The making of the CRE

Reef HQ was the brainchild of Dr. Graeme Kelleher, a former chairperson of the Great Barrier Reef Marine Park Authority, who wanted to create an example of the Great Barrier Reef on land. Making the reef accessible to everybody at a low cost and thereby gain community support for the protection of “the real thing”. Today, over 100 000 visitors come to Reef HQ each year to get up close and personal with the reef, while staying dry.

Reef HQ is the world’s largest living coral reef aquarium and is a must see attraction in the Townsville region. Reef HQ was built as a Bicentennial Commemorative project and opened in Townsville on 24th June 1987.

Keeping aquatic creatures in captivity is not an easy task. The primary requirement in the design and construction of Reef HQ was to replicate, as close as possible all the environmental conditions that could be found on a coral reef.

Water quality is central to the success of Reef HQ. From the smallest display tank to the massive coral reef exhibit, the aim is the same – to create and maintain a suitable environment for the inhabitants. Factors that are closely monitored are:

• Light
• Temperature
• Salinity
• Oxygen
• PH
• Nutrients

Some of the many engineering challenges…

Aerial view of Reef HQ during construction

Long before the coral reef could be built, engineering and design challenges had to be met. The task of designing a basin that would hold 4 million litres of water, complete with waves, currents and underwater viewing tunnel and 5 large windows, required experimenting with and application of novel technologies on a large scale.

The making of the coral reef exhibit began with the construction of a 38 metre long, 17 metre wide and 5 metre deep concrete basin, which was specified to withstand corrosion for at least 50 years. Major experiments using different water-cement mixes and additives were carried out with the Australian Cement and Concrete Association prior to construction, to come up with the perfect mix, thereby greatly expanding the existing technology in the process. To eliminate cracking of the concrete, another technique was used for the very first time in Townsville – liquid nitrogen was added to the cement in the trucks before delivery to keep the cement cool enough, which helped minimising cracking during the curing process.

A recipe for a reef

Diver places limestone rocks
for coral reef

It was estimated that around 200 tonnes of sand and 700 tonnes of coral substrate were needed to build a suitable foundation for a coral reef system of this size. Sourcing these quantities proved to be one of the major challenges of this project since mining and extraction of minerals of any kind are strictly prohibited in the Marine Park. Permits were issued that allowed for the collection of sand from the large Flinders Reef lagoon in the Coral Sea – 260 kilometres offshore. Using an ocean going barge with a crane operated lift bucket, the sand was collected from about 8 metre depth, all large benthic organisms recovered and returned to the lagoon floor and the sand finally transported to the aquarium to provide a seabed of about 50 centimetres.

Obtaining 700 tonnes of coral rock appeared to be much more difficult, but luck was on our side when a stockpile of large coral rocks was discovered on Hayman Island, where it had been excavated above the low water mark some years earlier for a harbour development. Once the rocks were shipped to Townsville, they were scrubbed vigorously to remove any resident lizards, spiders and insects that had made the rocks their home.

The rocks were sea-scaped to built a typical mid-shelf reef including a reef front, algal crest, back reef slope, lagoon and bommies, consistent with the light conditions (shading of walls) and desired wave and water circulation patterns.

The final ingredient of the “recipe for a reef” were 2.5 million litres of seawater, which were shipped in from Myrmidon Reef, one of the most amazing outer shelf reefs of the Great Barrier Reef. To make matters slightly more complicated, more than 20 voyages to the outer reef had to be made, since 200 000 litres was the maximum capacity that could be barged in at any one time

Stirred – not shaken: waves and currents

Primarily, water motion is created by a pneumatic wave machine at the opposite end to the viewing tunnel. This wave machine consists of two large chambers which are alternately pressurised and depressurised and thereby create a progressing wave. The wave machine is capable of producing waves of 2 m height. Much less dramatic, but much more effective our wave height is typically 50 to 75 centimetres, with a period of 2 to 8 seconds.

To create sufficient currents in the many smaller niches of the Coral Reef Exhibit, small water circulators are used, providing currents desired by corals of 8 to 30 centimetres per second.