Hereford Heights was a 90-lot greenfield subdivision on 6.95 Ha in Marton, adjacent to Folly Stream. The stream has a history of overtopping during storm events, so Horizons Regional Council required a 200-year flood design standard - stricter than the usual 100-year requirement. Every floor level on all 90 lots had to be set above that 200-year flood level.
A key issue was that the regional council's flood data used a different vertical datum (WVD1953) to the subdivision survey (NZVD2016). The difference at Marton is 0.543 m. If not reconciled correctly, every floor level on the site would be wrong. Mid-construction, a primary survey mark was destroyed by an unrelated roading project, requiring all affected floor levels to be recalculated and reissued.
Flood modelling established the 200-year flood extents along Folly Stream, and floor levels for all 90 lots were set with the datum conversion applied throughout. A detention pond was designed to ensure post-development stormwater flows did not exceed pre-development rates at the downstream boundary.
The full infrastructure - roads, stormwater, wastewater, and water supply - was designed to NZS 4404:2010 and drawn in Civil 3D. The 3D model was used by GPS-controlled machinery on site. S224c certification was delivered across three stages, with as-built surveys, producer statements, and council sign-off for each.
Full 3D design of all roads and pipe networks for GPS-controlled construction. Floor level engineering for all 90 lots to a 200-year flood standard, with datum reconciliation between two vertical datums. Detention pond design for stormwater neutrality. Construction supervision, as-built surveys, and S224c certification across three stages. The full package was accepted by Rangitikei DC and Horizons Regional Council, and titles were issued.
