Tuesday, January 10, 2012

Woody Debris

A couple of times in the past year I have got a bit of a bee in my bonnet about the use of woody debris, In spring a two page article appeared in the national angling press by a Wild Trout Trust expert extolling the use of woody debris and sounding the trumpet for everyone to bolt logs to the bottom of the river bed in order for the Wild trout to revive from the riffle subsequently created. On a couple of occasions I have been pulled up for my criticism of the article, but I maintain that it was irresponsible to suggest that all and sundry should start chucking branches in wherever they can, so, with the aid of a few badly taken photos, I will try and demonstrate why. We have used Woody debris here on several occasions, principally on the half mile long man-made channel dug to drive the wheel in the mill. Overwide for the amount of water flowing down it, the flow was sluggish and silt was deposited throughout its length, a hedge runs along one bank starving the channel of light so weed was thin on the ground.
About fifteen years ago we took the decision to narrow the channel and speed up the flow in order to make condtions more suitable for Mr and Mrs Trout and much more besides. The hedge was reduced in height and the far bank planted with sedge and other marginals behind a line of staked faggots. Fifteen years later this has developed into a thick line of sedge that can be edged in at times of high discharge and allowed to grow out when water is scarce. Ducks and much more love the new marginal growth, the fish love the increased flow and food derived from a clean gravel bottom and the weed loves the light. The top section of this channel curves away by around forty five degrees and subsequently the right hand bank is always in shade.
A similar strategy here would not work as the planted marginals would never get established. Instead we allowed the left hand bank to grow out as far as possible and used a couple of pieces of woody debris on the far bank to pinch the flow. Using woody debris always puts pressure on the opposite bank but because the marginal growth here was very thick no erosion of the bank occurred because of the protection of the thick marginal growth, it also had the effect of giving the channel a sexy wiggle.
If you look closely behind the woody debris in the picture you can just make out a two pound Brown Trout who looks to be thriving. On both of these sections, because the fringe has been allowed to grow in we have installed casting platforms for anglers to make it possible to fish.
In this picture, following high wind a length of wood has become lodged in the wrong place. In the space of a week it has already begun to erode the opposite bank that had little protection by marginal growth. Its action is far too aggressive for this type of stream. There are no fish in this riffle, most that were on this bend have moved downriver or upriver in search of an easier station. It’s an extreme example, but on this river damage such as this can occur over a period of months if you get your woody debris slightly wrong. I have looked after this stretch of river for twenty years and am reasonably confident in where and when I can use woody debris on a chalkstream, I would not be as confident on any other type of river and would want a good long look over a period of time before I made any judgement. Articles in the national angling press by “experts in the field” imploring all to throw wood into rivers just to see what happens, are irresponsible and typical of the "have a go and see what happens" policy that prevails in some quarters.

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