The River Tas

Chalk streams are a rare and marvellous thing, an irreplaceable part of our heritage and of great importance for wildlife. Both Jonah Tosney of the Norfolk Rivers Trust and the regional officer of the Environment Agency consider the Tas to be a chalk stream. It rises from a deep chalk aquifer. These rivers are globally rare habitats confined to the UK and Northern France. There are 210 in the whole world, Norfolk has twenty- five of them and we have one in Forncett.

 All rivers are lovely, but chalk streams are potentially the most beautiful of all. They are struggling and in need of protection. They have suffered, as the UK population has expanded, from poorly performing septic tanks, substandard local sewage works, agricultural abstraction and nitrate pollution and alteration of the river itself.

The permeable chalk bedrock in parts of Norfolk was laid down in prehistoric oceans by the remains of microscopic creatures raining down on the sea floor.  Geologically the Tas sits along a chalk bed for the whole of its length, but the sands, gravels and clays above it means that the river does not flow over chalk all the time as is the case with, for instance, the river Nar in north west Norfolk. A chalk stream is born from rainfall finding its way into porous white chalk, seeping through fissures and cracks into subterranean aquifers. Eventually the water is released, clean and mineral rich, rising from springs with a constant supply of water of a consistent temperature. The Tas rises from a network of springs at Carleton Fen and flows north for twenty miles before joining the Yare at Trowse.

In many places a wide variety of flora and fauna, typical of a chalk stream is still supported. Aquatic plants such as water crowfoot, starwort, iris, and marsh marigold are visible along the Tas, creating the conditions important for invertebrate life, for fish, birds and mammals, with a rich food chain running from fatty acid rich insects. In the SSSI water meadows in Forncett St Peter one of the owners told me how when she was shepherding a few years ago, up at night with lambing ewes, she could hear the gurgling of the chalk springs welling up. This area is suffused with them and accounts for the richness of plant species.

The Tas like many rivers has been physically modified so that the watercourse is wider and deeper than it would be naturally and leads to problems such as ‘siltation’ where the substrate should be more gravelly. In places the river is slowed up and choked with vegetation. This is visible in the Forncett St Mary water meadows. In places the Tas has been straightened, the meanders removed and floodplain meadows disconnected. Past dredging has created banks that prevent regular floodplain inundation occurring and can add to the risk of flooding.  There are some eels left in the Tas, but there could be many more fish. I still see the great grey heron and wonder if it survives on minnows and stickleback.

The Environment agency has told me that December’s catastrophic flooding [2020]in Forncett St Peter was essentially due to unprecedented levels of rainfall: 22mm falling in just seven hours on already saturated ground. The horizontal rails on the Wash Lane ford became blocked by debris and caused water levels to back up the junction with Aslacton road and back around the river. These rails have been modified. In October a maintenance team will be doing blockage removal, cutting and clearing. We are experiencing changing weather patterns with periods of more intense rainfall that can be directly related to global warming. The river would benefit from buffer strips rich with plants , silt traps to capture sediment and the restoration of its natural sinuous pattern in order to provide diverse habitat for pollinating insects, manage flood risk sustainably and improve its health. All this could happen with the support of local farmers and landowners.

There are no brown trout in the headwaters: these are a beautiful and classic fish of a chalk stream. This is because oxygen levels are periodically low, too much phosphate has shown up in the testing down stream. A Norfolk Rivers Trust representative commented that there is a lot of undetected pollution in our rivers, including the Tas. Medications, among them birth control tablets, and detergents remain largely unfiltered when they go through water treatment works and septic tanks leak into watercourses that flow into the river.

However, further down stream in the stretch that runs through Shotesham Park where the Tas flows in two channels, the old and new rivers, that join just before the Mill House in Shotesham St Mary, narrows have been put in by the Bailey estate. They have achieved washed gravel with deep pools and clear flowing water and brown trout of a good size, eels, pike and lampreys all exist – creatures characteristic of a chalk stream. The farm is three years into a regenerative agriculture scheme. They don’t plough in the interests of enhancing the soil and protecting its structure; they have a diverse rotation of arable crops and keep something in the soil all the time to protect it and keep the temperature constant. They use as little pesticides and chemical fertilizers as possible. This benefits the river, the insect pollinators and wild animals. I saw a profusion of mayflies and banded demoiselle dragonflies when walking nearby.

The wonderful English chalk streams are a gift from England’s unique geology and climate. Ours to enjoy, ours alone to protect or destroy.

September 2021

Sources

The Chalk Stream Index 2014