The city's $1.85-billion west leg of the Confederation LRT is expected to pass through a large Kanata floodplain at the request of developers in the area, but city staff expect developers to fill that same wetland before trains are ready to run.

If approved, a four-kilometre portion of the route will be elevated on an aqueduct-style structure so the train can pass over roads and creeks from Campeau Drive, around the Canadian Tire Centre to Hazeldean Road.

A swath of land was set aside as part of a potential bus rapid transit route through the area, but developers asked that the city to relocate the future line closer to Feedmilll Creek to make more room for them to build.

A city drawing of the proposed Campeau Station next to Feedmill Creek. (City of Ottawa ) The top choice for the Kanata LRT route would see the city swap the BRT land for a section in the floodplain along Feedmill Creek.

Changing the wetland

Building in the floodplain is strictly against city policy, but despite that the transportation department is counting on developers building in the floodplain in order to keep the future LRT line safe from water.

The Mississippi Valley Conservation Authority (MVCA), responsible for protection of watersheds in the area, has allowed developers to fill in the most sprawling part of the wetland, which will change where flood water is stored. That fill will make sure water stays away from the elevated LRT structure.

The cost of building the structure closer to the creek will be similar to the original BRT route, said transportation planning director Vivi Chi.

"We costed the structure, knowing that the structure would be in this kind of land, in this area," Chi said.

Flood mitigation measures to come later

We costed the structure, knowing that the structure would be in this kind of land, in this area, - Vivi Chi, director of transportation planning

More detailed design work won't be done until the city finds some funds, which isn't expected until after 2031.

But once the route is approved, it will be difficult to move if it turns out to be more expensive than anticipated. Development plans have already been submitted to the city that could box the LRT in.

The development documents lay out subdivision plans for the area directly next to the proposed Campeau LRT Station. They describe soft soil that's difficult to manage, and the years of work the developer has done to stabilize the ground for building.

City will need a permit before construction

The changing nature of the floodplain puts city and the MVCA in a regulatory no-man's land for the time being, said John Price, the director of water resources engineering for the conservation authority.

The MVCA is supposed to refer to the existing floodplain when making decisions about what can and cannot be built in the area. The city has been approving developments on the condition that they aren't built until the properties are properly filled, he said.

The city will likely need a permit to fill in the land near the creek to put up its structure for the future LRT line, but that won't happen until the project is almost shovel ready, a long time from now.

The route will not be final until city council votes on Wednesday.