Monday 10 February 2020
Chalk Streams across the Chilterns are springing back to life after one of the most severe droughts on record. After three consecutive years of low flows with long sections of most rivers dry, above average winter rainfall has helped them to start flowing again. In September 2019, at the height of the drought, almost two thirds of the total length of chalk stream habitat in the AONB was dry leading to widespread damage to chalk stream habitat and a number of fish rescues had to be carried out by the Environment Agency to relocate fish caught out by the receding waters. However, since the beginning of autumn, rainfall has been significantly above average and groundwater levels have begun to recover.
Over the winter recharge period (October to March) to date, rainfall has been 145% of average across the Chilterns. Helped by a wet September, effective rainfall – the proportion of the rain that falls which is available to recharge the aquifer (ie. the portion of total rainfall that soaks into the ground) – was 173% of the long-term average. With winter being much wetter than average so far, groundwater levels are currently rising quickly and the rivers are beginning to respond. The R. Misbourne has extended upstream as far as Missenden Abbey Park and the Chess has begun to flow through Chesham once more. Perhaps even more dramatically, both the Hughenden Stream and more recently, the Hamble Brook have both begun to flow again.
Further north in the Chilterns, the recovery of the rivers has been more muted. Whilst the Bulbourne has begun to flow through Berkhamsted, the Ver remains dry for over 9km of its length. Further north into the Lea catchment, December groundwater levels, though rising, remained below average for the time of year despite all the rain, showing just how far levels had fallen during the drought. Though the situation is rapidly improving, groundwater levels still have someway to go to get back to more normal levels for the time of year and ensure healthy chalk stream flows through the rest of the year and more rain is needed.
It is undoubtedly great to see many of the Chilterns rivers flowing more healthily again but it will take some time for them to recover ecologically. Some species will return very quickly, indeed some already have, but other species, particularly fish like brown trout & bullhead may take several years to make their way back into the headwaters, if at all. What it is clear is that the chances of full recovery rely on more resilient, reliable flows and more natural systems, free of impediments, such as weirs and culverts, to the movement of species.
High and increasing demand for water combined with the impacts of climate change and are having a negative impact on the health of these rivers. In the Chilterns we have the highest personal water use anywhere in the UK (173L per person per day) and one of the highest in Europe. The majority of water that we use is taken from the chalk aquifer that our precious rivers rely on for their flow. In many cases the water that we use never finds its way back to those rivers, leaving them depleted. Every litre of water less we use each day leaves a litre more in the aquifer to help our chalk streams flow.
In the longer term, as the population continues to grow and the impacts of climate change take greater effect, we must greatly reduce our reliance on the chalk aquifer for water so that the chalk streams, that contribute so much to the outstanding Chilterns landscape, can be restored to health for wildlife and for future generations to enjoy.