Correct Answer - Option 2 : 3
Explanation
- A rigid bed canal has one degree of freedom i.e. for a given channels a change in discharge would cause a change in the depth only.
- A man –made alluvial channel has three degree of freedom i.e. for a given channel, change in discharge can cause changes in width, depth and bed slope.
- Thus three equations independent of each other are needed, as given by Lacey, to represent three degrees of freedom viz. depth, width and gradient.
- A natural alluvial river has four degree of freedom as its planiform can also after.
Lacey’s regime theory:
According to Lacey,
If a channel is showing no silting – scouring, then also it can’t be said that it is in the regime or not.
The perfect regime conditions do not exist and the three types of regime possible in a channel are as follows:
a) True regime: A channel can be in regime if there is neither silting nor scouring is occurring and there is only one such channel present at which true Regime conditions prevail.
b) Initial Regime: It is the state of the channel that has only formed its section and is yet to form the longitudinal bed slope completely.
c) Final regime: This stage is achieved by the channel when both the slope and width of the channel can be adjusted.
- Lacey’s regime theory is applicable to true regime and final regime.
