Form Approved
REPORT DOCUMENTATION PAGE
OMB No. 0704-0188
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1. AGENCY USE ONLY (Leave blank)
2. REPORT DATE
3. REPORT TYPE AND DATES COVERED
May 1999
4. TITLE AND SUBTITLE
5. FUNDING NUMBERS
Ice Jams in River Confluences
Contract No.: DACA 4303900
6. AUTHORS
Robert Ettema, Marian Muste, and Anton Kruger
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
8. PERFORMING ORGANIZATION
REPORT NUMBER
U.S. Army Cold Regions Research and Engineering Laboratory
72 Lyme Road
CRREL Report 99-6
Hanover, New Hampshire 03755-1290
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
Office of the Chief of Engineers
Washington, DC 20314-1000
11. SUPPLEMENTARY NOTES
For conversion of SI units to non-SI units of measurement, consult ASTM Standard E380-93, Standard Practice for Use of the
International System of Units, published by the American Society for Testing and Materials, 100 Barr Harbor Drive., West
Conshohocken, Pennsylvania 19428-2959.
12a. DISTRIBUTION/AVAILABILITY STATEMENT
12b. DISTRIBUTION CODE
Approved for public release; distribution is unlimited.
Available from NTIS, Springfield, Virginia 22161
13. ABSTRACT (Maximum 200 words)
Two laboratory models of confluences are corroborated with observations interpreted from field observations
of ice jams in the vicinity of confluences. One model was used to identify the processes whereby ice can jam in
confluences and to determine how selected parameters (e.g., confluence angle) influence them. The confluences
of primary interest were those formed by channels whose beds are at about the same level. The second model
was used to examine ice jam formation in the confluence of the Mississippi and Missouri Rivers. Three rela-
tively complex processes were found to lead to ice jams: the merging of ice runs, hydrodynamic pressure from a
confluent flow impacting an ice run from the second confluent channel, and ice congestion at a confluence bar.
The latter process is a significant factor triggering ice jams at the confluence of the Mississippi and Missouri
Rivers. Also, three simple processes account for many ice jams at river confluences: ice blocked by an ice cover
in the confluence, large ice pieces arching at the confluence, and ice entering a region of sluggish flow. The main
practical contributions of the study are formulations for estimating the maximum rate of ice conveyance through
channel confluences, and the confirmation of the efficacy of a series of bendway weirs to mitigate ice jam for-
mation at the confluence of the Mississippi and Missouri Rivers. The bendway weirs have additional benefits,
such as greatly reducing the amount of ice accumulating in the approach to the Chain-of-Rocks Canal, which is
located at the confluence exit.
14. SUBJECT TERMS
15. NUMBER OF PAGES
70
Bendway weirs
Ice jams
16. PRICE CODE
Hydraulic models
River confluences
17. SECURITY CLASSIFICATION
18. SECURITY CLASSIFICATION
19. SECURITY CLASSIFICATION
20. LIMITATION OF ABSTRACT
OF REPORT
OF THIS PAGE
OF ABSTRACT
UNCLASSIFIED
UNCLASSIFIED
UNCLASSIFIED
UL
NSN 7540-01-280-5500 Go to contents page
Standard Form 298 (Rev. 2-89)
Prescribed by ANSI Std. Z39-18
298-102
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