CGU HS Committee on River Ice Processes and the Environment 15th Workshop on River Ice St. John’s, Newfoundland and Labrador, June 15 - 17, 2009
Modeling Ice Cover Consolidation during Freeze-up on the Peace River, AB
Faye Hicks1, Robyn Andrishak1,2 and Yuntong She2
1 Dept. of Civil and Environmental Engineering University of Alberta, Edmonton, AB, T6G 2G7 [email protected], [email protected]
2 ASH Hydrotechnical Engineering Inc., 20607 - 46 Avenue NW Edmonton AB, T6M 0C2 [email protected] ; [email protected]
Winter can be a time of severely constrained flow-peaking operations for hydro-power facilities, since there is often a concern that fluctuating water levels can destabilize a fragile, developing ice cover. If the resulting ice cover consolidation results in a severe freeze-up ice jam, flooding may occur. The Peace River in northern Alberta presents just such a situation; numerous consolidation events have been documented on the Peace River over the years, including a very large event in January 1982.
The weather over Christmas 1981 and into early January 1982 was extremely cold and the developing ice front on the Peace River propagated at a rapid pace. In response to increased power demands (also attributable to the severe cold weather) flows in the Peace River were increased from about 900 m3/s to approximately 1800 m3/s over a period of 5 days in early January 1982. A massive consolidation of the ice cover followed, producing record water levels. In response, groundwater levels increased to the point where basement flooding occurred in the Town of Peace River.
Since that time, in an effort to mitigate potential consolidation events, BC Hydro has undertaken voluntary flow controls in winter. However, consolidation events have still occurred on occasion. In fact, in January 2005, groundwater seepage flooding again occurred following a consolidation event. Although the causative factors for ice cover consolidation are relatively well known for this river, the ability to forecast these events remains limited. The purpose of this study is to develop a forecasting model for ice cover consolidation events on the Peace River based on the University of Alberta’s River1D ice jam formation model. This paper reports on the preliminary results of this study, focusing on the January 1982 consolidation event.
250 1.0 Introduction The period of ice cover development on regulated rivers can be prolonged, as a result of the influences of warm water outflows from large reservoirs on ice formation processes. In the case of hydro-power facilities, this period can also be one of severely constrained flow-peaking operations, since hydro-peaking poses a risk of consolidating a fragile developing ice cover and creating an ice jam flood. Such flow restrictions result in lost revenue to hydro-power companies, and the need to pursue alternative energy sources can increase electricity costs to consumers. Flow-peaking constraints often have environmental implications as well, because of the need to resort to fossil fuels to generate electricity (e.g. as in Alberta).
It would be ideal to be able to avoid overly conservative flow controls, and modeling should be useful for designing appropriate peaking schemes. Such models would also be useful to assess the potential effects of proposed new hydro-power facilities on the risk of freeze-up ice jam occurrence. For this study, we tested the capabilities of the University of Alberta’s River1D ice jam formation model for assessing the influences of hydro-peaking on developing ice cover stability, by attempting to model the consolidation event that occurred on the Peace River, AB in January 1982. The event is modeled for both steady and unsteady (hydro-peaking) inflows, in order to determine the relative significance of each to the consolidation event observed.
2.0 Peace River Site Description and the 1982 Consolidation Event Figure 1 shows the Peace River basin including the reach of interest, which extends approximately from Hudson’s Hope, BC to Fort Vermilion, AB. The river is regulated by two BC Hydro dams at the upstream end of this study reach: the W.A.C. Bennett Dam and the Peace Canyon Dam (PCD). Of particular interest to this study is the sub-reach including Dunvegan and the Town of Peace River (TPR), as shown in Figure 2. (River kilometres, in terms of distances downstream, of the Bennett Dam, are shown on this map to aid the reader’s interpretation of the ensuing discussion.) Figure 3 shows the river profile, based on known cross-section surveys and National Topographic Survey (NTS) maps. The Peace River has been regulated since 1972, and as there is significant reservoir storage capacity, released water is consistently above 0°C throughout the winter (Andres, 1994). Consequently there is an extended freeze-up period, and open water persists downstream of the dams for ~150 km, with the exact value depending upon ambient weather conditions. The ice cover typically initiates downstream of the Vermilion Chutes (Figure 3) and propagates upstream from there primarily by juxtapositioning in the lower (flatter) sub-reach, and by both juxtapositioning and consolidation in the steeper upper reach (Andres 1999, 2003). Details of the ice front progression have been documented for most years since 1973/74, as a result of joint efforts by BC Hydro and Alberta Environment. Figure 4 presents graphs of these data for those years in which ice cover consolidation events have been documented (Fonstad and Quazi 1982; Neill and Andres 1984, Andres 1994, 1999, 2003; Friesenhan and Mahabir 2005).
As Figure 4 illustrates, the consolidation event of January 1982 is the most significant documented to date, both in terms of the extent of consolidation and the speed with which it occurred. Details of this event are reconstructed below based on information presented by
251 Fonstad and Quazi (1982) and Neill and Andres (1984), as well as corresponding hydro- meteorological data collected by Environment Canada and the Water Survey of Canada. • Neill and Andres (1984) document that this consolidation event was triggered by two factors: first the rapid upstream progression of the ice cover during a period of extreme cold weather, and second, an increase in river flow from ~900 to ~1800 m3/s over a 5 day period, in response to increased energy demands. Figure 5 shows the air temperature record, the Peace Canyon Dam outflows, and the water temperature of those releases for the period of interest. • As Figure 5 shows, the air temperatures were relatively mild in mid-December. Neill and Andres (1984) report that, as a result, the propagating ice front did not reach the TPR until January 2, 1982. • Mean daily air temperatures cooled significantly over the holiday season, hovering in the -30 to -40°C range (Figure 5). During this same period PCD outflows were reduced to ~870 m3/s on 26-Dec-81, increased to ~1840 m3/s by Dec 30, then reduced again to ~930 m3/s on 1-Jan- 82, all in response to fluctuating energy demands over the holiday season. • This extreme and prolonged cold period precipitated a rapid propagation of the ice front. Neill and Andres (1984) report that the ice front reached a point 88 km upstream of the TPR on 5-Jan-82 (station 308 in Figure 2), and that the rate of progression was relatively constant at ~20 m/min from 2 to 5-Jan-82. From 1-Jan to 6-Jan-82, PCD outflows increased from ~930 m3/s to ~1830 m3/s. • Fonstad and Quazi (1982) report that by 7-Jan, the ice cover had progressed to somewhere between “…’a few’ and 50 km upstream” of Dunvegan. • Fonstad and Quazi (1982) document that, at ~20:30 on 7-Jan, a resident near Dunvegan reported that the ice was moving there. According to Fonstad and Quazi (1982) this moving ice was associated with the formation of an ice jam at the “downstream end of Verte Island (14 km downstream of Dunvegan) which occurred between 17:00 and 19:00 on 7-Jan”. They go on to say that the height of the jam was approximately 9m, and that this ice jam released just a few hours later. Fonstad and Quazi (1982) also report that “…the available evidence indicates that the ice jam released prior to the ice movement at the TPR.” • Fonstad and Quazi (1982) document that, according to a local resident, the ice cover in Peace River cracked and started moving downstream at 22:30 on 7-Jan-82. They also report that the stage in TPR rose 3.54 m between 21:00 on 7-Jan-82 and 01:00 on 8-Jan-82, bringing it to just 1.66 m below the top of dykes. • Neill and Andres (1984) report that subsequent visual inspection indicated that a significant consolidation of the ice cover had occurred, extending about 10 km downstream of Peace River, and that on 8-Jan-82 “12 hours after the peak in Peace River, the head of the [ice] cover was observed to be only 40 km upstream of Peace River.” That would be at station 355 km in Figure 2.
Figure 6 shows the high water mark and ice profiles measured after this event as presented by Neill and Andres (1984). Ice thicknesses were measured the week after 13-Jan-82. They report that full thickness ice measurements could not be made due to severe cold weather and rough ice conditions. Figures 7 and 8 illustrate the texture of the rough ice cover through the TPR
252 following this consolidation event. Fortunately, Neill and Andres (1984) were able to supplement those data by measuring the exposed shear wall thickness during breakup 1982. Based on both types of measurements, they found the typical ice thickness in the consolidated ice cover was 3.8 to 4.2 m, although at some locations it was as little as 2.3 m thick. In addition, for the non-consolidated ice cover, they report that the border ice was 0.5 to 1.0 m thick and the frozen crusts were ~0.3 m thick. Although no direct flooding occurred as a result of this event, the dynamic nature of the consolidation movement caused residents of the TPR immense concern and set the stage for seepage flooding into 40 to 60 homes in Lower West Peace River due to the resulting elevated groundwater levels1. It also caused the Joint Task Force (which includes Alberta Environment and BC Hydro, among other stakeholders) to include freeze-up in its mandate, and initiated the ‘controlled flow’ at freeze-up.1
3.0 Modeling Approach and Results Given the dramatic nature of the 1982 Peace River consolidation event, and the fact that it was associated with both extreme weather and significant hydro-peaking influences, it presents a good case study for testing the River1D thermal and ice jam formation model components. In particular, because of the voluntary flow controls which BC Hydro has implemented since that time, it provides the best available case for exploring the potential impacts of hydro-peaking on ice cover development.
The first step in the modeling process was to develop a geometric model of the Peace River for the study reach. As Figure 3 illustrates there is very little actual surveyed channel geometry along the river, especially downstream of the BC-AB border. This presents a challenge to any modeling effort of this type and the solution employed here was to use the limited geometry model of the Peace River developed and validated for open water flood routing by Hicks (1996), and for thermal ice process modeling by Andrishak and Hicks (2008). It consists of a rectangular channel approximation with the mean channel bed profile estimated as shown in Figure 3, based on the known cross section data and water surface slopes measured from NTS maps. The width of the channel is based on measurements of channel top width on NTS maps at 1 km intervals. Hicks (1996) describes the development and validation of this geometric model of the Peace River for flood routing applications.
The next step in the modeling process was to simulate the thermal ice cover development in the period leading up to the consolidation event, using the River1D thermal ice process model. This was achieved in the same manner as described by Andrishak and Hicks (2008), using the calibrated thermal ice process model developed for that study, along with the known PCD release flows and associated water temperatures (Figure 5) as the inflow discharge and water temperature boundary conditions for the 1981/82 winter season. Figure 3 also shows the air temperature used to drive the cooling process, based on three meteorological stations in the study area. The air temperature affecting each segment of the river was obtained from the data for nearest of these three stations. The date of bridging was unknown and so it was estimated to provide the best agreement with the observed ice front locations. Figure 9 shows the results of this analysis, which puts the ice front at 282 km, ~13 km upstream of Dunvegan on 7-Jan-82, just
1 Personal communication, Gordon Fonstad, Alberta Environment, September 27, 2002.
253 before the consolidation event occurred. Figure 10(a) shows the resulting ice profile obtained for the sub-reach Dunvegan (295 km) to TPR (Hwy 2 Bridge is ~396 km).
The results of the River1D thermal model simulation for 7-Jan-82 were then taken as the initial condition for the River1D dynamic ice modeling component (She et al., 2009). For this simulation, the Manning’s resistance coefficient for the consolidated ice was taken as 0.043 (Neill and Andres, 1984), the lateral thrust coefficient, Kxy, was taken as 0.5, the bank to ice friction coefficient, Kx, was taken as 1.035, and the passive pressure coefficient, Kp, was taken as 7.55. A preliminary analysis indicated that the model results were not particularly sensitive to reasonable variations of these parameters. Two inflow boundary condition scenarios were tested: in the first (steady) case, the inflow discharge was held steady at 900 m3/s; for the second (hydro-peaking) case, the discharge was increased from 900 to 1800 m3/s over a 5 day period. Figure 10 (b) and (c) shows the results for these two cases, respectively. As Figure 10(b) illustrates, the ice cover is not stable at the steady flow of 900 m3/s, and consolidates to a 48 km long accumulation. Results are similar for the hydro-peaking inflow case (Figure 10(c)), with the resulting accumulation 41 km long (i.e. within 1 km of the observed length). It was observed during the simulation that the ice accumulation had initially stabilized, and then started to consolidate again once the hydro-peaking wave arrived. These results suggest that, in this case, that the rapid ice front advancement rate was a key factor contributing to this consolidation event, and the role of the hydro-peaking wave was primarily in rupturing the fragile ice cover, facilitating this consolidation. Thus, it would appear that a brief spell of warm weather could have had nearly the same effect.
Figure 11 shows the initial and final ice cover thickness profiles for the two cases. For the hydro- peaking scenario, the ice thicknesses range from an average of about 1.2 m up to a maximum of about 1.8 m. This is substantively less than the values reported by Neill and Andres (1984) based on measurements conducted a couple of weeks after the consolidation event and exposed shear walls measurements at breakup; however, they are comparable to the minimum values observed. Since the solid thicknesses obtained for the thermal model are consistent with observations of the unconsolidated ice cover, and since ice mass is conserved in the model, this difference is possibly explained by suspended frazil (possibly frozen thoroughly by the time of the measurements) which was not accounted for in these simulations. Another, lesser, factor would be the additional (thermal) ice development not simulated during the dynamic event.
The modeled water level rise at TPR (~1.8 m) was similarly less than the observed (3.5 m); however, the simulation results do provide valuable insight into the relative importance of the hydro-peaking. The model results suggest that ~0.5 m of this 1.8 m rise can be attributed to the consolidation event itself, with the remaining ~1.3 m of water level rise directly attributable to the increase in inflow from 900 to 1800 m3/s.
4.0 Summary and Future Plans The River1D thermal and dynamic ice process model components were applied to simulate the ice cover consolidation event which occurred on the Peace River in January 1982. It was found that the thermal ice process model was effective in reproducing the rapid ice front progression observed in early January of that year. The dynamic model was successful in reproducing the extent of the consolidation, but both the ice thicknesses and water level increases were about half
254 of the observed values. Future plans include merging the thermal and dynamic ice model components, expanding the thermal model to include under cover frazil transport and deposition and testing for natural channel geometries.
Acknowledgements Funding provided by the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged. Thanks also to Bernard Trevor and Gordon Fonstad (retired) of Alberta Environment for providing the 1981/82 ice observation report and photos/captions, respectively, and to Martin Jasek of BC Hydro for providing the 2004/05 ice front progression data.
References Andres, D.D. (1994) The freeze-up regime of the Peace River, Taylor to the Slave River. Northern River Basins Study, Edmonton, AB, 89 pp. Andres, D. (1999) The effects of freezing on the stability of a juxtaposed ice cover. Proc. 10th Workshop on River Ice, CGU HS Committee on River Ice Processes and the Environment, Hydrology Section, Winnipeg, Manitoba, 209-222. Andres, D., Van Der Vinne, G., Johnson, B., and Fonstad, G. (2003) Ice consolidation on the Peace River: release patterns and downstream surge characteristics. Proc. 12th Workshop on the Hydraulics of Ice Covered Rivers, CGU HS CRIPE, Edmonton, AB, June 19-20, pp. 319-330. Andrishak, R. and F. Hicks (2008) Simulating the Effects of Climate Change on the ice Regime of the Peace River. Canadian Journal of Civil Engineering, 35: 461-472. Blackburn, J. and Hicks, F.E. (2002) Suitability of Dynamic Modelling for Flood Forecasting During Ice Jam Release Surge Events. American Society of Civil Engineering: Journal of Cold Regions Engineering , 17(1) : 18-36. Fonstad, G.D. and Quazi, M.E. (1982) Peace River 1981/82 Ice Observation Report. Alberta Environment, Edmonton, AB, 57 pp. Friesenhan, E. and Mahabir, C. (2005) Monitoring and data collection along the Peace River during the 2004-2005 ice season. Proc. 13th Workshop on the Hydraulics of Ice Covered Rivers, CGU HS CRIPE, Hanover, NH, 15 pp. Hicks, F.E., (1996) Hydraulic Flood Routing with Minimal Channel Data: Peace River, Canada. Canadian Journal of Civil Engineering, 23(2): 524-535. Neill, C.R. and Andres, D. (1984) Freeze-up flood stages associated with fluctuating reservoir releases. Proc. Third International Specialty Conference on Cold Regions Engineering, CSCE/ASCE, Montreal, Quebec, 249-264. She, Y., F. Hicks, P. Steffler, and D. Healy (2009) Constitutive Model for Internal Resistance of Moving Ice Accumulations and Eulerian Implementation for River Ice Jam Formation. Journal of Cold Regions Science and Technology, 55:286-294.
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Figure 1. Peace River basin map showing the study reach.
Figure 2. Peace River sub-reach including Dunvegan and the Town of Peace River.
256 500
Mean bed level from surveyed cross sections
Estimated mean bed profile 450 Water Surface Profile from NTS maps
400 juxtpositioned or juxtpositioned consolidated ice cover ice cover typical
Hudson's
tion, m 350 Hope a Elevation, mElevation, m Elevation, mElevation, m Taylor
300 B.C - Alberta border
Dunvegan Vermilion Town of Peace River Chutes 250
Fort Vermilion 200 0 100 200 300 400 500 600 700 800 900 1000 1100 1200
Distance Downstream of the the WW.A.C. A C Bennett Dam , km 257 Figure 3. Profile of the Peace River, AB based on surveyed cross-sections and National Topographic Survey (NTS) maps. 800 600 . . 400 Front ion (km) t e
Ice Front 200 a) 1979/80
Location (km) 0 80022-Nov 06-Dec 20-Dec 03-Jan 17-Jan 31-Jan 14-Feb 28-Feb 14-Mar 600 . . 400 tion (km) e Front
a 200
Ice Front b) 1981/82
Location (km) 0 80022-Nov 06-Dec 20-Dec 03-Jan 17-Jan 31-Jan 14-Feb 28-Feb 14-Mar 600 . . 400 e Front ation (km) c 200 Ice Front
c c) 1988/89
Location (km) 0 100022-Nov 06-Dec 20-Dec 03-Jan 17-Jan 31-Jan 14-Feb 28-Feb 14-Mar . . 800 600 400 200 Ice Front ation (km) d) 1991/92 c 0 Location (km) 100022-Nov 06-Dec 20-Dec 03-Jan 17-Jan 31-Jan 14-Feb 28-Feb 14-Mar . . 800 600 400 Ice Front ation (km) 200 e) 1992/93 c 0 Location (km) 80022-Nov 06-Dec 20-Dec 03-Jan 17-Jan 31-Jan 14-Feb 28-Feb 14-Mar 600 . 400
Ice Front 200
Location (km) f) 2000/01 0 80022-Nov 06-Dec 20-Dec 03-Jan 17-Jan 31-Jan 14-Feb 28-Feb 14-Mar . . 600 400 200 Ice Front ation (km) g) 2004/05 c 0 Location (km) 22-Nov 06-Dec 20-Dec 03-Jan 17-Jan 31-Jan 14-Feb 28-Feb 14-Mar
Figure 4. Documented ice cover consolidation events on the Peace River, AB. The red star indicates the approximate timing of the event.
258 20 Fort St. John, BC 10 Peace River, AB High Level, AB C 0
-10
-20
ir Temperature, C -30 Air Temperature, °C A Air Temperature, C -40
-50 29-Nov-81 13-Dec-81 27-Dec-81 10-Jan-82 24-Jan-82 2000 /s /s 3 3
1500
elease Flow, m elease Flow, 1000 R
500 Peace Canyon Release Peace Canyon Flow,m Peace Canyon Release Peace Canyon Flow,m
0 29-Nov-81 13-Dec-81 27-Dec-81 10-Jan-82 24-Jan-82
10
8 Peace Canyon Dam releases re, C u 6
4
2 Water Temperature, °C Water Temperature, C 0 29-Nov-81 13-Dec-81 27-Dec-81 10-Jan-82 24-Jan-82
Figure 5. Mean daily air temperatures, Peace Canyon Dam outflows, and Peace Canyon ouflow water temperatures for 29-Nov-81 to 24-Jan-82.
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325 Smoky R conf. WSC gaugeTPR
320
315
310 Geodetic Elevation (m) Elevation Geodetic
Thalweg 305 Maximum Water Level During Consolidation Post consolidation water level, 13-Jan-82 Series4 Bottom of ice Cover, 13-Jan-82 Series6 Exposed shear walls measured during breakup 1982 300 375 380 385 390 395 400
Distance downstream of WAC Bennett Dam (km)
Figure 6. Longitudinal profiles measured on the Peace River near TPR, 1982 (adapted from Neill and Andres, 1984)
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Figure 7. Photos of the January 1982 ice consolidation at TPR - views from the dike along the Kinsmen Park (photos courtesy of Alberta Environment).
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Figure 8. Photos of the January 1982 ice consolidation at TPR: (top) looking upstream to NAR bridge; (bottom) looking downstream to Highway 2 Bridge (photos courtesy of Alberta Environment).
262
1000
Observed ice front location
800 River1D thermal ice process model result .
600
TPR 400 Dunvegan Ice Front Location (km) (km) Front Location Ice 200
0 21-Dec 28-Dec 04-Jan 11-Jan 18-Jan
Figure 9. Observed and modeled ice front locations on the Peace River, 1981/82.
263 360 a) Thermal model - for 7-Jan-82 350
340
330
320 Elevation (m)
310
300 270 290 310 330 350 370 390 410 River station (km) 360 b) Dynamic model - steady inflow 350
340
330 vation (m) e 320 Elevation (m)
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300 270 290 310 330 350 370 390 410 River station (km) 360 c) Dynamic model - hydro-peaking inflow 350
340 n (m) 330
320 Elevation (m)
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300 270 290 310 330 350 370 390 410 River station (km)
Figure 10. River1D modelled ice profiles for the Peace River, January, 1982.
264 0.0
0.5
1.0 Ice thickness (m) thickness Ice 1.5 Thermal model: 7-Jan-82
Dynamic model: steady inflow
Dynamic model: hydro-peaking inflow 2.0 250 300 350 400 450 River station (km)
Figure 11. Modeled ice thickness profiles for the January 1982 Peace River ice cover consolidation event.
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