Water Movement Factors Important to the Design and Operation of Subirrigation Systems

Abstract

ABSTRACT THE factors affecting water movement in sub-irrigation-drainage systems are identified and discussed as they relate to the design of such systems. Methods for quantifying steady, upward water move-ment from the water table are reviewed. The effect on design of the functional relationships between rate of up-ward movement and water table depth is analyzed. Ap-proximate methods for calculating the position and shape of the water table during steady state and transient subirrigation are reviewed. Methods are presented for predicting, in terms of certain design parameters, the time required to raise the water table for certain initial and boundary conditions. The use of the water manage-ment model, DRAINMOD, for analyzing the operation of a subirrigation system under changing weather condi-tions is discussed. The methods presented and discussed for the design and analysis of a subirrigation system are demonstrated by a case study for a site near Farmville, NC. Results of analyses for steady state, transient and continuous operation of several alternative designs for both conven-tional drainage and subirrigation-drainage systems are presented. The results show that both subirrigation and drainage requirements can be satisfied with an 18 m drain spacing, while a 25 m spacing will be required for conventional drainage alone.