BGR Bundesanstalt für Geowissenschaften und Rohstoffe

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TC Jordan: Assessing the Potential for Managed Aquifer Recharge (MAR)

Report of the project:

Background
Jordan like many other (semi-)arid countries in the world is highly dependent on groundwater resources and face increasing demand and decreasing supply leading to groundwater level declines and potentially salinisation of groundwater resources. Managed aquifer recharge (MAR) could support an increase in water resources and is defined as the intentional recharge of groundwater for recovery or environmental purposes and includes the monitoring of recharge water quality and resulting impacts. It has been applied successfully internationally and its importance is increasing as a tool for adaptation to climate change.

Project aim and approach
With this project, the Federal Institute for Geosciences and Natural Resources (BGR) supports the Jordanian Ministry of Water and Irrigation (MWI) - by exemplarily evaluating the potential for MAR in two basins (Amman-Zarqa and Azraq basins) - in its potential to successfully use managed aquifer recharge via infiltration of stormwater runoff and in selecting suitable recharge sites. The main tasks comprise (1) the development of maps for MAR potential leading to the subsequent identification of suitable sites for potential pilot projects or measures to increase recharge effectiveness from existing structures and (2) the preparation of a guideline for the implementation and regulations of MAR in (semi-)arid regions like Jordan.

The first part of the guideline outlines international examples and it reviews some lessons learned and steps to be taken for a sustainable MAR scheme implementation. The second part is a case study on the two mentioned heavily overabstracted basins in Jordan. Here, the climatic, hydrological, hydrogeological and other factors are described in detail and used as criteria in a pre-feasibility study on their MAR potential. This is followed by recommendations for a feasibility study, implementation and necessary activities during operation. The guideline focuses mainly on the retention of flood water in ephemeral streams followed by recharge via infiltration.

Recharge release dam in Wadi MadonehFig. 1: Recharge release dam in Wadi Madoneh Source: BGR

Method
The main technical questions to be addressed are (a) source water availability, (b) availability of aquifer storage space and (c) the most effective method of transfer of source water to the aquifer. In (semi-)arid regions surface runoff commonly occurs in short flash floods which might flow unused towards the sea or saline depressions and hence could provide a non-committed water resource for storage in the aquifer for later use, also reducing evaporation compared to surface storage. Aquifer storage space is commonly sufficient when groundwater reservoirs have been overabstracted and groundwater levels have declined. The most cost effective method of transfer is infiltration and is widely applied where unconfined aquifers and permeable soils are present. Typical low cost techniques are recharge dams, recharge release dams (Fig. 1) or infiltration basins downstream of water harvesting structures.

Any regional pre-feasibility study looking at the potential for implementing MAR by harvesting surface water runoff and subsequent infiltration has to answer two separate questions:

  • Does the catchment generate sufficient harvestable runoff?
  • Does the site allow for the construction of a water harvesting structure and the transfer to a suitable aquifer?

Commonly only very limited information is available on the runoff quantity and quality of flash floods, and runoff has to be estimated based on other relevant parameter. This study uses regional information on rainfall, slope, existing water harvesting structures, land use, soil and hydrogeology. The minimum or constraint criteria for a suitable catchment are > 75 mm/a of rainfall, the absence of existing large dams and the absence of urban areas, mudflats or quarries. All criteria are then classified into unsuitable, less suitable and suitable e.g. zero, one and two (for example gentle slopes are less suitable for runoff generation than steeper slopes) and the criteria are weighted linearly to come up with a final score ranging between 0 – 100 % suitability (Fig. 2).

Catchment suitability map for runoff generation in the Amman-Zarqa and Azraq basinsFig. 2: Catchment suitability map Source: BGR

For the site suitability assessment the above mentioned six criteria plus additional criteria concerning the subsurface (thickness of aquifer, depth to water table, flow gradient, distance to faults) and groundwater quality (salinity, nitrate concentration, E.coli concentration) as well as infrastructure (distance to roads, distance to borders, distance to active governmental production wells) are also classified (for example flat areas are suitable for infiltration, while steep areas are not) and are weighted linearly for a site suitability map (Fig. 3). Additional constraint criteria are a slope of < 5 %, absence of an aquitard or unsaturated aquifer, aquifer thickness > 20 m, distance to a contaminated well of > 1 km, distance to international borders > 2 km, distance to a wadi < 2 km and catchment size > 18 km². In a final step, both maps are overlaid to be able to visually find a suitable catchment upstream of a suitable site. A more detailed feasibility study would then be needed for the most promising sites. Apart from the technical feasibility any pre-feasibility study should address socio-economic questions like demand, operation and maintenance, monitoring, cost benefit ratio as well as management capability and regulations. All these aspects are discussed for international examples and for the Jordanian case study in the guideline.

Results
MAR potential maps addressing water availability and site suitability were developed for two surface water basins in Jordan (Fig. 2 and 3). The regional assessment shows that 69 % of the basin area is unsuitable for generating runoff and 88 % is unsuitable due to site constraints. Apart from the subcatchments areas of existing water harvesting structures, only 3 % of the catchment area could be suitable for generating sufficient runoff and 9 % could be suitable for site selection requiring more detailed investigation. There is no convincing suitable site with an associated suitable catchment.

Site suitability map for MAR via infiltration in the Amman-Zarqa and Azraq basinsFig. 3: Site suitability map for MAR Source: BGR

The evaluation of existing data and experiences from existing structures shows that source water availability is the most restricting factor in regions with less than 200 mm/a rainfall. Another important restriction is the high sediment load of runoff requiring regular maintenance. If maintenance is not undertaken, the effectiveness of MAR schemes can decrease dramatically to the point where they result in an overall negative impact. It is recommended to improve operation and maintenance as well as monitoring at existing MAR sites in Jordan to be able to assess the actual effectiveness.

Institutional and socio-economic constraints are partially due to a lack of funding for maintenance and monitoring leading to a presumably low cost-benefit relation. In addition, there is limited institutional capacity to manage MAR projects at the ministerial level as well as limited awareness and understanding of MAR processes within the ministry and local residents.

It is recommended to increase the involvement of the local community in MAR activities to ensure maintenance and monitoring to evaluate the effectiveness of MAR schemes. For new MAR projects funding for maintenance should be obligatory and ownership given to local beneficiaries. In addition, a national MAR strategy and regulations should be developed.

The guideline was prepared for decision makers, funding agencies, interested stakeholders and the scientific community involved with managed aquifer recharge in (semi-)arid regions. The approach is a blueprint and could be applied for similar assessments of basins in other countries. Criteria selection, classification and weighting are adjustable to suit the local conditions and availability of data. The expressed recommendations are also transferable to other countries with similar conditions.

Literature:

Contact:

    
Dr. Anke Steinel
Phone: +84-24-36740494

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