All the water to irrigate nearly 300,000 acres in the Bow River Irrigation District (BRID) and 5,000 acres in the Siksika Nation is diverted from the Bow River near Carseland. A concrete weir across the river and a gated diversion structure direct water into the canal that supplies not only irrigators but many other uses including municipal water supplies, wildlife habitat projects, intensive livestock operations, and recreation on McGregor, Travers, and Little Bow reservoirs.
The diversion structure is located on an outside bend of the river, so floating debris including logs, branches, aquatic vegetation, and human litter naturally tends to accumulate there. A trashrack keeps this debris out of the canal, but it is easily plugged by debris, which reduces the amount of water flowing into the canal. The debris problem is most severe during high river flows, restricting diversion at a time when the canal should be operating at full capacity to fill reservoirs with surplus water without impacting other water users. The debris problem is often severe again in late summer when aquatic vegetation growth in the river peaks.
Cleaning of the intake trashrack, was a difficult and time-consuming process and normally carried out between one and four times daily. , When debris loads were heavy the canal gates on the diversion structure had to be closed completely to remove the debris. It was common to lose up to 30% of the diversion capacity between cleanings. This added up to millions of cubic metres of lost water each year.
The diversion works are operated by the BRID but are owned by the Government of Alberta (GOA). For many years the BRID requested the owner to implement a solution to reduce the amount of debris plugging the structure. After much discussion, the BRID offered to pay the full cost of implementing a solution approved by government.
The BRID engaged Revelstoke Design Services Ltd. and Begbie Contracting Services Ltd. to design, supply, and install a floating boom to divert debris away from the diversion inlet. Work began with the construction of a massive reinforced concrete anchor block on the river shore in October 2020 by Robin Hansen Construction Ltd, with the boom installed in May 2021.
The boom is attached to the anchor block at the upstream end and to a floating slide anchor bolted to the weir wall at the downstream end. Attaching the downstream anchor required divers to drill holes through the wall underwater. The boom is approximately 200 metres long and consists of Tuffboom XL floats (15 feet long by 24-inch dia.) from Worthington Products Ltd. with 36” deep UHMW plastic deflector plates attached to steel frames below each float. The boom is designed to be left in the river year-round.
The total project cost was just under $600,000.
Two days after its installation during high river flows the BRID’s headworks operator declared the boom was a “game-changer”. Its performance has been outstanding under all conditions through the 2021 water season, eliminating almost all debris accumulation on the trashrack, which now requires only infrequent cleanings for relatively minor amounts of debris.
With extreme drought experienced in 2021 this timely installation eliminated flow reductions due to plugging, helping the BRID to consistently divert water to all water users in the district during a challenging year.
Figure 1: Accumulation of debris on the diversion trash rack
Figure 2: Trash boom installation
Figure 3: Trash boom floats
Figure 4: Trash boom in service