CONSTRUCTION OF A FISH POND IN NIGERIA PROCESSES INVOLVED

Introduction

Before construction begins several factors must be considered when creating an aquatic habitat for ecological studies. Please Check with your Local Authority before beginning any construction.

Who is the pond for?

This is your main decision to begin with. If the pond is for a primary school then it need only be large enough to yield fauna for limited taxonomic identification. A secondary school on the other hand would require far greater use from a pond. To be able to explore micro-habitats, food webs and other abiotic factors a substantially larger pond is required.
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What is the pond for?

An important factor to take into account when planning the pond. You must decide what kind of studies are to be conducted within the habitat. Is it for netting macro invertebrates, amphibian surveys or vegetation surveys as well? These choices will affect the size, shape and planting of the pond.

What size of pond?

This is very much dictated by the number of students that will use it. The larger the number of students expected to use the pond then the larger the pond must be. It must be large enough to provide alternative areas for survey whilst used ones regenerate. The locations available to site the pond may limit the size; this may be overcome by creating a secure gated pond area.

Water supply

This is another important choice when considering the location of a potential pond, where will the water come from? The best wildlife ponds are unpolluted so finding a clean source of water is a good start. Several questions need to be asked before using a water supply such as where is its source? Could it be next to a possible pollution source?
The most important decision is going to be where the pond is sited. If sited poorly then the pond may not attract the wildlife needed for studies or worse yet fail to become established.
Below are several suggestions to consider when choosing the location and design of the pond.

Procedure to Site the pond

Safety

The pond should be visible from school buildings, classrooms etc. There must be a clear line of site from all angles. If the pond cannot be sited near any school building then it may be possible to construct a fenced or gated area containing the pond. This would provide security against children gaining access to the pond when not in use or unsupervised.

Location in school grounds

The pond must not be in an isolated position, unless it is secured when not supervised. It should be far enough off the "beaten track" to reduce noise pollution, litter and disturbance. It still has to be close enough to hold lessons there without using too much time for travel. Do not place the pond under a bush or tree as when autumn comes leaves will fall and need to be removed.
Only use/choose a site where you know the pond will provide a richer habitat than the one it is replacing. Never replace a more valuable habitat such as marsh land or temporary ponds. Depending on the size and location of your new pond, you may have to get consent from various public bodies before you start work.  Small garden ponds normally don’t require permission.  For other projects, you may need to talk to the local planning authority, the Environment Agency, the County Archaeologist, the Highways Agency, the local authority Rights of Way Officer or Natural England.

Utilities

The location of gas, electricity, telecommunications, and water supplies should be checked for any site a pond is planned. If plans prove to be unreliable then consultation with utilities companies may be required to trace underground services.

Water Supply

Rainwater- This is the best source of water for ponds. Rainwater can be collected off roofs and stored in tanks or water butts. This can then be used to top up the pond during the summer months, using hoses or buckets. Water collection systems may be utilized to channel the water from the roof straight into the pond. This offers a chance to demonstrate an ecologically sustainable water source.
Surface run-off- This is water that runs into the pond from higher ground. Usually through vegetation, soil, sub-surface or off tarmac, concrete etc. The cleanest water will come from unfertilized areas such as woodland or grassland. The most polluted will come from terraced area run off.
Groundwater- This is the naturally occurring water in the ground or water table in the catchments area which is usually occurring in sandy or gravel areas. In intensively urban areas this is the cleanest source of water as it has been pre-filtered through the sub-surface. A test pit can be dug however unless the substrate is very dense clay the water will not be retained. A lined pond cannot be easily fed this way.
Streams and ditches- These may seem the most attractive source of water for ponds; however these can be problematic for several reasons. The first is seasonal fluctuations in water levels, during the summer most streams and ditches dry up. The second reason is that many streams run off arable farms and can be heavily polluted by fertilizers and polluted sediments.

Orientation

Ideally the pond should be facing south or west with half the pond in sun and half in shade. The pond needs 5 or more hours of sun light per day to stay healthy. This allows the pond to warm quickly in spring, encouraging good tadpole and plant development. Do not place the whole pond in shadow such as under a tree or bush. The pond should not be placed in direct sun light, as it will warm too much and become anoxic killing the wildlife.

Habitats

This is less important however if there are other ponds situated somewhere in the area or if there are established habitats such as log piles, hedgerows and meadow these could become "wildlife corridors". This would encourage a quicker colonization of the pond and provide a safe migration route to amphibians.

Pond Design

There are several different designs that you can use each with its own benefits.

Size

Obviously the ponds constraints are mainly budget and available land. Ponds between 20 sq m and 60 sq m have been suggested to be the optimal size. However smaller ponds have proved equally successful attracting newts and invertebrates. If large school groups or intensive use of the pond is planned then the largest size possible should be built.

The Rectangle

A rectangular pond is the easiest to dig and provides nice neat sides that are easily paved. This option also allows for a raised pond to be constructed, if a raised pond is to be used then the liner should be of a light color to minimize heat absorption.

The Plate Design

The pond should be more plate like than bowl, allowing for the shallow edges to be formed with a gentle gradient with no sudden drop off. It is more aesthetically pleasing and bears the appearance to be more of a wildlife pond if it is constructed in an irregular shape. This is the recommended profile for wildlife ponds as it allows easy access to the water for amphibians and mammals.

Shallow Zones

The vast majority of pond life resides in the shallow shelves or parts of the pond. The pond should have maximized area available to shallow areas (less than 10cm deep). These should be 1 in 3 or 1 in 5 gradients to ensure animals can easily leave the pond but more importantly anyone that falls in is able to be rescued quickly and exit the water easily.

Drawdown Zones

Seasonal drawdown zones allow for a richer biodiversity of plants and invertebrates. They are similar to the shallow areas except they consist of hollows and hummocks with a depth of 5cm or less. This means during the summer the liner will be exposed and must be protected with stones or gravel. These areas will be submerged again during the winter months.

Vegetation Zones

It is a good idea to close off one side of the pond to students to ensure vegetation growth. This will not only increase biodiversity by adding extra habitat space but also offers a refuge to migratory amphibians and other pond life. Planting shelves may be incorporated to house submerged macrophytes such as oxygenators.

Depth

The pond depth should be between 0.75m and 1m. To ensure the pond does not dry out in the summer and that it is deep enough to not freeze in the winter. Check your Local Education Authority for health and safety regulations as to maximum depth allowed.

Waste

The spoil from digging the pond should not be cast over or piled on other useful habitats. If building a wildlife pond sieved substrate can be used for bedding plants and the top soil and turf may be reused as edging.

Lining Material - There a several options available for lining materials

Flexible pond liners- These types of liners are usually the best option if the pond is of a smaller size. Butyl, a rubber based liner is the strongest and most economical option. All liners though must be used in conjunction with some form of matting underneath to protect it from tree roots and sharp objects. You can also use 2.5cm to 7cm thick layer of damp sand as a protective layer. Alternatively a pile of old carpet, newspapers and magazines could be used, but last no way near as long as sand or matting. If the pond is going to be used for netting regularly then it is wise to have an extra layer of matting on top of the liner. This is the most likely candidate to fall into a reasonable budget and is the recommended option.

Puddled Clay- This is the traditional way of creating ponds. If the area is of particular dense clay you may simply be able to dig down to the water table to fill it that way. Otherwise the traditional way is to dig your pond, allowing for the thickness of 30cm of the clay on the soil, layer it with clay and puddle it. When laying the clay 1m3 equals 2 tonnes. It is essential to calculate the amount of clay needed to finish the pond within the day ensuring that there is surplus should a problem arise or after completion before filling. The most important thing is to stop the clay drying out during the puddling process. This can be achieved by using plastic sheets over the areas of clay already laid. The puddling process itself is a form of compaction where the structure of the clay is broken down and the air pressed out of the material. Traditionally this was done by corralling a herd of livestock or methodical marching by men. Nowadays it is done by a "whacker" plate. The clay is best laid in tiny sections like concrete slabs to ensure smooth joints and a perfect fit. This way it also stops slipping and allows the pond to be laid in sections so it can be puddled. The puddling forms a continuous layer of clay that is water tight. This requires specialists to be contact for advice, and most likely the design and construction.

Concrete - Concrete linings are used for all sizes and shapes of ponds. They have many advantages when employed in a school or urban environment. They can be used without fear of damaging the lining through netting or other survey techniques, including wading or use of tools such as spades etc. Because of the lack of a liner they are for all intense and purposes vandal proof. They are durable if constructed properly able to withstand erosion and can go for long periods of time with drops in water level.
However there are drawbacks to such a design. Specialists are needed to design and construct the pond. If a pond is larger than 8m x 5m then it will need to be reinforced. The cement used is harmful to aquatic life so requires a seasoning period. Where the pond must be emptied and refilled several times. If the concrete is improperly laid or damaged it can be costly or difficult to repair. This would require the water level to be dropped below that of the damage for a prolonged period of time.
If a concrete pond is to be used then specialized advise must be sought for the design and construction of it.

Preformed and Fiberglass ponds - These are not recommended as they require a specific shape to be excavated and are usually not wildlife friendly. They do not make an effective large pond as they are prone to becoming brittle and therefore are not long lasting.

Construction Process

This is best attempted during a dry calm day. The liner should not be laid or left exposed to frost or sun light as damage could occur. After choosing the location of the pond mark out the shape using string tied to posts, sand or spray paint. The best place to start digging the pond is from the centre out. This will ensure that you are able dig the deepest part first then construct the profile as you radiate out. Remember you need to dig deeper than the actual depth you want as you must allow for the thickness of lining and matting material.
Any turf that is removed could be used in other areas or replaced around the pond. Depending on the size of the pond it may be easier to hire a mechanical digger to speed the process up. If one is hired be sure there is access to the site and that the operator is well briefed as to the depth, size and profile of the pond. A supervisor should be on site during the excavation process. Final details such as shelves and draw-down areas should be completed by rake or spade. If it is a small pond then it could be done by hand, a small group of volunteers with spades could be persuaded if a day was made of it with a BBQ etc. Draw-down areas should be less than 5cm deep and contain hummocks and hollows.

As the pond is dug any sharp stones or tree roots should be removed, otherwise they could pierce the liner and the pond will leak. If large rocks are found they could be used around or in the pond to create new habitats. Shallow or draw-down zones, shelves or shallow areas should only contain pebbles or gravel.
The sides of the pond must be checked to ensure they are flat and even. The pond must be level otherwise the water will not collect evenly at either ends, exposing sides to harmful UV light which will damage the liner. To hide the liner dig a trench, 30mm deep and one spades width wide. After filling the excess liner is placed in the trench and then soil or turf is placed over it to anchor it in.

Once you are happy with the depth and profile of the pond the matting is laid down. This protects the liner, it can be 2.5cm to 7cm cm of builders sand, old carpet or layers of old newspapers (though these rot away quickly). There are commercial matting materials available such as geotextile matting; custom made materials which would protect the pond better however are considerably more expensive. It has been known for some ponds to have another layer of geotextile matting on top and below the liner. This offers some protection from nets.

The pond liner once laid should have a 300mm overlap around the edge. To work out how much pond liner you will need to use this equation
Length of Pond= A
Width of Pond = B
Depth of Pond = C
Size of Liner (Square Metres) = (A 2C 0.6) x (B 2C 0.6)
With the desired amount of liner bought it should be unfolded away from the newly dug pond, checking for damage. Once unfolded it should be scrunched back up to discharge any static electricity and lowered over the layers of without standing on or disturbing the matting/sand. Once placed over the matting temporary weights should be placed on the liners edges to stop it slipping in once water is put in. (If a second layer of matting is to be used to protect the liner it is to be placed at this stage, that way it can mould to the shape along with the liner.)

The pond is now ready to have water added. The best water to add to the pond is rain water. Slowly add the water ensuring that the liner is slowly molding to the profile shape intended. If adding soil to provide a substrate for planting the substrate must not be top soil, sieve the soil to remove all sharp objects and stones. Once in the pond and before filling with water, place a piece of polythene sheeting over the soil, this will help stop the scouring of the soil and can be removed later. Another option is to run the water over a pebble beach or stony structure. Once the pond is full you are able to hide the edges of the pond liner. The extra pond liner is then covered by turf or soil removed earlier or under paving
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