The Impact of Land use on the Quantity and Quality of Groundwater Recharge into the Coastal Plain Aquifer, Israel

A study designed to examine the impact of urbanization on the quantity and quality of groundwater recharge in the Coastal Plain Aquifer, Israel, is being carried out in the city of Ashdod, where urbanization in the last 40 years has been one of the most rapid in Israel. Infiltration processes under different urban land setups are being compared to those beneath nearby cultivated areas and the undeveloped sand dunes. Temporal variations in water content at various depths along the entire vadose zone were measured for two consecutive years at five sites that represent typical land uses. Water-content measurements were conducted using a monitoring system that includes flexible time-domain reflectometry (FTDR) sensors installed in slanted boreholes throughout the entire vadose zone. The variation in water content enables direct tracking of the wetting- front propagation velocities, variations in vadose-zone water storage and calculation of the infiltration fluxes. In addition to the FTDR system, a new monitoring system that allows continuous measurements of the water potential and frequent sampling of the sediment pore water was installed at a sand dune site. This new system is comprised of vadose-zone sampling ports (VSPs) and FTDR sensors installed in slanted boreholes. Preliminary results show that in addition to the expected changes in pore-water pressure due to changes in water content caused by the infiltration process, increases in pore-water pressure were detected simultaneously throughout the entire vadose zone after each of the major rain storms. This pressure wave was detected each time fast and significant propagation of the wetting front was observed. Vadose-zone pore water was frequently sampled by a second VSP system and analyzed for chemical and isotopic compositions presenting changes in the vadose zone chemical and isotopic profiles throughout the year.