First of all, my thanks again to the organisers and attendees for hosting the evening talk on the Trout in the Town initiative. I really enjoyed giving the talk and also the discussions that we had. As a follow up to a specific point that was mentioned on the Large Woody Debris on the river Goyt.

There was a concern that this might not be fulfilling its potential. Hopefully the information below should help to clarify:

These are initial trial installations to satisfy the concerns of the EA Flood Risk Management team that we can actually retain LWD within a spate river of this nature - especially so close to bridge parapets, roads, houses etc.

The current scale of introductions (i.e. amount of debris proportional to channel width and overall number of trees) is a small proportion of what was originally proposed. This limitation will be reviewed if the security of LWD anchorage is acceptable.

Having said that, the material that has been installed into the stream and allowed to swing parallel to the banks is already providing beneficial effects.

First of all - it is generating localised scour during spate events (and apparently is securely anchored!!)


Behind the main stem and between the toe of the bank - sediment is being trapped (preventing it from smothering the cobbled bed in the main channel)


Below where the sediment is trapped - the trailing branches and fronds are already fluffing up some cleaned gravel (as well as providing cover for juvenile fish against cormorants and goosanders)



Some more bright gravel with silt blown out from it by the trailing branches (all photos in this sequence are of the same tree on two separate visits under high and low water conditions)


The take home message is that 1.) We have first got to prove that we can securely retain the LWD in a powerful spate river before we can go on to introduce more dramatic "pinching" of the current (an ongoing programme)
2.) In contrast to ground-fed rivers - the LWD will be acting under a much bigger range of conditions (sudden dramatic spates). Scour and gravel sorting effects may be occuring at high water (which you might not see during visits at low water).