Pick up the incorrect statement from the following

Side walls of a venturi head flume are splayed out from the end of the throat at 1 : 10 for a length of 4.5 m

Length of side walls should be such that the width of the flume is made equal to $${\frac{2}{3}}^{\text{rd}}$$ the bed width of the distributary

Once the width of the flume becomes $${\frac{2}{3}}^{\text{rd}}$$ of the width of the distributary, the splayed walls are increased to 1 in 3 to get full bed width