Agriculture CanadaPrairie Farm Rehabilitation Administration

Engineering Service

DETERMINATION OF ICE THICKNESS

FOR SMAll WATER BODIES

IN THE CANADIAN PRAIRIE REGION

Hydrology Report '119

Regina, Saskatchewan

March, 1990

Prepared by:

D. E. Kelln, P. Eng.

Hydrology Division

Submitted by:

F.R.J. Martin, P.Eng.

Manager, Hydrology Division

SYNOPSIS

This report consolidates the PFRA data bases of ice thickness measure­

ments for dugouts and small reservoirs and presents procedures for determin­

ing (estimating or predicting) the ice thickness of small water bodies on

the Canadian Prairies. Although ice formation is primarily a function of

air temperature and snow cover, a pract ica1 procedure to determi ne ice

thickness could not be developed which encompassed both factors. However, a

map showing isopleths of mean annual ice thickness for small water bodies

was developed, along with an average monthly rate of ice formation through­

out the winter. A simple graphical relationship was developed to determine,

in a rather crude manner, the ice thickness for any year at any given loca­

tion using only the departure from normal of winter air temperature.

Depending upon the user's intent and available information, an estimation or

prediction of ice thickness could involve the use of the map of mean annual

ice thickness, the recorded data and/or the ice thickness-air temperature

relationship.

1. INTRODUCTION .

TABLE OF CONTENTS

...................

PageNumber

1

2. ICE THICKNESS DATA BASES

2.1 Dugout Data ....

2.2 Small Reservoir Data

3. PROBLEMS IN DETERMINING ICE THICKNESS ANDRATIONALE FOR THE APPROACH ADOPTED ....

4. ANALYSIS OF DATA

4.1 Mean Annual Ice Thickness (MAlT)

4.2 Monthly Ice Formation ..

3

3

3

9

11

11

14

4.3 Relationship Between Ice Thickness and Winter AirTemperature . 15

5. PROCEDURES TO DETERMINE ICE THICKNESSAND POTENTIAL APPLICATIONS . 21

5.1

5.2

5.3

Procedure 1: Using MAlT to Estimate Ice Thickness

for an Average Year .

Procedure 2: Using Recorded Ice Thickness Datafor 'Design' Purposes .

Procedure 3: Using Winter Air Temperature (WAT)to Determine Ice Thickness .

21

21

22

6. CONCLUSIONS

REFERENCES .

APPENDIX A - DEPARTURES FROM NORMAL OF WAT

AT VARIOUS LOCATIONS ....

25

27

A-I

Table

Number

lA

IB

2

3

4

5

6

FigureNumber

1

2

3

4

LIST OF TABLES

Location Information for Dugouts

Location and Size Information for Small Reservoirs

Dugout Ice Thickness Data ..

Small Reservoir Ice Thickness Data

Spatial and Temporal Ice Developmentin the Canadian Prairie Region

Winter Air Temperatures at Regina

Airport for the Period 1951-88 .

Departures from Normal of Winter Air Temperatureat Regina and Corresponding Regional

Average Ice Thicknesses for the Period 1976-88 .

LIST OF FIGURES

Locations of Dugouts and Small Reservoirsin the Ice Thickness Study .

Mean Annual Ice Thickness (MAlT)for Small Prairie Water Bodies

Regional Average Ice Thickness as a Functionof Departure from Normal of Winter Air

Temperature at Regina .

Determination of Ice Thickness at a Location

Using Winter Air Temperature (Procedure 3)

PageNumber

5

5

6

7

15

16

17

PageNumber

4

12

18

20

1. INTRODUCTION

In March of 1976, the Hydrology Division of PFRA (Prairie Farm Rehabili­

tation Administration) initiated a five-year study to investigate the

spatial and temporal variability of ice thickness on dugouts in the Prairie

region of western Canada[l]*. The study was intended to evaluate the

effect of factors such as air temperature, exposure, snow cover, orientation

and water depth on ice formation. In addition, it was anticipated that the

geographic distribution of the dugouts would reveal the pattern of ice

thickness across the region and any significant differences in ice develop­

ment over the wi nter season. Better knowl edge of ice formation woul d be

useful in the des ign and operation of dugouts and small reservoi rs and in

the design of appurtenant structures.

In 1979, near the end of the Dugout Ice Thickness Program, the Hydrology

Division of PFRA began collecting ice thickness data on the small reservoirs

that were included in its Spring Runoff Monitoring Program. These measure­

ments continue to be made.

This current report has been prepared to address two objectives:

1. To consolidate the PFRA data bases on ice thickness for small

prairie water bodies; namely, dugouts and small reservoirs,and

2. To analyze available ice thickness data, reports and infor­

mation with the intent of developing a practical, easy-to-use

procedure for determining (estimating or predicting) icethickness on small water bodies in the Canadian Prairie

region.

The following sections of this report describe the PFRA data bases of

ice thickness, the development of a map of mean annual ice thickness for the

Canadian Prairies and practical procedures that were developed to estimate

or predict annual and monthly ice thickness.

* Square brackets refer to references.

- 2 -

- 3 -

2. ICE THICKNESS DATA BASES

2.1 DUQout Data

Dugouts are extensively used in the Canadian Prairie region to

store runoff water from the surrounding land. Typically, a dugout stores

from 2000 to 12 000 m3 (2 to 12 dam3) of water and has a surface area of

1900 to 3800 m2 (0.19 to 0.38 ha) and a depth of 3 to 6 m. Smaller dug­

outs are commonly used for agricultural and rural domestic water supplies,

whereas larger dugouts are sometimes used for municipal purposes.

For five consecutive winters beginning in 1975, field officers from

each of the then twenty di stri ct offi ces of the PFRA Water Development

Service (now a part of the Soil and Water Conservation Service) measured ice

thickness on dugouts on the 15th of each month from October to April. Each

office was responsible for measuring and reporting ice thickness at two

separate poi nts on each of two dugouts located near the di stri ct offi ce.

The two measurements on each dugout were averaged to obtain one reading per

dugout. Figure 1 and Table lA provide the location of each pair of dugouts.

Besides ice thickness, a number of other parameters were either

measured or observed. These parameters included snow cover on the ice, dug­

out orientation, exposure and water depth.

The maximum recorded ice thickness on each

each of the five years of the program[ 1] is given

are identified by the year in which the winter ends.

omitted due to extenuating circumstances, as noted

table.

2.2 Small Reservoir Data

of the 40 dugouts for

in Table 2. The data

Certain data have been

at the bottom of the

In connection with the Hydrology Division's Spring Runoff Monitor­

ing Program, staff from the Division have measured ice thickness prior to

spring breakup at 27 small reservoirs in southern Saskatchewan over the past

decade. Figure 1 and Table IB provide the location of each of these reser­

voirs. Table IB also provides storage and flooded area at FSL (Full Supply

Level) information for the reservoirs. In addition to measuring ice thick­

ness, Hydrology Division staff estimated the average snow cover depth over

the ice surface.

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LEGEND:• Dugout•• Reservoiro Town or cIty

.po

Table 1A

Location Information for Dugouts

Dugout Location

Map

Water Development

Location

D18trict III

1

Brandon SW17-11-19-WPMRZ08-11-18-WPM

2Dauphin SIi11-2(-16-wJ.BW05-25-20-ll1

3Gravelbourg SIi0(-11-05-W3BW31-10-0(-W3

(Hanna BW06-33-13-114SB09-31-13-W(

5Lethbridge NEH-08-26-11(SIf31-09-2(-II4

6

Maple Creek NE22-11-26-l13BW32-10-25-W3

7

Medicine HatNE15-12-06-W(SW17-12-06-W4

8

Meltort SE03-(6-18-W2RZ2(-45-18-W2

9

Melville SW20-21-06-W2BW02-22-06-W2

10

Moose Jaw NW07-17-27-112SW23-17-28-W2

11

Morden SW21-03-05-wJ.SIf31-02-05-Wl

12

Rorth BattletordSW19-(7-17-W3NW18-(6-17-W3

13

Peace RiverNW34-83-21-W5SBH-8(-22-W5H

Red Deer SE32-36-27-W(SW36-36-28-W(

15

Roeetown SIi21-30-H-W3SW36-29-15-W3

16

Sbaunavon SE13-07-21-W3SI!l3(-07-20-W3

17

Swift CurrentRIil6-16-H-W3NW23-15-13-W318

Vegrevi11e SEl7-52-H-W(RZ2(-52-15-W4

19

Weetlock SW09-60-27-W(RZ26-59-27-W(

20Weyburn NE12-08-H-W2SW35-08-15-112

Table 1B

Location and Size Information for Small Reservoirs

StorageFlooded Area

Map

FSLat FSLat FSL

Location

ReservoirLand Location(Ill(daIl3)(ha)

21

Adair SW36-16-10-W2609.0245616.1

22

Brownhill SW31-16-07-W2629.4135513.7

23

Cabri SE28-19-18-W3629.6031216.0

24

Caron SE23-17-28-W222.56*73020.5

25

Ceylon SW13-06-20-W2696.5829011.6

26

Cleland NE33-31-15-l13624.383159.5

27

Craik NE23-24-28-W2554.8962H200.3

28

Davideon NE27-26-29-W2610.21752(0.6

29

Deadmocae Lake SWOl-39-23-112540.11132 0001 400

30

BHroe NW14-32-H-II255(.9(52(17.4

31

Eeterhazy NW33-19-01-112(91.342 983159.3

32

!IuIIIboldt(Burton Lake)SW17-38-22-1125(5.003 52263.7

33

Indian Head Ro. 1NEl1-18-13-W2599.(2482.7

34

Indian Head Ro. 2RIill-18-13-W2605.031365.3

35

Indian Head No. 3ANEl1-18-13-W2607.50723.0

36

Kerrobert NE18-3(-22-l1365( .902(217.2

37

Kipling (Rew) NEI0-13-06-W267(.7959518.1

38

Kipling CRR NE08-13-05-W2678.5328611.7

39

Lucky Lake NW2(-23-09-l13639.06H27.1

(0

Melville SW06-23-06-112559.(6( U6171.1

41

Muenster SIi19-37-21-W2573.6721511.9

(2

Parkbeg SE19-17-02-l1330.18*1023.1

43

Redvere NE2(-07-32-wJ.583.3031529.2

H

S••• ne SIi26-28-20-W2562.0525915.5

45

Welwyn NE02-16-30-wJ.33.30*(7919.2

46

Willowe (Rew) NE35-07-29-W2687.932 U747.3

47

willow. (Old) NEO(-08-29-W2699.7(60917.5

*a•• uaed datu.

(J1

- 6 -

Table 2

DUQout Ice Thickness Data

Annual Ice Thickness (m)**

MapWater Development Number of

LocationDistrictDugout19761977197819791980MeanObservations

1

Brandon I0.9140.8231.0361.3110.6400.90 10II

0.7010.8530.9751.0060.732

2

Dauphin I1.0670.9751.189**0.89 8

II1.0060.9140.6710.7010.610

3

Grave1bourg I0.7920.7620.8530.9450.7620.81 10II

0.6400.7320.9140.9450.762

4

Hanna I0.7320.6930.7771.0670.7920.82 10II

0.7620.5940.8830.9600.975

5

Lethbridge I0.2440.2740.5490.5790.3660.43 10II

0.3350.3050.5790.6710.396

6

Maple Creek I0.3660.3960.5180.6100.5490.53 10II

0.3960.4570.8230.7620.457

7

Medicine Hat I0.3350.3660.4880.7620.5180.50 10II

0.3660.3660.5180.7920.518

8

Me1fort I0.7920.8831.1581.1280.8230.90 10II

0.8830.9140.7620.8530.792

9

Melville I0.6400.9140.9140.9140.9140.78 10II

0.6100.6710.8830.7620.549

10

Moose Jaw I0.6100.851*1.1890.7010.84 8II

0.8230.732*1.1580.671

11

Morden I0.6100.8830.7620.6100.7010.87 9II

1.1280.975*1.1891.006

12

North Batt1eford I0.5790.8230.7920.5490.8230.79 10II

0.6400.8230.8231.0360.975

13

Peace River I0.6100.5790.6400.6100.7920.66 10II

0.7010.5490.6710.6710.762

14

Red Deer I0.7320.3690.6400.8840.8530.67 10II0.6550.4720.4570.7920.823

15

Rosetown I0.7010.945*0.8530.6400.82 8II0.7320.792*1.0360.823

16

Shaunavon I0.5790.6101.0970.9140.6710.76 10II0.6100.6400.7011.1580.640

17

Swift Current I0.838 ***0.762 -4II 0.6710.884***

18

Vegrevi11e I0.5640.4270.4880.823*0.60 8II0.5330.4570.6550.838*

19

West10ck I0.5640.5790.6250.5480.7320.59 10II 0.5180.5940.5330.4870.671

20Weyburn I1.1280.945*1.0360.8840.99 8II 0.9750.914*1.1890.823

Minimum

0.2440.2740.4570.4870.366

Maximum

1.1280.9751.1891.3111.006

Mean

0.6770.6860.7540.8740.720

* Certain data were excluded from this analysis due to unre1iabi1ity caused by local condi­tions. One of the most common conditions was early snowmelt runoff to the dugout and subse­quent freezing on top of the existing ice layer, making it impossible to determine a trueice thickness for the purposes of this study.

** The data contained in this table were originally reported in Imperial units and have been

converted to metric units for this study. Thus, the ice thicknesses are shown to threedecimal places, but the mean for each location is rounded to two decimal places to maintainconSistency with the values in Table 3.

- 7 -

Table 3 contains the annual ice thickness measurements that were

made under the Spring Runoff Monitoring Program. Typically, these measure­

ments were taken at the end of February or begi nni ng of March and are

indicative of the maximum thickness of ice that formed during the winter.

Table 3

Small Reservoir Ice Thickness Data

Annual Ice ~hickness (m)

MapNUmber of

LocationReservoir 1979198019811982198319841985198619871988MeanObservations

21

Adair -0.90 -------0.76 - 222

Brownhill -0.85 -------0.73 - 223

Cabri -0.69 -0.820.580.410.870.550.550.820.66 824

Caron 1.160.660.700.910.630.590.950.790.500.720.76 1025

Ceylon -0.70 -0.910.490.640.82-0.520.670.68 7

26

Cleland -0.860.761.040.760.721.000.850.700.840.84 927

Craik 0.980.91-0.760.610.63-0.740.660.790.76 828

Davidson 1.160.860.760.820.730.690.830.850.720.880.83 1029

Deadmocse Lake -----0.990.911.160.760.810.93 530

ElfroB -0.840.730.730.550.640.930.790.730.580.72 9

31

Esterhazy* 0.610.41--0.520.660.660.520.550.630.57* 832

Humbcldt (Burton Lake)-0.890.910.940.850.870.881.040.760.730.87 933

Indian Head No. 1**---0.560.430.430.46-0.440.460.46** 634

Indian Head No. 20.730.740.580.790.520.760.81-0.670.760.71 935

Indian Head No. 3A ---0.930.460.580.88-0.670.730.71 6

36

Kerrobert --------0.660.85 - 237

Kipling (New) -----0.730.910.580.640.670.71 538

Kipling CNR 0.950.86--0.670.610.98-0.640.760.78 739

Lucky Lake 0.950.79-0.910.700.530.87-0.460.870.76 840

Melville 0.950.81-1.02 -0.871.040.880.820.870.91 8

41

Muenster --------0.640.67 - 242

Parkbeg --------0.410.64 - 243

Redvers 1.160.70-0.850.550.670.91-0.700.790.79 844

Semans -0.970.610.940.690.811.010.850.730.810.82 945

Welwyn 1.07-0.700.790.670.810.88-0.760.760.81 8

46

willows (New) ----0.580.520.79-0.490.670.61 547

Willows (Old) -0.69 -0.820.52-0.77 -0.440.640.65 6

Minimum·**

0.730.660.580.730.460.410.770.550.410.58

Maximum

1.160.970.9l1.040.850.991.041.160.820.88

Mean***

1.010.810.720.870.620.690.900.830.640.75

* Aerator was located in the reservoir, producing an undetermined effect on ice thickness. A1so, above-normal snow coverwas observed at this site.

** Abcve-normal snow cover was observed at this site compared to others in the immediate area, yielding anomalous ice thick­ness values.

*** Ice thickness values for map locations 31 (Esterhazy) and 33 (Indian Head NO.1) were ezcluded from this portion of theanalysis.

- 8 -

- 9 -

3. PROBLEMS IN DETERMINING ICE THICKNESS ANDRATIONALE FOR THE APPROACH ADOPTED

From a review of the available ice thickness and associated data for

dugouts and small reservoirs, as well as previous studies, papers and

reports[2,3,4,5,6], a number of problems became apparent regarding the

development of a practical relationship between the ice thickness on a small

prairie water body and its two main determinants, namely air temperature and

snow cover.

Winter air temperature and snow cover data have different attributes

which affect their usability in a practical manner. Winter air temperature

data are readily available at many locations throughout the Prairies and

generally display variability on a geographic scale, having no sharp discon­

tinuities. On the other hand, snow cover information for small water bodies

in the region is not readily available and is very site-dependent, often

displaying sharp discontinuities over relatively short distances. (See data

for map locations 33, 34 and 35 in Table 3.) Furthermore, the effect of the

snow cover depends not only upon its depth, but is heavily dependent upon

when the snow accumulates and how it is redistributed over the ice surface

during the winter.

A number of observations regarding the accumulation and redistribution

of snow cover on reservoir ice surfaces have been made by field staff, and

these observations provi de ins ight to the vagari es of snow cover. One

observation relates to the shape of the reservoir and its orientation to the

wind direction. If the reservoir lies parallel to the direction of the

wind, snow is more readily blown about and removed. A second observation

suggests that the amount of trees and bush surroundi ng the reservoi r, as

we 11 as the steepness of the valley walls, affect the \snow catch' effi­

ciency of the reservoir. A third observation regards the nonuniformity of

snow cover on reservoirs. Snow cover on small reservoirs is usually not

uniform, with drifts and bare spots being quite typical.

In light of all these considerations and with some regard for

practicality, the most reasonable approach was to assess the ice thickness

data both alone and in conjunction with winter air temperature data only. A

map showi ng the pattern of mean annual (average maximum over-wi nter) ice

th ickness across the Pra irie regi on was developed along with an average

- 10 -

monthly rate of ice formation. In addition, a simple procedure to determine

ice thickness, in a rather crude manner, at any location for any year was

developed using only the departure from normal of winter air temperature and

the mean annual ice thickness.

The approach is based on the assumption that the ice data bases contain

a representat ive and adequate sample of ice th icknesses on small water

bodies in the Prairie region. The representativeness of the sample has two

aspects, namely the physical and the climatic. The physical aspect concerns

the physical features of the water bodies and their surroundings as men­

tioned previously in this and other sections. From this perspective, each

water body included in the study is generally assumed to be typical of its

particular area in the region. The climatic aspect pertains to the weather

cond itions, as characteri zed primari 1y by the wi nter air temperature and

snowfall, during the period of ice measurements. In this respect, the

inherent assumpt ion is that the weather cond itions throughout the Pra irie

region during the period of data collection were typical of the normal

climate. Finally, the adequacy of the sample can be subjectively assessed

by referring to Figure 1. From this figure, it can be seen that the number

of sample locations in southern Saskatchewan are ample to determine the

pattern of ice thicknesses in that area. However, due to the paucity of ice

measuring sites in Alberta and Manitoba, other related information was

required to extrapolate the pattern into these areas.

- 11 -

4. ANALYSIS OF DATA

4.1 Mean Annual Ice Thickness CMAIT)

The mean annual ice thickness (MAlT) map shown in Figure 2 is based

on the arithmetic means of the maximum over-winter ice thicknesses which

were measured for a number of years at 39 of the 1ocat ions shown in

Figure 1. A mean value was calculated and plotted for a small reservoir or

dugout pair only if five or more reliable observations were available.

(Although the data for locations 31 and 33 are 'reliable', they were ex­

cluded for other reasons which are discussed later. This exclusion reduced

the total number of available values from 41, as shown in Tables 2 and 3, to

39.) Upon plotting the 39 values at their locations on a map, no obvious

difference between the two types of mean ice thickness values was apparent.

The isopleths of Figure 2 were based primarily on the plotted data, with

appropriate consideration being given to the following information:

a) number of years of record at each site,

b) measured or observed snow cover depth on the ice surface at asite,

c) normal (1951-80) degree-days below freezing between November 1and February 28 at numerous locations,

d) a map of long-term mean JanuaryCanada[7], and

e) a map of forested areas in Canada[8].

air temperatures for

Of the total 39 values which were plotted, 32 are within 0.1 m of

the value that would be obtained by interpolation of the isopleths. The

remaining seven are considered anomalies; six are within 0.2 m of their iso­

pleth values, and the other one is within about 0.3 m. The anomalous data

are for six dugout pairs and one reservoir, whose map locations are 3, 4,

16, 18, 19, 20 and 30. (See Figure 1 for locations.) These anomalies and

the isopleth map are discussed in the following paragraphs.

Of the three anomalous dugout pairs in Alberta (map locations 4, 18

and 19), two have lower mean recorded values and one has a higher mean

recorded value than the respective isopleths would indicate by about 0.15 m

in each case. Because of the sparseness of sites and the apparent lack of

- 12 -

-r-------------1----------

\

;\~CHEW~ I

LEGEND:

Based on Dugout and Small Reservoir DataExtrapolation using Climatological and Forest Cover Data

MONTHLY DISTRIBUTION OF ICE FORMATION:November 30%

//f

,If//

,/(\___ ..-_l.om

\

\I

WInnipeg \

__-1a.8m

December

January

FebruaryTotal

35%

25%

10%

100%

NOTES:

1. Mean Annual Ice Thickness (MAIT) at a location was based on the arithmetic mean

of annual (over-winter) maximum ice thicknesses for either a pair of dugouts or a

small reservoir at 39 locations. No appreciable difference in ice thickness was found

between the two types of water bodies.

2. The ice thickness at a location on the map should be interpolated to the nearest 0.05 m.

Figure 2. Mean Annual Ice Thickness (MAlT) for Small Prairie Water Bodies (PFRA 1990)

- 13 -

an obvious pattern of ice thickness, the supplementary information mentioned

previously was heavily relied upon in drawing the isopleths in Alberta.

No particular explanation could be found for the anomalous data on

dugouts in southern Saskatchewan, namely for map locations 3, 16 and 20.

The dugout pair at map location 3 (Gravel bourg) had a mean recorded value

about 0.15 m higher than indicated by the isopleth map. This departure

could not be explained. The mean recorded value for location 16 (Shaunavon)

is about 0.2 m higher than ind icated by the isop1eth map . Although the

field staff's data sheets did not provide the evidence, freezing of early

snowmelt runoff on the ice surface is suspected to have occurred at this

site, similar to the situation at map location 17 (Swift Current) just a

little north. (See note for the Swift Current site at the bottom of Table

2.) No plausible explanation can be given for map location 20 (Weyburn),

whose data yielded a mean value almost 0.3 m higher than indicated by the

isopleth map.

At location 30 (Elfros Reservoir), the mean recorded ice thickness

value is about 0.2 m lower than indicated by the isopleth map. This devia­

tion may be partially explained by the somewhat higher-than-average snow

cover which has been observed at the site compared to the other reservoirs.

This site is more sheltered than others, enabling greater snow accumulation,

as well as reducing snow cover redistribution by wind action throughout the

winter.

As mentioned earlier, the mean recorded values for map locations 31

and 33 (Esterhazy and Indian Head No. 1 Reservoirs) were not plotted despite

their 'reliability'. If they had been plotted, they would have been at

least 0.3 m lower than indicated by the isopleth map. These departures can

be easily explained, as noted at the bottom of Table 3. Esterhazy Reservoir

contains an aerator which may disrupt ice formation, and both reservoirs

consistently accumulate much greater amounts of snow relative to other water

bodies in the area. The ice data for these two reservoirs are definitely

not representative of the MAlT in their locations because of these unusual

circumstances. However, they do provide a benchmark for ice thickness under

similar circumstances.

Since over 80% (32 of 39) of the mean recorded ice thickness values

are within 0.1 m of their corresponding isopleth values, the map shows

fairly accurately the pattern of mean annual ice thickness (MAlT) across the

- 14 -

Prairie region. It is recommended that the isopleths not be interpolated to

less than 0.05 m at any location. For example, the MAlT at Swift Current,

Saskatchewan should be read as either 0.60 or 0.65 m depending on the use,

but not as 0.63 m.

4.2 Monthly Ice Formation

In addition to the development of the MAlT map, the rate of ice

formation during the winter was investigated. For the dugout study (1976­

80), ice thickness was measured on the 15th of each month from October

through to April. From this information, two ice formation conditions were

distinguishable, each definable by geographic area. Dugouts in Area A

exhibited their maximum ice development by February 15 and those in Area B

by March 15. Area A is roughly a triangle bounded by dugouts whose map

locations are 18, 5 and 10, while Area B encompasses those expanses which

are outside of Area A.

Dugout ice data for Areas A and B were cons idered separately to

determine if the difference in ice formation with respect to time was

significant. Plotting the average rates of ice formation for each area and

interpolating to obtain end-of-month values (since the measurements were

taken in mid-month) resulted in the percentages shown in Table 4. As

ind icated by th is table, the difference in ice development occurri ng over

time between the two areas is not significant. Thus, for simplicity and

ease of use, a single temporal distribution of ice formation for the entire

Pra irie regi on (Areas A and B combi ned) has been determi ned by averagi ng

the values in Table 4 and rounding to the nearest five percent. The result­

ing percentages are shown in Figure 2.

Interestingly, this monthly rate of ice formation fits the general

pattern which the Water Survey of Canada has observed for river ice in

Alberta and Saskatchewan[9]. As these river ice measurements indicate,

ice begins to form sometime in November and increases in thickness quite

steadily well into January. Sometime in February, the insulating effect of

the snow and ice layer over the water and the generally warmer air tempera­

ture cause a dramatic decrease in the rate of ice development. Ice forma­

tion is negligible during March as air temperature continues to rise.

- 15 -

Table 4

Spatial and Temporal Ice Development in the Canadian Prairie Region

Monthly Ice Formation as a Percentage

of Maximum Ice Thickness

Time Period

Area A*Area B**

October 15 to November 30

32%29%

December 1 to December 31

34%34%

January 1 to January 31

27%22%

February 1 to February 28

7%12%

March 1 to March 15

0%3%

TOTAL

100%100%

* Maximum ice thickness attained by February 15.** Maximum ice thickness attained by March 15.

4.3 Relationshio Between Ice Thickness and Winter Air Temoerature

A simple procedure to roughly estimate ice thickness for other than

average years at any location in the Prairie region has been developed based

on the departure from normal of winter air temperature (WAT). The deriva­

tion of the procedure is described in this section.

The monthly mean winter air temperatures and the WAT (winter air

temperature) at Regina airport for each winter in the 1951-88 period are

shown in Table 5. Regina was selected because it is near the centre of the

area in which the majority of ice thickness measurements were taken (see

Figure 1). The WAT as shown in Table 5 is the summation of the monthly mean

temperatures for the four winter months (November to February) divided by

four. The year 1isted in Table 5 is the year in which the winter ends.

This arrangement allows for direct comparison by year between the

temperature data in Table 5 and the ice thickness data contained in Tables 2

and 3. As the values in the table show, the WAT over the 38-year period has

ranged from a high of -8.00C (1987) to a low of -17 .00C (1979), with

both extremes occurri ng when reservoi rice measurements were being taken.

The mean WAT over the 38-year period was -12.10C.

- 16 -

Table 5

Winter Air Temperatures at Reqina Airport for the Period 1951-88

Monthly Mean Air Temperature (oC)

WAT*Year**

NovemberDecemberJanuaryFebruary(0C)

1951

- 9.6-14.9-19.6-16.6-15.21952

- 7.7-17 .6-20.2-12.2-14.41953

- 3.0- 9.2-13.7-11.6- 9.41954

0.2- 8.1-22.4- 3.7- 8.51955

0.5- 6.4-13.4-16.3- 8.9

1956

-13.2-17 .6-17 .4-16.6-16.21957

- 3.8-12.9-18.9-14.1-12.41958

- 3.9- 8.5- 9.0-14.2- 8.91959

- 6.3-12.9-19.5-16.2-13.71960

- 7.8- 7.1-17.6-14.2-11.7

1961

- 6.3-10.5-13.0-11.1-10.21962

- 4.6-18.2-16.3-17.6-14.21963

0.6-10.5-19.5-12.4-10.51964

- 3.3-12.9-11.6- 8.7- 9.11965

- 5.6-19.9-19.9-16.2-15.4

1966

- 8.3-10.9-24.5-16.2-15.01967

-10.4-12.5-16.5-15.9-13.81968

- 4.4-12.3-16.6-11.5-11.21969

- 2.2-15.6-24.6-14.6-14.31970

- 2.8- 9.0-18.8-14.1-11.2

1971

- 6.5-17 .0-21.a-12.3-14.21972

- 4.2-16.4-21.9-18.5-15.31973

- 3.9-17.5-10.2-10.5-10.51974

-11.5-15.0-21. 2-13.6-15.31975

- 2.9- 6.7-14.5-15.9-10.0

1976

- 3.8-12.1-14.7- 8.8- 9.91977

- 5.5-12.3-20.0- 5.1-10.71978

- 6.5-17.6-22.2-16.3-15.71979

- 9.2-15.9-22.0-21.a-17.01980

- 5.2- 8.2-17 .0-13.3-10.9

1981

- 1.6-13.6-11.0- 9.2- 8.91982

0.1-14.1-25.4-15.7-13.81983

- 6.8-11.0-11.4- 9.2- 9.61984

- 2.8-21. 6-11.9- 3.7-10.01985

- 6.5-18.1-16.1-15.4-14.0

1986

-13.6-13.8- 8.1-13.9-12.41987

- 8.2- 8.6- 8.9- 6.1- 8.01988

- 0.7- 6.9-15.8-12.7- 9.0

Minimum

-13.6-21.6-25.4-21. a-17.0Maximum

0.6- 6.4- 8.1- 3.7- 8.0Mean

- 5.3-13.0-17 .0-13.0-12.1

* WAT is the winter air temperature and is the summation of the monthlymean temperatures for November to February inclusive, divided by four.

** Year in which the winter ends.

- 17 -

Table 6 contains the departures from normal of WAT at Regina for

each year of ice measurements plus a regional average ice thickness for each

data base as available. The normal WAT (-12.50C for Regina) for the 1951­

80 period was used. The regional average ice thickness for the dugout data

base in anyone year is the mean of all the dugout ice thicknesses in

Saskatchewan as shown in Table 2 for that year. Similarly, the regional ice

thickness values for the reservoir data base are the annual means as shown

at the bottom of Table 3, with the measurements for map locations 31 and 33

having been omitted as noted. (The mean values for the reservoirs could be

used directly from Table 3 because all the reservoirs are in southern

Saskatchewan.)

Table 6

Departures from Normal of Winter Air Temperature at Regina andCorresponding Regional AveraQe Ice Thicknesses for the Period 1976-88

Departure fromRegional Average Ice Thickness (m)Normal of WAT*Year

(OC)Dugout Data Base**Reservoir Data Base

1976

+2.6 0.70 -1977

+1.8 0.77 -1978

-3.2 0.85 -1979

-4.5 0.951.011980

+1.6 0.740.811981

+3.6 -0.72

1982-1.3 -0.87

1983+2.9 -0.62

1984+2.5 -0.69

1985-1.5 -0.90

1986+0.1 -0.83

1987+4.5 -0.64

1988+3.5 -0.75

* The normal WAT is for the 1951-80 Canadian Climate Normal period atRegina (-12.50C).

** Calculated using only the ten dugout pairs in Saskatchewan.

The fifteen data points in Table 6 were plotted on arithmetic graph

paper, produc ing a plot of ice th ickness versus departure from normal of

winter air temperature, which is shown in Figure 3. A curve was drawn pass­

ing through the points and intercepting the y-axis at +12.50C. (It was

assumed that no ice would form if the WAT were zero.)

+13

+12+11r--.

(.)+10

0 '--'" +9« Z +8H C) +7Wn:::: +6I- « +5

I-+4« 3 +3

LL+2a

.....J

+ 1

« :20

n:::: a -1z -2:2 a -3n:::: LL -4W

-5n:::: :JI- -6n:::: « -70... W

-80 -9-10

- 18 -

- -..•...•...•.

LEGEND:

••.. ••.. ,-

Dugout Data Base••..

....•Reservoir Data Base

" .... ,....,........

'-""•...~'"

•M

~

-" .'\~\

~\\\~\

.\\.

\\.\\

\.

-110.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

REGIONAL AVERAGE ICE THICKNESS (m)

Figure 3. Regional Average Ice Thickness as a Function of Departure from Normal of

Winter Air Temperature at Regina (PFRA 1990)

- 19 -

Although numerous ice measurement stations were util ized in the

preparation of Figure 3, only the temperature data from one station (Regina)

was used. The validity of using temperature data from only one location to

represent all of southern Saskatchewan was tested by analyzing temperature

data from six geographically widespread stations: Coronation, Swift

Current, Prince Albert, Yorkton, Brandon and Regina. (See Figure A-I in

Append ix A for 1ocat ions.) Averagi ng departures from normal of WAT for

various combinations of these stations and replotting the data points using

these new values did not significantly affect the relationship.

A procedure for determining the ice thickness at any location for a

year which is other than average is provided in Figure 4. The curve relates

differences from MAlT to departures from normal of WAT and is based on the

assumpt ion that MAlT occurs when the WAT is normal (i.e. departure from

normal of WAT is zero). The curve in Figure 4 was developed by selecting a

number of points from the curve of Figure 3. For each point selected, the

0.825 m ice thickness base value (where departure from normal of WAT equals

zero) was subtracted from the regional average ice thickness coordinate, and

the resulting difference was plotted against the departure from normal of

WAT coordinate. A curved line was then drawn through these points. The use

of this procedure for determining ice thickness is discussed and illustrated

in the next section.

If adequate information had been available, the Prairie region

could have been divided into a number of subregions, and the method

described in this section could have been employed on a subregional basis.

The outcome of such a approach would have been either the confirmation of

the relationship shown in Figure 4 or the development of a unique relation­

ship for each subregion. However, since the requisite amount of ice thick­

ness data was not available, the relationship shown in Figure 4 is assumed

to apply to the entire Prairie region.

- 20 -

4

10""

-I

" ""--I

" ""-I

""""

-I

,.

""-I

\ \\\-I

\ \-I

\

-I

\+

I

'\-I

\\,\\\\\

\\

\\\\\ -\ \

NO

ICE

10

MAIT = Mean Annual Ice Thickness

from Figure 2

Figure 4. Determination of Ice Thickness at a Location Using WinterAir Temperature (Procedure 3) (PFRA 1990)

- 21 -

5. PROCEDURES TO DETERMINE ICE THICKNESS AND POTENTIAL APPLICATIONS

The results from this study may be used to determine the ice thickness

on a small water body in the Canadian Prairie region for a variety of hydro­

logic, hydraulic and design assessments. The suggested procedures outlined

in the following three subsections may be used to determine the ice thick­

ness for an average wi nter, an histori c winter or even a hypothet ica1

winter. Some potential applications of the procedures and their limitations

are illustrated by examples.

It is strongly recommended that the user become acquai nted with the

limitations of the ice thickness data bases (by reading the previous

sections), which provide the foundation for these procedures, before utiliz­

ing any procedure(s). In general, the greatest confidence may be placed in

procedure 1, which pertains to an average winter. Of the remaining two pro­

cedures, which are used to determine ice thicknesses for other than average

conditions, more confidence should be placed in procedure 2 than in proce­

dure 3.

5.1 Procedure 1: Using MAlT to Estimate Ice Thicknessfor an Averaqe Year

Figure 2 can be used to determine the ice thickness that may be

expected on a small water body on the Canad ian Pra iries in an average

winter. After determining the appropriate MAlT (mean annual ice thickness)

to the nearest 0.05 m pertaining to the location of interest on the map, the

MAlT may be multiplied by the monthly percentages of ice formation presented

in Figure 2 to estimate the amount of ice development during each winter

month. This procedure provides a more realistic ice thickness value for use

in reservoir simulations, which assess available water supply for example,

than simply using a nominal value (such as 0.9 m) for all locations in the

Prairie region. As Figure 2 shows, 0.9 m is the appropriate MAlT for

Yorkton, Saskatchewan; however, only one-half that amount (0.45 m) is the

appropriate value for Lethbridge, Alberta.

5.2 Procedure 2: Using Recorded Ice Thickness Datafor 'Desiqn' PurDoses

The MAlT may be adequate for some uses, such as water supply anal­

yses, but is not appropri ate for other app1icat ions, such as determi ning

- 22 -

extreme ice thickness values for 'design' purposes. In these cases, a

perusal of Figure 1 (map showing locations of ice measuring stations) and

Tables lA and 18 (location and size information) should be made to locate

one or preferably two water bodi es whi ch are deemed representative of the

site and location being investigated. Then, by referring to Tables 2 and 3,

a review of the historical data should provide the user with a range of ice

thicknesses that may be expected. In addition, a frequency analysis may be

performed using this data, or possibly an analogue year may be selected and

compared with historical winter air temperature (WAT).

For example, assume that a user is interested in determining a

'design' ice thickness value for a small reservoir in the Moose Jaw area of

Saskatchewan. From Figure 2, the MAlT appears to be about 0.75 m. A per­

usal of storage and flooded area data contained in Table 18 reveals that

Caron Reservoir (map location 24) is similar to the reservoir under

consideration. A review of the data in Table 3 for Caron Reservoir indi­

cates that ice thickness has ranged historically from 0.50 m in 1987 to

1.16 m in 1979. Realizing that the winter of 1979 was the fourth coldest of

the 92 years on record for the area, the user could determine an appropriate

ice thickness value for design purposes based on this recorded ice thickness

and air temperature information. In addition, a frequency analysis of the

recorded ice thickness values could be performed. Then the results from

these two methods could be compared and a 'design' value could be

determined. If monthly values are required, the monthly distribution per­

centages in Figure 2 may be applied.

5.3 Procedure 3: Using Winter Air Temperature (WAT)to Determine Ice Thickness

If the recorded ice thickness data is deemed to be inappropriate, a

third procedure may be employed. This procedure, which is described in

Figure 4, simply uses the departure from normal of wi nter air temperature

(WAT) along with the MAlT to determine the ice thickness value. With the

appropriate 'departure from normal of WAT' (Step 2), the corresponding

'difference from MAlT' may be selected from the curve in Figure 4 (Step 3).

Applying this difference to the appropriate MAlT value from Figure 2 (Step

4) will yield a rough estimate of the ice thickness.

- 23 -

This procedure may be used to either estimate historical ice thick­

nesses or predict a hypothetical ice thickness. For instance, the histor­

ical approach may be used for the period prior to recorded ice thicknesses

to estimate a series of ice thickness values upon which, for example, a

frequency analysis could be performed. Alternatively, a hypothetical

'departure from normal of WAT' may be used to predict a 'design' ice

thickness value.

To aid in the application of this procedure, departures from normal

of WAT have been determined (Steps I and 2 of Figure 4) for various loca­

tions throughout the Prairie region for a number of years. These values are

presented in Appendix A along with a location map for reference. The data

conta ined in Append ix A can be used in conjunct ion with Figures 2 and 4

(starting at Step 3) to estimate the historic ice thickness for any year or

a period of years at any location in the Prairie region.

In spite of its ease of use, this procedure should be employed with

caution. Since it is based on a regional relationship between average ice

thickness and departure from normal of winter air temperature (Figure 3),

the procedure may underestimate high extreme values or overestimate low

extreme values at a specific location. Utilizing the example from procedure

2 illustrates this point. The 'departure from normal of WAT' for 1979 at

Regina from Table 6 (or Table A-I in Appendix A) is -4.50C (Step 2).

Entering Figure 4 with this value yields a 'difference from MAlT' of about

+0.15 m (Step 3). Adding 0.15 m to the MAlT for Moose Jaw (Step 4) yields

an ice thickness of 0.90 m, underestimating the measured value (1.16 m for

map location 24 in Table 3) by 0.26 m. Following a similar procedure for

1987 (departure from normal of WAT of +4.50C) leads to an overestimate of

the actual value by 0.06 m. Depending upon the use, these tolerances mayor

may not be acceptable.

- 24 -

- 25 -

6. CONCLUSIONS

The following conclusions have resulted from the study of ice thickness

on small water bodies in the Canadian Prairie region.

1. Mean annual ice thickness (MAlT) increases in a northeasterlydirect ion from 0.4 m in southern Alberta to 1.0 m on the

northern fringes of the region. (See Figure 2.)

2. The average rate of ice format ion over the wi nter does not

vary significantly throughout the region and has the followingtemporal di stri but ion: November 30%, December 35%, January25% and February 10%.

3. Developing a direct relationship between ice thickness and thema in causat ive factors of air temperature and snow cover is

not practical due to the vagaries in the amount of snow cover.However, a simple graphical relationship has been devised to

determine the maximum ice thickness that may be expected or

may have occurred in any winter at any location using only the

departure from normal of winter air temperature and the mean

annual ice thickness. (See Figure 4.)

- 26 -

- 27 -

REFERENCES

[1] Woodvine, R.J., Report on 1979-80 DUQout Ice Thickness, HydrologyMemorandum #34 (includes 1976-80 data), Hydrology Division, PFRA,Regina, October, 1981.

[2] Edwards, D., PFRA DUQout Ice Thickness Study, Co-op Work Term Report

(Engineering), University of Regina, September, 1983.

[3] Fertuck, L.J., Spyker, J.W., Husband, W.H.W., Numerical Estimation ofIce Growth as a Function of Air Temperature. Wind Speed and Snow Cover,

The Engineering Journal, EIC, Vol. 14, No. B-9, December, 1971.

[4] Donchenko, R.V., Peculiarities of Ice Cover Formation on Reservoirs, The

Role of Snow and Ice in Hydrology, Proceedings of Banff Symposium,

September, 1972 (International Association of Hydrological SciencesPublication 107, Vol. 1).

[5] Williams, G.P., Freeze-up and Break-up of Fresh Water Lakes, Proceedingsof a Conference on Ice Pressures Against Structures, Quebec City,November, 1966 (Technical Paper No. 286, Division of Building Research,National Research Council, Ottawa, October, 1968).

[6] Mitchell, S.C., Analysis of Ice Accumulation on Farm DUQouts Around

Saskatoon, Kel sey Institute of Appl ied Arts and Sci ences, Saskatoon,Saskatchewan, May 8, 1978.

[7] Fisheri es and Envi ronment Canada, Hydrol OQica1 Atl as of Canada, Supplyand Services Canada, Ottawa, 1978.

[8] Energy, Mines and Resources Canada, National Atlas of Canada, Map Number25.1, Supply and Services Canada, Ottawa, 1983.

[9] Water Survey of Canada (Calgary District), Ice Thickness of SelectedStreams in Al berta. Saskatchewan and the Northwest Territori es, Inland

Waters Branch, Calgary, September, 1971.

- 28 -

A-I

APPENDIX A

DEPARTURES FROM NORMAL OF WAT AT VARIOUS LOCATIONS

A-2

0---------I//r/,

LEGEND:

A-3

--T-------------r-----------\

;;;:J t: \TCHEW~ I

////////(\

\

\I

• Location for which historical Departures from Normal of WAT (Winter Air Temperature) are provided

LOCATION

Brandon

CalgaryCold Lake

Coronation

DauphinEdmonton

LethbridgePeace River

Prince Albert

Regina

Swift Current

WinnipegYorkton

1951-80 NORMAL

WAT (oC)

-13.9-7.5

-13.4-11.3-13.7

-7.5-5.6

-13.9-15.4-12.5-9.7

-13.3-14.0

Figure A-i. Location Map and Normal WATs for Stations in Table A-l(PFRA 1990)

A-4

Table A-I

Departures from Normal of WAT* at Various Locations

YEAR"" PEACE RIVERCOLD LAKEEDMONTONCORONATIONCALGARYLETHBRIDGE

1912

-1.0 -2.4-.6-.21913

-1.3 -2.5-1.8-.71914

.1-2.6-2.7 .71915

--2.1-2.1-.81916

---.1--1.2-3.41917

---1.0 --.7-2.91918

- .1-.5-.81919

2.4-3.9-4.32.91920

-.8-.0-.6-2.01921

.8-2.5-2.31.71922

-.7--.8--1.6-3.21923

1.0 .8-.4-.21924

.0-4.4-3.73.11925

-2.7 --2.1 --1.6-1.81926

9.4-4.8-6.14.91927

-.7--.9--.3-.51928

-.9--.6--.9-2.11929

1.4-.9-.4-2.61930

-.1-1.4-.7-.51931

7.3-8.2-7.27.21932

-.3-.5.9.3.71933

-4.0 --.2-.5.6.41934

-1.9 -1.8-2.72.71935

-1.9 -.7-2.21.91936

-3.3 --5.3 --4.2-4.21937

1.5--.9--1.4-3.41938

.0--1.1 --.8-.81939

2.1-.4-.7.81940

5.4-3.3-2.72.61941

.9--.7-1.41.01942

5.7-3.9-3.22.81943

-.1--1.8 --1.0-1.21944

7.0-5.6-5.14.71945

2.7-2.01.32.01.01946

-1.2 --1.4-1.1.1.91947

-1.5 --1.3-1.6-.5-1.01948

3.3-2.1.7.81.11949

-2.4 --2.0-2.5-3.0-3.31950

-2.7 --2.5-3.4-2.9-3.11951

-4.3-2.1-2.1-2.6-1.6-.71952

-.7-2.2-1.1-1.5-1.6-1.11953

4.12.53.83.32.63.21954

2.0.53.22.91.82.71955

4.84.25.44.44.23.91956

-5.5-4.9-4.9-5.6-5.8-5.01957

2.01.02.0.4.1-.31958

4.43.63.83.13.43.81959

-1.5-.7.1-1.0-.4-.81960

3.22.53.22.01.61.61961

2.93.43.32.73.73.61962

-2.1-2.4-1.8-1.7-.5-1.21963

2.11.53.03.42.72.71964

2.73.12.53.62.92.81965

-4.2-3.8-3.7-2.4-2.8-3.11966

-3.0-2.7-3.4-2.9-2.6-2.01967

-2.5-1.2-1.7-.9-.5.51968

.41.3 .81.81.3.71969

-5.6-2.4-5.3-3.6-5.5-6.21970

2.32.41.52.02.72.61971

-3.2-3.0-4.0-2.8-1.9-1.51972

-4.6-3.4-3.7-3.2-3.7-3.61973

.0.7-.11.0.5.91974

-3.1-2.7-3.4-1.9-1.7-.81975

2.33.11.72.21.51.01976

1.52.31.52.52.62.71977

6.04.14.22.84.93.61978

-1.4-2.0-2.9-3.8-3.9-4.41979

-3.4-3.6-3.6-4.5-3.7-4.81980

3.61.91.1.81.11.11981

4.13.73.63.34.43.61982

-2.9-2.0-1.8-1.4-1.5-1.91983

1.21.41.71.13.53.11984

3.32.62.5.72.01.31985

-1.6-1.7-1.5-2.5-.4-1.11986

1.5.41.1.61.3-.41987

5.14.14.44.15.14.11988

5.03.34.42.54.23.5

Minimum

-5.6- 4.9-5.3-5.6-5.8-6.2Maximum9.44.28.24.47.27.2

* WAT is the winter air temperature and is the summation of the monthly mean temperatures for November to February inclusive,divided by four. The normal for each location was calculated using A.E.S. records for the 1951-80 period. (See Figure A-I.)

** Year in which the winter ends.

A-5

Table A-I (continued)

Departures from Normal of WAT* at Various Locations

YEAR" SWIFT CURRENTREGINAPRINCE ALBERTYORKTONDAUPHINBRANDONWINNIPEG

1912

-2.0-2.5-.6.1-1.1-1.9-1.31913

2.0.11.2.91.5.0.21914

2.31.83.4.91.91.12.21915

1.71.82.31.62.91.71.21916

-1.7-2.6.0-1.7.7-1.9-.61917

-4.1-2.9-.9-2.0.0-2.9-2.71918

.1-1.5.2-.7-.5-.4-1.01919

3.62.75.42.25.22.63.61920

-.8-2.1.9-2.7.3-2.7-2.41921

3.83.24.53.94.22.52.91922

-1.2-1.5.5-.3.8-.8-.31923

-.7-1.31.9-.71.2-.7.61924

3.83.35.13.64.63.23.91925

-.6-.7-.1-2.8-.3-1.5-1.11926

4.44.96.24.75.24.53.21927

.1-1.9.2-1.6.4-1.5-.21928

-.8-1.3.3-.51.5-1.8.51929

-.4-.11.2-.12.0-.6.91930

1.1.0.8.0.9-.2-.41931

7.87.28.46.77.46.25.11932

1.92.03.02.93.93.33.81933

.6-1.5-.5-.8-.1-.9-1.51934

4.01.92.51.9-.1.8-1.31935

2.1.42.31.32.51.71.51936

-4.5-6.6-3.8-5.4-4.6-6.0-5.41937

-2.8-3.0-.8-2.3-.5-1.3-1.61938

.1-.9.4-.3.4-.8 .11939

.31.91.02.0.3-1.3-1.01940

3.23.04.73.85.74.84.31941

1.2-.61.3.91.61.21.21942

3.43.35.33.93.24.23.01943

-1.2-1.7-1.7-1.2-.5-.5-1.81944

4.64.45.34.35.14.93.11945

1.01.11.82.03.62.82.41946

-.4-1.4-1.6-1.2-2.9-1.6-1.11947

-1.6-2.4-1.5-.9.4-.2-.11948

-.2-1.1-.4-.9.1-.6-1.11949

-3.2-2.9-1.4-1.6-.2-1.2-1.21950

-2.8-2.7-2.7-2.5-2.3-1.2-1.61951

-2.2-2.7-1.6-2.0-1.4-1.1-1.01952

-1.8-1.9-1.6-1.5-.8-.6.31953

3.13.13.23.12.53.23.11954

3.54.02.73.84.13.73.31955

3.43.63.93.32.92.82.81956

-4.1-3.7-3.7-3.1-3.0-3.0-1.71957

-.2.1.8-.5.0-.5.31958

3.53.62.82.62.32.73.11959

-.4-1.2-1.3-.8-.3-.6-1.71960

.9.82.01.31.21.31.71961

3.12.32.42.42.11.71.61962

-1.8-1.7-2.3-2.1-2.6-1.8-1.51963

2.12.0.91.8.61.7.61964

3.33.42.92.62.52.32.11965

-2.7-2.9-3.4-2.5-2.6-2.7-2.31966

-2.1-2.5-3.4-2.7-2.2-2.7-2.41967

-.7-1.3-1.8-2.2-2.5-2.4-2.71968

1.11.31.51.11.3.8.61969

-3.3-1.8-1.7-1.5-1.4-.6.11970

1.81.32.32.01.81.3.91971

-2.1-1.7-2.9-1.6-1.7-.6-1.31972

-3.2-2.8-3.6-2.9-2.0-1.6-2.21973

1.72.0.3.4.31.1-.21974

-1.6-2.8-2.9-2.8-3.3-2.7-2.51975

1.92.53.53.12.82.52.21976

2.82.62.42.72.41.71.91977

2.11.82.11.3.8.0-1.01978

-3.7-3.2-2.3-2.6-2.2-2.1-2.01979

-5.1-4.5-3.5-4.5-4.3-4.9-4.41980

1.31.61.21.21.31.0.91981

4.23.63.44.24.24.02.91982

-1.6-1.3-.2.2.5.6.41983

2.62.92.22.12.53.93.61984

1.02.53.53.03.33.41.91985

-1.6-1.5-1.9-1.7-1.5-1.3-1.01986

-.3.1.6-.2.2-1.0-1.11987

4.84.54.64.54.93.93.81988

3.03.53.13.32.93.22.6

Minimum

-5.1-6.6-3.8-5.4-4.6-6.0-5.4Maximum 7.87.28.46.77.46.25.1

• WAT is the winter air temperature and is the summation of the monthly mean temperatures for November to February inclusive,divided by four. The normal for each location was calculated using A.E.S. records for the 1951-80period. (See Figure A-I.)

•• Year in which the winter ends.