SEASONAL-VARIATION OF CLOGGING OF AN ARTIFICIAL RECHARGE BASIN IN A NORTHERN CLIMATE

The decrease of infiltration rate, and the depth, cause, and hydraulic effect of clogging, were evaluated for a sandy, artificial-recharge test basin during the application of water containing between 51 and 61 mgl-1 suspended solids. Infiltration rate decreased by two orders of magnitude under fall operational conditions for a clean sand surface. Clogging was caused by clay deposition within the basin soil profile during early operation times (19-75 h) followed by the complete interception of sediment in the surface filter cake during later operational times. Impedance decreased by two to three orders of magnitude in the surface 8 cm, and by zero to two orders of magnitude from 8 to 38 cm. Increased clay content following basin operation was measured to a depth of 5 cm. During the spring test, sediment movement and deposition were similar to the fall test. In addition, carbonates and iron oxyhydroxides precipitated, causing cementation of the surface soil grains. The cementation caused increased hydraulic impedance and resulted in a decrease of total recharge. Carbonate precipitation was caused by increased basin-water pH resulting from algal photosynthesis. Allowing the basin to dry and crack for ten days resulted in a substantial recovery (64%) of infiltration rate. Following the drying treatment the basin reclogged more quickly than for the previous test on clean sands, and the impedance of the surface layer reached values larger than those prior to the drying treatment. The decrease of impedance caused by drying was confined to the surface layer, and no effect was observed below 8 cm. Following the natural drying treatment, total recharge was about half that of the clean basin.