Determine the ratio of hydraulic time to sedimentation time
The deposition in, and dredging requirements of, a navigational channel in a wide river are to be studied using a movable-bed model. The bed material in the river is sand (sp. gr. = 2.65) with a median size of 0.4 mm. A model bed with sp. gr. = 1.25 is proposed. Determine the necessary median diameter for the model bed and the required length scales. Assume that both prototype and model are sufficiently wide so that Rr = Yr.Assume also that the model is constructed and operated using the results obtained below.
One sediment transport equation that is not included in Chapter 8 states that the dimensionless sediment transport qs,'u,ds, is a function of the dimensionless T, from the Shields diagram. As given here, qr is the volumetric sediment discharge per unit width. Use this equation to obtain the sediment transport ratio qsr. and from this result determine the time ratio for sediment modeling.
If the model study indicates that dredging of the model channel is required every 100 hours, calculate the frequency with which the prototype channel will require dredging.