The correct answer is: A. Lacey’s theory.
Garnett’s diagrams are used for graphical solution of design equations of a canal by Lacey’s theory. Lacey’s theory is a method for designing canals that is based on the principle of minimum energy. The theory takes into account the factors of flow, sediment transport, and canal geometry to determine the optimal design for a canal.
Kennedy’s theory is a method for designing canals that is based on the principle of maximum discharge. The theory takes into account the factors of flow, sediment transport, and canal geometry to determine the maximum discharge that a canal can safely carry.
Gibb’s theory is a method for designing canals that is based on the principle of minimum cost. The theory takes into account the factors of flow, sediment transport, and canal geometry to determine the canal design that will minimize the cost of construction and maintenance.
Lindlay theory is a method for designing canals that is based on the principle of maximum efficiency. The theory takes into account the factors of flow, sediment transport, and canal geometry to determine the canal design that will maximize the efficiency of water conveyance.
In conclusion, Garnett’s diagrams are used for graphical solution of design equations of a canal by Lacey’s theory.