through the two channels, Riverfront Park visitors cannot detect the weir structures within the natural bedrock channels, indicating true success.
The total cost of the multi-year project was about $1.4 million. Although the additional generation benefits can be calculated, the overall value of the project to the more than 2.5 million annual visitors to Riverfront Park is impossible to quantify.
To the knowledge of Avista and the consultant teams (Louis Berger Group, Ch2MHill, Land Expressions, TD&H Engineering, CEMROCK) who worked on the project, nothing like this had been attempted before in North America. This effort, because of its innovation and success at restoring two river channels with aesthetically pleasing flows in the heart of Downtown Spokane was recognized by the National Hydropower Association in 2013 when it awarded Avista with an Outstanding Stewards of America’s Waters for Recreational, Environmental and Historical Enhancement.