2022 – Cleaning of Foundation Relief Drains in Concrete Dams – A Case Study of Mahinerangi Dam

Ross Campbell – Water Resources Engineer, Riley Consultants Ltd, Paul Rivett – Principal Water Resources Engineer, Riley Consultants Ltd, Bruce Walpole – Dam Safety Engineer, Manawa Energy Ltd

An effective and functioning foundation drainage network is a key part in ensuring the overall stability of concrete gravity dams. When foundation relief drains become blocked and uplift pressures increase beneath the dam, it increases the risk of failure.

Non-functioning relief drains, usually, have become plugged with calcium deposits, sediment, or biological growth. To clean out these plugs and restore function to the foundation relief drains, there are mechanical, hydraulic, and chemical methods.

Mahinerangi Dam is one of Manawa Energy’s most valuable assets and has a history of foundation relief drains not functioning due to plugs of calcium within them. Analysis of monitoring data from the relief drains shows that previous attempts to clean them has been unsuccessful and that two thirds of them were not functioning. A new mechanical cleaning method was attempted on the relief drains and was effective in removing the calcium plugs from the relief drains. This was proven through response testing of the relief drains.

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