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Hydrogeology of the Takaka Valley

By Jane Elizabeth Edgar

Abstract

The Takaka Valley, in Golden Bay, New Zealand, is renowned as the site of the freshwater spring system known as Waikoropupu Springs, and is also known for its marble karst aquifer. In this project the groundwater resources of the Takaka Valley have been described and evaluated in an integrated analysis, which uses the existing database records supplemented with specific hydrogeological investigations. The intention is to provide information pertinent to the development, management, and long-term protection of the groundwater resources in the region. The principal aquifer in the Takaka Valley is the karstic Waikoropupu Arthur Marble, referred to as W AM, with primary discharge site at Waikoropupu Springs. The minor karst aquifer is the East Takaka-Motupipi Limestone Aquifer, referred to as ETML. Locally important shallow aquifers are found in the Quaternary gravel deposits which floor the Takaka Valley. These are the Takaka Township Gravel Aquifer and the East Takaka Gravel Aquifer, and are referred to as TTG and ETG. The complex recharge system of the Waikoropupu Arthur Marble Aquifer is dominated by input via the Takaka river sinks. Other important sources include contributions from tributary stream sinks, the Waingaro river sinks, and allogenic and autogenic diffuse input. The Cobb power scheme, situated on the Takaka River upstream of the major recharge reach, can increase the recharge input into the Waikoropupu Arthur Marble Aquifer with its generation regime, as occurred in 1995-1997. The primary discharge sites of the Waikoropupu Arthur Marble Aquifer are the Waikoropupu Springs. This is a complex arrangement of three subsystems envisaged as a vertical hierarchy, with complex interrelations. The geological and hydraulic controls are complex, as is the water chemistry. The existence of a substantial offshore component of Waikoropupu Arthur Marble Aquifer discharge is refuted. A water balance conducted for the main aquifer shows minimal storage fluctuations. The offshore discharge is not supported by hydrographic analysis, and no affirmative geologic or water chemical information can be offered. The East Takaka-Motupipi Limestone Aquifer is the minor aquifer in the Takaka Valley and is an important domestic and agricultural supply. The total aquifer extent is subdivided into three sub-aquifers based on interpretation of the structural setting. More detailed hydrogeological subdivision is required before a water balance for the sub-aquifers can be attempted. The recharge system of the entire aquifer is comprised of both allogenic/autogenic, and concentrate/diffuse inputs. Discharge zones are on a small scale in comparison to the Waikoropupu Arthur Marble Aquifer. Water chemistry typifies that of a karstic limestone aquifer. The Takaka Township and East Takaka Gravel Aquifers are the two Quarternary gravel aquifers of the Takaka Valley studied in this project. They are relied on for domestic and agricultural supply, and both are recharged by diffuse rainfall and river inputs. Water chemical analysis has deemed both supplies suitable for drinking water purposes, but a particular zone in the Takaka Township has been identified with elevated levels of most major constituents. At the present time, adequate quantitative and qualitative monitoring of the karst and gravel aquifers is not being undertaken. Installation of water level recorders in the gravel aquifers and implementation of further sites in both karst aquifers are recommended. Present qualitative sampling strategies need to be reassessed for all the fore-mentioned aquifers, and specific monitoring in terms of recharge and discharge components requires attention. The preservation and protection of the water resources of the Takaka Catchment, in particular of the Waikoropupu Arthur Marble Aquifer, can be an important focus for the future benefit of all

Publisher: University of Canterbury
Year: 1998
OAI identifier: oai:ir.canterbury.ac.nz:10092/12444
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