carson city, nevada -...

CARSON CITY, NEVADA INDEPENDENT CITY

Revised January 16, 2009

Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER

320001V000A

Carson City

NOTICE TO FLOOD INSURANCE STUDY USERS

Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for flood plain management and flood insurance purposes. This Flood Insurance Study (FIS) may not contain all data available within the repository. It is advisable to contact the community repository for any additional data.

Selected Flood Insurance Rate Map (FIRM) panels for the community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map (FBFM) panels (e.g. floodways, cross sections). In addition, former flood hazard zone designations have been changed as follows:

Old Zone New Zone

A1 through A30 AE

B X (Shaded)

C X (Unshaded)

Part or all of this FIS may be revised and republished at any time. In addition, part of this FIS may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the FIS. 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.

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TABLE OF CONTENTS

Page

1.0 INTRODUCTION .................................................................................................................................. 1

1.1 Purpose of Study ................................................................................................................................. 1

1.2 Authority and Acknowledgments ....................................................................................................... 1

1.3 Coordination ....................................................................................................................................... 2

2.0 AREA STUDIED.................................................................................................................................... 3

2.1 Scope of Study .................................................................................................................................... 3

2.2 Community Description...................................................................................................................... 7

2.3 Principal Flood Problems.................................................................................................................... 8

2.4 Flood Protection Measures ................................................................................................................. 9

3.0 ENGINEERING METHODS ............................................................................................................... 10

3.1 Hydrologic Analyses......................................................................................................................... 10

3.2 Hydraulic Analyses........................................................................................................................... 14

3.3 Vertical Datum.................................................................................................................................. 21

4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS ......................................................................... 21

4.1 Flood Boundaries .............................................................................................................................. 21

4.2 Floodways ......................................................................................................................................... 22

5.0 INSURANCE APPLICATION............................................................................................................. 31

6.0 FLOOD INSURANCE RATE MAP .................................................................................................... 31

7.0 OTHER STUDIES................................................................................................................................ 32

8.0 LOCATION OF DATA........................................................................................................................ 32

9.0 BIBLIOGRAPHY AND REFERENCES ............................................................................................. 32

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Table of Contents – continued

FIGURES

Figure 1 – FLOODWAY SCHEMATIC .................................................................................................... 23

TABLES

Table 1 - INITIAL AND FINAL CCO MEETINGS.................................................................................... 3

Table 2 - FLOODING SOURCES STUDIED BY DETAILED METHODS .............................................. 4

Table 3 - FLOODING SOURCES STUDIED BY APPROXIMATE METHODS...................................... 5

Table 4 - LETTERS OF MAP CHANGE..................................................................................................... 6

Table 5 – SUMMARY OF PEAK DISCHARGES .................................................................................... 12

Table 6 – MANNING’S "n" VALUES....................................................................................................... 16

Table 7 - STREAM CONVERSION FACTORS ....................................................................................... 17

Table 8 - LIST OF LEVEES REQUIRING FLOOD HAZARD REVISIONS .......................................... 20

Table 9 - FLOODWAY DATA .................................................................................................................. 24

EXHIBITS

Exhibit 1 – Flood Profiles

Carson River Panels 01P-10P

Clear Creek Panels 11P-14P

Eagle Valley Creek Panels 15P-17P

Golf Course Creek A Panels 18P-19P

Golf Course Creek B Panels 20P-23P

Goni Canyon Creek Panels 24P-28P

Kings Canyon Creek Panels 29P-31P

PUBLISHED SEPARATELY: Flood Insurance Rate Map Index

Flood Insurance Rate Map

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FLOOD INSURANCE STUDY OF CARSON CITY, NEVADA

INDEPENDENT CITY

1.0 INTRODUCTION

1.1 Purpose of Study This Flood Insurance Study (FIS) revises and supersedes the FIS reports and/or Flood Insurance Rate Maps (FIRMs), Flood Boundary and Floodway Maps (FBFMs) in the geographic area of Carson City, Nevada (Independent City), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This study has developed flood risk data for various areas of the community that will be used to establish actuarial flood insurance rates and assist the community in its efforts to promote sound flood plain management. Minimum flood plain management requirements for participation in the National Flood Insurance Program (NFIP) are set forth in the Code of Federal Regulations at 44 CFR, 60.3. In some states or communities, flood plain management criteria or regulations may exist that are more restrictive or comprehensive than those on which this federally supported study is based. These criteria take precedence over the minimum Federal criteria for purposes of regulating development in the flood plain, as set forth in the Code of Federal Regulations at 44 CFR, 60.3(c). In such cases, however, it shall be understood that the State (or other jurisdictional agency) shall be able to explain these requirements and criteria.

1.2 Authority and Acknowledgments The sources of authority for this FIS are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. The hydrologic and hydraulic analyses for this study were performed by Boyle Engineering Corporation, for the Federal Emergency Management Agency (FEMA), under Contract No. H-4609. This study was completed in December 1982. Studies performed for the March 16, 1989 revision were carried out by Lumos Associates Inc. (LAI), in conjunction with Resource Concepts Inc. (RCI). The revision was based on more detailed topographic data and new hydrologic and hydraulic analyses of Saliman Road Tributary and H-Tributary (Lumos & Associates, Incorporated, and Resource Concepts, Incorporated, March 1987). The hydraulic analysis for revision dated September 30, 1993 was performed by the USGS for FEMA, using the hydrology developed by Boyle Engineering Corporation for the original FIS. This work was performed under Interagency Agreement No. EMW-89-E-2997 and completed in September 1991. The October 16, 1996 revision, were conducted by LAI, in conjunction with RCI. The revision incorporated two Letters of Map Revision (LOMRs) along Saliman Road Tributary. The hydrologic and hydraulic analyses for the LOMRs consisted of HEC-1 hydrologic computer modeling (U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, February 1, 1985), HEC-2 hydraulic computer modeling (U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, November 1976, Updated 1984), and other supporting data.

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In January 2009, HDR Engineering Inc. completed a DFIRM and FIS for Carson City. HDR Engineering Inc. was hired as an IDIQ study contractor for FEMA Region IX under contract number EMF-2003-CO-0045, Task Order 19. The DFIRM process included digitizing floodplain boundaries from the effective paper FIRMs and fitting them to a digital base map, thus converting the existing manually produced FIRMs to digitally produced FIRMs, referred to as DFIRMs. Planimetric base map information was provided in digital format for FIRM panels. Public Land Survey System (PLSS) and land ownership data were provided by Bureau of Land Management (BLM). Information on roads was provided by Great Basin Center for Geothermal Exploration. Aerial imagery was provided by the U.S. Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP). Users of this FIRM should be aware that minor adjustments may have been made to specific base map features. The coordinate system used for the production of this FIRM is Universal Transverse Mercator (UTM), North American Datum of 1983 (NAD 83), and GRS 1980 spheroid. Corner coordinates shown on the FIRM are in latitude and longitude referenced to NAD 83. Differences in datum and spheroid used in the production of FIRMs for adjacent counties may result in slight positional differences in map features and at the county boundaries. These differences do not affect the accuracy of information shown on the FIRM.

1.3 Coordination Consultation Coordination Officer’s (CCO) meetings may be held for each jurisdiction. An initial CCO meeting is held typically with representatives of FEMA, the community, and the study contractor to explain the nature and purpose of a FIS, and to identify the streams to be studied by detailed methods. A final CCO meeting is typically held with the representatives of FEMA, the community, and the study contractor to review the results of the study. Flooding sources requiring detailed study were identified at a meeting held on July 19, 1979. This meeting was attended by representatives of FEMA, the study contractor, and the community. Coordination with the community and FEMA was maintained throughout the study to ensure that study results would meet agency and community requirements. On October 16, 1980, the study contractor met with representatives of the Carson City Planning Department, Carson City Department of Public Works, and U.S. Geological Survey (USGS) to discuss flooding problems in Carson City. A technical coordination meeting was held between representatives of the study contractor and FEMA on September 25, 1981. At the meeting, the results of the hydrologic analyses were discussed and compared with previous studies. The preliminary results of the hydraulic analyses were also reviewed. The discussion centered on the suitability of applying alluvial fan and shallow flooding guidelines or detailed methods to specific flooding sources. On May 11, 1982, an intermediate community meeting was held in Carson City to discuss preliminary study results. Representatives of FEMA, the study contractor, and the community attended the meeting. The following were contacted and supplied information used in preparation of this study: U.S. Bureau of Reclamation, U.S. Army Corps of Engineers (USACE), USGS, National Resources Conservation Services (NRCS), formerly U.S. Soil Conservation Service (SCS), National Weather Service, Nevada Department of Highways, Nevada Department of Conservation and

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Natural Resources, Desert Research Institute, Carson River Basin Council of Governments, Carson City Planning Department, Carson City Department of Public Works, and Carson City Chamber of Commerce. The final community coordination meeting was held on September 4, 1984, and was attended by representatives of FEMA, the study contractor, and the city. No problems were raised at the meeting. On November 18, 1992, a Consultation and Coordination Officer meeting was held to review the results of the September 30, 1993 revisions. The attendees were representatives of Carson City, the State of Nevada, and FEMA. No problems were raised at that meeting. The dates of the initial and final CCO meetings held for Carson City and the incorporated communities in its boundaries are shown in Table 1, “Initial and Final CCO Meetings.”

Table 1 - INITIAL AND FINAL CCO MEETINGS

Community Name Initial CCO Date Final CCO Date

Carson City (Independent City)

July 19, 1979 N/A

March 31, 2007

September 4, 1984 November 18, 1992

N/A N/A- Not Available On March 31, 2007, the initial CCO meeting for the Carson City DFIRM and FIS was held. Attending the meeting were representatives of FEMA Region IX and Carson City. On April 22, 2008, the final CCO meeting for the Carson City DFIRM and FIS was held. Attending the meeting were representatives of FEMA Region IX, Carson City, and the Study Contractor.

2.0 AREA STUDIED

2.1 Scope of Study This FIS covers the geographic area of Carson City, Nevada (Independent City). The scope and methodologies used in preparation of this FIS were agreed upon in joint consultation between FEMA and Carson City. The areas studied by detailed methods were selected with priority given to all known flood hazard areas and areas of projected development and proposed construction. All or portions of the flooding sources listed in Table 2, “Flooding Sources Studied by Detailed Methods,” were studied by detailed methods. Limits of detailed study are indicated on the Flood Profiles and on the FIRM.

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Table 2 - FLOODING SOURCES STUDIED BY DETAILED METHODS

Ash Canyon Creek Carson River

Channels C Channels D

Clear Creek Combs Canyon Creek

Eagle Extension Eagle Valley Creek

F Tributary G Tributary

Golf Course Creek A Golf Course Creek B

Goni Canyon Creek H Tributary

King Canyon Creek Kings Split

Saliman Road Tributary Vicee Canyon Creek

Voltaire Canyon Creek Voltaire Split

The limits of the detailed studies are as follows:

• Carson River, for approximately 5.7 miles downstream of Mexican Dam;

• Clear Creek, for approximately 6.2 miles upstream of its confluence with the Carson River;

• Golf Course Creek B, for approximately 0.7 mile upstream from its confluence with the Carson River;

• Golf Course Creek A, for approximately 0.5 mile upstream from its confluence with Golf Course Creek B;

• Kings Canyon Creek, for approximately 6.6 miles upstream from its confluence with the Carson River;

• Goni Canyon Creek, from approximately 0.4 mile upstream from its confluence with Kings Canyon Creek upstream to Conestoga Drive;

• Eagle Valley Creek, from Graves Lane upstream to U.S. Highway 395;

• Ash Canyon Creek, for approximately 4.3 miles upstream from its confluence with Kings Canyon Creek;

• Vicee Canyon Creek, for approximately 3.8 miles upstream from its confluence with Ash Canyon Creek;

• Combs Canyon Creek, from its confluence with Ash Canyon Creek upstream to V&T Way;

• H Tributary, for approximately 2.3 miles upstream of East Fifth Street;

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• Voltaire Canyon Creek, for approximately 3.2 miles upstream from its confluence with H Tributary;

• Voltaire Split, for approximately 0.8 mile along Koontz Lane between Voltaire Canyon Creek and Saliman Road Tributary;

• Saliman Road Tributary, for approximately 2.6 miles upstream from its confluence with H Tributary;

• Eagle Extension, for approximately 1.8 miles upstream from its confluence with Goni Canyon Creek; and

• F Tributary, for approximately 0.6 mile upstream from its confluence with Eagle Extension.

In addition, a limited-detailed analysis was performed for reaches upstream of the detailed analysis on Clear, Kings Canyon, Ash Canyon, Vicee Canyon, Combs Canyon, and Goni Canyon Creeks. This limited-detailed study, which analyzed the 1-percent annual chance of occurrence (100-year) flood only, was also performed on the entire reach of G Tributary, Kings Split, and Channels C and D. All or portions of the flooding sources listed in Table 3, “Flooding Sources Studied by Approximate Methods,” were studied by approximate methods. Approximate analyses were used to study only those areas having a low development potential or minimal flood hazards.

Table 3 - FLOODING SOURCES STUDIED BY APPROXIMATE METHODS Ash Canyon Creek Carson River Channel D Clear Creek

Combs Canyon Creek E Tributary F Tributary G Tributary

Golf Course Creek A Golf Course Creek B H Tributary I Tributary

J Tributary Kings Canyon Creek Kings Split Prison Hill Creek

Saliman Road Tributary

Vicee Canyon Creek

Approximate analyses were performed for reaches on the Carson River extending upstream and downstream from the detailed study to the corporate limits. Approximate methods were also used upstream of detailed reaches on H Tributary, Saliman Road Tributary, F Tributary, and Golf Course Creeks A and B, and for reaches along I Tributary, E Tributary, and Prison Hill Creek. The March 16, 1989 revision, modified the 1 percent annual chance of occurrence (100-year) base flood elevation (BFE’s) and flood plain boundary delineations along a reach of Saliman Road Tributary, from its confluence with H-Tributary to a point 200 feet upstream of U.S. Highway 395, and a reach of H-Tributary from East Fifth Street to a point approximately 800 feet downstream of Curry Street.

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The revision dated September 30, 1993, incorporated the results of a detailed study of the Carson River affecting Carson City. The study reach begins 1.2 miles upstream of Mexican Dam at USGS Gaging Station No. 10311000, and extends upstream to the Carson City/Douglas County boundary, a distance of approximately 4 miles. The October 16, 1996 revision, incorporated two Letters of Map Revision (LOMRs) along Saliman Road Tributary, the first dated May 11, 1992, and the second dated February 27, 1995. The May 11, 1992, LOMR is based on updated topographic information resulting from road construction and lot grading for single-family house construction on Pinebrook Street and Saliman Road along Saliman Road Tributary. Based on the referenced analyses, the 1-percent annual chance period (recurrence interval) flood along Saliman Road Tributary is contained in Pinebrook Street from approximately 250 feet south of its intersection with Myles Way to its intersection with Damon Road. In Saliman Road, the 1-percent annual chance period (recurrence interval) flood is contained from approximately 700 feet south of its intersection with Damon Road to the intersection of Saliman Road and Damon Road. The February 27, 1995, LOMR is based on updated topographic information along Saliman Road Tributary resulting from a road improvement project for Saliman Road from its intersection with Sonoma Street to Koontz Lane. Based on the referenced analyses, the Special Flood Hazard Area (SFHA) has decreased along Saliman Road Tributary from Valley View Drive to approximately 450 feet downstream of Sonoma Street and the BFEs have decreased from approximately 500 feet downstream of Sonoma Street to just downstream of Valley View Drive. Based on the updated topographic information, the SFHA has also increased between Valley View Drive and Koontz Lane on the western side of Saliman Road and from approximately 300 feet downstream to approximately 800 feet upstream of Sonoma Street on the eastern side of Saliman Road. This FIS also incorporates the determinations of letters issued by FEMA resulting in map changes (Letter of Map Revisions [LOMR]), as shown in Table 4, “Letters of Map Change.”

Table 4 - LETTERS OF MAP CHANGE

Community Flooding Source(s)/Project Identifier Date Issued Type Case Number

Carson City Hydraulic Analysis – Saliman Road and H Tributary

05-29-2003 LOMR 01-09-592P

Carson City Goni Canyon Creek, between 2,300 and 3,300 feet downstream of Hot Springs Road

11-29-2001 LOMR 01-09-066P

Carson City H Tributary and I Tributary, Carson Quail Business Park

03-28-2005 LOMR 04-09-1128P

Carson City Carson River, 1,000 feet upstream to 2,000 feet upstream of Deer Run Road.

03-10-1998 LOMR 98-09-240P

Carson City Goni Canyon Creek, approx. 100 feet downstream to approx. 800 feet downstream of US50.

04-06-1999 LOMR 99-09-113P

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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 Carson City. The areas studied by detailed and limited-detailed methods were selected with priority given to all known flood hazard areas and areas of projected development or proposed construction through 1987.

2.2 Community Description Carson City, the State capital, lies at the west-centra1 edge of Nevada. It is bordered by Washoe and Lyon Counties to the north, Lyon County to the east, Douglas County to the south, and Placer County, California, to the west. The city population center is located 30 miles south of Reno and 14 miles east of Lake Tahoe. U.S. Highways 50 and 395 intersect in the central business district, providing all-weather access to other points in Nevada and California. The developed area of Carson City is located in Eagle Valley, an alluvial valley formed by streams draining the Carson and Virginia Ranges. These Carson River tributaries have caused flood damage since the time of the first settlement in the l850s. Carson City began its growth as a major commercial and transportation center in 1859 with the discovery of the Comstock Lode. Timber from adjacent mountain slopes was logged for use in the mines and new towns that were springing up throughout the area. Denuded watersheds resulted, causing increased flood severity and damage from sediment and debris in Carson City and adjacent areas (Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, November 1973). The population of Carson City mushroomed (more than doubling) between 1970 arid 1980. In 1980, the population reached 32,022 and was concentrated in the 7.5 square miles that form the Carson City urban core. In 2000, Carson City had a population of 52,457 (U.S. Census Bureau, State and County Quickfacts for Carson City, 2000). The economic base for this boom is tourism and light industry. Government services are also an important sector of its economy. New developments that serve the growing population are replacing the traditional land uses of open range and forage crops. The corporate limits of Carson City encompass what was once Ormsby County. A single city-county organization now governs the approximately 147-square-mile area. The climate within the extensive corporate limits ranges from humid alpine conditions in the Sierra Nevada to semiarid steppe in the valleys to the east. Precipitation in the urban district averages 11.83 inches a year, 75 percent of which falls between October and March. Winter precipitation results from westerly cyclonic storms and can be in the form of rain or snow. Winter temperatures are cool, averaging 35.2°F. However, average daily temperature extremes during the winter vary from a high of 52°F to a low of 23°F. Summers are warm, averaging 66.7°F. Recorded annual temperature extremes range from -18°F to 103°F (U.S. Department of Agriculture, Nevada, Undated). The major sources of flooding in Carson City are the streams that drain the Carson and Virginia Ranges and flow east-southeast across Eagle Valley to the Carson River. Most of the Carson City urban district lies across these drainageways, which are often shallow and indistinct on the valley floor. The major streams flowing through Eagle Valley from the Carson Range are Clear Creek, Kings Canyon Creek, and Ash Canyon Creek, which flow year round, and Vicee Canyon Creek, Voltaire Canyon Creek, and Combs Canyon Creek, which flow during only part of the year.

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Eagle Valley Creek drains a small watershed that is a tributary to Combs Canyon Creek. Goni Canyon Creek and the streams designated as Golf Course Creeks A and B flow south into the valley from the Virginia Range. These streams discharge into the Carson River, which flows through Carson City at the eastern edge of Eagle Valley. The two forks of the Carson River rise in the Sierra Nevada at elevations of 6,000 to 10,000 feet. They flow north into Nevada and join in the Carson Valley, south of Carson City. The Carson River then flows north-northeast to Lahontan Reservoir. Below Lahontan Dam in Carson City, all of the water is used for irrigation. The irrigation tailwaters end in the Carson Sink on the Stillwater Wildlife Management Area. The drainage area of the Carson River at Carson City is approximately 876 square miles.

2.3 Principal Flood Problems Historically, major flood damage to the developed areas of Carson City has been caused by the streams from the Carson and Virginia Ranges, referred to here as the Carson City watershed. The floodflows begin in steep mountain canyons, where they develop high velocities and pick up sediment and debris. When the flows reach Eagle Valley, they spread out in broad streams and drop much of their sediment and debris load. As the flows reach the urban district, they are channeled into the east-west streets, with some backwater and diversions flowing along the north-south grid. The downtown area between Second and John Streets has been flooded consistently in the past (Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, November 1973). Where flows encounter obstructions such as highway embankments, they pond and cause additional flooding upstream. Flooding from backwater effects may also occur as the streams discharge into the Carson River. In the past, flood damage along the Carson River has been restricted to loss of agricultural lands, destruction of bridges and irrigation works, and damage to flood plain industries such as mills (Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, November 1973). In addition, portions of the now-abandoned townsite of Empire have been flooded regularly by the Carson River. Carson City is affected by floods arising from three causes: dry mantle, wet mantle, and snowmelt combined with rainfall. The mantle refers to the saturation level of the soil. Dry-mantle floods result from localized, but intense, summer thunderstorms. Wet mantle and snowmelt combined with rainfall floods are winter or early spring occurrences. Wet mantle refers to flooding that results from rainfall on already saturated soil. The majority of floods and the greatest amount of damage have resulted from wet-mantle and snowmelt combined with rainfall conditions (Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, November 1973). The first major flood to be observed and described in the Carson City watershed occurred in December 1861-January 1862. The cause was snowmelt combined with rainfall. Four other wet-mantle or snowmelt combined with rainfall floods were recorded for the Carson City watershed during the 19th century, although none were measured. Most of the damage was flooded basements and first floors, washed-out roads and bridges, and lost cropland and irrigation works. Unpaved east-west streets in Carson City that carried the flows were severely scoured and gullied by these floods. From 1900 to 1980, 17 floods occurred as a result of snowmelt combined with rainfall conditions. None of these floods were measured, but the most destructive were in March 1907, December 1937-January 1938, January 1943, and November 1950. After 1950, the paving of downtown streets reduced erosion damage, and the installation of a 48-inch storm sewer along Washington Street eliminated nuisance flooding of the north-south streets between Washington and John Streets. However, total flood damage did not decrease because of new development

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along Mountain Street north of Washington Street (Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, November 1973). Flooding along the Carson River overlaps but does not duplicate flooding from the Carson City watershed. This variability results from different sizes of drainage area and separate locations of headwaters. In addition to the 19th century floods mentioned above, the Carson River flooded in May-June 1890 from snowmelt after an unusually heavy winter of snow, known as the White Winter of 1889. A snowmelt combined with rainfall flood also occurred on Christmas Day in 1892. During the 20th century, a flood not included above occurred in 1937 from snowmelt combined with rainfall. It was the largest flood on the Carson River since the beginning of the century, but no. measurement was made of the flow at the gaging station at Carson City. The largest estimated flow so far in this century occurred in December 1955. The peak flow of 30,000 cubic feet per second (cfs) at the gaging station at Carson City corresponds to a flood recurrence interval of approximately 59 years. Other large floods occurred in February 1963 (21,900 cfs) and in November 1950 (15,500 cfs) (Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, November 1973) and are estimated to have recurrence intervals of approximately 36 and 22 years, respectively. From January 1861 through January 1980, the Carson City area experienced 25 wet-mantle or snowmelt combined with rainfall floods, an average of one every 5 years. During that time, the area has experienced only four dry-mantle floods: July 1875, July 1913, August 1958, and July 1960. The 1875 flood was the most destructive because torrential rain fell on the logged, unprotected slopes of Ash and Kings Canyons. The floodwaters carried heavy loads of sediment, debris, and boulders to the canyon mouths, where the material was deposited. Croplands buried in this deluge have never been reclaimed (Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, November 1973). In 1913, several separate storms caused flooding and road damage in Kings Canyon and in Eagle Valley at Clear Creek. The 1960 storm also occurred over Kings Canyon. The 1958 storm occurred over C Hill, south of Kings Canyon Road. The hill had been burned over by wildfire 2 months before, leaving the slopes unprotected. Flows moved off the hill onto Circle Drive and Sharrow Way and into a development that was under construction at the time. Despite the regular recurrence of flooding, no lives have yet been reported lost in the Carson City area during a flood. This may be because most flooding is shallow and carried primarily by city streets.

2.4 Flood Protection Measures The Carson River basin, unlike many basins its size, has no existing dams or reservoirs upstream of Carson City (Nevada Department of Conservation and Natural Resources, Water Resources Reconnaissance Series Report 59, 1975). The U.S. Bureau of Reclamation has made feasibility studies, but has no immediate plans for construction of the proposed Watasheamu Dam on the East Fork of the Carson River. Nonstructural measures have been implemented by Carson City to reduce the potential of future damage. One measure is the mapping of high-risk flood areas and special requirements in the Building Code for structures built in these areas. In another program, the city is purchasing portions of the upper Carson City watershed in order to rehabilitate and protect the vegetative cover. This program is being carried out with the assistance of Federal and State agencies.

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All sections of the Carson City urban district are served by a storm drainage system. This system generally is adequate to carry only nuisance flooding and the runoff from smaller, frequent storms, but the system cannot handle flows from the watersheds to the west or overflow from the Carson River (Carson River Basin Council of Governments, March 1974 and SEA, Inc., December 1975). Major floods are carried through city streets and across open space areas and do not necessarily follow the course of the lower flows.

3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods in the community, standard hydrologic and hydraulic study methods were used to determine the flood-hazard 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-, 2-, 1-, or 0.2-percent annual chance 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 annual 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 shorter 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 100-year flood (1-percent annual chance of annual exceedence) 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 methods affecting the community. The NRCS publication, Computer Program for Project Formulation- Hydrology (U.S. Department of Agriculture, National Resources Conservation Service, Technical Release 20, 1965), was used in the hydrologic analysis of the Carson City watershed. The model was necessary because long-term streamflow records are lacking in the watershed. This rainfall-runoff model considers factors such as precipitation-duration-frequency data, hydrologic soil groups and land use, time of concentration, and storm type. The precipitation data were taken from National Oceanic Atmospheric Administration Atlas (U.S. Department of Commerce, National Oceanic and Atmospheric Administration, 1973). Precipitation duration and distribution used in the model were those recommended by the NRCS. Long-term records (39 years) were available for analyzing various frequency flows for the Carson River at the Carson City gaging station (USGS No. 10311000). A log-Pearson Type III analysis was performed on the annual peaks in accordance with U.S. Water Resources Council guidelines (U.S. Water Resources Council, Bulletin 17A, March 1977). In the March 16, 1989 revisions performed by LAI and RCI used the USACE’s HEC-1 hydrologic computer model, while the effective FIS used the NRCS’s TR-20 hydrologic model. In the effective FIS, the sub-basin curve numbers were adjusted to an antecedent soil-moisture condition I (drier than average). The curve numbers developed by LAI and RCI used an antecedent soil-moisture condition II (average condition). In the effective FIS, a 1 percent annual

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chance of occurrence, 24-hour point-precipitation value of 4.6 inches was assumed for the entire Carson City watershed. However, precipitation in the Carson City watershed varies with location and elevation. LAI and RCI estimated point-precipitation values for each sub-basin. The precipitation values and resultant discharges presented in the LAI/RCI report are more representative than the values used in the original FIS report. For the October 16, 1996 revision, the referenced HEC-1 model was used to develop discharge-frequency relationships. Watershed areas for the model were based on those used for the previous FIS (Federal Emergency Management Agency, Revised September 30, 1993). The design-storm event used for the model was developed using selected site-specific precipitation values from the National Oceanic and Atmospheric Administration Atlas (U.S. Department of Commerce, National Oceanic and Atmospheric Administration, 1973) and a balanced distribution. The NRCS curve number was calculated for each basin based on an analysis of soil type, vegetative cover and type, and soil moisture. The curve number developed used an antecedent soil-moisture condition of type II (average condition). The HEC-1 model developed runoff hydrographs for the 10-, 2-, and 1- percent annual chance period (recurrence interval) floods. For the 0.2-percent annual chance period event, linear regression extrapolation was used. A summary of the drainage area-peak discharge relationships for all the streams studied by detailed methods is shown in Table 5, “Summary of Peak Discharges.”

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Table 5 – SUMMARY OF PEAK DISCHARGES

Peak Discharges (cfs)

Flooding Source and Location

Drainage Area

(sq. mi.) 10-Percent-Annual-Chance 2-Percent-Annual-Chance 1-Percent-Annual-Chance 0.2-Percent-Annual-Chance

Ash Canyon Creek

Near Longview Way 6 220 950 1,660 5,550

Carson River

3 Miles Upstream of Lloyds Bridge (USGS No. 10311000) 876 8,420 23,800 36,000 90,400

Clear Creek

Approximately 1 Mile Upstream of U.S. Highway 395 (in Douglas County, Nevada 16 190 1,200 2,450 11,300

Combs Canyon Creek

At U.S. Highway 395 3 95 425 760 2,640

Eagle Valley Creek

Near the intersection of U.S. Highway 395 and Graves Lane 1 75 280 470 1,410

Golf Course Creek A and B

At U.S. Highway 50 5 330 1,185 1,930 5,555

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Peak Discharges (cfs)

Flooding Source and Location

Drainage Area

(sq. mi.) 10-Percent-Annual-Chance 2-Percent-Annual-Chance 1-Percent-Annual-Chance 0.2-Percent-Annual-Chance

Goni Canyon Creek

At Carson City Airport 6 150 780 1,465 5,730

At U.S. Highway 50 -- -- -- 2,776 --

Kings Canyon Creek

Near Canyon Drive 5 160 765 1,390 5,065

Vicee Canyon Creek

At Confluence With Ash Canyon Creek 2 45 250 475 1,950

Voltaire Canyon Creek

Near U.S. Highway 395 2 85 390 690 2,410

-- Data Not Available

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3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were performed to provide estimates of the flood elevations 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 or in the Floodway Data tables in the FIS report. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. 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. Cross sections were determined from topographic maps and field surveys. All bridges, dam, and culverts were field surveyed to obtain elevation data and structural geometry. All topographic mapping used to determine cross sections are referenced in Section 4.1. 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 (see 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 profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. All qualifying bench marks within a given jurisdiction that are cataloged by the National Geodectic Survey ( NGS) and entered into the National Spatial Reference System ( NSRS) as First of Second Order Vertical and have a vertical stability classification of A, B, or C are shown and labeled on the Firm with their 6-character NSRS Permanent Identifier. Bench marks cataloged by the NGS and entered into the NSRS vary widely in vertical stability classifications. NSRS vertical stability classifications are as follows: • Stability A: Monuments of the most reliable nature, expected to hold position/elevation well

(e.g., mounted in bedrock)

• Stability B: Monuments which generally hold their position/elevation well (e.g., concrete bridge abutment)

• Stability C: Monuments which may be affected by surface ground movements (e.g., concrete monument blow frost line)

• Stability D: Mark of questionable or unknown vertical stability (e.g., concrete monument above frost line, or steel witness post)

In addition to NSRS bench marks, the FIRM may also show vertical control monuments established by a local jurisdiction; these monuments will be shown on the FIRM with the appropriate designations. Local monuments will only be placed on the FIRM if the community has requested that they be included, and if the monuments meet the aforementioned NSRS inclusion criteria.

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To obtain current elevation, description, and/or location information for bench marks shown on the FIRM for this jurisdiction, please contact the Information Services Branch of the NGS at (301) 713-3242, or visit their website at www.ngs.noaa.gov. It is important to note that temporary vertical monuments are often established during the preparation of a flood hazard analysis for the purposes of establishing local vertical control. Although these monuments are not shown on the FIRM, they may be found in the Technical Support Data Notebook associated with this FIS and FIRM. Interested individuals may contact FEMA to access this data. The 10-, 2-, 1-, and 0.2-percent annual chance of occurrence water-surface elevations for the detailed-study reaches of the Carson River, Clear Creek, Kings Canyon Creek, Goni Canyon Creek, Eagle Valley Creek, and Golf Course Creeks A and B were computed using the USACE HEC-2 step-backwater computer program (U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, December 1968, with Updates). The 1-percent annual chance of occurrence (100-year) shallow flooding (average depths less than 3 feet) from Eagle Valley Creek, Eagle Extension, F Tributary, H Tributary, Voltaire Canyon Creek, Voltaire Split, and Saliman Road Tributary was analyzed using the HEC-2 program (U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, December 1968, with Updates). Shallow flooding from the combined flow of Ash and Kings Canyon Creeks was studied using normal-depth calculations. Alluvial fan methodologies were applied to calculate flow depths and velocities in portions of Combs Canyon, Vicee Canyon, Kings Canyon, and Ash Canyon Creeks (David R. Dawdy, Flood Frequency Estimates on Alluvial Fans, Journal of the Hydraulics Division ASCE, Proceedings, 1979). Alluvial fans are characterized by unstable channel systems due to slope and soil conditions. Consequently, flows rarely spread evenly over the surface of an alluvial fan and can be concentrated in an identifiable temporary channel or confined to only portions of the fan surface. The ability to scour and deposit sediment makes flow paths prone to lateral migration and relocation to any portion of the fan during a single runoff event and subsequent events. This erratic, unpredictable behavior subjects all portions of the fan to potential flood hazard, regardless of location. As the fan widens, the probability of flooding at a given depth and velocity at a specific point generally decreases. The 1-percent annual chance of occurrence (100-year) flooding in the upper portions of Clear Creek, Kings Canyon Creek, Ash Canyon Creek, Vicee Canyon Creek, Combs Canyon Creek, and Goni Canyon Creek, as well as the entire study reaches of G Tributary, Kings Split, and Channels C and D, was evaluated using the HEC-2 program (U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, December 1968, with Updates) and is shown as approximate flooding. Due to the unpredictable nature of several of the stream channel locations, a Profile Base Line used for horizontal control was developed for the analysis. The base line and channel and flood plain geometry was obtained using aerial photogrammetry. Aerial reconnaissance for this study was performed by Cooper Aerial Survey on November 16, 1980 (Cooper Aerial Survey Company, Aerial Photographs: Carson City, November 1980). Digitized cross sections, accurate to ± 1 foot, were also provided by Cooper Aerial Survey. Topographic mapping was compiled at a scale of 1:4,800, with a contour interval of 4 feet (Cooper Aerial Survey Company, Topographic Map, 1980).

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Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles. For those stream segments studied by shallow flooding, alluvial fan, or limited-detailed study methods, no profiles are shown. Dimensions of major drainage structures were obtained by the study contractor during field reconnaissance in October 1980. Underwater sections in the Carson River were obtained by determining flow depths at existing gaging stations and applying these average depths to adjacent stream reaches. Roughness factors (Manning’s “n”) used in the hydraulic computations were estimated using Open Channel Hydraulics as a guide (Ven T. Chow, Open-Channel Hydraulics, 1959). Table 6 contains a summary of Manning’s “n” values used in this FIS study.

Table 6 – MANNING’S "n" VALUES

Stream Left Overbank “n” Channel “n” Right Overbank “n”

Ash Canyon Creek 0.040 - 0.055 0.040 - 0.055 0.040 - 0.055

Carson River 0.035 0.030 0.035

Clear Creek 0.030 - 0.060 0.030 - 0.055 0.030 - 0.060

Combs Canyon Creek 0.040 - 0.060 0.040 - 0.060 0.040 - 0.060

Eagle Valley Creek 0.045 - 0.050 0.040 - 0.050 0.045 - 0.050

Golf Course Creeks A and B 0.025 - 0.062 0.025 - 0.050 0.025 - 0.062

Goni Canyon Creek 0.025 - 0.060 0.025 - 0.060 0.025 - 0.060

H Tributary 0.035 - 0.055 0.035 - 0.055 0.035 - 0.055

Kings Canyon Creek 0.025 - 0.060 0.025 - 0.060 0.025 - 0.060

Saliman Road Tributary 0.050 - 0.055 0.025 - 0.055 0.050 - 0.055

Vicee Canyon Creek 0.040 - 0.050 0.040 - 0.050 0.040 - 0.050

Voltaire Canyon Creek 0.035 - 0.060 0.035 - 0.060 0.035 - 0.060 Starting water-surface elevations were calculated using the slope-area method. The 1-percent annual chance of occurrence flood elevations for the approximate-study reaches were estimated using normal-depth calculations. The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. In the original effective FIS, digitized cross sections were used for the HEC-2 hydraulic computer model. The cross sections were obtained from aerial mapping with a scale of 1:4,800, and a contour interval of 4 feet. In the revised study dated March 16,1989 performed by LAI and RCI,

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digitized cross sections for the HEC-2 hydraulic computer model were obtained from aerial mapping with a scale of 1:2,400, and a contour interval of 2 feet. The original flood plain boundaries shown in the FIS are based on a topographic map with a scale of 1:4,800, and a contour interval of 4 feet, while the revised-study flood plain boundaries performed by LAI and RCI were based on a topographic map with a scale of 1:2,400 and a contour interval of 2 feet. The LAI and RCI analyses resulted in increases in the BFEs and changes in flood plain boundaries along Saliman Road Tributary and H-Tributary. The revised BFEs and flood plain boundaries along the Saliman Road Tributary and H-Tributary tie into the BFEs and flood plain boundaries both upstream and downstream of the revised reaches shown in the effective FIS. In the September 30, 1993 revision the water-surface elevations for the studied reach of the Carson River were computed using the Federal Highway Administration/USGS WSPRO Computer Program (U.S. Department of Transportation, Federal Highway Administration, 1986, Updated June 1, 1988). Channel and overbank roughness factors (Manning’s “n”) used in the hydraulic computations were selected based on field observations of the stream and flood plain area. Cross sections for backwater analyses were obtained by field surveys. Locations of cross sections used in the hydraulic analyses are shown on the Flood Profiles and on the FIRM. Table 9, “Floodway Data,” and the Flood Profiles for Carson River and Spring Creek (near the confluence with the Carson River) were revised to incorporate the results of this study. In the October 16, 1996 revision, the water-surface elevations along Saliman Road Tributary were developed using the referenced HEC-2 model. All cross-sectional data was obtained through photogrammetric digitization of topographic maps (Lumos & Associates, Incorporated, and Resource Concepts, Incorporated, March 19,1987), the Manning’s “n” values used were the same as used in the previous FIS, and the 1- and 0.2-percent annual chance period (recurrence interval) flood plain boundaries were delineated using water-surface elevations determined at each cross section; between cross sections, the boundaries were interpolated using the referenced topographic maps. The conversion factor for each stream studied by detailed methods is shown below in Table 7.

Table 7 - STREAM CONVERSION FACTORS

Stream Name Elevation (feet NAVD above NGVD)

Carson River + 3.7

Clear Creek + 3.7

Eagle Valley Creek + 3.7

Golf Course Creek A + 3.6

Golf Course Creek B + 3.6

Goni Canyon Creek + 3.6

H Tributary + 3.7

Kings Canyon Creek + 3.6

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Levee Hazard Analysis

Some flood hazard information presented in prior FIRMs and in prior FIS reports for Carson City was based on flood protection provided by levees. Based on the information available and the mapping standards of the National Flood Insurance Program at the time that the prior FISs and FIRMs were prepared, FEMA accredited the levees as providing protection from the flood that has a 1-percent-chance of being equaled or exceeded in any given year. For FEMA to continue to accredit the identified levees with providing protection from the base flood, the levees must meet the criteria of the Code of Federal Regulations, Title 44, Section 65.10 (44 CFR 65.10), titled “Mapping of Areas Protected by Levee Systems.” On August 22, 2005, FEMA issued Procedure Memorandum No. 34 - Interim Guidance for Studies Including Levees. The purpose of the memorandum was to help clarify the responsibility of community officials or other parties seeking recognition of a levee by providing information identified during a study/mapping project. Often, documentation regarding levee design, accreditation, and the impacts on flood hazard mapping is outdated or missing altogether. To remedy this, Procedure Memorandum No. 34 provides interim guidance on procedures to minimize delays in near-term studies/mapping projects, to help our mapping partners properly assess how to handle levee mapping issues. While 44 CFR Section 65.10 documentation is being compiled, the release of more up-to-date FIRM panels for other parts of a community or county may be delayed. To minimize the impact of the levee recognition and certification process, FEMA issued Procedure Memorandum No. 43 - Guidelines for Identifying Provisionally Accredited Levees on March 16, 2007. These guidelines will allow issuance of preliminary and effective versions of FIRMs while the levee owners or communities are compiling the full documentation required to show compliance with 44 CFR Section 65.10. The guidelines also explain that preliminary FIRMs can be issued while providing the communities and levee owners with a specified timeframe to correct any maintenance deficiencies associated with a levee and to show compliance with 44 CFR Section 65.10. FEMA contacted Carson City to obtain data required under 44 CFR 65.10 to continue to show the levees as providing protection from the flood that has a 1-percent-chance of being equaled or exceeded in any given year. FEMA understood that it may take time to acquire and/or assemble the documentation necessary to fully comply with 44 CFR 65.10. Therefore, FEMA put forth a process to provide the communities with additional time to submit all the necessary documentation. For a community to avail itself of the additional time, it had to sign an agreement with FEMA. Levees for which such agreements were signed are shown on the final effective FIRM as providing protection from the flood that has a 1-percent-chance of being equaled or exceeded in any given year and labeled as a Provisionally Accredited Levee (PAL). Communities have two years from the date of FEMA’s initial coordination to submit to FEMA final accreditation data for all PALs. Following receipt of final accreditation data, FEMA will revise the FIS and FIRM as warranted. FEMA coordinated with the U.S. Army Corps of Engineers, the local community, and other organizations to compile a list of levees that exist within Carson City. Table 8, “List of Levees Requiring Flood Hazard Revisions” lists all levees shown on the FIRM, to include PALs, for which corresponding flood hazard revisions were made.

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Approximate analyses of “behind levee” flooding were conducted for all the levees in Table 8 to indicate the extent of the “behind levee” floodplains. The methodology used in these analyses is discussed below. The approximate levee analysis was conducted using information from existing hydraulic models (where applicable) and USGS topographic maps. The extent of the 1-percent-annual-chance flood in the event of levee failure was determined. Base flood elevations and topographic information (where available) were used to estimate an approximate 1-percent-annual-chance floodplain and traced along the contour line representing the base flood elevation. If base flood elevations were not available they were estimated from effective FIRM maps and available information. Topographic features such as highways, railroads, and high ground were used to refine approximate floodplain boundary limits.

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Table 8 - LIST OF LEVEES REQUIRING FLOOD HAZARD REVISIONS

Community Flood Source Levee Inventory ID Coordinates Latitude/Longitude FIRM Panel USACE

Levee

Carson City1 Combs Canyon Creek 1 (-119.790, 39.189) (-119.784, 39.189)

320001C0083E No

Carson City 1 Eagle Valley Creek/ Combs Canyon Creek 2

(-119.777, 39.198) (-119.767, 39.180)

320001C0084E 320001C0092E

No

Carson City 1 H Tributary 3 (-119.767, 39.157) (-119.767, 39.153)

320001C0092E 320001C0094E

No

Carson City 1 Kings Canyon Creek 4 (-119.720, 39.164) (-119.717, 39.164)

320001C0111E 320001C0112E

No

1 Road

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3.3 Vertical Datum All FIS reports and FIRMs are referenced to a specific vertical datum. The vertical datum provides a starting point against which flood, ground, and structure elevations can be referenced and compared. Until recently, the standard vertical datum in use for newly created or revised FIS reports and FIRMs was the National Geodetic Vertical Datum of 1929 (NGVD). With the finalization of the North American Vertical Datum of 1988 (NAVD), many FIS reports and FIRMs are being prepared using NAVD as the referenced vertical datum. All flood elevations shown in this FIS report and on the FIRM are referenced to NAVD. Structure and ground elevations in the community must, therefore, be referenced to NAVD. It is important to note that adjacent communities may be referenced to NGVD. This may result in differences in Base (1-percent-annual-chance) Flood Elevations (BFEs) across the corporate limits between the communities. Flood elevations shown in this FIS report and on the FIRM are referenced to the NAVD. These flood elevations must be compared to structure and ground elevations referenced to the same vertical datum. For information regarding conversion between the NGVD and NAVD, visit the National Geodetic Survey website at www.ngs.noaa.gov, or contact the National Geodetic Survey at the following address:

NGS Information Services NOAA, N/NGS12

National Geodetic Survey SSMC-3, #9202

1315 East-West Highway Silver Spring, MD 20910-3282

(301) 713-3242 Temporary vertical monuments are often established during the preparation of a flood hazard analysis for the purpose of establishing local vertical control. Although these monuments are not shown on the FIRM, they may be found in the Technical Support Data Notebook (TSDN) associated with the FIS report and FIRM for this community. Interested individuals may contact FEMA to access these data.

4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound floodplain management programs. To assist in this endeavor, each FIS provides 1-percent annual chance floodplain data, which may include a combination of the following: 10-, 2-, 1-, and 0.2-percent annual chance flood elevations; delineations of the 1-percent annual chance and 0.2-percent annual chance floodplains; and 1-percent annual chance floodway. This information is presented on the FIRM and in many components of the FIS, including Flood Profiles, Floodway Data tables, and Summary of Stillwater Elevation tables. Users should reference the data presented in the FIS as well as additional information that may be available at the local community map repository before making flood elevation and/or floodplain boundary determinations.

4.1 Flood Boundaries To provide a national standard without regional discrimination, the 1-percent annual chance (100-year) flood has been adopted by FEMA as the base flood for floodplain management

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purposes. The 0.2-percent annual chance (500-year) flood is employed to indicate additional areas of flood risk in the community. For each stream studied by detailed or limited detail methods, the 1- and 0.2-percent annual chance floodplain boundaries have been delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:4,800, with a contour interval of 4 feet (Cooper Aerial Survey Company, Topographic Map, 1980). For the flooding sources studied by approximate methods, the boundaries of the 1-percent annual chance floodplains were delineated using topographic maps taken from the previously printed FIS reports, FHBMs, and/or FIRMS for Carson City. The 1- and 0.2-percent annual chance floodplain boundaries are shown on the FIRM. On this map, the 1-percent annual chance floodplain boundary corresponds to the boundary of the areas of special flood hazards (Zones A, AE, and AH), and the 0.2-percent annual chance floodplain boundary corresponds to the boundary of areas of moderate flood hazards. In cases where the 1- and 0.2-percent annual chance floodplain boundaries are close together, only the 1-percent annual chance floodplain boundary has been shown. Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown because of limitations of the map scale and/or lack of detailed topographic data. For the streams studied by approximate methods, only the 1-percent annual chance floodplain boundary is shown on the FIRM and was developed from normal-depth calculations and USGS topographic maps (U.S. Department of the Interior, Geological Survey, 1968, Revised 1974).

4.2 Floodways Encroachment on floodplains, such as structures and fill, reduces flood-carrying capacity, increases flood heights and velocities, and increases flood hazards in areas beyond the encroachment itself. One aspect of floodplain management involves balancing the economic gain from floodplain development against the resulting increase in flood hazard. For purposes of the NFIP, a floodway is used as a tool to assist local communities in this aspect of floodplain management. Under this concept, the area of the 1-percent annual chance floodplain is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that the 1-percent annual chance flood can be carried without substantial increases in flood heights. Minimum Federal standards limit such increases to 1 foot, provided that hazardous velocities are not produced. The floodways in this study are presented to local agencies as minimum standards that can be adopted directly or used as a basis for additional floodway studies. The floodways presented in this study were computed for certain stream segments on the basis of equal-conveyance reduction from each side of the floodplain. Floodway widths were computed at cross sections. Between cross sections, the floodway boundaries were interpolated. The results of the floodway computations are tabulated for selected cross sections (see Table 9, Floodway Data). In cases where the floodway and 1-percent annual chance floodplain boundaries are either close together or collinear, only the floodway boundary is shown. In areas of shallow and alluvial fan flooding, floodways were not determined because the unpredictable flow paths make delineation of a floodway meeting FEMA criteria impossible. In addition, no floodway was determined for those streams with a limited—detailed or shallow flooding analysis. Therefore, the streams for which no floodways have been delineated are portions of Clear Creek, Kings Canyon Creek, Goni Canyon Creek, Eagle Valley Creek and the

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entire reaches for Ash Canyon Creek, Vicee Canyon Creek, Combs Canyon Creek, N Tributary, Voltaire Canyon Creek, Voltaire Split, Saliman Road Tributary, Eagle Extension, and F Tributary. However, the community should regulate development in swales and identifiable stream channels because of historical evidence of flow in such areas. The floodways presented in this study were computed for certain stream segments on the basis of equal-conveyance reduction from each side of the floodplain. No floodway were computed for Ash Canyon Creek, Channels C, Channels D, Combs Canyon Creek, Eagle Extension, F Tributary, G Tributary, H Tributary, Kings Split, Saliman Road Tributary, Vicee Canyon Creek, Voltaire Canyon Creek, and Voltaire Split.

Encroachment into areas subject to inundation by floodwater having hazardous velocities aggravates the risk of flood damage, and heightens potential flood hazards by further increasing velocities. A listing of stream velocities at selected cross sections is provided in Table 9, “Floodway Data.” In order to reduce the risk of property damage in areas where the stream velocities are high, the community may wish to restrict development in areas outside floodway. The area between the floodway and the boundary of the 1-percent annual chance floodplain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain that could be completely obstructed without increasing the water-surface elevation of the 1-percent annual chance flood by more than 1.0 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown in Figure 1.

Figure 1 – FLOODWAY SCHEMATIC

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY WITHOUT FLOODWAY

WITH FLOODWAY INCREASE

Carson River A 0 266 2,763 13.0 4,583.2 4,583.2 4,584.2 1.0 B 1,140 162 1,921 18.7 4,590.5 4,590.5 4,590.6 0.1C 2,845 144 2,195 16.4 4,598.8 4,598.8 4,598.8 0.0D 4,045 170 3,441 10.5 4,603.3 4,603.3 4,603.4 0.1E 4,455 340 5,987 6.0 4,604.2 4,604.2 4,604.9 0.7 F 4,565 225 5,235 6.9 4,604.3 4,604.3 4,605.0 0.7G 4,645 275 7,460 4.8 4,604.8 4,604.8 4,605.3 0.5H 5,005 700 13,135 2.7 4,605.1 4,605.1 4,605.7 0.6I 6,185 500 8,876 4.1 4,605.1 4,605.1 4,605.7 0.6J 7,225 960 16,469 2.2 4,605.2 4,605.2 4,606.0 0.8K 10,375 2,501 37,726 1.0 4,605.4 4,605.4 4,606.2 0.8L 11,475 2,765 37,158 1.0 4,605.4 4,605.4 4,606.2 0.8M 13,195 2,342 28,053 1.3 4,605.4 4,605.4 4,606.2 0.8N 14,835 1,215 13,130 2.7 4,605.4 4,605.4 4,606.2 0.8O 16,680 1,253 11,609 3.1 4,605.7 4,605.7 4,606.5 0.8P 18,060 1,361 10,623 3.4 4,606.1 4,606.1 4,607.0 0.9Q 19,620 3,380 20,277 1.8 4,606.5 4,606.5 4,607.4 0.9R 20,760 3,404 18,706 1.9 4,606.7 4,606.7 4,607.6 0.9S 21,990 3,208 14,848 2.4 4,606.9 4,606.9 4,607.8 0.9T 23,410 2,186 6,035 6.0 4,608.3 4,608.3 4,608.6 0.3U 24,575 1,212 5,671 6.3 4,610.7 4,610.7 4,611.0 0.3V 25,020 1,104 3,756 9.1 4,612.8 4,612.8 4,612.8 0.0W 25,050 1,050 3,665 9.8 4,612.8 4,612.8 4,612.8 0.0X 26,815 445 4,814 7.5 4,616.2 4,616.2 4,617.0 0.8Y 28,845 185 2,449 14.7 4,618.2 4,618.2 4,618.8 0.6Z 30,380 180 2,995 12.0 4,622.1 4,622.1 4,623.1 1.0

AA 32,130 188 2,427 14.8 4,625.5 4,625.5 4,626.5 1.01 Feet Above Downstream Limit of Detailed Study (Located 150 Feet Downstream of Brunswick Canyon Road)

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOODWATER-SURFACE ELEVATION (FEET NAVD)

FEDERAL EMERGENCY MANAGEMENT AGENCY


FLOODWAY DATA

CARSON RIVER

TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 3 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 9


SECTION AREA

(SQUARE FEET)




Carson River (cont'd)AB-AF2

AG 40,600 195 2,744 13.12 4,643.3 4,643.3 4,643.3 0.0AH 41,965 300 5,335 6.75 4,646.6 4,646.6 4,647.3 0.7AI 42,397 457 7,591 4.74 4,647.2 4,647.2 4,647.9 0.7AJ 42,727 687 9,839 3.66 4,647.4 4,647.4 4,648.2 0.8AK 43,136 780 10,910 3.30 4,647.5 4,647.5 4,648.3 0.8AL 44,350 487 7,614 4.73 4,647.9 4,647.9 4,648.6 0.7AM 45,500 341 6,037 5.96 4,648.2 4,648.2 4,649.0 0.8AN 46,450 874 13,215 2.72 4,648.8 4,648.8 4,649.7 0.9AO 47,940 1,044 16,415 2.19 4,649.1 4,649.1 4,649.9 0.8AP 49,590 1,369 20,089 1.79 4,649.2 4,649.2 4,650.1 0.9AQ 51,640 2,372 31,431 1.15 4,649.3 4,649.3 4,650.2 0.9AR 53,560 2,492 31,581 1.14 4,649.3 4,649.3 4,650.3 1.0AS 55,260 3,505 40,151 0.9 4,649.4 4,649.4 4,650.4 1.0

1 Feet Above Downstream Limit of Detailed Study (Located 150 Feet Downstream of Brunswick Canyon Road)2 Not Used




FLOODWAY DATA

CARSON RIVER

TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 3 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 3 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 3 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 7 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 3 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 8 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 3 TABLE X TABLE 10 TABLE X TABLE 10 TABLE X TABLE 9


SECTION AREA

(SQUARE FEET)




Clear CreekA 1,200 282 433 6.6 4,648.7 4637.12 4638.12 1.0

B 4,360 213 559 5.1 4,661.5 4,661.5 4,662.5 1.0C 6,860 140 368 7.8 4,677.9 4,677.9 4,678.8 0.9D 7,760 85 271 10.1 4,689.5 4,689.5 4,690.1 0.6E 9,260 132 429 6.4 4,704.3 4,704.3 4,704.9 0.6F 11,230 3233 576 4.7 4,718.9 4,718.9 4,718.9 0.0G 11,260 2763 934 2.9 4,720.0 4,720.0 4,720.0 0.0H 13,410 215 357 7.5 4,743.2 4,743.2 4,743.5 0.3I 14,460 182 549 4.9 4,751.6 4,751.6 4,752.4 0.8J 14,745 66 245 10.9 4,758.9 4,758.9 4,758.9 0.0K 14,865 108 747 3.6 4,765.5 4,765.5 4,766.2 0.7L 16,065 123 338 7.9 4,773.6 4,773.6 4,774.0 0.4M 17,290 3333 493 5.4 4,782.5 4,782.5 4,782.5 0.0N 17,470 3503 2,468 1.1 4,787.2 4,787.2 4,787.3 0.1

1 Feet Above Confluence With Carson River 3 Floodway Lies Entirely Outside Corporate Limits 2 Elevations Computed Without Consideration

of Backwater From Carson River




FLOODWAY DATA

CLEAR CREEK



SECTION AREA

(SQUARE FEET)




Eagle Valley CreekA 0 51 100 4.7 4,756.6 4,756.6 4,757.6 1.0 B 700 80 87 5.4 4,766.9 4,766.9 4,767.3 0.4

C 1,045 70 87 5.4 4,774.8 4,774.8 4,775.0 0.2D 1,780 100 88 5.4 4,792.9 4,792.9 4,793.0 0.1E 2,070 136 97 4.9 4,803.7 4,803.7 4,804.2 0.5 F 2,370 50 78 6.0 4,811.2 4,811.2 4,811.8 0.6G 2,720 49 69 6.8 4,822.5 4,822.5 4,822.5 0.0H 3,715 24 55 8.6 4,882.5 4,882.5 4,882.5 0.0

1 Feet Above Eagle Valley Ranch Road




FLOODWAY DATA

EAGLE VALLEY CREEK


CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)




Golf Course Creek A

A 801 1,471 5,609 0.3 4,619.8 4,619.8 4,620.5 0.7B 7501 125 133 5.9 4,623.6 4,623.6 4,624.2 0.6C 15301 120 198 3.9 4,638.6 4,638.6 4,639.4 0.8

Golf Course Creek B

A 12402 543 842 5.6 4,609.0 4,609.0 4,609.7 0.7B 19502 846 952 2.0 4,615.8 4,615.8 4,616.5 0.7C 21102 1,471 4,531 0.4 4,619.8 4,619.8 4,619.8 0.0D 25802 170 190 6.1 4,620.0 4,620.0 4,620.1 0.1E 39602 130 310 3.7 4,634.6 4,634.6 4,635.5 0.9

1 Feet Above U.S. Highway 50 2 Feet Above Confluence With Carson River




FLOODWAY DATA

GOLF COURSE CREEK A - GOLF COURSE CREEK B



SECTION AREA

(SQUARE FEET)




Goni Canyon CreekA 1,710 783 1,175 3.2 4,635.4 4634.2 2 4634.4 2 0.2

B 2,500 911 889 4.2 4,639.0 4637.5 2 4637.6 2 0.1 C 3,285 843 2,419 1.5 4,641.7 4,641.7 4,642.2 0.5D 5,325 863 487 5.7 4,656.2 4,656.2 4,656.4 0.1E 6,680 800 535 4.8 4,666.0 4,666.0 4,666.7 0.2 F 6,745 451 390 6.7 4,667.7 4,667.7 4,668.7 0.4G 7,220 560 509 5.1 4,670.1 4,670.1 4,670.2 0.0H 7,300 678 520 5.0 4,671.6 4,671.6 4,671.9 0.1I 7,860 831 761 4.3 4,675.5 4,675.5 4,675.6 0.1J 7,930 961 624 5.2 4,676.8 4,676.8 4,677.1 0.3

K 9,135 840 320 5.0 4,687.6 4,687.6 4,688.0 0.4L 9,170 840 1,170 1.4 4,688.0 4,688.0 4,688.6 0.6M 10,250 599 311 5.1 4,696.0 4,696.0 4,696.0 0.0N 12,050 550 377 3.9 4,718.9 4,718.9 4,718.9 0.0O 12,085 550 330 4.4 4,722.1 4,722.1 4,722.1 0.0P 13,145 1,376 976 1.5 4,735.8 4,735.8 4,735.8 0.0Q 14,465 1,710 373 3.9 4,764.0 4,764.0 4,764.0 0.0

1 Feet Above Downstream Limit of Detailed Study2 Elevation Computed Without Consideration of influence from Kings Canyon Creek




FLOODWAY DATA

GONI CANYON CREEK



SECTION AREA

(SQUARE FEET)




Kings Canyon CreekA 4,600 1,173 1,963 6.6 4,607.6 4,607.6 4,608.6 1.0 B 5,840 333 2,047 6.4 4,618.5 4,618.5 4,619.3 0.8

C 5,955 338 1,565 8.3 4,618.9 4,618.9 4,619.6 0.7D 6,835 650 3,582 3.6 4,622.8 4,622.8 4,623.5 0.7E 6,905 850 5,408 2.4 4,622.9 4,622.9 4,623.7 0.8F 7,785 790 4,254 3.1 4,623.5 4,623.5 4,624.3 0.8G 9,255 8362 2,184 6.0 4,628.2 4,628.2 4,628.3 0.1H 9,325 1,1192 7,377 1.8 4,629.5 4,629.5 4,629.5 0.0I 10,325 2,650 14,132 0.9 4,629.8 4,629.8 4,630.0 0.2J 11,795 3,635 2,025 6.4 4,630.8 4,630.8 4,631.2 0.4

K 13,645 2,430 4,374 1.4 4,643.3 4,643.3 4,644.0 0.7

1 Feet Above Confluence With Carson River 2 Width Does Not Include Area in Island




FLOODWAY DATA

KINGS CANYON CREEK


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5.0 INSURANCE APPLICATION For flood insurance rating purposes, flood insurance zone designations are assigned to a community based on the results of the engineering analyses. These zones are as follows: Zone A Zone A is the flood insurance rate zone that corresponds to the 1-percent annual chance floodplain that is determined in the FIS report by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no BFEs or base flood depths are shown within this zone. Zone AE Zone AE is the flood insurance rate zone that corresponds to the 1-percent annual chance floodplain that is determined in the FIS report by detailed methods. Whole-foot BFEs derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Zone AH Zone AH is the flood insurance rate zone that corresponds to areas of 1-percent annual chance shallow flooding (usually areas of ponding) where average depths are between 1 foot and 3 feet. Whole-foot BFEs derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Zone AO Zone AH is the flood insurance risk zone that corresponds to the areas of 1-percent annual chance shallow flooding (usually sheet flow on sloping terrain) where average depths are between 1 and 3 feet. Average Whole-foot base flood depths derived from the detailed hydraulic analyses are within this zone. Zone X Zone X is the flood insurance rate zone that corresponds to areas outside the 0.2-percent annual chance floodplain, areas within the 0.2-percent annual chance floodplain, areas of 1-percent annual chance flooding where average depths are less than 1 foot, areas of 1-percent annual chance flooding where the contributing drainage area is less than 1 square mile, and areas protected from the 1-percent annual chance flood by levees. No BFEs or base flood depths are shown within this zone. Zone D Zone D is the flood insurance risk zone that corresponds to unstudied area where flood hazards are undetermined, but possible.

6.0 FLOOD INSURANCE RATE MAP

The FIRM is designed for flood insurance and floodplain management applications.

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For flood insurance applications, the map designates flood insurance rate zones as described in Section 5.0 and, in the 1-percent annual chance floodplains that were studied by detailed methods, shows selected whole-foot BFEs or average depths. Insurance agents use the zones and BFEs in conjunction with information on structures and their contents to assign premium rates for flood insurance policies. For floodplain management applications, the map shows by tints, screens, and symbols the 1- and 0.2-percent annual chance floodplains, floodways, and the locations of selected cross sections used in the hydraulic analyses and floodway computations. The current FIRM presents flooding information for the entire geographic area of Carson City. Previously, FIRMs were prepared for each incorporated community and the unincorporated areas of the county identified as flood-prone. The FIRM also includes flood hazard information that was presented separately on FBFMs, where applicable.

7.0 OTHER STUDIES Information pertaining to revised and unrevised flood hazards for each jurisdiction within Carson City has been compiled into this FIS. Therefore, this FIS supersedes all previously printed FIS Reports, FBFMs, and FIRMs for Carson City. A draft FIS was completed by the USGS in 1977, but was not accepted (U.S. Department of the Interior, Geological Survey, Water Resources Division, June 1977). Other studies have discussed the general flooding problems of Carson City in connection with development of a storm drainage master plan (Carson River Basin Council of Governments, March 1974, and SEA, Inc., December 1975). A Flood Hazard Boundary Map has been published for Carson City (U.S. Department of Housing and Urban Development, Federal Insurance Administration, May 24, 1974, Revised January 1, 1977). Due to the more detailed analyses used, this study supersedes the Flood Hazard Boundary Map. Flood Insurance Studies have been prepared for the unincorporated areas of Douglas County (Federal Emergency Management Agency, 1983), Lyon County (Federal Emergency Management Agency, 1982), and Washoe County, Nevada (Federal Emergency Management Agency, 1984), and Placer County, California (Federal Emergency Management Agency, 1983). The results of this study are in general agreement with those Flood Insurance Studies.

8.0 LOCATION OF DATA Information concerning the pertinent data used in the preparation of this study can be obtained by contacting FEMA, Region IX, Federal Insurance and Mitigation Administration, 1111 Broadway, Suite 1200, Oakland, California 94607-4052.

9.0 BIBLIOGRAPHY AND REFERENCES Carson River Basin Council of Governments, Regional Storm Drainage Plan, Phase II--Master Plan, March 1974 Cooper Aerial Survey Company, Aerial Photographs: Carson City, Nevada, Scale 1:9,600, November 1980

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Cooper Aerial Survey Company, Topographic Map, Scale 1:4,800, Contour Interval 4 feet: Portions of Carson City, Nevada, 1980 David R. Dawdy, Flood Frequency Estimates on Alluvial Fans, Journal of the Hydraulics Division ASCE, Proceedings, Vol. 105, No. HY11, 1979, pp. 1407—1413 Federal Emergency Management Agency, Flood Insurance Study, Carson City, Nevada, Revised September 30, 1993 Federal Emergency Management Agency, Flood Insurance Study, Douglas County, Nevada (Unincorporated Areas), Revised 1983 Federal Emergency Management Agency, Flood Insurance Study, Lyon County, Nevada (Unincorporated Areas), 1982 Federal Emergency Management Agency, Flood Insurance Study, Placer County, California (Unincorporated Areas), 1983 Federal Emergency Management Agency, Flood Insurance Study, Washoe County, Nevada (Unincorporated Areas), 1984 Lumos & Associates, Incorporated, and Resource Concepts, Incorporated, Area of 100—Year Flood for Saliman Reach, Current and Appeal Existing Condition, Scale 1:2,400, Contour Interval 2 feet, 4 Panels, March 19, 1987 Lumos & Associates, Incorporated, and Resource Concepts, Incorporated, Hydrologic and Hydraulic Assessment Supporting an Appeal of a Portion of the Federal Emergency Management Agency’s Carson City, Nevada, Flood Insurance Study, March 1987 Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, Water and Related Land Resources, Central Lahontan Basin, Carson River Subbasin, Nevada, California, Appendix 1, Soils, June 1971 Nevada Department of Conservation and Natural Resources and U.S. Department of Agriculture, Water and Related Land Resources, Central Lahontan Basin, Carson River Subbasin, Nevada, California, Special Report: History of Flooding, Carson Valley and Carson City, Watershed, November 1973 Nevada Department of Conservation and Natural Resources, The Resources Agency of California, and U.S. Department of Agriculture, Water and Related Land Resources, Central Lahontan Basin, Carson River Subbasin, Nevada, California, Flood Chronology, Lower Hale, Carson River Subbasin, 1861-1976, September 1977 Nevada Department of Conservation and Natural Resources, Water Resources Reconnaissance Series Report 39, Hydrologic Appraisal of Eagle Valley, Ormsby County Nevada, December 1966 Nevada Department of Conservation and Natural Resources, Water Resources Reconnaissance Series Report 59, Water-Resources Appraisal of the Carson River Basin, Western Nevada, 1975

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Nevada Highway Department, Hydrologic Report No. 3, Estimating Peak Discharges from Small Drainages in Nevada According to Basin Areas Within Elevation Zones, Donald C. Moore, Carson City, Nevada, 1976 SEA, Inc., Carson City Storm Drainage Study, Phase II--Master Plan, Sparks, Nevada, December 1975 U.S. Census Bureau, State and County Quickfacts for Carson City, http://quickfacts.census.gov/qfd/states/32/32510.html, 2000 U.S. Department of Agriculture, National Resources Conservation Service, Draft Flood Insurance Study, Douglas County, Nevada, Reno, Nevada, February 1978 U.S. Department of Agriculture, National Resources Conservation Service, Flood Insurance Study, Douglas County, Nevada, Hydrology of Carson River, Historical Summary of Flood Frequency Analysis, Reno, Nevada, February 1978 U.S. Department of Agriculture, National Resources Conservation Service, Hydrology, National Handbook, Section 4, August 1972 U.S. Department of Agriculture, National Resources Conservation Service, Technical Release 20, Computer Program for Project Formulation--Hydrology, 1965 U.S. Department of Agriculture, Soil Survey of Carson City Area, Nevada, undated U.S. Department of Commerce, National Oceanic and Atmospheric Administration, NOAA Atlas 2, Precipitation-Frequency Atlas of the Western United States, Volume VII--Nevada, 1973 U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Precipitation-Frequency Atlas of the Western United States, Vol. VII--Nevada, 1973 U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood Hazard Boundary Map, City/County of Carson City, Nevada (Unincorporated Areas), Scale 1:6,000, May 24, 1974, Revised January 1, 1977 U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, Computer Program 723-X6-L202A HEC-2 Water-Surface Profiles, Davis, California, December 1968, with Updates U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, HEC-1 Flood Hydrograph Package, IBM XT 512K Version, Davis, California, February 1, 1985 U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, HEC-2 Water-Surface Profiles, IBM-PC-XT Version 1.1, Davis, California, November 1976, Updated 1984 U.S. Department of the Interior, Geological Survey, 7.5-Minute Series Topographic Maps, Scale 1:24,000, Contour Intervals 20 and 40 feet: Carson City, Nevada (1968), Photorevised (1974); Genoa, Nevada (1968), Photorevised (1974); McTarnahan Hill, Nevada (1968), Photorevised (1974); New Empire (1968), Photorevised (1974)

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U.S. Department of the Interior, Geological Survey, Water Resources Division, Flood Insurance Study, Carson City, Nevada, June 1977 U.S. Department of Transportation, Federal Highway Administration, Bridge Waterways Analysis Model/Research Report, WSPRO, Shearman, J.O., and Others, FHWA RD-86-108, 1986 (Updated June 1, 1988) U.S. Water Resources Council, Bulletin 17A, Guidelines for Determining Flood Flow Frequency, March 1977 Ven T. Chow, Open-Channel Hydraulics, New York: McGraw—Hill, 1959

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