Nature Based Solutions for Flood Management in Clonmany

Presentation by Prof. Mary Bourke, Trinity College Dublin at a community event organised by the Inishowen Rivers Trust discussing flood management using nature based interventions on the streams and rivers of Clonmany, Inishowen, Co. Donegal. 23 July 2020.
Original scoping project funded by OPW.

[@threeriversforge1997]

Leaving the log structures open on the bottom is actually a pretty bad thing because it forces the water to scour and dig out the channel, increasing the erosion and silt in the water. In the US, we call these Beaver Dam Analogs because we learned from the beavers. The key to stopping flooding is to actually hold the water back in the Beaver Dam Analogs just like the beavers do. This raises the water table and increases the amount of vegetation that can grow along the river course. We've got gobs and gobs of scientific data on just how big of an impact a chain of BDA's will make in a catchment. 25% decrease in storm pulse isn't at all unusual, and downstream flooding is pretty much a thing of the past. But you have to build like the beavers build. Thinking that you know better is a recipe for disaster.
Better still is that you can build what I call "micro BDA's" on every crease and fold in the land because you know those are going to become gutters for the rain. So what do you do? A single small "dam" made from sticks and twigs, with some leaves piled against the uphill side, and you've created a structure that'll slow water down, spread it out, and give it time to soak in. Then it's just a matter of waiting on the rain to fall. No need for heavy equipment. No need to break out the shovels and mattock. Just do as the beavers have done for millennia and stack some twigs and leaves across the path of the flow. It takes just minutes for each "micro-BDA" and while they might not seem like they're doing much.... the pay off is quite significant. The more you add, the better the return on your investment. Plus, they're just fun to build.