CSCE 2007 Annual General Meeting & Conference Congrès annuel et assemblée générale annuelle SCGC 2007
Yellowknife, Northwest Territories / Yellowknife, Territoires du nord-ouest June 6-9, 2007 / 6 au 9 juin 2007
Snare River Hydro - A History Dedication Ken Johnson, Earth Tech Canada Greg Haist, Northwest Territories Power Corporation Abstract The Snare River hydro system is one of the most northerly hydro electric systems in Canada. The system produces electricity at four plants and supplies electricity to the communities of Rae- Edzo, N'Dilo, Dettah, and Yellowknife, and to the Giant and Con gold mines. Downstream sites to the original 1948 facility were developed at Snare Falls in 1961, Snare Forks in 1975, and Snare Cascades in 1996 as electricity demand increased in the region. Although challenges associated with cold region engineering were reasonably well defined after the construction of the Alaska Highway and the Canol Pipeline in the early 1940's, these were essentially transportation, structural and petroleum engineering projects. Water resource engineering had little opportunity for cold region engineering applications until the Snare Hydro project. Initial hydro power development in the NWT was the result of the demand for electricity by the gold mines operating around Yellowknife. The need for power was large enough to justify the expense of harnessing the energy from the Yellowknife River in 1938. The mines were the first to build a hydroelectric generating station in the NWT. The Federal Government saw the rapid expansion of the mining sector near Yellowknife as an indicator of the need for a coordinated utility industry in the North. Federal officials were reluctant to let another mine develop and own another hydro site. At the suggestion of the federal industry minister, a crown corporation (NWT Power Commission) was approved by parliament to oversee the development of the Snare River Hydro Project. In the spring of 1946, the Department of Mines and Resources commenced construction of a Hydro Power Plant on the Snare River 150 kilometres northwest of Yellowknife. The site was only accessible by air, or tractor train in the winter months. The eight megawatt facility was commissioned in October, 1948.
1. Background Between 1930 to 1940, when gold mining became a low priority to the more important activities associated with national defence, a series of promising discoveries occurred in the Yellowknife area of the Northwest Territories. The Consolidated Mining and Smelting Company was among the first to follow staking with development, and in 1933 the Con Mine was brought into production. The Giant Yellowknife Mine, which is located just miles north of the Con, was originally staked in 1935, but it was not until 1945 that extensive development began. The culmination of these activities in the summer of 1948 was the completion of a 500-ton mill, which ultimately need electrical power to operate.
Water power investigations were underway seeking power for the Giant Mine in several streams in the region in 1944. In 1944, detailed reconnaissance was underway, and in 1945 reconnaissance of the Snare River watershed ultimately chose a location on the Snare River as most advantageous site for hydro power development. In general, most streams in the Northwest Territories have similar characteristics. With the small amount of rainfall, the water supply is dependent largely on the snowmelt. Spring run off typically starts at an NWT river headwaters in June, and the flood stage affects the lower reaches of the river in late August. The remarkably late period of high water is due not only long winter and late spring, but also the nature of the watersheds and river channels. The Canadian Shield terrain of the region is made up of rounded granite knolls or hills, with the depressions between the hills containing muskeg or lakes. These terrain and vegetation features create a long retention for runoff, and remarkably small variations in seasonal flow. The first discharge measurements of the Snare River were made late in 1944, therefore four years of actual runoff records were available prior to construction of the Snare Hydro project. The highest measured discharge was 3,980 cfs on August 25, 1946, and the peak flow was estimated at 4200 cfs. The low discharge occurred on April 30 of the same year at. 393 cfs, and the mean flow for four years was calculated to be 1,430 cfs. Big Spruce Lake provides a storage basin 7 square miles in area, and the adjacent Kwejinne Lake provides an additional 27 square miles, resulting in a total reservoir area at 22,000 acres, and a usable storage of approximately 220,000 acre ft. Cost estimates were made and in January 1946, and preparation began for construction. Machinery was purchased and delivered to the in February of that year. As the construction of the power plant and transmission line began, Giant Mines resources were pushed their limits. As a result Giant officials approached the Government of Canada for assistance, and an agreement was reached for the Government to build the power plant and Giant to build the transmission line. Ultimately the Government of Canada took over the transmission line.
2. Project Mobilization The project is located on the Snare River, 2 kilometres south of the outlet of Big Spruce Lake, at latitude 63째30' north, and longitude 116째 00' west. The inaccessibility of the site presented a serious problem. The railheads at Grimshaw and Waterways, Alberta, were about 800 kilometres south by air, and the nearest source of supplies in Yellowknife was 140 km by air, and 210 kilometres by cat train. The closest water port, Fort Rae, was 60 kilometres by air and 100 kilometres by cat train. In placing orders for materials advance planning was essential, so that shipments would arrive in time to meet deadline dates for water or cat train transport.
Figure 1. Snare Hydro site location.
Furthermore, the post World War 2 shortages of many important materials were at a peak during the early stages of the project. A lot of the equipment was in transit for more than a year, transhipped in many cases from railway to riverboat at Waterways, to cat train at the portage around the rapids near Fort Smith, back to a river boat and ultimately unloaded near Fort Rae to await loading onto sleds in February for the final lap to Snare. The navigation season lasts roughly from July 1st to September 20. Transportation rates from Waterways to Frank's Channel, near Fort Rae, were $35 to $40 per ton. In 1948, a 600 km road was also constructed from Grimshaw, Alberta to Hay River, NWT on the south shore of Great Slave a distance of 600 kilometres. However, the Snare site was still another 400 kilometres from Hay River by cat train. Air transport in light aircraft was possible year round with the exception of the periods during freezeup or breakup, but the aircraft were limited to loads of less than 1500 lbs. Cat trains became the major means of transporting heavy freight during the late weeks of the winter when the ice reached a maximum thickness of nearly a metre. The period during which Great Slave Like may be crossed with a minimum of danger is limited to two months. The usual procedure for cat trains was to plow a plow a road with a bulldozer through the snow covering the ice, followed by a series of up to 10 cat trains, each containing up to ten heavy sleighs pulled by a tractor. The total pay load pulled by one tractor under favourable conditions could reach 125 tons, but the normal load was 50 to 75 tons. Each train was self contained with a caboose where the two crews would eat and sleep. The first freight to the Snare site was delivered during the late winter of 1945-46, and consisted of some construction equipment, dynamite and cement. During the summer of 1946 equipment, lumber, cement, dynamite and non-perishable food supplies were delivered by water to Frank's Channel. This, together with further construction materials from Grimshaw and Yellowknife, was brought by tractor to the project site in March of 1947. This winter mobilization operation involved 1,577 tons at a cost of $0.456 per tonmile. In the open water season of 1947, approximately 1200 tons of material, including the main transformers and the generator upper bracket were delivered to Frank's Channel. In February and March 1948, this tonnage was hauled to Snare, and in April, 220 tons of machinery, trucked from Grimahaw, was brought by cat train from Hay River. This tractor haul was done at a cost of $0.345 per ton-mile. At the same time, 250 tons of cement and small freight was flown frame Hay River to the site in DC3 aircraft at a cost of $149 per ton. The total cost of transportation of materials and manpower amounted to 13 percent of the total cost of the project.
3. Project Construction The site of the Snare River dam and plant is located in a narrow section of the river valley. The development consists of an earth fill dam spanning across a rock island for a total crest width of 763 ft, a concrete intake structure with trash racks and roller gate at the upstream end of the rock island, which admits water to a tunnel through the rock island. The foundation for the dam consists mainly of exposed bedrock. The power house is located at the downstream end of the tunnel, and contains one main unit of 5350 hp at 56 foot head. The entrance structure is a reinforced concrete tower at the tunnel portal with contains the roller type gate and host. The powerhouse building was a steel frame construction with walls consisting of a double course of concrete blocks made at the site. A void space between the two concrete block wall was filled with rock wool for added insulation. Water is admitted to the turbine through 13.5 foot diameter welded steel penstock, grouted into the lower end of the tunnel.
Dewatering of the project site was accomplished by tunneling 256 ft through the rock island. Since the floor of the tunnel was five feet below the tailwater, the upper half was tunneled while a timber crib coffer dam was being erected at the head of the north channel. Logs cut on Big Spruce Lake and yielded 280,000 feet of rough lumber for the job. The tunnels and channels were completed in November 1946. The earth fill dam has constructed of a rolled impervious fine silt core, and pervious embankments graded from fine sand, adjacent to the core, to quarried rock at the outer faces. The side slopes are 2.5 to 1 on the downstream face of the dam, and 3 to 1 on the upstream face of the dam. The impervious material for the core of was obtained in nearby swamps, and consisted of fine glacial silt with of a very uniform size, and low permeability. The sand required for pervious zones of the dam was found in great abundance and in a great range of grading within twelve hundred feet of the site. A total of 165,000 cubic yards of material is contained in the dam.
Figure 2. Profile of Snare Hydro dam. The core material in its natural state was permanently frozen, and entrained considerable excess moisture before it was placed. Considerable effort was initially undertaken to place the core material with an optimum moisture content, but this practice put the project seriously behind schedule because the material took a long period to dewater. A major revision to the original design occurred in placing saturated silt in the core, and in steepening the side slopes in the core to 0.45 to 1 within an elevation of 8 feet above the bedrock, which ultimately saved the placement of 12,000 cubic metres of core material. At the end of the construction season in 1947, the dam was left with a 5 foot cover of sand over the core to minimize frost penetration. In May of 1948, as soon as the mean temperature rose above freezing, the sand was removed and it was discovered that frost penetrated only 15 inches into the core material. The 90-mile power line from Snare River to Yellowknife travels across very rocky country, spotted with many lakes of varying sizes. Almost 10 miles of the 91-mile distance is over water. Digging postholes was a major chore, since 99% of the power pole holes were cut in rock. There was also the problem of gauging the correct tension on the three wire transmission line because annual extremes of temperature ranges from 60 degrees F below zero to 90 degrees F above. Construction of the power plant, presented many problems not usually encountered in small structures of this type. The season during which concrete could be poured, without frost protection, extended only from late May to mid September. Considerable concrete was poured in the periods outside these months, but heating of water and aggregate was required. Heating of forms was accomplished with burning stoves and gasoline Fuelled Herman Nelson "Jeep" heaters. On only one occasion did concrete freeze. The steel erection crew and their equipment were flown to the job early in April, 1948, and prior to erecting the superstructure were employed in welding and installing the penstock and scroll case. Handling of the steel members was done by a dragline with a 65-foot boom.
Assembly of the generator stator frame began June 1948, and the switchgear installation was started a few days later. The roof of the powerhouse was now partially completed, but the tar and felt had not vet been applied, and walls were only started. Despite delays, the bus was energized in September and power was supplied to the Giant Yellowknife Mine October 1, 1948.
Figure 3. Completed Snare Hydro project.
4. Project Legacy At the time of the Snare Hydro development Yellowknife was undergoing a metamorphosis from a primitive, "hell roaring" pioneer settlement to a modern, planned town. Old frame dwellings, and business structures that stood or leaned drunkenly askew for years gave way to up-to-date construction. Construction of the Snare River power development by the Canadian Department of Mines and Resources was a difficult job made infinitely more difficult by the weather. The permanently frozen soil, permafrost, its surface turned into a sticky, slippery mud by the Arctic sun's intensive rays, was but one of the problems. Transportation of incoming construction and installation equipment presented the supreme obstacle that had to be hurdled months and years before the power could be turned on. Almost $5 million (1949$) was spent on the new plant. The Snare River hydro system is one of the most northerly hydro electric systems in Canada, and continues to produce electricity at the original plant and 3 new plants, which supply electricity to the communities of Rae- Edzo, N'Dilo, Dettah, and Yellowknife, and to the Giant and Con gold mines. Downstream sites to the original 1948 facility were developed at Snare Falls in 1961, Snare Forks in 1975, and Snare Cascades in 1996 as electricity demand increased in the region.
5. References Eckenfelder, G, and Russell, B. Snare River Power Project. Engineering Journal, March, 1950. Plummer, H. The Power Line Comes to Yellowknife. Popular Mechanics, February, 1949.