Reservoirs - Construction Tips

Earthen water reservoirs for irrigation or other farm uses may be constructed above ground, below ground or a combination of above and below. Construction methods and size will depend on the water source for the reservoir and the volume of water required for the farm. Construction of above ground reservoirs is especially important as the failure of the reservoir wall could cause flooding and damage or even injury.

A reservoir

When to hire a consulting engineer?

The need to hire a consulting engineer will depend on the risk associated with your reservoir. These may be risks to other people and property, or the magnitude of the financial risk you bear for the
construction of the reservoir. Very large and expensive construction projects are best designed by a consulting engineer as this will reduce the likelihood of failure of the reservoir. If the reservoir has a raised bank greater than 5ft it should be designed by an engineer. Reservoirs close to neighbouring properties, houses, roads, railways etc. should also be designed by an engineer because of the potential risk to people or property if the reservoir should fail.

Location

Ideally reservoirs should be constructed away from roads, railways, or other areas of public access. Reservoirs should also be located away from neighbours’ property or laneways and especially away from houses or buildings. Reservoirs should be constructed at least 50ft from municipal drains, in order to allow for maintenance on the drains. Fencing of the reservoir may be necessary if it is located in a highly populated area.

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Re-vegetated outer bank

Without vegetation

Shape and dimensions

All reservoirs should have inside walls with 2:1 slopes (or more gentle). Steeper slopes lead to bank failures. For raised reservoirs outside slopes should be 3:1 so that they can be vegetated and mowed. The top of the banks should be at least 10-16 ft wide so that they can be used for vehicle access or to use a boom mower.

Leaks

Reservoirs must have a clay lining of at least 15% clay in order not to leak. If soil with sufficient clay content is not available on-site it will have to be brought in or consider a synthetic liner.

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Erosion (weather damage)

Before construction remove topsoil from construction area. After construction replace topsoil on outside banks of reservoir.

Outside banks of reservoir must be re-vegetated after construction. This will reduce the potential for erosion of the banks.

On the inside banks a band of armour stone should be placed around the reservoir at the high water level. This armour stone should be backed by a geotextile. This will reduce damage to the banks from wave action when the reservoir is full.

Without armour stone or the appropriate geotextile,
bank slopes on the inside

Permits

If you are planning to construct near a river creek or stream you will need a permit for construction from your local Conservation Authority (if you are in the designated flood plain). In order to take water from any source (river, creek, ditch, well, pond, tile drains etc.) you require a Permit To Take Water (PTTW) from the Ministry of the Environment.

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