Inside a warehouse in Manly, NSW, Seqwater dam engineers have been working with the University of New South Wales’ Water Research Lab team to evaluate the spillway upgrade options and optimise the designs for the proposed spillway upgrades for Lake Macdonald and Somerset Dams.

Rushing water is sent down scale model replicas of each dam, built of wood, concrete and gravel to test the hydraulic performance of each design and expose any weaknesses.

Data is collected on flow velocities, areas of turbulence, changes in flow depths and the dissipation of energy to allow the design of the upgrades to be refined for the full range of design flood events.

Seqwater Lead Storage Planning Engineer Craig Wiltshire said hydraulic modelling and analysis were critical components in the design of any dam project.

“Modelling provides important insights into different aspects of a dam’s design such as how excess water is safely passed through the dam and into the downstream river channel, where erosion could occur and understand the effects of natural floods,” Mr Wiltshire said.

“For Lake Macdonald and Somerset Dams we have used scaled physical models in the design and investigation of these dam upgrade projects.

“Another option is to use computer simulations to gain design information but sometimes the physical models more accurately show the hydraulic performance than computer modelling, especially in the case of chaotic things like water flow in highly turbulent zones.”

Mr Wiltshire said even though the models were small-scale replicas, they are still quite large.

“The Somerset Dam model was 50 times smaller than the existing dam with model being six metres wide and 16 metres long,” Mr Wiltshire said.

“A pump was used to discharge large amounts of water into the model to simulate extreme floods and we would adjust the flow of water to create different flood scenarios.”

“During these tests, we collect velocity, depth and pressure data to assist in the developing the preferred design of each upgrade.

"This is an important validation process - water behaves in a similar at the smaller scale and allows engineers to replicate the performance of the proposed upgrade during extreme floods."

Both Lake Macdonald and Somerset are set to undergo major upgrades in line with Seqwater’s Dam Improvement Program. with each project priced in the hundreds of millions of dollars.