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Erosion Management (Hillcrest Site):
FuMe Full Analysis Report
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WEPP FuME
Fuel
Management
Erosion Analysis Results
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Climate
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COLFAX CA
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Soil texture
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clay loam
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Hillslope length
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1000
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ft
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Hillslope gradient
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0 30 40
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%
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Buffer length
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250
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ft
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Wildfire cycle
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20
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y
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Prescribed fire cycle
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5
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y
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Thinning cycle
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10
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y
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Road density
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4
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mi mi-2
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Running Disturbed WEPP for
Undisturbed forest ...
Thinned forest ...
Prescribed burn ...
Wildfire ...
Lower thinning ...
Higher Rx fire ...
Lower Rx fire ...
Moderate wildfire ...
Low wildfire ...
Running WEPP:Road for
No traffic ...
Low traffic ...
High traffic ...
Output summary based on 50 years of possible weather
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Line
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Source of sediment
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Sediment delivery in year of disturbance
(ton mi-2)
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Return period of disturbance
(y)
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"Average" annual hillslope sedimentation
(ton mi-2 y-1)
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1
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Undisturbed forest
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1
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2809.6
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2
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Wildfire
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82880
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20
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4144.0
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3
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Prescribed fire
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12160
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5
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2432.0
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4
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Thinning
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3244.8
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10
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324.5
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5
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Low access roads
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77.3 to 150.9
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1
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77.3 to 150.9
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6
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High access roads
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132.4 to 150.9
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1
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132.4 to 150.9
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Summary of Analysis
The output summary table presents the predicted sediment yield rates from seven runs with the WEPP model.
The outputs from those runs were converted to common units of ton mi-2 y-1.
From these runs, several key watershed sedimentation values can be estimated.
Background sedimentation.
The background sedimentation rate -- the rate that will occur with no action --
can be estimated either with or without roads.
In the absence of roads, the background sedimentation rate is erosion from undisturbed forest
plus erosion from wildfire.
This value is the sum of lines 1 and 2, or
2809.6 + 4144.0 = 6953.6
ton mi-2 y-1.
If the existing low access road network is included in the background sediment rate,
then the background rate will be the sum of lines 1, 2, and 5, or
6953.6 + (77.3 to 150.9) = 7030.9 to 7104.5
ton mi-2 y-1,
depending on what percent of the road network crosses live water during major runoff events.
Thinning effects.
From the summary table, line 4, thinning will generate
3244.8
tons of sediment the year following thinning, and when averaged over the thinning period of once in
10
years, will average about
324.5
ton mi-2 y-1.
This is
an increase of about
5
percent above background without roads.
In order to carry out the thinning operation, however, traffic on the roads will have to be increased to the
high access level to support the traffic associated with an ongoing thinning operation in the watershed.
The total sediment yield from the watershed will then be the background value plus that from thinning and from
high access roads for a total of
6953.6 +
324.5 +
(132.4 to
150.9) =
7410.5 to
7429
ton mi-2 y-1.
This is an increase of
7 to
7
percent above the background rate, if roads are not considered in the background, or
5
to
5
percent if the road network is considered in the background rate.
Further comparisons can be made by assuming that thinning will eliminate wildfire from the watershed,
thus reducing the wildfire sedimentation value,
or that thinning will lead to a less severe wildfire,
and the moderate or low severity fire sedimentation rate from
the table below can be substituted for the wildfire erosion rate in line 2.
Prescribed fire effects.
From the summary table, line 3, prescribed fire will generate
12160
ton mi-2 the year of the prescribed fire, or when averaged over the prescribed fire return period of
5
y, it will generate
2432.0
ton mi-2 y-1.
This is
an increase of
35
percent above background.
As there will be no need for heavy traffic to carry out the prescribed burn,
there is no increase in sedimentation from the road network.
For a watershed with an active prescribed fire program, the total erosion will then be the background rate
plus the low access road rate and the average erosion from prescribed fire, or
6953.6 +
2432.0 +
(77.3 to
150.9) =
9462.9 to
9536.5
tons mi-2 y-1, or
an increase of
36 to 37
percent above background, if roads are not included in the background value.
If the prescribed fire eliminates the risk of wildfire, the background erosion rate will need to be set to
2809.6
(line 1 of the outputs summary) for the analysis.
Alternatively, the impact of the prescribed fire program may be to reduce the intensity of the wildfire,
in which case, the sedimentation associated with
a moderate or low severity fire from the following table can be substituted for the wildfire prediction
for the analysis.
Combined thinning and prescribed fire effects.
The combined effects of thinning and prescribed fire can be determined by summing up the background rate,
the thinning rate, the prescribed fire rate, and the high access road rate.
In this case, this leads to a total predicted erosion rate of
6953.6 +
324.5 +
2432.0 +
(132.4 to
150.9) =
9842.5 to
9861
ton mi-2 y-1,
an increase of
42 to
42
percent
above
the background erosion rate without roads.
If this intensive fuel management scenario can reduce the severity of wildfire in the watershed,
then the moderate severity fire sedimentation value of
38528
ton mi-2 can be substituted for the wildfire erosion rate once every
20
years to give an average value of
1926.40
ton mi-2 y-1.
Using this value to determine the total impact of fuel management gives
1926.40 +
3134.1 +
2432.0 +
(132.4 to
150.9) =
7624.9 to 7643.4
ton mi-2 y-1,
a decrease of
-8
to
-8
percent compared to background with roads or
-10
to
-10
percent compared to background without roads.
Road Impacts.
The range of values given for road sedimentation represent the amount of sediment delivered across the buffer,
and the amount delivered to a stream crossing.
Roads with buffers greater than
250 ft will generate less sediment.
The summary table shows that roads generate significant amounts of sediment within a watershed, even when traffic is low.
Road management strategies -- including
minimizing rutting,
minimizing stream crossings, and
maximizing the use of buffers between the road and the stream
-- are well established to minimize sedimentation.
The WEPP:Road interface can be used to evaluate the impacts of some of these improved practices.
Another alternative to reduce sedimentation from the road network is to reduce the road density
within the watershed by removing roads that are no longer needed with modern timber operations.
Watershed managers may wish to offset the increase in sediment associated with fuel management
with a decrease in sediment from improved road management or a reduction in road density.
Multiple Hillslopes.
This analysis was for a single hillslope.
Users are advised to run this simulation for a number of different hillslopes within the watershed,
and to report a range of sedimentation rates in the output table before completing the analysis.
Results from each hillslope can be copied and pasted into a word processor or spreadsheet
to serve as a log for a series of runs.
For further information, refer to the documentation.
Details of Inputs and Outputs
Refer to the documentation for details on the applications for the five
additional runs listed in this table, but not used in the initial
analyses.
Inputs (blue) and results (green) for individual Disturbed WEPP runs
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Disturbed WEPP
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| Upper element treatment |
Lower element treatment |
Upper cover
(%) |
Lower cover
(%) |
Upper length
(ft) |
Lower length
(ft) |
Upper rock
(%) |
Lower rock
(%) |
Upper top gradient
(%) |
Upper mid gradient
(%) |
Lower mid gradient
(%) |
Lower toe gradient
(%) |
Sediment yield
(t mi-2) |
Condition |
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20 year old trees
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20 year old trees
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100
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100
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750
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250
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20
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20
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0
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30
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30
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40
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2809.6
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Undisturbed forest
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5 year old trees
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20 year old trees
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85
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100
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750
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250
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20
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20
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0
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30
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30
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40
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3244.8
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Thinned forest
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low severity fire
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20 year old trees
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85
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100
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750
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250
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20
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20
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0
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30
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30
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40
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12160
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Prescribed burn
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high severity fire
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high severity fire
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30
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40
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750
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250
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20
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20
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0
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30
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30
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40
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82880
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Wildfire
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5 year old trees
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20 year old trees
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95
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100
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750
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250
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20
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20
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0
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30
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30
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40
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2771.2
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Lower thinning
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low severity fire
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low severity fire
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75
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85
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750
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250
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20
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20
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0
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30
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30
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40
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21440
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Higher Rx fire
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low severity fire
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20 year old trees
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90
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100
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750
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250
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20
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20
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0
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30
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30
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40
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10924.8
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Lower Rx fire
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low severity fire
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low severity fire
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50
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60
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750
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250
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20
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20
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0
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30
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30
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40
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38528
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Moderate wildfire
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low severity fire
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low severity fire
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70
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80
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750
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250
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20
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20
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0
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30
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30
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40
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23782.4
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Low wildfire
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Inputs (blue) and results (green) for individual WEPP:Road runs
WEPP Comments
WEPP FuME v.
2005.11.02
(for review only) Interface by David Hall and Elena Velasquez
Model by Bill Elliot and Pete Robichaud
USDA Forest Service, Rocky Mountain Research Station, Moscow, ID 83843
09:50 am Tuesday March 28, 2006 Pacific Time
278 WEPP FuME runs since release, December 2004
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