Project Overview
Weir was engaged by the designers of Watercare’s Māngere WWTP South West Interceptor Sewer By-pass System (i.e., Bellcon Ltd and ACH Consulting Ltd) to provide a hydraulic review of the proposed pump station (6 pumps in a 5N+1 arrangement, with a duty range of 0.28 to 1.90 m3/s) and risingmain (twin DN800 PE100 pipes). The by-pass system is a temporarily solution being implemented during the replacement of a failings section of the South Western Interceptor (1650NB concrete sewer at the Māngere WWTP).
The review comprised of four key parts, namely:
- CFD modelling of the pump sump(undertaken by our specialist modelling consultant, Submergent)
- Hydraulic transient analysis
- Review of general hydraulic performance of rising mains and pump station
- Review of potential impacts of connecting the proposed by-pass into the diversion and confluence chambers located upstream of the Māngere WWTP headworks
The review confirmed the proposed pump station and risingmain design, including connection into the existing diversion chamber, to be technically sound but recommended several enhancements to optimise the hydraulic efficiency and durability of the system including pumps (noting Watercare’s intention to reuse the pumps in other future ventures). Recommendations included the specification of appropriate two-way air valves in the pipelines, an L-shaped baffle at the inlet chamber, guide vanes in the pump sump and amendments to benching details to minimize sedimentation in low velocity zones within the pump station.
