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Erosion is the wearing down of a land surface by the action of water, wind or other geological processes. The resultant displaced material is known as sediment. Sedimentation is the depositing of this eroded material.
The main factors influencing soil erosion are climate, soil characteristics, topography, ground cover and evapotranspiration.
Climate affects the likelihood of erosion directly and indirectly. The direct relationship arises from the action of rain – a driving force of erosion – where raindrops dislodge soil particles and carry them away.
Soil characteristics are important in determining soil erodibility. Good soil structure increases water permeability and water holding capacity. Soil permeability refers to the ability of the soil to allow air and water to move through the soil. Soils with a higher permeability produce less run off at a lower rate than soils with low permeability.
When soil surface is compacted or crusted, water tends to run off rather than infiltrate. Erosion potential increases with increased run off.
Topography is also critical in erosion. Slope length and slope angle play a large part in determining the velocity of run off.
Soil erosion can be managed by mechanical and biological methods. Mechanical measures such as terracing, debris dams and other engineering structures have an immediate effect and operate at maximum efficiency, but their construction and maintenance costs will be high. Biological methods, such as use of live vegetation planted from cuttings, rooted plants and poles, are relatively cheaper but their immediate effect is smaller. However, once established the vegetation is self-perpetuating and permanently effective.
Waikato Regional Council’s catchment management officers can advise on soil conservation, riparian management and other good land management practices.
We can also advise and help you in planting willow and poplar poles/bare rooted plants, including various aspects of planting to ensure the best possible strike and survival rates.
Poplar and willow poles are ideal to plant on erosion-prone hillsides as their extensive root systems bind and hold the soil in place. Some varieties also suit shelter and windbreaks.
Successful establishment of poles requires careful handling, storage, siting, planting and follow-up management.
When transporting poles, make sure the bark is not bruised or damaged in any way which would allow diseases to strike. When securing loads, use straps or ropes and protective pads rather than chains.
If planting is to be delayed more than a day after delivery, cut the poles diagonally on the butt end with a sharp axe or slasher, to give two slicing cuts about 15cm long. This will facilitate water uptake. Then place the poles in clean, well aerated water, or keep moist under a sprinkler, to assist future root and shoot growth, and to increase survivability. Some varieties are susceptible to over soaking. We can advise on correct handling.
The council is organising a field day on sediment loss mitigation and pole planting on October 24 starting at 9.30am at Sir Don Rowlands Centre, Karāpiro. If you are planning to attend, please let us know.