Ruakākā Solar Farm (NZ)

Engineering challenges + innovation

The team balanced flooding and consent constraints, civil earthworks, geometric design and acid sulfate soil conditions to meet competing project requirements.

Varying ground conditions and flood hazards across the three sites required two Smart Transformer Station foundation solutions: driven steel piles with elevated platforms, and shallow foundations with plinths, geogrid-reinforced gravel rafts and preloading where needed.

Each site had very different flooding implications, and catchments/downstream impacts.

Fish passage requirements

The main drains on Site 1 and Site 3 contain several native fish species including shortfin eels and īnanga. The design was required to meet consented flooding requirements while also ensuring unobstructed passage for native fish species through the drains. On Site 1 and 3, this required solutions such as bunds placed around the site to attenuate stormwater without preventing the movement of fish in the main channel.

Acid sulfate soils

Site 3 is underlain by naturally occurring acid sulfate soils, and careful management is necessary to reduce corrosion risks for infrastructure. Stormwater elements had to be designed without any concrete, requiring polyethylene pipe and boulder-filled banks in place of traditional culvert and wingwall designs. Dewatering has been avoided during the construction of other structures.

Flood attenuation control

The design required a delicate balance between holding back enough water on the sites to prevent increases in flood effects downstream, while minimising excessive flood levels on site. Variable sizing was used for stormwater outlets on Site 2 to provide control of stormwater discharge rates for each design flood event.

River floodplain and tidal influence

Site 3 is located within the floodplain of the Ruakākā River with tailwater conditions heavily influenced by the tidal estuary immediately downstream. Careful design of infrastructure was required on Site 3 to prevent alteration of the natural floodplain leading to increased flood severity off site. Hydrological inputs to the flood model were developed in conjunction with Tonkin + Taylor’s coastal team to ensure tidal interactions were accurately assessed and allowed for in design.

Soft soils

Soft Tauranga Groups silts are present at the surface in Site 2 and 3 of the development. These soils are settlement prone and the foundation designs across these sites have had to consider this risk. Geogrid reinforced gravel rafts and preloading have been utilised where possible while piling below soft soils was required in some locations.

Liquefaction

The sands underlying the development are predicted to liquefy during a large earthquake. The occurrence of liquefaction can lead to settlement and loss of foundation capacity. Tonkin + Taylor assessed the liquefaction risk using the geotechnical investigation data that included Cone Penetration Tests (CPT) completed throughout the development area.  With this, foundation solutions for structures were tailored to the ground conditions and the principal’s requirements.

Find out more about the project here Ruakākā Energy Park | Meridian Energy