Pedestrians and cyclists will soon lose access to the top of the Glenmore Dam in Calgary for three years as it undergoes a $82-million renovation to improve flood protection on the Elbow River.

The renovation means the dam must be closed to the public starting this fall until 2020 while utility lines are removed and a new structure is built for the operation of steel control gates.

Those gates will mean better protection for downstream Calgary communities against minor flood damage.

Steven Dold, city's dam safety engineer, said the gates will significantly boost the capacity of the reservoir.

"It doubles the reservoir's storage for water supply and it also allows the city greater flexibility to manage run-off in the spring period," said Dold.

Water, gas lines now in tunnel

The city recently completed a tunnel under the Elbow River, just downstream of the dam.

A new water feeder main and a natural gas line are inside that tunnel, which clears the way for the removal of those utility lines that are currently running across the top of the dam.

Once those are taken away this fall, Dold said the next phase of the renovations can proceed.

The concrete deck of the dam will be replaced and then a new elevated hoist structure will be built across much of the top of the dam.

The renovated structure will give users a wider path and views of the Elbow River Valley and the city skyline. (City of Calgary)

That structure is needed to operate new steel control gates, which will boost the reservoir's capacity.

The new gates replace an older system of wooden stoplogs. However, even with the improvements, he said it won't prevent all flooding downstream on the Elbow.

"The project to construct and provide the new steel gate system will allow the city to mitigate flooding in the range of what occurred in the 2005 event," said Dold.

The extra capacity will also allow the city to keep more water in the reservoir during the winter months.

The reservoir is a key source for the Glenmore water treatment plant.

Public crossing on dam to close this fall

Dold estimates the top of the dam will not re-open until the spring of 2020.

Further details on that closure will be announced in August.

He expects users will like the new pathway space, which will be constructed across the dam.

The renovations will mean the top of the dam will be closed to the public until the spring of 2020. (Scott Dippel/CBC)

It's currently a narrow path because of the space that's taken up by the utility lines.

On the renovated structure, users will have a wider path and views of the Elbow River Valley below the dam with the city skyline in the distance.

"I think the access will be viewed by the public as improved over what's existing now," said Dold.