The upland environment isn't a floodplain, it's the lowlands. The prevention of upland soil erosion would create a thicker land mass to sponge water and hold it higher up,slowing its release into the lowlands. Recently Geomorphologists have acknowledged the potential of water retention and slow release systems as opposed to channeling water as fast as possible towards the sea; which often contributes towards the flooding issues we see today, of course- along with surface runoff and building on flood plains.
I live in one of the wettest places in Britain and the reason we have few floods here, on the west coast, isn't due to the slow release from "thick upland mosses" (or bottomless bogs as it actually is), it's due to the relatively short run off from the western watershed, geography and building infrastructure to cope with exceptional wet weather events, the propensity for which is a fact not lost on the local population.
As a keen fisher river water levels is something I keep a close eye on. During prolonged dry periods the vast bogs do dry out, a bit. Sometimes it can take a good deluge to get them filling to the point that river levels rise, so there is some retention capability in the bogs, that has at times; caused me much frustration.
However, whilst conceding that there is some water retention in our local bogs, it must be stressed, there's rain and there's rain and the kind of rain experienced during the worst phase of storm Desmond, 14" in 24 hours (that wasn't the total, just the measure for the heaviest 24 hour period) in upland Cumbria (thats almost west highland proportions
) would still need somewhere to go, almost all of it falling on already saturated ground.
One of the most memorable exceptional weather events I remember was during the late 80's when commuting to the A82 on loch ness side daily for work. A sudden thaw in the snow bound hills, a network of hydro lochs being a little too full and 9" or 10" of rain, caused loch ness to rise by 4 foot in a single afternoon, loch ness is the largest volume of standing water in the UK containing twice the standing water of all England and Wales combined. It's some 30k long and 1.5k wide, steep sided and 700 foot in depth.
So when you have something as brim full and on a serious geographical scale, as that, there's no stopping it. The river ness burst it's banks flooding the centre of town and washing away the 100+ year old ness rail bridge. As well as causing lots of flooding around it's shores, I had to help evacuate people from sheltered housing in Fort Augustus having been redeployed from my regular job, such was the emergency.
As others have said, in this country we have a lot of rain. The reason we have issues with flooding is that we drain land and build on it and under invest on drainage capacity.
Re-wilding? The guy wants to get a grip. Where I live (in the middle of bits being earmarked as "wild" land) it's not re-winding we need, it's reoccupying that interests us. If you want wild go to Canada or Russia, the UK is a pastoral environment shaped by 5 or 6000 years + of livestock husbandry. I believe the highlands should be covered in grazing cows, it's the missing cows (that were on the ground for thousands of years before deforestation the clearances (the husbanders) and then) intense over grazing by less environmentally friendly beasts such as sheep and deer that is largely responsible for the degraded state UK upland areas finds themselves in today, particularly so the Highlands.
