HYDROLOGICAL EFFECTS OF INTAKE STOPS

Abstract

The phenomenon of compressed air upon infiltration in an unsaturated zone is a well-known problem. For water companies producing drinking water from infiltrated surface water in the dunes this phenomenon can seriously hamper production due to initially low infiltration rates after the system restarts. For this MSc thesis five experiments are conducted to study the effect of air confining and air draining conditions on the infiltration rate. In the first experiment the saturated conductivity of the soil column was determined. In the second and fourth experiment water was infiltrated by increasing the water table from the bottom up, venting air freely from the top of the column. In the third and fifth experiment, water was supplied at the top of the column resulting in entrapment of air between the wetting front and the saturated zone at the bottom of the column. Results show a short lived effect of compressed air in the first 4.7 minutes of experiment V. A limited effect is seen between the air-confined and unconfined infiltration rates (0.98) for experiment set IV and V. The air is not effectively retained due to escape of air along the column wall and due to air bubbles erupting through the wetting front. This is attributed to the small length of the column, by which in comparison the capillary is relatively high. Therefore, the difference in soil moisture values between the top of the column and water table are quite low (10%).