Sediment is the greatest contaminant of the Ōpāwaho Heathcote River. It smothers the habitat of macrobiotic life that sustains fish and other life, it reduces visibility, it introduces heavy metals and it is visually unsightly. One of the sources of sediment, particularly on the hills, is from building sites. Each time we open the surface of the land to build, we give water the opportunity to wash sediment into the river. The sediment can also clog drains resulting in unfortunate flooding and other negative impacts.
Erosion and Sediment Control Plans The Building Code 2004 and the new CCC Stormwater and Land Drainage Bylaw require an Erosion and Sediment Control (ESC) plan to be approved before a building consent can be issued and for such controls to be implemented before ground is broken on a building site. This includes all sites where building work may result in disturbance of the ground, and includes the transfer of sediment off the site by vehicle movements.
The objective of these plans is to control muddy water flowing, or earth slipping, onto neighbouring properties or the road. Muddy water is defined as being water with a total suspended solids (TSS) concentration of greater than 50mg/L. That is not very muddy!
Hill Sites are High-Risk Sites are considered to be at high risk for erosion, and therefore are meant to have a higher level of assessment and inspection, where there is a disturbed area greater than 1,000 m2, or 500 m2 and the proximity to a waterway is less than 20m, or 500 m2 and the slope is greater than 5 degrees. That means that all building sites on the Port Hills are classified as “high risk”.
Building Inspectors The CCC’s Building Inspectors are required to check that the sediment controls are in place at the time of the first inspection. For high-risk sites, this will be after the ESC measures are in place, but before any excavations or site clearance begins. For other sites, this will usually be at the foundation or slab inspection.
The measures are also meant to be checked at each further inspection. A building inspection could fail if necessary measures are not in place. A ‘notice to fix’ could also be issued if the inspector is not satisfied that the sediment controls are being maintained. This may require work to cease until the issue is resolved. In these days of building constraints from other pressures, it might be hoped that this one, being under the direct control of the builder, will not often be implemented.
How you can help The CCC building inspection team have been checking erosion and sediment controls for over a year now. However, old habits die hard and it will take some time for builders and developers to make these erosion controls an integral and continuously functioning part of their programme and not just some box-ticking exercise.
Everyone involved – builders, developers and inspectors – will need a hand to get on board with sediment control. We, the public, need to take it upon ourselves to report (via Snap, Send, Solve or the ECan Pollution Hotline) whenever we see sediment leaving a construction zone in a rain event. It’s easy, and it is necessary. We have to be the river’s eyes to see where sediment is leaving building sites.
It is in everyone’s best interest, and especially that of the river, that erosion and sediment control measures work well.