International: Use of phase-sensitive radar to monitor discharge and recharge of Moroccan aquifers

点击翻译按钮获取中文摘要

The motivation for the proposed study is the difficulty in managing water abstraction in the absence of good information about the degree of charge of aquifers, the growing consensus that groundwater recharge will diminish in arid and semiarid areas in sub-Saharan and western Africa, and the ever-increasing pressure on aquifers from increased abstraction.The aim of the proposed work is to determine the feasibility of using a NERC-developed instrument (ApRES) to aid the management of water resources in arid and semi-arid regions by allowing water-table depths to be monitored without recourse to boreholes. The challenge has both technical and societal aspects.The Autonomous phase-sensitive Radio Echo Sounder (ApRES) was jointly developed by the British Antarctic Survey and University College London to monitor the changing thickness of the floating portion of the Antarctic Ice Sheet. Lightweight, robust and relatively inexpensive, ApRES was designed to be deployed on an ice sheet for a year or more, withstanding the harsh conditions of the Antarctic winter.The problem of detecting the changing depth of the base of an ice sheet is essentially the same as that of detecting the depth of the water table in an otherwise dry environment. ApRES can therefore potentially be used as relatively inexpensive (compared with boreholes) method for monitoring the depth of the water table, providing a tool to assist in the management of water abstraction.Our choice of country for this study is Morocco. Morocco boasts a useful range of soil types, climatic conditions, and water table depths. Its many boreholes provide the necessary ground truth by offering an independent measure of the depth of the water table.A short pilot study was undertaken in Morocco in March 2017, funded through a NERC ODA Innovation pump-prime grant, and locally facilitated by the partners on the present proposal. The results were promising. Several sites were visited, with varying water table depths, primarily to find a suitable location for a multi-hour deployment. The instrument was able to detect the water table at most of the sites and was able to monitor its changing depth over a 6-hour (overnight) trial.The promising results from the pilot now prompts the next step - a comprehensive study in Morocco, alongside our Moroccan partners, to determine more precisely the envelope of capability of the instrument, and to reduce impediments to its use in monitoring groundwater depth: ease of use, robustness, cost. In the proposed study visits to different field sites in Morocco will allow the utility of ApRES to be assessed for a range of soil types, soil moisture contents, water table depths, local conditions (urban/rural) and seasons (wet/dry). The instrument and antennas will be scrutinised to see where costs can be reduced and what hardening will be needed to deal with the non-polar conditions. Finally, the data-processing steps will be rationalised such that a non-expert could carry them out.The societal aspect of the challenge, how to ensure uptake of any new technique, will be addressed in two ways. An independently resourced, but parallel study that we have instigated (to be delivered by Development i-Teams in October and November 2017) will investigate how having the ability to monitor the discharge and recharge of aquifers in real time can be used to improve the sustainability of groundwater exploitation in water-scarce regions. Second, our project partners in Morocco will prepare an implementation pathways document to define how the technology could be rolled out in Morocco. Should the project that we are proposing here confirm the technical feasibility of using ApRES for ground water monitoring in arid regions, the outcomes of the i-Teams study and the implementation pathways report will put us in a strong position to take the project forward to the next level of application, both within Morocco and beyond.