Interaction of the saturated and unsaturated soil moisture zones : 1. analytical solution of the linearized Richards equation; 2. the role of climate in shaping the phreatic surface

This study presents a linear model of interactions between the water table and the unsaturated soil moisture zone (which links the saturated water table zone to the land surface). The effects of climate on the water table are also modeled. Part I of the study: (1) comments on the applicability of certain hydrologic equations of the soil-water zone developed for semi-infinite and finite soil columns; (2) deduces and solves a linearized Richards equation for soil-water movement in high water tables (including some effects of vegetation); and (3) examines the equation"s solutions for the infiltration of moisture into a soil system, finding them similar to nonlinear solutions; dimensionless expressions are derived to indicate when a finite domain analysis is needed. In Part II, quantitative relationships among soil-water content, water table depth, and net accretion to the groundwater for different soil types and climates are developed and used in a nonlinear model of the water table shape and of long-run climatic influences on it. Case studies are presented, using data from the El-Gizera and Bahr-el-Ghazal regions of Sudan. It is shown that the water table plays a significant role in many water balance problems. Appended are physically-based expressions for infiltration and ponding time and a 165-item bibliography (1921-81).