Take care to avoid erosion
As we come to the end of our third wet season in a row with above average rainfall, many property owners are faced with the task of tackling water flow issues.
Some building or landscaping undertaken during the drier times may not have taken into account waterlogged soil, temporary springs and inundation by rainfalls of 100mm or more in an hour. In fact some of these issues may have been compounded by the works.
It is difficult to pre-empt every issue resulting from rainfall. The recent flooding at Alexandra Headlands is a classic example of this. We can, however, take measures to reduce the impact of water on our property and our neighbour’s property.
Erosion is the most immediately noticeable result of rain. Erosion is an act of nature. In our gardens it is most unwelcome as we prefer to keep the soil for our own use.
Erosion most seriously occurs when water is allowed to build up speed on its way down hill toward a drain or natural gully. By installing drainage pits or gutters the water flow can be broken and redirected to an area where it will cause less concern. Just remember, the water coming out of a pipe in the ground will have a lot of speed and can cause damage. Rocks or strong rooted plants will slow the water.
If you have the room or it fits in with your design ideas, a dry creek bed is a great way to control water flow. It is a shallow gully set through the landscape and filled with materials which will not be washed away by flowing water. Some are simply turfed; others may have mulch and plants scatted along the course, though over a period of time soil may build up around the plants. The most common surface is a combination of river stone and larger rocks which can be arranged to look like a natural water course.
However you control the surface water flow, do not direct water onto neighbouring property unless there are facilities to deal with it.
Sub surface water and springs are another issue during periods of heavy rain. Subsurface water can lead to dampness in lower storeys of houses where the walls are in contact with the soil. Springs bring water to the surface of the soil, leading to boggy patches. Both of these problems can be remedied by installing a sub surface drainage system. Essentially, a subsurface drain is a trench cut into the soil and filled with gravel to intercept the flow of water. The water is then redirected through pipes to a stormwater system, dam or gully. The area downhill from the trench will then remain dry. The trench can be backfilled with soil and planted out or returfed.
Planning and preparation will prevent problems during the wet season. Remember, also to maintain any drainage systems, regularly checking for build up of materials which will cause blockages in the future.