Appendix G Noise Analysis with the SPreAD-GIS Modela123.g.akamai.net/7/123/11558/abc123/forestservic.download.akamai... · Appendix G Noise Analysis with the SPreAD-GIS ... potential

South Fowl Lake Snowmobile Access Project

Final Environmental Impact Statement G-1 Appendix G

Appendix G

Noise Analysis with the SPreAD-GIS Model

An alternative analysis, using the SPreaAD-GIS model for the area and sound levels affecting the

wilderness area near South Fowl and McFarland Lakes, was conducted to corroborate the analysis

provided in the Final Environmental Impact Statement (FEIS). The SPreAD-GIS model is

designed to assess impacts of motorized noise on receptors in outdoor and remote settings. The

results of the SPreAD-GIS model are used to either validate or to modify the analysis in section

3.2 of the FEIS.

The SPreAD-GIS model was developed by Sarah E. Reed, Ph.D., Jennifer Boggs and Jacob P.

Mann and was sponsored by The Wilderness Society. It is based on the research report

“Predicting Impact of Noise on Recreationists” by Harrison, Clark and Stankey (1980). SPreAD

is referred to in the Harrison et al. paper as „System for the Prediction of Acoustic Detectability‟.

This report describes methods to predict the impact of noise on recreationists while accounting

for effects to noise propagation from spherical spreading, atmospheric absorption, vegetation and

ground cover, weather (wind, temperature, relative humidity and cloud cover), topography, and

the ambient soundscape. The SPreAD-GIS model essentially completes calculations used in the

Harrison, Clark and Stankey report in a Geographic Information Systems (GIS) program

environment. The Harrison, Clark and Stankey report cautions that the model output is not the

final answer in evaluating noise impacts since there are limitations in the model (or any model),

and effects need to be interpreted according to the context of the situation, recreationist

expectations, and resource manager knowledge. These factors are addressed in the analysis in

section 3.2 of the EIS (e.g. the Affected Environment section, and the discussion for effects to

wilderness character).

For a full description of the SPreAD-GIS model and instructions on running the model, the

instructions (and the model itself) are available on the internet at

http://warnercnr.colostate.edu/~sereed/research/SPreAD-GIS.html and are in the project file.

SPreAD-GIS Model Parameters

The SPreAD-GIS model requires several parameters to be input with data (see Table G-1). These

were prepared according to the SPreAD-GIS instructions.

http://warnercnr.colostate.edu/~sereed/research/SPreAD-GIS.html



Table G-1: SPreAD-GIS Input Parameters

Parameter Data Source

Topography A topography layer was prepared from a

Digital Elevation Model covering the Superior

National Forest.

Landcover For the landcover/vegetation layer, a National

Land Cover Dataset was used and reclassified

according to the landcover classes listed in the

SPreAD-GIS instructions.

Sound Source (snowmobile along existing and

proposed routes)

The data input for the sound source came from

measurements taken with an ExTech HD 600

for the snowmobile sound levels in A-weighted

decibels, however the spectra levels were

drawn from the SPreAD-GIS User‟s Guide

Table 1 based on the corresponding spectra

levels for the sound level in A-weighted

decibels.

Ambient Soundscape Sound monitoring conducted with the ExTech

HD 600, along with validation from a Larson-

Davis 831 sound pressure measurement device

was used (see below). In addition, figures from

Table 1 of the SPreAD-GIS User‟s Guide were

used to simulate the lowest expected values.

Weather Data from the RAWS weather station located

near Seagull Lake, MN (the closest weather

station) was used to generate average

temperature, relative humidity, wind speed, and

wind direction for the winter months.

Larson Davis Data Collection

A Larson Davis 831 sound pressure meter was used to collect data for ambient sound levels over

a five day period in early March, 2011 at the edge of Royal Lake in the BWCAW. The device

was calibrated before use and advice from the U.S. Park Service Soundscapes program was

followed on setting up the meter and collecting data. Information on the setup, calibration and

data collection methods is in the project file. The data is summarized below in Table G-2 and

represents continuous 24 hour data collection over multiple days. The median dBA over a 24 hour

period, during the day, and during the night are displayed. The sound level recorded varies

according to wind and other natural sounds, and human generated sounds, that are present at a

given time. While these values represent a median value, sound levels may be lower at calm

moments, or higher due to factors such as high wind speeds. These values are considered to

represent natural ambient sound levels because the data was recorded after the close of the winter

fishing season, but before snowmelt. Sampling of the data did not indicate snowmobile sounds

were a substantial contributor to the sound levels. The minimum sound level event recorded

during the data collection period is also displayed in Table G-2. The full data output is more

extensive and is in the project file.



Table G-2: Larson Davis 831 Ambient Sound Level Results

2011 Royal Lake/South Fowl Lake Sound Monitoring March 2011

Daily sound pressure levels (LAeq) Decibels A weighted Larson Davis 831 meter

Royal Lake / South Fowl 3-Mar 4-Mar 5-Mar 6-Mar 7-Mar

Total Median dBA

Overall 24 hr data 43.4 32.5 29.3 33.8 23.9 32.6

Day 0700 - 2300 43.8 34.0 28.3 35.5 28.6 34.0

Night 2300 - 0700 16.6 25.4 30.7 18.8 19.8 22.3

LAFminimum 16.1 16.2 16.1 16.1 16.2 16.1

Wind speed average (mph) 4.8 5.3 4.2 2.5 4 4.2 mph avg

Precipitation 0.00 0.00 0.02 0.02 0.01 0.05" total

Minimum Temperature ( F) 2 15 -10 -6 10 Min Temp -10

Maximum Temperature ( F) 22 26 25 25 25 Max Temp 26

Mean Temperature( F) 15.2 20.2 10.6 13.9 10 Avg Temp 14.0

Weather data from Seagull Minnesota weather station

Note: Sound recording for 3-Mar and 7-Mar were <24 hours

Model Runs

Initially several simple model runs were completed for one third octave levels that may be

evaluated in the SPreAD-GIS model (ranging from 125 to 2000 Hz) to determine which input

values had the greatest impact (carried snowmobile sound the farthest). It was shown that using

the one third octave levels for 500Hz carried snowmobile sound the greatest distance and would

show the greatest impacts from snowmobile use. Therefore pressure levels at 500Hz were used

for each of the final model runs.

Results from model runs are displayed for sound levels at 500Hz whereas the sound levels

displayed from the analysis in section 3.2 of the EIS are A-weighted. The 500 Hz sound level

would not be experienced in the same way by a person as the same A-weighted sound level.

However, the SPreAD-GIS model runs would still display the greatest impact since 500 Hz

carried the greatest distance, and the field measurements used in Section 3.2 estimate the greatest

distance of impact that would occur. These two results can thus be compared in this manner.

The topography, landcover and sound source data was the same for all model runs. Landcover in

the vicinity of Royal Lake is a mixture of hardwoods and conifer. Our initial simple runs

demonstrated greater impacts from snowmobile sound when using “hardwoods” as the forest

cover type; therefore we selected that for all final model runs. Since our model runs were

completed for winter conditions where lakes and non-forest areas would be frozen and snow

covered, we typed all open areas as “barren ground” for final model runs.



The natural ambient soundscape and weather vary by model run since these variables may change

over time, changing the sound propagation and impacts to receptors. This allows for simulating

different environmental conditions (e.g. calm wind conditions) that were not present during the

field measurements described in Appendix C.

Several model runs were completed to estimate potential noise volume (i.e. sound level) and area

created by existing and alternative routes. The input parameters used, and noise contour maps are

displayed for the model run with the greatest impact. Results from other model runs can be found

in the project file. A comparison of the analysis in Section 3.2 of the EIS with the SPreAD-GIS

analysis is useful because the SPreAD-GIS model accounts for more factors that may affect noise

propagation than the analysis in section 3.2 of the EIS does.

The parameters used for each model run are shown in Table G-3. Maps showing the model run

results are displayed in Figures G1 through G12. The SPreAD-GIS model may be run to display

„baseline noise propagation‟1, which evaluates noise propagation from snowmobiles as affected

by all environmental variables (e.g. topography, vegetation, landcover, weather, and factors such

as atmospheric absorption) except the ambient soundscape. The SPreAD-GIS model may also be

run to display „excess noise propagation‟2 which takes into account of all the environmental

variables accounted for by the baseline noise propagation model, and also accounts for the

ambient soundscape. The excess noise propagation analysis displays less noise impacts than the

baseline propagation analysis since the ambient soundscape reduces the ability of a person to hear

an introduced sound. Both the baseline noise propagation and excess noise propagation model

runs are displayed in Figures G1 through G12. The model runs for Alternative 2 include an area

map, and a closeup of the wilderness near the route showing excess noise propagation.

The contour lines on the maps represent 3 decibel increments which decrease with increasing

distance from the snowmobile route. Beyond the final contour, there is no impact estimated by the

model. The contour lines generated from the SPreAD-GIS model that appear as black lines are

those representing the greatest distance the model estimates that sound from snowmobiles would

be propagated. Contour lines generated from the SPreAD-GIS model that appear as red are those

where snowmobile sound is estimated to be at levels that would be heard and more likely to

impact the visitor. The area impacted by red lines (excess noise propagation) estimated by the

SPreAD-GIS model are compared to the area estimated by the EIS to be above natural ambient.

1 The SPreAD-GIS model describes the baseline noise propagation model run as “the predicted pattern of

noise propagation around the source, accounting for attenuation due to spherical spreading loss,

atmospheric absorption, foliage and ground cover loss, upwind and downwind loss, and terrain effects.”

(SPreAD-GIS Users Guide V 2.0, p. 16)

2 The SPreAD-GIS model describes the excess noise propagation model run as “calculates the difference

between introduced noise and background sound levels. The excess noise calculation can be used to

identify areas where introduced noise is likely to be audible, or where it may impact species of concern.”

(SPreAD-GIS Users Guide V 2.0, p. 16)



Table G-3: Parameters used for SPreAD Model Runs.

Model Run

1 2 3 4 5 6

Frequency

(Hz)

Evaluated 500Hz 500Hz 500Hz 500Hz 500Hz 500Hz

Ambient Soundscape Decibels

Hardwood

Forest dB 17 23 23 23 23 23

Barren

Ground dB 17 23 23 23 23 23

Water dB 17 23 23 23 23 23

Run

Parameters

No Action

/Alt 3 and

4; Calm

No Action

/Alt 3 and 4;

6 mph

S wind

No Action

/Alt 3 and 4;

6 mph

W wind

Alt. 2

6 mph

W wind

Alt. 2

6 mph

W wind

Alt. 2

6 mph

W wind

Machine

dB at

500Hz at

50 feet

64 64 64 64 64 64

Temperatur

e 32 32 13 32 13 1

Wind

Speed 0 6 6 6 6 6

Wind

Direction 90 360 114 114 114 114

Relative

Humidity 67 67 67 67 67 67

Seasonal

Conditions

Clear,

Winter,

Snow,

Calm

Clear,

Winter,

Snow,

Windy

Clear,

Winter,

Snow,

Windy

Clear,

Winter,

Snow,

Windy

Clear,

Winter,

Snow,

Windy

Clear,

Winter,

Snow,

Windy

Vegetation

Layer

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

Elevation

Layer

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Extent

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area



Table G-3: Parameters used for SPreAD Model Runs (continued).

Model Run

7 8 9 10 11 12 13

Frequency

(Hz)

Evaluated

500Hz 500Hz 500Hz 500Hz 500Hz 500Hz 500Hz

Ambient Soundscape Decibels

Hardwood

Forest dB 23 23 23 17 17 17 36

Barren

Ground

dB

23 23 23 17 17 17 36

Water dB 23 23 23 17 17 17 36

Run

Parameter

s

Alt. 2

6 mph

S wind

Alt. 2

6 mph

S wind

Alt. 2

6 mph

S wind

Alt. 2

Calm

Alt. 2

Calm

Alt. 2

Calm

Alt. 2

11mph

S wind

Machine

dB at

500Hz at

50 feet

64 64 64 64 64 64 64

Temperatu

re 32 13 1 32 13 1 32

Wind

Speed 6 6 6 0 0 0 11

Wind

Direction 360 360 360 90 90 90 360

Relative

Humidity 67 67 67 67 67 67 67

Seasonal

Condition

s

Clear,

Winter,

Snow,

Windy

Clear,

Winter,

Snow,

Windy

Clear,

Winter,

Snow,

Windy

Clear,

Winter,

Snow,

Calm

Clear,

Winter,

Snow,

Calm

Clear,

Winter,

Snow,

Calm

Clear,

Winter,

Snow,

Windy

Vegetatio

n Layer

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

National

Landcover

Dataset

National

Landco

ver

Dataset

Elevation

Layer

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevation

Model

Digital

Elevatio

n Model

Extent

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS Noise

Analysis

Area

EIS

Noise

Analysi

s Area



Results:

Model Run #1

This run simulates the sound conditions under No Action and those under Alternative 3 and 4

relative to impacts to the BWCAW. This run would not provide information on impacts to

homeowners on McFarland Lake or the area where those alternatives would be routed south of

McFarland Lake.

The simulation is made under calm conditions with low natural ambient sound levels (20-25

dBA) as may be encountered in the hours between 11:00 PM and 7:00 AM (although

snowmobiles are unlikely to operate much at night). As may be seen in Figure G-1, baseline (PR)

and excess sound propagation (EX) predicted from the model are similar to those estimated in the

EIS Figure 3-7. The EIS (Appendix D and Section 3.2) predicted that 763 acres of wilderness are

currently impacted by sound above natural ambient (see Table 3-2) while the SPreAD-GIS model

predicts 962 acres are above ambient for calm conditions.

Model Run #2

Similar to Model Run #1, this run simulates the sound conditions under No Action and those

under Alternative 3 and 4 relative to impacts to the BWCAW. However this simulation uses

average daily wind speeds and natural ambient sound levels, with the wind coming from the south

(average wind speeds are taken from 10 year data from winter months, see Appendix C). Again

results presented in the EIS show an impact of 763 acres are currently impacted by sound above

natural ambient whereas SPreAD-GIS results for this run estimate 665 acres of wilderness are

impacted for southerly winds.

Model Run #3

Similar to Model Run #1, this run simulates the sound conditions under No Action and those

under Alternative 3 and 4 relative to impacts to the BWCAW. However this simulation uses

average daily wind speeds and natural ambient sound levels, with the wind coming from the west,

which the weather data demonstrates are most common (wind directions for a 10 year winter

average are shown in the “wind rose” in Appendix C). Seven year data from Seagull Weather

station shows an average winter wind direction of 246o (which is input as 114

o for model runs).

This would be the most often occurring weather conditions for the South Fowl Lake area. The

EIS (Appendix D and Section 3.2) predicted that 763 acres of wilderness are currently impacted

by sound above natural ambient (see Table 3-2) while the SPreAD-GIS model predicts 511 acres

are above ambient for average wind conditions.

Model Run #4

This model run displays results for Alternative 2 under the average conditions for wind speed and

direction. Temperatures were set at the higher level of 32o. Results indicated an area affected

by excess noise of 5 acres which represents an increase of 0.7% over existing conditions. The

distance along Alt. 2 where excess noise is projected into the BWCAW is 1330 feet.

Model Run #5




direction. Temperatures were set at the average of 13o. Results indicated an area affected by

excess noise of 4 acres which represents an increase of 0.5% over existing conditions. The

distance along Alt. 2 where excess noise is projected into the BWCAW is 1188 feet.

Model Run #6


direction. Temperatures were set at the average low of 1o. Results indicated an area affected by

excess noise of 3 acres which represents an increase of 0.4% over existing conditions. The

distance along Alt. 2 where excess noise is projected into the BWCAW above natural ambient is

1188 feet.

Model Run #7

This model run displays results for Alternative 2 under the average conditions for wind speed but

with a southerly direction (i.e. wind blowing from the south to the north). Temperatures were

set at the higher level of 32o. Results indicated an area affected by excess noise of 26 acres, which

represents a 4% increase over the existing condition. The distance along Alt. 2 where excess

noise is projected into the BWCAW is 1775 feet.

Model Run #8


with a southerly direction. Temperatures were set at the average of 13o. Results indicated an

area affected by excess noise of 25 acres which represents an increase of 4% over existing

conditions. The distance along Alt. 2 where excess noise is projected into the BWCAW is 1560

feet.

Model Run #9


with a southerly direction. Temperatures were set at the average low of 1o. Results indicated an

area affected by sound above natural ambient of 23 acres which represents an increase of 3% over

existing conditions. The distance along Alt. 2 where sound is projected into the BWCAW above

natural ambient is 1560 feet.

Model Run #10

This model run displays results for Alternative 2 under calm conditions. Temperatures were set

at 32o. Results indicated an area affected by excess noise of 3 acres which represents an increase

of 0.4% over existing conditions. The distance along Alt. 2 where excess noise is projected into

the BWCAW is 1043 feet.

Model Run #11


at the average of 13o. Results indicated an area affected by excess noise of 3 acres which

represents an increase of 0.4% over existing conditions. The distance along Alt. 2 where excess




Model Run #12


at the average low of 1o. Results indicated an area affected by excess noise of 3 acres which

represents an increase of 0.4% over existing conditions. The distance along Alt. 2 where excess


Model Run #13

This run was completed to assess the effects of higher southerly winds (11mph). Temperatures

were set at 32o. Results indicate very little excess noise enters the wilderness. Area of impact

with excess noise was less than one acre.

Evaluation and Conclusion

In general, the models3 predicted similar or less impacts than those displayed in the EIS. The

model runs for no action and Alternatives 3 and 4 (runs 1, 2, 3) display areas of baseline

propagation would suggest there is no audible sound around Royal Lake. However we know that

our listeners could hear snowmobile sound coming from both Little John and South Fowl Lakes.

This indicates the model is underestimating the impacts displayed in the EIS at Section 3.2.

However, the excess noise predicted by the model is similar to that predicted in the EIS Section

3.2. Excess noise under calm conditions is the greatest but that only occurs about 7.7% of the

daytime hours in the winter (see Windrose, Appendix C-6). Considering No Action and

Alternatives 3 and 4, SPreAD-GIS predicts that 962 acres of wilderness would be affected by

excess noise compared to the EIS predictions of 763 acres. However technicians measuring

sound for the EIS Section 3.2 estimates were unable to find calm conditions within which to

make their measurements, therefore it may not be unusual for SPreAD-GIS to estimate louder

impacts for the current condition.

For the most common condition with winds from the west (Runs 4, 5, 6) SPreAD-GIS estimated

lower impacts from snowmobile sound than did the EIS at Section 3.2. Winds from the most

common direction, westerly, result in 5 acres of impact above natural ambient (excess noise) at

the greatest level. Therefore, for 38% of the time (the percentage of time winds are from the

west), the impacts would be less than represented in the EIS at Section 3.2.

Comparing model runs (7, 8, 9) with winds from the south at 6 mph and an area of impact above

natural ambient of 26 acres (a 4% increase of excess noise above the existing condition) to the

DEIS estimate of 36 acres (a 5% increase of excess noise above the existing condition), the EIS

represents the greater impacts of sound projected into the BWCAW. Southerly winds as this

model run represents occur on a ten year average of 22% of the time, therefore these worst case

results would occur 22% of the time.

SPreAD-GIS model runs for calm conditions (runs 10, 11, 12) predict very minimal impacts of

sound above natural ambient. There seems to be some inconsistency between the runs for

3 We also completed a test run with the CADNA Sound Model (a commercial application) for Alternative 2

as shown in Figure G-13. Again, sound impact areas were within what was predicted in Appendix D.



Alternative 2 and runs made for Model Run #1, the current condition (which includes No Action

and Alternatives 3 and 4). Model Run #1 estimated higher excess noise impacts into the

wilderness than did Model Runs 2 and 3 which had wind. However Alternative 2 runs for calm

conditions predicted less impact than those with wind. Since calm conditions only occur for 7.7%

of the daytime hours in winter, this irregularity was not considered significant.

Model Run 13 (figure not shown) used the data the same as Run # 7 with the exception of wind

speed was input at 11 mph and the results demonstrate that the sound of the wind overpowers the

sound coming from the snowmobile and the area of impact of sound above ambient is less than

one acre. No further runs with higher wind speeds were considered necessary.

Over all, with the exception of calm conditions for No Action and Alternatives 3 and 4, the EIS in

Section 3.2 and Appendix D predicted a greater level of impact to the wilderness, therefore the

analysis of impacts based on those predictions should represent the worst case scenario.

Further, the length of Alternative 2 trail used to calculate the duration of sound level above

ambient was 2000 feet in the DEIS whereas SPreAD-GIS predicted the maximum length where

Alternative 2 would impact the wilderness would be 1775 feet. Therefore the EIS analysis for

duration in Section 3.2 and Appendix D represents the worst case scenario.

Summary of Impacts

Table G-4 displays the acres of excess noise impact inside the BWCAW for Alternative 2, and the

distance of Alternative 2 where snowmobiles traveling would propagate noise into the BWCAW.

The largest impact occurs under Model Run #7 (26 acres). Alternatives 1, 3 and 4 are not

displayed because these alternatives would not add excess noise to the BWCAW as analyzed by

SPreAD-GIS above the existing condition.

Table G-4: Summary of Impacts to BWCAW estimated by SPreAD-GIS from Alternative 2 route for different environmental conditions.

Model Run # Acres of Excess Noise Impact inside BWCAW

Distance in feet of Trail Impacting BWCAW with

Excess Noise Impact

1 (Alt 1, 3, 4) 0 0

2 (Alt 1, 3, 4) 0 0

3 (Alt 1, 3, 4) 0 0

4 (Alt 2) 5.3 1330

5 (Alt 2) 3.6 1188

6 (Alt 2) 2.7 1188

7 (Alt 2) 26.1 1775

8 (Alt 2) 24.7 1560

9 (Alt 2) 23.2 1560

10 (Alt 2) 2.7 1043

11 (Alt 2) 2.7 1043

12 (Alt 2) 2.7 1043



Figure G-1: Model Run #1. Sound Impacts Predicted by SPreAD-GIS for Alternatives 1, 3 and 4 under calm wind conditions



Figure G-2: Model Run #2. Sound Impacts Predicted by SPreAD-GIS for Alternatives 1, 3 and 4 under southerly wind conditions.



Figure G-3: Model Run #3. Sound Impacts Predicted by SPreAD-GIS for Alternatives 1, 3 and 4 under average wind conditions.



Figure G-4a: Model Run #4. Alternative 2 Route Noise Impacts Predicted by SPreAD GIS Model, average wind speed and direction, 32 degrees F.



Figure G-4b: Model Run #4. Alternative 2 Route Noise Impacts Predicted by SPreAD GIS Model, average wind speed and direction, 32 degrees F.



Figure G-5a: Model Run #5. Alternative 2 Route Noise Impacts Predicted by SPreAD

GIS Model, average wind speed and direction, 13 degrees F.







GIS Model, average wind speed and direction, 1 degrees F.







GIS Model, average wind speed, southerly winds, 32 degrees F.



Figure G-7b. Model Run #7. Alternative 2 Route Noise Impacts Predicted by SPreAD








Figure G-8b: Model Run #8. Alternative 2 Route Noise Impacts Predicted by SPreAD GIS Model, average wind speed, southerly winds, 13 degrees F.







Figure G-9b: Model Run #9. Alternative 2 Route Noise Impacts Predicted by SPreAD





GIS Model, calm winds, 32 degrees F.




GIS Model, calm winds, 32 degrees F.




GIS Model, calm wind winds, 13 degrees F.















Figure G-13: Test run of CADNA Sound Model for Alternative 2 and Existing Sound

Sources near the BWCAW.

Documents

Appendix G Noise Analysis with the SPreAD-GIS Modela123.g.akamai.net/7/123/11558/abc123/forestservic.download.akamai... · Appendix G Noise Analysis with the SPreAD-GIS ... potential