Water Balance Approach to the in Situ Estimation of Volume Flux Densities Using Slanted TDR Wave Guides

The water balance of mass or volume is the primary building block in the study of flow. Its strict application to soil water relations may help in the understanding of flow processes. We derived the volume flux densities from volume balance calculations based on rapid in situ measurements of soil moisture during sprinkling. The water contents were measured, at intervals of 30 s, with time-domain reflectometry (TDR) equipment using five pairs of obliquely installed wave-guides. We estimated flow rates from the water balance of 0.10-m thick soil layers. Volume flux density, the velocity of wetting fronts, and mobile soil moisture are the dependent variables. Their relations with depth, antecedent soil moisture, and the rate and duration of water input are statistically investigated.