We conducted near-surface geophysical surveys in and around the Majes I agricultural development (60 km west of Arequipa, Peru), where the nexus of geology and agriculture has increased landslide activity along the Majes–Siguas River Valley. Through DC resistivity, transient electromagnetics (TEM), and seismic surveys, we refined the understanding of local geology, characterized the agricultural impact on the local water table, and updated landslide modeling to help inform discussions on landslide mitigation strategies at Majes I and landslide prevention at the planned Majes II site. At the Majes I development, we identified an increase in water table and water saturation due to irrigation. At the planned Majes II site, which shares similar geology to Majes I, we interpret the regional water table that has yet to be affected by significant human development. We integrated these results into updated landslide modeling. Our modeling for Majes I suggests stable conditions prior to irrigation; as the water table rose from irrigation, landsliding began and evolved as a retrogressive failure that is now focused along the headscarp near critical infrastructure including the Carretera Panamericana (Pan-American Highway). Majes II is currently stable and irrigation management, such as drip versus flood techniques, must be supported. Soil ameliorants such as polymers and/or biochar should be encouraged to hold water near the roots to reduce the risk of landslide initiation. Combined this work shows the value of integrated hydrological and geophysical research for landslide management and optimized irrigation.
Insufficient access to safe drinking water is one of the most challenging global humanitarian issues. The development of low-cost microcontrollers and the widespread availability of cheap electronics components raise the possibility of developing and using low-cost geophysical instrumentation with open-source designs and software solutions to circumvent geophysical instrumentation capital cost issues. To these ends, we alter an existing low-cost DC resistivity meter design and develop an optional modular Raspberry Pi data-logging system to improve the unit's functionality, usability and to ensure data integrity. Numerical modeling and physical testing demonstrates that the system is more robust than previously published low-cost designs and works in a more diverse range of geological scenarios - especially conductive environments. Our instrument was tested in a Geoscientists Without Borders (GWB) project jointly run between researchers from Colorado School of Mines (CSM) and Universit矤'Abomey-Calavi (UAC), Cotonou, Benin. A key project component involved CSM and UAC students constructing and validating two low-cost DC resistivity meters and then using these instruments for fieldwork aimed at better characterizing and monitoring the health of a local aquifer used as a groundwater source for communities in the Cotonou region. The low-cost instruments were successfully used alongside a commercial resistivity meter to acquire data for 2D inversion of aquifer hydrostratigraphy , indicating the presence of a clay-sand contact. The cost of the redesigned instrument and data logger respectively are $177 and $108 (in 2021 USD) with future cost reductions possible, which are fractions of the price of commercial resistivity meters.
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