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 85 degrees C and 100 degrees C, and the overflow rate was about 9 l/s. Duri ng test discharges of nearby wells (1967-1972), the flow rate decreased unt il overflow ceased, then the water level fell by at least 9.5 m. After the tests, the water level rose but the pool did not overflow again (intermitte ntly) until 1981. Temperatures fell to about 70 degrees C during the early part of the testing but later recovered to about 100 degrees C, which was m aintained except during brief discharge tests in the late 1970s. The chlori de content remained near constant until 1980, after which it varied as a re sult of input of bore water. After commissioning of the Ohaaki power statio n (1988-1989), the flow rate again decreased and the water level fell. Reme dial work has been undertaken to restore the flow of hot water; this includ es blocking vents in the base of the pool and flowing separated bore water through the pool. (C) 2000 CNR. Published by Elsevier Science Ltd. All righ ts reserved.