Effects of Sediment on Drainage-Culvert Serviceability

Abstract

The primary function of a drainage culvert—to convey the design flow effectively—is often greatly impaired or completely lost due to the presence of deposited sediments. The effect of sediments on the total head loss within the culvert may be quite significant. A case study is presented that describes the performance of a roadway drainage culvert designed for clear-water flow conditions in an alluvial stream carrying sediments. The actual capacity of the culvert is approximately only 20% of the presumed design capacity, as a result of sediment deposition not accounted for in the design. The case study reviews design errors and demonstrates the necessity of sediment-transport calculations when designing roadway drainage culverts in ephemeral alluvial streams. Ignoring sediment transport may have adverse effects, including significant road and adjacent-property flooding as well as continuous and costly maintenance problems. It is more economical to undertake a complete sediment-transport study before design than to deal with continuous maintenance after the project is built.