Scientists identify the most dangerous spots on the Maipo River if winter rains repeat

Today, in the Green Room of the Luksic Building, on the San Joaquín Campus of the Catholic University, the Research Center for Integrated Disaster Risk Management (Cigiden) presented a report on the floods from June 21 to 26, 2023 in the basins of the Mataquito, Maule and Maipo rivers hydrometeorological event that affected the south-central area of ​​Chile.

According to the document, behind the frontal system were basins that showed a significant increase in runoff (flow of water flowing through the river), produced precipitation that occurred in pre-mountainous areas, which also had high temperatures.

The document was presented as part of the International Day for Disaster Risk Reduction and handed over to the government for better risk management in the event of future floods.

The study carried out an in-depth analysis of two areas of the Maipo River. On the one hand, the mouth (San Antonio and Santo Domingo), and on the other hand, the upper basin of the Maipo river (Cajón del Maipo sector), with the aim of identifying the main changes caused by the June 2023 event the impacts on the population and the main scientific requirements of local and regional authorities in the face of the threat of flooding.

Jorge Gironás, principal investigator of Cigiden and director of Department of Hydraulic and Environmental Engineering UC, indicated that The impact of the drought was twofold. “There is the impact of the drought itself, and the cultural impact of making you believe that it will never rain again, which amplifies the impact of a flood like the one we had. A flood in the bed of a river where the flood zone has been respected, losing a football field or a recreational area, is different from the same phenomenon, where houses and human lives can be lost.

Regarding the most dangerous areas, The report ranks six as the most critical for the oral area. In the municipality of San Antonio, these are the following

-Agricultural farms in Lo Gallardo

-Diamond tip

-Saint Jean.

And in the municipality of Santo Domingo in these areas:

-The “Maipo River Wetland” natural sanctuary

-Chacra of Santo Domingo

-Chacra Los Gómez

For the upper basin area of ​​the central Maipo River, the document establishes that the 87 macro-basins, all of which recorded a mass withdrawal event at some point landslides are more recurrent, so it is expected that during future rainy events, like last June, anyone could generate these phenomena.

Reviewing the region’s history of flooding and heavy rainfall, the report establishes what happened in 1952, 1960, 1982, 1986 and 2006 like major events. All of this would have been on a scale greater than that experienced in June 2023.

The Cigiden study also establishes a clear increase in the altitude of the 0° isotherm on the analyzed date, specifically increasing from 2,900 to 3,300 meters above sea level between June 22 and 23, but with a decrease from 3,459 to 3,050 meters above sea level between June 25 and 26.

Add this The maximum level of the 0° isotherm reached 3,459 meters above sea level, being within normal isothermal values ​​for central Chile, but being abnormal for winter storms in this region.

The mouth of the Maipo River during the pre- and post-flood period presented significant morphological changes due to the effects of extreme events. During the summer of 2023, a process of closing the mouth took place where two mechanical openings had to be carried out due to the risk of flooding of homes located on the banks of the river (February 2023), which modified the width of the mouth, specifies the document.

He adds that in February 2023, the width of the mouth after the first mechanical opening was 48 meters then from the second mechanical opening it was 62 meters while July 5 was 555 meters.

This is relevant, the study adds, because previous records did not reach this amount, far exceeding the available historical statistical data. This is due to several reasons, such as the characteristics and distribution of precipitation and the oversaturation of the soil due to high duration and intensity of precipitation.

To carry out this measurement, researchers used different techniques and technologies. Between them, drones, GPS equipment, geological techniques and field visits.

For each of the alluvial deposits that could be detected, a geological analysis and description of the deposit was carried out using a manual-visual methodology, in addition to recording its location and location. the collection of aerial images.