Impacts of development on a natural thermal feature and their mitigation — Ohaaki Pool, New Zealand

In its natural state, the temperature of Ohaaki Pool was generally between 858C and 1008C, and the over¯ow rate was about 9 l/s. During test discharges of nearby wells (1967± 1972), the ¯ow rate decreased until over¯ow ceased, then the water level fell by at least 9.5 m. After the tests, the water level rose but the pool did not over¯ow again (intermittently) until 1981. Temperatures fell to about 708C during the early part of the testing but later recovered to about 1008C, which was maintained except during brief discharge tests in the late 1970s. The chloride content remained near constant until 1980, after which it varied as a result of input of bore water. After commissioning of the Ohaaki power station (1988± 1989), the ¯ow rate again decreased and the water level fell. Remedial work has been undertaken to restore the ¯ow of hot water; this includes blocking vents in the base of the pool and ¯owing separated bore water through the pool. 7 2000 CNR. Published by Elsevier Science Ltd. All rights reserved.