Post-Fire Flood Risk in Northern Nevada - Nevada Division of Water Resources September 2018 - Nevada Floods
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Post-Fire Flood Risk in
Northern Nevada
Hardscrabble Creek Watershed, Photo Credit: USGS Nevada
Nevada Division of Water Resources
September 2018
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Table of Contents
Introduction…………………………………………………………………………………….…1
Fire Descriptions and Maps
Reno…….………………………………………………………………………………....7
Fernley…………….………………………………………………………………..……..9
Pyramid Lake……….……………………………………………………………………11
Washoe Valley…………………………………………………………………………...13
Minden/Gardnerville/Topaz..…………………………………………………………….15
Churchill County…………………………………………………………………………17
Lovelock…………………………………………………………………………………19
Winnemucca……………………………………………………………………………..21
Battle Mountain………………………………………………………………………….23
Elko………………………………………………………………………………………25
Conclusions………………………………………………………………………………………27
References………………………………………………………………………………………..29
Resources………………...………………………………………………………………………30
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Introduction
In the western United States, where the terrain is often defined by steep slopes along large
and numerous mountain ranges, wildfires threaten and damage communities every year. Not only
is fire itself a natural disaster, but the changes in the landscape caused by the fire increase the
risk of flooding during a post-fire precipitation event. Recent post-fire floods that resulted in loss
of life and property include floods that occurred after the Schultz Fire in Arizona (2010) and
Thomas Fire in California (2018). Understanding why these post-fire floods occur and gaining
awareness of at-risk areas in Nevada will help residents be prepared before disaster strikes. This
document describes why post-fire flooding occurs, and maps burn perimeters for fires that
occurred in Nevada during the 2016 and 2017 fire seasons.
In 2016, 24 fires in Nevada each burned more than 1,000 acres during fire season, which runs
from May through October (Figure 1a). Over 265,000 acres burned throughout the state. Much
of the western United States was still in a multi-year drought in 2016. Conditions across much of
western Nevada were classified as severe (Figure 2).
During the winter of 2016/2017, multiple large winter storm events improved drought
conditions in Nevada. Record precipitation led to runoff that filled reservoirs, caused widespread
flooding, and sustained elevated water levels in major waterways for extended periods of time.
Wet conditions led to a large grass fuel load in northern and central Nevada. When dry, these
grasses become easily ignitable fine fuels. Compared to 2016, 2017 was characterized by an
increase in the number of fires greater than 1000 acres from 24 to 63 (Figure 1b). Acres burned
totaled approximately 1.3 million.
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(a) (b)
Figure 1. a) Distribution of 2016 fire season wildfires greater than 1000 acres in Nevada. b) Distribution 2017 fire season wildfires greater than
1000 acres in Nevada.
2
Figure 2. Drought status across Nevada in 2016 according to the US Drought Monitor.
While wildfire is a major concern across Nevada, post-fire hazards also pose a risk to
communities due to the changed conditions of the burned areas. On a typical landscape, rainfall
is captured and retained by the soil. Vegetation slows runoff and holds soil in place. Fire
removes vegetative cover, roots, and litter. Additionally, a water-repellent layer of soil may form
below the surface during high-intensity burns, reducing water infiltration and retention (NWS,
n.d.; Figure 3). These changes lead to increased runoff and erosion.
3
Figure 3. Fire affects soil/water relationships. Water repellent layers may form under high intensity
burns, leading to increased runoff. Saturated conditions near the soil surface can cause mud and debris
flows. Credit: National Weather Service
Due to the increase in runoff, developed areas down-slope of a burn scar are at an increased
risk for flash flooding (Figure 4). After a fire, areas not historically prone to flooding may
become at-risk areas for several years. It is important to note that flooding is not confined to the
mapped FEMA flood zone boundaries used for flood insurance purposes, especially because
fires change landscape characteristics that define flow and infiltration patterns. Flooding after the
Schultz Fire in Arizona affected subdivisions 10 miles away from the burn scar, in areas that had
not previously experienced flooding (Klassen, 2011). Burned, barren mountainous areas are
especially prone to flash-flooding since water flows quickly down steep slopes and water levels
rise quickly in channels with limited adjacent floodplains. Water and debris moving quickly off
4
of the landscape creates concern for not only flash flooding, but also debris flows or mud flows.
These flows consist of a mix of moving water and loose debris and sediment. Typically, debris
flows occur on hillsides with slopes of 15 degrees (27%) or greater (Loverich et al., 2017). Flash
flooding can occur when at least half an inch of rain occurs in less than an hour (NWS, n.d.),
depending on factors including slope and burn severity.
Figure 4. Post-fire, flood risk below a burned area may increase during rain events due to the limited
absorption abilities of the soil. Steep landscape slope and high rainfall intensity also increase the risk.
Credit: FEMA
Flooding potential is greatest during the first two years after the fire has occurred (USGS,
2018a; NWS, n.d.). Recovery of the landscape depends on the intensity of the fire, ground cover,
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land use, and weather following the fire event (Pierson et al., 2015). In general, the longer a fire
burns, the more intense the burn scar and the longer it takes for the land to recover.
This report focuses on large wildfires that occurred during the 2016 and 2017 fire seasons
near communities and/or major highways. Fire perimeters were downloaded based on
availability on geomac.gov. Within each burn scar greater than 300 acres, slope was calculated
using a 30 m digital elevation model. HUC 10 watershed boundaries were also included in the
maps to help indicated the direction of runoff from precipitation events.
Examining the location, extent, and topography of burn areas with relation to Nevada’s
communities and infrastructure can help us anticipate where damage may occur during a
precipitation event over a recently burned area. The maps on the following pages can be used to
help make informed decisions concerning flood safety and preparedness before storm events in
upcoming years. Note that the variables included in this document were limited, and that
additional factors such as burn severity, change in vegetative cover, or soil characteristics should
be considered when assessing the level of flood risk. In the Great Basin, rainfall intensity and
bare ground are key factors for predicting runoff and erosion responses (Pierson et al., 2015).
6
Greater Reno Area
The Reno/Sparks area has seen a number of large fires within the last two years. 2016
had only one fire over 1,500 acres, the S Fire, and much of the same area burned again in 2017 in
the Prater Fire. Both fires burned right above the east side of Sparks, putting the community
below at risk of flooding. Earthstone was a much larger fire that burned between Sparks and
Fernley in 2017 alongside I-80. Runoff will flow down the hillside toward the interstate and
Truckee River.
In 2017, along Highway 395 north of Reno, the Cold Springs Fire burned the hills that
separate the communities of Red Rock and Cold Springs. Runoff and debris will move toward
Whites Lake, Silver Lake, and the highway. Located north of Sparks, the Winnemucca Ranch
was a larger fire in a less densely populated area. Its western extent bordered Highway 445,
which connects travelers from Sparks to Pyramid Lake.
Fire Name Date Started Date Contained Acres Burned
S Fire 7/06/2016 7/07/2016 2,540
Jackpot 8/6/2016 8/8/2016 1700
Earthstone 7/03/2017 7/09/2017 41,545
Winnemucca Ranch 7/04/2017 7/09/2017 4,799
Cold Springs 7/14/2017 7/15/2017 1,523
Prater 8/06/2017 8/07/2017 2,816
Aspen 7/08/2017 7/14/2017 315
Table 1. Dates and sizes of 2016 and 2017 wildfires in the Reno/Sparks area.
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Fernley Area
Three large fires burned near Fernley in 2017. West of the town, the Earthstone Fire
burned from Sparks nearly 18 miles toward Fernley. Its southeastern extent closely paralleled the
path of the Truckee River, which is also parallel to I-80, the major connection between the two
cities. Runoff, sediment, and debris from this fire will flow directly toward the lower Truckee
River, upstream of the community of Wadsworth.
Northeast of Fernley and Wadsworth, the Truckee and Hollywood Fires together burned
over 100,000 acres. The smaller Black Mountain fire also burned along the lower Truckee River.
Storm runoff from these burn scars would flow toward the Truckee River to the west, and I-80 to
the southeast. Water and debris may accumulate in the flood-prone flats below the burned area.
Runoff, debris flows, or mud flows may encroach onto the highway.
Table 2. Dates and sizes of 2016 and 2017 wildfires in the Fernley area.
Fire Name Date Started Date Contained Acres Burned
Earthstone 7/03/2017 7/09/2017 41,545
Hollywood 6/19/2017 6/21/2017 5,298
Truckee 7/03/2017 7/09/2017 98,960
Black Mountain 7/26/2017 7/27/2017 961
910
Pyramid Lake Area
The area west of Pyramid Lake had a cluster of lightning-started fires, known as the
Virginia Mountains Complex, in 2016. The Sage and Anderson fires burned watersheds that
drain away from the lake. Closest to the lake, the Tule Fire burned 36,000 acres parallel to NV-
445 along Pyramid Lake. The community of Sutcliffe is located below the burned area, creating
flash flood and debris flow concerns for residents. In fact, the US Geological Survey installed
gages in the Hardscrabble Creek drainage to allow for early detection of flash flooding (USGS,
2018b). During the January 2017 floods, multiple parts of NV-446 washed out, closing the road
between Sutcliffe and Nixon for over a month.
Table 3. Dates and sizes of 2016 and 2017 wildfires in the Pyramid Lake area.
Fire Name Date Started Date Contained Acres Burned
Sage 7/28/2016 7/31/2016 4,239
Anderson 7/29/2016 8/5/2016 16,283
Tule 7/28/2016 8/5/2016 36,142
Seven Lakes 7/28/2016 7/31/2016 3,063
Rock 7/28/2016 7/31/2016 2,293
1112
Washoe Valley Area
The Little Valley Fire grew from a prescribed fire, destroying 23 homes and 17
outbuildings (Corona, 2016). The fire was put out with the help of a storm which was intense
enough for the National Weather Service to issue a flash flood warning. Crews are in the process
of replanting trees and grasses within the burn scar to help accelerate landscape recovery
(Margiott, 2018). Runoff from the slopes will drain toward Washoe Lake.
Table 4. Dates and sizes of 2016 and 2017 wildfires in the Washoe Valley area.
Fire Name Date Started Date Contained Acres Burned
Little Valley 10/14/2016 10/19/2016 2,293
Brenda 7/14/2017 7/14/2017 632
1314
Minden/Gardnerville/Topaz
Two fires burned in Douglas County in 2017. The Preacher Fire burn scar is relatively
low-slope but increased runoff may still affect rural properties. Most of the acreage burned in the
Slinkard Fire was located in California, but the burn area covers steep land that drains into
Nevada and has potential to impact Highway 395. In fact, on May 21, 2018, a brief event of
heavy rainfall over the Slinkard fire scar triggered mud flows near the Topaz Lodge at Lake
Topaz, blocking the highway.
Table 5. Dates and sizes of 2016 and 2017 wildfires in Douglas County area.
Fire Name Date Started Date Contained Acres Burned
Preacher 7/24/2017 7/30/2017 5,333
Slinkard 8/29/2017 9/09/2017 8,925
1516
Churchill County
Fires in 2016 and 2017 affected remote areas of Churchill County near Highway 50. The
Draw Fire burned closest to Highway 50, but gentle slopes near the road will minimize the risk
of mud or debris flows crossing the highway. Increased runoff and flooding are still possible at
and downslope of the burn scars.
Table 6. Dates and sizes of 2016 and 2017 wildfires in Churchill County.
Fire Name Date Started Date Contained Acres Burned
Little Den 7/20/2016 7/24/2017 3,512
Draw 7/07/2017 7/15/2017 27,506
Bravo 17 7/12/2017 7/27/2017 23,387
Two Dens 8/22/2017 8/25/2017 574
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Lovelock Area
Three 2017 fires burned north of Lovelock. None of the burn scars are immediately
adjacent to I-80 or the Humboldt River (including Rye Patch Reservoir), but increased amounts
of runoff may reach the Humboldt River, especially from the steeper slopes of the Limerick burn
scar.
Table 7. Dates and sizes of 2016 and 2017 wildfires near Lovelock.
Fire Name Date Started Date Contained Acres Burned
Poker Brown 6/19/2017 6/21/2017 15,540
Trinity 6/20/2017 6/22/2017 8,895
Limerick 7/3/2017 7/11/2017 14,592
1920
Winnemucca Area
The Winnemucca area had several large fires in 2016 and 2017. The Rock Hill and
Monroe fires burned adjacent to each other in an undeveloped area. In 2017, the Grass Valley
and MM 155 Fires occurred south of town in areas with minimal development. MM 155
overlapped with the edges of the 2016 fires. Runoff from several of these burn scars will flow
toward I-80 and the adjacent Humboldt River, but the steep portions of the burn scars are
approximately 10 or more miles away in sparsely populated areas. The Barrett Springs Fire
occurred in a relatively flat area west of Winnemucca, where increases in runoff could impact the
river downstream of the city.
Table 8. Dates and sizes of 2016 and 2017 wildfires in the Winnemucca area.
Fire Name Date Started Date Contained Acres Burned
Monroe 8/16/2016 8/19/2016 11,220
Rock Hill 8/20/2016 8/24/2016 1,738
Barrett Springs 7/08/2017 7/10/2017 3,319
MM 155 7/14/2017 7/23/2017 22,360
Grass Valley 7/17/2017 7/22/2017 11,590
Dune 8/08/2017 8/09/2017 9,873
21Dates and sizes of 2016 and 2017 wildfires in the Battle Mountain area.
22Battle Mountain Area
The Battle Mountain area has had very large fire events in each of the last two years. In
2016, the Hot Pot Fire burned over 120,000 acres, and then in 2017 the Roosters Comb Fire
burned over 200,000 acres. The Roosters Comb Fire overlapped with the smaller perimeter of the
2016 Izzenhood Fire. The distance of these fires from the town reduces the risk of property
damage or injury due to flash flooding or mudslides.
Table 9. Dates and sizes of 2016 and 2017 wildfires in the Battle Mountain area.
Fire Name Date Started Date Contained Acres Burned
Hot Pot 7/02/2016 7/08/2016 122,390
Izzenhood 8/18/2016 8/21/2016 6,543
Midas 6/21/2017 6/22/2017 327
Roosters Comb 7/09/2017 7/25/2017 204,879
2324
Elko Area
The 2017 Oil Well Fire east of Elko burned 7,500 acres, destroying 14 homes and
multiple vehicles (Harris, 2017). This fire crossed I-80 and its eastern extent burned alongside
the Humboldt River. The burn scar is relatively flat. Similarly, the three fires that burned further
east occurred on low-slope terrain. Increased runoff from the burn scars may impact flows in the
Humboldt River through Elko.
Table 10. Dates and sizes of 2016 and 2017 wildfires in the Elko area.
Fire Name Date Started Date Contained Acres Burned
River Ranch 7/8/2017 7/09/2017 1,380
Tabor Flats 7/8/2017 7/15/2017 25,100
Oil Well 7/17/2017 7/20/2017 7,500
Pole Creek 7/30/2017 8/02/2017 6,540
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Conclusions
Despite being an arid state, Nevada is prone to flooding. Flooding is caused by several
different factors including fire. A few trends can be noted from the burn scar slope maps in this
document:
• Reno, Fernley, Pyramid Lake, and Topaz-area burn scars cover steep slopes adjacent to
both major highways and waterways/waterbodies. I-80 parallels portions of the Truckee
and Humboldt Rivers. Highway 395 at Topaz is adjacent to Topaz Lake. Floods, debris
flows, or mudslides could cause major safety and accessibility issues on roadways.
Additionally, water quality could temporarily decline due to the influx of sediment and
debris (USGS, 2018c).
• Fires in the Battle Mountain and Elko areas encompassed large areas with low slopes.
The flatter areas present a smaller flash-flooding risk. However, the lack of ground cover
and hydrophobic soils still contribute to increased runoff.
• Runoff from several burn scars will drain into the Truckee or Humboldt Rivers within
several miles upstream of major communities. As a result, flows through these
downstream towns may quickly increase in response to precipitation events over those
burn scars.
The impacts of natural disasters, including wildfires and floods, can be difficult to
predict. The data provided in this document offer only a basic analysis of areas at risk of post-fire
flooding. Other environmental factors must be included in a more rigorous analysis of flood or
debris flow hazard. For some large fires, USGS conducts more rigorous hazard assessments,
27which can be found at https://landslides.usgs.gov/hazards/postfire_debrisflow/. Regardless of the
information available on a burn scar, readers should be aware that flood risk increases with steep
slopes, decreased vegetative cover, and increased rain intensity.
Post-fire flash flooding is a serious risk to all communities that have been affected by
fires. The National Weather Service (n.d.) advises that if you can look upslope and see a burned
area, you are at risk. As communities continue to grow, development will expand the wildfire-
urban interface. With the resulting increased exposure to natural hazards, it is important to
continue examining maps and historic data so that we are able to better gage the risk of flooding
and prepare properly in order to protect human life and property as much as possible. Steps to
prepare for possible post-fire flooding include the following:
• Gather emergency supplies.
• Purchase flood insurance. The Standard Flood Insurance Policy includes coverage
for mudflows. Mudflows are defined as a river of liquid and flowing mud on the
surfaces of normally dry land areas, as when earth is carried by a current of water.
• Plan evacuation routes; stay informed before and during any potential events; and
be ready to evacuate if heavy rain occurs.
o Know how to access National Weather Service outlooks, watches, and
warnings.
• Keep important papers in a safe, waterproof place and conduct a home inventory.
Additional resources to use before, during, or after wildfire are listed at the end of this document.
28References
Corona, Marcella. Prescribed burn blamed fror Liittle Valley Fire. October 26, 2016.
http://www.rgj.com/story/news/2016/10/26/little-valley-fire-sparked-prescribed-burn/92799826/
(accessed January 11, 2018).
Harris, Jeremy. KUTV. July 17, 2017. http://kutv.com/news/local/14-homes-lost-to-oil-well-fire-
near-elko-i-80-opened (accessed January 11, 2018).
Klassen, Keith. The Schultz Fire & Subsequent Flooding. 2011.
http://www.firerescuemagazine.com/articles/print/volume-6/issue-1/features-0/the-schultz-fire-
subsequent-flooding.html (accessed April 2, 2018).
Loverich, Joseph B., Ann M. Youberg, Michael J., Kellogg, and Jon E. Fuller. Post-Wildfire
Debris-Flow & Flooding Assessment: Coconino County, Arizona. 2017. 63 pages.
Margiott, Ben. NDF crews start planting trees & grasses on Little Valley Fire burn scar .
January 5, 2018. http://mynews4.com/news/local/ndf-crews-start-planting-trees-grasses-on-little-
valley-fire-burn-scar (accessed January 10, 218).
National Weather Service (NWS). Flash Flood Threat Within Fire Burn Scar. n.d.
https://www.weather.gov/riw/burn_scar_flooding (accessed October 20, 2017).
Pierson, Frederick B., C. Jason Williams, and Peter R. Robichaud. "Assessing Impacts of Fire
and Post-fire Mitigation on Runoff and Erosion from Rangelands." Great Basin Factsheet Series,
2015: 1-6.
U.S. Geological Survey (USGS). Post-Fire Flooding and Debris Flow. 2018a.
https://ca.water.usgs.gov/wildfires/wildfires-debris-flow.html (accessed April 3, 2018).
U.S. Geological Survey (USGS). USGS 10351950 HARDSCRABBLE CK BLW TH RANCH
AT SUTCLIFFE, NV. 2018b. https://waterdata.usgs.gov/nv/nwis/uv?site_no=10351950
(accessed May 1, 2018).
U.S. Geological Survey (USGS). Water Quality after a Wildfire. 2018c.
https://ca.water.usgs.gov/wildfires/wildfires-water-quality.html (accessed April 2, 2018).
29RESOUCRES
Expectations After Fire
FEMA Flood After Fire Risk Fact Sheet: http://www.floods.org/ace-
images/FloodAfterFire_FactSheet.pdf
https://www.env.nm.gov/documents/What_to_Expect_Following_Storm_Events.pdf
National Weather Service Burn Scar Information
https://www.weather.gov/riw/burn_scar_flooding
Colorado Post-Wildfire Mudslide Brochure: http://coloradogeologicalsurvey.org/geologic-
hazards/fires/
New Mexico After Wildfire Flood Information: http://afterwildfirenm.org/flood-information
Additional Flooding Information
Flooding in Nevada: http://nevadafloods.org/
General Flooding Information: http://www.floodtools.com
National Flood Insurance Program: https://www.floodsmart.gov/
FEMA Mapping: https://msc.fema.gov
For more information contact:
Nicole Goehring
Floodplain Mapping Coordinator, Nevada Division of Water Resources
ngoehring@water.nv.gov
Parks, and Carol Miller. "Weather, fuelsm and topography impede wildalnd fire spread in western US
landscapes ." Forest Ecology and Management , 2016: 59-69.
Mapping,and Planning Partners.
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