Technical and design innovations in run-of-river projects17 March 2009
Since engineering its first hydroelectric scheme in 1926, Knight Piésold has gained considerable experience in the design of power generation facilities. In the 21st century, the company is working with its partners to create a legacy of clean, renewable energy through run-of-river hydro projects
In British Columbia (BC), Canada, Knight Piésold has worked closely with several private and institutional developers on project development, applying many new and innovative techniques in all aspects of designing hydro schemes. These include project identification, stream gauging and hydrological assessment, engineering design, project optimization, environmental assessment, permitting and licensing, and First Nations involvement.
In the early 1990’s, Knight Piésold worked with developers on identifying and optimizing run-of-river projects that were close to existing transmission lines. But in the last few years, as prime sites have been identified in more remote areas, it became one of the first BC companies to introduce the concept of clustering projects to share the substantial cost of longer transmission lines. For instance, at Plutonic Power’s East Toba and Montrose project, the two run-of-river developments will share a single 150km long, 230kV transmission line. Without this sharing arrangement, neither development would be financially viable. The environment also benefits from this arrangement, as line sharing reduces the potential development footprint. Furthermore, the lines are routed as much as possible along existing logging roads, resulting in less clearing for transmission line corridors. This environmental advantage is in turn important for First Nations partners, as transmission lines often cross their territory.
A similar sharing of transmission lines is occurring in Cloudworks Energy’s Kwalsa Development site, 90km northeast of Vancouver. The company is currently constructing four of eight planned run-of-river projects. This group of facilities is sharing the significant transmission and interconnection costs to tie into BCTC’s 360kV transmission system.
Stream gauging and hydrological assessment
Knight Piésold has developed considerable expertise for the collection and analysis of hydrological data in isolated, challenging environments, including watersheds in coastal mountainous BC, Arctic permafrost terrain on Baffin Island, and dense, tropical jungles in Africa. It currently operates over 150 stream gauging stations around the world. Most of these are in high velocity, glacier-fed streams in BC’s Coastal Mountain range. The quality and value of the data depend on several factors including gauging site selection, flow measurement technique, data quality assurance and control, rating curve development, and data analysis.
Proper gauging site selection is critical for ensuring a definable and consistent relationship between water stage and discharge. Considerable skill is also required to identify, assess and establish a proper gauging site. Accurate flow measurement is also of paramount importance, and for this the company uses several flow measurement instruments and techniques including a traditional velocity meter, an acoustic Doppler current profiler, and salt and rhodamine dye dilution. The method of choice depends greatly on channel characteristics and flow conditions: the salt and rhodamine dye techniques are generally preferred for the turbulent, fast flowing conditions that developers often face. These methods present challenges, however, as they involve expensive equipment that requires calibration and is sensitive to changing conditions. A high level of skill is also needed to select an appropriate site to ensure complete mixing of the tracer compound.
However, with constantly evolving knowledge of technological constraints in difficult field conditions, the quality of site data continues to improve. Knight Piesold is now developing an automated, multi-discharge rhodamine dye type measurement device that will remotely record a series of flow values at predetermined water levels. This will allow several stage-discharge points to be obtained during a single large flow event, thereby dramatically increasing the efficiency of stage discharge data collection.
The operation of so many gauging stations and the huge amounts of data they generate has necessitated the development of a specialized hydrology module for Knight Piésold’s centralized, web-based Fulcrum environmental data management system. This module was created specifically for the storage, management and processing of stream gauging data. It allows field staff to upload, view, and process all information from remote locations, and any changes to the database can be viewed in real time by staff and clients.
To assist with rating curve development, and particularly the extrapolation of a curve beyond the range of measured stage-discharge values, a ranked regression modeling approach has been developed. When combined with an understanding of the physical processes dictating hydrologic response in compared watersheds, this approach provides guidance for the delineation of a curve. This method has also improved the company’s ability to predict flows at one site on the basis of flows at another site, even if the relative timing of flows at both sites do not exactly coincide. The flow prediction methodology has proven to be acceptable for bankable feasibility studies, enabling clients to secure project financing, says the company.
A primary goal of a run-of-river intake design is to extract water from a river while excluding sediment and debris, which can cause impact damage and excessive wear to the conveyance system and turbines. Sediment exclusion has traditionally been achieved through the use of expensive and often extensive desanding facilities. Knight Piésold has refined the design of two types of intakes that incorporate efficient sediment exclusion systems, which have proven very effective in high energy, glaciated river systems: Coanda Screen and Rubber Weir Type Intakes.
Coanda Screen Intake
The Coanda screen intake relies on the Coanda effect of flowing water to stay attached to an adjacent curved surface to direct water through a fine meshed screen. It was used for the first time on a Canadian run-of-river project in 2004. Over the past five years, the company has worked closely with the manufacturer, Norris Screens and Manufacturing, and contractor partner, Peter Kiewit Sons, to optimize the screens’ design. The screens’ water diversion capacity has been designed to make it more “fish friendly”, while its ability to exclude sediment has been maximized and maintenance needs have been decreased. The new stainless steel screens are self-cleaning and eliminate particles of less than 2mm in diameter. They are substantially more robust than the first-generation type and better able to withstand the high flood levels and heavy debris loads of streams in BC’s coastal mountains. In 2005, the design for the McNair Creek Green Power project, which included a Coanda Intake, received an Award of Excellence from the Consulting Engineers of British Columbia (CEBC).
Rubber weir intake
The rubber weir intake incorporates a large diameter, cylindrical rubber weir that automatically inflates and deflates in response to sensors measuring water levels in the headpond. Under very high flows, the weir deflates completely, providing passage for flood waters and debris.
For the past five years, Knight Piesold has carried out physical model testing and combined those results with input from operators to improve the design of rubber weirs. Rubber weirs have been successfully used on several BC projects, including the Soo River, Lower Mamquam River and Rutherford Creek.
Knight Piésold recently completed the design of two rubber weir intakes that are now under construction at Plutonic Power’s East Toba River site and Cloudworks Energy’s Stave River site. Design work has resulted in improved flood discharge capability and sediment exclusion, lower maintenance requirements, a more stable operating environment, and a smaller environmental footprint.
Penstock costs typically account for a major portion of overall project capital costs, and the optimization of this design component can substantially influence project economics. Knight Piésold has worked closely with Peter Kiewit Sons and Amnis Engineering to improve the efficiency of penstock designs and lower their costs, through innovative material selection and the use of soil restraint. The company was the first to use large diameter, plastic profile-wall Weholite pipe in hydro power applications, borrowing this technology from the municipal sector. If used correctly, Weholite pipe can be very cost-effective because it is tough, corrosion-resistant, tolerates handling well and is easy to install.
It has successfully used large diameter Weholite pipes on the following projects:
• 49MW Rutherford Creek project – Innergex Renewable Energy
• 25MW Aberfeldie project – BC Hydro.
• 123MW East Toba project – Plutonic Power, currently under construction.
• 37MW Stave River project – Cloudworks Energy, currently under construction.
The advantages of using soil restraint to anchor buried penstocks, instead of more conventional large concrete anchor blocks, include reduced installation times and costs. Burying penstocks underground rather than placing them on the surface minimizes their visual impact, maintains wildlife migration corridors, and reduces susceptibility to potential earthquake damage.
Permitting and licensing processes
Typically in BC, the Environmental Assessment process for run-of-river projects requires over 50 permits, license approvals and reviews from agencies at all levels of government. These agencies normally include the Canadian Environmental Assessment Agency, the BC Environmental Assessment Office, Fisheries and Oceans Canada, Transport Canada, Natural Resources Canada, BC Ministries of the Environment and Forestry, and the BC Integrated Land Management Bureau, but can include several others depending on the project. Developers may also seek certification from the Environmental Choice Program (Eco Logo), a Government of Canada program that recognizes power sources that operate with minimal environmental impact.
Environmental and SocioEconomic Issues
Knight Piesold’s team of engineers and scientists work on key issues including environmental instream flow requirements (IFR), identifying and assessing habitat for fish and other aquatic resources, and developing mitigation measures for habitat and recreation loss where necessary. For example, at the Toba Montrose project, biologists are conducting monitoring studies on potential impacts on aquatic insects and building a fish habitat enhancement channel. At the Rutherford Creek project an artificial white water kayaking course was created to compensate kayakers for a reduced number of paddling days.
The company communicates its environmental studies to the public and stakeholder groups, and offers them input to the study scope and an opportunity to review the results.
First Nations Involvement
The company’s First Nations partners play an important role in project development right from project inception. It recognizes the asserted traditional territories of the First Nations where its projects are located, without prejudice to existing or asserted rights and title. It employs aboriginal members to work on environmental data collection and to contribute to site studies related to archaeology, wildlife and fisheries issues. These projects do not proceed unless the developer holds a “social license” to operate in the area. This is why it is so important to engage First Nation communities early in the project development process.
Developing run-of-river hydroelectric projects anywhere in the world today, especially with the tough economic conditions and permitting constraints developers currently face, requires a fully integrated team approach. This includes input from numerous engineering disciplines and the permitting, environmental, socio-economic, finance and construction fields. Run-of-river hydroelectric projects have to compete with all other forms of renewable and non-renewable energy for a piece of the energy market. Innovative design concepts and approaches are going to be vital to the continued success of the industry.
Jeremy Haile, President, Knight Piesold Canada. He has over 35 years experience in small and large hydropower, specializing in project concept development, contractual arrangements and project economics for hydroelectric projects in North and South America, South-East Asia and Africa. Email: [email protected]
Sam Mottram, Manager – Power Services, Knight Piesold, Vancouver. He has 15 years experience in the identification, design and construction of hydroelectric projects, including hydraulic and energy modeling and design of intakes, dams, weirs, canals and pipelines, throughout Africa and North and South America. Email: [email protected]
Dr. Jaime Cathcart, Specialist Hydrotechnical Engineer, Knight Piesold, Vancouver. He has over 15 years experience, oversees hydrology studies for projects throughout the world and works on the hydrotechnical design and water management aspects for resource developments. Email: [email protected]