HYDRAULIC STRUCTURES
AND WATER MANAGEMENT

1. GENERAL

Bill Meynink, who runs PSM’s Brisbane office, leads the work in hydraulics and water management. This work is usually closely linked to work done in regard to catchment and river hydrology which is covered in a separate capability statement.

2. SPILLWAYS AND OUTLET WORKS

Many of the hydraulic structures designed by PSM relate to outlet works or spillway structures for embankment dams. Examples of such projects are set out below:

Nakan Dam, East Kalimantan

This 126m high rockfill dam is designed to store 40 million tonnes of potentially acid producing waste rock, in perpetuity. The concrete spillway had to be designed in conjunction with the hydrology of the facility so as to ensure that the waste remains covered by at least 1m of water. At the same time, the spillway has to safely pass a probable Maximum Flood.

This dam also required some other unusual hydraulic structures including:

• a multi-level decant system to allow progressive filling of the reservoir so as to cover the gradually increasing level of potentially acid producing waste rock

• a temporary siphon spillway to maintain the water level at about 5m below FSL to allow dumping and topsoil stripping to continue.

A particular challenge had to be dealt with in mid-2003 when the 1m diameter high level diversion conduit, beneath the 76m high Saddle Dam, had to be plugged. The 1m diameter pipe had partly failed at some point beneath the dam, which meant that when the decant structure was closed there was still 50 lit/sec exiting from the downstream end of the pipe. The pipe had to be closed permanently to allow the dam to be filled. The work involved development of a 1m diameter inflatable packer which was tested under prototype conditions, of 50 lit/sec flow and 25m static head, at the Manly Water Research Laboratory (see photographs below).

1m diameter Hydraulic Packer	Packer installed in flow of 50 lit/sec

Divers had to be mobilised to clean out the 200m length of pipe before installation of the packer and grouting of the conduit. The grouting was performed by Austress Freyssinet in accordance with specifications prepared by PSM, and under the direction of PSM personnel. The work was successfully completed in May/June 2003.

Stratford East Water Storage, NSW

This 17m dam forms part of the water management system for the Stratford open pit coal mine. The dam stores water pumped from the pit and this water may not be released. Therefore a diversion channel system had to be designed so no natural runoff enters the storage. A simple bywash spillway is included to safeguard the structure against extreme rainfall events and/or failure of the diversion channel system.

Harapan and Prima Dams, Hatari Pit, Kaltim Prima Coal

These 24m and 36m high dams formed part of the major river diversion works for the Hatari pit at Kaltim Prima Coal. They are both about 4km upstream of the Murung Dam described above and shown in the adjacent photograph. They are linked by a pipeline system designed by Bill Meynink and both have simple bywash spillways to cater for extreme rainfall events.

Murung River Diversion, Kaltim Prima Coal

This 35m high earth/rockfill dam was constructed in 1993 to divert the Murung River around an area of open pit coal mining. Bill Meynink designed the 6 km long, high level channel for the diverted river together with associated energy dissipation structures at the downstream end, where the diverted river cascaded down to the original river bed.

3. DAM BREAK ANALYSES

PSM have been responsible for dam break analyses of the 60m high Namuk tailings dam and the 126m high Nakan dam at the Kelian Gold Mine. The study for the Nakan Dam was required as part of risk analysis for the mine closure works and form part of the requirements of the Dams Safety Unit of Indonesia. Failure of this dam would impact on Dayak communities dotted along the Kelian River.

4. HYDRAULIC MODELLING

Physical models can form an essential part of the design of certain hydraulic structures. This is particularly the case when sediment transport forms part of design considerations.

An example of a typical model is shown below. This model was constructed to study possible means of blocking the high level diversion conduit of the Nakan dam by developing a reverse filter within the conduit using varying sizes of gravel introduced into the 50 litre/sec flow. This was the fall back approach if for some reason the packer system described in Section 2 above did not work.