Chapter 9. Drainage Systems

Abstract

This chapter describes the basics of design, operation, and maintenance of subsurface drainage systems as needed for sustained irrigated agriculture. Emphasis is on the control and management of the water table as needed for crop production in harmony with environmental concerns. Two approaches to design of subsurface drainage systems are based on steady state and transient flows. Steady state design of drains is based on Hooghoudt's equations as modified by Moody. Two examples are presented in the form of spreadsheets. Transient flow design is based on procedures developed by Dumm and Glover and others in the U.S. Bureau of Reclamation (USBR). Spreadsheets are presented using the USBR transient approach for parallel relief drains. Spreadsheets are also presented for calculating drain spacing using the Hooghoudt equation and the USBR transient flow approach. Procedures are described for determining design variables. Drainage materials, construction methods, and equipment are described. The chapter concludes with brief summaries of system operation, maintenance, and performance evaluation.