Post-Fire Flood Risk in Northern Nevada

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1 Post-Fire Flood Risk in Northern Nevada Hardscrabble Creek Watershed, Photo Credit: USGS Nevada Nevada Division of Water Resources September

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3 Table of Contents Introduction. 1 Fire Descriptions and Maps Reno....7 Fernley 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

4 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 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. 1

5 (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

6 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

7 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.

8 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, 5

9 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

10 Greater Reno Area The Reno/Sparks area has seen a number of large fires within the last two years 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/ Earthstone 7/03/2017 7/09/ ,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/ Table 1. Dates and sizes of 2016 and 2017 wildfires in the Reno/Sparks area. 7

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12 Fernley Area Three large fires burned near Fernley in 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/ ,545 Hollywood 6/19/2017 6/21/2017 5,298 Truckee 7/03/2017 7/09/ ,960 Black Mountain 7/26/2017 7/27/

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14 Pyramid Lake Area The area west of Pyramid Lake had a cluster of lightning-started fires, known as the Virginia Mountains Complex, in 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/ ,283 Tule 7/28/2016 8/5/ ,142 Seven Lakes 7/28/2016 7/31/2016 3,063 Rock 7/28/2016 7/31/2016 2,293 11

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16 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/ /19/2016 2,293 Brenda 7/14/2017 7/14/

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18 Minden/Gardnerville/Topaz Two fires burned in Douglas County in 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 15

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20 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/ ,506 Bravo 17 7/12/2017 7/27/ ,387 Two Dens 8/22/2017 8/25/

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22 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/ ,540 Trinity 6/20/2017 6/22/2017 8,895 Limerick 7/3/2017 7/11/ ,592 19

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24 Winnemucca Area The Winnemucca area had several large fires in 2016 and 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/ ,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/ ,360 Grass Valley 7/17/2017 7/22/ ,590 Dune 8/08/2017 8/09/2017 9,873 21

25 Dates and sizes of 2016 and 2017 wildfires in the Battle Mountain area. 22

26 Battle 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/ ,390 Izzenhood 8/18/2016 8/21/2016 6,543 Midas 6/21/2017 6/22/ Roosters Comb 7/09/2017 7/25/ ,879 23

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28 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/ ,100 Oil Well 7/17/2017 7/20/2017 7,500 Pole Creek 7/30/2017 8/02/2017 6,540 25

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30 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, 27

31 which can be found at 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 wildfireurban 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. 28

32 References Corona, Marcella. Prescribed burn blamed fror Liittle Valley Fire. October 26, (accessed January 11, 2018). Harris, Jeremy. KUTV. July 17, (accessed January 11, 2018). Klassen, Keith. The Schultz Fire & Subsequent Flooding (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 pages. Margiott, Ben. NDF crews start planting trees & grasses on Little Valley Fire burn scar. January 5, (accessed January 10, 218). National Weather Service (NWS). Flash Flood Threat Within Fire Burn Scar. n.d. (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. (accessed April 3, 2018). U.S. Geological Survey (USGS). USGS HARDSCRABBLE CK BLW TH RANCH AT SUTCLIFFE, NV. 2018b. (accessed May 1, 2018). U.S. Geological Survey (USGS). Water Quality after a Wildfire. 2018c. (accessed April 2, 2018). 29

33 RESOUCRES Expectations After Fire FEMA Flood After Fire Risk Fact Sheet: National Weather Service Burn Scar Information Colorado Post-Wildfire Mudslide Brochure: New Mexico After Wildfire Flood Information: Additional Flooding Information Flooding in Nevada: General Flooding Information: National Flood Insurance Program: FEMA Mapping: For more information contact: Nicole Goehring Floodplain Mapping Coordinator, Nevada Division of Water Resources Parks, and Carol Miller. "Weather, fuelsm and topography impede wildalnd fire spread in western US landscapes." Forest Ecology and Management, 2016: Mapping,and Planning Partners. 30

COMMUNITY EMERGENCY RESPONSE TEAM FLOODS INTRODUCTION

COMMUNITY EMERGENCY RESPONSE TEAM FLOODS INTRODUCTION INTRODUCTION Floods are one of the most common hazards in the United States. A flood occurs any time a body of water rises to cover what is usually dry land. Flood effects can be local, impacting a neighborhood