Sustainable groundwater resources, Heretaunga Plains, Hawke's Bay, New Zealand

The Heretaunga Plains, Hawke's Bay, New Zealand, is underlain by Quaternary fluvial, estuarine-lagoonal, and marine deposits infilling a subsiding syn cline. Within the depositional sequence, river channel gravels form one of the most important aquifer systems in New Zealand. An interconnected unconf ined-confined aquifer system contains groundwater recharged from the Ngarur oro River bed at the inland margin of the plain, 20 km from the coast. At t he coast. gravel aquifers extend to a depth of 250 m. In 1993-95, 66 Mm(3) of high quality groundwater was abstracted for city and rural water supply, agriculture, industry, and horticulture. Use of groundwater, particularly for irrigation, has increased in the last 5 years. Concern as to the sustai nability of the groundwater resource led to a research programme (1991-96). This paper presents the results and recommends specific monitoring and res earch work to refine the groundwater balance, and define and maintain the s ustainable yield of the aquifer system. Three critical management factors a re identified. These are (1) to ensure maintenance of consistent, unimpeded groundwater recharge from the Ngaruroro River; (2) to specifically monitor groundwater levels and quality at the margins of the aquifer system, where transmissivity is <5000 m(2)/d and summer groundwater levels indicate that abstraction exceeds recharge; (3) to review groundwater-quality programs t o ensure that areas where contamination vulnerability is identified as bein g highest are covered by regular monitoring.