Horsefly Spillway successfully diverts high flows during significant early-season rain event

Posted on June 11, 2026 by Ryan Dahlman

St. Mary River Irrigation District

For the first time since the project’s inception in 2020, the Horsefly Regional Emergency Spillway was successfully operated to divert excess water to the Oldman River following the sustained heavy rainfall event with many areas within the SMRID recording upwards of five inches of rain since May 29.

Developed through the Southern Regional Stormwater Drainage Committee (SRSDC), the Horsefly Regional Emergency Spillway is one of seven flood mitigation projects identified in a report completed by MPE in 2014. Designed to safely divert excess water from the SMRID canal system into the Oldman River during high intensity storm events, what was once a growing regional vulnerability is being transformed into a collaborative engineered solution built through partnership and shared responsibility.

SMRID and partners with the SRSDC were thrilled to witness the spillway perform as designed for the first time on June 2. While Phase 2 of the project is still in progress, the spillway’s first operational use marks an important milestone for the project and provides a tangible demonstration of the role the spillway is expected to play safeguarding communities across southern Alberta during future high-water events.

“Seeing the spillway operate in real-time, protecting communities, reducing risk to stakeholders and taxpayers, and helping to prevent and mitigate the costly human and economic consequences of uncontrolled flooding fortifies the importance of the SRSDC investment. The repeated flooding in the 2010’s demonstrated that stormwater management can no longer be approached municipality by municipality, and that coordinated regional solutions are needed. Seeing the spillway operate as designed is a timely reminder that regional collaboration works,” said David Westwood, St. Mary River Irrigation District general manager.

The Spillway’s phased construction includes significant channel widening and bank raising, wetland development, culvert crossings and improvements to existing water management infrastructure. Phase 1, completed in May 2024,spans from Taber Lake to the Oldman River; Phase 3, completed in May 2025, connects the SMRID’s main canal to the Horsefly Reservoir; and Phase 2, the final phase, will span from the Horsefly Reservoir to Taber Lake, once completed. The maximum capacity for all phases is 55 m3/s. The MD of Taber’s November 2018 Public Works Progress Report showed over 400 sites of recorded damage following the 2018 floods.

“This was the first time the Horsefly Spillway was called upon to do its job, and it worked exactly as intended. While there is still work to be competed, this rainfall event showed that the investment made with the SRSDC to date is already delivering benefits to the communities it serves. Flood risk does not stop at municipal boundaries. Water moves across communities, infrastructure systems, agricultural land, transportation corridors and industry alike,” said Gary Franz, Southern Regional Stormwater Drainage Committee (SRSDC) co-chair.

Between 2010 and 2019, communities in Southern Alberta experienced repeated flooding and stormwater events that overwhelmed existing infrastructure, flooded farmland, damaged roads and culverts, stranded residents and placed enormous pressure on the SMRID’s canal system. These major events highlighted just how vulnerable the region had become to extreme rainfall and snowmelt runoff.

“The 2018 flood highlighted just how vulnerable the region had become to extreme rainfall and snowmelt runoff. The prosperity of Southern Alberta’s agricultural community relies heavily upon cross-boundary irrigation and transportation infrastructure.  As this project progresses, it is worth highlighting the value of continued investment in the SRSDC from all municipalities connected to the region it protects, not because the impacts are confined to just one community, but because the benefits are shared by all of us,” said Cory Nelson, current SMRID board chair.

Southern Regional Stormwater Drainage Committee (SRSDC)

Significant flooding from major rainfall and snowmelt events in the 2010s prompted various parties in southern Alberta to come together to find solutions to reduce the impact of flooding. A Regional Stormwater Management Plan was commissioned in 2014, resulting in the recommendation of seven flood mitigation projects in southern Alberta, including the Horsefly Regional Emergency Spillway. In 2020, $47 million in shared funding for the expansion of the Horsefly Regional Emergency Spillway project was announced.

In 2018, overland flooding required the MD of Taber to issue a local state of emergency. Impacts included municipal infrastructure repairs, transportation disruptions, crop losses, risk to drinking water, risk to homes and businesses, and millions of dollars in damages.