By Tiejun Wang
Groundwater is one of the most important natural resources in New Zealand, which by one estimate accounts for about 80% of the water present at any one time across and beneath the country. According to a 2010 review of water allocation , the number of groundwater consents accounts for 68% of all national consents. In terms of the allocated volume for consumptive use, groundwater allocation is about 12% (3.3Ã—109 m3/year; equivalent to 6% of the water in Lake Taupo) of the total annual allocation (26.9Ã—109 m3/year). Over the last decade, the demands for groundwater have increased dramatically in New Zealand, which is manifested in the volume of groundwater allocated and the percentage of groundwater allocation in the total allocation . Most of the groundwater resources have been allocated to irrigation purposes in NZ. For example, in the Canterbury region alone, 55% of the agricultural lands are irrigated by groundwater.
Compared to surface water, groundwater possesses some unique features. For example, groundwater is typically a more reliable resource, particularly in dry regions, and sometime has higher quality (e.g., temperature and minerals). My hometown (Qing Dao) is famous among other things for its beer (Tsingtao beer). The beer is made of groundwater that is brought up to the surface by springs that are rich in minerals. In fact, it’s the number one branded consumer product exported from China, which you can occasionally find here in NZ. However, the growing demand for groundwater resources in China has raised concerns about the sustainability of both agriculture and the economy. The overdraft of groundwater not only has economic consequences, but also may pose serious threats to the environment.
To start off, dropping groundwater tables, for example due to pumping, can significantly increase the cost of irrigation because the energy required to bring groundwater up to the surface increases with the depth to the groundwater. Secondly, there are numerous cases regarding the adverse impacts of overdraft of groundwater on the environment, which we should learn from. To name one example, the excessive pumping of groundwater, particularly in arid and semi-arid regions, can produce massive depression cones (e.g., in the North China Plain, more than 20 depression cones stretch over 50,000 km2), which can cause the Earth’s surface to subside just like earthquakes (most of the time it is an irreversible process!!), and intensify groundwater contamination.
The water problems that New Zealand is facing right now require us as hydrologists to take immediate actions on how to sustainably manage our water resources. As Ross mentioned earlier, groundwater and surface water are tightly coupled. Therefore, in order to more effectively manage water resources, hydrologists from different sub-disciplines (e.g., surface water hydrology, groundwater hydrology, and ecohydrology) should work together to tackle the problems. This is one of the major goals for the Waterscape project.