At the bottom of a slope in a dense Montreal neighbourhood, there's a new park with benches, an open field and a playground — along with two small pedestrian bridges. When there's heavy rain, water rushes down the streets and sidewalks into the green space, forming a small lake beneath the overpasses, in a carved-out area filled with grasses, shrubs and rocks. In the days that follow, the water slowly seeps into the soil and stormwater system. It's all been engineered to prevent flash flooding in nearby streets and homes, while nourishing the vegetation in the park.