MAR Guides: Aquifer Recharge
MAR Guides: “Operational framework for artificial aquifer recharge projects”
|Finances:||Comisión Nacional de Riego (CNR)|
|Beginning date:||March 2019|
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During the last decades, Chile has been experiencing a sharp decline in terms of available fresh water, largely attributed to a prolonged decrease in rainfall, between 25 and 45% less compared to the average rainfall for the period 1981-2010 (Garreaud et al., 2019). This has promoted the search for new ways of managing water resources in order to provide water security to society. For this reason, the Managed Aquifer Recharge (MAR) began to be explored as an alternative that could complement the efforts that are currently being carried out in the different regions of the country (ex: the construction of reservoirs). Since 2012, an increase in interest in the subject can be seen, especially on the part of some public authorities, which have carried out a series of pilot studies with the aim of gaining experience in MAR, knowing the costs of the works associated with different alternatives and understand their main technical, administrative and governance problems. Indeed, there is a variety of studies and experiences at different scales and in different locations in Chile.
However, the advancement of the RAG at the national level is not favored by the normative framework that regulates the management of water resources in the country, mainly because it does not address the issue directly, generating uncertainty for potential stakeholders in implementing a MAR project. The absence of an operational framework aimed at promoting new MAR projects in Chile does not encourage their development either.
In order to address these deficiencies, the National Irrigation Commission (CNR) promoted this project, called “Operational framework for artificial recharge projects in aquifers”, mainly in the context of the agricultural sector given the importance of the sector in the country, being the largest user of water, with a consumption equivalent to 82% (DGA, 2016).
Managed Aquifer Recharge (MAR), or Recarga de Acuíferos Gestionada (RAG) in Spanish, is a general term that designates the set of methods used to recharge additional water to aquifers intentionally for its recovery and subsequent use or with the purpose to generate an environmental benefit (Dillon, 2005). Generally recognized as artificial recharge of aquifers, MAR incorporates the concept of management as a key component to its development. Aquifers offer potential storage capacities of similar magnitudes to reservoirs, but with less capital investment and lower social and environmental impacts.
2. Project Objectives
The main objective of the project was to establish the technical and operational requirements and the preparation of a Methodological Guide aimed at Users and Organizations of Water Users (OUA), for the development of MAR projects in Chile, through the joint use of surface water and underground, in the context of an irrigation project, based on international experiences.
The Methodological Guide by itself is not official and, therefore, does not require compliance with it, its purpose is to guide the user and increase confidence in RAG projects, specifically in the use of recharged water for irrigation in the sector agricultural.
3. Scope of this guide
The implementation of this Guide for the recharge of unconfined aquifers to support irrigation is a step towards a safer water supply and better protection of groundwater than current practice in Chile. The application of this Guide is expected to accelerate the progress of low-risk MAR projects, reducing the uncertainty and stagnation of other recharge projects, in order to minimize future failures.
MAR applications are limited to the following conditions:
- Having surface water use rights (DAAs), that are possible to infiltrate.
- The water source is restricted to surface water without major prior intervention (i.e. rain or river water).
- The target aquifers are unconfined (or free) and unsaturated.
- The end use of the reclaimed water is restricted to support agricultural irrigation.
4. Recharging methods relevant to this Guide
A range of infiltration techniques can be applied to perform MAR in unconfined aquifers depending on local site characteristics. Ultimately, the decision on which method to apply will depend on a number of factors including cost, soil and local hydrogeological conditions, the quality of the water source, and the available land area, among other potential factors.
For this Guide, three groups of infiltration-based methods for recharging unconfined aquifers have been identified:
- Out of the riverbed
- Inside the riverbed
- Dry wells
Recharge method selection criteria
|*||Low||X||Not suitable to penetrate low permeability layers|
|**||Medium||✔||Suitable for penetrating shallow layers of low permeability|
|***||High||✔✔||Suitable for penetrating deep layers of low permeability|
5. Development framework and suggested methodological management for the development of MAR projects in Chile in the agricultural sector
This Guide has a phased development approach, which has two main advantages:
- An initial low level of effort, investment and complexity is required that gradually increases as the project progresses through the development phases;
- Financial risks are minimized by providing an earlier opportunity to stop projects that prove to be non-viable.
Project development workflow for the application of this Guide
If the Guide is considered applicable to the project, the scale is defined, which helps to understand the level of orientation required for its development. First-scale projects are those that are simpler (technically and economically) or lower risk and require only minor guidance from the Guide. Second-scale projects are those that require more guidance and therefore it is recommended to continue the development in phases.
Infiltration methods that are considered most relevant to this Guide and the agricultural sector in Chile:
Resumen de las fases de desarrollo de un proyecto RAG y los principales atributos a evaluar
Phase 1: Viability evaluation
Evaluates the apparent feasibility of a recharge project proposal using relevant existing data and information. Its objective is to inform the implementers of any fatal flaws in the planned project.
In this phase, the executing agency is expected to have a basic understanding of the type of recharge project being considered, for example, source of water, type of aquifer, and objective of recharge and / or final water use. An understanding of possible and feasible recharging methods is also required.
Main attributes to evaluate
- Water demand
- Availability of a water source
- Hydrogeological evaluation
- Space to capture and treat water
- Capability and experience
- Governance and economic sustainability
- Preliminary economic evaluation
Phase 2: Evaluation of degree of difficulty
Evaluates technical aspects with the results of field investigations that will be programmed based on the results of the study of existing information from Phase 1, focusing on the areas of greatest risk and uncertainty.
Potential risks associated with the project are identified and prevention measures are prepared. Includes conducting a sanitary survey to assess potential public health hazards that may arise.
It is recommended to carry out a detailed economic evaluation and to continue with the feasibility evaluation in this phase 2, updating those carried out in Phase 1, when the system implies a significant cost (i.e. it requires a pilot scheme before its final operation), thus determining whether the project requires a higher investment.
Main attributes to evaluate
- Source water quality (clogging)
- Aquifer storage capacity
- Impacts on neighbors and ecosystems
- Presence of reactive / fractured rock (potential mobilization of arsenic)
- Sanitary survey (potential sources and routes of contamination)
- Development approval
- Detailed economic evaluation
Phase 3: Design and operation
It is recommended to conduct a pilot or at least recharge tests at the chosen site before its final operation, particularly if it is a relatively large scheme, allowing for more controlled scaling.
The data collected in the field will be used to carry out evaluations similar to those described above (Phase 1 and 2), but at a more detailed evaluation level.
The results will allow the formation of an operation and maintenance plan for the execution of the long-term scheme, as well as a risk management plan.
Design and construction generally represents the majority of the expenses of a RAG project. The design phases can be divided into ‘functional’ and ‘detailed’ design, a key input for the final economic evaluation (updated from Phase 1 or Phase 2).
Main attributes to evaluate
- Water Security Plan (PSA)
In order to facilitate the executing agency to follow the development phases of their MAR project, a form has been provided that explains the most important considerations in the development of each phase step by step.
6. Reflexiones y recomendaciones
Managed Aquifer Recharge Guide
- Develops a robust and flexible operating framework for the development and management of MAR projects in the agricultural sector in Chile;
- It allows to know the different MAR techniques and technical, economic and administrative requirements to implement a project of this type, reducing the uncertainties that surround its design and operation;
- Helps stakeholders and regulators assess and manage the potential risks associated with MAR projects;
- It is recommended that the Guide be expanded towards other purposes, and other sources; for example, through the incorporation of potable water and recycled water into MAR projects.
Promote the implementation of MAR
To move towards a more sustainable management of the resource and at the same time to promote the adoption of MAR projects in Chile, three key recommendations are presented:
- Encourage projects that benefit multiple stakeholders and strengthen the Water User Organizations (OUAs);
- To promote the gathering, exchange and analysis of information and data related to he MAR in Chile;
- Build trust in MAR project applications through the development and dissemination of successful projects.
Dillon, P.J. (2005). Future management of aquifer recharge. Hydrogeology Journal, 13 (1) 313-316.
Dirección General de Aguas (DGA) (2016). Guía Metodológica para Presentación de Proyectos de Recarga Artificial.
Garreaud, R., JP. Boisier, R. Rondanelli, A. Montecinos, H. Sepúlveda and D. Veloso-Águila, 2019: The Central Chile Mega Drought (2010-2018): A Climate dynamics perspective. International Journal of Climatology. 1-19. https://doi.org/10.1002/joc.6219
Sánchez, J. (2014). Conceptos Fundamentales de Hidrología; https://docplayer.es/5767013-Conceptos-fundamentales-de-hidrogeologia.html
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