Study to estimate aquifer recharge at the Maule and Maipo aquifers allows determining most suitable areas for infiltration

  • The results of the analysis “Estimate of recharge through the WetSpass model for the Maule and Maipo Basins”, commissioned by Escenarios Hídricos 2030 as an instrument to develop roadmaps that will contribute to achieving water security in both territories, were presented at a seminar in early July by their authors, Portuguese engineers João Palma Nascimento and Nuno Barreiras.

This new research, with updated data for Maule and Maipo, was prepared for Escenarios Hídricos 2030 (EH2030) by João Palma Nascimento, water resources engineer, and Nuno Barreiras, geological engineer, both working for Water Ways, Portugal. As Nascimento explained, they used the best available sources and information regarding land slope maps, land use, soil texture, precipitation, temperature, potential evapotranspiration, wind speed, and depth of the piezometric level (elevation of water in a well in relation to a specified horizontal surface, such as sea level).

In addition, land use change impact over the last 20 years (1995 to 2016) was evaluated on aquifer recharge and pollution risk assessment (IS). This was based on the study “Analysis of the current state of the ecosystems in two basins present in central Chile; Maipo and Maule”, (Pliscoff, 2020 for Water Scenarios 2030).

The goal of the study was estimating the recharge and contamination risk of aquifers in the pilot basins (Maipo and Maule), as well as the territorial distribution of these areas, using the Water and Energy Transfer between Soil, Plants, and Atmosphere (WetSpass) model and the Susceptibility Index (SI).

A report was prepared for each basin, each of them addressing three main aspects: estimation of the areas of greatest infiltration, delimitation of the preferential recharge zones, and evaluation of groundwater contamination risk.

As Claudia Galleguillos, EH2030 coordinator for the Maule Basin, explained that as a result of the study, it can be concluded that “There are highly relevant areas for conservation, given the aquifers’ current high recharge capacity. In addition, an important part of these areas are at low risk of contamination, so it is possible to promote very short term actions to increase the recharge of aquifers in these areas.”

Galleguillos added that these areas have a high potential to promote infiltration works that make it possible retaining water longer in the soil and, thus, increase recharge in a soil that already has an adequate capacity for this purpose. Many of the techniques that can be applied are natural (native forest) and ancestral, with low investment costs.

Meanwhile, Ulrike Broschek, EH2030 leader and coordinator for the Maipo Basin, pointed out that “within the high recharge capacity zones, there are areas with moderate or high contamination risks, which are mainly associated with agricultural activity and the use of pesticides and agrochemicals. In spite of that, it is very feasible to take advantage of these areas infiltration potential, requiring an integrated soil management plan alongside agricultural producers to significantly reduce the addition of agrochemicals.”

Furthermore, she valued the results of the report, given that the identification of each of these zones, carried out with the WetSpass model, makes it possible to implement the appropriate actions in the areas with the greatest recharge potential, and to take the necessary measures in the event of contamination risk.

MAIN CONCLUSIONS

In the case of the Maule Basin, the areas with the greatest recharge were found in the central part of the basin, where the topography is smoother and the type of soil favors infiltration. Recharge values range between 0 and 1123 mm/year, with an average value for the entire basin close to 97 mm/year (47 m3/s), for the year 2016.

  • 26% of the total territory of the basin (5315 km2) contributes 55% of the total recharge, with an average of 211 mm/year, reaching a total volume of 1,122 hm3/year. The main recharge areas are located in the central and southwestern part of the basin, matching the agricultural lands. 
  • As for the groundwater contamination risk assessment: the highest risk categories are associated with agricultural areas and are located on gently sloping terrains with a significantly sandy composition.

Meanwhile, at the Maipo Basin, the recharge values for the entire basin range between 0 and 292 mm/year, with an average value close to 93 mm/year (45 m3/s) for the year 2016.

  • Twenty-five percent of the total basin territory (3781 km2) contributes 46% of the total recharge, with an average of 171 mm/year, reaching a total volume of 674 hm3/year. The main recharge areas are located in the plains to the south of the basin, as well as along the territories adjacent to the main watercourses of the Maipo River’s hydrographic network.
  • The distribution of pollution risk is highly variable and is essentially conditioned by the existence of agricultural practices and by the urban fabric existing in the basin. The highest risk categories are directly associated with agricultural lands, on gentle slopes and with a significantly sandy composition (southern and southwestern areas of Santiago).

All this information is of great relevance for the work that is being carried out by Escenarios Hídricos 2030, an initiative undertaken to contribute in achieving the country’s water security since 2016, under the coordination of Fundación Chile, Fundación Futuro Latinoamericano, and Fundación Avina. EH2030 is currently developing its second phase, which began in 2020 and seeks to implement Water Transition, the strategy proposed by EH2030 to achieve the country’s water security and which has  4 fundamental pillars: Water management and institutionality, Protection and conservation of our water ecosystems, Efficiency and strategic use of the resource, and Migration and incorporation of new water sources

As a result of this work, this year EH2030 will deliver a number of products, among which the following stand out: Proposal for a new water institutionalism, both at a national level and for governance in the territories; Methodology for the selection of integrated solutions in basins, to be replicated in all basins of the country; Roadmaps for the Maule and Maipo pilot basins, aimed at achieving water security in said territories, with the optimal combination of measures, actions, and solutions (MAS); and, the Proposal for a National Water Security Plan.

The reports “Estimate of recharge through the WetSpass model for the Maule and Maipo Basins”, which were presented on Wednesday, July 7 during a  webinar, can be revisited here:

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