Active tectonics, geomorphology and groundwater recharge to the Waipara - Kowai Zone, North Canterbury

• Main Author: Dodson, Matthew Michael
• Language: en
• Published: University of Canterbury. Geological Sciences 2009
• Subjects: Hydrogeology; Geomorphology; Active tectonics; North Canterbury; Waipara
• Online Access: http://hdl.handle.net/10092/3193

The Waipara – Kowai groundwater allocation zones (referred to as zones) are located 50 kilometers north of Christchurch. Land use in the Waipara zone has evolved from dry land farming towards horticultural and irrigated pastoral farming, and as such the demand for groundwater resources has increased significantly. Recent 14C age dating has shown that deep wells tap >1000 years old water, raising concerns about possible resource mining. The Kowai groundwater allocation zone has had minimal regional hydrogeological investigations and previously little is known about the groundwater resources here. The Waipara – Kowai groundwater allocation zones are located near obliquely convergent plate margin and the Porters Pass Fault System. Recent (early Quaternary) deformation has been noted by workers along margins and associated with emerging structures within basins. These emerging faults and folds within the basin are acting as hydrological barriers, hindering the passage of groundwater within the basin. A geomorphic map was constructed for this study based on existing soils maps, limited field soil surveys and morphometric analysis. Nine geomorphic surfaces are described, with inferred ages of modern to >73 ka. The geomorphic investigation revealed that the Kowai groundwater allocation zone surface is stepped, with increasing thickness of loess up gradient on the downlands. Near the coast there is intercalated terrestrial and marine sediments, to the west overlying the Kowai Formation are small alluvial fans. In the Waipara Basin the Waipara fan dominates the central portion of the basin, with smaller fluvial and alluvial fans building out from the margins. Groundwater recharge was investigated using chemical, isotopic, water level observations and a simple water balance. It was found that in the Kowai zone the major recharge sources were the rainfall, losses from the rivers and streams. The southern region of the Waipara zone is recharged by rainfall with small contributions from the Kowai River (North Branch). In the South region of the Waipara Basin groundwater recharge is derived from rainfall and losses from streams. The groundwater systems are conceptualized as being topographically driven, with slope – basin floors interactions being an important source of groundwater recharge.