Migration and deposition of fine particles in a porous filter and alluvial deposit: laboratory experiments

The filtration of fine solid particles suspended in water by two porous media, a column of glass beads (2-mm diameter) and a column of artificial sand (1–1.6-mm diameter), was studied. A suspension of fine particles (equal and lower than silt size—called silt in this paper) in water (concentration, δ, of 25 mg/L) flows vertically through the columns. The hydraulic head and time—distance—varying δ in seeping water were measured along the depth of the column for a period of about 80 h. In the column of glass beads, most of the silt gets retained in the upper part of the column. The silt-retention front migrated downward continuously during the 80 h that the experiment lasted. In artificial sand, during the first 30 h, the top few centimeters of the filter contribute the most to the total retention of suspension. At a later stage, however, it is a deeper section of the column that contributes the most. This downward shift continues until the top layers of the column start to fully clog and the silt front stops moving down. The hydraulic conductivity, K, shows a sharp change at the interface below and above the silt retention front. It drops by 30–50 % due to the clogging for glass beads and artificial sand, respectively. The findings of this study are of paramount importance for properly managing and administrating the recharge dams especially in arid climate.