Warragamba Dam

Members students undertook a field trip to various dam sites in the Sydney Basin. These included inspections of the Warragamba dam site and recently constructed spillway, an inspection Darling Mills Creek Dam at North Rocks, and the subsequent trip to Manly vale, water research/hydraulics laboratory to observe, models associated with the dam sites visited. The field trip was coordinated, by the guidance of Warragamba staff, and professional staff from the Civil and environmental group.

Major learning outcomes (significance) of this site visit included:

 An improved perception of the surrounding geology of the dam site and how it affected the dam, as indicated by staff member. The initial tour guide indicated Narrabean and Hawkesbury sandstone were covered by fresh concrete to prevent seepage.

 Understanding of dam's extent. Staff indicated, the size of catchments at 16000Km^2, the water supply was a "large, integrated system", beginning at Shohaven rivers, and was part of the hydroelectric power scheme, the dam, diverts tow ways either to Sydney or Wollongong, and also brings water for Oberon. The demonstrator alerted visitors that a new pumping station was being constructed at the current time.

 Knowledge of dam's purpose and operation. Staff indicated this dam was built purely for water supply rather than flood mitigation, and does not pre release water. The dam consists of a central 250 tone, steel drum gate. If the dam reaches full storage level, and then surpasses it, by 80mm the drum gate control then opens gradually, if water continues to rise then four radial gates begin to open both drum and radial "work as a pair".

 Learnt of past, present and future additions and projects to the dam. The actual dam was indicated to have been raised 5 meters and post tensioned due to a greater flood risk, staff indicated, 60 multithreaded cables of about thumb thickness, were dropped into bedrock leading boreholes, and then grouted in place, the stretched cables act not dissimilar to an anchor, holding the dam down.

The next site visit occurred at the Darling Mills Creek dam, on loyalty road. The dam was seen in the flesh after, the previous presentation on the dam a week earlier. The vegetation associated with Darling Mills Creek and is typical for the Hawkesbury Sandstone landscape, remaining in steep sided sandstone valleys. Since the 80's flood waters have caused considerable damage to along the darling mills creek and also the upper Parramatta River. In 1994 the upper Parramatta River Catchment Trust proposed to build a flood mitigation basin on darling mills creek. The wall is approximately 25m high. During heavy rain, when the water cannot flow through the tunnel, so is temporarily stored behind the wall. Environmental impacts during construction were minimal although one marsupial had to be relocated.

The Final leg of the trip involved participants traveling to the water research/hydraulics laboratory in Manly. For the inspection of Darling Mills and the Warragamba dam model. Here interrelations between the models and the actual dam's could be observed. Hydraulically operated models, are routine when dams are to be upgraded to safely handle floods, moreover they are also used for the investigation on the performance of spillways.