To comply with the above points the ground level was raised by 1.5 metres by the importation of and compaction of 250mm layers of silty-sandy clay.
Twelve engineered nursery ponds featuring an average surface area of 300 square metres were constructed using sustainable materials including bentonite lining and bezinal coated gabions infilled with aggregate.
Water circulation and treatment:
Water is extracted at a rate of 1000 litres per minute from The River Don by using an ex-colliery, diesel generated pump. Future research will focus upon the feasibility of converting the pump to a renewable energy powered system that could possibly comprise of solar, wind or biogas driven energy. River water travels via 110 metres of 10cm diameter steel pipe to the inlet reed bed.
The Vertical Flow Reedbed:
Once completed the four beds will cover 1000 m2. Each bed is in operation for one day and then drained and allowed to rest for the next three days before being used again. The beds are 0.6 m deep with pea gravel on the surface and limestone gravel underneath.
The water is sprayed onto the bed from surface pipes and trickles down through the gravel to the drainage pipes underneath. As the water passes over the surface of the gravel the bacteria consume many of the pollutants and any suspended particles present in the water are filtered. The water leaves the beds via the outlet pipe at the top of the stream.
The Open Water Channels:
Reed bed cleansed water flows through open ditches designed to consider natural flow forms (or eddies that) reintroduce dissolved oxygen to the water, previously decreased by the biological action of the reed beds. The multi purpose ditchwork also creates a rich ‘brook’ type habitat with a variety of water plants and amphibians. Water insects are attracted to the running water and larvae swept into the culture foods to assist natural feeding regimes.
The Earth Ponds:
Water circulation in the nursery ponds utilises a parallel delivery system where each pond is individually fed by clean water. The liquid fish waste returns via a separate circuit to flow into the outlet treatment lagoon. The benefits of a parallel method are the isolation of any outbreaks of fish diseases to an individual pond. In a ‘series system’ all the ponds are linked to the same ‘flow through ‘circuit. This shared water system, can quickly spread disease throughout ponds.
Outlet Water Treatment:
Fish farming is a polluting industry and it is necessary to clean the water we use before being discharged back into the river. Treatment of outlet fish culture water is via settlement and a wetland horizontal flow ecological filtration process. This arranged in a natural wetland surrounding is to illustrate plant beds multi-functional purpose of water filtration, plant production and habitat conservation. The clean water in the lagoon can also be used to irrigate most of the site.
Biological design:
The foremost biological pond design considers the combination of existing practical and productive aquacultural methods with the increased utilisation of natural aquatic food chains.
The development of a controlled littoral (emergent aquatic plant) zone is a significant factor for the bio-structure of vegetable (phytoplankton) and animal (zooplankton) infrastructure.
Not only does this provide a food source, but contributes to the breakdown of organic chemicals via bacteriological actions. Which in turn reduces toxic organic and chemical concentrations to acceptable water quality levels for freshwater cultured organisms.
The Hatchery and Aquatic Ecology Centre:
Incorporates an attractive, practical design comprising of a 15m x 10m wooden building, partly below ground level with insulation and solar energy features.
There is an extensive solar gain that contributes to the stimulation and growth of algae as a first stage fry food. The energy saving building design extends fry production facilities from six to twelve months.
River water is pumped to an external planted tank running the length of the building and a series of stop taps control the gravity feed and added aeration of water running to the internal tanks.
The internal, flexible working configuration, creates an opportunity for visitor observation to the developing stages of freshwater fish production. The hatchery is also the base for pond dipping equipment from the adjacent ‘community pond’. Here a variety of interpretative instruments such as microscopes, ‘touch and feel trough and literature both expressive and electronic can be found.
THE CIRCLE TIP SUSTAINABLE WETLAND SITE:
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
sandstone, coal fines, red ash 500mm- 1100 mm slag, etc..)
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Sandy clay greater than 2000mm
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 was dug to an average depth of one metre and seeded with emergent plant species. Tests on the impermeability of coal spoil has 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.
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 has been 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 in 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.
Author:
Stephen Bedford Clark:
Director of Aquatic Ecology & Sustainable Aquaculture:
