FLOOD INSURANCE STUDY

Transcription

1 FLOOD INSURANCE STUDY SANTA FE COUNTY, NEW MEXICO AND INCORPORATED AREAS Santa Fe County COMMUNITY NAME COMMUNITY NUMBER COCHITI, PUEBLO OF EDGEWOOD, TOWN OF ESPANOLA, CITY OF NAMBE, PUELBO OF POJOAQUE, PUEBLO OF SAN ILDEFONSO, PUELBO OF SANTA CLARA, PUEBLO OF SANTA FE, CITY OF SANTE FE COUNTY UNINCORPORATED AREAS SANTO DOMINGO, PUEBLO OF TESUQUE, PUEBLO OF EFFECTIVE DATE: PRELIMINARY FEBRUARY 18, 2011 FLOOD INSURANCE STUDY NUMBER 35049CV001B

2 NOTICE TO FLOOD INSURANCE STUDY USERS Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study (FIS) report may not contain all data available within the Community Map Repository. Please contact the Community Map Repository for any additional data. Part or all of this Flood Insurance Study may be revised and republished at any time. In addition, part of this Flood Insurance Study may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the Flood Insurance Study. It is, therefore, the responsibility of the user to consult with community officials and to check the community repository to obtain the most current FIS components. Initial Countywide Effective Date: June 17, 2008 Revised Countywide Effective Dates:

3 TABLE OF CONTENTS Table of Contents Volume INTRODUCTION... 1 Page 1.1 Purpose of Study Authority and Acknowledgments Coordination AREA STUDIED Scope of Study Community Description Principal Flood Problems Flood Protection Measures ENGINEERING METHODS Hydrologic Analyses Hydraulic Analyses Refinement Vertical Datum FLOODPLAIN MANAGEMENT APPLICATIONS Floodplain Boundaries Floodways INSURANCE APPLICATION FLOOD INSURANCE RATE MAP OTHER STUDIES LOCATION OF DATA BIBLIOGRAPHY AND REFERENCES FIGURES Figure 1 Floodway Schematic i

4 Table of Contents Volume 1 TABLES Table 1 CCO Meeting Dates... 3 Table 2 Stream Reaches Studied by Detailed Methods... 3 Table 3 Stream Reaches Studied by Limited Detailed Methods... 4 Table 4 LOMRs Incorporated into Initial Countywide FIS dated June 17, Table 5 LOMRs incorporated in this PMR... 6 Table 6 Stream Name Changes... 6 Table 7 Summary of Discharges Table 8 Stream Hydrologic Methods Used Table 9 Summary of Roughness Coefficients Table 10 Stream Hydraulic Methodology Table 11 Floodway Data Table Table 12 Community Map History EXHIBITS Exhibit 1 - Flood Profiles Admin Arroyo Panels 01P-02P Arroyo Barranca Panels 03P-11P Arroyo de La Paz Panels 12P-15P Arroyo de La Piedra Panels 16P-25P Arroyo de Los Amigos Panels 26P-30P Arroyo de Los Antores Panel 31P Table of Contents Volume 2 EXHIBITS continued Exhibit 1 - Flood Profiles (continued) Arroyo de Los Chamisos Panels 32P-64P Arroyo de Los Chamisos (North Fork) Panels 65P-67P Arroyo del Rosario Panel 68P Arroyo En Medio Panels 69P-87P Arroyo Hondo Panels 88P-113P Arroyo Hondo Split Flow Panels 114P-116P Arroyo Mascaras Panels 117P-120P Arroyo Ranchito Panels 121P-128P ii

5 Table of Contents Volume 3 EXHIBITS continued Exhibit 1 - Flood Profiles (continued) Arroyo Saiz Panels 129P-133P Arroyo Seco Panels 134P-135P Arroyo Torreon Panel 136P Bachelor Draw Panels 137P-138P Big Tesuque Creek Panels 139P-144P Canada Ancha Panels 145P-158P Canada Rincon Panels 159P-162P East Arroyo de La Piedra Panels 163P-170P Little Tesuque Panels 171P-176P NE Arroyo de Los Pinos Panels 177P-182P Pojoaque River Panels 183P-187P Rio Tesuque DS Panel 188P Rio Tesuque US Panels 189P-197P Santa Cruz River Panels 198P-201P Santa Fe River Panels 202P-216P Unnamed Stream 31 Panels 271P-224P Water Street Panel 225P Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Map iii

6 FLOOD INSURANCE STUDY SANTA FE COUNTY, NEW MEXICO AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and supersedes the FIS reports and Flood Insurance Rate Maps (FIRMs) in the geographic area of Santa Fe County, New Mexico, including the Cities of Española and Santa Fe; the Town of Edgewood; the Pueblos of Cochiti, Nambe, Pojoaque, San Ildefonso, Santa Clara, Santo Domingo and Tesuque; and the unincorporated areas of Santa Fe County (hereinafter referred to collectively as Santa Fe County), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of This study has developed flood risk data for various areas of the community that will be used to establish actuarial flood insurance rates. This information will also be used by Santa Fe County to update existing floodplain regulations as part of the Regular Phase of the National Flood Insurance Program (NFIP), and by local and regional planners to further promote sound land use and floodplain development. Minimum floodplain management requirements for participation in the NFIP are set forth in the Code of Federal Regulations at 44 CFR Please note that the City of Española is geographically located both in Rio Arriba (Reference 1) and Santa Fe Counties. The Pueblo of Santa Clara is geographically located in Rio Arriba, Sandoval (References 1 and 2) and Santa Fe Counties. The Pueblos of Cochiti, San Ildefonso and Santo Domingo are geographically located in both Sandoval (Reference 2) and Santa Fe Counties. The Town of Edgewood is geographically located in Bernalillo (Reference 3), Santa Fe and Torrance Counties. See these separately published FIS reports and FIRMs for the countywide map dates and flood hazard information outside of Santa Fe County. In some states or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum Federal requirements. In such cases, the more restrictive criteria take precedence, and the state (or other jurisdictional agency) will be able to explain them. 1.2 Authority and Acknowledgments The sources of authority for this Flood Insurance Study are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of Information on the authority and acknowledgments for each of the previously printed FIS and FIRMs for communities within Santa Fe County was compiled and is shown below. In the original City of Santa Fe study, the hydrologic and hydraulic analyses were prepared by Bohannan-Huston, Inc., for the Federal Emergency Management Agency (FEMA) under Contract No. H-4061 for the following streams: the Santa Fe River, Arroyo de la Piedra, Arroyo de los Chamisos, Arroyo de los Chamisos North Fork, Arroyo Mascaras, Arroyo Saiz, Arroyo Torreon, Canada Ancha, and Canada Rincon. The study was completed in January The hydrologic and hydraulic analyses for the Santa Fe River, Arroyo de los Chamisos, and Arroyo Hondo were prepared by Bohannon-Huston, Inc. for FEMA under Contract No. EMW-85-C This work was completed in October The information for the Santa Cruz River was obtained from the limited detail flood insurance study for Rio 1

7 Arriba County, prepared by the U.S. Geological Survey (USGS) under Inter-Agency Agreement No The Santa Cruz study was completed in April In the 1993 City of Santa Fe FIS revision, the hydrologic and hydraulic analyses for the Santa Fe River, Right Over Bank (ROB) Flow path, and Arroyo Saiz were prepared by the U.S. Army Corps of Engineers (USACE), Albuquerque District, for FEMA under Inter-Agency Agreement No. EMW-89-E This work was completed on December 19, As part of the update for the City of Española, New Mexico, Rio Arriba and Santa Fe Counties Flood Insurance Study, a portion of the Santa Cruz River was studied by Watershed Concepts and completed in February Initial Countywide FIS The hydro1ogic and hydraulic analyses for the initial countywide study were performed by Mapping Alliance Partnership VI (MAPVI) for FEMA Region VI, under Task Order J014 of Contract No. EMT-2002-CO MAPVI was a joint venture of URS Corporation, Greenhorn & O Mara, and Spectrum Mapping. These studies were completed in November This Physical Map Revision (PMR) and FIS Update For this PMR and FIS update, Risk Assessment, Mapping, and Planning Partners (RAMPP) conducted approximately 13 miles detailed study along the Arroyo Hondo, Rio Tesuque and Santa Cruz River; 32 miles of limited detailed study along the Arroyo Barranca, Arroyo de La Paz, Arroyo de La Piedra, Arroyo de Los Amigos, Arroyo de Los Antores, Arroyo En Medio, Arroyo Hondo, Arroyo Ranchito, Arroyo Saiz, Big Tesuque Creek, Canada Ancha, East Arroyo de La Piedra, NE Arroyo de Los Pinos, Little Tesuque Creek, Rio Tesuque US and Unnamed Stream 31; and 52 miles of approximate analysis in Santa Fe County. Also, several Letters of Map Revision (LOMRs) were incorporated into this revision and are listed in section 2.1. This work was completed in December 2010 under Contract No. HSFEHQ-09-D Base map information shown on this FIRM was provided in digital format by City of Santa Fe, 2009 and 2010; and Santa Fe County, Additional information was taken directly from the previous Countywide FIRM dated June 17, Other information was photogrammetrically compiled at a scale of 1:12,000 from U.S. Department of Agriculture aerial photography dated The projection used in the preparation of this map was New Mexico State Plane, Central Zone (FIPS 3002). The horizontal datum was NAD83, GRS80 spheroid. Differences in datum, spheroid, projection or State Plane zones used in the production of FIRMs for adjacent jurisdictions may result in slight positional differences in map features across jurisdiction boundaries. These differences do not affect the accuracy of this FIRM. Flood elevations on this map are referenced to the North American Vertical Datum of Coordination The purpose of an initial Consultation Coordination Officer s (CCO) meeting is to discuss the scope of the FIS. A final CCO meeting is held to review the results of the study. The known dates of the initial and final CCO meetings held for the previous FIS for Santa Fe and the incorporated communities within its boundaries are shown in Table 1, CCO Meeting Dates. 2

8 Table 1 CCO Meeting Dates Community Name Initial CCO Date Final CCO Date City of Santa Fe May 1976 April 24, 1979 Unincorporated Areas of Santa Fe County February 13, 1985 November 17, 1987 Initial Countywide * July 13, 2006 * Date not available 2.0 AREA STUDIED For this countywide PMR and FIS update, an initial CCO meeting was held on November 4, 2009, and was attended by representatives of the community, the study contractor, and FEMA. The final CCO meeting was held on, and was attended by representatives of the community, the study contractor, and FEMA. 2.1 Scope of Study This FIS covers the geographic area of Santa Fe County, New Mexico, including the incorporated communities listed in Section 1.1. The areas studied by detailed and approximate methods were selected with priority given to all known flood hazards and areas of projected development. Flooding sources studied by detailed methods, along with the limits of study, are shown in Table 2, Stream Reaches Studied by Detailed Methods. Streams studied by Limited Detailed Methods are shown in Table 3. Approximate analyses were used to study those areas having a low development potential or minimal flood hazards. The scope and methods of study were proposed to, and agreed upon, by FEMA and community officials. Table 2 Stream Reaches Studied by Detailed Methods Stream Name Downstream Limit Upstream Limit Arroyo de La Piedra Confluence with Arroyo Approximately 2,030 feet Mascaras upstream of Bishops Lodge Road Arroyo de Los Chamisos Arroyo de Los Chamisos (North Fork) Arroyo del Rosario Approximately 550 feet upstream of the confluence with Arroyo Hondo Confluence with Arroyo de Los Chamisos Upstream face of Rio Grande Avenue Approximately 2,560 feet upstream of road to St. John College Approximately 50 feet upstream of Burlington Northern and Santa Fe (BNSF) Railway Approximately 2,400 feet upstream of Rio Grande Avenue 3

9 Table 2 Stream Reaches Studied by Detailed Methods - continued Stream Name Downstream Limit Upstream Limit Arroyo Hondo Arroyo Mascaras Arroyo Torreon Canada Ancha Canada Rincon Confluence Arroyo de Los Chamisos Approximately 1,400 feet upstream of BNSF Railroad Confluence with Santa Fe River Confluence of Arroyo de la Piedra with Arroyo Ranchito Confluence with Santa Fe River Approximately 1,160 feet upstream of West Alameda Street Confluence with Santa Fe River Approximately 1,200 feet upstream of Cerro Gordo Confluence with Arroyo Mascaras Approximately 930 feet upstream of State Highway 599 / Veteran s Memorial Highway Rio Tesuque (Upstream) 2,100 feet downstream of confluence with Unnamed Stream 31 Confluence of Big Tesuque Creek and Little Tesuque Creek Santa Cruz River Santa Fe County Boundary Approximately 8,075 feet upstream of State Road 106 Santa Fe River Water Street Confluence of Santa Fe River Approximately 300 feet upstream Tributary 7 of Cerro Gordo Road Confluence with Santa Fe River Cathedral Place Table 3 Stream Reaches Studied by Limited Detailed Methods Stream Name Downstream Limit Upstream Limit Admin Arroyo Approximately 1,100 feet upstream of Confluence with Rio Tesuque Approximately 4,700 feet upstream of US Highway 84/285 Arroyo Barranca Confluence with Arroyo Mascaras Approximately 1,600 feet upstream of Camino Encantado Arroyo de La Paz Arroyo de La Piedra Arroyo de Los Amigos Arroyo de Los Antores Confluence with Arroyo de Los Antores Approximately 2,030 feet upstream of Bishops Lodge Road Confluence with Arroyo de Los Chamisos Confluence with Arroyo de Los Chamisos Approximately 900 feet upstream of Rodeo Road Approximately 1,400 feet upstream of Barranca Road Approximately 1,400 feet upstream of Saint Michaels Drive Intersection of Calle de los Ninos and Calle Campeon 4

10 Table 3 Stream Reaches Studied by Limited Detailed Methods - continued Arroyo En Medio Arroyo Hondo Arroyo Ranchito Stream Name Downstream Limit Upstream Limit Confluence with Arroyo de Los Chamisos Approximately 1,400 feet upstream of BNSF Railroad Confluence with Arroyo de La Piedra Approximately 1,200 feet upstream of Cloudstone Drive Approximately 500 feet downstream of Happy Trails Approximately 600 feet upstream of Camino Encantado Arroyo Saiz Confluence with the Santa Fe River Approximately 200 feet downstream of Gonzales Road Arroyo Seco Santa Fe County Boundary US Highway 84/285 Bachelor Draw Upstream face of Abajo Drive Approximately 70 feet downstream of Quiet Valley Loop Big Tesuque Creek Confluence with Rio Tesuque Approximately 2,600 feet upstream of Bauer Road Canada Ancha East Arroyo de La Piedra Approximately 1,200 feet upstream of Cerro Gordo Road Confluence with Arroyo de La Piedra Approximately 1,300 feet upstream of La Entrada Approximately 3,500 feet upstream of Calle Conejo Little Tesuque Creek Confluence with Rio Tesuque Approximately 1,300 feet upstream of Bauer Road NE Arroyo de Los Pinos Pojoaque River Upstream face of Saint Michaels Drive Approximately 2,260 feet upstream of Confluence with the Rio Grande Approximately 1,200 feet upstream of Luisa Street Confluence of Rio Tesuque and Pojoaque Creek Rio Tesuque (Downstream) Confluence with Pojoaque River Downstream face of US Highway 502 Unnamed Stream 31 Confluence with Rio Tesuque Approximately 500 feet upstream of Sangre De Cristo Drive Table 4 lists LOMRs that were incorporated into the initial countywide update for Santa Fe County. Table 4 LOMRs Incorporated into Initial Countywide FIS dated June 17, 2008 Case Number Effective Date Flooding Source Community P 6/14/1999 Arroyo De Los Chamisos City of Santa Fe P 9/24/2003 Canada Ancha Unincorporated Areas 5

11 Table 5 lists LOMRs that were incorporated into this PMR update and FIS Update. Table 5 LOMRs incorporated in this PMR Case Number Effective Date Flooding Source Community A 1/6/1999 SW Arroyo de los Pinos City of Santa Fe P 11/24/2009 SW Arroyo de los Pinos City of Santa Fe P 1/13/2010 Canada Rincon City of Santa Fe P 1/13/2010 Arroyo del Rosario City of Santa Fe Table 6, Stream Name Changes, lists those streams whose name has changed or differs from that published in the previous FIS for Santa Fe County or any of the communities within. Table 6 Stream Name Changes Old Name New Name Old Name New Name Arroyo de Los Chamisos (North Fork) (Portion) Arroyo de Los Chamisos (South Fork) SW Arroyo de Los Pinos Cloudstone Arroyo Tributary to Arroyo de Los Chamisos Unnamed Tributary to Arroyo de Los Chamisos Arroyo de Los Amigos Arroyo de Los Amigos 2.2 Community Description Santa Fe County is located in north-central New Mexico, northeast of the City of Albuquerque. It is bordered by San Miguel County to the east; Torrance County to the south; Bernalillo County to the southwest; Sandoval and Los Alamos Counties to the west; Rio Arriba County to the north; Mora County to the northeast. The population of Santa Fe County in 2009 was estimated at 147,532 (Reference 4). The area is growing at a moderate rate, and continued growth is anticipated in the future. Presently, the main economic sources are tourism, government operations, trade, agriculture, manufacturing, and mining. The area has a significant amount of tourism income due to the historic and cultural activities, as well as the pleasant climate and recreational facilities. The Santa Fe Trail was a major thoroughfare from the east in the 1800s. This trail, along with the railroad, made the area a major trade center in the southwest. While trading was a major economic factor, the area also prospered from agriculture, lumbering, and various mining interests. Santa Fe County is bordered by the Sangre de Cristo and Jemez Mountain ranges to the north, east, and west, while the southern portion of the county lies in the central New Mexico plains. Gently sloped areas characterize much of the county, however slopes can be very steep (over 40 degrees), especially in the upper reaches of the watersheds. Vegetation in the high mountain areas consists of a variety of forest cover, including large spruce, pines, juniper, and piñon trees. Heavy understory vegetation of brush, grasses, and wildflowers exists. In the lower elevations near the City of Santa Fe, vegetation changes dramatically due to the heat and lack of moisture. Sparse areas of 6

12 smaller piñon and juniper exist with shrub brush; however, the largest percentage of cover consists of gramma and other grasses scattered across the exposed sandy soil. Generally, the climate around Santa Fe County is semiarid below elevations of 7,000 feet. The high mountain streams receive a significant amount of snowfall; however, for the most part, the populated areas of the County receive a majority of their moisture from rainfall in the summer months. The average annual precipitation in the City of Santa Fe is approximately 14 inches (Reference 5). Average high temperatures range from 70 to 80 degrees Fahrenheit (ºF), while average low temperatures range from 40-50ºF. The City of Santa Fe is located in the heart of Santa Fe County and is the oldest capital city in the United States. Various Indian tribes were the original inhabitants of the county. In the early 1600s, the Spanish began settling in the area. The northern Pueblo Indians drove the Spaniards out of the City of Santa Fe in 1680 and they held the settlement until 1692, when the Spanish recaptured the capital. In 1821, Mexico won independence from Spain, and the area that is now Santa Fe County was officially under Mexican jurisdiction. The U.S. occupied the area in 1846 and made New Mexico a U.S. Territory. The City of Santa Fe has an estimated population of 73,979 in 2009 (Reference 4). The Santa Fe River and Arroyo de Los Chamisos flow through the City of Santa Fe, while Arroyo Hondo lies just south of the corporate limits of the city. The Santa Fe River is the principal drainage stream in the area, with Arroyo de Los Chamisos and Arroyo Hondo as tributaries. The Santa Fe River has a total drainage area of approximately 250 square miles where it enters the Rio Grande. The Santa Fe River headwaters are in the Sangre de Cristo Mountains at an elevation of over 12,000 feet, and the river eventually flows into the Rio Grande, which lies at approximately 5,200 feet above mean sea level. The river is an ephemeral stream with two perennial reaches: one is located between its source at Santa Fe Lake and the Alameda Street/Camino Cabra Bridge, and the other is located between the wastewater treatment plant and La Bajada (Reference 6). These flows are captured in a series of three reservoirs for municipal water supplies, and any remainder is lost to the sandy soil in the lower elevations near the City of Santa Fe. The river flows southwest about 25 miles before discharging into the Rio Grande in Sandoval County. Residential areas flank the Santa Fe River on its east and west ends, while commercial and cultural areas are along the river in the historic downtown area. There a number of tributaries to the Santa Fe River within the City of Santa Fe. High-density residential zones line Arroyo de La Piedra, while both commercial and residential zones flank the Mascaras, and Saiz Arroyos; and Canada Rincon. Arroyo Torreon flows through an underdeveloped area. Flows for Arroyo de Los Chamisos and Arroyo Hondo develop in the western foothills of the Sangre de Cristo Mountains overlooking the City of Santa Fe at elevations between 6,500 and 8,000 feet. Arroyo de Los Chamisos flows in a generally westerly direction near the southern limits of the city. The North Fork of the Arroyo de Los Chamisos is contained entirely within the city. This arroyo is ephemeral, with the exception of some downstream sections where springs provide small perennial flows. The City of Española is located in Rio Arriba and Santa Fe Counties, approximately 25 miles north of the City of Santa Fe, along U.S. Highway 84 and on the banks of the Rio Grande near Santa Cruz Lake. Española is located in the Rio Grande Valley between two mountain ranges and is surrounded by mesas. The topography of the City of Española is 7

13 generally characterized by the river valley and flatter regions immediately adjoining the Rio Grande as well as mountainous regions surrounding and sloping toward the valley. The population of Española, in 2009, was estimated at 9,708 (Reference 4). The Santa Cruz River flows through northern Santa Fe county and the City of Española and is a tributary of the Rio Grande River. The Town of Edgewood is a rural community about 30 miles east of Albuquerque along I-40. The Town covers approximately 44.4 square miles of Land in Bernalillo, Santa Fe and Torrance Counties on the eastern side of the Sandia and Manzano Mountains. The estimated population of Edgewood in 2009 was 2,916 (Reference 4). Bachelor Draw rises in the Sandia Mountains and runs southeast through the community. Northern Santa Fe County is home to several Tewa speaking pueblos, all of which have long histories from before the Spanish Conquest. All of these Pueblos are federally recognized tribes and with the exception of the Pueblo of Nambe are census designated places (CDPs). These pueblos include the Pueblo of Santa Clara which is located outside of the City of Española along the Santa Cruz River. The 2000 population of the Pueblo of Santa Clara was 980 (Reference 4). The Pueblo of San Ildefonso is located southwest of the Pueblo of Santa Clara near the confluence of the Rio Pojoaque with the Rio Grande. The 2000 population of the Pueblo of San Ildefonso was 458 (Reference 4). The Pueblo of Pojoaque is located just east of San Ildefonso and southeast of Santa Clara, near the confluence of the Rio Pojoaque and Rio Tesuque. The population of the Pueblo of Pojoaque in 2000 was 1,261 (Reference 4). The Pueblo of Nambe is located just east of the Pueblo of Pojoaque, along Pojoaque Creek. The Pueblo of Tesuque is located south of the Pueblos of Pojoaque and Nambe and just north of the City of Santa Fe, along Rio Tesuque. The population of the Pueblo of Tesuque in 2000 was 909 (Reference 4). Western Santa Fe County contains the parts of the Pueblos of Cochiti and Santo Domingo. The bulk of these Pueblos are in neighboring Sandoval County. These pueblos are also Tewa speaking. The Pueblo of Cochiti had a population in 2000 of 507 (Reference 4). The Pueblo of Santo Domingo is located south of Cochiti and had a 2000 population of 2,550 (Reference 4). 2.3 Principal Flood Problems Most of the storms that produce large amounts of runoff occur in the months of June through October. Over 70 percent of the average precipitation is received during this time. Summer rainfall is usually a result of thunderstorm activity with maximum rainfall occurring in July. Flood stages sometimes occur in these months when moist tropical air moves north out of the Gulf of Mexico forming intense thunderstorms across the hot New Mexico land. Runoff occurring from these storms is generally termed flash flooding due to the large volumes of water that surge down the normally dry arroyo channels with high velocities. Most historical information on past floods in Santa Fe County center around the Santa Fe River. Arroyo Hondo and Arroyo de Los Chamisos are subject to the same flood conditions as the Santa Fe River and can be expected to behave in a similar manner. Major floods of record occurred on the Santa Fe River on August 24, 1957, and July 25, 1968 (Reference 7). Major floods have been recorded in the Santa Fe area in 1872, 1904, 1914, 1921, 1929, 1957, and The USACE indicates that there are no reliable flood records prior to Over $1 million in damages were caused throughout the City of Santa Fe by the 1968 flood of the Santa Fe River. No major flooding had been reported in Santa Fe since 8

14 1968; however, minor flooding, with no reports of property damage, occurred July 12, 1976 (Reference 8). Between 1995 and 2008, nine flood events were reported in various areas of Santa Fe, causing one fatality and $421,000 worth of damage in total (Reference 9). Elsewhere in the county, flash flooding occurred along the Santa Fe River at La Cienega, destroying several corrals, washing away several horses and sheep on the ranch. Debris filled in 200 feet of acequia (irrigation channel). Damages were estimated at $70,000. In August 1997, roads and bridges were damaged during heavy rains near the Village of Arroyo Seco. Damages were estimated at $250,000. Heavy rains and flash flooding in June and August, 2008 in the Village of Arroyo Seco caused damages estimated at $7,000 (Reference 9). 2.4 Flood Protection Measures There are no existing or authorized flood control structures in the study area or upstream in the watershed other than limited bank protection work mainly adjacent to bridges. The three municipal water supply reservoirs located on the upper Santa Fe River are a part of the city s water supply system and do not provide for flood water storage. The reservoirs tend to attenuate peak discharges for small storms; however, they do not have designated flood control storage and will not attenuate major peak flows significantly. For purposes of this study, the reservoirs are assumed to have no effect on the Santa Fe River discharges. The City of Santa Fe has adopted a floodplain management ordinance to provide for non-structural measures for the prevention of flood damages. 3.0 ENGINEERING METHODS For the flooding sources studied by detailed and enhanced approximate Type 1 methods in the community, standard hydrologic and hydraulic study methods were used to determine the floodhazard data required for this study. Flood events of a magnitude that are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or 500-year period (recurrence interval) have been selected as having special significance for floodplain management and for flood insurance rates. These events, commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10-, 2-, 1-, and 0.2-percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the long-term, average period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood that equals or exceeds the 1-percent-annual-chance in any 50-year period is approximately 40 percent (4 in 10); for any 90-year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes. 3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish peak discharge-frequency relationships for each flooding source studied by detailed or enhanced approximate Type 1 methods affecting the community. Peak discharge-drainage area relationships for Santa Fe County are shown in Table 7, "Summary of Discharges." 9

15 Table 7 Summary of Discharges Flooding Source and Location DRAINAGE AREA (mi 2 ) 10% Annual Chance PEAK DISCHARGES Cubic feet per second (cfs) 2% Annual Chance 1% Annual Chance 0.2% Annual Chance ADMIN ARROYO Confluence with Rio Tesuque 2.3 * * 1,730 * ARROYO BARRANCA Confluence with Arroyo Mascaras 1.1 * * 560 * ARROYO DE LA PAZ Confluence with Arroyo de Los Antores 0.6 * * 540 * ARROYO DE LA PIEDRA Confluence of East Arroyo de La Piedra 0.3 * * 230 * Confluence with Arroyo Mascaras 1.9 * * 1,876 * ARROYO DE LOS AMIGOS Confluence with Arroyo de Los Chamisos 0.5 * * 600 * ARROYO DE LOS ANTORES Confluence of Arroyo de La Paz 0.3 * * 380 * Confluence with Arroyo de Los Chamisos 1.0 * * 940 * ARROYO DE LOS CHAMISOS Cross Section BT ,080 3,100 Cross Section BL ,580 4,500 Cross Section AU ,175 1,900 5,400 Cross Section AQ ,510 2,400 6,900 Cross Section AF ,800 2,850 8,200 Cross Section P ,250 3,600 10,250 Cross Section F ,375 3,750 10,600 Cross Section A ,800 4,400 12,500 From Rodeo Road to State Route ,060 4,590 6,050 10,510 From State Route 85 to confluence of Arroyo Hondo ,470 5,410 7,080 12,060 ARROYO DE LOS CHAMISOS (NORTH FORK) Cross Section AP ,380 3,900 Cross Section H ,550 4,400 Cross Section B ,140 1,800 5,200 *Data not computed 10

16 Flooding Source and Location Table 7 Summary of Discharges - continued DRAINAGE AREA (in mi 2 ) 10% Annual Chance PEAK DISCHARGES Cubic feet per second (cfs) 2% Annual Chance 1% Annual Chance 0.2% Annual Chance ARROYO DEL ROSARIO Just Upstream of Rio Grande Ave 0.3 * * 512 * ARROYO EN MEDIO Confluence with Arroyo de los Chamisos 3.4 * * 1,800 * ARROYO HONDO 0.25 mile upstream of BNSF Railroad 10.8 * * 1,650 * Confluence with Canada del Rancho ,910 2,490 4,040 Confluence with Arroyo de Los Chamisos ,150 2,630 3,400 5,460 ARROYO MASCARAS Cross Section Z ,080 3,100 Cross Section Y ,580 4,500 Cross Section X ,175 1,900 5,400 Cross Section C ,510 2,400 6,900 Cross Section ,800 2,850 8,200 ARROYO RANCHITO Confluence with Arroyo Mascaras 0.7 * * 300 * ARROYO SAIZ Upstream of South Avenida Primera 0.1 * * 100 * Confluence with Santa Fe River 0.3 * * 220 * ARROYO SECO Santa Fe County Boundary 21.7 * * 4,410 * ARROYO TORREON Cross Section H ,450 BACHELOR DRAW Approximately 0.25 mile upstream of Thunder Mountain Road 9.2 * * 2,820 * Abajo Drive 32.2 * * 4,970 * BIG TESUQUE CREEK USGS # Gage 11.2 * * 1,440 * Confluence with Rio Tesuque 12.3 * * 1,480 * *Data not computed 11

17 Flooding Source and Location Table 7 Summary of Discharges - continued DRAINAGE AREA (in mi 2 ) 10% Annual Chance PEAK DISCHARGES Cubic feet per second (cfs) 2% Annual Chance 1% Annual Chance 0.2% Annual Chance CANADA ANCHA Confluence with Santa Fe River 1.97 * * 1,150 * CANADA RINCON Cross Section V ,475 Cross Section D ,150 3,300 EAST ARROYO DE LA PIEDRA Confluence with Arroyo de La Piedra 0.9 * * 1,170 * LITTLE TESUQUE CREEK Confluence with Rio Tesuque 8.9 * * 1,440 * NE ARROYO DE LOS PINOS Upstream of St. Michaels Drive 1.2 * * 570 * POJOAQUE RIVER Confluence of Arroyo Jacona * * 5,800 * Approximately 0.1 mile upstream of Evergreen Lane * * 6,340 * Confluence with the Rio Grande * * 7,020 * RIO TESUQUE Confluence of Unnamed Stream ,830 2,680 5,230 South Boundary of Tesuque Pueblo ,870 2,730 5,330 Confluence with Pojoaque River 77.8 * * 5,810 * SANTA CRUZ RIVER USGS gaging station No * * 2,140 * 1,300 feet downstream of State Highway ,600 3,590 7,420 Confluence with the Rio Grande * * * 4,160 * *Data not computed 12

18 Flooding Source and Location Table 7 Summary of Discharges - continued DRAINAGE AREA (in mi 2 ) 10% Annual Chance PEAK DISCHARGES Cubic feet per second (cfs) 2% Annual Chance 1% Annual Chance 0.2% Annual Chance SANTA FE RIVER Confluence of Arroyo Saiz ,260 1,780 3,550 At the confluence of Arroyo Mascaras ,469 3,090 4,190 7,370 Approximately 0.25 mile upstream of El Rancho Road ,548 3,220 4,350 7,620 Approximately 0.46 mile downstream of Alejandro Street ,558 3,250 4,390 7,690 Confluence of Arroyo Calabasas ,017 4,360 5,930 10,660 Confluence of Santa Fe River 3, Tributary ,650 10,080 17,020 UNNAMED STREAM 31 Confluence with Rio Tesuque 1.0 * * 270 * *Data not computed Table 8, "Stream Hydrologic Methods Used" lists the study streams and shows the most recent type of study that was performed for each stream and the methodology selected where known. Pre-Countywide Analyses Information on the hydrologic analyses for each of the previously printed FISs for communities within Santa Fe County was compiled and are shown below (References 10-12). City of Española The original hydrologic analysis for the Santa Cruz River was obtained from the FIS for the unincorporated areas of Rio Arriba County (Reference 13). The peak flood discharge with a 1-percent-annual-chance of exceedance was modeled. Santa Cruz River has its headwaters in the mountains that flank the Rio Grande floodplain to the east and west. Headwater elevations are as much as 8,000 feet above sea level for tributaries like the Santa Cruz River that lie on the east side of the Rio Grande. The elevation at the confluence with the Rio Grande is between 5,000 and 6,000 feet above sea level (Reference 10). 13

19 Table 8 Stream Hydrologic Methods Used Study Stream Name Study Type Study Date Hydrologic Method Used Admin Arroyo, Arroyo Saiz, Arroyo Seco (portions), Bachelor Draw, Pojoaque River, Rio Tesuque DS Arroyo Barranca Arroyo de La Paz Arroyo de La Piedra Arroyo de Los Amigos Arroyo de Los Antores Arroyo En Medio Arroyo Hondo Arroyo Ranchito Arroyo Saiz (portions) Big Tesuque Creek Canada Ancha (portions) East Arroyo de La Piedra Little Tesuque Creek NE Arroyo de Los Pinos Unnamed Stream 31 Enhanced Approximate Study Type I Enhanced Approximate Study Type I 2005 USGS Regression Equations 2010 HEC-HMS Santa Fe River Detailed Study with Floodway 2005 USGS Regression Equations Rio Tesuque US, Santa Cruz River Detailed Study without Floodway 2010 HEC-HMS Arroyo Hondo Detailed Study with Floodway 2010 HEC-HMS City of Santa Fe The original hydrologic analyses for the Arroyo de La Piedra, Arroyo de Los Chamisos, Arroyo de Los Chamisos (North Fork), Arroyo Hondo, Arroyo Mascaras, Arroyo Saiz, Arroyo Seco, Arroyo Torreon, Canada Ancha, Canada Rincon, ROB Flow path, and the Santa Fe River were taken from the Hydrology Report for the Pojoaque River that was prepared for the USACE by Ken O Brien and Associates in April 1976 (Reference 14). The Pojoaque River Basin lies adjacent to and north of the Santa Fe River Basin and is very similar in size, topography, soils, and land use patterns. As stated in the referenced report, all efforts made to develop rainfall-runoff relationships proved unsuccessful due to lack and/or inconsistency of data available for analysis. The former modelers were unsuccessful developing rainfall-runoff relationships for the watershed; instead they applied the Pojoaque River hydrologic model to the Santa Fe River for the following reasons: the strong similarities of the watershed; the fact that the basins are adjacent; and the referenced hydrologic analysis could be transposed directly from basin to basin. Adjustments were made for the various watershed parameters (Reference 11). Santa Fe County (Unincorporated Areas) Flood flow frequency discharges determined for Arroyo de Los Chamisos, Arroyo Hondo, and the Santa Fe River were studied by detailed methods and were based on statistical analysis of USGS gage data in the Santa Fe region with similar basin 14

20 characteristics. A linear regression relationship was developed from 10 different gages that have drainage areas ranging from 0.5 to 120 square miles and periods of record from 20 to 35 years. Log-Pearson Type III frequency discharges were determined for each gage using USGS Bulletin 17B (Reference 15). A discharge versus drainage area equation was then found for each frequency using linear regressions of the discharges (Reference 12). Initial Countywide FIS The National Flood Frequency (NFF) Program, Version 3.2 (Reference 16), was used for computation of the 10-, 2-, 1-, and 0.2-percent annual chance storm event discharge values. Based on physiography, elevation, and precipitation, New Mexico is divided into eight hydrologic regions. Santa Fe County falls within the Central Mountain Valley Region. The Central Mountain Valley Regression Equations (Reference 17) are valid for: Drainage areas between 0.60 square miles and 3,660 square miles Average channel elevations ranging from 5,310 to 9,280 feet above mean sea level 10-year interval 24-hour precipitation maximum intensity between 2.15 and 3.00 inches. No other applicability restrictions exist for this region. The NFF software extrapolates the 500-year event flow rate from the flow rates calculated for the other storm events. No weighting estimates can be performed on the study reaches due to the lack of available gage data. Another set of equations, which is valid for nationwide use, was developed for urban watersheds. The Nationwide Urban Regression Equations were used for several subbasins of the Santa Fe River study reach. These equations are valid for urbanized areas that do not contain peak controlling structures and should not be used if any of the seven required input parameters are larger or smaller than those used in the original regression study. No other applicability restrictions exist for use of these equations. The NFF software program is designed to calculate peak discharge values for the watershed as a whole. In cases such as the restudy streams where watersheds have been divided into two or more sub-basins, cumulative drainage areas were used in the regression equations. One exception is the Santa Fe River, for which the application of cumulative drainage areas was modified in order to account for urban areas within the watershed. Given that the peak discharge values are cumulative; these values are typically not added at each basin break. The Santa Fe River hydrologic analysis, however, required that separate analyses be performed on urban and rural sub-basins, and therefore, urban and rural regression results were added at each basin break. The drainage area for the middle portion of the Santa Fe River is comprised of the developed portion of the City of Santa Fe. This portion of the watershed was analyzed using the Urban Regression Equations. The remaining drainage areas of the Santa Fe River (i.e., the area outside of the developed portion of the City of Santa Fe) are rural and were analyzed using the Regional Regression Equations. Stream gage data was not used for hydrologic analysis on any of the streams studied in Santa Fe County. Although there are stream gages on the Santa Fe River and the Rio Tesuque, they do not conform either to USGS Bulletin 17B (Reference 15) or FEMA 15

21 Guidelines and Specifications for Flood Hazard Mapping Partners (Reference 18). USGS Bulletin 17B states that the log-pearson Type III distribution methodology is not valid on watersheds where flood flows are appreciably altered by reservoir regulation. The FEMA Guidelines and Specifications for Flood Hazard Mapping Partners limits drainage basin area to between 50% and 200% of the gage drainage basin area. There are two gage stations on the Santa Fe River; one located approximately 9 miles downstream of the study reach and the other located approximately 4.5 miles upstream of the study reach. Since the upstream gage is located at a dam with two reservoirs, the Santa Fe River study reach is no longer an unobstructed (i.e., natural flowing) river, and gage data could not be employed. Drainage areas of sub-basins of the Rio Tesuque study reach exceeded 200% of the gage station drainage area. Thus, data from the gage stations could not be used. Due to the lack of comparable data, the models were not calibrated based on the stream gage data. Topographic data obtained from Santa Fe County were used in conjunction with USGS Digital Elevation Model (DEM) data to create a terrain model of Santa Fe County. The watersheds were delineated using USGS Quadrangle maps with 20-foot contour intervals. Along with the other restudy reaches; the Santa Fe River sub-basins were delineated based on either prior effective FIS locations or major tributary confluences. The centroid of each watershed for the study reaches was approximated based on the watershed delineation. The coordinates of the centroid were input into the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 website (Reference 19). The NOAA Atlas website uses the coordinates of a fixed location to interpolate the average precipitation values for that location. Updated Precipitation Frequency Data for the state of New Mexico were released by NOAA in August These data supersede NOAA Atlas 2 data. Watershed characteristics, such as sub-basin area and cumulative basin area, were obtained through field investigation, available topographic data, and available orthophotogrammetric data. As part of the update for the City of Española, New Mexico, Rio Arriba and Santa Fe Counties Flood Insurance Study (Reference 10) drainage basins for the Santa Cruz River were delineated using a combination of Light Detection and Ranging (LiDAR) data (Reference 20) and USGS 1/3 arc-second DEM data (Reference 21). Peak dischargefrequency relations were computed using the USGS regression equations for New Mexico (References 15 and 17). This PMR and FIS Update Detailed and Enhanced Approximate Type 1 Study Streams At request of Santa Fe County, rainfall runoff modeling was the hydrologic method used for the streams studied by detailed and enhanced approximate methods. The Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) version 3.1 software package (Reference 22) was used to determine discharges of those these streams. HEC- HMS is designed to simulate the precipitation-runoff processes. The HEC-HMS model requires basin area, land use, and hydrologic soil type. Topographic data obtained from Santa Fe County (Reference 19) were used in conjunction with USGS DEM data (Reference 23) to create a terrain model of Santa Fe County. The terrain model was used to delineate drainage basins and other watershed characteristics, such as time of concentration and average basin elevation. The methodology selected for computation of time of concentration was the Soil 16

22 Conservation Service (SCS) Technical Release 55 (Reference 24) method. This method is based on dividing the watershed flow path into sheet flow segments, shallow concentrated flow segments, and channel flow segments. Sub-basins were delineated based on either prior effective FIS locations or major tributary confluences. Precipitation data was determined using NOAA Atlas 14 and NOAA Precipitation Frequency Data Server (References 18 and 25), and using the New Mexico SCS Type II- 70 storm. The centroid of each watershed for the study reaches was approximated based on the watershed delineation. The coordinates of the centroid were input into the NOAA Atlas 14 website which uses the coordinates of a fixed location to interpolate the average precipitation values for that location. These values were used to calculate an input hyetograph for the HEC-HMS model. The land use was determined using the National Land Cover Data and the New Mexico Land Cover Key (Reference 26). The hydrologic soil group was determined from information obtained using the Soil Survey Geographic (SSURGO) published in2008 obtained from the US Department of Agriculture Geospatial Data Gateway (Reference 27). This SSURGO information supplemented with SSURGO information published in 2006 for the areas of the Santa Fe National forest obtained from the Natural Resources Conservation Service (NRCS) web soil survey website (Reference 28). Stream gage data from gages on Big Tesuque Creek and the Santa Cruz River were compared to the results of the rainfall-runoff model (References 29 and 30). Results of these comparisons were similar to the rainfall-runoff model. Regional regression equations were used as the hydrologic methodology for streams studied by approximate methods that were not tributary to streams studied by detailed or enhanced approximate methods. Based on physiography, elevation, and precipitation, New Mexico is divided into nine hydrologic regions. Although Santa Fe County falls within the Northern Mountain and Central Mountain Valley Region (Reference 31), all streams studied by this method were all located in the Central Mountain Valley Region. The Central Mountain Valley Regression Equations (Reference 31) are valid for: Drainage areas between 0.18 square miles and 7,220 square miles The presence of a large flood retention reservoir on Galisteo Creek complicated its analysis. There is a stream gage downstream of the reservoir but the stream gage on does not conform to either USGS Bulletin 17B (Reference 15), or FEMA Guidelines and Specifications for Flood Hazard Mapping Partners (Reference 18), which states that the log-pearson Type III distribution methodology is not valid on watersheds where flood flows are appreciably altered by reservoir regulation. The gage information was analyzed, however, to determine the discharge downstream of the Galisteo Dam (Reference 32). This discharge was added to the discharge computed by the regional regression equations for watersheds downstream of the Galisteo Dam to determine a cumulative discharge. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles (Exhibit 1) or in the Floodway Data Table in the FIS report. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. 17

23 For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS in conjunction with the data shown on the FIRM. Locations of selected cross-sections used in the hydraulic analyses are shown on the Flood Profiles. For stream segments for which a floodway was computed (Section 4.2), selected cross-section locations are also shown on the FIRM. The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the Flood Profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. Channel and overbank roughness coefficients (Manning s n ) used in the hydraulic computations were estimated by engineering judgment and based on field observation at each cross-section and adjusted with known high-water marks and stream gage rating curves where possible. Table 9, "Summary of Roughness Coefficients," provides the known roughness coefficients that were used for streams studied by detailed methods. Table 10, "Stream Hydraulic Methodology," provides a summary of the recent hydraulic methodologies used for the streams studied by detailed methods where known. Pre-Countywide Analyses Information on the hydraulic analyses for each of the previously printed FIS for communities within Santa Fe County was compiled and is shown below. The vertical data for all detailed streams not listed in Table 10 were adjusted to the North American Vertical Datum of 1988 (NAVD88) and redelineated using the most current topographic data, which was obtained from Santa Fe County in NAVD88 (Reference 20) during the initial countywide update. New hydraulic analyses were not performed on the redelineated flooding sources. Not all cross-sections for redelineated streams are shown on the FIRM, as they were not shown previously on historic maps. City of Española A portion of the Santa Cruz River was studied as part of the update for the City of Española, New Mexico, Rio Arriba and Santa Fe Counties Flood Insurance Study (Reference 10). That analysis included cross sections placed every 500 to 700 feet. Structure information was incorporated from measurements of structure dimensions collected in the field. RMA2 (Reference 33), a depth-averaged two-dimensional finite element numerical model, was used to model the sheet flow behavior that characterizes the flatter regions east and west of the Rio Grande in the City of Española. The starting water surface for the Santa Cruz River was derived from RMA2. City of Santa Fe For the flooding sources within the City of Santa Fe that were previously studied in detail, the following hydraulic analysis methodology was taken from the pre-countywide FIS report for the City of Santa Fe (Reference 11). Cross-section data for the streams in the study area were obtained from photogrammetric and field survey. All bridges and culverts were field surveyed to obtain elevation data and structural geometry. Cross sections were located at close intervals upstream and downstream of bridges and culverts in order to compute significant backwater effects of these structures. 18