Surveillance of Bedford and Bramhoek Dams

Surveillance of Bedford and Bramhoek Dams

Author: Edwin Lillie
Conference: 84th Annual Meeting of International Commission on Large Dams
Date: May 15-20, 2016

ABSTRACT
Bramhoek and Bedford Dams are the two reservoirs for the Ingula Pumped Storage Scheme. Bedford Dam is the upper storage dam which is a 41m concrete faced rockfill dam. Bramhoek Dam is the lower storage dam which is a 32m high roller compacted concrete dam. Both Bedford and Bramhoek Dams have been provided with a wide range of instrumentation to measure their performance. Bedford Dam is currently below the minimum operating level. Bramhoek dam starting impounding water in November 2010 before the end of the construction period. Bramhoek dam filled very quickly during January 2011 and was at the full supply level by the end of April 2011.

The instruments in Bramhoek Dam have provided useful information of its performance. Some of the main findings were; not all the induced joints in the RCC dam opened, the RCC left bank rotated after first filling more than the right bank, the piezometers all showed a rapid increase in uplift pressure during first filling which stabilised quickly, the strain gauges indicated a maximum negative 200 micro strain in the core of the dam, the temperature rise in the RCC after placement was about 10 degrees Celsius and post construction the temperature in the core of the dam ranges by 2 degrees between summer and winter. The measured leakage from the dam was about 4.5l/s immediately after construction but is now less than 1l/s.

INTRODUCTION
This paper presents the dam safety surveillance approach for Bedford and Bramhoek dams. At the time of writing this paper, Bramhoek Dam has been full since April 2011, Bedford Dam water level remains below the minimum operating level. Bramhoek Dam forms the lower storage reservoir and Bedford Dam forms the upper storage reservoir for the 1332MW Ingula Pumped Storage Scheme (IPSS). The hydropower scheme will make use of an active water storage capacity of 19 million m3. Although neither Bedford nor Bramhoek Dams are very large dams, they are very important structures as the IPSS depends on their reliability. There are also complex environmental release requirements that must be adhered to in terms of the Water Use Licence issued by the Department of Water Affairs and Sanitation. These releases must also be effectively measured for auditing purposes.

 

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