The St. Mary River Irrigation District’s (SMRID) Chin Reservoir is located roughly 10 km South/Southwest of Taber, Alberta. The Chin Reservoir stores roughly 154,000 ac-ft of raw water primarily used in irrigated crop production but also as a raw water supply for local municipalities, water co-ops, and to support various industrial activities. The Chin Reservoir is formed by the impoundment of water between the Chin West and Chin East dams, spaced ~25 km apart within the Chin Coulee Glacial meltwater channel. This off-stream reservoir is supplied by the SMRID main canal which conveys diverted water from the headworks reservoirs owned and operated by Alberta Agriculture and Irrigation. The point of demarcation begins 74 km upstream at the North Outlet of the Milk River Ridge Reservoir, south of the town of Raymond, Alberta.

1920s Dam at Chin West

The Chin West dam is situated at the southern toe of Chin Butte, roughly 8 km south of the unincorporated community of Cranford, Alberta along Range Road 182.

The 1950s-era structure at Chin West Dam that is visible today, was preceded by a modest structure constructed in about 1920. This initial dam structure impounded a small amount of irrigation water within the Chin Coulee, supplying irrigation to the Bountiful Coulee/Taber  areas. Photos of the original 1920s dam in Chin Coulee are provided below.

1920s Dam at Chin West
1949 photo of 1920's Dam at Chin West

Proposed Chin West Damsite, showing 1920s dam, and Lakeside Colony, 1949

PFRA Involvement -1940s

Beginning in 1945, and becoming formally ratified in 1950, a significant investment by the Government of Canada funded the construction of several headworks reservoirs and a connecting network of conveyance canals to form the St. Mary Project under the direction of the newly formed Prairie Farm Rehabilitation Administration (PFRA). Construction was expedited in order to leverage the Canadian share of water from the St. Mary and Milk Rivers. South of the US border, the American Dam development program had full intention of utilizing the unused Canadian portion of the two rivers. The political climate of the time favored public investment in irrigation infrastructure. The key individuals, Wally Foss, Ben Russel, and P.M. Sauder, held influential positions within the PFRA, leading to development of the St. Mary Project. During this time, the PFRA oversaw the construction of the Waterton, St. Mary, Jensen, Milk River Ridge headworks dams, along with several other dams such as Chin West and Chin East, all connected by a conveyance canal which eventually delivered water to Medicine Hat in the late 1950s.

Chin Reservoir Structures

The design of the Chin Reservoir and its appurtenant structures began in 1949 at the direction of PRFA engineers. This included the Chin East Dam, the Chin Chute Spillway, and the Chin West Dam. The Chin West dam would host the irrigation outlet, discharging to the downstream Stafford Reservoir and main canal and was the only outlet structure for Chin Reservoir.

At the Chin West Dam site, (see picture below) numerous investigations were carried out to assess the foundation characteristics of the site. Samples collected by the team of engineers supervising the design were submitted for laboratory analysis to a materials testing facility located at the St. Mary River Damsite. From these investigation programs, the Chin West damsite was characterized as having a foundation made up of “relatively soft unconsolidated overburden”. It was stated that the foundation of the dam could settle up to 4 feet at the center line of the dam, as the foundation soils consolidated.

History of Chin Coulee

The Chin Coulee is a significant glacial meltwater channel which formed during the retreat of the Laurentide ice sheet roughly 20,000 years ago. The retreating ice sheet shaped the regional topography, creating a transformed landscape marked by extensive glacial meltwater channels and prominent hills and ridges rising above the gently sloping prairie, including the Chin Coulee.

Among these topographical features is the Chin Butte, which, in present day, is visible from HWY 3 and is marked by Acciona Wind Energy’s Chin Chute Windfarm. Prior to the arrival of European settlers, this area was utilized by the Blackfoot Nation as part of their traditional territory.

The traditional Blackfoot name for Chin Butte is “Mistoamo” which roughly translates to “Beard”. Blackfoot inhabitants camped at the base of Chin Butte, using its topography to their advantage as a lookout point for the herds of Bison, and other game inhabiting the area. The name “Chin” is a reference to the appearance of the Butte as “Chin” from a distance. (Glenbow Museum)

Geotechnical Drilling at Chin West Dam 1950

Original Design

The original proposed height of the Chin West dam would be 869.27 m, but was lowered to elevation 865.56 m due to concerns regarding foundation settlement (PFRA, 1950). The original 1949 recommendations by the PFRA engineers were to construct the Irrigation Outlet structure in the south abutment of the dam on top of the sandstone bedrock, similarly modelled after the  Berry Creek Damsite, now Carolside Reservoir, completed in 1948. However, this recommendation would not be carried forward into final design, possibly due to the expense of bedrock excavation and limitations of the equipment of the time. The final design would position the low-level outlet structure near the north abutment of the dam, on top of the poorly consolidated soils of the Chin Coulee floor.

Foundation Conditions - 1953

“In view of the soft foundation conditions existing to a depth of approximately 80ft. at the Chin Dam No. 1 site, the monolithic concrete conduit barrel of approximately 480ft. in length has been specifically designed to withstand differential settlements of up to 4 ft (1.2 m). To facilitate this, the conduit barrel has been heavily reinforced and provided with a longitudinal sliding joint running its total length, located at mid-height. The conduit is provided with a gate control tower located about 25ft. upstream from the dam centreline and rising to the dam top so that the water flow through the conduit may be controlled from the surface of the dam. The 36x7ft. conduit barrel is provided with five passages through it, consisting of two openings at 4×5 ft and three at 4x6ft. The five openings will provide for the necessary flow to supply the main canal downstream from the dam and which has a capacity of about 3200 cfs.” (PFRA 1953).

Construction

The construction of Chin West Dam commenced in 1952, with excavation and foundation preparation for the new dam and conduits taking place first. The new conduit structure was constructed of reinforced concrete. Rather than being fastened with wire ties, the reinforcement cage was arc welded. The concrete embedding the reinforcement cage was one of the first documented projects in western Canada incorporating air entrainment additives as a means to prolong the structures’ ability to withstand freeze thaw deterioration. After 58 individual concrete pours, the outlet structure was completed. The gate control well was fitted with 5 Hardisty cast iron slide gates, two of which remained functional until 2021.

PFRA Outlet Structure Drawing
Geotechnical Drilling at Chin West Dam 1950
Chin West Dam As Constructed 1952-1956
Construction of Chin West Dam

Concurrently, construction of the earthen embankment took place over 3 consecutive construction seasons. Earth materials were excavated from the adjacent areas, conditioned with moisture, and compacted in lifts. The upstream face of the dam was finished with riprap sourced from the “Harris Pit” located north and east of Cranford, Alberta.

Chin West Dam Performance

Construction of the Chin Reservoir was completed in 1955. As expected, a significant amount of settlement took place at the west dam, as the foundation consolidated under the weight of the 21 m tall dam. Originally constructed to an elevation of 865.56 m, the dam has settled to elevation 864.24 m, a total of 1.31 m over its life, indicating that the initial predictions of 1.21 m (4 ft) by the PFRA engineers was reasonably accurate. However, during this settlement, severe structural cracks developed on the downstream side of the buried irrigation outlet structure. These cracks were quickly noticed by PFRA engineers monitoring the dam during the post-construction period, and required prompt action to avoid failure of the outlet structure, which would have caused a structural failure of the Chin West dam.

Chin West Dam Performance
Chin West Dam Performance
Chin West Dam Performance

As part of SMRID’s dam safety program, the irrigation outlet structure at Chin West Dam has required continual monitoring and maintenance to ensure the safety and reliability of the structure to deliver irrigation water for downstream users. At 70 years old, the dam and its outlet structure are reaching the end of design life that is typical of PFRA structures, and requires extensive rehabilitation to bring the dam in compliance with modern standards.

The Project at Chin West Dam

The primary goal of today’s Chin West Dam project is the renewal of the dam along with a complete replacement of the irrigation outlet structure. A modern low-level irrigation outlet structure will be constructed in the south abutment of the Chin West dam. This new structure will be a reinforced cast-in-place concrete structure, placed directly on the sandstone bedrock. The structure will be equipped with modern sluice gates that will remotely regulate flow to the downstream Stafford Reservoir and SMRID’s main canal. The existing outlet structure may be repurposed as a raw water intake for irrigation or municipal purposes, while the downstream half of the structure will be filled with grout and abandoned in place.

Figure 1. Plan View of Chin West Dam Rehabilitaion)

The new outlet structure will be situated in an excavated channel, excavating up to 34 m through glacial till and underlying bedrock, and will have approximate length of 1,000 metres. At about the midpoint of the channel, a grout curtain will be injected into the underlying foundation, and the structure erected. The structure will be buried in a 23 m tall dam of it’s own, as outlined in the below image. A gate house tower will rise through this “outlet dam”, where an operational control building will house the equipment controlling the slide gates of the structure.

Figure 2. Proposed Outlet Structure and Channel

The project will require an excavation in excess of 2 million m3 of glacial till and bedrock. The excavated soils will be used to widen and raise the existing Chin West dam, such that the geotechnical stability of the dam can be improved, and to facilitate the future Chin Reservoir expansion project, which includes raising the operational level of the reservoir by 2.6 m. Excess soils will be used to recontour an adjacent farmed field in partnership with local landowners. Conceptual illustrations of the completed project are provided below:

Rendering of Chin West Dam

Rendering of Chin West Dam

Rendering of Chin West Dam

Rendering

Rendering

The project is anticipated to take place over a minimum period of 3, possibly 4, construction seasons. The project is funded through the Government of Alberta’s AIM Program. The Raymond Irrigation District (RID) is a 10% contributing partner in this project. Under the AIM program, the SMRID secured 30% grant funding from the Government of Alberta; 20% of the project will be covered by SMRID/RID reserves, and the remaining 50% is funded by a loan through the Federal governments Canada Infrastructure Bank which will be repaid by SMRID and RID.

During the project period, local residents should expect road closures to occur during key points of the project, particularly as the embankment materials are being placed to raise the dam. Road users are encouraged to pay attention to road closure notices provided by the MD of Taber and Lethbridge County, and obey speed limits when traveling in the area. The SMRID has taken provisions, such as a public bypass route, that will maintain through traffic of Range Road 182A for the majority of the construction period.

The project is scheduled to break ground in Q2/Q3 of 2026, following a Request for Qualifications and Tendering process beginning in Q1 2026.