Tuesday, October 21, 2008

Shifting gravels and deepening pools......

There were a couple of occasions on the Eden last week, when I was reminded of the degree to which our Northern spate streams are in a constant state of flux. The gradual shifting and re-shifting of the balance between erosion and deposition causes our rivers to creep across their flood plains and periods of exceptionally high flow – typically the big winter floods – exacerbate this effect to the extent that sometimes significant stretches of the channel are completely altered in character. On a river like the Eden, which flows for some distance through pasture overlying an unconsolidated sand, it is possible to see the effect that a succession of spates have had on the outside of a bend – a steep, even undercut cliff of dangerously loose material, which visibly deteriorates over time, depositing lumps of soil and turf into the water as the bank recedes.

The trade-off of course, is the release of eroded sediment into the system which inevitably builds up as energy is lost in slacker water zones elsewhere. So without wanting to turn this into a high school geography lesson, the effect as far as we anglers are concerned, is that our little bit of river constantly changes from one year to the next. Of course, most of you will probably know this happens already. I did too, but I guess I forgot how fast.

It’s been a while since I last fished the Bolton Willows beat – maybe 18 months or more – but I was still surprised to find one or two real differences. One little run I fished was barely worth a look a couple of years ago, but on Friday I found a deep channel of powerful water pushing through beneath a heavily eroded sandy bank. When I got in to explore, I found the going underfoot to be a mixture of large cobbles and sods of turf from the field edge above – awkward wading in a previously gravelly run.

Similar things happened further downstream – a scoured out channel in a previously benign pool tail, a massive cluster of dead trees accumulated against a much smaller one which has been lodged there for a few seasons, and a once sandy run scoured out at least a foot deeper to reveal a substrate of unpleasantly large cobbles.

I really shouldn’t be surprised though; back in my college days, I carried out an exercise where I overlaid a series of Ordnance Survey maps dating back as far as the late 19th century, to compare the changing extent of the main channel of the River Lune around Claughton. What I discovered was surprising – the river had shifted across its floodplain not by feet or inches, but by dozens of yards. And it was continuing to do so at a seemingly accelerating rate, possibly due to changes in land use and an increase in hard surfaced (thus fast draining) areas in general. Indeed, Terry was telling us on Friday how the Eden at Bolton has changed considerably even in his lifetime – from a once narrower, swifter stream, to the wider, more sedate one we see today.

The Eden valley witnessed at first hand the immense power that flowing water can possess when heavy rains in January 2005 caused massive flooding in and around Carlisle. The first time I got a chance to fish following the floods, was on the PAA beat at Little Salkeld. When I left the car and set across the fields to the river, I was amazed to find the high water ‘flotsam’ line a full 220 yards from the edge of the channel itself; and when I began fishing down through the willows, I noticed that the bushes behind me held the carcasses of long dead salmon in their branches – a good 5 feet above my head!



Needless to say, some of the pools I knew and loved were almost unrecognisable that following spring, meaning that I had a lot of finding out to do all over again!
And therein lies one of the joys of spate stream fly fishing, I suppose. Every new season brings new conditions and with them, new challenges. I don’t think it is possible to ever truly know a stretch of river and one of the best things about returning each spring is to begin the task of finding all the new lies and holding spots which have been created over the winter.


This picture was taken in early February 2004.



The same pool in January 2005, following the floods.


In this picture, taken from the previous post, Terry Cousin is wading directly below the tree seen above. It has now accumulated further clutter and this has made some quite significant changes to to bed of the pool tail below.

1 comment:

Phil said...

Matt,

Great Post, it has made me think more about the rivers which I fish and that our rivers are constantly changing. New challenges as always.

Phil