Modeling changes in hydraulic conductivity due to siltation using soil columns from Alshuwaib dam site, United Arab Emirates

Abstract

Changes in soil hydraulic conductivity (K) as a function of total suspended solids (TSS) concentration in the infiltrating water were studied in the laboratory using the constant-head technique. Soil samples collected from Alshuwaib dam site in the United Arab Emirates were selected for the study. The soil samples were collected from two distinct layers at the dam site; an upper layer which is composed of silt and clay and a lower layer which is mainly composed of sand. Formation of the upper layer is believed to be due to deposition of TSS originally present in the intercepted stormwater or due to dust deposition at the site. Temporal variations in the saturated K of the soil were studied using water with various TSS concentrations. The infiltrating turbid solution was prepared using tap water mixed with soil samples collected from the upper layer. Results show that presence of TSS in the water introduced into the columns caused a drop in K over time. Changes in K follow a sharp drop shortly after injecting the turbid solution and a slower drop at later times. The sharp initial drop was more pronounced for cases with higher injected TSS concentration. For an experimental time of about 80 h, K dropped an order of magnitude for cases with low influent concentration. Changes in K were simulated using a mechanistically based model that assumes formation of new layers with lower K values as a result of particle entrapment below the soil surface followed by particle deposition on the surface. The developed layers model closely predicts variations of K over time, with no observed particle entrapment, except at low TSS concentration. Meanwhile, predicted deposited masses of TSS are in agreement with those determined after the completion of the experiments. Results presented here could also be useful to managers of surface recharge facilities in the country and elsewhere.