Eaglerise Farm Water Management
Swales at Eaglerise Farm
In 2020 we started implementing our farm swale design. One of our aims with swales is to develop a broad habitat linkage for squirrel gliders, Petaurus norfolcensis, by planting Eucalyptus blakelyi every 30 metres along them. This increase in the edge effect will greatly increase the habitat area as it links our existing revegetation areas. Gliders were present in this landscape in the past and we would love to get them back. It will take many years until the trees are suitable habitat, but we are patient. These redgums will also provide shade and a windbreak as they act as paddock trees for our livestock. The Blakelyi are being inter-planted with acacias. Being legumes, the acacias will impact on the paddock soil nitrogen through direct nitrogen fixing and through their seeds and leaves being consumed by our livestock and deposited around the paddock.
We chose to space our swales approximately 18m (60feet) to 20m (65feet) apart. This was largely to allow us to maneuver our chicken caravan without driving over and damaging the swales.
It is possible to calculate the size and spacing. Our swale design constructs swales averaging 1.2m (4feet) wide and 250mm (10inches) deep. This comes to a cross-section of 1500cm2 (230inch2). Along a 1m (39inches) of swale, this holds 150litres (40US gallons).
If the swales are 18m apart, then the runoff can be calculated for any given rainfall event. We use 50mm (2inch) because this is the limit that we are likely to get in a single event. (Perhaps more on rare occasions.) If we assume that we get 100% runoff – highly unlikely, then the runoff into the swale per metre will be 18m x 50mm x 1m. This equates to 9litres (2.5US gallons).
That means we can expect 9litres of runoff in a large rainfall event to run into our swale that can hold 150litres. This allows for the swale to settle over time and get trodden down by livestock and fill with silt and vegetation. We are assuming that the 150 litre capacity can be diminished to 20% i.e. 30 litres (8US gallons) and we’ll still have a fully functional system.
Another aim is to slow the rain runnoff from the paddock and increase soil moisture. To increase the water infiltration we are planning to gradually, rip contours between the swales. The process here is to rip very slowly to ensure we don’t bring up any sub-soil. With a wider tractor, it is an option to roll in the previous rip-line. Our small tractor put us too close and, the relatively narrow tyres, caused rip-line collapse when we tried to roll the line in, so, we spaced the rip-lines wider. This ripping also breaks up any hard pan..
In June 2020, three months after constructing the swales, we had a 43 mm rainfall event. Here you can see the effectiveness of the swales as water harvesting. The higher swales are in coarser, sandy gravel soil and most of the rainfall has been absorbed through the rip lines. As we walk down the paddock, you can see the different soil where the onion grass is growing. This has increased runnoff and this can be seen in the water laying in the swales.
The exciting thing here is imagining the effect of this increased ground water on soil biology, pasture growth and eventually farm and native animal improvement. We need to employ the permaculture principle of “small and slow solutions”
Months later the revegetation and stabilisation can be seen.
Eaglerise Farm Seasonal Spring
After we have any significant rainfall event, the soil profile fills with water. This water flows through the coarse, granitic soil profile until it encounters deeper rock when it then flows along this rock until it emerges as a spring.
This is our main, most reliable spring. In any year with reasonable rainfall, it flows for about eight to nine months. It will only flow during the hot dry season if we have a wet, hot dry season (summer rainfall event) with at least a 40 mm rainfall.
It is fortunate that this spring is high in our catchment. The rock wall we created dams the water and directs it through the pipe. It flows under gravity to our tanks near the house and maintains our stock watering troughs along the way. Surplus water overflows and proceeds down the drainage line. This water fills the Ruth’s Vineyard dam before exiting the farm.
The rock wall was made in 2000 and is showing the effect of age. Our work program includes waiting for the spring to dry up. Then pressure washing the wall and re-rendering the inside. This will reduce the leaks and encourage increased retention and flow down the pipe.
Eaglerise Farm Water Distribution Lines.
Here is our Eaglerise Farm Water Distribution map. The main line is in blue. It is a 1 inch poly pipe and commences at the seasonal spring in Gully 3 and feeds most of the farm, including 2 tanks above the house that act as a low supply buffer. It was installed in 2004 when the only farm enterprise was Dorper sheep. Generally, there was amply water available then.
In 2020, we installed our high tank to supply water to two troughs above the seasonal spring. This opened up two paddocks to improved grazing efficiency when the stock didn’t need to walk quite a distance to the nearest trough. It is shown as a pink line,
The red line is a 45 mm line that was installed in 2019 to supply water to the vineyard. It also establishes another line from the vineyard dam to the double tanks.
The pale green line was originally installed, but the end is too high for water from the tanks to supply.
The troughs are, generally, 500 litre plastic round troughs. It is possible to move and install these light troughs manually, by yourself. However, the pigs did not respect the plastic sheep/cattle troughs!
The orange line is a system being developed to provide water for the paddocks at the top of the hill. It will be supplied by delivering tanks of water via ute and pumping into the tanks.