Stoplog Closure—Model Prototype Correlation

Hydraulic model tests give accurate solutions to problems involving complicated flow conditions but designers should adopt designs which avoid unpredictable situations. To achieve one stage of diversion at Kainji Dam, Nigeria, for a River Niger flow of about 2,000 m³/s (71,000 cfs), reinforced concrete stoplogs were placed into guide slots by a specially built handling beam. The system was developed by extensive model tests prior to construction. Records kept during prototype operations enabled correlation to be made with the model tests which indicated good agreement apart from one event of severe overloading. Prototype conditions were subsequently reconstructed in the model but the phenomenon could not be reproduced. It was found that a late change in the type of seals between stoplogs could have contributed to the problem. Some speculation on possible mechanical and hydraulic explanations are given.