ARE THERE LESSONS TO BE LEARNED FROM THE MANAGEMENT OF THE NORTH SOMERSET LEVELS?
North Somerset has a drainage district of almost 14,500 acres (5,829 hectares). This is split into three areas — the Gordano Valley catchment (973 hectares) between the Tickenham Ridge and the coastal ridge of Portishead down. The North Area catchment (4,856 ha) lies south of Tickenham Ridge, extending out to the coast between Clevedon and the River Congresbury Yeo. The South Area (5,860 ha) lies across the low-lying North Somerset Moors and levels, inland from Weston-super-Mare.
All three of these catchment areas are below sea level at Mean High Water Spring tides. They’re protected from flooding by the sea defences, by natural high ground and by a network of rivers, rhynes, drains and other interconnecting watercourses. These predominantly man-made watercourses have provided several hundred years of water control since the Enclosures Acts of the early 19th century. They have succeeded in creating the current, valued, wet grassland landscape from a natural marsh and moorland. The North Somerset drainage board has a supervisory role relating to all matters concerned with the drainage of land.
A rhyne is a drainage ditch, or canal, used to turn areas of wetland at around sea level into useful pasture. Water levels (and hence the level of the water table) are controlled by a system of sluice gates and pumps, allowing the land to become wetter at times of the year when this will improve grass growth. Rhynes represent an early method of swamp or marsh drainage. Large sections of swampland were surrounded by trenches deep enough to drain the water from the encircled mound and leave the land relatively dry. Regular clearing and dredging is necessary to keep the rhynes clear of debris so that they flow freely.
Whilst the Board has powers to undertake works on any non-main river watercourse within its Drainage District, direct maintenance is limited to the Viewed Rhynes, which form the strategic arterial drainage system. These Viewed Rhynes extend to 185.4km length (118.2miles), of which 8.8km are in the Gordano Valley catchment, 81.6km are in the North Area and 95km are in the South Area. The Board also operates 62 water control structures and 2 sea outfalls.
One of the Board’s principal roles is to manage water levels in the strategic arterial drainage system — particularly during summer months, to maintain an adequate water supply for agricultural purposes and wetland conservation, and in winter for land drainage and flood defence. The balance between these, sometimes conflicting, functions can be very fine and present management practices have evolved from close co-operation between the Board, the farming community and the needs of those living in the urban areas served, over many years.
In the Gordano Valley catchment, water level management is the responsibility of the Environment Agency, as the control structures are all on the ‘main rivers’. The Agency’s management of water levels enables a Raised Water Level Area to be maintained on Walton Moor by the Avon Wildlife Trust, to provide a site for over-wintering wetland wildfowl.
With the exception of ‘main rivers’, which are watercourses under the control of the Environment Agency and the ‘Viewed Rhynes’ (watercourses under the control of the Internal Drainage Board), the responsibility for maintenance of all other watercourses and field ditches rests with the adjoining landowner, known in law as the ‘riparian owner’.
The long-term cooperation that has existed between local farmers and those responsible for drainage in the area has resulted in an effective and efficient flood management programme.
While there are important differences, including the extent of land and the distance from the sea, it is worth noting that while the South Somerset levels are underwater, the North Somerset levels remained relatively dry. Perhaps there are lessons that can be learned from excellent cooperation with local farmers, keeping the rhynes clear and adopting a slightly more at length relationship with the Environment Agency.