Abstract
A 30° small model aquifer with fine sand was used to simulate the process of groundwater recharge through wells under gravity flow. The sediment-laden water was characterized by suspended solids which were a mixture of 50 percent bentonite and 50 percent kaolinite, tested in low, medium and high concentration.
Suspended solids in the recharge water were filtered out in the model aquifer. Time and spatial distribution of suspended solids in the aquifer were measured. The experimental data showed exponen- tial decrease of suspended solids in the aquifer medium during recharge. The proportionality factors of these exponential pro- cesses also logarithmically decrease with time. The accumulation of suspended solids near the well occurred more rapidly than in the far Measurement of hydraulic pressure distribution in the aquifer indicated that a greater variation in hydraulic gradient was ex- perienced near the well as compared to the far zo: zone. In fact, hydraulic gradients near the well increased with time, because of huge accumulation of suspended solids there. On the contrary, horizontal flow occurred in the far zone where the hydraulic gradients showed slow decrease with time.
Therefore, the experimental data analysis described the aquifer medium in two distinct zones. One was near the well, which showed extreme complexity in the medium; the other was the far zone where there were ample justifications to assume horizontal flow. With regard to the continuity of groundwater flow from a well, the pre- diction of recharge rates was made for the far zone, using the well discharge formula for steady-state flow at different times for non- steady state condition. The predicted rates showed close relation- ship with those of the experiment for lower influent concentration of suspended solids. Predicted rates were, however, significantly
different from the experimental values when using a higher concentration.