By Todd Layt
Research in Queensland is demonstrating how turf grass is an effective means of controlling and minimizing erosion. Turf grass is capable of reducing erosion by protecting the ground from the impact of rainfall. It also reduces the speed of runoff water, holds soil and sediment particles in place and enhances the ground’s ability to absorb water.
Turf is proving an effective means of erosion control on batters of a gradient less than 33.3 percent and stabilizing areas of concentrated flows such as channels and drains, provided the flow velocities do not exceed 1.5 m/s. If flows are higher, combining turf with geotextiles seems to be a well proven concept.
There have been studies showing turf and geotextile combinations once established can withstand up to 5.5 m/s depending on the geotextile. With the invention of fast stapling devices it is now easy to secure turf in place. These devices are readily available in the USA, and are now becoming available in Australia. Current research is investigating various methods of using these staples to secure turf both in small and big rolls.
Turf employed skillfully and/or in combination with other mitigation technologies can also be highly effective in trapping sediment. Silt fences, coir logs and erosion socks used on their own have very limited benefits, and are far less effective than you think. Combined with turf in the appropriate method, the results are greatly improved. Many examples of these techniques were seen at a demonstration site in Brisbane. Many who attended clearly saw how much better Turf was at preventing erosion than silt fences, coir logs and erosion socks.
Infiltration of rain is far better than using jute matting. Unfortunately dense Jute matting becomes hydrophobic after a while in the sun. It may stop weeds, but it really harms plant’s ability to grow, and years after installation there is rarely any plants still alive. Jute netting with holes in it works better, but it is far more expensive than turf when you calculate the cost of the netting, plants and installation.
However if plants are preferred over turf, jute netting is a good alternative. Another alternative on moderate slopes is to use pine flake mulch as it is less likely to wash away. Turf however remains the most practical and cost effective method of erosion control, and unlike any mulch it can be used in water flow situations. It is a better alternative to rock, as turf is a living organism helping to remove nutrients and heavy metals.
If installed to resist erosion in the warm months turf only requires a maximum of seven days to bind to the underlying soil. In cooler months it can take a little longer, and can be pegged. Turf with rhizomes or underground runners is best, as it provides a three dimensional long term protection, binding the soil to a greater depth.
Kikuyu and Couch have been traditionally popular types for erosion control, however recently Zoysia varieties are also regularly being used due to their ability to better cope with wet feet, their greatly reduced mowing needs, and the extra soil strengthening they provide. Nara Native Zoysia Turf, being a local species is becoming popular for erosion control particularly amongst native vegetation. Buffalo does filter out sediment very well, but its lack of Rhizomes, its cost, and its lower drought tolerance make it relatively unsuitable.