Hydrology
Carlton Complex – Southwest Quadrant, Carlton Fire
September 2014
Katherine Foster, Cherokee NF - kfoster01@fs.fed.us
Edward Huffmann, Umpqua NF - elhuffman@fs.fed.us
Ben Stratton, GMUG NFs - bstratton@fs.fed.us
Mike Natharius, Gila NF – mkatharium@fs.fed.us
Note: this report is limited to the National Forest System lands in the southwest portion
of the Carlton Fire.
Summary
The southwest portion of the Carlton Fire is in two watersheds – the Lower Methow River, and
Swamp Creek/Columbia River. The primary watershed responses of the Carlton Fire area are
expected to include 1) an initial flush of ash; 2) rill and gully erosion in drainages and on steep
slopes within the burned area; 3) flash floods with increased peak flows and sediment
deposition; 4) debris flows. The watershed responses are dependent on the occurrence of
storm and melt events and should be greatest with initial storm events. The disturbances will
become less evident as vegetation is reestablished, providing ground cover and increasing
surface roughness.
The primary hydrologic mechanisms of damage are flooding, debris flows, and debris jams.
After a field reconnaissance, the BAER team identified the Gold Creek, McFarland Creek, Squaw
Creek, and Black Canyon subwatersheds of particular concern. The Soil Burn Severity map and
modeling coupled with field observations were used to assess the level of threat and risk to the
values at risk in and adjacent to the burned area, and to develop treatment recommendations.
The percentage of the watershed burned was used to indicate the post-fire hydrologic
response. Seventeen percent of the Gold Creek subwatershed and 5% of the South Fork of
Gold Creek is burned. Thirty-three percent of the McFarland subwatershed, 49% of the Squaw
Creek subwatershed, and 41% of the Black Canyon subwatershed is burned. Modeled post-fire
runoff indicates an increase of at least one order of magnitude for all the subwatersheds of
concern. The model does not assess the probability of debris flows. Several debris flows have
emanated from adjacent portions of the Carlton Fire; similar and larger flows are expected from
the burned area addressed in this report. The USGS has completed an assessment of post-fire
debris flow hazards for the Chiwaukum Fire; the interactive map to locate information for this
fire is available at http://landslides.usgs.gov/hazards/postfire_debrisflow.
I. Potential Values at Risk (identified prior to the on-the-ground survey)
Life and safety
National Forest System and private roads
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Campground and associated infrastructure
Private residences and associated infrastructure including access roads
State Highway 153 and County roads
Privately operated fish hatchery (Squaw Creek)
II. Resource Condition Assessment
A. Resource Setting
The watersheds of the Wenatchee and Okanogan National Forest represent a combination of
folded metamorphic and sedimentary geologic landforms, modified by alpine glaciation
processes in the upper basins. Hillslopes are dominated by steep continuous slopes (45-85%)
with shallow soil mantled over bedrock. The landforms are highly dissected by first order
drainages (>4 miles/sq.mi.), with steep channel gradients (25-45%). Headwater stream
channels and swales are filled with colluvium (bedrock hollows). The combination of colluvium
filled bedrock hollows and bedrock formations increase the risk of localized shallow rapid mass
wasting.
The terrain is steep and rocky. The tributary stream channels are steep and culminate in alluvial
fans in the valley of the Methow River.
There are State, County, private, and National Forest System roads in the burned area.
Average annual precipitation ranges from 15 inches along the lower portions of the watersheds
to 65 inches towards the headwaters. Summer thunderstorms are typically localized and of
short duration and high intensity. Fall and winter storms are typically Pacific maritime frontal
storms dominated by rain from mid-October through mid-November. Fall rain storms are
typically low intensity and long-duration. Snowfall accumulation begins in higher elevations from
mid to late November with snowfall accumulations continuing through April. Rain-on-snow
events are common, typically occurring from November through January, and range in their
magnitude of hydrologic responses.
The streams have a flashy hydrologic response due to shallow depth to bedrock and steep
headwater slopes. They have naturally high fine and coarse sediment load and channel
responses alternate between floodplain aggradation and channel incision. There is a history of
debris flows following fires in the watershed.
B. Findings of the On-The-Ground Survey
Resource condition resulting from the fire
The Carlton Fire started on July 14, 2014 and was not contained as of September 4, 2014. The
fire is in the Lower Methow and Swamp Creek/Columbia River watersheds. The subwatersheds
affected by the fire are:
Acres
Total
Percent of
Burned in
Watershed
Subwatershed
HUC12
Watershed
Watershed
SW Carlton
Acres
Burned
Fire
Lower
Alta Coulee –
20030
4252
21%
170200080709
Methow
Methow River
2
Total
Watershed
Acres
Acres
Burned in
SW Carlton
Fire
Percent of
Watershed
Burned
Watershed
Subwatershed
HUC12
River
Black Canyon
Creek
170200080708
15871
6476
41%
Gold Creek
170200080704
38934
6743
17%
Libby Creek
170200080701
25850
898
3%
170200080706
25302
8256
33%
170200080703
17935
976
5%
Squaw Creek
170200080707
10167
5007
49%
Texas Creek –
Methow River
170200080702
20436
1876
9%
Antoine Creek
170200050506
21132
218
1%
Lake Pateros –
Columbia River
170200050505
24999
192
1%
McFarland Creek
– Methow River
South Fork Gold
Creek
Swamp
Creek –
Columbia
River
The affected streams in the southwest portion of the burned area include Libby, Gold,
McFarland, Squaw, and Black Canyon Creeks.
Based on knowledge of the effects of other wildfires in the area, the anticipated increases in
streamflow and the potential for debris flows causes concern for public safety, private
structures and property, and Forest Service property and infrastructure. After a field
reconnaissance, the BAER team identified the Gold Creek, McFarland Creek, Squaw Creek, and
Black Canyon subwatersheds of particular concern. The BAER team noted good revegetation in
part of the adjacent 2012 Goat Fire.
A Burned Area Reflectance Classification (BARC) map of the burned area was prepared by the
Remote Sensing Applications Center (RSAC). The BAER Team adjusted the preliminary BARC
map based on field observations and analysis. Based on the resulting Soil Burn Severity map,
7% of the fire area is burned at high severity, 21% at moderate, 61% at low, and 10% is
burned at very low severity or is unburned.
Consequences of the fire
The primary watershed responses of the Carlton Fire area are expected to include: 1) an initial
flush of ash; 2) sheet, rill and gully erosion in drainages and on steep slopes within the burned
area; 3) floods with increased peak flows and sediment deposition; 4) debris flows. The
watershed responses are dependent on the occurrence of storm and melt events and should be
greatest with initial storm events. The disturbances will become less evident as vegetation is
reestablished, providing ground cover and increasing surface roughness.
A rainfall-runoff hydrograph model, the Soil Conservation Service Runoff Curve Number (SCSCN) method, was used to determine pre-fire and post-fire runoff. The WILDCAT5 software
package was used to run the SCS-CN. This program is designed to assist watershed specialists
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in analyzing rainfall-runoff events to predict peak flow and runoff volumes generated by single
event rainstorm for a variety of watershed soils and vegetation conditions, including postwildfire conditions.
The design storm used for modeling represents a statistically historic convective thunderstorm
producing a one hour high intensity rainfall event. The design storm of 25 years has a 4%
chance of occurring in any given year and about an 11% chance of happening during the first 3
years following the fire. The amount of precipitation for the 25 year, 1 hour duration storm is
0.77 inches. But instantaneous short duration (15 min.) intensities during the design storm can
range between 0.3 and 3.2 inches/hour.
In developing information for modeling, the BAER team summarized the Soil Burn Severity
information to identify the percent of the catchments that burned at moderate and high
severity. This combination of severities is used to indicate the hydrologic response for the
catchments modeled because it is these severity ranges that produce the majority of the postfire runoff. The catchments modeled range in size and were delineated to represent the area
affecting the values at risk. See Appendix A for a map of the soil burn severity and catchments.
Table 1 – WILDCAT5 model predictions
The WILDCAT5 model showed a post-fire increase in peak flows and runoff in every catchment
modeled, see Figure 1. In Figure 1, Q Pre is the pre-fire streamflow modeled for the design
storm using the WILDCAT5 model; Stream Stats Pre Q100 is the 100 year flood flow estimated
using USGS regression equations; Q Post is the post-fire streamflow modeled for the design
storm using WILDCAT5; and Bulked is the estimated post-fire flow with debris and sediment.
Although Stream Stats Pre Q100 was calculated using a different model, it is included in Figure
1 as a comparison of the magnitude and/or significance of the post-fire changes. In other
words, the 100 year event is a significant hydrologic event; therefore, a post-fire event of that
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scale or larger would be of concern. Modeling methods, parameterization, and assumptions
have been summarized in a separate document if further details are needed (Appendix B).
The model does not assess the probability of debris flows.
The primary hydrologic mechanisms of damage are flooding, debris flows, and debris jams.
Figure 1 – Results of Hydrologic Modeling For The Burned Area
Consequences of the fire on values at risk and emergency determination
The assessment of values at risk is based on direction in FSM 2520.
The values at risk in Gold Creek include the Foggy Dew Campground, private residences and
infrastructure, and National Forest, State, County, and private roads.
The values at risk in McFarland and Squaw Creeks and Black Canyon include private residences
and infrastructure, and National Forest, State, County, and private roads.
Life and safety may be affected by events emanating from all these subwatersheds.
The following risk matrix (Table 2) is from FSM 2520, Interim Directive 2520-2013-1 and is the
basis for the determination of risk in Table 3. Risk is evaluated in the matrix as a function of
the probability and consequences of event-caused damage or loss.
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Table 2 - Risk Matrix from FSM2520
Probability
of Damage
or Loss
Magnitude of Consequences
Major
Very Likely
Very High
Very High
Low
Likely
Very High
High
Low
Possible
High
Intermediate
Low
Unlikely
Intermediate
Low
Very Low
Moderate
Minor
RISK
.
In Table 3, emergency treatment is an activity such as road work needed to mitigate a threat;
emergency action is an administrative action such as a closure needed to prevent exposure to a
threat.
Table 3 – Evaluation Of Values At Risk From Flooding and Debris Flows
Values at risk
Human life and safety on National Forest System (NFS)
roads.
All roads in the burned area may be affected in some way –
ravel; rock fall or trees blocking the roadway; culverts
blocked and overtopped with and without embankment
failure; debris flows depositing on the roadway or removing
portions of the road prism. Egress from National Forest
System and private lands could be lost.
Human life and safety in Foggy Dew Campground.
A portion of the campground could be affected by flooding
and/or debris flows from tributaries of Gold Creek.
Human life and safety at private homes in and adjacent to
the burned area.
Modeled post-fire watershed response indicates an order of
magnitude increase in storm runoff and associated debris.
Those residences adjacent to stream channels have an
increased risk due to the fire.
Damage to infrastructure for Foggy Dew Campground.
The BAER team evaluated infrastructure location relative to
severity and concluded there was little threat due to the fire.
Damage to private property in and adjacent to the burned
area.
Modeled post-fire watershed response indicates an order of
magnitude increase in storm runoff and associated debris.
Those residences adjacent stream channels have an
increased risk due to the fire. Ad hoc water diversions were
noted by the BAER team in several areas; these could be
affected.
Risk and emergency
Probability of damage or loss = possible
Magnitude of consequence = major
Risk = high
Emergency treatment needed = yes
Probability of damage or loss = possible
Magnitude of consequence = major
Risk = high
Emergency treatment needed = no
Emergency actions needed = yes
Probability of damage or loss = very
likely
Magnitude of consequence = major
Risk = very high
Emergency treatment needed = no
Emergency actions needed = yes
Probability of damage or loss = unlikely
Magnitude of consequence = moderate
to minor
Risk = low
Emergency treatment needed = no
Probability of damage or loss = very
likely
Magnitude of consequence = major
Risk = very high
Emergency treatment needed = no
Emergency actions needed = yes
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Values at risk
Damage to National Forest System roads
All roads in the burned area may be affected in some way –
ravel; rock fall or trees blocking the roadway; culverts
blocked and overtopped with and without embankment
failure; debris flows depositing on the roadway or removing
portions of the road prism.
Damage to Highway 153.
Highway 153 generally parallels the burned area from north
to south. Modeled post-fire watershed response indicates an
order of magnitude increase in storm runoff and associated
debris in many of the catchments adjacent to the highway.
Risk and emergency
Probability of damage or loss = very
likely
Magnitude of consequence = moderate
to major
Risk = very high
Emergency treatment needed = yes
Probability of damage or loss = very
likely
Magnitude of consequence = moderate
to major
Risk = high to very high
Emergency treatment needed = no
Emergency action needed = yes
III. Recommended Actions or Treatments to Mitigate the Emergency
Emergency action to close a portion of the Foggy Dew Campground for a minimum of
three years.
The BAER team recommends the closure of one site to over-night occupancy. In addition to
the physical closing of the site, a Supervisor’s closure order may be necessary.
Emergency action to provide information to cooperating agencies and adjacent
landowners.
The BAER team recommends the installation of an alert station to provide information about
storm events that could affect Highway 153.
Soil burn severity and other relevant information should be given to cooperating agencies for
any additional action. Affected landowners should be briefed about increased risk by
cooperating agencies or the Forest.
Road treatments as prescribed by the Engineers.
IV. References
http://streamstats.usgs.gov/. USGS Stream Stats application.
Hawkins, Richard H.; Barreto-Munoz, Armando. Wildcat5 for Windows, A Rainfall-Runoff Hydrograph
Model. September 30, 2011.
VI. Appendices
Appendix A-Burn Severity Map
Appendix B-Modeling Methods Report
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