Addressing sedimentation and pollution

Coastal land development has had a significant impact on the quality of coastal waters through increasing sediment and pollutants flowing into the ocean. Early Māori burnt areas of coastal forest and established agriculture around coastal plains. Sediment cores demonstrate that this caused increased amounts of silt and mud to accumulate in estuaries and harbours. Further vegetation clearance, significant changes in land use and rapid modification of coastlines following European settlement, have exponentially increased soil erosion and sediment accumulation rates in many New Zealand estuaries.

In the mid-1900s a large proportion of sewage was being discharged untreated into the sea or waterways in New Zealand. Most of what was treated, only received primary treatment, which simply involved removing solids before discharge. By the 1970s untreated discharges had almost halved. In 1991 the RMA was enacted resulting in tighter controls on point source discharges, but diffuse discharges still remain a challenge.

d094b966-e058-4e84-a430-20aca8728666  There is likely to be continued deterioration of coastal water quality, even without new development, if remedial action is not taken. This is because the legacy of past activities has resulted in the accumulation of pollutants and nutrients in soils. Sediment often still contains materials now banned, such as DDT, tin from antifouling and lead from petrol. Coastal works that involve disturbing these sediments can redistribute the pollutants.

Vision

Issues

New Zealand Coastal Policy Statement

Enhancement of water quality

Managing sedimentation

Reducing the discharge of contaminants

Best Practice Planning Elements

Regional and district plans can include the following in order to address sedimentation and pollution:

(1) Undertake a wide assessment of sedimentation

(2) Control land-based activities that can generate increased levels of sediment and pollution

(3) Control generation and disposal of stormwater and sewage

(4) Control generation of sediment and pollution from marine-based activities

(5) Support the use of other methods and tools

Best Practice Design Elements

The level of attention to sedimentation and other water-borne pollutants should be influenced by the significance of likely effects, including consideration of such matters as the scale of the project and sensitivity of the receiving environment. Development designed to address sedimentation and pollution can include the following elements:

(1) Incorporate sediment retention mechanisms into earthworks

(2) Forward planning and use of cutting edge technologies

(3) Reduce runoff from urban activities

(4) Reduce runoff from agricultural activities

(5) Reduce runoff from forestry activities

  1. Parliamentary Commissioner for the Environment, 2012, Water quality in New Zealand: Understanding the science, Wellington, available at www.pce.govt.nz, at 20

  2. Section 15

  3. http://www.mfe.govt.nz/publications/water/anzecc-waterquality-guide-02/index.html

  4. Ministry for the Environment, 1997, The state of New Zealand’s environment 1997, Ministry for the Environment, GP Publications, Wellington

  5. Board of Inquiry, 2009, Proposed New Zealand Coastal Policy Statement (2008), Board of Inquiry report and recommendations, volume 1: Findings, recommendations and recommended NZCPS (2009), Wellington, at 9

  6. http://www.mahurangi.org.nz/Action-Plan/PDF/Mahurangi-Action-Plan.pdf

Last updated at 4:32PM on February 2, 2018