Description of the Main Aspects of the Regime Theory - Sediment Transport in Irrigation Canals: A New Approach - page 263

APPENDIX D
Description of the Main Aspects
of the Regime Theory
For the regime theory a set of simple, but empirical equations are avail-
able. The equations are derived from observations of alluvial canals that
are relatively stable or in regime (HR Wallingford, 1992). The regime
method considers the three canal characteristics, namely the perimeter of
the canal, the amount of water and the amount of sediment flowing in the
canal as a whole and attempts to derive the features of a stable (non silting/
non scouring) canal primarily on the basis of empirical studies of the
interaction of the above-mentioned factors (Naimed, 1990). The regime
theory is completely empirical and is based on measurements and observa-
tions of canals and rivers in regime. The theory originates from India and
Pakistan, where most of the canal designs follow this theory, especially the
Lacey regime theory. The main equations for the design of stable canals
are based on field observations and experiences that are still collected and
evaluated. The equations of the regime theory present a long-term average
profile rather than a instantaneously variable state. Therefore, they spec-
ify the natural tendency of channels that convey sediment within alluvial
boundaries to obtain a dynamic stability.
The expression canals in regime means that the canals do not change
over a period of one or several typical water years. Within this period,
scour and deposition will occur in the canal, but they do not interfere
with canal operation. The regime theory can only provide some approx-
imate design values as the equations are based on observations of many
canals in regime. These canals have received different amounts of water
and sediment from a variety of rivers that have different sediment loads
and characteristics. Moreover, some of the canals in regime may have
sediment excluders or ejectors at the head works that have influenced the
erosion and deposition. Nevertheless, the experience obtained from the
design and operation of these canals give some guidance for the design of
stable channels with erodible banks and sediment transport. However,
the regime theory should be applied in a very careful way, especially
when the design involves a canal network with highly time-dependent
operational regimes as practised in many irrigation systems at present
(Bruk, 1986).