New Zealand: Erosion Control on Expressway Construction Project

After more than two days of heavy rain during the IECA’s (International Erosion Control Association) Australasian Conference in July, the skies in Hamilton, New Zealand cleared just in time.  For the day following our conference, the organizers had scheduled a field trip to the TeRapa Section of the Waikato Expressway Construction Project.  It was a real treat to be out on a large highway project before it was open to traffic.

This project will enable highway traffic between New Zealand’s largest city, Auckland, and the central and southern parts of the North Island to by-pass traffic congestion in the city of Hamilton.  Work has been underway for two years on the NZ$150 million (US$120 million) TeRapa Section of the project which involves 10.5km (6.5 miles) of “motorway” (divided, limited access highway) and an equal length of connecting roads.  The contractor, Fletcher Construction (headquartered in Auckland) is expected to complete the work six months early and has won an erosion and sediment control award for the project two years in a row.

Our tour was by bus starting from the south end and heading north with several stops to observe various erosion and sediment control situations.  Because of two days of heavy rains preceding our visit, the relatively flat, boggy local topography was a mess of ponding but the BMPs (best management practices) appeared to be doing a good job as no off-site erosion or sedimentation was observed.  We saw examples of sediment basins, swales with vegetation plantings, mulching, erosion control mats, hydromulching, and a major river crossing.  Fletcher’s Construction Manager told us about several of the environmental challenges they were dealing with including areas of protected bat habitat, farmland protection, alligator weed (a noxious species), protection of fish at stream crossings (especially the Waikato River), and poorly drained peat areas where fill was necessary prior to construction.  

Following are some photos of the highlights of our visit:



Sediment pond water is very silty but effluent is relatively clear.
Perforated pipe skims water from top of pond.



Revegetation using erosion control blankets. IECA Australasian President, Michael Francombe,
pointed out to me that the downhill blanket mistakenly overlaps the uphill one.

Good environmentally-related signage was observed in the project area.

Conference attendees observe work at the Waikato River crossing.

Dewatering and use of sheet pilings has been necessary at the Waikato River crossing.

Hydromulching a slope above the Waikato River.

Construction has dealt with organic peat soil areas with a naturally high water table