than this rain event, the soil moisture drops off

as expected with the sharp decline caused by

the onset of freezing conditions. As expected,

the probe at the 6-in. depth froze first, followed

Run 2

%*DW *= 0.72834 *K * 0.89248

10 points

Run 3

%*DW *= 0.81027 *K * 0.89230

10 points

by the 12- and then the 18-in. probes. The curves

Both

%*DW *= 0.75435 *K * 0.81060

20 points

of soil moisture and temperature verify that

this was in fact the case (Fig. 4, 5, and 6).

The data indicate that not all the available

Run 2

%*DW *= 3.01952 *K * 29.51577

9 points

moisture became frozen. Since the coldest tem-

Run 3

%*DW *= 1.96994 *K * 14.18193

9 points

peratures recorded during the entire winter

Both

%*DW *= 2.23573 *K * 18.11893

18 points

never went below 6C (at the 6-in. depth, and

even warmer at the 12- and 18-in. depths), in

addition to the fact that there were several rain

Run 2

%*DW *= 1.66865 *K * 9.29265

4 points

events during the winter, it is possible that this

Run 3

%*DW *= 1.65982 *K * 8.90202

4 points

is in fact the case. Other researchers have noted

Both

%*DW *= 1.59654 *K * 7.94469

8 points

that unfrozen water exists in soils below 0C.

The curves in Figures 4 through 7 and the

percent soil moisture contents shown in Tables

11, 12, and 13 are based on the dry soil densities

dry soil densities at the test site. For example, a

typical dry density for soils in the test site area

Run 2

%*V *= 1.00431 *K * 1.27854

might be 1.7 or so. If this density is representa-

Run 3

%*V *= 1.20894 *K * 1.36324

tive of the site, then all soil moisture contents

Both

%*V *= 1.07080 *K * 1.12668

shown in these graphs and tables would be too

large and should be reduced by the ratio of the

calibration densities to the test site densities

Run 2

%*V *= 4.16044 *K * 40.74224

(1.425/1.7, or 0.838 on average). Note that a

Run 3

%*V *= 2.93798 *K * 21.23448

year later it is still possible to correct the soil

Both

%*V *= 3.08706 *K * 24.40191

moisture figures in these graphs and tables just

by finding the average dry density of the soil at

the test site.

Run 2

%*V *= 2.30714 *K * 13.04434

The data from these tests are actual soil

Run 3

%*V *= 2.47365 *K * 13.38361

Both

%*V *= 1.68080 *K * 1.165411

moisture measurements determined by mea-

20

Using the procedure described,

15

curves of soil moisture in percent dry

weight vs. elapsed time for 6, 12, and

18 in. are shown in Figures 4, 5, and 6.

10

The temperature data are also shown

for each depth. The data used to gen-

Moisture Content

erate these curves are in Tables 11, 12,

5

and 13. Figure 7 presents a comparison

of moisture content at the three depths

Temperature

during the entire freezethaw cycle of

0

the winter season.

All three summation curves in Fig-

ure 7 show a gradual decline in mois-

5

ture content, starting in early Decem-

0

32

64

96

128

160

19 Nov 1990

10 Apr 1991

Elapsed Days

ber, that takes a sudden sharp rise in

mid-December due to a heavy rain that

occurred over a 36-hour period. Other

13