Changes in channel roughness values following large sediment inputs
Madej MA. 2001. Changes in channel roughness values following large sediment inputs. In Proceedings of gravel-bed rivers 2000 Conference. New Zealand. New Zealand Hydrological Society. New Zealand
A study conducted by the U.S. Geological Survey Western Ecological Research Center. From the Abstract: "Large inputs of coarse sediment entering a river can change the flow resistance characteristics of the channel. Trends in channel roughness values at five gauging stations were examined for a 20-year period of record, using measurements of velocity and channel geometry. At four stations, the river had aggraded one to two meters during floods and associated landslide input in the 1970's, and the streambed was relatively smooth. Since the mid-1970's the channel has downcut through the flood deposits, bed topography has become more variable, bed relief has increased, and bedload transport rates have decreased. Concomitantly, the value of Manning's roughness coefficient ('n') has significantly increased through time at these stations, after adjusting for discharge. During the same period, there was no statistically significant increase in channel roughness in the control stream, which did not aggrade. The relationship of channel roughness and discharge was also explored. The control stream exhibited the typical pattern in gravel-bed rivers of decreasing flow resistance with increasing discharge. In contrast, however, the other four stations with high sediment supplies displayed a pattern of decreasing flow resistance with discharge only at low to moderate flows. At flows greater than a 1.1 year recurrence interval, values of Manning's n increase with increasing discharge. This may be due to high bedload transport rates and scour of the stream bed at higher flows, which leads to greater bed relief and turbulence, and consequently greater flow resistance."
- Type
- Conference Proceeding Paper
- Authors
- Madej, Mary
- Units
- REDW
- Keywords
- Aquatic Studies, bed topography, channel roughness, Gaging Stations, Geology, gravel-bed, Physical Processes, Redwood Creek, Rivers, sediment input, Streams, Water Discharge