Borderflow: Exploring an aquifer to create a Model

The Allende–Piedras Negras Transboundary Aquifer Pilot Project

The Allende–Piedras Negras Transboundary Aquifer (APN-TBA) aquifer is located between the states of Texas (United States) and Coahuila (Mexico) (Figure 2.1). The Rio Grande crosses the aquifer, acting as a natural and political divide between the two countries. However, it remains unclear whether the APN-TBA can be considered a truly transboundary aquifer flow system, which would potentially require joint or coordinated management by two different administrative jurisdictions.

Figure 2.1. The Allende - Piedras Negras Transboundary
Aquifer. Source: Rodriguez et al. (2020)

Recently, a numerical model was developed for the APN-TBA (Figure 2.2), whose simulations numerically demonstrated that there is probably cross-boundary flow between the U.S. and the Mexico regions of the aquifer categorizing it as transboundary (Rodriguez et al., 2020).

Figure 2.2. Allende Piedras Negras aquifer modeled
drawdown between January 2000 and December 2017.
Source: Rodriguez et al. (2020)

Notwithstanding, the simulated area is rather local, and the layers considered in that study are the shallow aquifers. Therefore, important questions remain on the APN-TBA project at the intermediate and regional scales, as well as the vertical scale of the deeper layers and aquifers. Further, some key processes are not included in the model, such as the effects of fracking, surface water/groundwater interaction, natural climatic variations, and effects of over-pumping on both sides of the border.

The existing APN-TBA model does not include the full spectrum of horizontal and vertical scales on both sides of the border; thus, the scales of the dynamics of groundwater (i.e., use and movement) either as a flux or in storage, and the eventual impacts of over-exploitation, in a larger area cannot be assessed with the current version of the model.

The major cities of interest in the region are Zaragoza, Morelos, Allende, Villa Union, Nava, El Moral, Guerrero, and Piedras Negras on the Mexico side (State of Coahuila). The U.S. side has Quemado, Spofford, Brackettville, and Eagle Pass as its main cities. Piedras Negras and Eagle Pass stand as the biggest urban centers in the area, with a total population of 271,410 (2020 census).

Due to the growing groundwater dependency in the region for its economic activities, restrictions on water extraction were established for the APN-TBA on the Mexican side due to the high risk of overexploitation and the low recharge rates owing to the semi-arid climatic conditions (DOF, 2013).

The Allende–Piedras Negras Transboundary Aquifer Pilot Project

To develop a framework of transboundary cooperation to address transboundary water issues along the US/Mexico border issues. The resulting framework will serve as a model and can be applied in other transboundary water basins.

  • To develop scientifically-based knowledge on assessment and management of transboundary aquifers specifically applied on the APN TBA between Coahuila and Texas.

  • To develop specific feasible recommendations on water management strategies and short-term initiatives based on social and economic priorities and current and future water availability scenarios.

  • Use this knowledge to support long-term sustainable economic development with social responsibility through inclusive decision-making process, transparency, stakeholder involvement and shared governance schemes.

  • To develop strategies aligned to the current ESG requirements and goals.

  • To develop communication strategies to socialize and translate scientific findings into useful and executable information for different types of audiences and users.

  • To build social capital and trust among involved institutions/stakeholders.

  • Develop scientific binational publications on technical journals.

  • To evaluate the feasibility to develop and maintain a groundwater monitoring network (public and accessible) for groundwater levels and water quality.

Proposed study zone and scales

Three different extents will be used to assess nested watersheds and aquifers framework and groundwater flow systems (Figure 2.3):

Figure 2.3. Synoptic region to be studied in the pilot project

  • Use GRACE signals to evaluate regional groundwater-storage changes for the periods 2002-2017 and 2018-2022.

  • Assess flow rates from the Pecos, Devils and Grande rivers.

  • Apply structural and sedimentary geology to evaluate the regional-scale geology

  • Generate 2D cross sections to define hydrostratigraphic units at 1000-m depth.

  • Assess potential and actual evapotranspiration and surface hydrological components using remote sensing data (e.g., CHIRPS, MODIS, DAYMET, BCM etc.).

  • Generate the DEM.

  • Refine the 2D cross sections and hydrostratigraphic units. These sections will be used to display and communicate results in digital format.

  • Evaluate vertical recharge using physically-based and/or water-budget models (e.g., EALCO, SWB Model, BCM model, or similar).

  • Identified/design groundwater flow system (GWFS) with distinct geological, topographical, geomorphological and climatic features mostly based on groundwater discharge, and in some cases a combination of areas of groundwater recharge and discharge.

  • Assess groundwater residence times using GW dating, when available, or with analytical solutions.

Project phases

The specific objectives of the APN-TBA pilot project are divided into four phases:

Prepare an executive synthesis of the current situation of the transboundary surface and groundwater conditions centered around Piedras Negras/Eagle Pass region. This synthesis will provide an overview of current socio-economic conditions, analysis of existing governance arrangements in place for managing water (a stakeholder mapping of existing public-private relationships). The most pressing issues, physical and socio-economic elements, as well as governance and policy challenges, will be addressed to provide a full contextual scan of the system from a broad scale. Identification of data gaps and priorities accordingly.

Proposed activities

  1. Prepare an executive synthesis of the current situation of the transboundary surface and groundwater conditions centered around Piedras Negras/Eagle Pass region.
  2. Overview of the socio-economic current conditions, stakeholder mapping, needs, priorities and public-private relationships. Most pressing issues, physical and socio-economic elements as well as governance and policy challenges will be addressed to provide a picture of the system from a broad scale.
  3. Conduct an analysis of existing institutional and governance architectures for managing water in the regio:a. Identify existing binational and domestic institutions and their respective laws and regulations for managing cross-border water resources;

    b. Identify existing mechanisms for (1) domestic and cross-border stakeholder participation; and (2) data/information collection, sharing, and dissemination;

    c. Evaluate institutions, stakeholder participation and information-sharing mechanisms through application of water governance indicator matrix and gap analysis.

  4. Overview of the international cooperation of this transboundary aquifer.
  5. Communicate proposal’s objectives to main stakeholders to seek support and endorsement of the project, and get their feedback on expected outcomes. Schedule follow up interviews and workshops to communicate advances, changes, and improvements to the project.
  6. Identification of main data gaps, research needs, and research priorities.
  7. Research gaps will be translated into further research needs and significance of those future steps for the overall objectives of the project.
  8. Research needs will be translated into potential impacts and short and long term specific measurable actions at different levels of governance systems.


Annex A_Extensive Technical Report of Data Gaps, Information and Research Needs: Allende Piedras Negras-Maverick Transboundary Aquifer

This report is part of the Allende-Piedras Negras Transboundary Aquifer (APN-TBA) Pilot Project, a project of the Permanent Forum of Binational Waters (PFBW). This project is intended to provide scientifically-based knowledge on transboundary aquifers and watersheds, and transboundary groundwater and surface water using a holistic approach on the assessment and management of transboundary aquifers toward their sustainable development.

The objective of this report is to integrate existing data and information from previous geological, hydrogeological, geochemical, and environmental studies of the APN-TBA, in order to develop an integrated dataset for study of the full aquifer system. This report represents Annex A, it should be consulted together with the two other Annexes, B and C. The three annexes constitute a comprehensive review of previous and current data, information, and a variety of studies of the APN-TBA on both sides of the Mexico/US border. These have been compiled, analyzed, and are synthesized in this report; thus, this deliverable represents a synthesis of knowledge on the aquifer as per 2024.

Download the full Annex A here

Annex B_References of Technical Report

This document is the Annex B entitled “Main data, gaps, and research needs” which is part of the Allende-Piedras Negras Transboundary Aquifer (APN-TBA) Pilot Project, a project of the Permanent Forum of Binational Waters (PFBW).

This Annex lists the most relevant literature, scientific manuscripts, and technical reports to describe six domains of information, including geology, hydrogeology, groundwater, surface water, hydrogeochemical, and environment characteristics of the transboundary region formed by the limits of the Allende-Piedras Negras (APN) aquifers, Región Carbonífera, Serranía del Burro, Cerro Colorado – La Partida, Palestine, and Hidalgo, in Mexico; and the Edwards – Trinity, and Carrizo, in the U.S.A. These aquifers cover three spatial scales of analysis: a regional scale (500 km), an intermediate scale (250 km), and the local scale (100 km), which can be consulted in the Executive Report or Annex A – Extensive Technical Report.

Download the full Annex B here.

Annex C_Collected Data and Information

This document describes the data and information collected for the purpose of this project. The project’s database contains a comprehensive list of the retrieved information used to produce the extensive technical report, with technical information divided into eight categories: Geology, Hydrogeology, Surface water, Groundwater, Hydro-geochemistry, Environment, Remote Sensing, and Figures. Each domain in the database has a brief summary of its contents, along with information on the institutions from which the data was retrieved and the access URL links. The collected information for each domain is described on the corresponding Table  the Annex. 

Download the full Annex C here.

Develop an initial conceptual model of hydrogeology, climate, and sustainability of water resources including: data compilation, identification of data gaps, analysis of existing data, and assessment of the suitability of existing monitoring networks. Data collection and methods assessment to evaluate the physical and managed water systems, as well as the relevance of current public policies on groundwater.

Proposed activities

  1. Define the main issues and questions the pilot project will seek to resolve both on the physical and socio-economic conditions of the aquifer-system and with respect to shared management of the resource.

  2. Collect and integrate hydrological, geological, geochemical, and hydrogeological data and information REPDA, SINA-CONAGUA, INEGI (LAYERS), data from TWDB/USGS/IBWC-CILA, CB, INEGI, and other related state and federal institutions.

  3. Perform punctual field work to fill in knowledge gaps (physical, environmental, social, economical, and governance/policy data).

  4. Perform analysis from existing data in support of development of the conceptual models where possible.

  5. Build watershed and hydrogeological conceptual models of the transboundary groundwater flow systems in a multi-aquifers framework centered around both sides of the US/Mexico border in Piedras Negras (MX)/Eagle Pass (US), including:

    a. Edwards-Trinity Plateau

    b. Rio Grande Systems

    c. Pecos and Devils Rivers

    d. Allende – Piedras Negras/Eagle Pass

    e. Maverick Basin Aquifer

    f. Region Carbonifera

Develop a recharge/runoff model and groundwater modeling, and evaluate supply-and-demand components of historical periods, effects on river flows from groundwater extractions, water quality, and changes in rates of transboundary water flows. Environmental, water availability, and socio-economic risk assessment analysis to be conducted. Simultaneously, undertake full characterization of uncertainties present in the basin (natural, socio-cultural, governance and technical).

Proposed activities

  1. Build a numerical model based on the conceptual model.

    a. Use the model to simulate stresses, transboundary fluxes, indicators (e.g., GW stress, GW sustainability, degree of transboundariness) and future management and climate scenarios.

    b. Define, simulate, and evaluate in more refined or nested models, critical subregions that may be subject to overexploitation or unsustainable uses or triggering secondary effects such as surface-water capture, interference with other groundwater uses, or water-quality degradation.

    c. Use the model to evaluate possible sustainable scenarios.

    d. Use the model results to develop a risk assessment analysis (water availability, environmental, socio-economic)

  2. Use the strategy developed in this pilot project as a detailed example for all other TBAs located along the U.S./Mexico border.

Use the results of Phases 1-to-3 to develop governance- and related policy-proposals for the sustainable management and use of the APN-TBA, to assure a socially and economically responsible use of water resources considering both its domestic and transboundary characteristics and socio-economic and institutional implications.

Proposed activities

  1. Develop governance and related policy proposals for the sustainable management and use of the APN-TBA, to assure socially and economically responsible scenarios.

    a. If appropriate, propose new institutions, priorities, regulations/laws and/or responsibilities (or, modifications) at both levels of governance

    b. If appropriate, propose new mechanisms for stakeholder participation and information sharing at both national and binational levels of governance

    c. Evaluate economic impact assessment of different groundwater availability scenarios (risk assessment analysis)

    d. Evaluate the socio-economic impact on GW governance by different model scenarios (risk assessment analysis)

    e. Development of a conceptual model of the socio-environmental system

    f. Sustainability of groundwater management according to levels of transparency, inclusion, and groundwater governance.

What will this project bring?

The goals for the short, medium, and long terms, are described below in detail. These goals are designed to address the main issues and questions the pilot project will seek to resolve.

Expected time: 6 to 12 months

  1. Define the main questions and issues from the physical system as well as the socio-economic-institutional water governing system.

  2. Design a project flyer or factsheet as a communication tool with executive objectives in brief.

  3. Identify information/data gaps and data exchange needs.

  4. Description of the state-of-affairs of the APN-TBA (its situation, or set of circumstances).

  5. Identify short-term potential strategies/initiatives (“quick wins”) and areas of opportunity in terms of water efficiency and best management practices.

  6. Mapping of stakeholders, needs and priorities, and their relationships.

  7. Identify governance, institutional, and policy challenges on the APN-TBA.

  8. Identify socio-economic concerns and potential water availability scenarios for the region.

  9. Integrate a group of main stakeholders that will be participating as advisors of the project throughout the process.

Expected time: 12 to 23 months

  1. Collect, integrate, and analyse physical and socio-economic data.

  2. Analysis of existing data in support of conceptual and numerical models.

  3. Perform punctual field work to fill-in knowledge gaps, including survey work.

  4. Build conceptual models.

  5. Build and calibrate numerical models.

  6. Publish preliminary results, provide workshops, and develop communication strategies.

Expected time: 24 to 36 months

  1. Advanced, quantitative description of the physical scheme of the APN-TBA.

  2. Governance gap analysis: Identify the governance and management architectures needed to support quick wins and best management practices identified and what is missing.

  3. Communicate results and implications of the field analysis (focus groups interview) and existing information (social responsibility, legal framework, and economic statistics).

  4. Technical evaluation of the social responsibility and economic impact of Constellation Brands.

  5. Provide a risk assessment on environmental impacts and/or reducing water resources.

Project timeline

The activities will be developed following the diagrams of Timeline (Figure 2.4) and Roadmap (Figure 2.5).