AWARD OF EXCELLENCE_ East Arrowwood Syphon Replacement, Alberta - Canadian Consulting Engineer

11/28/2015 AWARD OF EXCELLENCE: East Arrowwood Syphon Replacement, Alberta - Canadian Consulting Engineer

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AWARD OF EXCELLENCE: EastArrowwood Syphon Replacement,AlbertaCategory: Water ResourcesUMA ENGINEERINGThe East Arrowwood Syphon is anessential link in the Carseland-Bow River Headworks main canal, serving to conveywater flow across the valley of East Arrowwood...

Concrete being pouredinto sliding form toconstruct the syphonbarrel; the syphon is 5metres outer diameterwith 500-mm thick wallsand completely buried.

Aerial view of site with oldinlet canal (at top), beingrestored to a wetland, andthe new canal and syphonbeing cut in a straighterand shorter alignment (at

centre).

Check drop structure,equipped with overshotgates that maintain

upstream water levels andare controlled usingintelligent actuators.

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Category: Water ResourcesUMA ENGINEERING

The East Arrowwood Syphon is an essential link in the Carseland-Bow River Headworks maincanal, serving to convey water flow across the valley of East Arrowwood Creek, 31 kilometresdownstream of Carseland, Alberta. The system provides water to 230,000 acres of irrigatedfarmland in the Bow River Irrigation District and the Siksika Nation, and supports sport andcommercial fisheries on Lake McGregor and Travers Reservoirs.

By the 1990s the original wood-stave syphon had badly deteriorated. It was leaking and theflow capacity was insufficient to handle the projected demands from downstream, or theinflow from floods upstream. As well, creosote-treated wooden staves were contaminatingadjacent land. In 1996 the Alberta government hired UMA Engineering’s Lethbridge office toprovide design and construction management services for replacing the old syphon.

Replacement presented major challenges in both design and construction. These included:

steep, high, unstable slopes leading to the creek valley;

a high water table in the creek valley and heavy groundwater seepage on the west slope

shallow bedrock in the creek valley

risk of flood damage in the creek valley

environmental issues regarding fish passage, animal migration and preservation of thehabitat

a requirement to maintain water flow in the canal during the irrigation season (the oldstructure and canal could not be disturbed during construction)

severely restricted access and area available for construction operations in the valley.

The designers examined several conveyance options and routes across the valley. Afterconsidering all factors and using value added and life-cycle analysis, they decided that themost cost effective solution was a single-barrel, reinforced concrete inverted syphon, buried



7 metres below the creek bed, and located 150 metres south of the existing syphon. Onereason for this choice was the opportunity to reuse steel formwork from a previous syphonreplacement project.

The replacement structure is a 437-metre long, 5 metres outer diameter, cast-in-placeconcrete barrel with 500 mm thick walls. It has a design flow capacity of 51-m3/s, a peakflood capacity of 60 m3/s, and a maximum operating head of 51 metres. The project involvedbuilding the syphon structure, 1,500 metres of tie-in canals, a major check drop structure and3,800 metres of access roads.

The syphon is close to the Foothills seismic zone, so concerns for the structural stability ofthe barrel and the need for safe access to enable its inspection required cutting back the 45-metre high valley slopes from 30 to 35 degree grades, to 14 to 16 degree grades. This workinvolved excavating 132,000 cubic metres of material, including 16,000 cubic metres ofbedrock. Much of the excavated material was used to build access road embankments.

The check drop structure accommodates a 1.8-metre drop upstream of the syphon inlet. Thedrop creates the head differential for the syphon to operate effectively. The check drop isequipped with automatically activated overshot gates that measure the flow and control thewater level upstream. The gate system includes “intelligent” actuators that respond tocommands from, and transmit gate level information to, a programmable logic controller viaa communications protocol. All communication is delivered through one cable.

The tie-in canals include 1,100 metres of armoured canal at the inlet and 450 metres at theoutlet. An upstream hairpin curve of the old canal had significant seepage and stabilityproblems. One of the value-added features of the project was the use of 158,000 cubicmetres of excavated materials from the inlet canal construction to cut off this troublesomereach. The strategy reduced the material handling costs, increased the hydraulic efficiencyand reduced the long-term operation and maintenance requirements of the canal. Twelvehectares around the old canal are being reclaimed for wildlife habitat.

The project had to be executed within the time constraints of the irrigation and winterseasons. Almost all of the slope stabilization, inlet canal and syphon earthworks werecompleted within the first three months. The syphon barrels were built using the salvaged



sliding forms. The crossing construction was done in three stages to maintain flowdownstream. Operations included rescuing fish, mitigating siltation, and preserving sensitiveriparian habitats.

UMA and Alberta Infrastructure worked closely to resolve protracted issues over landacquisition, water use and labour, and addressed the various concerns of the parties affectedby the project. One of these, the Siksika First Nation, has territory bordering the north bankof the main canal and provided much of the labour and gravel armour requirements.

The syphon was commissioned to operate on schedule in May 2000. The final constructioncontract cost within 1% of the engineer’s estimate, and the total project cost, includingongoing site reclamation, was $12 million.CCE

Project name: East Arrowwood Syphon Replacement Project

Client: Alberta Infrastructure/Alberta Environment

Award-winning firm: UMA Engineering, Lethbridge, Alta.

Project team leaders: Dale Miller, P.Eng., Rod Bower, P.Eng., Dennis Miller, Nick Hernadi,P.Eng., Paul Kemp, P.Eng., Irv Martens, P.Eng., Dave Chalcroft, P.Eng., Steve Eberhardt,P.Eng., Roberto Rogue, P.Eng.

Other key players: Kiewit Management (prime contractor), Thurber Engineering(geotechnical)

Documents

AWARD OF EXCELLENCE_ East Arrowwood Syphon Replacement, Alberta - Canadian Consulting Engineer