Hertfordshire’s Chalk Rivers

 

River Beane, Bengeo

Nicholas Blatchley

If your favourite walks in Hertfordshire take you alongside a river, the chances are that will be a chalk stream. While you may appreciate how beautiful these rivers are, however, you may not realise just how unusual they are and how privileged we are to have so many special rivers in our county.

Unfortunately, many of these wonderful rivers are under threat, partly from the increasingly low rainfall we’ve been having and partly from excessive water extraction.

What Are Chalk Streams?

When streams rise from chalk aquifers, they tend to consist of unusually clear, highly oxygenated water. Although the water may contain minerals, there’s very little silt, resulting in a largely transparent river running over a gravel bottom, which maintains a fairly regular water temperature and is pH neutral, allowing it to support a wide array of wildlife.

Chalk streams are extremely rare worldwide. Estimates vary a little, but there are about 210 in the world, of which 160 are found in England, all in the south or east of the country, in an arc from Dorset to Yorkshire. Of the 50 or so chalk streams outside England, most are in western Europe, including the River Somme in France.

The Chalk Streams of Hertfordshire

Most of Hertfordshire’s rivers derive from the chalk of the Chilterns which, besides the more obvious hills in Buckinghamshire, extend across the north of Hertfordshire. Broadly speaking, they form two catchment areas, feeding the River Lea in the east and the River Colne (which isn’t itself a chalk stream) further west. Both systems eventually drain into the Thames.

The Lea catchment area consists of:

• River Lea
• River Stort
• River Ash
• River Rib
• River Quin
• River Beane
• River Mimram

The Colne catchment area consists of:

• River Ver
• River Gade
• River Bulbourne
• River Chess
• River Misbourne

In addition, the county has a number of small chalk streams. Some of these are intermittent, usually flowing during the winter and drying up in the summer months. The best known of these is the Bourne Gutter, to the south of Berkhampsted.

Chalk Streams and Wildlife

Imagine a riverbank scene — perhaps out of The Wind in the Willows. A clear, lively river winds its way between green banks, its clear water showing fish like brown trout darting around. Insects such as mayflies skim the surface and a kingfisher swoops down, while water-voles and otters dive in from the side.

You’ve just imagined a chalk river.

Chalk streams support a diversity of plant life as well, such as water crowfoot and water starwort. The excellent growing conditions have also made watercress farming a traditional Hertfordshire industry.

Chalk streams have been described as Hertfordshire’s rainforests, for the richness and diversity of the wildlife they support. Unfortunately, like the rainforests, they are under serious threat.

The Threats to Hertfordshire’s Chalk Streams

Although the threats to Hertfordshire’s chalk streams have reached a critical point today, the problems have been developing for centuries. Changes in land usage due to intensive farming have damaged the banks, and management of rivers has often resulted in altering the course or straightening the river, compromising the conditions that make chalk streams what they are. More recently, industrial pollution has reduced the water purity that’s essential for the ecosystem to survive.

The two biggest threats to Hertfordshire’s chalk streams, though, are water extraction and climate change.

Water has been extracted from the county’s chalk aquifers for centuries, going back at least to the building of the New River in 1613. However, the population explosion in the county since the Second World War has created an ever-growing demand for water that the chalk streams struggle to meet.

At the same time, climate change is reducing the average rainfall, and the combination of these two factors puts a strain on Hertfordshire’s chalk streams. At the time of writing, during the hot, dry summer of 2022, much of the River Ver has dried up, and most of the other chalk streams have dangerously low levels of water.

The Efforts to Restore the Chalk Streams

There are moves afoot to reverse some of this damage, involving partnerships between local and national government, water companies and organisations like the Herts & Middlesex Wildlife Trust. This includes the Trust’s Living Rivers project, part of a national strategy by The Wildlife Trust following on from the Chalk Streams Charter, launched on the River Beane near Stevenage.

Strategies include removing some of the artificial alterations, such as restoring meanders and taking out weirs that prevent the movement of fish. The Trust is also strengthening banks and creating wildlife habitats.

Some invasive species need to be removed, as well, such as Himalayan Balsam, while threatened species are being gradually reintroduced. In one of the most exciting moves, 130 water voles were released into the Beane at the Woodhall estate, just outside Watton at Stone, in July 2022. There have been no water voles on the Beane since 2000, but the Trust is aiming to restore populations to all Hertfordshire’s chalk rivers by 2030.

At the same time, the chalk aquifers must be allowed to recover. Affinity Water has pledged to reduce the amount of water it takes, but it remains to be seen how the needs of water supply and conservation can be balanced.

A Vital Part of Hertfordshire’s Ecosystem

Like other conservation projects around the world, restoring Hertfordshire’s chalk streams is far more than making the countryside beautiful again — important though that is. They are a vital part of a unique ecosystem, and restoration will have many benefits. For example, strengthening the banks and creating wetland habitats are vital for flood prevention.

Hertfordshire’s chalk streams are a rare and precious asset to the county and should be prized like the rainforests or the Great Barrier Reef. The ecosystem will no doubt change with the climate, but it’s up to us to ensure that it can be allowed to evolve naturally and healthily, rather than being destroyed.