Characterization of preferential flow in undisturbed, structured soil columns using a vertical TDR probe

Area of Science:

• Soil Science
• Environmental Science
• Hydrology

Background:

• Preferential flow pathways in soil accelerate agricultural chemical movement to groundwater, causing contamination.
• Time domain reflectometry (TDR) has shown potential for characterizing solute transport, but its application to preferential flow is limited.

Purpose of the Study:

• To extend the application of TDR for determining preferential flow properties in soil.
• To compare TDR-derived mobile/immobile model (MIM) parameters with those obtained from effluent data.

Main Methods:

• Laboratory experiments using undisturbed soil columns with a vertically installed TDR probe.
• Application of a tracer pulse to obtain residual mass (RM) breakthrough curves (BTC) via TDR.
• Estimation of MIM parameters using TDR data and comparison with conventional CXTFIT method using effluent data.

Main Results:

• TDR-derived RM BTC closely matched those from effluent data.
• TDR-estimated parameters showed strong correlations (0.95-0.99) with effluent-derived parameters for immobile water fraction, mass exchange, and dispersion.
• Calculated effluent BTC using TDR parameters demonstrated high similarity (R²=0.94) to observed BTC, indicating representative preferential flow properties.

Conclusions:

• The TDR method is a simple, minimally destructive technique for characterizing soil preferential flow.
• TDR provides reliable estimates of solute transport parameters, crucial for assessing groundwater contamination risks.