Q. Evaluate the Length of guide bund?

For encouraging axial flow through the bridge, upstream length of guide bund may be kept 1.0 to 1.5 times the bridge length and downstream length 0.25 to 0.40 times the bridge length. Length necessary for keeping worst possible embayment behind the guide bund sufficiently away from the approach bank is also required to be ascertained by fitting of sharpest loop as indicated in Figure 5.2 in Chapter 5. If field data of acute bends in river when cut offs occurred is not available, It may be assumed that radius of such a bend can be equal to 0.4 times the radius of average bends if maximum river discharge is up to 5660 m³/s and equal to 0.5 times the radius of average bends if the maximum discharge is more than 5660 m³/s. In case of braided rivers, the length determined on basis of both the considerations of axial flow through bridge and keeping away the worst loop may be found to be insufficient for protection of long approaches. Additional protection works like spurs, revetments etc. may then become necessary.