What are balancing ponds and why are they important? September 19th 2018, by Ian Lishman

Features of sustainable urban drainage systems (SUDS) designed for smaller development sites are not necessarily appropriate, and cannot necessarily be scaled up, for larger sites. Alternative drainage features have therefore been developed to deal with more substantial quantities of water.

One such feature is a balancing pond, also called a retention pond, which acts as a temporary storage facility for watercourses like streams. Rather than water being discharged directly into the watercourse, potentially overwhelming it and causing flooding, the water is stored in the balancing pond.

How does a balancing pond work?

The flow into the watercourse from the pond is attenuated, slowed to a rate which avoids the overwhelm and mimics the storage capacity of the ground prior to it being built upon. Typically, the flow is naturally restricted based on the volume of water stored and the size of the outlet flow, but more advanced systems may be computer-controlled.

The design of the system depends on the scale of the development. The larger version of a balancing pond is a balancing lake, examples of which have become permanent environmental features.

Do balancing ponds only deal with water flow?

Another feature of balancing or retention ponds is their ability to treat the water that flows into them. The longer the period of time water is stored in the pond, the greater the potential level of treatment as pollutants fall to the bottom of the pond through sedimentation.

Balancing ponds are carefully specified as part of a package of measures for developments of certain sizes. They can play a part in the ecosystem of an area, and must therefore be constructed as accurately as they are designed. Drainage contractors with experience of constructing balancing ponds have a significant role to play in ensuring the success of development schemes and their mitigation of flood risk.

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