Design, construction, installation and performance of a new headwater level gauge for Aviemore Dam

Existing water level instruments measuring the headwater level at Aviemore Dam on the Waitaki River were affected to different degrees by wind-generated waves, resulting in variable measurements of headwater level. This paper describes the selection of a new gauge site and the design, construction, installation and performance of the new gauge at Aviemore Dam to provide reliable and accurate measurements of headwater level for the purposes of fuel resource management, resource consent compliance and, above all, dam safety and security. The design of the new gauge was based on the theoretical behaviour of a linear tide well (Noye, 1974b) incorporating a large diameter stilling well and a long, horizontal intake pipe of small bore, and assuming unsteady laminar flow through the intake pipe. The new gauge was predicted to have an amplitude response inside the stilling well of less than 0.006% for short period waves with a maximum incident height of 2.5 m and a period of 3 seconds. The gauge was fabricated in May and June 2013, installed in August 2013 and commissioned in September and October 2013. The performance to date has been excellent, with stilling well oscillations of less than 2.5 mm when the incident waves were predicted to be in the order of 1.0 m high with a period of about 3.0 seconds during the severe wind storm of 10 September 2013.