Assessing aquifers in semiarid rural regions ofers significant social and economic benefits. The "Loma Alta" community, located northeast of Santa Elena, Ecuador, primarily depends on agriculture as its leading economic activity. However, the community requires suficient water resources for irrigation and domestic purposes. This research aims to investigate groundwater resources in the upper Valdivia-California River basin by applying Geographic Information Systems (GIS) and hydrogeological studies to propose sustainable water resource management strategies in line with the Sustainable Development Goals (SDGs). The methodological framework is structured into three phases: i) hydrologic and hydrogeologic analysis, encompassing hydrology, geology, geophysics, and water quality assessments of wells; ii) GIS application to delineate potential areas; and iii) setting of strategies for water sustainable management. The findings indicate that the highest water extraction occurs between January and April during the dry season and extends until the end of May in the wet season. The area with the most significant extraction potential was between the "Loma Alta" and "La Unión" communities. It features a saturated layer approximately 20 m thick in sandy soil capable of retaining up to 150 mm of water. This study underscores the potential for sustainable groundwater management in Loma Alta, which could contribute to the region's socio-economic development while addressing the challenges of water scarcity.
Groundwater is the world’s second most vital water source, providing for approximately half of the
global population [
In recent decades, ecosystems with arid or semi-arid climates worldwide have become vulnerable to
the efects of climate change, causing a greater deficit than surplus water resources [
In coastal aquifers, reducing groundwater levels and rising sea levels are driven by climate change
push the interface zone inland, increasing the risk of seawater intrusion [
In arid regions, rural communities rely on pumps to extract groundwater to address the scarcity
of surface water, particularly during droughts [
As population growth intensifies and water demand increases, it is imperative to identify new areas
for resource extraction [
At a global level, there are multiple experiences in the benefits of using geoelectrical methods for
the characterization of hydrogeological parameters, such as the delimitation of saline intrusion zones
present in alluvial aquifers [
In Ecuador, there is a legal framework that recognizes the right of people to access water, in addition
to its correct use in productive activities. Currently, the National Irrigation and Drainage Plan (PNRD)
(2021–2026) [
In the province of Santa Elena, Ecuador, there is the Loma Alta commune, whose primary need is
the supply of water to carry out activities such as agriculture, livestock, and domestic consumption.
Some factors that cause this problem are population growth, increased agricultural land, and climate
change, which causes droughts. The inhabitants use the surface water of the Valdivia-California River
and some artisanal wells from which groundwater [
The study area is located in the province of Santa Elena within the parish of Colonche, with an estimated
population of 40,058 [
This study employs a multidimensional analysis that integrates geological-geophysical factors, precipitation and recharge (isohyets), hydrodynamics (flow direction), static and dynamic groundwater levels, and water quality (including physical-chemical and microbiological parameters) within a GIS framework to identify potential zones for hydrogeological utilization. Both 1D (VES) and 2D (ERT) geoelectrical methods and spatial analysis tools were utilized to generate thematic maps and establish correlations between hydrological and hydrogeological factors. The phases of this study are schematically shown in Figure 2.
Phase I involves analyzing the hydrology and hydrogeology of the study basin. The initial stage included
evaluating precipitation and mean annual temperature data to perform the water balance. We obtained
data from 1981 to 2020 from GeoEye-1 satellites using the ’Five-Degree Blocks of Cells’ extension, the
National Aeronautics and Space Administration (NASA) Satellite, Prediction Of Worldwide Energy
Resources (POWER) [
The study gathered cartographic information on rivers, contour lines, geology, lithology, settlements,
and roads from the IGM Geoportal [
In the second stage, the research conducted geophysical surveys using 16 Vertical Electrical Soundings
(VES) with the Terrameter SAS 1000 equipment, employing a Schlumberger electrode array (AB/100
m and MN/10 m). Also, three Electrical Resistivity Tomography (ERT) surveys were performed using
the Terraloc equipment with the Wenner method, obtaining ground resistivity and the approximate
depth of layers with both methods. This combination of geophysical prospecting methods reduces
exploratory costs and provides reliable information by minimizing the uncertainty generated by indirect
measurement methods [
This phase created isohyet maps using the Kriging method of Spatial Analysis in ArcGIS Pro (version 3.2.0) to obtain the groundwater flow direction map. The VES resistivity measurements were processed in the IPI2win program (version 3.0.1), which yielded the diferent resistivities and apparent thicknesses of the layers or strata composing the subsoil of the area of interest. Additionally, the pseudo-sections of the ERT were generated using the RES2DINV program, producing 2D graphs of the resistivity values for each substrate and the stratigraphic columns using Strater 5 software to graph the lithology observed in the field.
Phase III involved generating a map of suitable sites for groundwater use in the upper Valdivia-California
River basin. This map integrated the hydrology and hydrogeology factors from Phases I and II in a
GIS and applied the Delphi method to develop guidelines and reach a consensus [
The study conducted three rounds of open interviews. In the first round, the researchers presented the maps generated in Phase II, and the experts suggested adjustments to the thematic maps. In the second round, the experts selected the primary areas for groundwater use and requested an evaluation of the geological stations and a correlation of the geophysical campaigns. The panel identified areas with the most significant water potential in the third round. It delimited the layers with the most substantial thickness and groundwater content for extraction and developing productive activities through a controlled irrigation system. During this final round, the experts formulated strategies to assess zones for the future development of Managed Aquifer Recharge (MAR) projects.
Of the two dry intervals, the one with the lowest amount of precipitation is from 2002 to 2020, with a total of 455.94 mm per year, while in the interval from 1981 to 1996, it was 553.85 mm. The humid sequence had an annual precipitation of 974.13 mm. The months of reserve recharge for all sequences begin in February and continue until March only in the dry sequences; for the humid sequence, it extends until April. In the interval from 1981-1996, the reserves were depleted in May, while in the interval from 2002-2020, the reserves were depleted in April; for the humid interval from 1996 - 2002, the reserves were depleted in July. (a) Water balance for dry sequence of 1981 – 1996 (b) Water balance for the humid sequence of 1996 – 2002
(c) Water balance for dry sequence from 2002 to 2020
The precipitation analysis in the study area from 1981 to 2020 resulted in three intervals (Figure 4): the first considered a dry season from 1981 to 1996, the wet season from 1996 to 2002, and the dry season that continues until 2020. The average annual temperature for the first interval is 24.06 °C, the second interval is 24.17 °C, and the last dry season is 24.54 °C. The soil’s field capacity or water retention capacity was estimated to be 148.5 mm. With the elaboration of the water balance according to the mentioned intervals, it is distinguished that for a dry season, the months with the highest rainfall are February (145.90 mm), March (136.42 mm), and April (81.18 mm), subsequent months the rainfall varies between 3.00 mm to 72.51 mm. The situation is similar during the wet season, with the diference that the months of most significant rainfall extend from February to the end of May, with rainfall of 233.34 mm to 60.06 mm. In the second dry sequence, the months of most significant rainfall are repeated concerning the first season; these range from 148.61 mm to 68.67 mm.
The analysis of the physicochemical parameters carried out in the 12 wells distributed in the study area (Table 1) indicates that 9 of them have suitable conditions for use, while well-02, well-09 and well-11 presented values of conductivity (> 2500 µs/cm), TDS (> 900 mg/L) and salinities (> 800 ppm) that exceed the permissible values according to the TULSMA regulations, this is due to poor conditioning, landslides, plant decomposition and the inactivity of the wells.
The results of the microbiological analysis of the water samples are presented in Table 2 and were compared with National Regulations (TULSMA, INEN 1108 Standard) and International Regulations (World Health Organization Drinking Water Guide, 2006) and indicated the absence of Salmonella and Shigella, while the presence of Fecal Coliforms, Total Coliforms and Escherichia Coli did not exceed the permissible limits. A2LA: American Association for Laboratory Accreditation.
SAE: Society of Automotive Engineers.
A geological field survey was conducted in four outcrops distributed in the study area (Figure 6). In the outcrop O_LA1 (Figure 6a) we found diaclases, sedimentary structures such as cross-stratification, ifne-grained beige sandstones without compacting, some layers contained subrounded grains of pebble size of poor classification, shale layers containing clay particles, and the presence of fine-grained silt of grayish to dark brown color. In outcrop O_LA2 (Figure 6b) laminar layering of ortho conglomerates with pebble-sized clasts, layers of grayish-white shales weathering to yellow and gypsum-filled reverse faults were identified. In outcrop O_LA3 (Figure 6c), yellowish-white fine sandstones, cross-stratification, erosion, and gypsum layers were observed. The description of outcrop 4 is divided into 2, the lower part which is the O_LA4_1 (Figure 6d) that corresponds to the flank of a syncline with dip 15 ° and strike 50° SE, it was identified as a collapse of layers by gravity, thick brownish yellow sandstones, silicified shale intercalations and a layer of matrix-supported conglomerate with pebble size clasts with good classification; the middle and upper part of the outcrop called O_LA4_2 (Figure 6e) is the other flank of the syncline with strike 82° SW and dip 20° also shows gravity landslides, thick brownish-yellow sandstones, intercalation of silicified shales and layers of matrix-supported conglomerates with pebble size clasts were observed.
The correlation of the data obtained by the VES together with the geological survey allowed the identification of the saturated layers associated with a potential aquifer present resistivities associated with clasts with a sandy matrix (30-50 Ω) (Table 3) at depths ranging from 3 to 40.5 m, and the impermeable layers are associated with a lithology of compact clays (0-5 Ω).
By correlating geoelectric profiles (Figure 7), layers of water interest were located in sections A-A’, B-B’, C-C’, D-D’, E-E’ (Figure 8, 9, 10), where it is inferred that the saturated layers (clasts with sandy matrix) are approximately 10-12 m thick at shallow depths (no deeper than 3 m).
Within the three ERTs a layer of interest was located in ERT-01 (Figure 11a), with resistivity values associated with saturated sandstones (2.45 Ω) at a depth of approximately 5 m, this profile reached an error of 3.9% in its processing, being the highest among the three profiles. In ERT-02 (Figure 11b) the sandstone layer (5.0 Ω) is found from 15 m with an undefined thickness covered by a layer of saturated silty sands. Profile ERT-03 (Figure 11c) is similar to profile ERT-01 with the diference that the saturated sandstone layer (15.8 Ω) is located from 2.30 m reaching 23.5 m depth. (a) C-C’ Section (VES 02, 09 y 14) (b) A-A’ Section (VES 01, 10 y 16)
The interest area of a groundwater well was between the towns of "Loma Alta" and "La Unión" (Figure
12), with thicknesses varying between the categories "Excellent" (30-35 m) and "Highly recommended"
(25-30 m). The thickness in the "Very good" range continues toward the river towards the SW. The
study highlighted the possible existence of a semi-confined or confined aquifer at variable distances
between 15 and 40 m below the Quaternary aquifer. A panel of experts developed strategies for the
sustainable use of underground resources, grouped into four pillars:
1. Establish continuous monitoring networks that record the quantity and quality of the groundwater.
2. Integrate the "Map of potential hydrogeological exploitation sites" into land use and cover
planning.
3. Community participation must include water boards, local communities, and farmers in the
decision-making and implementation of aquifer recharge strategies.
4. Future studies are essential to identify MAR project areas to take advantage of resources during the
wet period. A multicriteria decision analysis based on remote sensing and GIS of the river basin
is recommended, combining the factors established in this study with biophysical, hydrological,
and socio-ecological data usually applied in similar environments [
The study identified groundwater use sites between the communities of "Loma Alta" and "La Unión", consisting of a saturated layer approximately 20 meters thick in sandy soil, capable of retaining up to 150 mm of water. Generally, the thickness of the saturated layers ranges from 15 to 31 meters, associated with clasts in a sandy matrix, while the impermeable layers consist of compact clays. The water balance analysis revealed that the months of highest precipitation occur from January through June, during which the soil regains moisture, benefitting agriculture, livestock, and domestic consumption through aquifer recharge. The analysis of physicochemical and microbiological parameters indicated (a) ERT-01 (b) ERT-02 (c) ERT-03 that 75% of the wells have good water quality; however, wells 2, 9, and 11 exhibited elevated levels of dissolved solids and conductivity, attributed to neglect and poor maintenance of the hydraulic structures. Future research should focus on identifying recharge areas to comply with environmental and water management regulations, thereby facilitating the planning of climate change adaptation measures for the associated communities and ecosystems.
This research was funded by the “Registry of geological sites of Interest in Ecuador for sustainable development strategies”, grant number CIPAT-004-2024. Additionally, the authors would like to express our gratitude to Mr. Wilson Tomalá, President of the Loma Alta Commune, and the local communities for their openness and collaboration in the fieldwork for the geophysical studies conducted in the study.