- journal_title：Geological Society of America Bulletin
- Contributor：JIM E. O'CONNOR ; ROBERT H. WEBB ; VICTOR R. BAKER
- Publisher：Geological Society of America
- Date：1986-
- Format：text/html
- Language：en
- Identifier：10.1130/0016-7606(1986)97<410:POPPDB>2.0.CO;2
- journal_abbrev：Geological Society of America Bulletin
- issn：0016-7606
- volume：97
- issue：4
- firstpage：410
The low-flow channel morphology of Boulder Creek is characterized by a well-developed pool-and-riffle pattern. The riffles consist of accumulations of basaltic boulders deposited from upstream source areas during extremely large flows. Paleoflood water-surface profiles defined by high-water indicators such as slack-water sediments and silt lines indicate that discharges of up to 400±50 m<sup>3sup>/s have affected the lower reaches of this bedrock stream system. Stratigraphic relationships and archaeologic and radiometric age constraints indicate that at least four large-magnitude, low-frequency flow events have occurred within the past 500 to 1,000 radiocarbon years B.P.
Step-backwater hydraulic reconstructions of these large flows suggest that the positions of the boulder-comprised riffles are controlled by spatial variations in large-flow stream power. Boulder deposition occurs where channel stream power drops below critical-power thresholds necessary for boulder transport. High-discharge stream-power minima occur in reaches immediately upstream of canyon bends and constrictions and downstream of canyon expansions. The low-flow riffles occur at these sites. Comparison of calculated stream-power values and measured boulder sizes with established coarse-particle transport relationships indicates that a 400-m<sup>3sup>/s flow is approximately the minimum discharge competent to affect this pool-and-riffle pattern.