| Abstract: | Geomorphologists can contribute to the mitigation of sediment disasters by using geologic records of past sediment processes and channel response to constrain probable future scenarios, and by identifying situations in which standard engineering approaches to channel processes do not adequately describe or predict these processes. Mountain rivers are an example of river systems for which standard engineering assumptions may not be adequate. Mountain rivers act as sediment conveyors from hillslopes to surrounding lowlands. The steep bed gradients and confined valleys of these rivers minimize attenuation of flood and debris-flow discharge, and mountain rivers are prone to catastrophic instability at varying timescales. The geomorphic response of a channel to an extreme debris flow or flood will depend on channel and valley geometry, boundary resistance, recurrence interval of the flow, magnitude of the flow relative to the magnitude of more frequent flows, and the availability of sediment during the flow. Records of past geomorphic changes may be used in connection with slope and channel stability analyses to estimate the spatial distribution and recurrence interval of flow-related changes. This information can then be incorporated into land-use zoning to reduce geomorphic hazards, as illustrated by a case study from the western United States. |
