Lacey's Regime Theory MCQ with answer and solution

Concept

Lacey's Regime Theory Conditions

Formula

N/A

Step-by-step solution

1. Review the conditions required for an ideal regime channel according to Lacey's regime theory. 2. Recognize that regime silt must consist of incoherent (non-cohesive) material, whereas clay-sized particles are cohesive. 3. Conclude that requiring clay-sized particles is not a condition for ideal regime and select Option D.

Explanation

According to Lacey’s regime theory, an ideal or true regime channel must flow through incoherent (non-cohesive) alluvial material of the same grade as the sediment being transported. Clay-sized particles are cohesive rather than incoherent, so requiring the silt to consist of clay-sized particles is not a condition for an ideal regime.

Shortcut

To remember Lacey's Regime Theory conditions, use the rule "Incoherent Silt, Constant Flow & Grade": - Incoherent Silt: Silt must be non-cohesive/incoherent (NOT cohesive clay). - Constant Flow & Sediment: Constant discharge, uniform flow, and constant grade/quantity of sediment. - Alluvial Soil: Channel flows through the same grade of alluvium as the transported sediment.

Common mistake

A common mistake is selecting options A, B, or C by confusing the requirements for a true regime condition with the incorrect statement. Students often overlook that Lacey's theory requires incoherent (non-cohesive) alluvial silt rather than cohesive clay-sized particles. Another frequent error is misreading the question and picking a valid condition instead of identifying the option that is NOT a requirement.