GO WITH THE FLOW: MAPPING RECHARGE ZONES OF PERCHED SPRINGS ON BANKS PENINSULA, NEW ZEALAND

Fresh, potable water is a highly valued resource. The volcanic landmass of Banks Peninsula, New Zealand is home to thousands of people in small valley and harbour confined communities, sourcing drinking water from perched springs. These spring systems are relative understudied with current management plans reflecting this lack of knowledge. This study starts addressing this knowledge gap by mapping springs and understanding flow and recharge mechanisms to inform better management practices in volcanic terrain. This study analyses QuickBird satellite images as a remote sensing tool to map springs in the south-eastern quarter of Banks Peninsula. Springs were identified primarily with the naked eye, due to distinctive spring morphology and vegetation. Spring identification was further supported by Normalized Difference Vegetative Index (NDVI) analysis, calculated and applied to the images using Geographic Information System (GIS) software. > 148 springs were identified in the southeast quarter of Banks Peninsula. In mapping springs, a bimodal distribution is evident, with springs clustered below 300m elevation and others at higher elevation >400m in upper valley regions and erosional crater rim. We suggest that spring locality is controlled by lava flow dip and stratigraphy, and where lava flows outcrop / intersect hillslopes. The relative lack of springs between 300 and 400m is probably a result of a lack of higher level recharge and infiltration, with fluid flow directed into the lower elevation spring zone. This is significant as it provides links between recharge, aquifer (permeable / impermeable zones), and springs. In understanding the linkage between lava flow dip and spring horizons, a hypothetical reservoir / recharge zone can be defined. Mapping of the spring bearing lava flow, and extension of this up dip slope provides constraints on both the vertical and lateral spread of the recharge zone. For many of the upper valley springs, this recharge zone includes ridgelines, and slopes on the inner harbour and outer slopes of the crater rim. These recharge zones when overlaid with a typical catchment outline do not align, and highlight the necessity for spring specific guidelines when utilising springs as a potable water source, and have important implications for future land use and water management.