Design and fabrication of a lysimeter for groundwater recharge measurement under arable land-use

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Lovett, A.P.; Cook, R. 2017 Design and fabrication of a lysimeter for groundwater recharge measurement under arable land-use. Lower Hutt, N.Z.: GNS Science. GNS Science report 2016/69 11 p.; doi: 10.21420/G2MS3R

Abstract: More than twenty-two groundwater recharge monitoring sites have been installed in New Zealand, and are currently operating in five regions (Canterbury, Bay of Plenty, Hawke’s Bay, Southland, and Auckland). As of 2016, all currently-operating monitoring sites were located on pastoral land. Although understanding recharge through arable land-use is an important component of land-use management, there was little knowledge of the rates of recharge since existing lysimeter design was unsuitable for arable land-use. The standard lysimeter design (e.g., 500 mm wide and 700 mm deep, and constructed of steel casing) was unsuitable for installation under cultivated land since the steel casing would impede mechanical cultivation. The need for a lysimeter to measure recharge under arable land-use was identified by scientists and technical specialists at a National Lysimeter Workshop in 2014, and further explored in a literature review in 2015. Subsequently, this project was established and equally co-funded between GNS Science and Hawke’s Bay Regional Council, with objectives of: 1) facilitate an arable lysimeter workshop to review the previous Wakanui trial, identify prototype designs for the arable lysimeter, and select the best design based on practicality and maintenance of soil column structure; and 2) fabricate the prototype lysimeter for proof-of-concept. Details of the arable lysimeter workshop and fabrication are provided in this report. Overall, six designs for an arable lysimeter were put forward during group discussion at the workshop. A concept for each design was discussed, and each design was evaluated regarding practicality, cost-effectiveness, maintenance of soil structure, and the perceived ability of the lysimeter to accurately measure recharge under arable land-use. A modified lysimeter with upper plastic casing was selected as the best option for fabrication and trial. A prototype design for the arable lysimeter was developed, based on the standard lysimeter with two modifications (e.g., increased depth to 100 mm; and an upper ring constructed of polyethylene). Three lysimeters were fabricated by Lincoln Agritech. In a subsequent project, the lysimeters were installed at a groundwater recharge monitoring site in Otane, Hawke’s Bay, which was commissioned in early 2017. (auth)