Sediment, the matter that settles to the bottom of a liquid, occurs naturally during the process of erosion in the form of clay, dirt and sand. These are natural substances – so what’s the problem?
Sediment contained in runoff can have significant effects on aquatic environments. If sediment levels get too high, they can disrupt ecosystems and kill mahinga kai. Excess sediments can cause damage by blocking light that allows algae to grow, harming fish gills, filling up important habitats, and stopping fish from seeing well enough to move around or feed.
To address these potential negative outcomes, Council’s have developed sediment controls, which aim to eliminate or minimise the amount of sediment entering stormwater drains, streams and the sea. For this reason, sediment needs to be considered in any development project, including those where resource consent is needed. There are several critical factors to consider.
Forward planning is key: before you start works think about timing large scale ground disturbance for dry weather, check where any run off is likely to go, and identify receiving environments such as kerb channels, stormwater drains and natural water bodies. You will also need to make sure the person responsible for ensuring environmental practices and controls has followed and implemented these prior to starting works.
Use of environmental practices and controls: it’s a good idea to retain existing vegetation wherever possible, as grass and shrubs do an excellent job of catching sediment. Where possible, you can also minimise the area of earth exposed by staging works over smaller areas, removing soil from the site and rehabilitating the disturbed area as soon as possible.
Erosion controls: you may be required to identify potential environmental risks and prepare a Compliance Management Plan. In this case a range of erosion controls can be used to manage sediment runoff, including diverting water using sandbags or earth bunds, keeping stockpiled material well away from kerb channels and overland flow paths and keeping it well covered.
Sediment controls: depending on the scale or your earthworks, these may include the installation of stormwater catchpit protection measures such as filter bags, silt fences and filter socks.
Monitoring and maintenance: it’s important that you regularly inspect the site to make sure that practices and environmental controls are working as required. Keep the work site tidy and clean, and clear out sediment control measures before they are 50% full, so that sediment caught in them doesn’t become resuspended when it rains.
Finally, it’s important to keep an eye on the weather and have a plan to respond should your sediment control measures be swamped or blown-away.
See Auckland Council’s Best Management Practice Sediment and dust management sheet here. If you want further advice on managing sediment during your development or assistance preparing a Compliance Management Plan or designing a stormwater mitigation control, we have a network of highly experienced engineers and project managers that we can refer you to. In Auckland, many sites are now affected by a Stormwater Management Area Overlay (SMAF), and if your site is within an area affected by flooding hazards, overland flow paths or other environmental hazards you will need to carefully consider your site management options as this could affect any resource consent application. For any questions on how this impact on resource consent requirements, please get in contact with our team.
Tracy Roe is a Planner with an M.Sc. in Resource Management.
Tracy has worked assisting Senior Planners with the preparation and lodgement of resource consent applications, as well as planning. She also provided support in client liaison, contractor engagement and general communications.
As with all our blogs, the information detailed here is general in nature and meant as a preliminary guide only. This should not be substituted for your own investigations or use of your own professional’s. Planning Plus is not liable for any errors or omissions.