Monday, 5 December 2011

Running dry

Last week I was down by my local rivers, the Kennet and Dun, to look at how they might be improved by bank regrading and suchlike. On the bank of the Kennet was a large Brown Trout with a bite out of it - something that wouldn't have been seen a year ago, as the culprit was one of the local otters. It is good to know we have otters back, but maybe not such a popular animal with our local fly fishers! (Although I know they would be thrilled to see one.)

The really bad news is low flows. Our rivers are fed by chalk aquifers that surround Hungerford and Marlborough. They act like big sponges, soaking up rain and then releasing water slowly into the watercourses. The aquifer naturally has low points but normally gets 'recharged' this time of year when we can expect a good amount of rain in the autumn and winter. This year the rain hasn't come yet. Coupled with overall low rainfall the rest of the year, including a prolonged spring drought, the fear is that the aquifer will not get sufficiently recharged and the springs will therefore not 'break' and refill the Kennet and its tributaries this winter. The surge of cold spring water is a vital feature of local chalk streams upon which its aquatic life depends. Brown Trout, for instance, will spawn after Christmas and their eggs need a high level of oxygenated water flowing over them to develop. Currently, the level of flow in the River Dun is almost at a historic low (since records began around 95 years ago), although not yet as low as it was in the 1976 drought. Forecasts associated with climate change suggest this area may be one to suffer increasingly from drought, so low flows may become a permanent and threatening feature to our chalk streams and rivers.

One piece of good news is that by fencing the river, it is beginning to recover a more natural, narrower channel. In some places, brush groynes have been put in to speed up the restorative process of slowing the flow at the edges. In others, just by fencing it alone has allowed emergent plants like the watercress (see picture) to flourish. Under the water these plants are alive with freshwater shrimps which the fish will feed on. The plants will also naturally slow the flow at the river edges, eventually leading to silt deposition and the creation of a narrower watercourse where the flow will be faster and cleaner.

No comments:

Post a Comment