New Mexico Flood Disaster Information and Risk Analysis Report. March 2015

Transcription

1 New Mexico Flood Disaster Information and Risk Analysis Report March 2015 Federal Emergency Management Agency Department of Homeland Security 800 N. Loop 288 Denton, TX 76209

2 SUBMITTED BY: 723 South Interstate 35E, Suite 230 Denton, TX DATE SUBMITTED: February 2015 All illustrations and all photographs in this document were created or taken by FEMA or a FEMA contractor unless otherwise indicated.

3 Table of Contents ACRONYMS AND ABBREVIATIONS... V SECTION ONE INTRODUCTION SECTION TWO HISTORY OF FLOODING IN NEW MEXICO Rio Grande River Arroyos Flash Flooding North American Monsoon Overview of Past Flooding Events SECTION THREE EXISTING CONDITIONS IN NEW MEXICO Soils Vegetation Slope Development DROUGHT SECTION FOUR FLOOD DISASTERS OF 2013 AND Flood Events DR-4147 and DR-4148: New Mexico Severe Storms and Flooding DR-4151 and 4152: New Mexico Severe Storms, Flooding, and Mudslides Flood Events DR-4197: New Mexico Severe Storms and Flooding DR-4199: New Mexico Severe Storms and Flooding SECTION FIVE RECOMMENDED MITIGATION STRATEGIES Floodplain Mapping and Identification Unmapped Areas / Outdated Maps Strategies for Unmapped Areas and Outdated Maps Post-Fire Hydrology Impacts of Post-Fire Hydrology Mitigation Strategies for Post-Fire Hydrology Alluvial Fan Identification Impacts of Alluvial Fan Flooding Strategies for Identifying and Mitigating Alluvial Fans Non-Regulatory Products Changes Since Last FIRM Flood Depth and Analysis Grid APR-15 i

4 Table of Contents Flood Risk Assessment Strategies for Non-Regulatory Products Arroyo Safety Mitigation Strategies for Arroyo Safety Flash Flooding / Extreme Erosion Mitigation Strategies for Erosion / Flash Flooding SECTION SIX CONCLUSION SECTION SEVEN REFERENCES APPENDIX A: NEW MEXICO DATA-GATHERING EFFORT AND SILVER JACKETS INFORMATION... A-1 8-APR-15 ii

5 Table of Contents Figures Figure 3-1 Santa Clara Canyon profile Figure 5-1 Status of Flood Insurance Rate Maps in New Mexico as of Figure 5-2 Estimated probability of post-wildfire debris flows in the 2012 Whitewater-Baldy burn area, southwestern New Mexico Figure 5-3 Diagram of an alluvial fan Figure 5-5 Visualization of CSLF Figure 5-6 Visualization of the depth grid in 1% chance (100-year) floodplain Figure 5-7 Visualization of the velocity grid... Figure 5-8 Visualization of the Percent Chance of Flooding Over 30-Year Period Grid APR-15 iii

6 Table of Contents Tables Table 2-1 Federal Wildfire Disaster Declarations in New Mexico, 2000 to Table 2-2 Federal Disaster Declarations for Flooding in New Mexico, 2006 to Table A-1 NMFMA 2014 Data Gathered... A-1 8-APR-15 iv

7 Acronyms and Abbreviations Acronyms and Abbreviations BFE CRS CSLF CTP DR EWP FEMA FIRM Hazus IA IBWC LFD LOMA LOMR MRGCD n.d. NMDHSEM NRCS NWS PA RAMPP Risk MAP SFHA State Plan USACE USDA USFS USGS Base Flood Elevation Community Rating System Changes Since Last FIRM Cooperating Technical Partner Disaster Recovery Emergency Watershed Protection Federal Emergency Management Agency Flood Insurance Rate Map Hazards U.S. Individual Assistance International Boundary and Water Commission Letter of Final Determination Letter of Map Amendment Letter of Map Revision Middle Rio Grande Conservancy District no date New Mexico Department of Homeland Safety and Emergency Management Natural Resources Conservation Service National Weather Service Public Assistance Risk Assessment, Mapping, and Planning Partners Risk Mapping, Assessment, and Planning Special Flood Hazard Area 2013 New Mexico State Hazard Mitigation Plan U.S. Army Corps of Engineers U.S. Department of Agriculture U.S. Forest Service U.S. Geological Survey 8-APR-15 v

8 Introduction SECTION ONE INTRODUCTION New Mexico is prone to flooding even though the majority of the state is considered arid. In the past 2 years (2013 and 2014), the State of New Mexico has had six Presidential (or Federal) Major Disaster Declarations for flooding. Flooding disasters in New Mexico between 2003 and 2012 resulted in more than $110 million in FEMA recovery funding to date (FEMA, 2014b). This estimate does not include open claims still in progress on many of the disaster declarations during this period. Final figures are subject to increase. Lack of awareness that flooding is a problem in the state is due partly to the perception of New Mexico as a desert State. The purpose of this report is to raise awareness of the complex environmental factors that impact flooding in New Mexico and provide recommendations for communities for flood mitigation strategies. It is especially important for communities to be aware of these opportunities so that they can utilize disaster funds, as well as other available funds, to improve disaster resilience. Information about the occurrence of flooding and the risk factors for flooding in New Mexico will be discussed. Average annual precipitation ranges from less than 10 inches over much of the southern desert and the Rio Grande and San Juan Valleys to more than 40 inches at higher elevations in the State. Summer rains fall almost entirely during brief, but frequently intense thunderstorms. July and August (North American Monsoon season) are the rainiest months over most of the State, with from 30 to 40 Figure 1-1: Severe erosion due to flash flooding in Doña Ana County (September 2013) Courtesy, Doña Ana County Floodplain Administrator percent of the year s total moisture falling at that time (State of New Mexico, 2013), creating greater potential for flooding than the remainder of the year. New Mexico is generally dry for the remaining 10 months of the year, which increases the potential for wildfire. This report provides an overview of the types of flooding that occur in New Mexico along with role that wildfires and burn scars play in exacerbating flood conditions and damages. A flood is commonly defined as an overflow of water that submerges land which is usually dry Flooding may occur as an overflow of water from water bodies, such as a river or lake, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries, or it may occur due to an accumulation of rainwater on saturated ground (BBC, n.d.). 8-APR

9 Introduction Floods can develop slowly or quickly. Flash floods can develop within minutes and without visible signs of rain. Flash floods are more common in New Mexico than other types of flooding. (State of New Mexico, 2013) Floods can be local, affecting a neighborhood or community, or very large, affecting entire river basins. Rivers can flood when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses that are located in the natural floodplains of rivers. The potential for damage from riverine flooding can be reduced or eliminated by moving away from rivers and other bodies of water. Even so, people have traditionally lived and worked by rivers because the land is usually flat and fertile and because rivers provide easy travel and access to commerce and industry. The types of flooding that occur in New Mexico are flash flooding, riverine flooding, and alluvial fan flooding. Flash flooding A flash flood is a rapid flooding of geomorphic low-lying areas: washes, rivers, dry lakes, and basins. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may occur after the collapse of a debris dam or a human structure such as a manmade dam. Flash floods are distinguished from other types of floods in how quickly they develop usually 6 hours or less after a heavy rainfall. The 2013 State Hazard Mitigation Plan lists flash flooding as one of the greatest weather hazards in New Mexico. New Mexico ranks 10th in the Nation in flash flood deaths per capita, based on the National Weather Service storm data from 2006 to Flash flooding is largely the result of the following two factors: (1) thunderstorm frequency from July through September (thunderstorm frequency in some parts of New Mexico is among the highest in the Nation) and (2) excessive moisture during the summer, which can lead to large volume runoffs enhanced by the terrain. See Section 2.5 for more information on flash flooding. Riverine flooding River flows rise to floods levels at different rates, from a few minutes to several weeks, depending on the type of river and the source of the increased flow. Slow-rising floods most commonly occur in rivers with large drainage basins. The increase in flow may be the result of sustained rainfall, rapid snowmelt, monsoons, or tropical cyclones. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, ice, and debris, as well as burn scar debris flows. In New Mexico the larger river Basins are controlled by structures designed to manage river flows, in conjunction with Levee systems, which tend to reduce the frequency of large scale riverine flooding. 8-APR

10 Introduction Alluvial fan flooding An alluvial fan generally occurs when drainage from mountainous areas and valleys spills down onto a canyon floor carrying rocks, sediment, and debris. Fans are typically found where a canyon draining from mountainous terrain emerges out onto a flatter plain and especially along faultbounded mountain Figure 1-3: Flood damage in San Miguel County (2014) fronts. Alluvial fans are often found in desert areas subject to periodic flash floods from thunderstorms in nearby hills. The typical watercourse in an arid climate has a large, funnel-shaped basin at the top, leading to a narrow pass or gorge that opens out into an alluvial fan at the bottom. Multiple braided streams are usually present and active during water flows. When the swift moving waters exit the narrow mountain canyons, the water deposits its debris load rapidly and many jump channel to follow another path to the valley floor. This makes predicting exact flow paths on alluvial fans challenging. 8-APR

11 History of Flooding in New Mexico SECTION TWO HISTORY OF FLOODING IN NEW MEXICO Floods occur regularly across the country, causing evacuations, widespread damage and even death. Those living near waterways or other low-lying areas are most at risk, but anyone in a community susceptible to flooding can be affected. Several geographic features in New Mexico contribute to flooding hazards in the state. These include Arroyos found throughout the state which are susceptible to frequent flash flooding, and the Rio Grande River, running the length of the state. Conditions that often exacerbate floods throughout New Mexico include the North American Monsoon season, playa lakes and post wildfire burn scars. Each of the contributing factors unique to New Mexico are described further in this section. 2.1 RIO GRANDE RIVER The Rio Grande River is the second largest river in the Southwest and has an expansive riverside cottonwood forest in New Mexico, referred to as the bosque. The river is a valuable part of the lives and history of the people throughout New Mexico. The Rio Grande originates in the San Juan Mountains of southern Colorado and flows south through the entire length of New Mexico (Figure 2-1). It continues south and forms the border between Texas and Mexico. The portion of the Rio Grande watershed that is in New Mexico covers approximately 1.9 million acres (USDA, 2013). Most lands in the Rio Grande watershed are under Federal ownership and/or governed by federal Figure 2-1: Major New Mexico Rivers 8-APR

12 History of Flooding in New Mexico regulations. The major streams that drain into the Rio Grande in New Mexico are the Rio Chama, which is the most significant tributary and joins the Rio Grande in north central New Mexico; the Jemez River, which joins the Rio Grande near the City of Bernalillo; and the San Jose/Rio Puerco drainage, which also joins the Rio Grande near the City of Belen. Flow in the Rio Grande is affected by snowmelt and summer rains. The typical annual cycle is characterized by a low winter flow, a spring peak between early April and mid-may corresponding to snowmelt, a low flow in June followed by smaller peaks associated with monsoon rains, and decreasing flow through the fall. The Middle Rio Grande Conservancy District (MRGCD) provides the following history of flooding of the Rio Grande (MRGCD, n.d.): Development and deforestation in Colorado since the 1880s raised the levels of silt in the river, which has increased sedimentation. These deposits generally collect in the middle Rio Grande valley where the river first widens and slows thus raising the level of the riverbed and the surrounding water table. The shallow water table throughout the valley turned over 60,000 acres of farmland into swamps or alkali and salt grass fields. Frequent floods often destroyed entire villages; one scoured a path right through what is now downtown Albuquerque. Also, the existing irrigation systems were insufficient and primitive; many were hundreds of years old and desperately needed rehabilitation. The Middle Rio Grande Conservancy District was created to provide flood protection from the Rio Grande, drain swamplands and provide irrigation water to farmlands. By 1935, the Conservancy District had built the storage dam at El Vado and the diversion dams at Cochiti, Angostura, Isleta, and San Acacia to manage its water. The Conservancy had also dug 17 miles of new drainage and irrigation canals, and incorporated another 214 miles of existing canal into the system. Nearly 200 miles of riverside levees and a system of jetties and checks alongside the river protected against floods. The drains funneled water away, lowered the water table, dried the land and reclaimed it for agriculture Through development and the implementation of flood control measures, the river features an intricate system of ditches and canals and levees that prevent the river from overflowing its banks while allowing for irrigation, agriculture, recreation, and environmental sustainability. The river has been altered by irrigation diversions and agricultural reservoirs. Irrigation flows have increased the relative magnitude and duration of summer peaks and reduced peak flows historically associated with snowmelt. 8-APR

13 History of Flooding in New Mexico 2.2 ARROYOS Arroyos are natural fluvial landforms or constructed flood control channels usually following natural drainage patterns. The term usually applies to natural drainage areas in sloped or mountainous terrain in dry (xeric) and desert climates. Flash flooding can create deep arroyos or lead to the deposition of sediment on flooded lands. This process can lower the groundwater level of the surrounding area, making the area unsuitable for agriculture. However, a shallow water table lowered in desert arroyo valleys can reduce saline seeping and alkali deposits in the topsoil, making it suitable for irrigated farming. Natural arroyos are created through a process called arroyo-cutting, which occurs in arid regions such as New Mexico where heavy rains can lead to the enlargement of rivers that then cut into surrounding rock, creating ravines that are dry under normal weather conditions. The arroyocutting that occurred in the Southwest in the 1900s caused serious farming issues such as a lowered water table and the destruction of agriculture and grazing lands. In agricultural areas where irrigation is needed because of the climate, farmers have traditionally relied on small constructed arroyos or acequias and ditches for the distribution of water. Arroyos and flood control channels typically move water from mountains and mesas to the Rio Grande as quickly as possible. Most of the time arroyos are dry, but when it rains, the arroyos can quickly fill with water without warning. It may be sunny in the downstream city but raining in the mountains. Water can come down from the mountains at such a fast rate that it poses a threat to health and safety as well as property. Within seconds, water can overtake cars and pedestrians unaware of rainfall at higher elevations. Mandatory flow levels and man-made diversions can also compound flood issues. For example, only water flow exceeding the minimum needed for the habitat of the Rio Grande silvery minnow, a federally endangered species, is available for municipal water supply diversion. Therefore, a certain level of flow must be maintained. While New Mexico is a state bound by western water rights laws, rainwater harvesting (e.g., 55-gallon rain barrels, cisterns) by residential owners is generally permissible by the Office of the State Engineer (OSE): Most homeowners can install and use a rainwater harvesting system for landscape irrigation without public health and water rights concerns. For larger-scale commercial projects, it is a good idea to check with the local OSE Water Rights Division to make sure the project does not inappropriately affect rainwater runoff into a stream system, therefore impacting a public water supply. (New Mexico Office of the State Engineer / Interstate Stream Commission, 2015) 2.3 PLAYAS Playa lakes are round hollows or circular depressions in the ground in the Southern High Plains of the United States. They are ephemeral, meaning that they are only present at certain times of 8-APR

14 History of Flooding in New Mexico the year. Most playas fill with water only after rainstorms when freshwater collects in the round depressions of the otherwise flat landscape of portions of eastern New Mexico. There are many theories as to the origin of playas, but the most widely accepted are that playas are either carved by wind or formed by land subsidence (they are sinkholes). Whatever their origin, playas are important wetlands to humans, animals and plants of the High Plains (EPA, n.d.). Playas are important because they store water in a part of the country that receives little annual rainfall and where there are typically no permanent rivers or streams. Playas help support the surrounding agriculture by providing irrigation water. Compared to other wetlands, playas go through frequent, unpredictable, wet/dry cycles. In wet years they support the production of annual plants, such as smartweeds and millets. These plants produce a tremendous crop of seeds that are favored by dabbling ducks and other seed eating birds. The wet/dry nature of playas, along with their high plant production, means they produce an abundance of invertebrates. This productivity makes playas havens for birds and other wildlife throughout the year (TPWD, n.d.). While playa lakes provide a variety on environmental benefits, consideration must be given to the risks associated with playas when planning and regulating development. 2.4 BURNS New Mexico has many areas that are mountainous and/or forested. Due to the dry climate, these areas become susceptible to fire. After a fire, areas that are downhill and downstream of burned areas are susceptible to flash flooding and debris flows, especially near steep terrain. The severity of the burn impacts the volume and content of the debris flow. Rainfall that is normally absorbed runs off extremely quickly after a wildfire because vegetation cannot slow the flow, and soil may become hydrophobic. Some species of trees are water silos that intercept significant portions of initial rain in most storms. Loss of trees to wildfires Figure 2-2: Flood damage in San Miguel County with typical debris flows in burn scars (September 2013) Courtesy, Las Vegas Emergency Management significantly contributes to post-fire flood volume and velocity. As a result, much less rainfall is required to produce a flash flood. According to the National Weather Service (NWS), a good rule of thumb is If you can look uphill from where you are and see a burnt-out area, you are at risk (NWS, 2014). In addition, NWS advise that half an inch of rainfall in less than an hour is 8-APR

15 History of Flooding in New Mexico sufficient to cause flash flooding in a burn area with steeper slopes and severe burn scars (NWS, 2014a). The susceptibility of burned areas to flash flooding is greatest during the first 2 years after the fire (NWS, 2014a). However, according to NMDHSEM, the re-establishment of vegetation in many areas of New Mexico can take 3 to 5 years due to the climate conditions predominant in the state. The re-establishment of vegetation is the primary factor in reducing the potential for flash flooding and debris flows in burned areas because the vegetation slows the precipitation runoff, and anchors the soil, but it can take many years for vegetation to become reestablished. Factors such as proximity of the burned area to population centers, burn severity, steepness of terrain, and size of the burned area also contribute to the risk of flash flooding. New Mexico is highly susceptible to wildfires. Since 1998, there have been 37 Presidential Disaster Declarations for New Mexico. Since 1998, more than $43 million in Federal assistance has been provided to New Mexico as a result of wildfires. This represents federal recovery assistance and does not include expenses incurred by state and local governments. Table 2-1 is a list of the Federal disaster declarations and Federal assistance for wildfires in New Mexico from 2000 to Table 2-1: Federal Wildfire Disaster Declarations in New Mexico, 2000 to 2012 DR # Name Incident Period DR-2978 Whitewater-Baldy Fire Complex Federal Assistance 5/23/2012 7/31/2012 $181,858 DR-2979 Little Bear 6/4/2012 7/30/2012 $4,314,040 DR-2933 Las Conchas 6/26/2011 8/25/2011 $1,651,694 DR-2918 Track Fire 6/12/2011 7/28/2011 $4,300,099 DR-2935 Donaldson 6/28/2011 7/15/2011 $3,173,062 DR-2917 Wallow 6/10/2011 7/12/2011 $515,274 DR-2866 Quail Ridge 3/7/2011 3/11/2011 $267,934 DR-2818 Buckwood 5/6/2009 $339,716 DR-2762 Trigo 8/21/2008 7/2/2008 $2,175,243 DR-2777 Big Springs 6/25/2008 $406,862 DR-2647 Rivera Mesa 6/18/2006 $2,718,248 DR-2636 Ojo Feliz 4/12/2006 $2,406,368 DR-2631 Casa Fire 3/1/2006 3/7/2006 $262,647 DR-2522 Bernarda 6/18/2004 6/24/2004 $238,140 DR-2472 Atrisco (formerly Bosque) 6/25/2003 $1,749,609 DR-2414 Turkey Fire 6/2/2002 7/14/2002 $561,240 DR-2424 Roybal Fire Complex 6/12/2002 7/13/2002 $258,389 8-APR

16 History of Flooding in New Mexico DR # Name Incident Period Federal Assistance DR-2415 Cerro Pelado 6/2/2002 7/3/2002 $558,524 DR-2416 Ponil Fire 6/2/2002 6/16/2002 $6,435,257 DR-2408 Borrego Fire 5/22/2002 6/10/2002 $958,865 DR-2402 Peñasco 4/30/2002 6/3/2002 $2,505,601 DR-2404 Dalton 5/6/2002 5/17/2002 $298,474 DR-2398 Kokopelli Fire Complex 3/23/2002 4/1/2002 $739,293 DR-1329 New Mexico Wildfire 5/5/2000 6/9/2000 $5,652,344 New Mexico currently includes multiple flash flooding regions of concern. Located below burn scars, these areas are at-risk from significantly increased peak flows, debris torrents, and excessive sedimentation. Burn scar areas can yield approximately 400 percent greater flows than typical thunderstorm or flood events, which means they are extremely erodible, lacking in vegetation, and lack soil absorption. There is a dramatic increase in the resulting flow rate with the same rainfall event. Even during a normal or drier-than-normal monsoon season, it only takes one moderate to heavy rainfall over a burn scar area to create a forceful debris flow carrying significant amounts of ash, soil and vegetation, trees and boulders, and other debris downstream, wreaking havoc in areas downstream. Burn scar areas throughout New Mexico that the Federal Emergency Management Agency (FEMA) has determined to be at higher than previously assessed risk for flash flooding and debris flow are associated with the following wildfires (FEMA, 2014a): Thompson Ridge Fire, north-central New Mexico, May 2013 Las Conchas Fire, north central New Mexico, June 2011 Tres Lagunas Fire, north central New Mexico, May 2013 Signal Fire, southwestern New Mexico, May 2014 Silver Fire, southwestern New Mexico, June 2013 Whitewater-Baldy Fire, southwestern New Mexico, May 2012 Little Bear Fire, south-central New Mexico, June APR

17 History of Flooding in New Mexico 2.5 FLASH FLOODING The intensity of flash flooding is a function of the intensity and duration of rainfall, steepness of the watershed, stream gradients, watershed vegetation, natural and artificial flood storage areas, and configuration of the streambed and floodplain. Flash floods that are the result of too much rain, in too small an area, in too short a time. They generally travel down arroyos and involve a rapid rise in water level, high velocity, and large amounts of debris. These can lead to significant damage that includes the uprooting of trees, undermining of buildings and bridges, and scouring new channels. Dam failures and ice jams can also lead to flash flooding. Neighborhoods areas are increasingly subject to flash flooding because of the removal of vegetation, replacement of ground cover with impermeable surfaces, and construction of drainage systems. Local drainage floods may occur outside recognized drainage channels or delineated floodplains as a result of a combination of locally heavy precipitation, lack of infiltration, inadequate facilities for drainage and storm water conveyance, and increased surface runoff. Winter flash floods are usually caused by unseasonably high levels of rain on a snowpack. Excessive runoff is the result of water release from the snowpack combined with the rainwater. Winter flash floods can last for less than a day or can evolve into longer term flooding events that last up to 2 weeks. Winter flooding generally occurs between November and February. Flash floods that occur in the spring (between April and June) vary from winter-type flash floods in which rain falls over the remaining winter snowpack to events in the eastern plains, which are often associated with cold fronts, abundant moisture from the Gulf of Mexico, and upslope conditions. Flash floods occur in all of the eastern plains, but are most common in Eddy and Lea Counties in the southeastern corner of the State. Figure 2-2: Guadalupe County Flood Damage/Erosion Caused by Flash Flooding (2014) Most of the flash floods in New Mexico are associated with the monsoon season in the summer (see Section 2.6). Approximately 60 percent of the flash floods in the State occur in July and August. 8-APR

18 History of Flooding in New Mexico 2.6 NORTH AMERICAN MONSOON The North American monsoon is a period of pronounced increase in rainfall that affects the Southwest and that generally lasts from June 15 to September 30. With the onset of the monsoon, New Mexico is typically affected by a variety of weather hazards that can put the population at risk for serious injury or death, with the greatest impacts to the region felt from mid-july through September 15. Thunderstorm frequency increases during this period, and exceptionally hot days are common. Significant weather events associated with the monsoon result in property damage, injuries, and fatalities every year. The monsoon season generally dissipates in the northern part of the State in early September. In mid- to late-summer, the Pacific winds bring humid subtropical air into the State. Solar heating triggers afternoon thunderstorms that can be devastating. July and August 2012 brought intense flooding in burn scar areas that produced up to 400 percent greater flows than the predicted flows in the 1-percent-annual-chance storm event. Since 2011, monsoon-related events have led to a total of at least five fatalities in New Mexico (NWS, 2014b). 2.7 OVERVIEW OF PAST FLOODING EVENTS According to the U.S. Army Corps of Engineers (USACE) Post Flood Report: Record Rainfall and Flooding Events During September 2013 in New Mexico, Southeastern Colorado and Far West Texas (USACE, 2014), widespread flooding in the Southwest stems from spring runoff or tropical cyclones (or remnants). The following tables (Table 2-2 and 2-3) provide a summary of the flood events that are described in the USACE report: Table 2-2: Historic Spring Floods Year Location Event Description 1903 Upper Rio Grande and Rio Chama Watersheds 1920 Upper Rio Grande and Rio Chama Watersheds Excessive amount of snowfall fell before May, and the snow melted slowly during May creating two separate flood events Rapid melting of abnormally high snowpack of southern Colorado and northern New Mexico resulted in significant flooding. High temperatures and general warm rains induced a high rate of runoff. Several heavy rainfall events augmented the flood Northern New Mexico Following the drought of , excessive snowfall was the heaviest on record at some locations. Abnormal temperatures and rainfall during the runoff period, combined with excessive snow cover, produced a large flood event. The duration of the flood was in excess of two months Northern New Mexico Spring flooding occurred due to snowmelt in the mountainous 8-APR

19 History of Flooding in New Mexico regions of northern New Mexico and southern Colorado and augmented by rain in April 1958 Otowi and Bernalillo Heavy snowpack runoff from the mountainous areas of the Rio Grande Basin produced flooding in Santa Fe County at the Otowi Historic District and the City of Bernalillo 1973 Albuquerque area Peak discharge at Albuquerque was produced by the runoff of heavy snowpack in the mountains of Colorado and northern New Mexico in May The flood flows stressed sections of the existing levees Northern New Mexico Higher than average snow accumulation was augmented by two late storms in May, and lower than normal temperatures through the winter delayed runoff peaks 1985 Rio Grande Basin Above average snowpack, and above average precipitation resulted in the snowmelt runoff exceeding 250 percent of normal in many areas of the basin 1986 Rio Grande Basin Observed snowmelt runoff in the Rio Grande Basin was approximately 200 percent of normal 1987 Rio Grande Basin Heavy snowpack and above normal runoff Table 2-3: Historic Tropical Cyclone Flood Events Year Location Event Description 1904 Region-wide Intense, widespread rainfall and resulted in property damages in excess of $1 million dollars [1904 dollars]. Circumstantial evidence points to tropical storm, storm remnant, or trough as the primary moisture source 1942 Canadian and Pecos Rivers Flood was caused by moderately widespread rainfall from a tropical storm that moved inland from the Gulf of Mexico. The storm crossed into New Mexico in the vicinity of Roswell then moved northnortheastward, reaching the Tucumcari area. As much as 8 in of rain fell in the 84-hr storm at Rancho Grande (near Santa Rosa), Maxwell, and Chico, NM Region-wide Flood from a hurricane from the Gulf of Mexico led to intense, widespread rainfall and damage in the tens of millions of dollars across northeastern, southeastern and parts of the northern areas of New Mexico 1983 Gila River Basin Closed low developed east of Baja California on September 29. This low was stationary between September 29 and October 2nd, steering numerous shortwave troughs rapidly northeastward across Arizona and New Mexico. This storm produced flood peaks on the San Francisco River that are considered the maximum of record and in the frequency of the 100-year event. 8-APR

20 History of Flooding in New Mexico Since 1954, New Mexico has had 25 Federal Disaster Declarations for flooding. All 25 were Major Disaster Declarations. A major disaster declaration provides a wide range of federal assistance programs for individuals and/or public infrastructure, including funds for both emergency and permanent work. The 11 most recent disaster declarations occurred from 2004 to These 11 disasters included making available Federal assistance in excess of $132 million in approved Public Assistance (PA) for recovery and repair (FEMA, 2014b). This figure does not include ongoing repair work or open public assistance claims for many of the disasters and is subject to increase substantially. All major disaster declarations make available Hazard Mitigation Grant Program (HMGP) funds to state, tribal and local jurisdictions to implement sound mitigation projects that eliminate or reduce future disaster losses. The disaster declarations in New Mexico have generated millions of dollars in HMGP funds. Table 2-4 shows the jurisdictions included in the Federal Disaster Declarations in New Mexico from 2006 to DR # Table 2-4: Federal Disaster Declarations for Flooding in New Mexico, 2006 to 2014 Declaration Date Public Assistance Individual Assistance Jurisdictions included in the Declaration DR /29/2014 In progress N/A Colfax, Eddy, Lea, Lincoln, Otero, San Miguel, Santa Fe, and Sierra Counties DR /6/2014 In progress N/A Guadalupe, Rio Arriba, and San Miguel Counties; Pueblo of Acoma Lincoln, Otero, and Sandoval Counties and the Santa Clara Pueblo were added on 10/24/14 DR /29/2013 $32,425,648 N/A Catron, Chaves, Cibola, Colfax, Eddy, Guadalupe, Los Alamos, McKinley, Mora, Sandoval, San Miguel, Santa Fe, Sierra, Socorro, and Torrance Counties De Baca, Doña Ana, Harding, Lincoln, Otero, Rio Arriba, and San Juan Counties; Isleta, Sandia, and Taos Pueblos and the Navajo Nation were added later to the declaration. DR /30/2013 $8,737,280 N/A Santa Clara Pueblo DR /30/2013 $5,058,413 N/A Bernalillo, Colfax, Luna, Sandoval, Socorro, and Sierra Counties; Cochiti, Santa Domingo (Kewa), Navajo Nation, San Felipe, and Sandia Pueblos Sierra County and the Navajo Nation were added on 11/22/13. DR /30/2013 $68,919 N/A Santa Clara Pueblo DR /24/2012 $16,310,672 N/A Lincoln and Sandoval Counties; Santa Clara Pueblo 8-APR

21 History of Flooding in New Mexico DR # Declaration Date Public Assistance Individual Assistance Jurisdictions included in the Declaration DR /23/2011 $19,496,461 N/A Cibola and Sandoval Counties DR /13/2010 $9,865,507 N/A Cibola, McKinley, Mora, San Juan, and Socorro Counties DR /14/2008 $11,972,843 N/A Lincoln and Otero County DR /30/2006 $33,155,697 $1,734,451 Cibola, Doña Ana, Lincoln, Luna, Otero, Socorro, Valencia, McKinley, Taos, and Rio Arriba Counties Source: FEMA website ( The New Mexico Department of Homeland Safety and Emergency Management (NMDHSEM) reports 40 State Declared Disasters for flooding between 2003 and This number is based on how many Executive Orders were signed by the governor for flooding or flood threat. The total cost of State-declared flood events from 2003 through 2012 was $31,866,315 (State of New Mexico, 2013). The total does not reflect all costs for Federal disasters as many remain open and are subject to change. 8-APR

22 Existing Conditions in New Mexico SECTION THREE EXISTING CONDITIONS IN NEW MEXICO The factors that are unique to New Mexico that contribute to flooding are its soils, rainfall, vegetation, slope and drought conditions. Development in any location can exacerbate flooding. All of these factors need to be considered in assessing flood risk and in developing potential mitigation measures. 3.1 SOILS The soils in much of the State are derived from underlying parent materials rich in carbonate and mixed clays. As a result, soils are typically fine grained and have low infiltration rates and high runoff potential. Vegetative cover is either mixed shrubs or mixed grasses. Sparse vegetative cover combined with soils with high runoff potential results in significant flooding hazards in ephemeral washes (arroyo s) and adjacent areas (State of New Mexico, 2013). Wildfires result in extreme soil damage. Soil damage usually occurs where burn intensities are severe to moderate. The loss of the organic components in the soil greatly decreases the ability of rain to infiltrate. Large floods can occur in these burned areas from average monsoonal rainstorms. 3.2 VEGETATION New Mexico has the following four vegetation zones outside of urbanized areas, which are determined mainly by elevation: The Lower Sonoran Zone, in the southern sections of the Rio Grande and Pecos valleys and in the state s southwestern corner, usually occurs at elevations below 4,500 feet. It includes nearly 20,000 square miles of New Mexico s best grazing area and irrigated farmland. This area is typically classified as herbaceous or desert brush. The Upper Sonoran Zone, comprising about three-fourths of the state and including most of the plains, foothills, and valleys above 4,500 feet, is a region of prairie grasses, low piñon pines, and juniper shrubs. At higher elevations, better stands are a result of more abundant rainfall. This area is typically classified as Juniper-Grass. The Transition Zone, covering some 19,000 square miles, is identified chiefly by the ponderosa pine. The Canadian Zone, covering 4,000 square miles at elevations of 8,500 to 9,500 feet, contains blue spruce and Douglas fir. This area is typically classified as Mountain Brush or Ponderosa Pine. 8-APR

23 Existing Conditions in New Mexico The Hudsonian and Arctic-Alpine zones, above 9,500 feet, are too small in area and too sparsely covered to be of great importance (McNamee, 2014). Factors such as elevation, exposure, temperature, and moisture availability determine the type of native vegetation that grows in drainage basins throughout New Mexico. The type of vegetation along a flood path can prevent further erosion of the channel banks. A structure that lies along a flood channel that has no surrounding vegetation is at risk of having its foundation undercut, which can cause structural damage or collapse. Many channels in more urban areas of the State such as Bernalillo County are concrete lined and contain little to no vegetation. Even the channels that are not concrete-lined are sparsely vegetated at best. Therefore, the majority of the channels are clean and smooth, which, combined with the steeply sloped topography of New Mexico, leads to larger conveyance due to supercritical flow conditions and enables the channel to flow fast and full (Bernalillo County, 2012). The recent drought has led to sparse vegetation in lower elevations throughout the State. In addition, when combating the concern of fuel load in the wildland-urban interface, vegetation is sometimes removed to reduce the threat of wildfires. While vegetation removal can effectively reduce the fuel load, it can also result in excess flood damage due to erosion and property damage where standing water occurs. Freshly burned landscapes are at risk of damage from postwildfire erosion hazards such as those caused by flash flooding and debris flows. Burn scar areas have a tremendous impact on flood and debris flow following short-duration, high-intensity rainfall. These high-volume, low-frequency floods result from typical monsoon summer rains and occur in and downstream of the burn scar areas. Dramatic changes in runoff, erosion, and deposition have been documented in watersheds affected by wildfire. 3.3 SLOPE The mountainous areas of New Mexico contribute to the volume and velocity of flooding. The mountains, which generally run north-south in New Mexico, serve as barriers to the prevailing westerly wind pattern. This barrier influences the origin of floodwaters through the melting of snowpack and trapping clouds during the monsoon season, which leads to precipitation over steep terrain. According to the Luna County/City of Deming/Village of Columbus Hazard Mitigation Plan: The slope that a flash flood traverses has a definite relation to the overall speed in which the water will travel. The steeper the incline, the faster the water will travel. The incline on which the water moves affects the width of the flooding area. Generally, the faster the water moves, the narrower the channel will be created, since the water digs the channel deeper as it flows. When the water flows on a shallower slope, the water tends to spread 8-APR

24 Existing Conditions in New Mexico out more, which can decrease its potential to cause mass damage (Luna County, 2014, p ). The impact of slope on flooding becomes even greater when other conditions such as development or a burn scar are present, both of which remove vegetation. Because vegetation serves to retain and slow runoff, reduced vegetation increases both the quantity and velocity of runoff. Figure 3-1 is an elevation profile of the Santa Clara Canyon, which is on Santa Clara Pueblo lands. The figure shows a drop in elevation of approximately 2,000 feet over 6 miles. Runoff can start in the highest reaches of the Pueblo, which have elevations up to 11,000 feet. A burn scar in the upper reaches of the canyon has greatly increased flood problems. See Section 5.2 for more information on post-fire hydrology. 3.4 DEVELOPMENT Figure 3-1: Santa Clara Canyon profile (USACE, 2011) Changes in land use associated with urban development affect flooding in many ways. Removing vegetation and soil, grading the land surface, and constructing drainage networks increase runoff to streams from rainfall and snowmelt. As a result, the peak discharge, volume, and frequency of floods increase in nearby streams. Changes to stream channels during urban development can limit their capacity to convey floodwaters. Roads and buildings constructed in floodprone areas are exposed to increased flood hazards, including inundation and erosion, as new development continues. According to USGS (2014): In undeveloped areas such as forests and grasslands, rainfall and snowmelt collect and are stored on vegetation, in the soil column, or in surface depressions. When this storage capacity is filled, runoff flows slowly through soil as subsurface flow. In contrast, urban areas, where much of the land surface is covered by roads and buildings, have less capacity to store rainfall and snowmelt. Construction of roads and buildings often 8-APR

25 Existing Conditions in New Mexico involves removing vegetation, soil, and depressions from the land surface. The permeable soil is replaced by impermeable surfaces such as roads, roofs, parking lots, and sidewalks that store little water, reduce infiltration of water into the ground, and accelerate runoff to ditches and streams. Even in suburban areas, where lawns and other permeable landscaping may be common, rainfall and snowmelt can saturate thin soils and produce overland flow, which runs off quickly. The number of housing units in New Mexico increased from 780,579 in 2000 to 901,388 in 2010, an increase of approximately 15 percent in 11 years (Census Bureau, 2014). Increases in housing development are typically accompanied by the development of infrastructure and commercial outlets. Increased development is most prevalent in and around larger metropolitan areas including Albuquerque, Las Cruces, Santa Fe, and Farmington. However, many smaller towns and cities throughout the State are also experiencing upward pressure on development. Sound floodplain management practices and implementation of mitigation techniques will be critical in managing the increased flooding potential throughout New Mexico as development continues. 3.5 DROUGHT In New Mexico, Drought is a regular event. Experts predict that drought conditions are likely to continue for the foreseeable future. Drought increases the probability and severity of wildfire. Drought also increases the severity of flash flooding due to soils becoming hydrophobic, repelling or incapable of dissolving in water, resulting in increased runoff and erosion. Economically, prolonged drought can have devastating effects on agriculture and food supply. The State of New Mexico has recorded periods of drought for the past few years. In every drought, agriculture is adversely impacted, especially in non-irrigated areas such as dry land farms and rangelands. Droughts impact individuals (farm owners, tenants, and farm laborers), the agricultural industry, other agriculture related sectors, and other industries such as tourism and recreation. There is increased danger of forest and wildland fires. Loss of forests and trees increases erosion, causing serious damage to aquatic life, irrigation, and power development by heavy silting of streams, reservoirs, and rivers. New Mexico is entering the tenth year of a drought, which magnifies the challenge of balancing our limited water supplies with growing demand. A drought is caused by a variety of factors. Scientists who study climate changes believe that conditions in the North Atlantic Ocean and the Eastern Pacific Ocean play a significant role in determining the amount of precipitation that New Mexico and the rest of the country receive. Studies show current conditions in those two oceans are similar to conditions that existed during the severe drought of the late 1940s and 1950s in New Mexico. (State of New Mexico, 2013) 8-APR

26 Existing Conditions in New Mexico Drought in the state of New Mexico ranges from abnormally dry to extreme drought. Figure 3-2 shows state drought conditions as of February Increased rainfall in recent years has slowly improved drought conditions in the state. However, according to the National Weather Service, nearly 62% of the state is in moderate to extreme drought conditions with 26% of the state still in severe to extreme drought. Given that drought is a slow-moving hazard without an event to mark its arrival, a one-time drought can be difficult to define. However, the consequences of a severe to extreme drought in the state pose significant challenges. Long-term solutions for coping with a limited water supply will require increased cooperation between urban users and agricultural use. Figure 3-2 New Mexico Drought Monitor 8-APR

27 Flood Disasters of 2013 and 2014 SECTION FOUR FLOOD DISASTERS OF 2013 AND and 2014 saw very heavy flooding throughout the state of New Mexico. The flooding during this time resulted in over $44,000,000 in damage and six Presidential Disaster Declarations. This figure represents federal dollars obligated to date and is expected to dramatically increase as repair work continues. Overall, the State has had seven flood disaster declarations since 2010 and 11 since For comparison s sake, from 1973 to 2003, a 30-year period, there were 11 flood declarations. There is a potential that this level of damage could continue as a result of extreme weather, climate change, floods after fires, and increased development. All of the disaster declarations listed were public assistance and Hazard Mitigation Grant Program (HMGP) only declarations. This indicates that the developed environment that was damaged by the recent New Mexico flooding consisted primarily of infrastructure and public facilities However, flooding in a developed environment can also affect residential areas. Damages to residential structures on tribal owned lands would be managed through public assistance claims/worksheets FLOOD EVENTS A series of significant storm events occurred New Mexico starting in June The most significant periods resulted in two Presidential Disaster Declarations for the State (DR-4148 and DR-4152) and two declarations for the Santa Clara Pueblo (DR-4147 and DR-4151). Showers and thunderstorms brought torrential rains to many regions in the State, resulting in devastating floods that damaged homes, washed out roads and bridges, caused rivers and streams to overflow, and resulted in at least one death. Several storms also produced damaging winds DR-4147 and DR-4148: New Mexico Severe Storms and Flooding FEMA announced on September 30, 2013, that Federal disaster aid had been made available to the State of New Mexico to supplement State, local, and tribal recovery efforts in the areas affected by the severe storms and flooding from July 23 to 28, The DR-4148 declaration was for public assistance and HMGP-only was in the amount of $5,058,413, but is subject to significantly increase as repair work continues. The flood incident period was preceded by a number of smaller, less severe storm and rain events that are common during the monsoon season. Severe thunderstorms and torrential rains slammed southern New Mexico and portions of west Texas over several days. Damage was widespread, affecting multiple counties and jurisdictions. The following jurisdictions were included in the declaration on September 30, 2013: Bernalillo, Colfax, Luna, Sandoval, and Socorro Counties and the Cochiti, Santa Domingo (Kewa), San Felipe, and Sandia Pueblos. On November 22, 2013, Sierra County and the Navajo Nation were added to the declaration. An 8-APR

28 Flood Disasters of 2013 and 2014 additional disaster declaration was made, for roughly the same incident period, providing Federal disaster aid to the Santa Clara Pueblo (DR-4147). It was declared on September 27, 2013, for flooding events from July 19 to 21, 2013 for public assistance and HMGP-only. The more significant impacts of the storm events were chronicled in local newspapers, NWS reports, NCDC incident narratives, as well as federal and state press releases. The following list is a summary of the notable storm damages and impacts: Santa Clara Pueblo o Torrential rain fell over the Santa Clara Canyon, producing a significant flash flood wave on Santa Clara Creek. o A 9-foot wave of water surged through Santa Clara Canyon, wiping out Highways 601 and 602. The flood wave moved downstream and affected the NM 30 bridge at Santa Clara Pueblo. Sandoval County o The Village of Corrales reported damages to public infrastructure including roads, culverts, bar ditches, roadside ponds, bridges and irrigation facilities. Damages were estimated in excess of 3 million dollars. o Slow-moving thunderstorms across the Thompson Ridge burn scar produced flooding, overwhelming several creeks in the area and producing flash flooding along the western periphery of the burn scar. o Flash flooding was observed along Forest Service Road 105 where culverts were destroyed by mud and debris. o Sandoval County Emergency Manager reported that culverts were blown out along the Sulphur Springs drainage in the Thompson Ridge burn scar area. Figure 3-1: Culvert Damage and Severe Erosion (July 2013). Courtesy, Village of Corales Floodplain Administrator o Roads were impassable because the blow-out culverts included three or four culverts along the Sulphur Springs drainage under a 1.5 lane road. The culverts had been getting clogged with debris with previous flood events, and this event the water and debris took out the road. o One home flooded in the city of Bernalillo and three or four homes flooded in El Llanito. Mud and debris from the flood waters significantly affected the area, and the clean-up cost thousands of dollars beyond the damage to structures. 8-APR

29 Flood Disasters of 2013 and 2014 o The County Emergency Manager reported that the entire city of Corrales was flooded due to heavy rains. Several businesses, many cars, and neighborhoods were flooded. Many roads were also washed out. Trees were knocked down due to the wind, and many traffic lights were out. o A culvert on Forest Service Road 105 was destroyed due to fast flowing water, mud, and debris. Bernalillo County Figure 4-2: Road damage due to severe erosion (July 2013) Courtesy, Village of Corales Floodplain Administrator o Bernalillo County officals reported flood damages to culverts and roadways along Gallegos Creek, Yrissari Creek and Gallegos Draw. o The Interstate 25 corridor around Bernalillo into north Albuquerque was one of the hardest hit areas. Widespread flooding was reported in Bernalillo due to the heavy rainfall and a breached acequia. o Up to 5 feet of water was reported in one home in Bernalillo. o Power outages reported for nearly 30,000 customers in Albuquerque due to lightning strikes o Two feet of water was reported at the Albuquerque Zoo. Santa Fe County o Frequent cloud-to-ground lightning strikes created numerous power outages across Santa Fe. Valencia County Figure 4-3: Lecco Road Flooded at Gallegos Creek Crossing (2013) Courtesy, Bernalillo County Floodplain Administrator 8-APR

30 Flood Disasters of 2013 and 2014 o Valencia County Floodplain Administrator reported severe flooding in the El Cerro Monterey Park area. Access roads become impassable, stranding 27 residents. Figure 4-4: El Cerro Access Road (July 2013) Courtesy, Valencia County Floodplain Administrator o The county Emergency Manager reported water in homes in Meadow Lake and Los Lunas, two homes in Belen, and an apartment building in Albuquerque. Socorro County o There were numerous reports of roads that were flooded, washed out, and damaged along the Socorro County stretch of U.S The county Emergency Manager indicated the cost of damage was approximately $1.2 million. Grant County o Flooding was reported near Gila along with a large hail storm. o Heavy rains flooded Highway 244 near Elk Silver. o Rain around the Silver Fire burn scar caused flooding on Forest Service Road 150 near Camp Thunderbird. 8-APR

31 Flood Disasters of 2013 and 2014 Luna County o The Mimbres River flooded near Mimbres, making low water crossings impassible. o High water in Mimbres left cars stranded in roads. o A wet microburst with 90 mph winds destroyed several buildings in Columbus. o In the County, water levels reached a depth of 3 feet, closing the road to Rockhound State Park. Torrance County o Torrance County officials reported extensive damage to county roads and debris fields in excess of 210 wide in places. Doña Ana County o High winds and flooding Figure 4-5: Ansley Ranch Road Damage (July 2013) was experienced in the Courtesy Torrance County Floodplain Administrator county, with some roads impassable. o In the City of Las Cruces, flooding was reported at Sierra Middle School o A water rescue occurred due to high waters at Sonoma Ranch Blvd. o In the Town of Vado, 20 people were evacuated after four mobile homes flooded. o Heavy rains flooded Interstate 25 and other roads near the Village of Hatch. o The County Floodplain Administrator reported damages from flooding through the declaration period, as well as smaller flood events earlier in the year, including culverts, roadways and other drainage infrastructure. Figure 4-6: Flooded County Road (n.d) Courtesy, Doña Ana County Floodplain Administrator 8-APR

32 Flood Disasters of 2013 and DR-4151 and 4152: New Mexico Severe Storms, Flooding, and Mudslides FEMA announced on October 29, 2013, that Federal disaster aid had been made available to the State of New Mexico to supplement State and local recovery efforts in the area affected by severe storms, flooding, and mudslides from September 9 to 22, The following jurisdictions were part of the original declaration on October 29, 2013: Catron, Chaves, Cibola, Colfax, Eddy, Guadalupe, Los Alamos, McKinley, Mora, Sandoval, San Miguel, Santa Fe, Sierra, Socorro, and Torrance Counties. De Baca, Doña Ana, Harding, Lincoln, Otero, Rio Arriba, and San Juan Counties and the Isleta, Sandia, and Taos Pueblos and the Navajo Nation were added later. The DR-4152 declaration was for public assistance and HMGP-only, exceeding forty million dollars in approved federal assistance. An additional disaster declaration was made for the same incident period, providing Federal disaster aid to the Santa Clara Pueblo ( DR-4151). This declaration was made on October 24, 2013, for flooding events from September 13 to 16, The declaration was for public assistance and HMGP-only, exceeding nine million dollars in approved federal assistance. As indicated earlier, all disaster dollar figures are subject to change and likely to increase as repair work continues. According to the USACE, many factors were in place that contributed to the September 2013 flood event. These factors are summarized below (USACE, 2014): southwesterly monsoon flow was strong over New Mexico and Colorado two tropical storms present in monsoon moisture source regions in Mexico trough present over northern Arizona and Utah, steering airflow over New Mexico and Colorado with a high pressure to the east saturated soils (later in the event) played a role in perpetuating flooding despite decreases in precipitation in the latter days of the event. prolonged winter and summer drought contributed to the die-off of many annual grasses and plants and some perennial shrubs and trees throughout the region leading to: o increased rain splash erosion o reduced infiltration o heightened overland flow o increased runoff In areas where wildfires in previous years had resulted in denuded slopes, large floods were produced. This was particularly evident in the drainages along the eastern side of the Jemez Mountains that were affected by the Las Conchas Fire, including Santa Clara, Frijoles, and Peralta Canyons; in southwestern New Mexico in the tributaries of the San Francisco and Gila Rivers that head in the vicinity of the Whitewater Baldy Wildfire burn scar; and along Fountain 8-APR

33 Flood Disasters of 2013 and 2014 Creek in Colorado, a tributary of the Arkansas River, whose headwaters and tributaries are located in the Waldo Canyon Wildfire burn scar area. All three of the burn scars received significant quantities of rain during this event, and severe flooding and extensive flood damage resulted in downstream reaches of the streams (USACE, 2014). The more significant impacts of the storm events were as follows: Santa Clara Pueblo o Culverts at road crossings were damaged or destroyed in multiple locations. o Floodwaters inundated the old village, damaging historic structures including the church. o Over 2 feet of water flooded the Indian Health Clinic, damaging the structure and contents. o Flooding along the Santa Clara, Frijoles, and Peralta Canyons was significant due to the more densely developed areas and the exacerbated flood conditions resulting from the 2011 Las Conchas Fire. Soils quickly became saturated, and drainage detentions were overwhelmed. Santo Domingo (Kewa) Pueblo o Floodwaters damaged more than 100 homes as well as irrigation works. (Flood damage was also reported at the San Felipe and Santa Ana Pueblos.) Sierra County o Significant flooding occurred in the vicinity of Truth or Consequences, flooding the Palomas and Animas Creeks, requiring the evacuation of more than 200 households at the peak of the event. Flood waters washed out several bridges including one Figure 4-7: Palomas Creek Flooding (September 2013) Courtesy, Local Resident Carol Slad at Highway 187. o Widespread flooding was reported in large portions of downtown Truth or Consequences. 8-APR

34 Flood Disasters of 2013 and 2014 o Authorities found the body of a man in his partially submerged rental car along a State road in Ash Canyon.State police investigators believed the driver of the vehicle died after his car was washed into a ravine and carried nearly 1 mile from the road. Grant County o In the Village of Santa Clara flooding overtopped a foot bridge, flooded several homes, destroyed a mobile home and an outbuilding, damaged several vehicles, caused gas leaks, and broke water and sanitary sewer lines. Navajo Nation o Flooding in the Crownpoint area caused the Navajo Technical University to evacuate its Crownpoint campus. o A number of the roads leading to the university were washed out, and several cars became stuck. o The university s administration building, student services building, and several family housing units were significantly damaged. o The nursing department buildings suffered the most damage, and portable buildings were required in order for classes to resume while repairs were completed. Catron County o Portions of Bursum Road to the community of Mogollon, was completely destroyed by flash flooding. o All homes and business along the creek in Mogollon were flooded and damaged, many severely. o Several vehicles were carried away, destroyed, and left in the bottom of the creek bed. o An 83-year old Arizona man was found dead 8 miles downstream from where his vehicle was located, destroyed in Mineral Creek. o A levee at Circle Drive in Glenwood was breached, flooding 16 residences with approximately 3 feet of water. o A large metal barn was moved into the river bed. o The Catwalk area northeast of Glenwood was completely destroyed. o A 30-foot section of a concrete girder bridge was also destroyed. o Water was reported in several homes in Alma. o Multiple roads throughout the county were overtopped or washed out. 8-APR

35 Flood Disasters of 2013 and 2014 Chaves County o The Pecos River remained above flood stage for several hours and above action stage for several days. o Farmlands flooded and evacuations took place along River Road. o Eight to 15 homes were reported damaged from flooding between Dexter and Lake Arthur. o Numerous roads were closed into Dexter. o Portions of NM 246 washed out between mile markers 36 and 61. o Several vehicles were rescued along the U.S. 70 relief route due to Rio Hondo flooding. o A water rescue also occurred along NM 246 near Berrendo Creek. o River Road was closed along the Pecos River, and a small neighborhood was evacuated where 3 houses flooded. Cibola County o 25 to 30 homes were partially under water around Bluewater Village. o The Grants West CenturyLink box was flooded, and cell phone services were temporarily out in the area. o County Road 23-A was closed due to high water. o One lane of Interstate 40 was closed due to a sink hole at the Tohajiilee exit. o Numerous accidents were reported along Interstate 40 due to deep water ponding near McCartys. o A total of 50 structures were damaged. Colfax County o A bridge was washed away northeast of Maxwell near Colfax County RoadA-7 with severe bank erosion along the Canadian River. o A large culvert was washed out south of the Raton Crews Airport along County Road A-6. o Severe bank erosion also occurred in this area of the Canadian River and Tinaja Creek. o Numerous other culvert and road wash outs were reported across Colfax County. 8-APR

36 Flood Disasters of 2013 and 2014 Doña Ana County o Suffered a breached earthen dam that caused flash flooding in Vado. o A small trailer park that was in the path of the breach was evacuated, and local street flooding occurred. o Flooding was reported throughout the cities of Anthony and La Union. o An earthen dam was Figure4-8: Sunland Park Flooding (September 2013) Courtesy, Doña Ana County Floodplain Administrator breached in La Union, causing significant flooding of homes and streets in the area. o Several mobile homes in Vado were flooded in an arroyo flood, forcing the evacuation of more than 25 people. o Sunland Park suffered flooding to four homes and an apartment complex. o A 50-year-old earthen dam was breached, washing out roads, damaging at least seven homes, and leaving approximately 300 residents without water and natural gas Guadalupe County o Major flooding occurred along El Rito Creek and at Power Dam. o NM 91 was closed between mile markers 0 and 9. o Large chunks of concrete from Power Dam were destroyed. o A railroad bridge over El Rito Creek was compromised, and engineers closed rail traffic to assess the bridge. o A bridge carrying a water line to Puerto de Luna was damaged extensively. o Low-lying areas near Brush Dam were flooded in Puerto de Luna. o City and county roads were damaged extensively. Otero County o Highway 244 was closed near Silver Lake with 5 to 6 feet of water over the road. o U.S. Highway 82 and U.S. Highway 130 were closed around Cloudcroft. o Two bridges in area canyons were washed out. o The floodwaters pushed over utility poles and trees and damaged some buildings. 8-APR

37 Flood Disasters of 2013 and 2014 San Juan County o Widespread flash flooding was observed in the City of Farmington o Numerous crashes and stalled vehicles were stranded in floodwater. o Several flooded and damaged drainage systems along Peace Valley Road, Hubbard Road, East Navajo Street, Main Street, Butler Street, Apache Street, and San Juan Boulevard caused widespread flooding of parking lots, low-lying areas, homes, and businesses. o North 562 Road in Fruitland was completely undermined, completely isolating nearly 300 residences. o A 72-inch pipe was damaged by floodwater o North 36 Highway was also damaged. Figure4-9: Stranded Vehicles (September 2013) Courtesy, San Juan County Floodplain Administrator San Miguel County o Las Vegas officials reported extensive flooding in Las Vegas and the surrounding county with greater damages and erosion along the Gallinas River. Evacuations were ordered in San Miguel County for areas along the river from Montezuma east to Las Vegas. o A major breach occurred on the Storrie Lake Diversion Figure 4-10: Washed out Road near Las Vegas (September 2013) Courtesy, Las Vegas Floodplain Administrator Channel. An estimated 1-year supply of water storage was lost for drinking water due to the breach. o NM 283 was closed west of Las Vegas. 8-APR

38 Flood Disasters of 2013 and 2014 o A sink hole was reported near the South Diversion River Crossing Catwalk with damage to wastewater components. o A total of 1,040 structures were damaged in this multi-day event. Sandoval County o The entrance road to the Bandelier National Monument park was undermined and nearly destroyed, and several points of infrastructure were damaged. o The Jemez River was out of its banks along NM 4 near San Ysidro, damaging a major fiber line and water supply infrastructure. o Several homes were flooded with up to 3 feet of water. o NM 4 was damaged. o Water entered several business and homes in Bernalillo. o NM 313 was impassible between Bernalillo and Tramway Road because of water and mud on the highway. o All roads washed out in the community of Sile. o Mud and water washed into several homes in the San Felipe Pueblo. Santa Fe County o Ten businesses were flooded in Madrid including Mine Shaft Tavern and nearby museums. o A mudslide was reported along NM 502 at a Totavi gas station, and power lines were knocked down in the area. o Flood waters were estimated at 6 to 7 feet deep in Bachelor Draw, which crosses Dinkle Road about 3 miles west of NM 344. Socorro County o The County Emergency Manager indicated that at least 16 roads in the county were washed out and severely damaged. o A breach in a levee on the Rio Puerco flooded several homes, and the community of San Francisco was evacuated. o The U.S. 380 bridge east of San Antonio was overtopped, and U.S. 60 was closed at mile marker 166. o NM 1 was also closed between mile markers 21 and 22 due to a wash out. o Water flooded several homes near San Antonio. Valencia County 8-APR

39 Flood Disasters of 2013 and 2014 o Forty families were evacuated from the Highland Meadow neighborhood due to flooding. o A culvert 25 feet wide by 10 feet deep was completely destroyed, and the National Guard assisted with the recovery by using a mobile bridge. o Seven structures were damaged FLOOD EVENTS The North American monsoon season of 2014 caused two Presidential Disaster Declarations in New Mexico: DR-4197 and DR-4199, both for severe storms and flooding DR-4197: New Mexico Severe Storms and Flooding DR-4197 was declared on October 6, 2014, for State, tribal, and local recovery efforts in the areas affected by severe storms and flooding in New Mexico from July 27 to August 5, The declaration was for public assistance and HMGP-only, and the amount has not been determined. Figure4-11: Flood damage in Otero County (September 2014), Courtesy, Otero County The flood incident period was preceded by a wetter than normal spring and one of the wettest Julys on record for New Mexico. Severe thunderstorms sparked floods in Albuquerque s South Valley and portions of eastern New Mexico over several days. Damage was widespread, affecting multiple jurisdictions. Initially the declaration included Rio Arriba, San Miguel, and Guadalupe Counties and the Pueblo of Acoma. It was amended on October 24, 2014, to include Lincoln, Otero, and Sandoval Counties and the Santa Clara Pueblo. Some of the more significant impacts of the storm events were as follows: Sandoval County o Rapid runoff from an estimated 2- to 4-inch downpour resulted in a breached levee that flooded several homes across from the Algodones fire station. 8-APR

40 Flood Disasters of 2013 and 2014 o A water-conveyance channel was overtopped, causing water to flow over service roads just west of the Santa Clara Pueblo. o The County Emergency Manager reported that dangerous flows overtopped the intersection of Indian Service Routes 601 and 602 on the Santa Clara Pueblo. o Residents of Sile were cut off due to flooding across a low-water crossing that formed due to repeated flooding from the Las Conchas burn scar. Santa Fe County o A berm in Santa Fe estimated to be 4 or 5 feet high was completely washed out along an arroyo. San Juan County o Heavy rains washed out two roads near Navajo Dam. Doña Ana County o Heavy rain in Hill caused the closing of Doña Ana Road, which was under water. o Several houses flooded, and damage to trucks and a horse trailer were reported. o Water entered the basement of the historic St. Mary s at the Hill Anglican Church. Guadalupe County o 5 to 6 feet of water from the Alamogordo Creek drained over Highway 156, stripping off pavement. o A half mile of fence line was torn out by floodwater. o A bunkhouse located near the water crossing had water damage, and water filled up the basement. o Two water retention ponds were overtopped. o Part of the Pacific Railroad tracks were left dangling because the base was washed out from the heavy rains. De Baca County Eddy County o Highway 84 in De Baca County was temporarily closed due to flooding from the Alamogordo Creek. 3 to 4 feet of water drained over the highway, making it impassable. o Heavy rain moved across the County and produced flash flooding in Carlsbad. 8-APR

41 Flood Disasters of 2013 and 2014 o Lea Street in Carlsbad was flooded, and cars were partially submerged according to a report from local law enforcement. Catron County o At least two roads were washed out near Beaverhead from heavy rainfall DR-4199: New Mexico Severe Storms and Flooding DR-4199 was declared on October 29, 2014, for flooding caused by the remnants of Tropical Depression Odile between September 15 and September 26. The declaration is for public assistance and HMGP-only, and the amount has not been determined. The declaration included Colfax, Eddy, Lea, Lincoln, Otero, San Miguel, Santa Fe, and Sierra Counties. Remnants of Hurricane Odile brought record rainfall to southeastern New Mexico over 4 days, causing extensive flooding and dangerous flash floods to the region. Some areas received more than 1 inch of rain in less than half a day. Significant events included: Doña Ana County o La Uñion and Berino had flooded roads. The American Red Cross opened a temporary shelter in Sunland Park after three families were flooded out of their homes. o The most significant flooding reported to date in the County was in Anapra. o The unincorporated village of La Uñion reported some flooding and debris at the intersection of Sentenario and Conejo Roads. o The Las Palmeras neighborhood in Berino reported flooding. One family had to evacuate their home and stays with relatives elsewhere until the floodwater subsided. o A train car waiting for water to recede from the tracks prompted a hazardous materials response in Rincon. Luna County o Sheriff's deputies saved a 78-year-old motorist after his vehicle was swept away by a strong current of floodwater. o Deming logged a 30-year record for September rainfall, with nearly 5 inches from the storm in a month that typically averages little more than 1 inch. o Extensive flood damage required closing Highway 152 indefinitely for repairs. 8-APR

42 Flood Disasters of 2013 and 2014 Eddy County o Severe flooding hit the oil and gas country of Eddy County, which saw between 1 and 5 inches of rain in different areas. o A surging stream trapped two Texas oilfield workers on their way home from work, killing one of them. o Flash flooding was reported in Carlsbad with rapidly flowing water up to four feet deep on San Jose Boulevard o Tansil Dam saw a rise in water of 1.5 feet in only ten minutes o Flooding was reported into the back of houses on James Street in the lower Tansil Dam area. o Road closures in the county included Whites City Road, Dog Town Road, and McDonald Road. Lea County o Highways 176 and 248 were closed due to flooding after heavy rain fell across the county. o Flash flooding was reported in several areas of the county due to rain over previously saturated soils. 8-APR

43 Recommended Mitigation Strategies SECTION FIVE RECOMMENDED MITIGATION STRATEGIES As described in SECTION Three, New Mexico has unique conditions that influence the nature of flooding in the State as well as the level of impacts. These conditions can also influence how the built and natural environments are affected by flooding. This section presents various recommendations for mitigating the potential impacts of flooding in New Mexico. The recommendations fall into the following categories: Floodplain mapping and identification Post-fire hydrology Alluvial fan identification Non-regulatory products Arroyo safety Flash flooding / extreme erosion 5.1 FLOODPLAIN MAPPING AND IDENTIFICATION New Mexico is a large State that is dependent on a few industries and the Federal Government for its economy. Outside the major population centers, the economy is more localized, and the population is spread out over vast acreage. New Mexico is a low populated state of about 2.8 Million people (United States Census Bureau, 2014). There are a few population centers which make up the majority of this, however the remaining population is spread over a vast 121,298 square miles (United States Census Bureau, 2014). Because of the size of the state it is difficult to allocate resources to provide flood risk analyses everywhere. As a result, fewer jurisdictions receive initial or updated mapping. The major population centers have zoning and regulatory authority that is adequate to control development and offer some regulatory protections to the population, limiting or restricting development in high hazard areas. In more remote locations, communities may be eager to encourage development and less prepared to educate the public about the risks from natural hazards ahead of an event. Resources in remote locations for assisting communities after a hazard event are also limited. Remote locations present challenges to providing adequate floodplain mapping to programs such as FEMA s Risk Mapping, Assessment, and Planning (Risk MAP), which can lead to inadequate information on existing maps or a lack of flood maps. Figure 5-1 Shows the status of Flood Insurance Rate Maps (FIRMs) in the State of New Mexico as of As can be seen in the figure, 11 counties had outdated or no FIRMS in APR

44 Recommended Mitigation Strategies Figure 5-1: Status of Flood Insurance Rate Maps in New Mexico as of 2014 (some maps in Doña Ana have been adopted) Unmapped Areas / Outdated Maps The majority of New Mexico is in great need of hazard mapping using updated topographic information. Because of the low population density in New Mexico, preparing FEMA flood maps has a relatively high cost per capita. Several areas are not mapped. Even in areas that are mapped, there are areas that still have not been identified as having flood hazards. Engineering and mapping that has been completed is generally done at an approximate level where the horizontal extent of the floodplain is known but not the flood elevation. With approximate mapping, it is difficult for community officials to use the information for mitigation purposes because elevation heights are not known. 8-APR

45 Recommended Mitigation Strategies Almost all of New Mexico s recent disaster declarations have been flood related, and all of the flood declarations since 2008 have been for public assistance (infrastructure) and HMGP only. This means that vital infrastructure such as roads and bridges are being affected by flooding. While approximate flood mapping allows for flood insurance rates to be determined, it does not provide information about whether bridges and roads may be overtopped or the true depth of flooding. Therefore, the heights that structures and infrastructure need to be elevated to are unknown. Newer, detailed maps would help communities build and regulate more appropriately. It is critical that this information rely on updated topographic information or survey where available. Outdated maps pose similar problems in some jurisdictions. Flood events can alter the floodplain over time or, in some cases, during a single event. The City of Corrales saw up to three feet of silt and sand deposited in areas and extreme erosion in other during the July 2013 floods. The silt and erosion caused significant changes in elevations in some areas, decreasing or eliminating the usefulness of effective FIRM maps for the area. There are several potential mitigation techniques that can be applied here. The first would be to update FIRMs which would allow communication of updated risk. Another would be to account for debris in drainage infrastructure since it is a known problem. One other option would be to apply bank stability and erosion protection in the areas where the silt and debris originates Strategies for Unmapped Areas and Outdated Maps The following strategies for unmapped areas and outdated maps are recommended for communities: Keep records of high water marks from floods and mark these areas/heights with signs to inform the public of the potential danger of floods. Utilize high water marks along with available mapping to develop more effective regulations for future development. 8-APR

46 Recommended Mitigation Strategies OCT. 2, FRIDAY THE 13TH 2013, FLOOD EVENT-- HIGH WATER MARKS & BRIDGES CITY OF LAS VEGAS, NM KNOWN BM HEIGHT OF KNOWN HEIGHT NAME OF ELEVATION BRIDGE BFE WATER MARK BRIDGE MILLS AVE FT FT. HISTORIC BRIDGE ST FT FT. PEDESTRIAN HIGH SCHOOL FT FT PLUS INDEPENDENCE FT FT. GRAND AVE. HWY FT FT Figure 5-2: High Water Marks taken after the September 13, 2013 flood (2013) Courtesy, Las Vegas Floodplain Administrator Use the records to help with flood mapping by marking the locations on existing maps and retaining backup information that will show reasons hazard identification is needed. Continue to make FEMA and the State aware of the need for mapping and updated mapping including depths of flooding at road crossings so that the information can be submitted to FEMA for entry into the Coordinated Needs Management System (CNMS) If possible, use available funding to identify and study potential flood hazard areas that can be used for development. Install in stream depth gauges and low water crossing signage Some available methods that should be considered include First Order Approximate or Zone A studies. First order approximate studies can help show where there are major changes that will affect a particular floodplain. Where Zone A studies are available, local knowledge and historic data can be combined to further refine best available data that can guide land use planning and regulate development. Any Zone A studies completed after 2007 have hydrology and hydraulic models associated with them. In larger population areas, especially those downstream of forested basins, a post-fire hydrology mapping methodology should be developed in which a percentage of the basin is modeled as if burned, and the resulting depth grids and velocity mapping are derived. This information would give floodplain management and community officials important information for mitigation activities and facility updating. See the next section for more information. 8-APR

47 Recommended Mitigation Strategies 5.2 POST-FIRE HYDROLOGY Impacts of Post-Fire Hydrology Wildfires in the higher elevations of New Mexico can significantly affect the hydrology downstream in the watershed. The vegetation upstream in watershed areas, especially on steeper slopes, is instrumental in absorbing and slowing down the flow velocity of water. When the vegetation in these mountainous areas is destroyed by a fire, areas downstream can expect higher flood levels and water moving with greater velocities during the summer monsoon season. The burning of the forest at high elevations also creates a virtually impervious surface because of the destruction of forest floor vegetation, burned tree material such as sap, and ash. The melted sap and other burned organic matter spread over the ground surface. Rainfall simply runs off this hardened surface, known as hydrophobic (water-repellent) soil, and there is little ground absorption of the water. The resulting diminished water storage and the steep slopes of upper watersheds create much greater runoff volume and velocity flows. The location, extent, and severity of wildfire and the subsequent rainfall intensity and duration cannot be known in advance, but it is possible to determine the likely locations and sizes of postwildfire debris flows using available geospatial data and mathematical models. Debris flow hazards can also be assessed for areas that have not burned but are at high risk of wildfire. The U.S. Geological Survey (USGS) has developed a model for estimating post-wildfire debris-flow probability and volume for watersheds originating in basins of concern or areas most at risk for loss of life and property. Flood frequency predictions and debris flow hazard assessments could help land managers plan for and mitigate the effects of post-fire flooding and debris flows (State of New Mexico, 2013). The debris flows can be estimated in areas that have not experienced wildfire but are at high risk for a wildfire. More information, including an application of the models after a fire, is provided in Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater Baldy Fire Burn Area, Southwestern New Mexico (USGS, 2012). Figure 5-2 shows the estimated probability of post-wildfire debris flow in the 2012 Whitewater-Baldy burn area. 8-APR

48 Recommended Mitigation Strategies Figure 5-3: Estimated probability of post-wildfire debris flows in the 2012 Whitewater-Baldy burn area, southwestern New Mexico 8-APR-15\\ 5-6

49 Recommended Mitigation Strategies The USGS has taken the analysis a step further and applied it to areas that have not experienced a burn to assist with identifying areas at risk from fire and also areas downstream of the firesusceptible areas that are most vulnerable to post-fire hydrology. An example of projecting the impacts of debris-flow hazards that would likely occur after a large wildfire/subsequent rainfall event is the USGS study of unburned areas of the Sandia and Manzano Mountains. The study, which used the empirical debris-flow models described in USGS (2012) along with fire behavior and burn probability models developed by the U.S. Department of Agriculture (USDA), is described in Tillery et al. (2014). Pre-wildfire studies such as Tillery et al. (2014) can identify the watersheds with the highest risk of debris-flow events. From the report, it was determined that the locations of watershed subbasins at greatest risk from debris-flow hazard were areas with the steepest slopes and simulated crown-fire behavior. With this information, resource managers can initiate watershed restoration efforts to protect against catastrophic wildfire. The results of the report can help select the optimal locations that are likely to provide the best return on investment based on risk. Figure5-4: Fire Danger sign in the east mountain area of Bernalillo County Courtesy, AECOM A recent example of the destructive power and repetitive nature of flood damage in burn scar areas is the Santa Clara Pueblo, which has received four flood disaster declarations since the highly destructive Las Conchas Fire in 2011 (also a disaster declaration). The USACE Albuquerque District studied the altered hydrology post-fire in Santa Clara Pueblo after the Las Conchas Fire. The hydrologic discharge increased from 25 percent to 400 percent for the 100-year flood (1- percent-annual-chance flood) after the fire. These changes are for the 2 to 3 months after the fire when the soils were extremely hydrophobic. While the vegetation will eventually grow back and the ash soil will wash away, an increase in hydrologic discharge will continue for several years until pre-fire conditions have returned. The post-fire watershed effects in the Pueblo were also ripe for massive landslides and debris flow. Retention basins designed to catch upstream flows could quickly fill with sediment and overtop and even breach. Another issue related to flood risk after fire is that with mountainsides denuded of protective vegetation, rainfall events cause severe erosion resulting in debris flows and damage to water control facilities that quickly become full of sediment. The drought/wildfire/flood cycle in the western United States from 2000 to the present has caused 8-APR

50 Recommended Mitigation Strategies extensive damage in many parts of New Mexico. Developed areas downstream from forested areas with steep terrain are especially vulnerable. USGS recently released a number of post-wildfire debris-flow hazard assessment reports for recent New Mexico wildfires including the 2011 Track Fire, the 2011 Las Conchas Fire, the 2012 Little Bear Fire, and the 2012 Whitewater-Baldy Fire (see Appendix A for links to full reports) Mitigation Strategies for Post-Fire Hydrology Below are some mitigation strategies communities can implement. Mitigation strategies before a fire: Maintain the health of the upper slopes forests to the extent possible. Thin trees that have died from drought and beetle damage. Remove understory vegetation through various means, including prescribed burn. Raise awareness of the risks of fire danger among residents and visitors to forest lands. Begin mitigation projects in areas prone to fire using practices in FIREWISE: Mitigation strategies in the burn scar after a wildfire: Figure 5-5: U.S. Senator Tom Udall (top), Santa Clara Pueblo Governor Walter Dasheno (left), and Kris Schafer inspect flooding in the pueblo in July 2012; Flooding following the 2011 Las Conchas Fire Courtesy, Santa Clara Pueblo Mulch and seed (usually by air) steep slopes in the upper watershed to help keep sediment in place and encourage new vegetative growth. Install check dams in the middle part of the watershed to control water discharge. Install debris catchment devices in the watershed and maintain them after floods. Consider additional retention basins, wider channels, and erosion protection measures in the lower watershed 8-APR

51 Recommended Mitigation Strategies Strategies for post-fire hydrology estimation: Use the USGS model to estimate post-wildfire debris-flow probability and volume. Utilize USGS post-wildfire debris-flow hazard assessment reports (See Appendix A) for recent New Mexico fires to target mitigation efforts and regulate development in higher high risk areas. Map potential extents of debris flow in the event of a fire/flood combination. For communities in fire-risk areas, consider higher levels of flood protection in the design of buildings and infrastructure. Mitigation strategies for structures that may be affected by flooding: Provide higher safety margins such as freeboard for elevated structures Resources: FEMA, USGS, USDA, USACE, State of New Mexico 5.3 ALLUVIAL FAN IDENTIFICATION Impacts of Alluvial Fan Flooding Alluvial fan flooding is a phenomenon that is prevalent in the arid, mountainous areas of the American West. An alluvial fan generally occurs when drainage from mountainous areas and valleys spills down onto a canyon floor carrying rocks, sediment, and debris. When the swift moving waters spread out onto the relatively flat canyon floor, the water spreads out into a wide fan or cone-shaped area. See Figures 5-5. The resulting movement of the water, while generally shallow, carries a great deal of debris and sediment that is left behind. Areas at greatest risk in an alluvial fan are in the apex part of the fan where the water (and accompanying debris) emerge from the mountain and start to spread. This area is subject to the deepest and highest velocity as well as the greatest concentration of debris. The flow paths of alluvial fans are uncertain and can change over time due to debris and sediment deposition and erosion. 8-APR

52 Recommended Mitigation Strategies Figure 5-6: Diagram of an Alluvial Fan The 2013 New Mexico State Hazard Mitigation Plan (State Plan) (State of New Mexico, 2013) describes the risk from alluvial fan flooding as follows: According to multiple studies, alluvial fan flood risk can cause high velocity flow (as high as feet per second) producing significant hydrodynamic forces, erosion/scour to depths of several feet, deposition of sediment and debris (to depths of several feet), deposition of sediment and debris (depths of feet have been observed), debris flows/impact forces, mudflows, inundation, producing hydrostatic/buoyant forces (pressure against buildings caused by standing water), flash flooding with little, if any, warning times (p. 97). 8-APR

53 Recommended Mitigation Strategies Due to the fact that alluvial fan flooding involves uncertainty regarding its flow path it may change over time due to sedimentation and debris deposition which may cause water to find new channels. Flood mitigation efforts need to incorporate buffers and safety factors because of the inherent uncertainty of the flow path. Another issue with alluvial fan flooding is that it generally strikes without warning. The State Plan also reports that the impacts of alluvial fans are generally underestimated or overlooked because of the long periods of time between flooding and the misconception that gently sloping terrain would not cause alluvial fan flooding. Mapping alluvial fans is critical to identifying them accurately and establishing regulations for development within them. While Zone AO on FIRMs may show alluvial fans, many parts of New Mexico have not been mapped recently or at all. Other methods of detection are evaluating surficial geologic maps in areas where alluvial fans exist. The State of Idaho uses a geologic analysis of more recent deposition and debris (Quaternary and latest Holocene alluvial-fan and wash deposits) to detect more active and therefore more high-risk alluvial fans (Garceau et al. 2013). There is a need for alluvial fan identification and mapping. According to the State Plan, there are no confirmed studies of alluvial fan flooding risk in New Mexico. Some FEMA Flood Insurance Rate Map studies have included analyses of alluvial fan flooding. However, these are not near complete. Areas along the base of the Rocky Mountains, and other Mountains throughout the state should be identified at risk before development continues to encroach on alluvial areas as it has in Maricopa County, Arizona. Communities like Alamogordo, Las Cruces, and Albuquerque could benefit from these determinations where development is proceeding toward the mountainous areas Strategies for Identifying and Mitigating Alluvial Fans The recommended strategies for identifying alluvial fans in New Mexico are as follows: Seek mapping opportunities with FEMA Region VI and New Mexico Cooperating Technical Partners (CTPs). Engage local universities and agencies that can provide assistance in identifying soil types using tools such as the Natural Resource Conservation Service s (NRCS) Soil Survey Geographic Database (SSURGO). Install warning systems in the upper reaches of the watershed using weather forecasts and rainfall information (e.g., rain gauges). Install check dams upstream. 8-APR

54 Recommended Mitigation Strategies Protect existing structures at the base of the fan by using nonstructural mitigation measures such as elevation and floodproofing. Acquisition could be used where the channels are deepest and consistent debris flows occur. Use structural mitigation as a last resort. For the protection of future development, use land use planning to avoid placing certain types of development and infrastructure to avoid the most severe impacts of alluvial fan flooding. As an example, the Idaho Local Land Use Planning Act requires each community in the State to address natural disasters in the community land use plan. If identified, the data can be used to manage appropriate types of development in the alluvial fan. While leaving the ground undeveloped may be the best course, outdoor recreational uses are also compatible. According to the USGS, In high-risk zones where development and reconstruction are inevitable, steps such as orienting a building so that its length is oriented parallel to the direction of flow will minimize the width of building exposed to a debris flow. Additionally, orienting streets parallel to the downslope direction of the fan allows the streets to serve as overflow channels, limiting potential damage to structures. Monitoring, warning, and evacuation are non-structural approaches to hazard mitigation that reduce potential loss of life (USGS, n.d) 5.4 NON-REGULATORY PRODUCTS FEMA s Risk MAP program provides communities with flood risk information and tools that can be used to better understand flood risk to inform citizens and officials (e.g., floodplain administrators, planners, building permit officials, emergency managers, engineers), enhance mitigation plans, and prepare mitigation grants. Risk MAP provides more understandable flood risk information and more accurate flood maps than previous NFIP mapping efforts. Risk MAP also provides flood risk assessment tools, and outreach support. A recent innovation are the nonregulatory products, which are derived from flood mapping efforts, and are tailored to meet the informational needs of local, tribal, and State officials as well as the public. These products include: Flood risk datasets Changes Since Last FIRM Flood Depth and Analysis Grids Flood Risk Assessment Areas of Mitigation Interest Flood risk products Flood Risk Database 8-APR

55 Recommended Mitigation Strategies Flood Risk Report Flood Risk Map Non-regulatory products are not always part of the Risk MAP package and need to be requested. They can also be other products necessary for the unique characteristic of the state such as analysis of debris flows. These products allow officials to prepare new (or build on existing) mitigation plans, enhance public safety management activities, identify areas of high flood risk that may require use of flood-resistant designs and construction materials, identify potential mitigation projects, and collaborate with other officials on important planning processes where land suitability is a key consideration (e.g., comprehensive plans, capital improvement plans). Communities could also generate these items with available FIRM information and other data that is available. The remainder of this section describes the non-regulatory products with the most potential to help better portray flood risk in New Mexico. These products are as follows: Changes Since Last FIRM (Section 5.4.1) Flood Depth and Analysis Grid Datasets, which include the Depth Grid, the Velocity Grid, and the Percent Change of Flooding Over 30-Year Period Grid (Section 5.4.2) Flood Risk Assessment (Section 5.4.3) Changes Since Last FIRM The Changes Since Last FIRM (CSLF) dataset is provided to help communities understand the changes to the extent of the mapped floodplain since the prior FIRM was published. It can help mitigation planners understand which areas are now at greater flood risk for future mitigation plan updates. It can also demonstrate how flood risk has changed historically to give a better understanding of how it will change in the future. This is especially important in New Mexico that has changing flood patterns in areas with alluvial fans and arroyos. In rapidly urbanizing areas, the increased impervious surface may change floodplain dynamics. Figure 5-7 is an example of a CSLF map that includes areas that have been added to the Special Flood Hazard Area (SFHA) and floodway as well as the areas that have been removed. 8-APR

56 Recommended Mitigation Strategies Flood Depth and Analysis Grid Figure 5-7: Visualization of CSLF The multiple Flood Depth and Analysis Grid datasets assist with determining and visualizing flood risk. The datasets include Depth Grids, Velocity Grids, and the Percent Chance of Flooding Over 30-year Period Grid. The Depth and Velocity Grids can be used to identify areas of higher risk within the SFHA that could then be used to develop higher regulatory standards. For example, knowing the depth of flooding from multi-frequency flood events at various locations could influence siting of future infrastructure. These datasets could also help guide strategic infrastructure investment and the resulting future land use in rapidly growing areas. Descriptions of the Depth Grid, Velocity Grid, and the Percent Chance of Flooding Over 30- Year Period Grid are as follows: The Depth Grid represents flood depth values across the entire mapped floodplain to enable an understanding of true flood risk in the identified floodplain. This dataset can help enlist the support of elected officials and key local leaders by identifying areas of highest flood risk according to frequency and magnitude (depths) for possible mitigation actions, even if that action is to maintain property as open space. Figure 5-8 shows how flood depth across the SFHA can vary and range from very shallow flooding (less than 1 foot) to deep flooding (over 3 feet). This information can encourage local officials to consider higher standards or to avoid areas of deeper flooding. 8-APR

57 Recommended Mitigation Strategies Figure 5-8: Visualization of the depth grid in 1% chance (100-year) floodplain The Velocity Grid describes the average flood velocity for a specific location in the mapped floodplain for a given percent-annual-chance flood frequency profile. Due to the steep slopes in many New Mexico communities and the chance of flash floods, velocity grids can help communities determine which areas have potential for high flood velocities that would endanger people and result in additional damage to infrastructure. High velocity floodwater can sweep people away, cause erosion and scour to infrastructure, and where strong enough, can rip through roads and sweep buildings off their foundations. Both Depth and Velocity Grids can help with evacuation planning and implementation by showing which roads and bridges would be flooded first and which ones would be subject to fast-moving water so local officials can direct evacuation routes and shelter sites away from these areas. The Percent Chance of Flooding Over 30-Year Period Grid shows the likelihood of flooding at least one time during a 30-year period to relate to a typical mortgage lifespan for all areas within the identified floodplain. This grid can help frame flood risk from the perspective of the homeowner using a timeline that is familiar to them. For homeowners who have not experienced a flood, it can show the relative risk in the future. For areas with 8-APR

58 Recommended Mitigation Strategies a high chance of flooding in the 30-year time frame (over 40 percent), it can influence the homeowners to take mitigation actions. Figure 5-9 is an example Percent Chance of Flooding Over 30-Year Period Grid. Figure 5-9: Visualization of the Percent Chance of Flooding Over 30-Year Period Grid Flood Risk Assessment The Flood Risk Assessment dataset helps guide community mitigation efforts by quantifying future potential flood losses and shows the location of areas most likely to be severely affected by future floods in terms of dollar losses. This dataset, which is normally derived using Hazards U.S. (Hazus), estimates potential flood losses for different flood scenarios, and provides results at the census block level. These flood loss estimates provide valuable information for local planners and emergency managers to develop a mitigation plan vulnerability assessment and then strategies based on the vulnerability assessment. This information can be used by local and tribal officials to scope out projects in areas where flood mitigation actions may produce the highest return on investment. Although Hazus comes prepackaged with census-based general building stock and critical facilities data, local officials may have more up-to-date data that could be used by a mapping partner such as a Cooperating Technical Partner (CTP) to conduct the flood loss analysis and refine the loss estimates. Communities are encouraged to use the Flood Risk Assessment data to form a scientific basis from which their mitigation strategy is developed. See FEMA s Operating Guidance 6-11: User Guidance for Flood Risk Datasets and Products (FEMA, 2011) for more information on non-regulatory products. 8-APR

59 Recommended Mitigation Strategies Strategies for Non-Regulatory Products The recommended strategies for communities for non-regulatory products are as follows: Request the non-regulatory products when the community is being remapped through the Risk MAP process; work with CTPs to see if they can provide this type of information. Partner with other agencies, such as USACE, USGS or U.S. Forest Service, to share data and enhance risk identification tools and awareness. Use the non-regulatory products to enhance local and tribal mitigation plans, develop mitigation grant applications, and guide development decisions including more restrictive zoning in high flood hazard areas. Use CSLF to predict potential areas of future change to use for regulating development. Use depth grids and velocity grids for risk outreach to communities and to focus mitigation efforts. Use velocity grids with depth grids to inform evacuation strategies in the community. Use the Percent Chance of Flooding Over a 30 year period grid to inform homeowners of the risk of flooding within the life of their mortgage. Use flood risk assessment data to determine projects that would reduce the most future potential losses. Use a combination of these datasets to form an area of mitigation interest dataset that can be used to prioritize mitigation and outreach efforts. 5.5 ARROYO SAFETY Arroyos are typically dirt-lined channels and waterways and are usually in areas where natural drainage occurs to convey water from areas of higher elevation to rivers and streams. For example, in the Albuquerque area, arroyos carry water from the mountains or mesas to the Rio Grande as quickly as possible. Arroyos in populated areas typically wind through cities and towns and are therefore accessible to the public. In many instances, because of their linear right-of-way and local ordinances not to build next to them, arroyos are sometimes Figure 5-10: San Miguel County Arroyo Courtesy, Las Vegas Emergency Preparedness 8-APR

60 Recommended Mitigation Strategies flanked by bike trails, adding a recreational amenity on the land adjacent to them. Figure 5-11: Flooding along the Osuna Bike Notch (July 2013) Courtesy, Albuquerque Metro Arroyo and Flood Control Authoriy for even the strongest swimmer to get away from the arroyo. However, the fact that arroyos are typically dry the vast majority of the time presents a temptation for play including walking, jogging, skateboarding, rollerblading. While it can be a sunny day in the area directly over the arroyo, rain in the mountains many miles away can occur and can bring water travelling up to 40 miles per hour into the arroyo. Within minutes or even seconds, water that entered the arroyo several miles away can sweep people away and lead to injury or death. The rapidly moving water contains a strong undertow and may also carry debris, both of which make it difficult The fact that these arroyos are so common and that they are rarely seen with water in them leads to a sense of complacency or unfamiliarity with their dangers. Even to those who may know of their flooding potential, the lure of using them as a playing surface is strong Mitigation Strategies for Arroyo Safety The recommended strategies for arroyo safety are as follows: Include education for younger children and signs and postings where arroyos intersect with roads and public access to trails. Promote the website for awareness of the risks of arroyos. Use pictures and films of the arroyos when full of water to demonstrate their danger. Prepare written and video testimonies by those who have been rescued from a full arroyo to help bring a voice to the danger. Wherever possible, use fencing to limit access to arroyos, but the length of fencing that would be needed and the difficulty in limiting access mean that education will continue to be the primary focus of safety in the arroyos. Develop partnerships between local or tribal governments, soil and water conservation districts, and flood control authorities to help provide the educational resources needed. 8-APR

61 Recommended Mitigation Strategies Depending on the location, consider installing flood warning systems upstream in the arroyo as an effective means of providing rapid notification to downstream areas as storm water enters the arroyo in the higher elevations. Create a plan to monitor and evacuate arroyos in the event of a flood. 5.6 FLASH FLOODING / EXTREME EROSION Flash flooding is the most common type of natural disaster event in New Mexico and typically results in damage to infrastructure and roads. For the purposes of this report, flash floods are events caused by normal rainfall events and not the erosion/debris flows resulting from rainfall events after large wildfire events. Erosion can play a significant role in flash floods. Extensive erosion damage can occur with major flooding. Erosion results in access disruption, road closures, driving hazards, drainage facility damage and blockage, and sedimentation. Erosion can occur rapidly during a storm event or can occur over time due to minor storms or breaks in water lines. Accelerated soil erosion has created problems ranging from loss of productive agricultural soil to displacement of human structures to sediment buildup in water reservoirs. Figure 5-12: Severe Erosion in Valencia County (September 2013) Courtesy, Valencia County Floodplain Administrator The detachment and transportation of soil particles by water can cause sheet erosion, rill erosion, or gully erosion. Sheet erosion occurs with soil being removed in a uniform manner across the surface but is often accompanied by tiny channels cut into the surface, creating rill erosion. Where the volume of runoff water is more concentrated, larger channels or gullies may occur within the landscape, creating gully erosion. Rill and gully erosion can cause serious land use problems. Storm events in New Mexico can result in flash floods, which also creates serious rill and gully erosion. Flash floods and the resulting erosion and potential debris flows lead to damage to infrastructure and exacerbate flooding. In the City of Corrales, severe silt and debris deposits clogged the grate at Corrales Heights Dam during the July 2013 floods, allowing minimal flood water through the open spillway. Erosion can impact water quality and recreational amenities like streams. The 8-APR

62 Recommended Mitigation Strategies flooding in mountainous areas can sever important access roads. Severe flash flooding can cause channels to migrate. Erosion over many years can create unstable slopes that lead to landslides. Undercutting of a slope reduces the slope s resistance to the force of gravity by removing much-needed support at the base of the slope (State of New Mexico, 2013), which can also lead to a landslide as well as the weight of saturated water in the soil on a slope. Erosion affected roads and infrastructure in New Mexico after the flooding in 2013 and Figure 5-13: Severe Erosion threatening homes on San Juan River, NM Mitigation Strategies for Erosion / Flash Flooding The recommended mitigation strategies for erosion and flash flooding are as follows: For existing development, make mitigation measures site-specific and in line with the available budget. Individual property protection may be appropriate for residential structures as well as armoring channel banks to resist erosion. Drainage retention to absorb excess storm water and reduce velocity is another potential measure. Infrastructure subject to flash flooding and erosion may need to be elevated and then armored. For example, roads are typically subject to damage by flash floods and erosion. Elevating the road to 8-APR