How to develop a low impact natural solution for a community?
The client (urban HOA) had a grass-lined storm water conveyance channel that was eroding away in the center and creeping up the banks. Several large willow trees had grown where the water came under a road and through a concrete box culvert, those trees inhibited water flow. But once water flowed around the trees, it accelerated quickly and eroded the soil in the channel.
Objective was to restore the original grade of the channel, prevent more channel erosion thereby slowing future downstream sedimentation into the onsite retention ponds, reducing the future need for expensive dredging projects. The client did not want the expense or aesthetics of a concrete-lined channel to solve their problem. The Flexamat armor is a permeable, flexible concrete grid mat that allows grasses to grow through the mat, creating a more eco-friendly, better functioning and more aesthetically-pleasing experience to the community and homeowners that back up to the channel.
How to address the client's problem?
Not only do the raised concrete grid help slow the velocity of water coming down the channel, but the permeable grid allows grasses to grow through it, creating more energy dissipation and a biological filter for the water. The plants will help capture nutrients and other harmful elements before the water flows downstream into the retention ponds where the water is used for irrigation purposes.
We removed the upstream willow trees, regraded the channel to fill in the holes that had eroded away and established a flow line in the channel that would ensure water moved downstream without ponding. Seed was planted in the newly graded channel and Flexamat armor was installed in the centerline of the channel to prevent future soil erosion while also acting a energy dissipation device as the water flowed downstream.
How did it all come together?
The community now benefits from enhanced water quality due to the stream improvements, so less treatment has to be performed to the irrigation water before it is used around the community.