HR: 1340h
AN: H23F-1488    [Abstracts]
TI: Rainwater and Groundwater Chemistry in the Eritrean Highlands - Inference for Groundwater Recharge
AU: * Haile, E
EM: ehaile@kth.se
AF: Department of Land and Water Resources Engineering, Royal Institute of Technology, Stockholm, SE-10044 Sweden
AU: Jacks, G
EM: gunnjack@kth.se
AF: Department of Land and Water Resources Engineering, Royal Institute of Technology, Stockholm, SE-10044 Sweden
AB: Fractured aquifers made of metamorphosed volcanic and sedimentary sequenced are the major sources of groundwater across the highland region of Eritrea. Areas of relatively high recharge rate are located in riverbeds and fracture zones. The significance of groundwater as potential resources for usage in the area is related to the amount of recharge that occurs as well as factors that may affect the water quality within the aquifers. Chemical data from rainwater, groundwater, and soil samples were collected. Using the chloride mass balance method groundwater recharge rate was estimated. Chloride concentration determined from wet deposition has an average value of 2 mg/L. Dry deposition was considered to be small, which seems to be a reasonable assumption for inland sites with little vegetation. Soil water chemistry collected from selected profiles show considerable variation from site to site pointing to lateral surface runoff. Only comparisons between rainwater and groundwater chemistry allowed to quantify the amount of meteoric water input into the groundwater. The largest proportion of the groundwater recharge occurs due to direct percolation through alluvial sediments along riverbeds. From an average annual rainfall amount of 550 mm, about 10~% of it forms the groundwater recharge. This figure is a little higher than found in similar environments elsewhere in Africa. Although the area is of semi-arid region, less is known about the roll of evaporation to affect the chemical composition of the groundwater. The dominant water type of Ca-Mg-HCO₃ is considered to be as a result of water-rock interaction. Such an interaction would take place given the extended dry period of a year, during which groundwater and aquifer material have longer contact time.
DE: 1830 Groundwater/surface water interaction
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: Fall Meeting 2005