The hydrology and hydrogeology of the Aammiq Wetland

Marsh hydrology surveying team

The Aammiq Wetland is situated in the Bekaa, a fertile plain that lies between the Lebanon and Anti-Lebanon mountain ranges at an altitude of between 850 and 1100 m. Aammiq marsh is a small remnant of extensive wetlands that once covered a large proportion of the Bekaa. It is of major ecological significance for birds (especially migrants), mammals, amphibians and plants. Since 1996 A Rocha Lebanon has been involved with the management of the Aammiq Wetland with the remit "to maintain, and where possible, enhance the size, functionality and biodiversity of the wetland ecosystem."

As with any wetland, the critical factor for Aammiq is the quantity and quality of the water supply. Increasing population growth and per capita demand for water in Lebanon, coupled with the predicted effects of global warming, suggest that Aammiq’s status as a wetland is threatened. For various reasons the hydrology and hydrogeology of the Aammiq area has been little studied and this has hindered the management of the wetland. To help achieve this aim, a detailed hydrological and hydrogeological survey was undertaken over a full 12-month period between 2002 and 2003.

The purpose of this study was not only to try to answer fundamental questions about how the marsh functioned, but also to provide baseline data on which future monitoring of Aammiq could be based.

This study involved the assembling of all available data, a study of the geology of the marsh and the adjacent mountainside, the mapping of the marsh and measurements of water depths throughout the year. In addition, as many as possible of the water inflows (springs, rainfall) and outflows (stream flow, evaporation) to the marsh were quantified or estimated throughout the monitoring period in order to create a water budget. A number of tests were also carried out. These included determining the hydraulic conductivity (permeability to water) of the marsh sediments, and using fluorescein dye tracer studies to determine the pathways and rates of water flow within the soil. Water samples from springs were also analysed for major nutrients, pH and total dissolved solids.

Results showed that the maximum flooded area of the marsh was 107 ha, and the water budget showed a total throughflow of 454 million cubic metres. It should be noted, however, that this was based on an exceptional year’s rainfall of approximately double the average.

The results allowed the creation of a tentative hydrogeological model for the area. Clearly most of the groundwater originates in the mountains to the west and flows downslope in limestone aquifers to the plain. When this groundwater reaches the valley floor, the picture becomes more complex. Evidence suggests there is a strong southwards component to its flow.

The study also proved that groundwater pumping for irrigated croplands in the region is affecting the water supply to the springs and reducing both marsh water levels and the duration of the wet period. Because of the southward flow, efforts to change water management in the Aammiq region should concentrate on reducing groundwater use north of the marsh.

Locational map of the Aammiq marsh

Continuous monitoring of the water extraction in the area and its effects on the Aammiq Wetland is strongly recommended.

The study also suggests that in order to increase the flooded area during the wet season, the best strategy is not to add more water (since there is an abundance at this time of year), but rather to reduce the rate of outflow from the marsh. Specific recommendations for this have been made.

The data recorded suggest that it would not be difficult to create areas of permanent water within the marsh. For example, in 2002 the water table in the marsh dropped only 1–2 m below much of the marsh surface, and in fact some deep pools and ditches remained wet throughout the summer. Therefore more permanent pools could be created by relatively shallow excavations.

In terms of water quality, the Aammiq Wetland appears to have no serious problems at present, although a thorough examination of pesticide levels is needed. The analyses in this study, however, caution against complacency. A microbiological analysis of spring water showed >100 Escherichia coli and >100 intestinal enterococci per 100 mL, definite indicators of contamination by farm run-off and/or human sewage. Therefore there remains a possibility of ecologically-damaging nutrient levels, as well as diseases and toxic chemicals entering the marsh water supply. Ongoing monitoring is recommended.

Irrigation in the Bekaa

In summary, the water supply to the Aammiq Wetland is under serious threat. Water across the entire Aammiq region must be managed carefully and efficiently if in future the marsh is to maintain sufficient water levels to support wildlife and essential ecological processes during the long annual dry period. It is recommended that a critical next step in the management of water resources at Aammiq is to identify minimum flows and minimum water levels that will sustain wildlife and ecological processes at different times of year.

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Project leader: Richard Storey. For further information contact lebanon@arocha.org

Partners: MAVA, Skaff family