The 16 MW Box Canyon hydroelectric projectranks among the most hydraulically complex ofany run-of-river hydro project in North

America, if not the world. The project, which is locat-ed in the McNab Creek watershed, 40 km northwest ofVancouver, British Columbia, has nine intake struc-tures on different creeks and tributaries. All nine feedinto a single, high-pressure penstock that directs waterto the powerhouse containing a single six-jet verticalaxis Pelton generating unit.

The owner, Box Canyon Hydro Corp (a subsidiary ofElemental Energy Inc.) retained Knight Piésold Ltd toassist with:• concept development, optimization, environmentalassessment, and permitting; • detailed design; and, • operational monitoring of the facility.

Initial investigations began in 2004, at which timethe project concept was a 7 MW facility with a singleintake on Box Canyon creek. Through optimizationstudies, which included site investigations and detailedhydrological studies, Knight Piésold revised thedesign to the current 16 MW arrangement. The designrequired addressing hydraulic, waterhammer and envi-ronmental flow release complexities, which are nottypical for a single intake, run-of-river hydro project.

The project is within the traditional territory of theSquamish Nation, a valued partner on the project, andincludes intake structures on three main tributaries toMcNab Creek (Box Canyon, Marty, and CascaraCreeks) as well as six minor tributary diversions. Eachintake is designed to meet unique water licence condi-tions that are intended to address the various hydrolo-gy, river morphology, and fish species distributionsalong the creeks and tributaries. The general arrange-ment and a schematic of the project are shown in Figs.1 and 2. Key components of the project are highlight-ed in the photographs, and details for the major com-ponents of the project are summarized in the Table.

Project optimizations and overall hydraulicdesign of the schemeThe design of the project required innovative designsolutions and equipment selection, which include:• The water intakes are designed to operate with theBox Canyon intake as the turbine controlling intake(water level controlled by plant PLC) while MartyCreek and Cascara are operated as passive non-instru-mented intakes. Both are located at higher elevations

44 Hydropower & Dams Issue Four, 2017

Main features of the project

Rated capacity of the plant (MW) 16 Intakes (No and type) 3 main and 6 tributary Design flow (m3/s) 3.96 Penstock length (km) 8.6 Penstock inside diameter (mm) 665 to 967Gross head (m) 516.9 Turbine type Pelton unit, 6-jet vertical axisTransformers (kV) 13.8 to 138 Transmission line: 2.8 km of 138 kV

Design of the Box Canyon schemeT. Perkins and B. Otis, Knight Piésold Ltd, Canada

The article outlines the innovation and challenges involved in the hydraulic design of the Box Canyon run-of-river hydro project in Canada, which is equipped with nine intakes on different waterways.

Fig. 2. Schematic highlighting the complexity of the Box Canyon project.

Fig. 1. Generalarrangement of theBox Canyon schemeshowing itscomplexity.

The Marty Creek intake.

than the Box Canyon intake and provide generationflows up to the design capacity of the intakes. Theplant’s PLC is used to limit generator hunting by con-trolling the water level at the Box Canyon intake andcontrol ramping events at the intakes.• A tilting disk check valve was designed on the BoxCanyon penstock to prevent water backing up the BoxCanyon penstock to the headpond when the water con-veyance system is experiencing net head levels abovethe Box Canyon intake elevation. The check valve pre-vents the backing up of water during events such asstart-up, operation below design flow, or when theplant is in not operating. Valve stroke cushioning wasrequired to reduce the transient conditions during thevalve closure and opening strokes to acceptable levels.• The water intakes were designed with Coanda screenspillways to divert the generating flows while exclud-ing debris and fine sediments, which could decrease thelife of the water conveyance and generating equipment.• Generation flows are regulated by the six-jet Peltonturbine and generator. The Pelton unit can operate atlow minimum turbinable flows and provide controlledramp-down of the generation flows.

Head loss estimatesAlthough the hydrology at each intake is relatively sim-ilar, there are differences in the timing and magnitude offlows available for generation at each intake. This, com-bined with differences in the penstock length, diameterand material in each penstock branch, mean that a uniquenet head versus plant flow relationship cannot be definedfor the facility. A good understanding of the net head atdifferent generation flow conditions was required todefine the terms of the water-to-wire contract (turbinedesign criteria and generating unit performance guaran-tee) and estimate potential energy generation. The tur-bine manufacturer was requested to design and demon-strate that the turbine and generator are capable of reli-able, smooth, stable and vibration-free operation overthe entire range of flows and operating heads.

The theoretical range of net head versus turbine flow,under numerous possible operating conditions, is shownin Fig. 3. Head losses were estimated for the water con-veyance system using the classic equation developed byDarcy-Weisbach for energy loss of pipes network inseries. Experience with the hydraulic design of long pen-stocks for run-of-river facilities allow the designer toselect friction factors and minor loss coefficients, basedon experience comparing theoretical values to measuredvalues of other penstocks. Hydraulic design of the sys-tem was then verified with KYPIPE Pipe 2010 andSurge software packages.

The project has been operational since April 2016.Nine months of measured operational head and plantflow data were compared with the predicted conditions,and as shown in Fig. 3, there is generally good agree-ment. At higher flows, the predicted net head tends tounderestimate measured conditions. ConclusionThe Box Canyon hydro project is a unique and hydrauli-cally complex facility. Knight Piésold combined provenapproaches with unique solutions to design this facility.A comprehensive understanding of the hydraulic opera-tion parameters of a multi-intake hydroelectric facilitywas important to determine generation capacity and foroptimal equipment selection. Validation of classic theo-ry was achieved using numerical hydraulic modellingsoftware for pipe systems in series, and through experi-ence to better understand the implications of equipmentselection and head loss effects. The plant has been suc-cessfully operating since April 2016. ◊

Hydropower & Dams Issue Four, 2017 45

Toby Perkins, MASc PEng, is a Senior Engineer withKnight Piésold Ltd. He specializes in hydrology andhydraulics for design and environmental assessment. He hascontributed to many run-of-river projects developed inBritish Columbia in the past 10 years and was ProjectManager for Owner’s Engineering services on the BoxCanyon project.Benoit Otis, PEng, is a Senior Engineer with Knight PiésoldLtd. He specializes in the design of hydraulic structures andthe development of hydro projects. He has contributed tomany run-of-river schemes developed in British Columbia inthe past nine years and was responsible for the design of thewater conveyance system on the Box Canyon project.Knight Piésold, Suite 1400, 750 West Pender, Vancouver,British Columbia V6C 2T8, Canada.

Aerial view of the powerhouse and substation.

Nine intake structures feed into this high-pressure penstock.

B. Otis

T. Perkins

Fig. 3. Net head atthe turbine. Duringthe design phase,each possible flowcondition wasanalysed with thesynthetic streamflowdata to define therequired turbineoperational range.Measuredoperations datawere provided forAugust 2016 toMarch 2017.