Marlborough District Council – Caseys Creek Upgrade

Caseys Creek Upgrade – Separable Portion A

CLIENT: Marlborough District Council.

CONTRACT VALUE: $1.1m

CONTRACT PERIOD: December 2018 – May 2019

SCOPE

Upgrade of 750 meters of the spring-fed creek. Re-grading and improving the hydraulic capacity of creek. Placing of rock armouring/riprap. Construction of 170m of Timber Retaining Wall.  Construction of 4 new box culvert crossings and 7 new DN1800 concrete pipe culvert crossings and associated headwalls, rails and timber fences. Landscaping and reinstatement of a roadside berm.

TECHNICAL DIFFICULTY

Marlborough District Council (MDC) contracted Grant Hood Contracting to undertake Separable Portion A of the upgrade to Casey Creek. This is the first of 2 separable portions aimed at increasing the stormwater capacity of this spring-fed waterway to cope with the expected run-off from a subdivision development currently underway further along Old Renwick Road.

Upstream was a rural reach, from chainage 0 to 380. The lower reach, an urban section from chainage 380 through to chainage 740. Works in the rural reach involved minor re-shaping of the banks, the replacement of 2 pipe culverts with box culverts, rock rip-rap protection along both banks, and landscape planting.

Works in the urban reach required the creek to be dammed, a fish recovery and relocation exercise completed, then de-watering. The creek through this section was re-profiled and graded. Four culverts were replaced with box culverts, and another 5 replaced with 1800 diameter concrete pipes. 170m of piled timber retaining wall was also constructed.

A considerable dewatering exercise was required to construct the 1.2m deep raft foundations for the culvert crossings. This involved the use of Envirosieve Filter bags and pumping to open grassland some 780m away using both 6-inch and 8-inch pumps.

A significant effort was made to speed up each culvert installation to minimise the length of time dewatering was required. Days and weeks of planning each culvert installation meant some culverts were demolished and replaced in a day, while also negotiating under live power lines and reducing Old Renwick Road to single lane traffic.

Grant Hood Contracting has since been awarded Caseys Creek Upgrade—Separable Portion B, as a direct result of the quality outcomes from separable portion A.