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Post-Fire Flood Risk in Northern Nevada

2016-2018

Hardscrabble Creek Watershed, Photo Credit: USGS Nevada

Nevada Division of Water Resources

December 2018

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Contents Introduction ................................................................................................................................................... 4

Burn Scar Slope Maps

Reno………………………………………………………………………………………............11

Fernley……………….…….………………………………………………………………..…....12

Pyramid Lake………………..……………………………………………………………………13

Washoe Valley…………………………….……………………………………………………...14

Carson City………………………………….……………………………………………………15

Minden/Gardnerville/Topaz..………………………………………….………………………….16

Lyon County………………….…………………………………………………………………..17

Churchill County………….………………………………………………………………………18

Lovelock……………………………….…………………………………………………………19

Northern Nevada Overview……………………………………………………………….……...20

Winnemucca…………………………………………………….………………………………..21

Battle Mountain………………………………………………………………….……………….22

Elko……………………………………………………….………………………………………23

Eastern Nevada…………………………………………………………………………………...24

Big Smokey Valley……………………………………………………………….………………25

USGS Debris Flow Hazard Maps

Elko County………………………………………………………………………………….…...26

Perry and Broad Fires……………………………………………………………………….……27

USFS Burn Severity Map for Range Two and Echo Fires………………………………………………..28

2016-2018 Wildfire Index ........................................................................................................................... 29

Conclusions ................................................................................................................................................. 36

Resources .................................................................................................................................................... 37

References ................................................................................................................................................... 38

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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 Thomas Fire in southern California

(2018). Understanding why these post-fire floods occur and gaining awareness of at-risk areas in

Nevada will help communities be prepared before disaster strikes. This document describes why

post-fire flooding occurs; maps burn perimeters for fires that occurred in Nevada during the

2016, 2017, and 2018 fire seasons; and links to resources and examples of outreach materials for

communities.

Most of the land burned in Nevada over that past three years is located in the northern

portion of the state. In 2016, 24 fires in Nevada each burned more than 1,000 acres during fire

season, which runs from May through October. Over 265,000 acres burned throughout the state

with a total of 36 wildfires. Much of the western United States was still in a multi-year drought

in 2016.

During the winter of 2016/2017, multiple large winter storm events drastically improved

drought conditions in Nevada. Record precipitation led to runoff that filled reservoirs, caused

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 1,000 acres from 24 to 63. A total of 138 fires burned

approximately 1.3 million acres.

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In 2018, 163 fires burned over 1 million acres. Thirty two fires were greater than 1,000 acres.

The largest of these fires was the Martin Fire, encompassing 432,000 acres across remote rural

Nevada. Burned areas for all three years (2016, 2017, and 2018) are shown in Figure 1.

Figure 1. Overview of Nevada wildfires, 2016-2018

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While wildfire itself is a major concern across Nevada, post-fire hazards also pose a risk to

communities due to the changed conditions of the burned areas. Fire removes the vegetative

cover, roots, and litter that slow runoff and hold soil in place. 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 2). These changes lead to increased runoff and erosion.

Due to the increase in runoff, developed areas down-slope of a burn scar are at an increased

risk for flash flooding (Figure 3). 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

Figure 2. 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

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2010 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 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.

Flooding potential is greatest during the first two years after the fire has occurred (USGS,

2018; NWS, n.d.). Recovery of the landscape depends on the intensity of the fire, ground cover,

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.

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This document includes maps of wildfires that occurred in 2016, 2017, and 2018 near

Nevada communities. Available fire perimeters were downloaded on geomac.gov. Within each

burn scar greater than 100 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. In addition to the burn scar slope maps, this document contains burn

severity maps for a small subset of fires that burned predominantly on land managed by the US

Forest Service. Burn severity was determined based the differences between before-fire and

after-fire satellite images. Lastly, USGS debris flow modeling results were mapped for a subset

of burn scars. Additional debris flow modeling data for burn areas in the western US under

Figure 3. 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

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different precipitation scenarios are available at https://landslides.usgs.gov/hazards/

postfire_debrisflow/. USGS models accounted for a combination of several variables, namely

slope, burned area reflectance, normalized burn ratio, soil erodibility factor, elevation range, and

burn severity. A table with additional data about wildfires greater than 100 acres is included after

the maps.

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 used for analysis in the burn scar slope maps 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).

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Burn Scar Slope Maps

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2016-2018 Wildfire Index (alphabetical, color-coded by year)

Fire Name Year Acres Map (if included) At-Risk Features 4 Mile Ridge 2017 293 Far Northern Nevada Low risk due to flat terrain Anderson 2016 16283 Pyramid

Antelope 2018 2323 x Flows would move toward NV-140, north of Denio Summit

Apple 2018 344 Pyramid Adjacent to I-80, but relatively flat terrain reduces risk of debris flows

Arc 2018 435 Pyramid Flows may impact development in the Tahoe-Reno Industrial Center

Aspen 2017 315 Pyramid Near rural development Barrett Springs 2017 3298 Winnemucca Low risk due to flat terrain Beaver Dam 2017 115 x Black Mountain 2017 966 Pyramid, Fernley Adjacent to NV 447 Black Point 2017 12602 Far Northern Nevada Boone Springs 2018 3073 Eastern Nevada Flows may impact or parallel US 93 Alt Bottom 2017 109 x

Boulder Creek 2018 1029 Battle Mountain, Far Northern Nevada

Bravo17 2017 24179 Churchill Debris flows may impact Navy's target area

Brenda 2017 633 Washoe Valley Near rural development

Broad 2018 525 Smokey Valley Flows would move toward NV 376 and impact rural development near Carvers

Brooks 2018 361 Battle Mountain, Far Northern Nevada Low risk due to flat terrain

Butte 2018 224 Eastern Nevada

Canyon 2017 192 Reno Flows would move toward Lockwood and the Truckee River

Carico 2016 4389 x Chase Spring 2017 560 Eastern Nevada Low risk due to flat terrain

Chaves 2018 3437 Lyon Flows may impact local roads and Carson River

Chimney 2018 1138 Far Northern Nevada Low risk due to flat terrain Chimney 2 2018 184 Reno, Pyramid Chin Creek 2018 356 Eastern Nevada Flows may move toward US 93

Cold Springs 2017 1525 Reno Steep slope facing Red Rock Road; adjacent to NV 395

Cole Creek 2017 5951 Elko, Far Northern Nevada

Debris flows may back up or overflow at culverts under NV 278

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Copper 2018 716 x Cornucopia 2017 1559 Far Northern Nevada Low risk due to flat terrain Corral Creek 2018 154 x

Cortez 2017 1832 Battle Mountain, Far Northern Nevada Low risk due to flat terrain

County Line 2018 12978 Elko, Far Northern Nevada

Flows may impact Pine Creek and Humboldt River, NV 278

Crum 2018 2880 Battle Mountain, Far Northern Nevada

Flows may impact Hill Top Road and move toward rural development

Delano 2017 10829 x Dixie 2018 2522 Elko Low risk due to flat terrain Dolly 2017 293 Far Northern Nevada Draw 2017 27544 Churchill Near US 50 Dry Creek 2018 434 x Flows would move toward US 50 Dry Gulch 2017 54249 x Dry Hill 2017 2000 Far Northern Nevada Low risk due to flat terrain

Dry Hills 2017 435 Battle Mountain, Far Northern Nevada Low risk due to flat terrain

Dry Lake 2017 434 x Dune 2017 9873 Winnemucca Earthstone 2017 40247 Reno, Pyramid Parallel to I-80 and Truckee River Echo 2018 6093 Eastern Nevada Flows may impact US 93

Emigrant 2018 1525 Elko, Far Northern Nevada

Flows would move toward Humboldt River

Fort Churchill 2017 200 Lyon

Only a small portion of the burn scar is on steep terrain. Local roads, Koch ditch, and Carson River may be impacted in the event of a debris flow.

Francis 2018 1276 x

Gance 2018 5363 Elko, Far Northern Nevada Flows would move toward NV 225

Goose Creek 2018 132127 x Flows may impact Crittenden Reservoir and rural roads

Goshute Cave 2018 31861 Eastern Nevada Flows would move toward US 93 Granite Creek 2017 918 Far Northern Nevada Low risk due to flat terrain

Grass Valley 2017 11589 Winnemucca Impacts would be south of the Grass Valley community

Gray 2018 324 Churchill

Green Saddle 2018 182 Winnemucca, Far Northern Nevada Flows may move toward I-80

Gregg 2018 10229 Winnemucca, Far Northern Nevada

Flow would move along Pumpernickel Valley toward I-80 (10+ miles away)

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Halleck 2017 148 Elko Low risk due to flat terrain Happy Creek 2017 513 x Hatchery 2017 1169 x HD 2018 5039 x HD Summit 2017 1386 x Hobson 2017 338 x

Hogan 2018 10900 Eastern Nevada Flows would cross Shafter Road to railroad

Hogue 2018 192 Reno Flows may move down drainages connecting to Keystone Canyon

Hollywood 2017 5299 Fernley Within a few miles of Nixon and NV 447

Horse Canyon 2018 132 x Flows may impact county road at mouth of drainage

Horseshoe 2016 6591 x

Hot Pot 2016 122390 Battle Mountain, Far Northern Nevada

Hot Springs 2017 1222 Far Northern Nevada Low risk due to flat terrain

I-80 2018 134 Reno Burn scar adjacent to I-80 and Truckee River

Ibapah 2017 194 x Iron Point 2017 1318 Far Northern Nevada

Izzenhood 2016 6543 Battle Mountain, Far Northern Nevada Flows may impact Izzenhood Reservoir

Jackpot 2016 1699 Reno Jackpot 2017 118 x

Jacks 2018 162 Battle Mountain, Far Northern Nevada

James Loop 2018 270 Carson City Low risk due to flat terrain Jungo 2018 520 Winnemucca Low risk due to flat terrain King Valley 2017 2046 x

Kiowa 2018 120 Reno, Pyramid Flows would move toward Virginia St and Lemmon Drive, near US 395

Kumiva 2018 3758 x Lahontan 2017 263 x Lancaster 2018 265 Winnemucca Low risk due to flat terrain Leonard Creek 2017 5156 x Limbo 2017 7975 x

Limerick 2017 14600 Lovelock Debris flows would move toward I-80 and may impacts Lovelock-Unionville Road

Little Den 2016 3509 Churchill Flows would drain toward NV 722

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Little Valley 2016 2293 Washoe Valley Flows may impact structures in the Franktown area

Lyons 2017 1626 x

Maggie 2016 9367 Elko, Far Northern Nevada

Mahogany 2017 3720 x Flows may move toward NV 140 Maidens Grave 2017 152 Far Northern Nevada Low risk due to flat terrain

Marigold 2016 294 Battle Mountain, Far Northern Nevada

Martin 2018 432093 Far Northern Nevada

Flows may impact Paradise Valley, Chimney Dam Reservoir and tributary creeks/rivers, Desert Ranch Reservoir, South Fork Owyhee River. Greater impacts likely on western, steeper portion of burn scar.

McClintick 2018 148 x

Midas 2017 328 Battle Mountain, Far Northern Nevada

Mill 2017 4831 Battle Mountain, Far Northern Nevada

Debris flows along the channel would flow to/toward NV 305

Mine 2018 751 Battle Mountain, Far Northern Nevada

Missouri 2017 229 x

MM 155 2017 22376 Winnemucca Steepest slopes direct flow toward Grass Valley, south of most development

Monroe 2016 11227 Winnemucca Nightingale 2017 450 x Nine Mile 2017 310 x

Oil Well 2017 7471 Elko

Overall, the burn scar is low slope. The steepest areas are along drainages that run near or through developed neighborhoods.

Orovada 2017 119 x

Owl Creek 2018 1071 Elko Flows may move toward rural development in Spring Creek

Owyhee 2018 5086 Far Northern Nevada Flows may impact Owyhee, NV 225, agricultural infrastructure

Paine 2018 727 x Flows would move toward county road

Perry 2018 51369 Pyramid

Flows possible in multiple directions, possibly impacting the Truckee River, Nixon, NV 447, NV 446, NV 445, and rural development in Warm Springs Valley

Phoenix 2017 4378 Far Northern Nevada

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Pine 2017 292 Elko, Far Northern Nevada

Flows would drain toward Humboldt River near I-80

Pinto 2016 1911 x Piper 2018 314 x Flow would move toward US 50 Alt Poker Brown 2017 15532 Lovelock Pole Canyon 2018 2106 Elko Low risk due to flat terrain Pole Creek 2017 5037 Elko Poodle 2016 2923 x Potato 2017 823 x Potosi 2017 431 x

Power 2018 1086 Battle Mountain, Far Northern Nevada Low risk due to flat terrain

Prater 2017 2700 Reno, Pyramid Flows would move toward Sparks and I-80, along with the Truckee River

Preacher 2017 14573 Minden-Gardnerville-Topaz

Flows along Pine Nut Creek would move toward rural development

Pyramid 2016 287 Pyramid Quinn 2017 1124 Far Northern Nevada

Range Two 2018 9197 Elko Flows may impact Lamoille Creek, Lamoille, and the community of Spring Creek below Seitz Canyon

Raven 2017 424 x Red Hill 2017 316 x

Red Springs 2017 4680 Elko, Far Northern Nevada

Rifle Range 2018 218 Carson City Flows would impact the Carson River River Ranch 2017 1379 Elko Low risk due to flat terrain

Road 2018 1833 Elko May impact county road adjacent to steeper areas of the burn scar

Rock 2016 2293 Reno Upslope of rural development Rock Hill 2016 1695 Winnemucca Upslope of agriculture Rocky 2018 1617 Lovelock Low risk due to flat terrain Rodeo 2018 232 x

Roosters Comb 2017 204879 Battle Mountain, Far Northern Nevada

Agricultural and mining properties may see impacts

Round Hill 2018 958 Winnemucca Low risk due to flat terrain Rye Patch 2018 378 Lovelock Low risk due to flat terrain

S Fire 2016 2540 Reno, Pyramid Steepest slopes direct flow toward I-80 and the Truckee River; flows may also head toward Sparks

Sage 2016 4238 Pyramid Sampson Creek 2018 188 Eastern Nevada

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Secret 2017 121 Eastern Nevada Low risk due to flat terrain Seven Lakes 2016 3063 Pyramid Upslope of rural development

Sheep Creek 2018 59789 Battle Mountain, Far Northern Nevada

Flows may move toward the railroad, NV 806, and the Humboldt River

Shelton 2017 160 Far Northern Nevada Low risk due to flat terrain

Silver State 2018 3816 Elko, Far Northern Nevada

Flows may impact rural development off of Last Chance Road, Humboldt River, and railroad

Six Mile 2017 185 x Flows would impact Six Mile Canyon Road

Slaven 2017 423 Battle Mountain, Far Northern Nevada

Slinkard 2017 8923 Minden-Gardnerville-Topaz

Flows would impact US 395 and possibly structures the Topaz Lake development. Debris flow occurred May 21, 2018, affecting Hwy 395.

Snowstorm 2017 158135 Far Northern Nevada

South Sugarloaf 2018 233608 Far Northern Nevada

Flows may impact NV 225, Wild Horse Reservoir, Dry Creek Reservoir, Bull Run Reservoir, Sheep Creek Reservoir, Mountain City, and local roads

Spanish 2017 207 Winnemucca Upslope of agriculture Spring 2018 237 x

Stag 2018 4358 Elko May impact county road adjacent to steeper areas of the burn scar

Stewart 2017 158 Far Northern Nevada Low risk due to flat terrain Strawberry 2016 4603 x Flows would move toward US 50 Summer 2017 1246 x Summit 2018 128 x Sweeney 2018 394 x

Tabor Flats 2017 24896 Elko Near Mary's River but low risk due to flat terrain

Tamara 2017 151 x

Tank 2017 829 Battle Mountain, Far Northern Nevada Adjacent to railroad

Telegraph 2018 295 x Flows would move toward NV 305 Tolicha Peak 2017 2162 x Toulon 2017 2268 x

Transfer 2017 1000 Battle Mountain, Far Northern Nevada Low risk due to flat terrain

Trinity 2017 8896 Lovelock

Truckee 2017 98954 Fernley Burn scar adjacent to lower Truckee River and I-80 east of Fernley

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Tucker 2018 359 Far Northern Nevada Adjacent to Bruneau River Tule 2016 36142 Pyramid Drains to Pyramid Lake and Sutcliffe Twin Buttes 2017 562 x Two Dens 2017 574 Churchill Flows would move toward NV 722

Upper Colony 2018 1202 Douglas Flows would impact Upper Colony Road, Colony Ditch, and nearby development

Varden 2017 280 Eastern Nevada Low risk due to flat terrain

Voltaire 2018 517 Carson City Flows would move toward development near Curry St.

Voltaire Canyon 2017 134 Carson City Flows would move toward Carson St,

between Moses St and Clearview Dr. Wally 2016 1761 x West Duck 2018 11192 Far Northern Nevada Low risk due to flat terrain White Horse 2017 2625 Eastern Nevada Flows would drain toward US 93 Alt Willow 2018 317 Winnemucca

Willow 2018 1086 x Flows may impact Charleston Reservoir, Bruneau River, and Charleston-Jarbidge Road

Winnemucca Ranch 2017 4797 Reno, Pyramid Flows may impact NV 445 and

surrounding rural development

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Conclusions

The impacts of natural disasters, including wildfires and floods, can be difficult to predict.

The data provided in this document offer only a limited analysis of areas at risk of post-fire

flooding. The more rigorous USGS modeling results for certain large fires can be explored

online 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. As recently as May 21, 2018, these

factors came together and caused a debris flow within the Slinkard Fire burn scar to move across

Highway 395 at Topaz, closing the road for approximately 18 hours.

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 for

residents 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 at www.weather.gov.

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• 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.

RESOURCES

Expectations After Fire

FEMA Flood After Fire Risk Fact Sheet: http://www.floods.org/ace-images/FloodAfterFire_FactSheet.pdf

National Weather Service Burn Scar Information: https://www.weather.gov/riw/burn_scar_flooding

New Mexico After Wildfire Flood Information: http://afterwildfirenm.org/flood-information

New Mexico Post Fire Expectations Document: https://www.env.nm.gov/documents/What_to_Expect_Following_Storm_Events.pdf

Tools for Communities

FEMA Flood Outreach Toolkit: https://www.fema.gov/media-library/resources-documents/collections/12

Other FEMA Flood After Fire Materials: https://www.fema.gov/media-library/assets/documents/93830

Oregon Silver Jackets Post-Wildfire Flood Playbook: https://silverjackets.nfrmp.us/Portals/0/doc/Oregon/PostFireFloodPlaybook_2018-09-30.pdf?ver=2018-10-04-203119-453

Colorado Post-Wildfire Mudslide Brochure: http://coloradogeologicalsurvey.org/geologic-hazards/fires/

USGS Post-Fire Debris Flow Hazard: https://landslides.usgs.gov/hazards/postfire_debrisflow/

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 Floodplain Mapping: https://msc.fema.gov

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For more information, contact:

Nicole Goehring Floodplain Mapping Coordinator, Nevada Division of Water Resources ngoehring@water.nv.gov

REFERENCES 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.

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. 2018. https://ca.water.usgs.gov/wildfires/wildfires-debris-flow.html (accessed April 3, 2018).

and Planning Partners.