To control the silt entry into a distributary at head regulator, King’s vanes are provided which are the walls A. Of R.C.C. or steel plate 8 cm thick B. Of height $${\frac{1}{3}^{{\text{rd}}}}$$ to $${\frac{1}{4}^{{\text{th}}}}$$ the depth of water in the main canal C. Spaced at interval of $$1\frac{1}{2}$$ times their heights D. All the above

The correct answer is D. All the above.

King’s vanes are walls made of R.C.C. or steel plate 8 cm thick. They are of height $\frac{1}{3}^{{\text{rd}}}$ to $\frac{1}{4}^{{\text{th}}}$ the depth of water in the main canal. They are spaced at interval of $1\frac{1}{2}$ times their heights.

King’s vanes are used to control the silt entry into a distributary at head regulator. They are placed in the main canal just upstream of the distributary. The vanes deflect the flow of water, which helps to reduce the amount of silt that is carried into the distributary.

King’s vanes are an effective way to control silt entry into a distributary. They are relatively simple to install and maintain, and they can be used in a variety of water conditions.