The upland lagoons of the New England Tablelands are mostly intermittent or ephemeral wetlands, meaning that they fill and dry in response to rainfall and evapotranspiration, with some often drying up completely for years or even decades at a time. Each individual lagoon has its own unique pattern of wetting and drying, known as it’s water regime. To be able to manage these lagoons and monitor their health, we need to know what these patterns in water level are over time are, what drives these patterns, and what might cause them to change.
One useful tool to help us understand the bigger picture of what is going on across all lagoons is to summarise their water regimes in much the same way as we do for colours, by dividing them up into groups. To describe something’s colour, we split what is actually a continuous spectrum up into classes; red, orange, yellow… etc.
Our lagoons can be best divided into four groups:
- Cluster 1 – lagoons which are dry most of the time and fill then dry again rapidly in response to significant rainfall events
- Cluster 2 – lagoons which contain water almost all the time and have a relatively stable water level
- Cluster 3 – lagoons which contain water almost all the time and have distinct cycles of wetting and drying
- Cluster 4 – lagoons which often dry out completely but also have distinct cycles of wetting and drying
Almost all of the lagoons have been heavily modified in the past to allow for agricultural and other use of the land. Most commonly they had been drained, while others have been impounded or contain smaller features such as farm dams.
Lagoons which are essentially intact are divided evenly between the four groups. This suggests that there is naturally a large spectrum of water regimes across the lagoons presumably due to differences such as their area, shape, and depth. Even the mostly dry lagoons should not be discounted as unimportant just because they only contain water for a few weeks at a time every couple of years. Over 60% of the driest lagoons, however, are in this class because they have been drained, preventing them from retaining water the same way they would have in the past. Impounding lagoons has the opposite effect, causing them to retain more water and become more stable.
From this research we now know the range of water regimes across the lagoons, which group of water regime each lagoon belongs to, and the effects that modifications have on water regime.
Gillian Backhouse
Dynamic Lagoons 