Rosedale Dam - Issues Associated with a High-Hazard Dam in an Urban Area
Author: S Singleton, D Tate and P Riley
Presented/Published: IPENZ Proceedings of Technical Groups 26/1
Keywords: High-hazard, dams, remedial works, urban development, safety evaluation, Rosedale, North Shore.
Abstract:
The Rosedale Dam retains the No 1 oxidation pond at the Rosedale Wastewater Treatment Plant facility. The pond has a surface area of 36 hectares and an impounded volume of over 1 million cubic metres. The dam owner, the North Shore City Council, is presently applying to the Auckland Regional Council and the North Shore City Council for renewal resource consents for the Rosedale Wastewater Treatment Plant facilities. The treatment plant handles all of the sewage from the North Shore area, which has undergone rapid growth since the plant was commissioned in the early 1960s. Stormwater flows from the surrounding catchments are diverted around the reservoir by a ring drain.
Growth of the North Shore has enveloped the dam, transforming rural landscape into residential and industrial suburbia. Consequently, the hazard rating of the dam has escalated from Medium to High, requiring increasing dam safety standards. public awareness of the dam and its functions has also increased with aesthetic awareness.
Various upgrade works to the dam were completed in the period 1992 to 1994 to alleviate concerns with various aspects of the dam's performance, principally with respect to seepage and internal erosion. In 1996 a further safety evaluation highlighted uncertainties with respect to the capability of the emergency spillway to safely discharge extreme storm events. Remedial measures have been implemented in 1999/2000 to raise the crest level, and improve the emergency spillway.
The consent process has highlighted discharges from the emergency spillway and potential downstream impacts as a significant issue of concern. The is paper describes the issues associated with a high-hazard dam in an urban area which has been subject to rapid downstream development and some of the complicating factors when the retained reservoir is a key component to the city's sewerage infrastructure.
