UBC Theses and Dissertations

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UBC Theses and Dissertations

Experimental investigation of the effects of upstream conditions on culvert efficiency during debris flow events Hughes, Carlie


In British Columbia, culverts are designed to pass the 100-year clearwater flow for a given stream. However, the design criteria does not account for the influence that entrained sedi ment will have on the flow characteristics. It is common in the British Columbia mountainous regions to experience sediment entrainment during flooding events which lead to the genera tion of debris flows. To account for the impact that entrained sediment and debris may have on the culvert’s ability to pass the flow, BC guidelines vaguely suggest site visits or con sultations with professionals. For my thesis, I ran experiments to compare culvert efficacy when experiencing clearwater flows as well as debris flows. Debris flows containing large grains and large wood were run to compare the effects that different materials may have on the impact a debris flow could have on a forest service road crossing. The experiments were run using the Debris Flow Simulator in the UBC Ponderosa Laboratory. This study focuses on small, mountainous streams that cross forest service roads which are prone to culvert failures but are not frequently monitored. Protoype streams were found in the Chilliwack River watershed that were 2.5-meters wide with a drainage area of 0.27 km2 and on slopes ranging from 32%-45%. The results show that sediment entrainment led to a bulking factor of 1.5-2 and an event as small as a 5-10 year clearwater flow event can lead to the failure of a culvert system. Large grains did not significantly affect the flow characteristics or the impact on the culvert system. The addition of large wood resulted in several culvert fail ure events due to the jamming that took place at the culvert inlet. These results will aid in understanding debris flow impacts and encourage appropriate culvert designs which will decrease the amount of resources put into restoring damaged culvert crossings over time.

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