Robert B. Haehnel, Charles H. Clark and Susan Taylor April 1996

SPECIAL REPORT 96-7

Dusting River Ice with

Leaf Mulch to Aid in

Ice Deterioration
Abstract

In an effort to find a low cost means of reducing ice jams on small rivers 

England, dusting with organic matter was field tested during the spring of 1

and 1994. Test squares on a pond located at CRREL in Hanover, New Ha

shire, were dusted with several materials to evaluate their effectivene

accelerating snow melting and ice deterioration. Leaf mulch was included i

materials tested because, unlike other materials used in the past to weake

(e.g., fly ash or coal slag), leaves are naturally found in rivers and shoul

adversely affect aquatic organisms when applied in small quantities. It

found from these tests that the leaves perform about the same as the traditi

used dusting materials. To transfer what was learned at the pond tests to a

application, two rivers in Vermont, with a known history of ice jams, were d

using leaf mulch during the spring of 1994. Since these sites were locat

narrow rivers that wind through highly populated areas, aerial dusting was

possible. For these sites we used a hydroseeder to spread the leaves on th

Application of leaf mulch with a hydroseeder was found to be an efficient m

of putting the leaves on the ice. After the rivers were dusted we had a

snowfall, and were not able to determine the effectiveness of the leaf m

melting the ice. Observations suggest, however, that the leaf mulch helped

the overlying snow. More work is needed to determine the effectiveness

mulch to weaken ice and how much ice weakening is necessary to redu

severity of ice jams.

Cover:

For conversion of SI units to non-SI units of measurement consult ASTM Sta

E380-93a, Standard Practice for Use of the International System of U

published by the American Society for Testing and Materials, 1916 Rac

Philadelphia, Pa. 19103.

This report is printed on paper that contains a minimum of 50% recy

material.
Special Report 96-7

U.S. Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory

Robert B. Haehnel, Charles H. Clark and Susan Taylor April 1996

Prepared for

OFFICE OF THE CHIEF OF ENGINEERS

Approved for public release; distribution is unlimited.

Dusting River Ice with

Leaf Mulch to Aid in

Ice Deterioration
PREFACE

This report was prepared by Robert B. Haehnel, Research Mechanical Engineer,

and Charles H. Clark, Electronics Technician, Ice Engineering Research Division,

and Susan Taylor, Research Physical Scientist, Geological Sciences Division, Research and Engineering Directorate, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire. Funding for this research was provided through the U.S. Army River Confluence Ice Program, Work Unit 32972.

The authors thank Lawrence Gatto and James Wuebben for technically reviewing the manuscript of this report.

The contents of this report are not to be used for advertising or promotional

purposes. Citation of brand names does not constitute an official endorsement or

approval of the use of such commercial products.

ii
INTRODUCTION

The decay of river ice depends not only on the

ambient air and water temperature, but also the

absorption of solar radiation into the ice. Ashton

(1985, 1986) shows that once the ambient air temperature reaches freezing, the rate of deterioration

of the ice cover (i.e., structural weakening of the

cover) depends greatly on the absorption of the

solar radiation by the ice cover. Thus reduction of

the albedo (reflected solar radiation/solar radiation incident to the surface) of the ice surface can

contribute to accelerated decay of an ice cover.

This, in turn, can reduce the potential for ice jam

formation on a given river reach during ice

breakup.

Dusting (application of a dark material to a

snow/ice surface) can be used to hasten ice cover

deterioration by reducing the albedo of the snow/

ice surface (for a review of dusting applications,

see Slaughter 1969). Typical albedo values for

“black” or clear ice are about 20% (Perovich 1992),

while “white” ice—which contains air bubbles,

snow ice or frazil—can have albedo values as high

as 60 to 80% (Prowse and Demuth 1992). Albedo

values for fresh snow can be as high as 90%. However, as snow ages the albedo decreases. A typical

value for this old snow is around 50% (Colbeck

1988). Depending on the type of “dust” used and

the amount applied, dusting can reduce the albedo

of a snow or ice surface to 15 to 20% (Williams

1967). Thus, dusting can be used to increase absorption of solar radiation in all but black ice.

However, if snow is on top of this black ice, dusting can be used to accelerate the ablation of the

overlying snow, allowing the sunlight to get to and

melt the ice faster than would occur naturally.

The dusting material is frequently put on the

ice using an aircraft. Examples of this include dusting operations on Yukon River in Galena, Alaska

(U.S. Army Corps of Engineers 1968) and on the

Platte River near Omaha, Nebraska (U. S. Army

Corps of Engineers 1979, 1994a). During the first

few years that the Yukon River was dusted, a

modified B-25 aircraft was used to spread river

sand on the ice. More recently crop-dusting aircraft have been used to spread the river sand on

the ice. The dusting operations that have been carried out on the Platte River use crop dusting aircraft as well; however, on the Platte coal slag was

used as the dusting material.

Although aircraft are well suited for dusting

large rivers, such as the Platte, many rivers, such

as those found in New England, cannot be dusted

using aircraft because they are narrow and are

lined by trees and dwellings. We found it necessary to develop a new way to apply dusting materials on these small rivers. Also, coal dust and

slag are considered a threat to the riverine aquatic

life due to the contaminants they contain. Furthermore, small particles such as sand, coal dust, and

slag can also be a problem in many New England

rivers since they tend to clog the spaces between

rocks where the fish like to lay their eggs and

thereby inhibit reproduction. The above environmental concerns led us to explore the use of biodegradable dusting materials that might be more

environmentally friendly.

This report details the use of leaf mulch, which

was spread on two rivers in Vermont using a

hydroseeder. We describe the performance of the

leaves as a dusting material, and the usefulness of

a hydroseeder in applying the leaves.

EVALUATION OF DUSTING MATERIALS

During the winters of 1993 and 1994, several

dusting tests were conducted on an ice covered

pond at CRREL in Hanover, New Hampshire. Figure 1 shows a typical test plot setup on the pond.

The purpose of these tests was to evaluate the effectiveness of several organic dusting materials at

melting snow and ice. During these tests the snow

Dusting River Ice with Leaf Mulch to

Aid in Ice Deterioration

ROBERT B. HAEHNEL, CHARLES H. CLARK AND SUSAN TAYLOR
and ice thickness was measured and compared to

a control area that was not dusted. We also measured the albedo of these materials and of the

snow.

Dusting tests

In March of 1993 four, 65-in. (1.65-m) square test

plots were marked on the pond’s surface. In this

test we compared the performance of bark, hay

and leaves to sand. Each test square was dusted

with 960 mL of material, one material on each

square. The control was the ice cover adjacent to

the test squares. All the test materials were immersed in water overnight and were applied wet,

to prevent them from blowing away. A day after

this test was started (20 March) 13 cm of snow fell.

Within two days of the snowfall (22 March) the

snow over the test plot with leaves on it had melted

off. The other test materials also melted the overlying snow more quickly than untreated areas but

they did not become uncovered until the 26th of

March, four days after the leaves were exposed.

Due to heavy snowfalls the remainder of the winter no further evaluations could be made.

On 18 February 1994 a test site was again set

up on the pond with five test squares. There was

30 cm of ice and between 5 and 10 cm of snow on

the test area. Again, hay, sand, bark and leaves

were used but this time both wet and dry leaves

were applied. During the first day the wet leaves

melted further into the snow than did the dry

leaves; wetting the leaves decreased their albedo

about 5–10%. By the following day the leaves that

were applied dry were wetted by their meltwater,

and thereafter the two plots of leaves performed

similarly. The snowfall and cold weather over the

next few weeks resulted in little melting. However, by 1 April the snow over the test areas was 9

cm below the surrounding snow level, suggesting that the underlying test materials were melting the overlying snow. By 14 April the snow in

the test area was gone and the entire test area was

under 13 cm of water; both the hay and the bark

were floating on the water. There was still, however, snow on the ice adjacent to the test areas.

Since the ice had become too weak to walk on, no

further measurements were taken.

Figure 2 shows the measured snow and ice

thicknesses throughout the test. The ice measurements are indicated by the thick lines, while the

snow depths are indicated by the thin lines. Figure 2 shows that the sand and leaves performed

equally well at melting snow and ice. However,

the bark was not only less effective at melting

snow, but there was no noticeable melting of the

ice under the bark.

We also noted that since both the hay and bark

float and they were easily washed off, so that they

Figure 1. Test setup for evaluation of dusting materials on ice-covered pond (March 1994).

2
were not effective once the surface was covered

with meltwater. Leaves and gravel were heavier

than water and stayed on the ice surface even

when there was meltwater on the surface of

the ice. We also found that wetting the organic

materials had the advantage of hastening melting in the early stages of the tests, and prevented the material from being blown around

by the wind during and immediately after application.

Albedo measurements

In March of 1994 we made albedo measurements of snow and dusted snow on the frozen

pond. Also, spectral reflectance* measurements

were made of samples of snow and of the pure

dusting materials (hay, leaves, bark, sand, and coal

dust). These measurements allowed us to identify

what materials might be most effective for reducing the albedo of a snow or ice surface.

All of the measurements were made using a

Analytical Spectral Devices field portable radiometer. The measurements covered the visible and

near-infrared portion of the spectrum (400–1000

nm).

The albedo measurements were made on separate test plots from those described above. No

special preparations were made to the snow before application of the materials. The dusted areas were 60 × 60 cm and all the measurements

were made 30 cm from the ground. The test

areas had 1000 cm3 of material spread on their

surfaces (except the coal dust which had only

had 750 cm3 of material). The albedo was measured with a hemispherical cosine collector. This

gathered radiation from the entire 3600-cm2 test

area. Photographs of the test plots are shown in

Figure 3. The albedo measurements are shown in

Figure 4.

Figure 3a shows that the snow in the control

area is coarse grained and dirty, an observation

confirmed by a low albedo of 50%. This is a typical value for late winter “corn” snow. The dusting

materials decreased the albedo of the snow by

varying amounts, with hay being the least effective and coal dust being the most effective. Of the

organic materials leaves were the most effective

at reducing the albedo of the surface.

For measuring the reflectance of the of pure material samples, each material was placed in a separate container that was about 7.5 cm in diameter.

*Spectral reflectance is the ratio of radiation reflected

by the sample to that reflected from a standard (the standard reflects greater than 99% of the solar radiation,

Labsphere 1988).

40

30

20

10

0

17 Feb ‘94 27 9 Mar 19 29 8 Apr 18 Depth (cm)

ICE

THICKNESS

SNOW

DEPTH

Ambient Ice,

Bark

Sand

Leaves

Ambient

Snow

Bark

Sand

Leaves

Figure 2. Snow depth and ice thickness in test plots and control on ice-covered pond.

3
Due to the small area of these samples (about 45

cm2) we required an instrument with a much smaller

footprint than a cosine collector used for albedo

measurements. Thus, for these samples we made

spectral reflectance measurements using an attachment with a 1° field of view (the resulting footprint

was 0.75 cm2). These measurements were taken

30 cm from the surface of the samples. The results

of these measurements are shown in Figure 5.

Figure 5 shows that all of the pure materials,

except snow*, are quite dark in the visible (400–

700 nm). The sand has the highest reflectance of

the materials at the 400–550-nm wavelengths (blue

Figure 3. Surfaces on which the albedo measurements in Figure 4 were made (March 1994).

a. Old snow. b. Hay.

c. Leaves. d. Bark.

e. Sand. f. Coal dust.

*The spectral reflectance measurements shown in Figure 5 for are for fresh snow; consequently the reflectance for this snow is higher than that of the old snow

shown in Figure 3.

4
1.0

0.5

0

400 600 800 1000

Wavelength (nm)

Old Snow

Hay

Bark

Leaves

Gravel

Coal

Albedo

100

80

60

40

20

0

400 600 800 1000

Wavelength (nm)

Percent Reflectance

Fresh

Snow

Hay

Bark

Leaves

Sand

Coal

Figure 5. Spectral reflectance measurements of fresh snow and the pure materials used on the

test areas shown in Figure 3 (March 1994).

Figure 4. Albedo measurements of the dusted surfaces (March 1994).

5
and green) and reflects about 15% of the radiation

it receives. Hay, bark and brown leaves have a low

reflectance through most of the visible region but

have higher reflectance in the infrared than coal

or gravel. The high reflectance of the plant materials in the infrared is due to the plants’ cell structure (Hoffer 1978). We note that the wavelengths

at which dead leaves absorb the most radiation

(400–700 nm) are those where snow is the most

reflective (Fig. 5) and also those wavelengths corresponding to the sun’s peak radiation (Fig. 6).

Consequently, we found that leaves could be used

to effectively lower the albedo of snow, and would

likely be an effective dusting material.

FIELD TESTS OF LEAF MULCH

Having determined from the tests on the pond

that leaves might be an effective alternative to

dusting with coal dust, slag or sand, we conducted

two field trials during the spring of 1994. The purpose of these trials was to test using a hydroseeder

to apply biodegradable dusting materials to river

ice. Additionally we measured the depth of the

snow and ice in the test reaches during the test to

further document the performance of the leaves

as a dusting material. The field trials were conducted on the Winooski River in Montpelier, Vermont, and on the White River in Hartford, Vermont. The sites were chosen because they are locations where ice jams have frequently formed in

the past, resulting in flooding and damages.

In addition to measuring ice thickness, snow

depths, and air temperature during the melt period, we estimated the incident solar radiation.

Estimates were obtained by decreasing the expected solar radiation (computed from the time

of day, latitude, and Julian day) using hourly cloud

cover data and the procedure outlined in Appendix A.

We also documented the areal coverage (fraction of the ice covered by the leaves) by photographing the dusted area and then using an image analysis program to determine the relative

fractions of the snow and leaves. The process is

illustrated in Figure 7. Figure 7a is a photograph

of the dusted ice surface and Figure 7b is the same

photograph converted to a binary image. The areal coverage was then estimated using a computer

program that determines the area covered by black

(the leaves and stems) in relation to the total area*.

In this example, 30% of the area was covered by

leaves and stems.

The leaves used for this study were mulched

by the Town of Montpelier. The objective in mulching the leaves was to reduce the leaves to mulched

particles that were approximately the size of a

postage stamp. Mulched to this size, about four

bags of leaves yield one bag of leaf mulch.

The hydroseeder used for this operation was a

Bowie model 2500 hydroseeder. We found that 18

to 20 fifty-gallon bags of leaf mulch added to the

2,500 gal. (9,500 L) of water produced a slurry that

could be easily sprayed. By volume that is roughly

2.7 m3 of leaf mulch. By weight it was an estimated

540 kg of leaf mulch.

Montpelier, Vermont

The Winooski River has repeatedly had ice jams

2000

1000

0 123

λ, Wavelength (μm)

E , Spectral Irradiance [W/(m – μm)] λ 2

Figure 6. Solar spectral irradiance at the earth’s surface (from Swain and Davis 1978).

*The value for the aerial coverage depends on how the

analyst classifies the gray areas when creating the binary image from the black-and-white photograph.

6
which caused flooding in Montpelier, Vermont, the

most recent of which occurred on 11 March 1992.

Figure 8 shows a map of the area of concern in

Montpelier. From the historical record we find that

jams frequently formed at or near Cemetery Bend

(indicated in Fig. 8). The annual formation of a

stable ice cover, that extends from the I-89 bridge

to the Bailey Avenue bridge, causes the broken ice

from upstream to arrest and jam at this location

(U.S. Army Corps of Engineers 1994b). It was hypothesized that thinning or weakening the ice

through this reach may allow the broken ice to be

carried out of the city rather than jamming there.

We selected two locations along this problem area

for testing the hydroseeder and leaf mulch on the

Winooski River. The locations are indicated by the

cross-hatched sections in Figure 8. The area labeled

A was located between the railroad trestle and

Bailey Avenue Bridge. Businesses are located on

both sides of the river at this site; thus it provided

a good test of the ability of the hydroseeder to work

in tight confines. The area labeled B extended upstream from the I-89 bridge to Cemetery Bend. This

site had easy access from Route 2, which allowed

us to evaluate deployment of the mulch using the

hydroseeder’s cannon. Both of these sites were

dusted on 9 March 1994.

Bailey Avenue (Site A)

For the test section at the Bailey Avenue Bridge

(site A), wood markers were placed on the ice to

indicate the location to be dusted and the amount

of thinning of the ice that occurred in the test section. Holes were drilled in the ice and one end of

the wood cross was put into the hole with the

cross-piece laying on the ice (see Fig. 9). As the ice

thinned, the bottom of the cross-piece indicated

the elevation of the top of the original ice surface.

If snow fell on the leaves the markers indicated

where the leaves were located under the snow.

The leaf mulch was put on the ice by using a

200-ft (60-m) length of fire hose with a 3/4-in. (1.9-

mm) nozzle (the hydroseeder is capable of operating with up to 400 feet [120 m] of hose). The area

covered using the hose is indicated in Figure 10

and was approximately 4,000 m2. It took about 1

hour to do this. The remainder of the 9,500 L slurry

was spread using the hydroseeder’s cannon aimed

upstream from the Bailey Avenue Bridge, and

Figure 7. Dusted surface in Montpelier, Vermont.

a. Photograph. b. Binary image of the dusted surface (black portions

are interpreted as leaves).

Montpelier Sewage 

Treatment Plant

USGS

I-89

Gage

Bailey Ave.

Bridge

Taylor St.

Bridge

Montpelier

N

Site B

Site A

Cemetery

Bend

Green Mountain

Cemetery

Dog River

Route 2

North Branch River

Winooski 

River

Figure 8. Location of the test sites on the

Winooski River in Montpelier, Vermont.

7
across the river at the railroad bridge (Fig. 11 shows

the cannon in use). At both of these locations the

hydroseeder was about 4.5 m above the ice surface. The spray from the hydroseeder projected out

about 40 m across the ice. The area covered using

the cannon was approximately 3,200 m2. It took

roughly 10 minutes to cover this area. Thus the

total area covered using both the hose and cannon was almost 8000 m2 (the total river area in

this reach was 13,200 m2). The areal coverage was

about 30%; there was approximately 70 g of material per square meter.

The dusting pattern shown in Figure 10 was

chosen in an attempt to weaken the ice cover using a minimum amount of mulch. Rather than melt

all of the ice, the rationale was to melt break lines

into the ice for it to fail along. Then these smaller

Marker

13 cm

Amount of Melt

Initial

Ice surface

New Ice Surface

Figure 9. Schematic of stakes used to locate leaves and document ice depletion.

Figure 10. Detail of dusting at site A in Montpelier, Vermont.

pieces would easily wash out with the spring runoff. The chevrons (Fig. 10) were oriented to try to

channel surface runoff from the adjacent parking

lots out to the middle of the ice cover, thereby accelerating the ice decay.

Interstate 89 (Site B)

We spread 9,500 L of slurry at this site from

Route 2 using the hydroseeder’s cannon. We covered 0.5 km of the river between I-89 and cemetery bend in about 20 minutes. The total area of

coverage was again about 8,000 m2. The density

of coverage was about the same as at the Bailey

Avenue Bridge.

History of the ice decay

The initial thickness of the ice at site A and B

Bailey Avenue

Montpelier and Barre R.R.

215 m

275 m

60 m

Spread

with Hose

Spread

w/Cannon

N

8
was about 50 cm, and was covered by 5 to 15 cm

of snow. The leaves were applied on top of the snow.

The estimated solar radiation and air temperature

for Montpelier* and snow depth at the site A during the test period is plotted in Figure 12.

The day after the leaves were put on the ice 6.5

cm of snow fell, burying the leaves. By 18 March

the leaves at site A were covered by about 15 to 20

cm of snow. Nevertheless, on the 23rd the overlying snow had completely melted in the dusted area

at both sites, while the undusted area was covered by an estimated 10–15 cm of snow. When the

ice washed out of both test sections on the 27th,

there was still snow on the undusted ice, but the

dusted ice was free of snow.

Although no snow measurements were taken

at site B, observations indicated that the melting

in this area was probably similar to that at site A.

This section of the river was less shaded than site

A so we expect the melting may have been accelerated in this reach compared to site A.

*The met data were obtained from the Barre–Montpelier Airport, which is located about 4 miles from the test

sites.

Figure 11. Hydroseeder being used to put leaves on the White River in Hartford, Vermont (March 1994).

White River Junction, Vermont

The White River, from the confluence with the

Connecticut to the Hartford Village Bridge (Fig.

13), has a history of ice jams with no fewer than

nine major jams forming in this reach since the turn

of the century. The most recent jam occurred in

the spring of 1990 and resulted in the collapse of

two piers and loss of a span on the Bridge Street

crossing. The two sites we chose to dust (sites C

and D in Fig. 13) are historical ice jam locations.

The dusting was accomplished on 17 March 1994.

We placed six stakes in the ice at each test section

so we could measure the amount of thinning in

this region. The configuration of the stakes is

shown in Figure 14.

Bridge Street Bridge (Site C)

Due to a dwindling supply of mulched leaves,

only eleven bags of mulched leaves were added

to the 9,500 L of water and used at the Bridge Street

Bridge. Stakes were placed on the ice at regular

intervals perpendicular to the north bank of the

river, so we could measure the distance the

hydroseeder could spray the leaves using the cannon. We found using the 1-in. (2.5-mm) nozzle the

hydroseeder had a range of 40 m. The flared nozzle

cut down the range to 30 m. From the bridge,

9
shooting with the wind, the range increased to

about 43 m.

Only half of the 9,500 L slurry was used at this

site. The areal coverage was around 50–80%, or

about 190 g/m2 by weight. The total area of coverage was about 2,800 m2.

Hartford Village Bridge (Site D)

At this site 11 bags of leaves were added to the

4,800 L of slurry left over from the Bridge Street

Bridge. The hydroseeder was also refilled to its

9,500-L capacity, so for this site we had a mixture

of approximately 18 bags of leaves in the 9,500-L

slurry.

This bridge is about 15 m above the ice; thus

we were able to get far better range with the 1-in.

nozzle previously used. As a result we used the 1-

in. nozzle to spread the leaves farther away from

the bridge and the flared nozzle to deliver the

leaves closer to the bridge. The areal coverage here

was in the 80% range, or about 190 g/m2 by

weight. The area of coverage was about 2,800 m2.

History of the ice decay

The air temperature and estimated incident solar radiation during the test period are shown in

Figure 15. These data come from the Lebanon Regional Airport, which was about 2 miles from the

test sites. Also Figure 15 gives a plot of the ice thickness for site C and snow cover for both sites during the tests.

From Figure 15 we can see that leaves were effective in melting the snow and ice in the test sections. The average ice thickness in the test reach is

about 3–5 cm thinner in the test reach than in the

control after 13 days. This represents a lost in ice

thickness of about 0.3–0.4 cm/day. We note that

the 6 cm of snow that was deposited on the ice on

the 22nd was melted off the test section the following day. However, in the control section the

5

4

3

2

1

0

Daily Short-wave

Radiation (kWh/m ) 2

30

20

10

0

9 Mar ‘94 11 13 15 17 19 21 23 25 27 Snow Depth (cm)

Test

Section

Control

Leaves

6

4

2

0

Average

Air Temperature (°C)

Figure 12. Meteorological conditions and snow cover depth during the field

tests on the Winooski River in Montpelier, Vermont.

10
VERMONT

NEW

HAMPSHIRE Connecticut R.

White R.

White River

Junction

Bridge Street

I-91

Rte. 5

Rte. 4

Rte. 10

Rte. 5

Rte. 4

Rte. 14

N

Site C

Site D

Hartford

Village

Figure 13. Location of the test sites on the White River in Hartford, Vermont.

Figure 14. Layout of stakes on the ice for both the Bridge St. and Hartford Village Bridge test sites.

2.6 m

Stakes

Flow

Bridge

Treated

Area

2.6 m 2.6 m

11
snow lingered on the ice for another week before

melting off. This insulating snow can be very effective at shielding the ice from solar radiation as

well as protecting the ice from warmer air temperatures. Both of these factors combine to delay

ice melt and deterioration.

Cost estimates

The costs for dusting using the hydroseeder are

enumerated below. The base costs listed below are

the costs per day of the equipment and labor used

in this project. Since we were not charged for the

labor or front loader (both were supplied by the

City of Montpelier) we provide estimates of those

base costs. There was no cost for the leaves since

these were annually collected and disposed of by

the City of Montpelier. Thus, the only additional

costs to the city for the leaves was mulching them.

Base Costs

Hydroseeder $1600/day

Mulching leaves

Leaf mulcher 50/day

Labor (2 laborers @ $25.00 /

hour each) 400/day

Loader and operator $300/day

Since it took about an hour to fill the hydroseeder with leaves and water and to dust 8,000

m2 using the cannon, we estimated that using the

hydroseeder for a full day (8 hours) we could dust

64,000 m2. A front-end loader was used to load

the leaves into the hydroseeder and we have included one day’s service for a loader and operator. From our experience we required 18 bags of

mulch to cover 8,000 m2. It takes 8 hours for two

workers to mulch 20 bags of leaves; thus to mulch

12

8

0

17 Mar ‘94 19 21 23 25 27 Snow Depth (cm)

4

29 31

Snow in

Control Section

Snow in

Test Section

Hartford Village

Daily Short-wave

Radiation (kWh/m )2

6

4

2

0

White R.

Air Temperature (°C)

8

6

4

2

White R.

0

Ice in

Control Section Ice in

Test Section

Snow in

Test Section

Snow in

Control Section

60 Bridge St.

40

20

0

Thickness (cm)

Figure 15. Meteorological conditions, snow cover depth, and ice thickness during the field tests on the White River in Hartford, Vermont.

12
enough leaves to cover 64,000 m2 (144 bags) would

take 7.2 days. The rent for the leaf mulcher would

then be for 8 days, since we could not rent the

mulcher for a fraction of a day.

Based on the above discussion the cost per covered hectare (10,000 m2) is listed below.

Estimated costs for covering one hectare using the

hydroseeder cannon

Hydroseeder $247

Leaf mulcher 62

Labor 450

Loader and operator 47

Total $806/hectare

If we were to recalculate that based on the rate of

application using the hose instead of the cannon,

we would need to effectively double the amount

per hectare for the hydroseeder and loader. This

would total about $1,100/ha.

We compare these costs to the costs incurred

for the dusting operations in Galena, Alaska, and

on the Platte River in Nebraska. The best estimate

of costs for the dusting in Alaska come from the

records of the Alaska Division of Emergency Services, which has coordinated the dusting operation for the last nine years. Here we present the

costs for the most recent dusting operation at Galena which was done in 1993. In this application

92 m2 of sand were used. The application rate was

about 0.27 kg/m2 and that sand weighs about 1300

kg/m3 (U.S. Army Corps of Engineers 1968). The

total cost for the operation was $33,000. The cost

estimate per covered hectare is about $754 (in 1993

dollars).

In the spring of 1994 the Omaha District initiated a dusting operation on the Platte River. Here

it used 27,200 kg of coal slag. This operation cost

$20,000 to dust 8 ha with coal slag (U.S. Army

Corps of Engineers 1994). This cost included $4,500

for use of a National Guard helicopter to document the operation and the ice decay. The cost per

hectare for this operation was $2,470. If we remove

the cost for the helicopter, the cost for the operation drops to $1,938/ha. Even at this, the cost is

more than double the cost of the operation at Galena, Alaska. We attribute the lower cost for the

operation at Galena to the 25 years of experience

in dusting and the attendant cost optimization that

can occur with such experience.

Environmental considerations

As previously mentioned coal dust and slag are

considered a threat to the riverine aquatic life due

to the contaminants they contain. Before using the

leaves in a field trial we had the leaves chemically

analyzed using X-ray fluorescence (Hewitt 1994)

to check for the presence of heavy metals, as these

could be harmful to the stream habitat if present

in high concentrations. For comparison we present

the chemical composition of the coal slag used on

the Platte River in Table 1.

The results of the X-ray fluorescence analysis

of the leaf mulch shows that the leaves did not

contain any heavy metals. The only metal constituent found in the leaves was iron, with a concentration of 0.05 percent by weight. We note that the

coal slag (Table 1) has an iron concentration over

100 times greater than the leaves. The coal slag

also contains other metals that the leaves do not,

namely aluminum, magnesium, titanium and sodium, all of which occur at high levels. From these

chemical analyses we conclude that the leaf mulch

is more environmentally acceptable than the use

of coal slag. However, to avoid unnecessary introduction of contaminants to the riverine environment, we recommend that leaves collected for such

a dusting operation should be taken from a “clean”

area to avoid the inclusion of insecticides, lubricants, etc., in the leaves.

Aside from the introduction of contaminants,

small particles such as sand, coal dust and slag

can be a problem in many New England rivers,

since they can clog the spaces between rocks where

the fish like to lay their eggs and thereby inhibit

reproduction. Since leaves are biodegradable and

are naturally deposited in rivers, they are readily

absorbed into the river with only a fraction of their

total weight going to silting. Thus, in principle,

using leaves should not adversely impact the fish

Table 1. Chemical analysis of coal slag (or bottom slag) (U.S. Army Corps of Engineers 1979).

Ingredient Amount (%)

Silicon 23.3

Aluminum 11.3

Calcium 5.4

Iron 5.2

Sulfur 3.1

Magnesium 1.4

Potassium 0.93

Titanium 0.64

Undetermined 0.54

Sodium 0.20

Phosphorus 0.11

13
habitat, provided the amount of leaves added to

the river by dusting does not exceed the aerobic

capacity of the river (i.e., the decaying leaves use

all of the dissolved oxygen in the river).

Minshall et al. (1983) indicate that the leaf concentration that falls into Northeastern rivers of the

size like the Winooski and White is around 100 to

200 g/m2. The estimated leaf coverages from these

dusting tests on the Winooski and White Rivers

were 60 and 190 g/m2, respectively. Thus, the

amount of leaves spread on the ice in both Montpelier and Hartford is about the same as what falls

naturally on the river in the fall, effectively doubling the annual amount of leaves going into the

treated reach. This increased leaf loading is expected to affect the acidity and turbidity of the

water as well as affect the level of dissolved solids

and fine particles in the water. To what degree this

impacts the riverine habitat requires further study.

Discussion of field test results

From the tests both at Montpelier and White

River we demonstrated the effectiveness of spreading leaves on the ice using a hydroseeder. We

found that considerable amount of area can be

covered in a short time using this method. Taking

into consideration time for refilling the seeder’s

tank and travel time from the filling station to the

river, 6.4 hectares could be covered per day using

this method. At this rate of application we estimate the cost per dusted hectare to be about $806.

This compares favorably with dusting using aircraft, which we estimate could cost $754/ha. Accessibility to the river is necessary for using a

hydroseeder. A location where a road runs parallel to the river is ideal for using a hydroseeder.

Even with the 120-m hose that is available for the

hydroseeder, there needs to be good access to the

river if the hydroseeder is to be used for dusting.

Rates of coverage using the hydroseeder are cut

in half if the hose is used instead of the cannon.

Consequently we could expect the cost per hectare using the hose to be around $1,100.

The leaves proved to be effective for melting

snow even when covered by up to 33 cm of snow.

It may be effective for snow depths greater than

this, but that was the deepest snow we observed

during our test period. From Dozier et al. (1989)

we find that incident solar radiation can penetrate

snow depths of 10 to 20 cm, but the fraction of

transmitted radiation decreases exponentially with

snow depth. Thus, we expect that snow depths

much greater than 18 cm may block any radiation

from reaching the leaves. Even though the ice may

not deteriorate while the leaves are covered by

snow, the presence of the leaves melts the overlying snow sooner. Thus, the ice surface will be

exposed to solar radiation, thereby hastening ice

decay.

The conditions under which this evaluation was

performed were less than ideal. There were only

seven days of cloudless weather during the 21-day

evaluation at Montpelier and five cloudless days

during the 13 days at Hartford. Nevertheless, at

Montpelier we observed the snow deteriorated

faster in the test section over the 16-day period

from 9 March to 25 March. We saw similar results

at the test sites in Hartford. Additionally, at the

one Hartford site we saw a noticeable decrease in

the ice cover thickness in the test section of about

0.3–0.4 cm per day as compared to the control.

Since this is a modest amount of ice loss we hesitate to say that the leaves were effective in

melting the ice cover, since variability in the

river hydraulics throughout the test reach could

confound these results. Nevertheless, the trend

shows promise, and requires further work to confirm the effectiveness of leaves for melting an ice

cover.

We cannot say that we promoted premature release of the ice due to our efforts. Nonetheless, it

is clear that the leaf mulch was effective in reducing the thickness of ice in the Bridge Street test

area, which would result in weaker ice in that area

than otherwise would have existing naturally.

CONCLUSIONS AND RECOMMENDATIONS

From the tests conducted on the ice-covered

pond, we found that dusting can reduce the albedo of the snow and ice from 0.5–0.9 to 0.1–0.2.

This reduction in surface albedo was shown to accelerate the melting of the snow cover and the thinning of the ice cover on the pond. Of the materials

tested we found sand, coal dust and leaves were

the most effective at reducing the albedo of snow

and ice surfaces. We found that the leaves and sand

were about equal in their ability to accelerate the

melting of snow and ice. The leaves naturally occur in New England rivers and are biodegradable;

thus, used in moderate amounts, they should not

adversely affect the stream habitat.

From the field trial conducted on two Vermont

rivers we found the leaves were effective at melting the snow cover, even when covered with up

to 13 cm of snow. It is less clear how effective the

leaves were at melting the ice cover, although the

14
15

results show a trend toward reduced ice cover

thickness in the test section as compared to the

control. The use of a hydroseeder for spreading

the dusting material is effective and is comparable

in cost to aerial dusting. However, there must be

good access to the river bank to use the hydroseeder to spread the leaves. The ideal situation

would be where a road runs along the side of a river.

More work is required to find the extent to

which dusting can reduce the ice volume and

strength. This will require measurements of the

ice thickness and strength in the dusted and

undusted reaches during the spring melt period

leading up to breakup. Concurrent measurements

of solar radiation, ice temperature, water temperature, air temperature and other standard meteorological data will also be required to document

the decay process and all the pertinent heat and

mass transfer processes occurring at the ice surface. Also a greater understanding of when and

where to dust to achieve maximum benefit needs

to be established. To do this, a relationship linking ice volume and ice strength to ice jam

potential needs to be developed. Finally, further

work is required to determine the environmental

impact of dusting with leaves on the riverine

habitat.

LITERATURE CITED

Ashton, G.D. (1985) Deterioration of floating ice

covers. Journal of Energy Resources, 107: 177–182.

Ashton, G.D., Ed. (1986) River and Lake Ice Engineering. Littleton, Colorado: Water Resources Publications.

Colbeck, S.C. (1988) Snowmelt increase through

albedo reduction. USA Cold Regions Research and

Engineering Laboratory, Special Report 88-26.

Dozier, J., R.E. Davis and A.W. Nolin (1989) Reflectance and transmittance of snow at high spectral resolution. Proceedings of International Geoscience and Remote Sensing Symposium ‘89, p. 662–

664.

Hewitt, A.D. (1994) Screening for metals by X-ray

fluorescence spectrometry/response factor/

Compton Kα peak normalization analysis. American Environmental Laboratory, June.

Hoffer, R.M. (1978) Biological and physical characterizations in applying computer aided techniques to remote sensor data. In Remote Sensing:

The Quantitative Approach (P.H. Swain and S.M.

Davis, Ed.), p. 227–290.

Labsphere, Inc. (1988) Spectralon product data

sheet. North Sutton, New Hampshire.

Minshall, G.W., R.C. Peterson, K.W. Cummings,

T.L. Bott, J.R. Sedeil, C.E. Cushing and R.L.

Vannote (1983) Interbiome comparison of stream

ecosystem dynamics. Ecological Monographs, 53: 1–

25.

Perovich, D.K. (1992) Light reflection from sea ice

cover during the onset of summer melt. Ocean

Optics XI, p. 3351–3358.

Prowse, T.D and M.N Demuth (1992) Spatial and

temporal variability of river ice-cover strength. 9th

International Northern Research Basins Symposium/

Workshop, p. 405–421.

Slaughter, C.W. (1969) Snow albedo modification:

A review of literature. USA Cold Regions Research

and Engineering Laboratory, Technical Report 217.

Swain, P.H. and S.M. Davis, Ed. (1978) Remote

Sensing: The Quantitative Approach. New York:

McGraw Hill.

U.S. Army Corps of Engineers (1968) Operation

Dusty Alaska. U.S. Army Engineer District, Alaska.

U.S. Army Corps of Engineers (1979) Ice dusting

of the Platte River. U.S. Army Engineer District,

Omaha, March.

U.S. Army Corps Of Engineers (1994a) Ice dusting of the Platte River. U.S. Army Engineer District,

Omaha, September.

U.S. Army Corps of Engineers (1994b) Winooski

River flood control reconnaissance study, City of

Montpelier, Vermont. Prepared for U.S. Army Engineer District, New York.

Williams, G.P. (1967) Ice dusting experiments to

increase the rate of melting ice. National Research

Council, Ottawa, Canada, Technical paper No. 239.
16

APPENDIX A: ESTIMATING THE INCIDENT SOLAR RADIATION USING

CLOUD COVER DATA

Since the solar radiation was not measured at the test sites in Montpelier and

White River, we estimated the incident solar radiation on our test plots. The procedure for this is described in Ashton (1985, 1986). We outline that procedure here

and add to it our procedure for incorporating hourly cloud cover information in

the calculation.

The solar radiation incident to the earth’s atmosphere is called the solar constant, Io, and is taken to be 1380 W/m2. The proportion of Io that strikes the earth’s

surface on a clear day φso,c is a function of latitude, L, declination angle, δ, and time

of day:

 

φ α

α α

so,c o

a

= +++

I

e

sin

(sin . ) . sin . –

2

3 2 7 10 1 085 0 10 (A1)

where ea is the vapor pressure of water in the atmosphere, and

sin α = sin L sin δ + cos L cos δ cos H. (A2)

In eq A2, H is the hour angle of the sun that is computed from

H (hour – 12)15°. (A3)

The declination angle is determined from

 

δ= ° 



 

 23 45  360

365 . cos [ – ] 172 D (A4)

where D is the Julian day. The vapor pressure ea is

ea = esatRH (A5)

where esat is the water vapor saturation pressure at the given air temperature, Ta,

and RH is the relative humidity. The saturation pressure can be found from

 

e e

T

T sat

a

= a + 6 11

17 3

237 3 .

.

. . (A6)

The incident solar radiation with a cloud cover, φs, is

φs = φso,c (1 – 0.6C) (A7)

were C is the percent cloud cover. The constant 0.6 is empirically determined and

may be adjusted to make this expression better fit local conditions. However, for

our sites we found that 0.6 gave good agreement with measured solar radiation.

The cloud cover, as reported by the Barre–Montpelier Airport and Lebanon Regional Airport, is reported as falling into one of seven categories shown in Table

A1. For each category we assigned a value for C as shown in Table A1. The exception to this is for missing data; in that case the cloud cover was interpolated from

the data before and after the missing point(s).

The daily solar radiation values were then determined by summing the hourly

estimates from eq A7 and Table A1. These results are plotted in Figures 12 and 15.

This procedure was checked by comparing actual solar radiation measurements

made at the CRREL meteorological test cell in Hanover, with the solar radiation
17

estimates based on the cloud cover reported at the Lebanon Regional Airport, in

West Lebanon, New Hampshire. These two locations are separated by a distance of

about 6 miles. The results of the comparison are shown in Figure A1. In Figure A1

we plot the total daily solar radiation and the accumulated solar radiation. The

accumulated solar radiation is a summation of the daily radiation to date. The accumulated solar radiation is set to zero on the day the leaves were put on the ice.

The discrepancy between the two sites is generally less 25%. The largest discrepancies occur on thickly overcast days where the estimates overpredict the incoming radiation by a factor of 2 to 5. However, looking at the accumulated solar radiation, we found that on average the errors in the estimate seem to cancel each other

out over the long term. As a result we see that both the measured and estimated

values agree very well.

Table A1. Cloud cover categories.

Category Cloud cover, C

Clear 0

Scattered 0.33

Broken 0.67

Overcast 1

Obscured 1

Partially obscured 1

Missing —

Figure A1. Comparison of solar radiation measurements taken at the Hanover

test cell located at CRREL and the estimated solar radiation based on cloud

cover data at Lebanon Regional Airport, Lebanon, New Hampshire.

0

6

4

2

0

1 Mar 6 11 16 21 26 31

Hanover

Test Cell

Lebanon

Airport

Daily Short-wave Radiation

(kWh/m )2

60

40

20

1994

Accumulated Radiation

(kWh/m )2

Hanover

Test Cell

Lebanon

Airport
1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

6. AUTHORS

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

 REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING

 AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

14. SUBJECT TERMS 15. NUMBER OF PAGES

16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

 OF REPORT OF THIS PAGE OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and

maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,

including suggestion for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington,

VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

April 1996

Dusting River Ice with Leaf Mulch to Aid in Ice Deterioration

Robert B. Haehnel, Charles H. Clark, and Susan Taylor

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road

Hanover, N.H. 03755-1290

Special Report 96-7

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

In an effort to find a low cost means of reducing ice jams on small rivers in New England, dusting with organic

matter was field tested during the spring of 1993 and 1994. Test squares on a pond located at CRREL in Hanover,

New Hampshire, were dusted with several materials to evaluate their effectiveness in accelerating snow melting

and ice deterioration. Leaf mulch was included in the materials tested because, unlike other materials used in the

past to weaken ice (e.g., fly ash or coal slag), leaves are naturally found in rivers and should not adversely affect

aquatic organisms when applied in small quantities. It was found from these tests that the leaves perform about the

same as the traditionally used dusting materials. To transfer what was learned at the pond tests to a field application, two rivers in Vermont, with a known history of ice jams, were dusted using leaf mulch during the spring of

1994. Since these sites were located on narrow rivers that wind through highly populated areas, aerial dusting was

not possible. For these sites we used a hydroseeder to spread the leaves on the ice. Application of leaf mulch with

a hydroseeder was found to be an efficient method of putting the leaves on the ice. After the rivers were dusted we

had a heavy snowfall, and were not able to determine the effectiveness of the leaf mulch in melting the ice. Observations suggest, however, that the leaf mulch helped melt the overlying snow. More work is needed to determine

the effectiveness of leaf mulch to weaken ice and how much ice weakening is necessary to reduce the severity of ice

jams.

Office of the Chief of Engineers

Washington, D.C. 20314-1000

24

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

Dusting Leaf mulch

Hydroseeder Snowmelt

Ice weakening

U.S. Army River Confluence

Ice Program

Work Unit: 32972