Drainage, Tracks and Fencing
When planning and laying out a property’s tracks and fences it is usually beneficial to work with nature and the natural landscape and slopes of the land. Drainage will always run down slope by the steepest path, that is at right angles to the contours of the land. Interrupting that natural flow can cause problems and / or add to the expense of the tracks and fences.
This section covers managing the drainage on the property, the ideal location for tracks and fences and some of their design options.
Drainage and Creek Crossings
As much rainwater as possible should remain where it falls and soak into the soil. However, there will be times when the intensity of the rain outstrips the soil’s infiltration capacity to take in the water, and runoff ensues. (Keeping the soil surface covered with plants or mulch will help to maintain the soil’s infiltration capacity and minimise soil and fertility erosion.)
Runoff may run into natural, well defined channels and flow down slope and off the property, which is fine. Should channels start to form gullies and obviously erode the likelihood is that Nature is trying to make the channel larger because it needs to carry a larger flow of water than previously. So before trying to fix the erosion, ask yourself ‘What has changed in the catchment?’ Without addressing such catchment changes it will be difficult to repair the erosion problem.
Sometimes and in some places runoff can be a problem; at other times and in other locations runoff is an important resource. Runoff is needed to fill dams to provide water - particularly in summer and autumn. Runoff can be ‘captured’ by grade banks that direct the flow of runoff into dams. Ideally, such grade banks should discharge their flow into a silt trap upslope of the dam. Here the water movement is slowed, and the water will drop a lot of the ‘silt’ it is carrying before entering the dam. This minimises the need to clean out dams in order to maintain their water capacity.
Where tracks must cross drainage lines, they can be in the form of a ford, a culvert or a bridge. The amount of money spent on the crossing may depend on the crossing’s important and if it is required to be an all weather crossing.
In the case of a ford, a firm base is required, which could be made of local rock, the stems of trees or old fence posts (with all sharp metal removed!). Attention should be paid to the sides of the crossing to stop them eroding and becoming too slippery for vehicle traction.
A single large pipe or a bundle of pipes could be used to make a culvert. The culvert should have sufficient flow capacity to allow the majority of peak runoffs to pass. (Backed up runoff could become a problem if it overtops the crossing or cuts its way around the culvert.)
For more information on culverts try:
Short bridges can be constructed with tree trunks, again ensuring that there is capacity for peak runoff to flow. Regarding the construction and load bearing ability of such a bridge it is advisable to consult a suitable engineer.
The following reference from the WA Department of Water is a particularly useful document on the design and construction of all sorts of creek crossings:
Where fences have to cross drainage lines the main considerations are minimising fence damage during peak water flow and designing the fence crossing to be stock-proof in all situations.
Also Google: Water and Rivers Commission Water Notes 19
The strength of a fence comes from the strength and quality of the strainer assemblies. Strong strainer assemblies allow the fence to be strained up tightly whatever the fence design. A tight fence can allow the upright posts to be spaced wider apart whether they are wood or steel pickets. Adding steel droppers into a fence design, which help to keep the fence wires from getting twisted up, allow the inline fence posts to be spaced even further apart. Fencing is expensive. Any of these designs that reduce the amount of materials in a fence help to keep the price of materials down as well as help reduce the time taken to construct a given length of fence.
Here are some useful articles and short videos on fencing:
Google ‘rural fencing’ for much more information about suppliers, contractors, designs and tools.