Slowing the flow – naturally reducing floods

Flanders Moss NNR, Blawhorn Moss NNR and Loch Lomond NNR

We have had a lot of rain recently. All 3 of our reserves are very, very wet. Interestingly they are wetter than the surrounding farmland. This is because they are wetlands – the clue is in the name, land that is wet. Wetlands are often in a fairly natural state and offer homes to a wide range of wildlife hence these 3 being nature reserves. We work to keep them wet and in some cases like Flanders and Blawhorn to make them even wetter.

Good for wildlife but there are other benefits. We make them wetter by slowing the flow of water that comes onto the site, either from the sky or through streams, and letting it off the site slowly. This helps the surround land by reducing the amount of water they receive. At times of flood this can help. It can also help other types of land further downstream such as houses and settlements.

For instance at the Loch Lomond reserve the extensive wetlands can hold huge amounts of water – almost the whole of reserve can go underwater. Downstream of the reserve is Dumbarton at the mouth of the river Leven, the outflow of Loch Lomond. The water held on our reserve won’t stop flooding in Dumbarton but it could reduce its impact a little bit.

Likewise at Flanders Moss. In an effort to rewet the moss and restore the bog habitat we have dammed about 45 km of ditches and built about 10.5 km of bunds that hold water and release it slowly. These ditches and bunds hold a large quantity of water as well as filling up the sponge of the moss. In effect this is taking 868 ha (equivalent of about 2200 football pitches) of land out of the catchment area of the river Forth that drains towards Stirling. If across the whole of the moss we have raised the water table by 30 cm (in places it has been raised much more) then on the moss we have soaked up some 2.5 million cubic metres of water. Again this won’t stop flooding in Stirling but if it takes an inch or two off the height of flood water then that could save some houses from flooding for which those house owners would be very grateful.

So what if this natural flood management work was extended to other land? Flanders Moss accounts for only about half of the peatlands in the Forth Valley. If you throw in a bit of helped through the work of the beavers that are gradually spreading through the area, it could be a real help to reduce the heartbreaking impact of flooding lower down in the Forth valley. Worth considering?

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