Artificial aquifer recharge: systematic mapping study

AAR

Artificial aquifer recharge

EPPI-Centre

Evidence for Policy and Practice Information and Co-ordinating Centre

SCIE

Social Care Institute for Excellence

SMS

Systematic mapping study

In countries where surface water is difficult to access, insufficient or scarce, groundwater, if it exists, remains the solution to meet the water needs of society. The heavy reliance on groundwater has put great pressure on these resources and as a result, they are no longer able to produce as much as the demand that has led them to depletion. Many countries are seeing their groundwater levels in perpetual decline (Wada et al. 2010) and many measures have been taken to stop this depletion or at least lower its rate such as the establishment of monitoring networks to control groundwater levels, the regularization of groundwater use through the implementation of rules and laws and sometimes a requirement of groundwater withdrawal licenses for groundwater use. However, these measures have proved to be insufficient and unsuccessful, especially when the aquifer has been excessively withdrawn and the natural recharge is no longer sufficient to make up for the drop in level caused by the over-abstraction. It shouldn't be forgotten that this excessive lowering of the level and overexploitation of groundwater resources can have several negative economic, environmental, and social consequences including threatening and endangering groundwater-dependent ecosystems, land subsidence, high groundwater abstraction costs, and poor-quality water invasion. So artificial aquifer recharge (AAR) remains the best way to tackle this situation. AAR is the effective practice invented by a human being to recover groundwater put in an alarming situation. Actually, AAR is the practice of raising, through human-controlled means, the amount of water that enters an aquifer. AAR has been implemented in many places and is still being implemented in others, as evidenced by numerous recently published scientific studies on AAR (Arshad et al. 2022; Hussaini et al. 2022; Maskey et al. 2022; Perdikaki et al. 2022; Tao et al. 2022). It has become a common practice worldwide as it plays an integral role in groundwater management and, above all, ensures the persistence of these resources.

As many artificial recharge projects are emerging in recent years around the world and especially in our country, Morocco, it is of vital importance and very beneficial for a project that is going to be placed for the first time to have a basis on which to rely, in particular the experiences of other countries that have already started the exploitation of AAR several years ago and are considered to be the pillars in this area. Hence the importance of scientific publications, which are considered as an image to see in detail the different scientific, technical, financial, and social aspects of the implementation of an artificial recharge project in a corner of the world without having to move around. Thus, the objective of this paper is to structure the existing AAR literature, detect the research work carried out on it so far, and obtain an overview of the current state of the research in this field.

Since this review is a part of our research project that we started in 2016 so the period chosen was 2013–2015 to identify the aspects that have been covered and locate the open issues, aspects that require improvement and highlight the research trends in that field. To this end, a systematic mapping study (SMS) has been conducted on the literature published about AAR from 2013 until 2015 to categorize and summarize the existing publications concerning the research in that field and to present what has been achieved so far in this field based on the relevant evidence.

An SMS is a methodology defined as a form of evidence synthesis. It was first developed by the UK centre Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre), and after that, it was adjusted by the UK agency Social Care Institute for Excellence (SCIE) in reaction specifically to a need of a methodology that portrays broadly the literature of an area of interest and was labelled ‘systematic mapping’ (James et al. 2016). In fact, an SMS is designed to give, through the existing literature, a visual summary map and a coarse-grained overview of a research area using visualization means such as graphs, maps, tables, graphics, etc. SMS is conceived to structure a research, area through classification, categorization, and counting of research, especially primary studies that have been published about it (Wortmann et al. 2017), led by a collection of research questions to identify types and frequencies of researches and detect gaps and trends in that field as well as to acquire a greater knowledge of concepts and determine new possibilities for future studies (da Mota Silveira Neto et al. 2011; James et al. 2016; Akoka et al. 2017; Dimauro et al. 2020). Moreover, It is a common method used to structure medical, software engineering, and social science research fields, especially medicine, which was one of the first areas to be systematically studied as it is a discipline of fundamentally evidence-based knowledge (Dimauro et al. 2020) but SMS is rarely used in other research areas which may be explained by the fact that the method is so far little known and there are no instructions on how to use it in other fields. SMS plays a meaningful role in evidence synthesis and is attracting growing attention as a technique for evidence synthesis (Petersen et al. 2015) because it is capable of covering in a methodical way the full range of science often required to initiate research in a given subject area.

Research questions should be defined because they are paramount. They highlight the objective of conducting the SMS so they constitute general questions to a topic to which we seek answers through the SMS. Actually, the research questions are used to define and guide the study. The papers that will be selected at the end will have to provide answers to these questions. In other words, research questions cover the review scope by specifying the target behind the SMS as well as helping in the definition of forums and platforms for searching the information about the field of study.

Conducting the research is the second main step in the SMS. It is defined as the data collection step. Actually, it is dedicated to searching for all papers by using a search string, which is a combination of popular keywords and their alternatives about the subject of interest, and the operators to gather all the publications that exist in the literature. The result of this step is a set of papers that will constitute the raw material of the study.

This step is very important because it allows the screening of relevant papers based on a set of inclusion and exclusion criteria derived from research questions and should be defined before conducting the search. In fact, exclusion criteria are used to eliminate papers that don't satisfy research questions, so the screening process selects appropriate studies that validate the inclusion criteria.

In other words, this step consists in identifying and clustering all the keywords related to the application areas of the subject of interest which exist in abstracts of selected papers and then constituting categories based on them and taking into consideration research questions that result in the classification scheme.

After the establishment of the classification scheme by the previous step, the current one is devoted to the extraction of answers to research questions, it results in the systematic map which means the visualisation of answers to research questions through means of visualisation (graphs, tables, maps, graphics…)

Firstly, the search by research string (Figure 2) in the Scopus source engine has given 3595 documents, and the existed filters offered by Scopus were used. The first inclusion criterion was applied, which is the inclusion of all papers of the period 2013–2015 because the current study is conducted to take into account papers produced from 2013 until 2015 so the result became 490 documents. Afterward, the second criterion was applied, which is the limitation of the search to papers published in the English language; therefore, the result became 465 documents. Afterward, the third criterion was applied, which is the exclusion of papers out of the AAR field by excluding subject areas considered as far from the subject of AAR and are not close to it. Consequently, the result became 449 documents. Subsequently, the fourth criterion was applied, which aims at specifying targeted document types, so limiting the result to articles and conference papers. Thus, the number of resulting documents was reduced to 409 documents, and then the fifth criterion was applied, which targets journals and conference proceedings as source type, so the number of remaining documents using just Scopus filters is 395.

Secondly, the papers collated are stored in an Excel sheet in the form of metadata, so each paper appears in (e.g. author, title, year, abstract, document type, country of origin, etc). After that, the papers went for another appraisal, starting from the evaluation of titles, to the examination of abstracts, and ending with the evaluation of the full text of each paper. In fact, titles that do not refer to or are far from the AAR topic are excluded, as a result, the number of retained papers after the evaluation of titles is 326. Abstracts that are not relevant to answer the research questions were excluded, this examination gave 278 appropriate papers and the evaluation of the full text of each paper resulted in 246 papers. Subsequently, the exclusion of articles of whom the full text was not found resulted in 241 retained papers. Besides, eliminating duplicates gave 240 papers and eliminating papers that belong to journals without peer review gave 212 papers. Since SMS is based on synthesizing primary studies so removing review papers has resulted in 204 retained documents which are the relevant papers for this study.

Consequently, the screening of papers step was based on the one hand on the existing filters in the Scopus source engine and on the other hand on the appraisal of titles, abstracts and full text of the papers, the (Figure 3) illustrates each stage of the screening step and the number of excluded and retained papers.

The classification scheme which is illustrated in (Table 3) is a result of the keywording step or the coding step as it is termed in (James et al. 2016) which is the step following the screening of papers as indicated in (Figure 1). In fact, terms, concepts, and keywords describing the focus and reflecting the contribution of each study were extracted from the abstracts and collated to construct categories. Introductions and sometimes conclusions were inspected if abstracts were insufficient for providing meaningful keywords. Thus, 6 categories were constructed from the evaluation of all the collated keywords. Those categories allow us to classify each paper and enable us to understand the different types of papers considered in this study.

The data extraction and mapping process is presented in the Results section.

In this part, results obtained after applying all the SMS steps are presented, especially, the data extraction and mapping process step, which will be detailed in the following. In fact, answers to the research questions cited above will be provided and detailed based on the deduced relevant papers:

Depending on the word cloud, the Top 5 authors to refer to when dealing with AAR are:

• Dillon P.

• Page D.

• Wang Z.

• Ahmed S.

• Drewes J.E.

The above answer provides information about who are the active authors who have done a lot of effort to investigate the field of AAR. Actually, knowing who are the influential authors of a field, in this case, AAR enables one to have a reference to refer to and a base on which to draw when needed more information, when needed to understand certain related concepts in the domain or just get a complete idea of the domain.

The 204 documents selected were published in different sources during the period 2013–2015 but most of the sources hosted only one publication so it was chosen to present in a table (Table 4) the sources that hosted more than 5 publications. This selection allows one to identify sources where there have been many publications about AAR and gives an idea about sources that have been solicited to publish works about AAR, so highlighting these sources permits one to know where one can search for further information about AAR and help future researchers identify the best sources containing papers about AAR.

The reason that drives a country to implement the AAR project depends on the problem it suffers from. The problems are numerous and those that have been most identified in the relevant publications are aquifer depletion, groundwater contamination, water quality, water shortage, natural hazards such as floods, land subsidence, etc. To summarize the reasons behind the implementation of an AAR project, which have been found in the relevant publications. They were gathered in groups. The first group is groundwater recharge enhancement, which is the reason most often mentioned in the papers, the second group is water quality improvement, the third group is protection against possible disturbances, and the fourth group is water banking. Besides, each group was given examples that were picked from relevant publications. They are organized and well explained in Table 5. The latter allows us to know the different reasons that push the water decision-makers to implement a project of AAR, from 204 relevant publications and according to the same table (Table 5) the most frequently found reason is aquifer replenishment. This gives an idea about the state of aquifers in the world. In fact, many aquifers are experiencing the phenomenon of depletion, others are in the process of depletion while others are already drying up, so AAR turns out to be necessary.

The water sources used for an AAR project depend on several parameters, especially the objective of the recharge project. For example, if the objective of the project is to mitigate the adverse effects of floods, then the source of water is the flood water harvested and injected into aquifers after possible treatments.

Possible water sources found in the relevant papers are as follows:

• River water

• Tap water

• Harvested rainwater

• Irrigation water

• Lake water

• Desalinated seawater

• Reclaimed wastewater

• Stormwater

The results obtained from the application of the SMS will certainly help the future implementation of AAR projects. In fact, the importance of review methods that are organized and have steps to follow like the SMS lies in their ability to facilitate to a researcher interested in a given subject or a water manager to understand that subject, to know important statistics, leading countries, names of people that have done a lot of studies and published them in the matter and especially to see different experiences of different countries to benefit from them.

For example, in our study, the results obtained will guide the researchers and water managers to know which type of document will offer them much more information and detail, knowing that the articles are much more numerous than conference papers. The results will also guide them to consult papers of authors who have done many publications in the field of AAR and to consult necessarily the publications of journals that publish papers on AAR in a very frequent way. Moreover, having in their hands a map that shows the geographical distribution of AAR studies in the world will guide them to see all the studies that have been done by countries that have experienced many AAR projects, which will enable them to discover all the facets of such a project, as well as the different problems and obstacles encountered by these countries, which will allow them to get to know them and to prepare plans to try to avoid them. This study is also important because it highlights the different reasons behind the implementation of an AAR project, and that the latter is not only useful to revive an aquifer in depletion but also for many other reasons that were detailed in Table 5. AAR can be implemented for several reasons at the same time. This is the case for example of countries that suffer from water scarcity and at the same time are known by occasional severe floods so, AAR can be used to alleviate the impact of these floods by storing the runoff in aquifers which will also increase the groundwater storage. Besides, this review is also valuable in the sense that it clearly shows the main sources of water that can be used for an AAR project so that the project managers can choose the source that is appropriate and above all, the source for which the cost of transfer of water to the recharge points should not be expensive. A diagram such as Figure 8 is very significant and useful for an AAR project because it details different AAR structures and this will give an idea of the appropriate structure to implement depending on the characteristics of the region. For example, even if a region has favourable geological characteristics that allow for the construction of infiltration basins but this region is known to have an arid climate, in this case, an infiltration basin and dams are not appropriate as the high evaporation rates will make the recharge operation ineffective.

Consequently, review studies such as a SMS are important to consult before embarking on a project of this magnitude such as AAR. Those in charge must seek to benefit from the experiences of other countries and try to cover all the facets of such a project to gain knowledge, save time, and also have an idea of the costs of the different structures of the AAR and know what are the possible problems and obstacles that can hinder the smooth running of the project and try as much as possible to avoid them. Therefore, this will allow the project to be improved even more.

The objective of this study was the application of an SMS to the topic of AAR from 2013 to 2015. Synthesizing relevant publications following exclusion and inclusion criteria, formulating 7 research questions for which we tried to give answers to identify the most recent stage and aspects that have been covered and what are the open issues, knowledge gaps, aspects that require improvement, and what are the research trends in that field so as to develop a better understanding and a broad overview of this field to help direct and guide future research. The SMS method resulted in 204 relevant documents on which this study was based to answer the 7 research questions that were formulated. The answers to these questions were provided in the form of tables, graphs, maps, and illustrations to ensure better visualization of the results. Ample results were obtained, which will serve as a basis for future research as it was for our research, which we started in 2016.

The authors certify that they are not affiliated with or involved with any organisation or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this paper.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.