BTC SOLUTE-TRANSPORT PARAMETERS FOR THREE SEDIMENTS

Solute transport is concerned with irrigation and soil salinization, fertilization and pollution. A locally
manufactured fraction-collector was used for BTC runs on three disturbed sediments from Egypt to get
transient chloride-transport parameters under steady-state saturated flow. Thirty-cm long columns were
packed with dune Sands, Nile-bank sediments, and clayey Calcareous-aggregates.
Experimental BTC data were fitted to two analytical solutions in CfitM code that solves the CDE
equation corresponding to boundary conditions. The parameters included the retardation factor, Peclet
number, longitudinal dispersivity, hydrodynamic dispersion coefficient and tortuosity. RETC was used to
get the hydraulic parameters by fitting the samples’ pF data.
Sands showed retardation factor of about unity (no reaction), intermediate values for both Peclet
number (49-61) and dispersivity (0.49-0.62cm) (moderate leaching-efficiency). Smaller dispersivity
(better leaching) would be expected if saturation was realized. Nile-bank sediments monitored high Peclet
number (117-180), small dispersivity (0.17-0.26cm) (efficient leaching) and slightly less than unity
retardation-factor (some anion exclusion). The Clayey-aggregates have shown wide range of small Peclet
numbers (9-34), large dispersivity (0.90-3.4cm) increasing with aggregate size (low leaching in large
aggregates) and retardation factor significantly less than unity (rapid exit due to high anion-exclusion). In
contrast to Clayey-aggregates, the high Peclet number of the Nile-bank and Sands reflects dominant
mass-flow transport compared to dispersive transport.