Investigation of groundwater-surface water interaction in the Te Arai River, Gisborne, using radon-222 and concurrent stream flow gauging

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Martindale, H.; van der Raaij, R.W. 2018 Investigation of groundwater-surface water interaction in the Te Arai River, Gisborne, using radon-222 and concurrent stream flow gauging. Lower Hutt, N.Z.: GNS Science. GNS Science report 2018/13. 27 p.; doi: 10.21420/G2SD24

Abstract: Understanding of groundwater - surface water (GW-SW) interaction processes is integral for comprehending the hydrological characteristics of a catchment. Knowledge of the relationship between surface- and ground-water is required for effective management of water resources, such as setting of minimum flow and water allocation limits. To investigate GW-SW interaction processes, a combined approach of using radon-222 and concurrent stream flow gauging can be used. This report details a study commissioned by Gisborne District Council to assist in planning and interpreting a radon and flow gauging survey in order to investigate GW-SW interaction processes along a 20 km reach of the Te Arai River, Poverty Bay. The study identified that groundwater discharge occurs along a significant proportion of the 20 km reach. However, in at least two locations the concurrent stream flow gauging appeared to provide contradictory results to radon. This is most likely caused by surface water abstraction for horticultural/agricultural use or parafluvial exchange. (auth)