Design Criteria for Irrigation Canals - Sediment Transport in Irrigation Canals: A New Approach - page 57

CHAPTER 4

Design Criteria for Irrigation Canals

4.1 INTRODUCTION

The objective of an irrigation canal is to meet the varying irrigation
requirements during the irrigation season at the individual farms and
therefore the canal design should preferably be based on the following
criteria:
- Capacity : the capacity of an irrigation canal depends on the water deliv-
ery method. The delivery methods differ from each other through the
scheduling of the water supply in time and place. The World Bank
(1986) classifies the following delivery methods:
•

on demand : the water delivery reacts instantaneously to the water
demand;

•

continuous : the irrigation canal supplies a continuous, either constant
or varying, flow during the whole irrigation season;

• fixed rotation: the water delivery is scheduled with a constant flow

and a regular pattern of rotation;

variable rotation : the water delivery is programmed either for a fixed
supply with variables periods (rotation) or for a variable supply and
variable periods;
- Command : the requirement that most of the area must be irrigated
(commanded) determines the water level in the canals. At any delivery
point, the water level in the canal must be above the ground surface. Due
to the presence of structures and the need to meet the varying irrigation
requirements during the irrigation season the flow in an irrigation canal
varies in time and space. The command level is also influenced by the
method of flow control. For instance, the water level for downstream
control and zero discharge in a canal is horizontal and above the level for
full discharge (see Figure 4.1); the downstream control requires canal
banks with a level top to facilitate the zero flow conditions (Ankum,
1995);
- Sedimentation and/or erosion : irrigation canals should be designed
based on the criterion that no sedimentation and no erosion occur
during a certain period. The design of a stable cross section will be
the end result of this criterion;

•