Conceptual models of aquifer systems can be refined and complemented with geophysical data, and they can assist in understanding hydrogeological properties such as groundwater storage capacity. This research attempts to use geoelectrical methods, Electrical Resistivity Tomography and Induced Polarization parameters, for mapping the subsurface in alluvial fans and to demonstrate its applicability; the Punata alluvial fan was used as a case study. The resistivity measurements proved to be a good tool for mapping the subsurface in the fan, especially when used in combination with Induced Polarization parameters (i.e., Normalized Chargeability). The Punata alluvial fan characterization indicated that the top part of the subsurface is composed of boulders in a matrix of finer particles and that the grain size decreases with depth; the electrical resistivity of these deposits ranged from 200 to 1000 Ωm, while the values of normalized chargeability were lower than 0.05 mS/m. The bottom of the aquifer system consisted of a layer with high clay content, and the resistivity ranged from 10 to 100 Ωm, while the normalized chargeability is higher than 0.07 mS/m. With the integration of these results and lithological information, a refined conceptual model is proposed; this model gives a more detailed description of the local aquifer system. It can be concluded that geoelectrical methods are useful for mapping aquifer systems in alluvial fans.

In Bolivia climate change and anthropogenic activities such as extensive agriculture, industries and urbanization have increased the groundwater demand and extraction, which is leading to severe stress on groundwater resources in several regions of Bolivia. This research aims to present an overview of different geophysical surveys performed in Valle Alto (central Bolivia), in particular in the Punata and Toco alluvial fans. The application of geophysics can have an implication in broadening the knowledge about local aquifers, which later might assist in proposing sustainable groundwater exploitation and protection plans. The geophysical results revealed two similar aquifer systems contained in unconsolidated sediments. A refinement of the hydrogeological conceptual models in terms of layering, lateral variation and thicknesses was performed in both areas. Moreover, geophysical surveys revealed geological features such as faults and saline regions which have not been reported previously in other studies. Such information is aimed to be the basis for further debates on groundwater protection, management, planning, and decision-making between local water user organizations and municipalities.

The semiarid Punata alluvial fan is located in the central part of Bolivia. The main activity of this region is the extensive agriculture, and groundwater is the main water supply. Local villagers who use groundwater reported that in some places groundwater has a salty taste. In order to investigate the origin of this problem, several TEM soundings were performed in the study area, and they were complemented with ERT surveys. The results show top layers with resistivity values ranging from 30 to 200 Ωm and a bottom layer with resistivity values ranging from 1 to 20 Ωm, which might be interpreted as the main aquifer and a layer with high clay content, respectively. Between the top and bottom layer, a transition zone with saline water has been identified, with resistivity values ranging from 0.1 to 1 Ωm. The origin of this closed-basin brine might be a product of the evaporation of paleolakes during the lower Pliocene, where saline clays were deposited. This study demonstrated the effectiveness of TEM sounding for mapping very low resistivity zones such as saline water.

Groundwater plays a vital role in human consumption and irrigation in many parts of Bolivia; yet, the absence of policies to regulate its extraction and protect groundwater recharge areas has led to a decline in water tables and threatened food security. Some municipal initiatives have been implemented to develop regulations, but the lack of reliable hydrogeological data (such as aquifer geometry, groundwater level data, location of potential groundwater recharge zones, and flow dynamics) hinders their effective implementation. The case study presented herein focuses on a municipal policy in Tiraque, Bolivia, aimed at protecting groundwater recharge zones, in addition to the need for a reliable methodology for their technical identification. The EARLI approach (an acronym for “Enhanced Algorithm for Recharge based on the Rainfall and Land cover Inclusion”) is suggested as a participatory-simplified multi-criteria decision method to address the absence of hydrogeological data. This approach was adjusted to the basin’s specific conditions, including local vegetation communities and their influence on infiltration, and was applied as a pilot study in the Virvini micro-basin. The EARLI model emphasizes the spatial distribution of rainfall as an input indicator for potential recharge in addition to the biophysical characteristics of the catchment area. The methodology successfully mapped the degree of groundwater recharge potential and was validated by traditional hydrogeological models, field infiltration measurements, and the local community’s application of the tool. Therefore, the results of this study provide the necessary technical bases for groundwater-integrated management in Tiraque.

No abstract

Climate change and variability are likely to increase in most parts of the world, leading to more extreme events, which may increase the stress on already threatened water resources. This study focuses on the effects of the El Niño Southern Oscillation in the rainfall of Pucara basin and in the groundwater levels of the Punata alluvial fan in the Bolivian sub-Andes. Climate change and variability were assessed using the Quantile Perturbation Method, by detecting anomalous temporal changes in extreme quantiles of annual precipitation in the Pucara watershed and the correlation with groundwater levels in the Punata fan. The results show oscillatory behavior over periods of 28 to 33 years for the occurrence of wet and dry extremes at all studied meteorological stations. This suggests a similar oscillatory behavior of the groundwater levels; however, longer groundwater level observations are needed in order to confirm the link between precipitation variability and groundwater fluctuations. Local actors such as water managers, farmers and decision makers must take into consideration this climate variability in order to plan for these multi-decadal variations in response to the changes.

No abstract