Irrigation System Designing - Practices of Irrigation and On-farm Water Management - page 90

3.4.3.8 Advance Function

Both the infiltration depth and water advance rate on soil surface in furrow irrigation
is a function of irrigation time. These relationships, expressed in empirical forms,
are known as advance function.

3.4.3.9 Surge Flow/Irrigation

Surge irrigation is the practice of applying water to a set for a while, then switching
the water to another set, then switching back and forth between the sets periodi-
cally. Surge flow is identified as a strategy to improve the performance of the furrow
irrigation system.

3.4.3.10 Gross Water Needed for Furrows

Gross water to apply

1

WR N
DU ×

R
100

WR G = − × F S

where

WR G = gross water to be applied (mm)

WR N = net water required for root zone soil (determined with any

recommended technique) (mm)

R = percent of water which runs off field and is not re-circulated to that field

DU = distribution uniformity expressed as a decimal (DU = 0.80 is often used)

F S = salinity factor, a factor to account for the increased irrigation requirement

due to maintenance leaching. Guidelines are according to the salinity of
the irrigation water. If salinity is not involved, F S =

1.

3.4.4 Factors Affecting Performance of Furrow Irrigation System

3.4.4.1 Soil Characteristics

Soil characteristics and field conditions are major factors controlling the efficiency
of furrow irrigation systems. Advance rates are influenced by both soil conditions
and furrow inflow rates.

3.4.4.2 Stream Size

When selecting the furrow stream size, consider furrow erosion. Use a furrow stream
that does not cause serious erosion. In general, the maximum non-erosive stream
size decreases as furrow slope increases. The use of high inflow rates (stream size)
will result in more runoff but less deep percolation losses or vice versa.