5.3 Circle Tip Wetland Site


5.3.1 Characteristics

The underlying land was previously liable to extensive flooding and has over the years been raised with various spoil materials:

An average cross section is as follows:

Top soil 200mm - 300mm
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Coal spoil (comprising of sandstone, coal fines, red ash , slag, etc..) 500mm- 1100 mm
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Sandy clay greater than 2000mm

5.3.2 Engineering specifications

The overlying flat scrubland area was excavated with heavy machinery to an average depth of 500mm. The resultant spoil was transferred to create raised islands planted with trees and shrubs. A further 8000m2 of fish stock ponds were dug to an average depth of one metre and seeded with emergent plant species.

Tests on the impermeability of coal spoil indicated a figure of 10-9 m/sec relative to clay at 10 -11 m/sec. Fringed areas were top soiled and left to naturally regenerate.

5.3.3 Biological design

The United Kingdom is rapidly losing wetland habitats due to land demand, loss of agricultural and commercial exploitation. Even where successful conservation schemes do exist the financial burden of maintenance must be met from dwindling funds. It is further recognised that a well-established wetland is said to be up to 50 times more productive than similar grassland and up to 8 times more productive than a similar area of cultivated land.
This innovative design considers eco-sensitive production and maintenance of conservation wetlands and is used to demonstrate to landowners that 'conservation does and can pay'. While recognising the habitat requirements of a variety of plants, birds and animals - a series of fish ponds has been constructed within the wetland. Plants and fish can be sporadically harvested in this system and regular maintenance to the productive areas assists in discouraging the transition of wetland to terrestrial habitats.

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