Each NSW property has a maximum volume of water (harvestable right) that can be stored in dams that is based on the area of the property. Before building a dam you need to calculate the capacity of existing dams to see if you have any more harvestable rights available (see NSW Office of Water Maximum Harvestable Right Calculator).
If you have harvestable rights available then you need to work out whether a licence is required to build a dam (see NSW Office of Water Harvestable Rights – Dams). The easiest option is to build a dam on a first or second-order stream. Dams on third-order waterways require a licence. The order of streams is based on the pattern of blue lines for watercourses shown on topographic maps (eg look up SIX maps for your property). There is an explanation about how to work out what order watercourse you are dealing with in NSW Office of Water Dams in NSW: Where Can They be Built Without a Licence. [Your Council may also require you to lodge a development application before constructing a dam – Ed.]
Good spillway design is crucial to ensuring that excess water can be released safely when there is lots of rain. It is desirable to have good ground cover on the spillway to protect it from erosion and also to keep it dry as often as possible. A trickle pipe can be installed to release small amounts of water so the spillway is kept dry.
Farm dams can be made wildlife friendly and more attractive by excluding stock and planting riparian plants. See The Farm Dam Handbook (Water NSW) for design ideas and strategies.
What makes dams leak?
- topsoil not removed before dam wall is constructed so water seeps out through topsoil layer in dam wall
- inadequate compaction of dam wall
- a waterproof dam requires 10-12% clay
- typically dams built in basalt soils will leak
Leaking dams are expensive to repair. Options for repair include polymer material applied when dam is full or rubber or plastic liners. Contrary to popular opinion, throwing Bentonite into a dam will not fix leaks.
It is also good practice not to plant trees on dam walls to reduce the risk of their roots causing leaks when the tree dies.
Silted up dams
Aim to maintain groundcover in the dam catchment to minimise silt flowing into the dam. Silt can be cleared out of a dam by emptying the water and then bucketing out the mud and spreading it on the dam wall or elsewhere. Sometimes dams leak after this has been done because the silt has been sealing leaks.
Erosion around dams
Generally erosion is caused when a dam is built on steeper ground so that the water drops down the front edge of the dam. The eroding areas can be protected by spreading rock on them. It might also help to build a berm across the front of the dam to direct the water into a narrow channel flowing into the dam that can be protected with rock. Strategies for dealing with erosion involve slowing the water moving down the slope, covering exposed soil and re-establishing ground covers.
The NSW Government Soil Conservation Service provides consultants who can help design dams and provide advice for solving problems with existing dams.
There are three key things to consider when planning your water supply for stock:
- Quantity – how much is needed (see NSW DPI Primefact 326 Water Requirements for Sheep and Cattle), will you have enough in dry times? Remember that wildlife will use stock water too and you also need water for fire fighting, garden watering and to allow for evaporation (25-30% from farm dams in the Southern Tablelands).
- Quality – different quality water is needed for different purposes (eg drinking water for humans, drinking water for stock, irrigation water for garden). You can test your water to check that it is fit for purpose. Testing is important in dry summers when salt levels can build up in dams. Blue Green Algae (which is also sometimes red/brown) is toxic and stock should be kept away from it. The NSW DPI website has more information on water quality and testing for livestock and blue green algae testing.
- Reliability – see NSW DPI Primefact 269 Stock Water: A Limited Resource
Stock water can be provided by giving access to a dam or pumping water to troughs. Generally stock should be fenced out of dams to maintain water quality but you can fence so that they have limited access to a dam over rocky ground. Water troughs need to be kept clean and you need to make sure that all animals have access to troughs – sometimes there are bullies who keep the other stock away from the trough.
The water in the dam will be cleaner if you fence to stop stock camping in the dam catchment. It is also important to maintain 100% ground cover in the dam catchment and 80% elsewhere to reduce silt and nutrient run off into the dam.
Most farms store rainwater collected from roofs in tanks for use in the house including drinking. While this tank water is relatively low risk, good hygiene is critical for ensuring water is safe for drinking. People with compromised immune systems and the elderly are most at risk.
Key actions are
- clean house roof gutters to remove dirt and debris
- first flush diverters can keep the dirtiest water out of the tank but they need regular maintenance to work properly
- tanks can be cleaned (say annually) using technology similar to cleaning a swimming pool while the water is still in the tank
- pumps should be regularly cleaned and maintained
- drinking water can be filtered using charcoal and paper filters which should be replaced annually
- home test kits are available to check the quality of the tank water
If the water becomes contaminated (eg dead animal in tank), water can be made safe for drinking by boiling. UV filters can also be used to clean water but are more expensive.
This field day was made possible with funding from the Australian Government, in-kind support from South East Local Land Services, the Soil Conservation Service and Veolia. Thank you to our sponsors of the network, the Palerang Local Action Network for Sustainability, and our host farm.