Streambank width, culvert width, and embedment depth recommendation

A cross section of a culvert showing large rocks on the left half that depicts loss of fines and loss of surface flow. The rocks have a D100 greater than the bankfull width divided by 4 and there is no small material between the large rocks. The left half of the structure is not recommended. The right half of the structure is recommended and shows a well graded substrate where surface flow is maintained. The minimum bank width is 1.5 times the D100. The minimum depth of substrate from the thalweg to the culvert invert is 1.5 times the D100. There are small and medium sized rocks and gravel between the larger rocks. The larger rocks are less than the bankfull width divided by 4.