Stormwater, erosion and sediment control

Stormwater can be defined as rainwater which has landed either on the ground, a roof or other impervious area. State highways intercept and affect natural waterways and drainage patterns. The routes and alignments selected as well as state highway infrastructure used to control drainage patterns, increase erosion rates, and potentially increase flood flows. During construction and maintenance activities which involve earthworks, rainwater hitting the ground can cause erosion and generate sediment laden runoff.

Vehicles on state highways shed waste products from braking (copper), tyres (zinc) and exhaust emissions (products of incomplete combustion). During the regular operation and maintenance of roads, road runoff (storm water) carries these waste products to receiving land and watercourses. The quality of the water can be decreased by high turbidity and dissolved substances that are environmentally harmful. Run-off during construction, especially during major earthworks, can carry sediment which is then deposited in nearby watercourses.

Stormwater management overlaps with other technical disciplines and so needs to take into consideration engineering, water quality science, freshwater and riparian ecology, landscaping and cultural values.

Stormwater management practices are being used internationally to address stormwater quantity and quality concerns on highways. We have taken a proactive approach to minimising the adverse effects of our activities on receiving systems and are recognised as a national leader in the implementation of stormwater treatment practices. 

What we attempt to do with erosion and sediment control is to mitigate the negative impacts associated with land disturbing activities related to state highway construction. The Agency's role is to ensure careful planning and design to avoid, remedy or mitigate effects of soil erosion, sediment runoff and sediment deposition.

For further information contact environtment@nzta.govt.nz .