Matawii Water Storage Reservoir
Matawii Water Storage Reservoir was constructed by MAP for Te Tai Tokerau Water Trust, with the primary objective of supplying Kaikohe with water for irrigation, which will create sustainable employment opportunities in horticulture and agriculture for the surrounding regions. It will also be back up for clean, reliable drinking water
The reservoir, a zoned embankment structure, stands up to 24 meters high and stretches over 550 meters in length. Given its elevation and proximity to Kaikohe, it is classified as a High PIC reservoir, demanding the highest design, construction, and operational safety standards for the community’s welfare.
At full supply level, the reservoir has a storage capacity of 750,000 cubic meters. The water is sourced from a nearby river during floods and transferred to the reservoir, while two intake pipes facilitate water withdrawal as required.
To enhance the dam’s stability and minimize foundation seepage, curtain grouting has been implemented within the central valley of the main dam. Additionally, downstage grouting with packers has been used to reinforce the foundation further.
Matawii Dam features two free overflow spillways: a 12-meter-wide concrete primary spillway, designed to handle regular floods, and a 45-meter-wide auxiliary spillway that provides additional capacity to accommodate extreme floods.
During construction, the main culvert running through the dam was instrumental in stream diversion and flood bypass. It has since been sealed off with an intake structure housing two penstock gates, allowing for rapid dewatering of the reservoir during emergencies.
The construction process involved the removal of 25,000 cubic meters of fill from the dam foundation. Subsequently, 300 cubic meters of dental concrete were poured into the foundations, and approximately 100,000 cubic meters of fill were carefully placed in the dam from four different borrow sites, presenting various challenges due to over optimum water content and continuous wet weather conditions, with a challenging 4178mm of rainfall during the project.
Furthermore, 150 meters of concrete wave walls were meticulously placed on the dam crest, each poured on-site using steel forms.
Matawii Dam stands as a testament to engineering excellence, sustainability, and community empowerment, providing Kaikohe with essential water resources and fostering prosperity in the region through job creation and agricultural development.