T
ECOLOGICAL ENGINEERING
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5.0 Design

5.1 Aquaculture Centre

5.1.1 Schematic plan

5.1.2 Engineering specifications

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.

5.1.3 Water Extraction

Water is extracted at a rate of 1000 litres per minute from The River Don by using an ex-colliery, diesel generated pump, housed in the pumphouse illustrated to the left of the picture below.

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.

5.1.4 Intake Reedbed

To achieve the initial concept of optimum water quality the ecological treatment of source water was recognised prerequisite to conform to best practice of sustainable aquaculture at the Earth Centre.
The principle aim of this element is to efficiently reduce the organic loading of the source water using a vertical flow system designed to consider the following:

* Space restriction in masterplan design specifications and a high flow rate of pumped source water at 1m3 per minute

* A relatively low organic loading (average Biological Oxygen Demand at 10 mg/l)

* An educational exhibit to display varying methods of reed filtration i.e. in this case a Vertical Flow Reed Bed

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 (ringed yellow circle in the picture below).

5.1.5 Open Water Channels

It was acknowledged that an open water circulation system is essential to interpret the progression of water through the varying stages of the demonstration fish farm.

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 intermittent planting of wetland plants furthers the cleansing of water on it's journey to the nursery ponds, this includes a large stand of watercress located in a stepped area, which is particularly useful increasing the efficiency of the uptake of water borne nitrates.

5.1.6 Nursery Ponds

Water circulation in the nursery ponds utilises a parallel delivery system whereby each pond is individually fed by to a maximum of 0.1 m3 per minute of clean water if required.
The lining material was a pre-hydrated bentonite matting which effectively discouraged the upward transport of toxins from the coal spoil below.
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.

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 unlike a 'series system' where all the ponds are linked to the same 'flow through 'circuit.

5.1.7 Outlet Reedbed

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 to reduce BOD, Ammonia, Nitrate and Suspended Solid levels .

This was arranged in a natural wetland surrounding is to illustrate plant beds multi-functional purpose of water filtration, plant production and habitat conservation.

The intention was to also create a natural wetland surrounding, for aesthetic purposes and for the production and cyclic harvesting of water plants

The clean water in the lagoon can also be used to irrigate a variety of horticultural initiatives on the site or finally discharged cleaner than previously extracted.

5.1.8 Biological design

The foremost consideration for the biological pond design was 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. This in turn reduces toxic organic and chemical concentrations to acceptable water quality levels for freshwater cultured organisms.

5.2 Hatchery and Aquatic Ecology Centre

Incorporates an attractive, practical design comprising of a 15m x 10m sustainable timber and glass building, partly below ground level with insulation and solar energy features.
An average optimum temperature of 18° Centigrade also utilises the hatchery for temperate (and exotic) species culture. There is an extensive solar gain which also 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 towards 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' troughs and literature both expressive and electronic can be found.

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
Coal spoil (comprising of sandstone, coal fines, red ash , slag, etc..) 500mm- 1100 mm
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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© 2007 Fishace