The Quantitative Influence Of Sallnity On The Apparent Resistnity On A Physical Model Upon Saltnation

The excessive exploitation of groundwater aquifers leads to water table drawdown, and<br>subsequentfy to the contamination of these aquifers by the intrusion of sea water or other hazardous<br>sources. This wortdwide environmental problem is becoming increasingly critical in coastal agricultural<br>areas, where the fine grarned materials develop a thick fringe zone. By evapo-transpiration the moisture<br>of this zone pumps up the satt in the dry season, which cannot be efficiently washed away in the wet<br>season. Over the years the salt will accumulate at different rates for different terrarns and climates.<br>which will uttrmately cause the deterioration of the land Lebanon is not an exception and the moderate<br>precipitation rate together with a strong water flow in wmter cannot, in the long term, compensate for the<br>consequences of chaotrc and uncontrolled exploitation of coastal aquifers.<br>The current study investigates the possibility of an early detectron of salination. through<br>systematic observation of electrical resistivity in selected positions with fixed electrode arrays A direct<br>current electrtcal profiling system of Wenner configuration was tested in the laboratory using a physlcal<br>model. The model was constructed of wood and plastic filled with saturated sand and hawng a constant<br>water flow of 1.6 Vmn. The model size is 148 by 85 cm for lateral dimensions and 25 cm of sand<br>thickness. with a total porosity of 36%. Upon salination the salt was increasingly added to fhe system to<br>reach a concentration of 32 gn. Upon desalinahon satt water was replaced by fresh water to dilute the<br>water In the system to a concentration of 0.25 g/t. The results show that the relationship between<br>sallnrty and electrical resistivity is inversety proportional and characterized by linear loganthmlc function.<br>the velocity of water flow calculated by abrupt resistivity changes is tower than the hydraulic velocity; the<br>reslstivity values for low salinity upon desalination are much different (smaller) than those upon<br>salination of equivalent salt concentrations; the relative change of resistivity upon salination and<br>desatination involves almost equally all features of the tank that have distinctive resrstrvrty values.