Q. Can you determine the Quantity of apron stone?

Quantity should be sufficient to cover the scoured face down to maximum depth of scour obtained using scour factor c of 2.5 at upstream curved head and 1.5 for the rest of the length in Lacey formula

wherein D is depth of flow below H.F.L. in m, q is discharge intensity in m³/s per metre width within guide bunds on bridge section, f is the silt factor and c the scour factor. It has been observed that the above Lacey formula does not give a good fit for data of some of the rivers. As an alternative, the Laursen formula for guide bund contraction can therefore be applied in the following form to obtain average depth of flow D within guide bunds.