December 2015

Queensland drought

23.12.2015 - Posted by Selene Conn
Queensland is in drought. As of November 2015, 86% of Queensland was drought declared. Those of us who live in Townsville are now on water restrictions as our water supply (Ross Dam) is down to 27% capacity. Australia’s November mean temperatures were the third warmest on record and NASA recently published climate statistics showing that October 2015 was the warmest ever recorded globally.

This blog gives you a stark and visual illustration of what those statistics look like on the ground. What exactly does the drought look like along the usually wetter regions of the east coast of Queensland?

Through repeat annual monitoring of vegetation communities at static locations that Alluvium has been conducting, we have seen that the effect of the drought is dramatic. While several native tree and shrub species are known to be semi-deciduous, substantial leaf-drop has occurred in the last two years including non-deciduous species, with visual browning of leaves in others and the complete desiccation of groundcovers. These photos were taken at fixed locations at a site near Emerald, Queensland in 2013 before the onset of drought and recently in 2015 during drought conditions. Please note these sites are not grazed.

Before the drought

After the drought

Endemic Australian native species have evolved to cope with variable rainfall, so most of these drought effected vegetation communities will be able to recover with the onset of rain and an increase in soil moisture.

However, human induced changes to groundwater, overland flow paths, patch fragmentation and introduction of grazing lowers the resilience of many of these communities. Where disturbance is at its greatest, recovery will be slow. Let’s hope it rains!

Tony Weber joins Alluvium

15.12.2015 - Posted by Matt Francey
Many people will be aware of this but I’d like to formally welcome Tony Weber to Alluvium as the National Leader, Catchment Modelling. Tony will be well known to many people for his work within industry and academia into catchment modelling and water quality management.

We have believed for a while that there are great opportunities to bring together some of the environmental flow, catchment strategy and physical processes work that Alluvium already does with a much stronger broad scale modelling approach. Ultimately we think this will lead to better outcomes in situations such as the Great Barrier Reef catchments where understanding of the complex systems is key to providing the most effective action.

Tony starts in early January.  It is going to be great to have him on board – we very excited about the possibilities.

How do you test a fish ladder?

13.12.2015 - Posted by Josh Tait
The presence of fish in rivers across Australia is affected by many factors, but a significant one is the presence of weirs and other structures that stop fish migrating up and down a river. There are several different designs to allow fish to navigate up or around a weir, and we had the pleasure of testing one of them with a physical model with the Australian Irrigation and Hydraulics Technology Centre at the University of South Australia recently.

In this blog we describe what a fish lock is, how it works, and what we learnt from building a scaled down physical version in the lab.

A fish lock operates in a similar fashion to a ship lock. However it requires a constant ‘attraction flow’ to be provided through the lock to attract fish into the entrance and out of the exit. The fish lock operates in four key phases:
  1. Phase 1 - Attraction: provide attraction flow to lure fish into the lock chamber
  2. Phase 2 - Filling: the chamber is sealed and water level rises
  3. Phase 3 - Exit: the upstream gate is opened and the fish swim through to the weir pool
  4. Phase 4 - Emptying: the upstream gate is closed and the lock chamber is drained until the tailwater level of the fishway entrance is achieved

Modelled fish lock (scale 1:10)

The fish lock system at Uni SA was built in two sections – the fishway (1:10) and the weir (1:15). Crucially, a number of key components of the model needed to be adjustable, including; the tailwater level, the baffle slot width, the upstream lay flat gate and the pipe diameters. We were lucky to have the opportunity to use fish during the testing, which allowed us to observe their actual behaviour in this environment and flow conditions.
We learnt several things in this process: the number of water level sensors that would be required, the optimal pipe diameter, the filling flow rate (during Phase 2), the location and configuration of the fishway entrance, and the height of the new apron weir for the plunge pool to facilitate downstream migration.

Modelled river/weir system (scale 1:15)

For this reason we believe that the physical model achieved its aim of optimising the design and therefore was a worthwhile part of our design process. The increased confidence in design should translate to a more economical outcome for our client.