Erosion on Cohesive Deposition in Storm Sewers

Erosion of sediment deposition in storm sewers is dominated by the bed shear stress and the deposition characteristics. A laboratory study investigated the critical shear stress and erosion processes for different types of deposition in storm sewers. The critical shear stress increased from 0.19 to 0.41 N/m2 for the 0.4-mm sand when the weight content of silt-clay changed from 0% to 20%, whereas the critical shear stress increased from 0.98 to 1.98 N/m2 for the 1.8-mm sand deposition. A prediction method for the critical shear stress was developed based on the particle size and silt-clay content. The erosion patterns can be classified as ripple surface, dune surface, flat surface, and rugged surface, mainly determined by the cohesive effect, particle size, and bed shear stress. The erosion rate is a function of the sediment transport rate per unit width and particle transport distance. A field sampling program was conducted to obtain sediment deposition characteristics in a storm trunk sewer. Based on the sediment characteristics and estimated flow rate, the predicted deposition profile using the method developed in this study compared well with the field measurements.