Karangi Coffs Harbour Dam Geological Completion Report

Abstract

Karangi Dam has a 30m high wall which forms an off-creek pumped storage reservoir for the Coffs Harbour regions water supply. Extremely close spaced grouting was undertaken in an endeavour to minimise potential leakage. Earthfill was acquired from within the storage and comprised highly w weathered rock. Rip rap armour stone was won from a quarry inv silicified argillite located to the southeast and just outside of the storage catchment. The dam wall is a homogenous impervious earthfill embankment with downstream chimney and blanket filters. The upstream face is armoured with rock rip rap. A side discharging concrete lined spillway is located on the right abutment. The dam nominal centre line as constructed is 24m upstream of the axis investigated. The outlet works comprise a right abutment culvert (steel pipe in concrete encasement) with atrunion inlet. During stripping, considerable variation from antic pated foundation rock conditions was encountered. Strata types present include bedded cherts, schistose mudstone and massive silicified argillite.