Assessing downstream variation of fluvial processes for recommending maintenance flows in regulated rivers
- McBain and Trush, Arcata, CA (United States)
- Hoopa Valley Tribe, CA (United States)
Potential effects of dams on channel morphology typically decrease downstream as flow and sediment contributions from tributaries return dynamic fluvial processes to the mainstem channel. As part of a multi-agency flow study below Lewiston Dam on the Trinity River, Northern California, we evaluated the river`s downstream geomorphic and riparian vegetation response to experimental high flow releases and natural flooding. Downstream changes in channel bed surface-to-subsurface particle size distribution ratios (D50s/D50ss) and the recurrence of flood peaks that cause incipient channel mobility were two potential criteria for locating and evaluating the downstream influence of Lewiston Dam on alluvial processes. Relatively low D50s/D50ss ratios (1.5) at 10 km (the Gravel Plant site) indicated significant dam influence on alluvial processes this far downstream. By 20.5 km (the Steelbridge site), the D50s/D50ss ratios (1.5 to 6.0) were wide-ranging, and this was typical of sampled alternate bar units for the next 30 km downstream. More bulk samples are being collected within the first 38 km to better define downstream trends and within-alternate bar trends. As the second alluvial criterion, it is characteristic for alluvial rivers to have incipient mobilization of the channel bed at discharges approaching eighty percent of the 1.5 to 2.0 year annual maximum flood stage height (bankfull stage). Recurrence intervals for discharges at incipient motion decreased downstream, achieving this condition within 30 km below Lewiston Dam.
- OSTI ID:
- 219933
- Report Number(s):
- CONF-9507190-; TRN: 96:000708-0015
- Resource Relation:
- Conference: Waterpower 1995: international conference, San Francisco, CA (United States), 25-28 Jul 1995; Other Information: PBD: 1995; Related Information: Is Part Of Waterpower`95. Volume 1-3; Cassidy, J.L. [ed.]; PB: 2869 p.
- Country of Publication:
- United States
- Language:
- English
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