Dam Good!


Which Dam? – When to use peat and when to use plastic

It can be difficult choosing which dam suits your chosen environment better. Peat dams are easily constructed and cheaper to create however they can actually only be used when the peat is sufficiently deep! Large ditches can be more expensive to create dams for therefore often peat dams will be chosen to save money but these dams won’t actually work; if the pool is more than 120cm deep the water will flow over the peat dam causing erosion and ultimately dam failure (SNH, 2014). Large ditches or deep pools should be dammed using plastic sheet piling which is high enough and sturdy enough to support the water flow. Bog sites often have large slopes located in different areas and it is important to create dams to hold back the water whilst keeping the site wet; this should be done using plastic dams as peat dams are highly unstable on slopes. It is important not to build a plastic dam in shallow peat as cracking will occur leading to dam failure (SNH, 2014).

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Constructing dams!

Peat

Peat dams can be created both by hand or using machinery. It is not recommended to build them by hand unless the dam you are creating is very small. Peat dams are more common as they use less materials and are less expensive. To build a peat dam using machinery you will need access to a digger or excavator. The digger/excavator is used to simply dig out the peat from one area creating a pool that will fill with water, the peat removed is then placed beside the newly formed pool to hold back any water that gathers in it (SNH, 2014). It is vital that the top layer of peat is removed and not used for the dam as its exposure to air has already weakened it, to use the best quality peat for your dam you should ensure it is completely saturated but still firm (bottom and sides from the newly created ditch).

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Plastic

Plastic dams require a bit more work as the materials must first be gathered and brought on site (plastic sheet piling). The plastic sheet piling connects together using joints but they still have to be hammered together. Flexing the separate plastic sheets against each other before hammering ensures the dam will be more watertight as well as this the plastic should be flexed in the same direction as the water flow to increase the effectiveness of the seal formed (Scottish Government, 2009). The plastic sheet piling should be ridged in order to fit together more efficiently. Although these dams are plastic it is recommended to use some peat to fill in any gaps formed between the plastic sheets to prevent any leaking and extend the life of the dam.

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Happy dam building!

Top Tips!

Now that you know which dam to choose and how to construct it here are some tips to ensure you get the most from your dam!

  • Never place a dam in a location where trees are abundant or very close by unless you remove the trees and their roots first as the trees will absorb so much water that the dam wouldn’t be of much use (FEMA, 2005).
  • Know your site. Before choosing where to build your dam you must make sure that the location you have chosen is appropriate; this could be in terms of how many dams are there already, it is vital that there is no less than 20-30 metres between dams or flooding problems could occur, it is also important to ensure you are within the law to build a dam therefore it is good to research your chosen sight before planning to build one (Farmers Bulletin, 1935).
  • Finally once you have checked the suitability and legality of your chosen location, you should then find out the peat depth in that area in order to choose the most suitable dam (peat or plastic) as well as ensuring it will work efficiently.

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Dam Happy!

To maintain your new dam it is important that you monitor it simply by paying it a visit once in a while in order to repair any cracks or leaks. You can see how well your dam is holding back water by looking at the other side of it, if it is working well the opposite side from the pool should be lower in water level. Signs of dam failure can be spotted before they get any worse such as cracks, leaking, and sounds of running water, bare peat and water at the same level at both sides of the dam.

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If you spot sphagnum moss and other vegetation growing on the pool and dam it is a sign that you have built a healthy dam that is developing well. The CEI love building dams! Bog sites the CEI have used to build dams on include Airds Moss and Dalmellington Moss. Airds Moss is the site with the most dams!

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By Zoe Jamieson