Big capacity, small footprint infrastructure delivers for Kaiapoi stormwater project.
2.5 to 3.5 cumecs is, as Waimakariri Shovel Ready Delivery Manager Rob Kerr wryly puts it, “A lot of water.” But it’s what North East Kaiapoi’s McIntosh Drain needs to handle in a flood event.
The drain is a modified natural water catchment area servicing 1,500 hectares of largely rural land. Forming a long, narrow corridor between the Kaiapoi River and ancient sand dunes, it is prone to flooding.
Waimakariri District Council earmarked McIntosh Drain for development but had lacked the funds for the work. The launch of the Government’s Shovel Ready initiative changed that.
Execution of the McIntosh Drain project took around ten months. Commissioned in July, it is one of three recent stormwater management upgrades completed by Waimakariri District Council.
Rob Kerr says McIntosh Drain had quite specific challenges, and uncertainties. In addition to flood events, these included earthquake risk (Kaiapoi suffered badly in 2010), and, like other coastal and low-lying areas, climate change.
“The McIntosh Drain site is in a rural location beside a stop bank. The objective was to get water from one side of the stop bank to the other – particularly at high tide. It called for a different type of solution.”
Resilience was key.
“As things change, we as a council need to be able to change easily too. That’s really important.”
“We don’t know how quickly climate change is going to happen or the frequency of storm events. We do know the Council is going to have to be able to respond. We need to be adaptable and flexible.”
Prime Pump partnered with Kirk Roberts Consulting, and their pump supplier, Netherlands-based BBA Pumps to provide the Waimakariri District Council Shovel Ready projects team with a solution to address their needs, and those of the district.
Rather than a traditional below-ground pump station, the Council decided on a New Zealand first – a mobile ‘pad and pump’ set up.
Two high-volume, relocatable BBA BA500G diesel pumps are situated on a simple, 150mm thick, concrete pad. The future-proofed approach allows for a third pump if and when required. A control shed and diesel storage complete the set-up - significantly less infrastructure than for an underground pumping station.
Prime Pump Team Leader Hayden Powell says what makes the solution unique is that the large volume pumps can be easily disconnected and moved as required.
Powell says the BBA pumps can be lifted using a hiab and disassembled and reassembled inside of 12 hours.
“In addition, to flexibility, the ‘pad and pump’ approach provides a cost saving for the Council of close to 50% compared with an underground pumping station.”
Powell says the comparatively small amount of concrete used in the design helped reduce the project’s carbon footprint.
While having initially considered an underground option, Rob Kerr says there were limitations. “There was the lack of ability to relocate the pumps to other areas of flooding, and to change in the future.
“Having the pumps above ground also provides general ease of accessibility. “When pumps are underground, they’re a lot harder to fix, if something does go wrong.”
In the event of an earthquake, the underground pumping station could also have been at risk of damage – resulting in the need for costly repairs or replacement.
The set-ups can also suffer from inundation themselves. Powell says in Napier recently, pumps were needed to remove water and debris to gain access to the stormwater network to repair it.
In the early design stages, electric pumps were also in the mix. But running 11kv cables from 800-900 metres away would’ve resulted in a cost blow out. It also left the pumps reliant on the grid, often the first thing to go down in a major flood event or earthquake. “That helped sway our thinking,” Kerr says.
For the Council’s particular needs, Powell says it was a “no brainer” to go with diesel. “When you combine the fact that they’re only running 3-5 times a year with a significant reduction in in-ground infrastructure, the environmental impact is minimal.” The highly efficient pumps minimise fuel consumption and use a special, non-degenerating diesel fuel stored on site.
He had equal confidence in the pumps themselves. Fully-bunded, the robust pumps are used around the globe for flooding, sewage and groundwater transfer. Each is capable of pumping 1.25 cumecs.
With the sea close by, it was also important to have pumps that were suited to the saline environment to ensure longevity, performance, and durability. With corrosion-free hot dip galvanised canopies and corrosion-free composite door panels and powder coated plating the BBA pumps were fit for purpose.
“Prime Pump has worked closely with Netherlands-based BBA since 2007. Around 1/3rd of Holland is below sea level so they know how to make pumps!”
Their commitment went beyond simple supply. Prime Pump brought out a technician from Holland to make sure the pumps worked optimally, and to train the team.
“It was the perfect opportunity as we’re always looking to learn and improve,” said Powell.
Rob Kerr says the whole process went smoothly. “The pumps were delivered when promised and on budget. We’re pretty happy. Prime Pump did what they promised.”
Less than two weeks after commissioning the pump station had its first test. Heavy rainfalls triggered the operation of one of the pumps.
It passed with flying colours.