Approximation of Groundwater Table The water table acts as a boundary between saturated zone and unsaturated zone. The soil matrix is fully saturated below the water table. At the same time, the soil just above the water table is also saturated due to the capillary effect. The depth of capillary rise may be from few centimeters to few meters. A suggested by Silin Bekchurin (1958), capillary rise may be around 2-5 cm in case of course sand, may be around 12-35 cm in case of sand, around 35-70 cm in case of fine sand, around 70-150 cm in case of silt and around 2-4 m and more in case of clay soil. Fig.1.4 shows the actual and approximate distribution of the moisture content. The actual distribution can be approximate by a step function which is necessary to approximate the elevation of the groundwater table. The step defines the depth of the capillary rise, hc. |
Fig. 1.3 Moisture distribution in a soil column |
It can be assumed that up to the distance of hc, above the phreatic surface, the aquifer is fully saturated. The aquifer above hc line is completely dry, i.e. no moisture is present. The upper end of the capillary fringe may be taken as the groundwater table. However, when depth of capillary fringe, hc is much smaller than the thickness of the aquifer below the water table, the capillary fringe may be neglected in solving real world problems. The depth of the capillary fringe can be approximated as (Mavis and Tsui 1939)
 |
|
where dm is the mean diameter of the soil grain, n is the porosity.
Polubarinova - Kochina (1952, 1962) approximated the capillary fringe as
where d10 is the partical size at which 10% of the total partical is finer than that size. |
 Fig. 1.4: Approximation of groundwater table |
