Q. Determine Length of guide bunds?
Length of a guide bund has to be such that the flow approaching even from behind the guide bund would pass through the bridge with minimum obliquity ensuring optimum utilisation of waterway. Length has also to be adequate to keep worst embayment of the river at the back of the guide bund away from the approach bank at a safe distance.
In addition, bend flow analogy is relevant in this case. The analogy of flow, downstream of a curved channel indicated suggests that flow distribution within guide bunds would become more uniform if radius of curved head is increased rather than increasing the length of the guide bunds as was exemplified by the left guide bund of the Kosi barrage.