Frazil Ice Jam Flooding on the Kenai River

by David Streubel

Problem
  • Frazil ice jams on the Kenai River have flooded low lying roads, destroyed docks, and caused minor damage to structures.
  • Does hydrometeorologic data exist which can be forecast to help predict frazil ice problems on the Kenai River?
  • Specifically, is there a quantifiable relationship between air temperature, discharge and the formation of damaging frazil ice jams?

    Background Literature

  • Frazil ice crystals form in supercooled water. The frazil ice crystals accumulate and move downstream forming ice pans or adhering to solid in place ice creating hanging dams. Frazil ice can also adhere to the stream bed or to man made structures.
  • Pariset et al. (1966) conducted some of the initial studies describing the formation of ice cover and jams in rivers.
  • More recent work by Earickson and Gooch (1986) found that accumulated freezing degree days could be calculated during different temperature regimes in the winter to provide ice jam potential.
  • Zufelt & Billelo (1992) analyzed air temperature and ice jam records and developed a relationship between the intensity and duration of severe cold period, and ice jams on the Salmon River in Idaho.

    Procedure

  • Air temperature, wind speed, discharge, and river observer data was collected from 1981-1998.
  • Accumulated freezing degree days (AFDD) were calculated during two different temperature regimes called phase 1 and phase 2 following a procedure developed by Zufelt & Billelo (1992).
  • Phase 1: the period when average daily temperatures are less than 32 degrees F and greater than 0 degrees F prior to a major cold snap (phase 2) or freeze up.
  • Phase 2: extreme cold snaps when average daily air temperature are less than 0 degrees F for more than 2 consecutive days prior to freeze up.
  • The relationships between phase 2 AFDD, phase 1 AFDD, and frazil ice jams were graphed. An equation representing the threshold conditions for the formation of frazil ice jams was determined.
  • The average discharge during the freeze up process was calculated to try and determine the effect discharge had on frazil ice problems on the Kenai River.

    References

    Earickson, J. and G. Gooch (1986) Salmon River Ice Control Study. USA Cold Regions Research and Engineering Laboratory. US Army Engineer District, Walla Walla

    Pariset, E., R. Hauser, and A. Gagnon (1966) Formation of Ice Covers and Ice Jams in Rivers. ASCE J. Hydr 92:1-24

    Zufelt, J. and M. Billelo (1992) Effects of Severe Freezing and Discharge on the Formation of Ice Jams at Salmon, Idaho. CREEL 92-14

    Conclusions

  • The presence of phase 2 temperature regimes prior to freeze up are a primary indicator of potential frazil ice jam flooding. Between 1981 and 1998 three out of the five occurances of phase 2 temperature regimes were followed by frazil ice jam flooding.
  • A preliminary equation was created to estimate the threshold for frazil ice jams based on phase 1 AFDD and phase 2 AFDD. Temperature forecasts from long range meteorological models can be used with the equation to forecast the likelihood of frazil ice jams.
  • The preliminary analysis of limited data indicated that the average discharge during the freeze up period had little effect on the formation of frazil ice jams.
  • More data is needed to better evaluate the relationship between frazil ice production, air temperature, and discharge. 
    


		Kenai River at Soldotna														
																	
WATER	FREEZE UP	EST WATER LEVEL	FREEZE UP	EST Q	PHASE 1	PHASE 1	PHASE PHASE2							
YEAR	PERIOD	CHANGE (ft)	DATE	(CFS)	#DAYS	AFDD	START	#DAYS	AFDD	FRAZ							
1982 	12/29-12/31	7.3 	12/31 	1700 	31 	301 	12/10 	16 	672 	82 							
1983 	12/22-12/27	3.8 	12/25 	2640 	61 	633 	12/26 	2 	72 	9 							
1984 	12/26-12/27	0.2 	12/27 	1700 	78 	483 											
1985 	12/24-12/26	1.5 	12/26 	1450 	60 	364 											
1986 	NO FREEZE UP																
1987 	NO FREEZE UP																
1988 	1/02-1/06	3.9 	01/02 	1700 	66 	701 											
1989 	12/4-12/9	5.0 	12/09 	2200 	41 	276 											
1990 	12/30-1/03	6.4 	01/03 	2000 	77 	597 											

  • 1991	12/09-12/21	8.5 	12/21 	1800 	44,60	882 	11/28,12/13	9 	382 	59 		afdd	170,212 	4,5	fraz	59 	
1992 	1/22-1/24	3.2 	01/24 	1500 	111 	692 											
1993 	12/25-12/27	5 	12/27 	2200 	76 	628 											
1994 	2/16-2/19	6.6 	02/19 	1300 	108 	884 											
1995 	11/24-11/26	5 	11/26 	2200 	34 	383 											
1996 	12/3-12/5	4 	12/17 		29 	391 											
1997 	11/19-11/26	1.7 	11/26 		75 	1118 	11/23 	3 	96 	20 							
1998 	12/29-12/30	3.2 	12/30 		82 	704 	12/14 	8 	333 	38

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