Irrigation System Designing - Practices of Irrigation and On-farm Water Management - page 67

to put the required depth of water into the soil. Runoff from the field can be elimi-
nated through controlling the inflow rate at which inflow decays with time exactly
coincides with decay of the average infiltration rate with time for the entire length
of the field. Inflow is usually cut back in discrete steps.

3.1.2 Variables in Surface Irrigation System

Important variables in surface irrigation system include the following: (i) infiltration
rate, (ii) surface roughness, (iii) size of stream, (iv) slope of land surface, (v) ero-
sion hazard, (vi) rate of advance, (vii) length of run, (viii) depth of flow, (ix) depth
of water to be applied, (x) infiltration depth. These are schematically presented in
Fig. 3.1 .

Fig. 3.1 Schematic showing
of different variables in a
surface irrigation system

Q

Water front

Length of run, L

(a)

Water depth

0

L

Depth of infiltration

(b)

3.1.3 Hydraulics in Surface Irrigation System

In general, there are the following three phases of water-front in a surface irrigation
system: