Starting Point

Erosion of the earth’s surface is a slow natural process, but is greatly increased by human activity. Run off from disturbed sites carries sediment into our streams and rivers, affecting water quality and ecosystems. Controlling erosion and sediment run off from earthworks is an important requirement in protecting the environment.

Canterbury terrain

The Canterbury region has varying terrain from the foothills of the Alps, through the gravels of the plains to the loss-covered volcanic soils of Banks Peninsula and the Port Hills in Christchurch City. Environment Canterbury’s new guidelines have tools to cover all these areas.

Port Hills prone to erosion

As was seen in the liquefaction after the earthquakes, the Canterbury Plains gravels contain fine particles that need to be controlled during excavation. In Christchurch City, the Port Hills are particularly prone to erosion as there is a layer of loss beneath the topsoil. Loss is composed of very fine particles and is easily eroded by rain if the protecting layer of soil is removed. The steep topography only increases the rate of erosion. These fine sediments can be particularly damaging to the ecosystem when they smother the bottom of the receiving waterways.

New toolbox helps to minimise sediment loss

Previous guidelines for erosion and sediment control have not particularly targeted this fine sediment. This new toolbox has more tools available to help minimise the amount of sediment leaving a disturbed site, and with better controls for the finer sediments. There have been significant recent advances in treatment regimes using flocculants and these are included.

As kaitiaki for this region, we should all make a concerted effort to improve the environment for our children and the animals, fishes and flora that need water to survive. Embracing these tools and integrating the philosophies into your everyday activities shows a desire to improve our soil and water health.

The Christchurch/West Melton Zone Committee welcomes the introduction of this toolbox to further protect our environment.