INFILTRATION AND SOLUTE TRANSPORT EXPERIMENTS IN UNSATURATED SAND ANDGRAVEL, CAPE-COD, MASSACHUSETTS - EXPERIMENTAL-DESIGN AND OVERVIEW OFRESULTS

A series of infiltration and tracer experiments was conducted in unsat urated sand and gravel deposits on Cape God, Massachusetts, A network of 112 porous cup lysimeters and 168 time domain reflectometry (TDR) p robes was deployed at depths from 0.25 to 2.0 m below ground surface a long the centerline of a 2-m by 10-m test plot. The test plot was irri gated at rates ranging from 7.9 to 37.0 cm h(-1) through a sprinkler s ystem. Transient and steady state water content distributions were mon itored with the TDR probes and spatial properties of water content dis tributions were determined from the TDR data. The spatial variance of the water content tended to increase as the average water content incr eased. In addition, estimated horizontal correlation length scales for water content were significantly smaller than those estimated by prev ious investigators for saturated hydraulic conductivity. Under steady state flow conditions at each irrigation rate, a sodium chloride solut ion was released as a tracer at ground surface and tracked with both t he lysimeter and TDR networks. Transect-averaged breakthrough curves a t each monitoring depth were constructed both from solute concentratio ns measured in the water samples and flux concentrations inferred from the TDR measurements. Transport properties, including apparent solute velocities, dispersion coefficients, and total mass balances, were de termined independently from both sets of breakthrough curves. The disp ersion coefficients tended to increase with depth, reaching a constant value with the lysimeter data and appearing to increase continually w ith the TDR data. The variations with depth of the solute transport pa rameters, along with observations of water and solute mass balance and spatial distributions of water content, provide evidence of significa nt three-dimensional flow during the irrigation experiments. The TDR m ethods are shown to efficiently provide dense spatial and temporal dat a sets for both flow and solute transport in unsaturated sediments wit h minimal sediment and flow field disturbance. Combined implementation of lysimeters and TDR probes can enhance data interpretation particul arly when three-dimensional flow conditions are anticipated.