Ohaaki Ngawha; Ohaaki Pool

Abstract

In its natural state, the temperature of the Ohaaki Pool was generally between 85 and 100"C, and the overflow rate was about 9 Us. Historic records show that at least one episode of cessation of flow followed by a temporarily increased flow (>23 Us) occurred. During test discharges of nearby wells (1967 - 1972), the flow rate decreased until overflow ceased, then the water level fell by at least 9.5 m. After the test, water level rose but the pool did not overflow again (intermittently) until 1981. Temperatures fell to about 70?C during the early part of the testing but later recovered to about 100"C, which was maintained except during brief discharge tests in the late 1970s. The chloride content remained near constant until 1980, after which time it varied as a result of input of bore water. After commissioning of the Ohaaki Power Station (1988-1989), the flow rate again decreased, and the water level fell. Remedial work has been undertaken to restore the flow of hot water to the Te Ohaaki o Ngatoroirangi Marae; this includes blocking vents in the base of the pool and flowing separated bore water through the pool.