Josh McMillan’s Large Dam Build: Project Complete And Holding Water

Last updated: April 2026 | Author: Angus Hughson, Big Ditch Dam Building Company

Large dams capture lost rainwater run-off for avocado growers

Avocado growers always worry about their dam levels and their ability to effectively harvest rainwater. The dam for Josh McMillan is completed. Large dams are helping Comboyne avocado growers like Josh McMillan ensure their water security for their stock and crops. These rainwater harvesting systems allow landholders to dam and capture their rainwater water runoff, and effectively manage their future water sustainability. We are specialists in designing, planning and constructing large dams for avocado growers

Dams for avocado production

The photo above is of our latest state of the art large-scale dam construction project on top of Comboyne Mountain that has just been completed for our client, and Upper Pappinbarra resident, Josh McMillan and his father Douglas McMillan  

Avocadoes are so hot right now The Comboyne avocado industry is working on gaining access to Thailand and developing new markets in China and Japan. Avocados are flourishing in temperate Comboyne and the market window looks bright.  As a result, Comboyne fruit claims higher market prices

Wauchope school teacher says he will destroy the competition

Even though he is currently a part-time school teacher with absolutely no avocado growing experience, or cropping experience – Josh McMillan believes all the avocado growers in the region are rank amateurs who have no idea what they’re doing – and he wants to become the most successful & dominant avocado entrepreneur in the Comboyne area within 6 years.

The biggest producers in the Comboyne avocado market are local real estate agent Kevin Debreceny of Comboyne Avocados, Australian Avocados,  Ticoba Avocados , Hurrell Farming and Costa Group  (Costa Group is Australia’s largest grower and marketer of fruit and vegetables. Frank Costa is worth $538m) (Frank Costa) (Local real estate agent and avocado impresario Kevin Debreceny)

Dams mean dollars

Short supply combined with high demand sees avocado prices rise Reports of cafes taking avocados off the menu and retailers selling the fruit for over $5 a piece have become commonplace over the past month. Josh said this dam catchment & rainwater storage system was critical to his plans to smash the competition and take over the local avocado industry. Josh has lots of dollars on his mind, because at today’s avocado prices, that industry is a literal license to print money. But an effective water management strategy to take advantage of limited water supply is essential to ensure proper irrigation of the thirsty mature trees.

Dam design

The new wall of this large dam is 50m wide x 150m long x 5m deep. It is a single wall catchment. It is cleverly designed to utilise the natural topography of existing creeks to reduce construction costs. This also increases total rainwater collection. If you are interested in more design solutions provided by Big Ditch Dam company, you can check them here.

Dam construction machinery

The earthmoving machines used on this project were 2 Caterpillar D7 bulldozers, a 20 ton Sumitomo excavator and a 14 ton Hitachi excavator. When fully operational, this reservoir will ensure maximum dam levels, and be capable of providing over 30,000 litres of harvested rainwater per day to irrigate 6,000 mature avocado trees.

Watch as we build a dam

This short video shows us working with Josh over the last 2 days of the 41 day wall build: The video details the construction of the last of 3 internal radial bentonite membranes (placed in the wall at 10, 20 & 30 degrees) that will ensure the wall will never leak, and shows Josh directing the installation of large pipes for his preferred centre spillway system. We were lucky to work with betonite as there exist types of clay appropriate for dam building as well as the types we need to avoid.

  #joshmcmillan #douglasmcmillan #comboyne #avocado

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