Critical flow constrains flow hydraulics in mobile-bed streams: A new hypothesis

被引:184
作者
Grant, GE
机构
[1] Pacific Northwest Research Station, USDA Forest Service, Corvallis, OR
[2] USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR 97331
关键词
D O I
10.1029/96WR03134
中图分类号
X [环境科学、安全科学];
学科分类号
08 ; 0830 ;
摘要
A new hypothesis predicts that in mobile-bed river channels, interactions between the channel hydraulics and bed configuration prevent the Froude number (Fr) from exceeding 1 for more than short distances or periods of time. Flow conditions in many steep, competent streams appear to be close to critical. Froude numbers of steep (slope approximate to 0.01) sand-bed streams with considerable freedom to adjust boundaries oscillate between 0.7 and 1.3 over 20- to 30-s cycles, with an average of 1.0 at the channel thalweg. Critical flow in these streams is maintained by the interaction between the mobile bed and free water surface at high Fr, which results in a cyclical pattern of creation and destruction of bed forms. Field observations support that a similar mechanism of flow-bed form interaction constrains Fr less than or equal to 1 in active-bed braided gravel rivers, step-pool streams, laboratory rills, lahar-runout channels, and even some bedrock channels. Empirical and analytical results show that as slope increases, competent flows tend to asymptotically approach critical flow. An assumption of critical flow would dramatically simplify paleohydraulic flow reconstructions and modeling of flow hydraulics in high gradient streams.
引用
收藏
页码:349 / 358
页数:10
相关论文
共 92 条
[1]   STEP-POOL STREAMS - ADJUSTMENT TO MAXIMUM FLOW RESISTANCE [J].
ABRAHAMS, AD ;
LI, G ;
ATKINSON, JF .
WATER RESOURCES RESEARCH, 1995, 31 (10) :2593-2602
[2]   BED FORMS AND UNSTEADY PROCESSES - SOME CONCEPTS OF CLASSIFICATION AND RESPONSE ILLUSTRATED BY COMMON ONE-WAY TYPES [J].
ALLEN, JRL .
EARTH SURFACE PROCESSES AND LANDFORMS, 1976, 1 (04) :361-374
[3]   A SIMPLIFIED CASCADE MODEL FOR TRANSVERSE STONE-RIBS IN GRAVELLY STREAMS [J].
ALLEN, JRL .
PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, 1983, 385 (1789) :253-266
[4]  
ALLEN JRL, 1982, DEV SEDIMENTOLOGY A, V30, P383
[5]  
ANDREWS ED, 1984, GEOL SOC AM BULL, V95, P371, DOI 10.1130/0016-7606(1984)95<371:BEAHGO>2.0.CO
[6]  
2
[7]  
ANDREWS ED, 1983, GEOL SOC AM BULL, V94, P1225, DOI 10.1130/0016-7606(1983)94<1225:EOGFNS>2.0.CO
[8]  
2
[9]  
[Anonymous], 1993, 274 GEOL SOC AM
[10]  
ASHIDA K, 1973, P 15 C INT ASS HYDR, V1, P475