Gestão Adaptativa das Águas Subterrâneas no aquífero de Benalup

The Benalup aquifer in the Barbate River basin (MAS 062.14) is affected by the productive model of the region: livestock and agriculture that for years have been overexploiting the aquifer affecting its quality and quantity. The University of Cádiz, through the RNM-373 Geosciences group and the REMABAR project, has proposed alternatives for management based on the knowledge generated regarding the aquifer and its social and geographical environment. In order to generate proposals and manage the conflict between the use and the state of the body of water, the aquifer state and s and investigated the relationship between pressures and impacts, being relevant the existence of unauthorized catchments.

This project presents an innovative methodology on an environmental, social and economic scale in the context of climate change applicable to the SUDOE region

Responsible entity

The Geosciences group of the University of Cádiz (UCA) led by Santiago García López is responsible for the project formed by 12 researchers The group was founded in 2009 participating to this day in 83 projects, 35 journal publications, 6 patents and other various activities.

At present, the Group’s activity is diverse and comprises the following areas:

• Dynamics of extinctions in marine environments.
• Groundwater: systems modelling and water resources assessment.
• Functioning of karst aquifers: hydrodynamics and hydrochemistry.
• Diagnosis and evaluation of groundwater contamination.
• Genesis, uses and contamination of soils.
• Integrated biostratigraphy.
• Storage and capture of CO2.
• Paleoclimatic and paleoecological reconstructions.
• Paleoceanography.
• Carbonation of alkaline solid waste.

Detailed explanation

The Benalup aquifer is located in the “La Janda” region of the Barbate watershed. The productive model of the regionlargely supports agricultural and livestock activity. The surface water comes from the reserves of Barbate, Celemín and Almodóvar. However, groundwater is obtained from the Barbate and Benalup aquifers that are subject to a high degree of exploitation and lack a regulatory entity, resulting in an uncontrolled situation of overexploitation of the aquifer. In the case of Benalup, you can find multiple unauthorized and unregistered farms, adding to this factor, the use of the land, the state of the water bodies is reduced both in quality and quantity.

To resolve the conflict between the state of these bodies of water, the uses and the environment, this “REMABAR” project is being developed.

The project has the following tasks:

Data collection by consulting cartographic databases, hydrogeological data, information and documents prior to the project, as well as data from the existing monitoring network. This information combined with GIS gives the possibility to manage and analyze to obtain significant information for the project.

The levels and qualitative status of the aquifer are then monitored. This campaign allows to define the recharge and discharge zone, the direction of the flow, the relationship between the river and the aquifer and the influence of the exploitations. Thus, the 1993 data were taken as a reference to study the evolution of the aquifer. The Benalup aquifer has a free / semi-confined aquifer behavior, the aquifer is mainly constituted by Myocene biocalcarenites with calcareous fossiliferous remains. The permeable formations of quaternary wind sands that form the upper part of the aquifer contribute greatly to the infiltration of rain (20-30%). The aquifer interpretation describes a conceptual model in which there is no connection between the aquifer and nearby rivers. In this context, the importance of the return of irrigation water and its influence on the state of the aquifer should be highlighted. On a hydrochemical scale, facies are mostly calcium bicarbonates, given the abundance of limestone in the region).

A geophysical campaign (ERT) provided knowledge regarding the geometry of the aquifer, allowing to discern the productive levels. Of the three formations that constitute the aquifer, the lower one is the most productive, being formed by calcareous rocks (biocalcarenites) The upper level formed by a mixture between sands and silts of the Quaternary presents lower porosity.

To characterize the properties of the aquifer, the porosity, permeability, transmissivity and storage coefficient of the materials were evaluated.

Through satellite images through the NDMI (Normalizad Difference Moisture Index) identified those plots that in the dry season and without previous rains, were wet, attributable to irrigation. With the official bases of land authorized for irrigation of the Junta de Andalucía (SIGPAC) and the identified plots, it was possible to discriminate between those authorized irrigations and those that did not have the permit.

Finally, dialogues were held with users to transmit knowledge and transmit the state of the aquifer to its users, round table sessions and information sessions were held where different agents involved in the use and management of water congregated. Likewise, a survey campaign was carried out to understand the vision of the users and their knowledge related to exploited water bodies and climate change.

Thus, the study of the Benalup aquifer has allowed the identification of multiple aspects to be taken into account for groundwater management (Vélez-Nicolás, 2020).

1. Geometry and storage volume of the aquifer.
2. The recharge and unloading areas.
3. The hydraulic disconnection of the aquifer from the main hydrographic network.
4. Define the 3 hydraulically differentiated aquifer sectors that constitute the aquifer and the direction of flow.
5. The chemical characteristics of water.
6. Approach to the possibility of carrying out actions of artificial recharge of the aquifer in order to achieve a joint management of surface water-groundwater and improve the qualitative status of the aquifer.

The use of surface water as a complement to supply the population is considered, a factor that will contribute to improving the quantitative status of the aquifer.

Future outlook

The work carried out within the framework of the REMABAR project is a step for the local water resource to improve quality and quantity.

With the evidence of the water need in the territory, it is expected that new policies focused on self-regulation by users will be necessary.

To contribute to the good practice and management of users, it is necessary to promote the study and generation of knowledge related to the aquifer system.

Political and economic regulations together with the necessary knowledge provide three pillars to recover and maintain the good state of the local water resource