Nestled between Minehead and Porlock the Holnicote Estate is visited by thousands of tourists every year attracted by the beauty of its landscape and traditional Somerset villages. Few will know that is part of an exciting DEFRA funded project to look at how water flow in the upper catchment of a river can be 'slowed' so that during heavy rainfall the danger of flooding further down the catchment can be prevent or lessened.
The Holnicote Estate, owned by the National Trust, is 5042 ha of land draining the Rivers Aller and Horner water from Exmoor northwards through woodland, grassland and arable areas towards Porlock Bay.
The upper catchments of both rivers are very steep meaning that when it rains the river responds quickly and water hurtles down to the villages of Allerford, West Lynch and Bossington. Houses in these villages have flooded - often with very little notice to villagers.
The rivers are so prone to this 'flash' flooding that the Environment Agency have installed sirens to warn villagers.
The project used hydrological data and modelling to see where 'holding' water would slow the rivers' response to heavy rain over a number of days. These included:-
Creating five temporary water storage areas by bunding an area in the upper catchment. In practice all you see are some grassed raised areas at the edge of normal fields (about 1.5m tall). They blend well into the landscape and the only clue to their use in dry conditions are grates that allow water to be released gradually when the river level has dropped enough to take more water. These flood meadows have been planted with a wild flower / grass mix.
In the rivers and feeder streams some fallen trees are allowed to remain in the water forming natural wood dams. Some wood dams have also been created by fixing trees across the span of the streams. These dams slow down, rather than divert the water where it is not wanted.
Runoff from agricultural land use has also been decreased by helping farmers adapt their methods of soil and pasture use. This means that soil stays in the fields and means that less silt ends up in the watercourses.
Work in the moorland area of the catchment includes heather restoration and better drainage management (on tracks, paths and roads).
The project has recently started planting bands of trees to slow water runoff during heavy rain.
But the million dollar question is what happened last winter?
The answer is that the project reduced peak flow in the rivers by 12%. This was enough to stop any of the village houses flooding - it was touch and go at one stage but they remained dry during a very wet winter.
FLAG would like to thank Nigel Hester, Estate and Project Manager for inviting us to visit the project. The group included the Deputy Leader of the County Council, David Hall and Gill Slattery, Councillor Taunton Deane District Council.
Every field and every stream can make a difference
FLAG members Jenny Winslade, Rhona Light, Phil Brewin and Bryony Sadler plus Gill Slattery meet
Nigel Hester, Holnicote Estate and Project Manager
The group included the members of FLAG Core plus Deputy Leader of the County Council, David Hall and Gill Slattery,
Councillor Taunton Deane District Council.
Exploring the estate
Small interventions can make a big impact
Going with the flow
Some elements of the project are hidden but play a vital role
Going with the flow - how the National Trust manages water and flooding on the Holnicote Estate
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