SHERIDAN COUNTY, WYOMING contractor. The initial CCO ... This Flood Insurance Study covers all areas...

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SHERIDAN COUNTY, WYOMING AND INCORPORATED AREAS Community Name Community Number CLEARMONT, TOWN OF DAYTON, TOWN OF RANCHESTER, TOWN OF 560107 560045 560046 SHERIDAN, CITY OF 560044 SHERIDAN COUNTY (UNINCORPORATED AREAS) 560047 JANUARY 16, 2014 Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 56033CV000A

Transcript of SHERIDAN COUNTY, WYOMING contractor. The initial CCO ... This Flood Insurance Study covers all areas...

  

SHERIDAN COUNTY, WYOMING AND INCORPORATED AREAS

Community Name

Community Number

CLEARMONT, TOWN OF DAYTON, TOWN OF RANCHESTER, TOWN OF

560107

560045

560046

SHERIDAN, CITY OF 560044 SHERIDAN COUNTY (UNINCORPORATED AREAS) 560047

   

 

 JANUARY 16, 2014

 

Federal Emergency Management Agency

FLOOD INSURANCE STUDY NUMBER 56033CV000A 

 

bsmith
Sheridan County

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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) may not contain all data available within the repository. It is advisable to contact the community repository for any additional data. 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 report. 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 report components. Initial FIS Report Effective Date: January 16, 2014 Selected Flood Insurance Rate Map panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map panels (e.g., floodways, cross sections). In addition, former flood hazard zone designations have been changed as follows:

Old Zone(s) New Zone A1 through A30 AE V1 through V30 VE B X C X

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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 2

2.1 Scope of Study 2

2.2 Community Description 3

2.3 Principal Flood Problems 3

2.4 Flood Protection Measures 6

3.0 ENGINEERING METHODS 7

3.1 Hydrologic Analyses 8

3.2 Hydraulic Analyses 10

3.3 Vertical Datum 13

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS 14

4.1 Floodplain Boundaries 14

4.2 Floodways 15

5.0 INSURANCE APPLICATION 24

6.0 FLOOD INSURANCE RATE MAP 24

7.0 OTHER STUDIES 26

8.0 LOCATION OF DATA 26

9.0 BIBLIOGRAPHY AND REFERENCES 26

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TABLE OF CONTENTS

FIGURES Figure 1 – Floodway Schematic 16

TABLES

Table 1 – Summary of Discharges 10 Table 2 – Manning’s “n” Values 12 Table 3 – Floodway Data 17 Table 4 – Community Map History 25

EXHIBITS

Exhibit 1 - Flood Profiles Big Goose Creek Panels 01P-22P Fivemile Creek Panel 23P Goose Creek Panels 24P-28P Little Goose Creek Panels 29P-46P Soldier Creek Panels 47P-58P Tongue River Panels 59P-60P Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Maps PUBLISHED SEPARATELY Flood Insurance Rate Map Index Flood Insurance Rate Map

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FLOOD INSURANCE STUDY SHERIDAN COUNTY, WYOMING and INCORPORATED AREAS

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) in the geographic area of Sheridan County, Wyoming, including the Towns of Clearmont, Dayton, and Ranchester, the City of Sheridan, and the unincorporated areas of Sheridan County (hereinafter referred to collectively as Sheridan County), 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. This information will also be used by Sheridan 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, 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 these federally supported studies are based. 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 1973. The hydrologic and hydraulic analyses for the Tongue River and Fivemile Creek within the Town of Ranchester were performed by the U.S. Geological Survey, Cheyenne, Wyoming, for the Federal Emergency Management Agency (FEMA), under Interagency Agreement No. IAA-EMW-85-E-1823, Project Order No. 24. This study was completed in September 1986.  The hydrologic and hydraulic analyses for the Tongue River, Fivemile Creek, and Piney Creek within the unincorporated areas of Sheridan County were performed by Foothill Engineering Consultants, Inc. (FEC), for the Federal Emergency Management Agency (FEMA), under Contract No. EMW-93-C-4150. This study was completed in November 1996.

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The new hydrologic and hydraulic analyses for Big Goose, Little Goose, Goose, and Soldier Creeks within the City of Sheridan and the unincorporated areas of Sheridan County were performed by the U.S. Army Corps of Engineers (USACE), Omaha District, Hydrologic Engineering Branch, under the Section 22 Planning Assistance to the States (PAS) program. PAS was authorized by Section 22, WRDA 1974 (P.L. 93-251) and amended in Section 221, WRDA 1996 to include 50/50 cost sharing of the study with the non-federal sponsor, in this case, the City of Sheridan and Sheridan County. This study was completed in December 2010.

The base map information is current as of September 2008 at a scale of 1:24000 as provided by county and community GIS departments. The base map data is based on NAD83 horizontal datum and projected to UTM Z14N.

1.3 Coordination

The initial Consultation Coordination Officer (CCO) meeting for the unincorporated areas of Sheridan County was held in April 1995, and attended by representatives of FEMA, Sheridan County, the Town of Ranchester, and the study contractor. The initial CCO meeting for the Town of Ranchester was held March 6, 1985. It was attended by representatives of the USGS (the study contractor), FEMA, and the Town of Ranchester. On June 2, 1987, the results of that study were reviewed at a final CCO meeting attended by the same representatives. The initial Consultation Coordination Officer (CCO) meeting for this Countywide FIS was held November 21, 2008 in the City of Sheridan. The meeting was attended by representatives of FEMA, Sheridan County, the City of Sheridan, the study contractor, and the FEMA Production and Technical Services contractor. The meeting collected the community flood hazard mapping needs and incorporated them into the final scope of work for the project. The final CCO meeting was held June 28, 2012, attended by representatives of FEMA, Wyoming Office of Homeland Security, Sheridan County, City of Sheridan, Town of Dayton, and the Technical Services contractor. All questions and issues raised were addressed at the meeting or in this report.

2.0 AREA STUDIED

2.1 Scope of Study

This Flood Insurance Study covers all areas within Sheridan County, Wyoming. Big Goose, Goose, Little Goose, and Soldier Creeks were studied in detail by the Hydrologic Engineering Branch of the USACE Omaha District for the City of Sheridan and Sheridan County. Big Goose Creek was studied from the confluence with Little Goose Creek to approximately 5.3 miles upstream of Big Goose Road. Goose Creek was studied from approximately 3 miles downstream

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of Interstate Highway 90 to the confluence with Big and Little Goose Creek. Little Goose Creek was studied from the confluence with Big Goose Creek to approximately 1.8 miles upstream of Brinton Road (South). Soldier Creek was studied from the confluence with Goose Creek to approximately 7.2 miles upstream of Soldier Creek Road. The Tongue River was studied by detailed methods from approximately 3 miles upstream of Sixmile Creek to approximately 0.25 mile west of the Town of Ranchester corporate limits and including the Town of Ranchester, and Fivemile Creek was studied by detailed methods from the confluence with the Tongue River to approximately 3,000 feet upstream of U.S. Highway 14 within the Town of Ranchester. Streams studied by approximate methods include a 4-mile reach of Clear Creek at Clearmont, a 4-mile reach of Clear Creek at Leiter, and a 4- mile reach of the Powder River at Arvada, performed by ICON Engineering, Inc., as a sub-consultant to GG3 A Joint Venture. Approximate studies performed by FEC for FEMA include a 4-mile reach of the Tongue River, from Dayton upstream to the National Forest boundary; a 15-mile reach of the Tongue River, from northeast of Acme to the Montana State line; and a 16-mile reach of Piney Creek, from the Sheridan County line to the U.S. Highway 14 bridge at Ucross.

2.2 Community Description

Sheridan County is located in the northeast portion of Wyoming on the Montana State boundary, with the Big Horn Mountains to the west and the grasslands of Wyoming to the east. The mean annual temperature is approximately 46°F, with an average rainfall of 14 inches and an average snowfall of 72 inches, at an average elevation of 3,964 feet. According to the 2010 Census, the current population is 29,116, approximately 17,444 of which reside in the City of Sheridan, a city located roughly in the center of the county (References 22-23). 2.3 Principal Flood Problems

There is great potential for flood damage in many areas along the Tongue River. Fivemile Creek also causes some flooding due to the wide, flat floodplain near the Tongue River. Damage from flooding is principally experienced in basements of homes in the flood-prone area near Big and Little Goose Creeks.

Following is a history of flooding recorded within Sheridan County: Damaging floods: Sheridan, Big Goose Creek, Little Goose Creek, 29-Sep-1923. An overabundance of rain caused flooding resulting in wooden paving blocks washed downstream, flooded basements, and flooded bridges. Also, accumulated debris under bridge caused water backup; amount of damage estimated at $500,000. Powder River at Arvada had a discharge of 100,000 CFS.

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Sheridan, Little Goose Creek, Big Goose Creek, 3-Jun-1944. A 15-year flood from an overabundance of rain resulted in flooded basements and bridges. According to WEMA Flood Damage Inventory the Tongue River near Dayton had a discharge of 3,400 CFS and according to FEMA Flood Insurance Study January 19, 2001 it had a discharge of 4,040 CFS. Sheridan, Prairie Dog Creek, 27-Jun-1953. Heavy rain (3.4 inches in one hour) caused flooding damaging ranches and loss of equipment Sheridan, Big Goose Creek, Little Goose Creek, 1956. A less than 10-year flood caused by heavy rain flooded basements and destroyed crops and gardens. Discharge amount was 3,360 CFS Sheridan, 15-Jun-1962. Heavy thundershowers caused flash flooding in Sheridan area. Sheridan, 29-Jun-1962. Flash flooding from heavy rains occurred in Sheridan area. Arvada, 12-Jul-1962. Heavy rains on both afternoons caused flash flooding with damage to crops, reservoirs and roads in the Arvada vicinity. Sheridan, Goose Creek, Clear Creek, 15-Jun-1963. Heavy rains combined with snowmelt runoff, including a storm sewer backing up, caused flooding, resulting in damage of basements and US Army Corps of Engineers Flood Protection project damaged. There was 1 death in Sheridan according to the Wyoming Floods and Droughts, National Weather Summary 1988-90. The following are discharge values from WEMA Storm Data: South Piney Creek near Story (June 15) - 2,090 CFS, North Piney Creek near Story (June 15) - 1,820 CFS, Piney Creek at Ucross (June 16) - 3,570 CFS, East Goose Creek near Big Horn (June 16) - 1,230 CFS, Middle Fork Powder River near Barnum (June 16) - 7,110 CFS, Largest recorded at Sheridan Gauge (June 16) - 5,450 CFS. According to WEMA Storm Data and Flood Damage Inventory it was a 45-year flood and according to Wyoming Floods and Droughts, National Weather Summary 1988-90 it was a 20 to greater than 100-year flood. Wind River, Absaroka, Big Horn Mountains, 15-Jun-1963. Heavy rains in the Wind River, Absaroka, and Big Horn Mountains caused flash flooding during Saturday and Sunday, the 15th and 16th. Considerable damage done to homes, equipment, crops, irrigation canals, roads and bridges. Sheridan, 20-Jun-1975. Heaviest rainfall was in the city of Sheridan. 2.51 inches of rain - the second greatest 24-hour amount recorded for June - fell at the Sheridan Airport between

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11:00 p.m. on the 20th and 1100 MST on the 21st. Many basements were flooded in the city of Sheridan. Central and North portions of Wyoming, 15-May-1978. Heavy wet snow and record rains did very extensive damage to property, crops, and livestock in 12 counties. Hundreds of homes were damaged, and many totally destroyed. Numerous bridges and sections of roads were washed out, power lines downed, with much damage to cars and personal property. Total estimated damages came to $15.5 million. Storm discharges are available from WEMA Storm Data. The event was estimated to be a 20- to greater than 100-year flood Clearmont to Leiter, 29-Jul-1985. Very heavy rain from storms caused flooding along Clear Creek from Clearmont to Leiter. Some irrigation equipment was damaged. Sheridan, Goose Creek, 24-Feb-1986. A 300-foot ice jam along Goose Creek, near Sheridan, blocked the creek, causing water to spill over the banks and into a mobile home park. Two hundred and fifty people were evacuated from the Woodland Park Village Mobile Homes. Big Horn, Story, 9-May-1995. A combination of moderate to heavy rain and snow melted from the adjacent Big Horn Mountains caused some creeks and streams to over flow their banks. In the town of Big Horn (eight miles south of Sheridan), the Jackson Creek flooded several roads. In Story (16 miles south of Sheridan), the North Piney Creek washed out portions of two roads and closed two other roads due to high water. Big Goose Creek, Little Goose Creek, Piney Creek, 16-Jun-1995. A combination of snowmelt from the Big Horn Mountains and some rainfall led to flooding along the east side of the mountains in Sheridan County. The Big Goose Creek, the Little Goose Creek, and Piney Creek all overflowed their banks and produced flooding. The Big Horn reservoir and the Park reservoir overflowed and this added to the volume of water that roared down those creeks. Flooding of roads and a few homes was reported in Story (16 miles south of Sheridan). Big Horn (8 miles south of Sheridan), and in the town of Sheridan. Some evacuations were necessary due to the flooding. Sheridan City Park was under water and some farmland in Sheridan County experienced flooding. No injuries or deaths occurred. Damage estimates were not available. Sheridan Foothills, 7-Feb-1996. Warm temperatures produced flooding in Sheridan County. Some basements were flooded. Some small streams and creeks went over their banks and flooded low lying areas and some streets. 6 NE Sheridan, 19-Aug-1998. The Little Goose Creek flooded a small subdivision when a slow moving

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thunderstorm produced over 1.50 inches of rainfall in 20 minutes. A house basement was reported to have been flooded. Sheridan, 21-Aug-2002. Business owners reported flooded basements downtown. Sheridan Foothills, 7-May-2005. Early Creek and irrigation ditches flooded near Ranchester, as well as, basements flooded in Ranchester. Sheridan Foothills, 11-May-2005. Bridge washed out 25ESE Sheridan on County Road 161 west of Ulm; Big Goose Creek flooded out of its banks; massive flooding occurred 5S Sheridan on U.S. Highway 87 between Sheridan and Big Horn. Water was up to many homes in this area; Water up to car doors at the 2000 block of Main Street; Long Drive in Sheridan was under four feet of water near the hospital. Numerous cars were stalled in the high water.

Multiple non-damaging floods have been recorded in state emergency management data. For instance, on June 15, 1996, flash flooding was observed in Sheridan, Wyoming. However, the waters subsided quickly. There were no known damages. Another in Sheridan, 14-Jul-2001, minor flooding over roads with hail floating on the flood waters. In the foothills near Sheridan, 8-May-2005 water ran across 5th Avenue on the west side of town. Water also filled parking lots.

2.4 Flood Protection Measures

Some channel stabilization work has been done in the Town of Ranchester to reduce bank erosion in that portion of the Tongue River. Construction of the Sheridan Flood Control Project was authorized by the Flood Control Act approved 17 May 1950 (Public Law 516, 81st Congress, 2nd Session). The City of Sheridan is the project sponsor and is responsible for the operation and maintenance of the project. The Sheridan Flood Control Project is located within the city limits of the City of Sheridan and consists of a system of levees, channel improvements, drainage structures, concrete chute, concrete drop structures, steel sheet pile and bin walls which were designed to protect the city from flood discharges in Goose and Little Goose Creeks. The Sheridan project was designed to provide three feet of freeboard on the levees and two feet minimum clearance at the bridges for the design discharges.

In this study, as in the previous FIS, the 100-year flood event is contained within the channel and therefore the levees located within the City of Sheridan have not required accreditation by FEMA as providing protection to the community from

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the 100-year flood event and as such have never been shown on the flood insurance rate map as providing that level of protection. The original design plan of the Sheridan Flood Control Project consisted of three phases, Phase I of the project which is located on the Big Goose Creek (Upper and Lower) and implements a system of channel improvements and levees to more effectively convey flood flows through the City of Sheridan. Phase I begins 2,500 feet upstream of the confluence of Big Goose Creek’s and Little Goose Creek and continues downstream to approximately 1,000 feet downstream of the Fort Road Bridge. This portion of the project consists of 8,455 feet of channel improvements with 60 to 90 foot bottom widths and 1 vertical on 2 horizontal side slopes and a 8,700 foot levee along the right bank with a 10 foot crest width and 1 vertical on 2 horizontal side slopes. In addition to the earthen levee there is 330 feet of flood and retaining walls. Stage I was started in August 1961 and was completed in August 1963. A contract for flood damage repair work because of the June 1963 flood event began in September 1963 and was completed in November 1963.The Stage I portion of the project was turned over to the City of Sheridan in December 1963. Phase II construction began in June 1965 and consisted of improvements to the lower reach of Little Goose Creek just upstream of its confluence with Big Goose Creek. The improvement measures incorporate a concrete chute that is 1,674 feet long with a 50 foot bottom width and 9 to 13 foot high side walls in the lower reach and extends upstream into a 11,340 foot system of earthen levees that also includes 12,036 feet of channel improvements with a 45 foot bottom width and 1 vertical on 2 horizontal side slopes. Construction on stage II was completed in 1966.

A project to replace the original 8-foot vertical drop structure with a series of four

low-head grouted riprap drop structures was begun in October 1994 and was completed in August 1995. This modification was undertaken primarily over public safety concerns.

The Corps of Engineers, along with the project sponsor, continue to conduct annual inspections of the project to ensure that the sponsor is operating and maintaining the project according to the regulations set forth in Section 208-10, Title 33, of the Code of Federal Regulations and which is further required for continued participation in the Corps’ PL 84-99 Rehabilitation and Inspection Program.

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-, 50-, 100-, or 500-year

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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 l00-year flood (1-percent 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 l00-year discharge for the Tongue River at the Town of Ranchester was obtained by interpolation of a logarithmic relation between l00-year discharge and drainage area using data from two U.S. Geological Survey (USGS) stream gages. Upstream of the Town of Ranchester is the gage along the Tongue River at Dayton, Wyoming (Gage No. 06298(00), which has records from 1919 to 1929 and 1941 to 1988. Downstream of the Town of Ranchester is the gage at Acme, Wyoming (Gage No. 06306(00), which has records from 1939 to 1957 but is presently nonoperational. Using the log-Pearson Type III analysis for the station near Dayton, as recommended in U.S. Water Resources Council (WRC) Bulletin No. 17B, "Guidelines for Determining Flood Flow Frequency," the l00-year discharge can be calculated (Reference 2). The same type of analysis was used for the station near Acme. The l00-year discharges determined for other stations in this same geographical area also agree with the logarithmic relation defined by the two stations mentioned previously. Hydrology for the l00-year flood for Fivemile Creek was computed using a procedure from USGS Water Resources Investigative Report 88-4045, "Streamflows in Wyoming" (Reference 3), to estimate the peak discharge, and a procedure from USGS Water Supply Paper 2056, "Analysis of Runoff from Small Drainage Basins in Wyoming" (Reference 4), to estimate the runoff volume and hydrograph. No new estimates of 100-year peak discharges were prepared for the two reaches of the Tongue River at Acme and Dayton because flows for those reaches were computed previously and reported in the 1988 Flood Insurance Study for the

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Town of Ranchester (Reference 5). The hydrologic analysis for Piney Creek consisted of obtaining annual peak streamflow records for Piney Creek and performing a frequency analysis fitting a log-Pearson Type III distribution, in accordance with guidelines contained in Bulletin No. 17B (Reference 2). The analysis was completed using the HECFFA computer program written by the U.S. Army Corps of Engineers (USACE) (Reference 6). Stream-gage records for the Piney Creek gage near Ucross (Gage No. 063235(0) were obtained and consist of data for the years 1917 through 1923 and 1950 through 1982. Several reservoirs are located in the upper reaches of the drainage area and were, therefore, judged to have minimal impact on the peak flows recorded at Ucross. Based on Bulletin No. 17B (Reference 2), a regional-map skew coefficient of 0.05 was selected and used in the computations. The estimated 100-year peak discharge at the Town of Ranchester for the 23.7-square-mile basin is 2,140 cubic feet per second (cfs) and includes the flood-routing effects of the existing Fivemile Reservoir in the upper half of the drainage basin. That reservoir is privately owned and maintained, but is under the jurisdiction of the Wyoming State Engineer's Office (SEQ) and is, therefore, included in its regular inspection program. During the most recent inspection of the dam on August 15, 1991, the Wyoming SEQ noted that there were no major deficiencies with the dam. For flood routing, it was conservatively assumed that no dedicated flood-storage volume was available, but rather the normal pool was at the emergency spillway crest. The reservoir would reduce the inflow hydrograph peak of 2,790 cfs to a routed outflow of 870 cfs. Because of the reservoir attenuation and the travel time in the downstream channel, the peak flow at the Town of Ranchester is governed entirely by the subbasin runoff downstream of the reservoir. The peak discharge of the lower basin was calculated using the USACE HEC-l computer program (Reference 7). For Big Goose Creek, Goose Creek, Little Goose Creek, and Soldier Creek, several different methods were used to develop frequency curves at gaged and non-gaged locations in the Goose Creek Basin (Reference 8). Frequency curves were developed using the USACE’s Hydrologic Engineering Center Statistical Software Package (HEC-SSP) version Beta 1.0 (Reference 9), three Wyoming Regional Studies (References 10-12), two Transform methods, and a Regression Equation method (Reference 2). For the gaged locations in the drainage basin, specifically along Goose Creek, HEC-SSP frequency curves were selected as the final frequency curves. The final frequency curves selected for Little Goose Creek and Big Goose Creek were Rocky Mountain regional regression curves from a 2003 study, “Peak Flow Characteristics of Wyoming Streams” (Reference 12). These analyses incorporated the regression equations from the 2003 Wyoming regional study into

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the standard log-Pearson Type III method, as outlined in WRC Bulletin 17B, “Guidelines for Determining Flood Flow Frequency” (Reference 2). To obtain floodflows for the needed drainage basins, a simple regression analysis was used, regressing floodflows of the required recurrence interval onto drainage basin size in square miles. Peak discharge-drainage area relationships for the Tongue River and Fivemile, Piney, Soldier, Goose, and Big and Little Goose Creeks are shown in Table 1, "Summary of Discharges."

TABLE 1– SUMMARY OF DISCHARGES

Flooding Source and Location

Drainage Area (Square Miles)

Peak Discharges (Cubic Feet per Second) 10-Percent-

Annual-Chance

2-Percent-Annual-Chance

1-Percent-Annual-Chance

0.2-Percent-Annual-Chance

Big Goose Creek 1,900 feet Upstream of Beaver Creek Road 120 1,170 1,730 2,000 2,690 Upstream of Confluence With Little Goose Creek 206 1,880 3,300 4,060 6,260

Fivemile Creek 23.7 --1 --1 3,940 --1 Goose Creek Upstream of Confluence With Soldier Creek 356 2,750 4,830 5,940 9,150 At Downstream Study Limits 392 3,230 5,950 7,450 11,900 Little Goose Creek 2,600 feet Upstream of U.S. Highway 87 51.6 906 1,270 1,430 1,850 At Confluence with Big Goose Creek 150 1,630 2,870 3,530 5,430 Piney Creek At USGS Gage No. 06323500 Near Ucross 267 --1 --1 2,140 --1 Tongue River At Town of Dayton 204 --1 --1 3,647 --1 At Town of Ranchester 397 --1 --1 5,800 --1 At Town of Acme 894 --1 --1 10,300 --1 Soldier Creek At Confluence with Goose Creek 34 850 1,175 1,320 1,690

1Data not computed

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.

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Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Exhibit 1). For the backwater analyses on the Tongue River at the Town of Ranchester, 10 cross sections were obtained from a field survey and two were synthesized. The synthesized cross sections were estimated from adjacent surveyed sections and topographic maps. Structural geometry and elevations for one bridge and road section, at Wolf Creek County Road, were also obtained from the field survey. Cross sections were located above and below the bridge in order to compute the backwater effects of this structure. Limited-detail hydraulic analyses for the Tongue River at Acme, Tongue River at Dayton, and Piney Creek were completed using version 4.6.2 of the USACE HEC-2 computer program (Reference 13). Cross-section data were obtained directly from USGS 7.5-minute series topographic maps (Reference 14) and stream cross-section geometry and flow characteristics were supplemented by photographs and detailed notes made during a September 1995 site visit. Cross-section spacing for each reach was approximately one per stream mile.

Water-surface elevations for the 100-year flood for the Tongue River at the Town of Ranchester were computed by WSPRO, a step-backwater computer program developed by the USGS for the Federal Highway Administration (Reference 15). The starting water-surface elevation for the portion of the Tongue River studied in detail was determined by a slope-conveyance computation at the downstream end. For the Fivemile Creek HEC-2 model, nine cross sections were surveyed and five were synthesized from the surveyed sections. Numerous surveyed spot elevations in the Town were also used to confirm shallow flooding less than 1 foot deep, southeast of the creek and in the Town, resulting from approximately 440 cfs breaking out of the main channel upstream of the U.S. Highway 14 crossing. Due to the approximate nature of the analysis for the Tongue River at Acme, Tongue River at Dayton, and Piney Creek, the HEC-2 results were used only to delineate the 100-year floodplain limits. No base (100-year) flood elevations (BFEs) were determined. Channel roughness factors (Manning's "n") for the hydraulic computations were assigned on the basis of field inspection of the floodplain areas, observations from aerial photos, and photos from bridge survey data. Roughness values for all streams studied in detail are shown in Table 2 below. The water-surface profile for the 100-year flood on Fivemile Creek was computed using version 4.6.2 of the USACE HEC-2 computer program (Reference 13). The starting water-surface elevation for the Tongue River at the Fivemile Creek confluence was taken from the 1988 Town of Ranchester Flood Insurance Study (Reference 5).

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TABLE 2 – Manning’s “n” Values Stream Name Manning’s “n” Channel Manning’s “n” Overbanks Big Goose Creek 0.03-0.035 0.05-0.075 Fivemile Creek 0.04-0.05 0.05-0.07 Goose Creek 0.03 0.05-0.070 Little Goose 0.017-0.035 0.05-0.075 Soldier Creek 0.035 0.045-0.07 Tongue River 0.035-0.05 0.035-0.15

The water-surface profiles for Big Goose, Goose, Little Goose, and Soldier Creeks were computed using version 4.0.0 of the USACE HEC-RAS computer program (Reference 16). Cross sections were generated from a triangular irregular network (TIN) collected from LiDAR data, and from survey data collected at 57 bridges, both provided by the local co-sponsors as in-kind services as part of the cost share agreement. Because the provided TIN lacked detailed channel topographic information, cross sections were supplemented in channel areas with geometric information from the original FIS, information from flood damage reduction project operations, and maintenance manuals for the communities, field verified with additional survey data collected by the study co-sponsors. Both Big Goose Creek and Little Goose Creek used known water surfaces from Goose Creek as their downstream boundary condition, while Goose Creek and Soldier Creek used normal depth (Reference 17). Water-surface elevations for the 100-year flood for the Powder River at Arvada, and Clear Creek at Clearmont and Leiter were computed using version 4.0.0 of the USACE HEC-RAS computer program. The starting water-surface elevations for the Powder River and Clear Creek were determined by normal depth computations at the downstream end. Due to the approximate nature of these analyses, the HEC-RAS results were used only to delineate the 100-year floodplain limits. No BFEs were determined. For the Fivemile Creek HEC-2 model, nine cross sections were surveyed and five were synthesized from the surveyed sections. Numerous surveyed spot elevations in the Town were also used to confirm shallow flooding less than 1 foot deep, southeast of the creek and in the Town, resulting from approximately 440 cfs breaking out of the main channel upstream of the U.S. Highway 14 crossing. Due to the approximate nature of the analysis for the Tongue River at Acme, Tongue River at Dayton, and Piney Creek, the HEC-2 results were used only to delineate the 100-year floodplain limits. No base (100-year) flood elevations (BFEs) were determined. The hydraulic analyses for this study were based on unobstructed flow and the effect of ice was not considered. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail.

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3.3 Vertical Datum

All FISs 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 (NGVD29). With the finalization of the North American Vertical Datum of 1988 (NAVD88), many FIS reports and FIRMs are being prepared using NAVD88 as the referenced vertical datum.

All flood elevations shown in this FIS report and on the FIRM are referenced to NAVD88. It is important to note that adjacent communities may be referenced to NGVD29. This may result in differences in base flood elevations across the corporate limits between communities. As noted above, the elevations shown in the FIS report and on the FIRM for Sheridan County and Incorporated Areas are referenced to NAVD88. Ground, structure, and flood elevations may be compared and/or referenced to NGVD29 by applying a standard conversion factor. The conversion from NGVD29 to NAVD88 ranged between 2.15 to 4.00 feet for this county. According to Appendix B of FEMA Guidelines and Specifications, due to the range in conversion factors, a stream by stream conversion factor was established for each flood source originally studied in NGVD 29 by detailed methods in the entire county. The elevations shown in the FIS report and on the FIRM were, therefore, converted to NAVD88 using a stream by stream approach in which an average conversion was established for each detailed study stream. The conversion factor for NGVD29 to NAVD88 is 2.5 feet for both Fivemile Creek and the Tongue River. Because all other detailed studies were recently accomplished in NAVD88, these were the only vertical datum-converted flooding sources in Sheridan County. The BFEs shown in the FIRM represent whole-foot rounded values. For example, a BFE of 1202.4 will appear as 1202 on the FIRM and 1202.6 will appear as 1203. Therefore, users who wish to convert the elevations in this FIS to NGVD29 should apply the stated conversion factor to elevations shown on the Flood Profiles and supporting data tables in the FIS report, which are shown at a minimum to the nearest 0.1 foot. For more information on NAVD88, see the publication entitled, Converting the National Flood Insurance Program to the North American Vertical Datum of 1988 (FEMA Publication FIA-20/June 1992), or contact the Vertical Network Branch, National Geodetic Survey, Coast and Geodetic Survey, National Oceanic and Atmospheric Administration, Rockville, Maryland 20910 (Internet address http://www.ngs.noaa.gov).

14  

Qualifying bench marks within a given jurisdiction that are cataloged by the National Geodetic Survey (NGS) and entered into the National Spatial Reference System (NSRS) as First or 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 catalogued by the NGS and entered into the NSRS vary widely in vertical stability classification. 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 abutments) Stability C: Monuments which may be affected by surface ground movements (e.g., concrete monument below frost line) Stability D: Mark of questionable or unknown vertical stability (e.g., concrete monument above frost line or steel witness post) To obtain up-to-date elevation information on NGS bench marks shown on the FIRM, please contact the Information Services Branch of the NGS at (301) 713-3242, or visit their website at www.ngs.noaa.gov. Map users should seek verification of non-NGS monument elevations when using these elevations for construction or floodplain management purposes.

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 associated with this FIS report and FIRM for this community. Interested individuals may contact FEMA to access this data. 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound floodplain management programs. Therefore, each Flood Insurance Study provides l00-year flood elevations and delineations of the 100-and 500-year floodplain boundaries and l00-year floodway to assist communities in developing floodplain management measures.

4.1 Floodplain Boundaries

To provide a national standard without regional discrimination, the 1-percent annual chance (l00-year) flood has been adopted by FEMA as the base flood for

15  

floodplain management 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 methods, the 100 and 500-year 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 1:24,000, with a contour interval of 20 feet (Reference 14). Along Big Goose, Goose, Little Goose, and Soldier Creeks, the flood boundaries were delineated using the computed water surface elevations at each cross section. Between cross sections, the flood boundaries were interpolated linearly using graphical information system (GIS) software (Reference 17). Topographic information for delineation was taken from the aforementioned TIN. The 100-and 500-year floodplain boundaries are shown on the Flood Insurance Rate Map (Exhibit 2). On this map, the l00-year floodplain boundary corresponds to the boundary of the areas of special flood hazards (Zones A and AE), and the 500-year floodplain boundary corresponds to the boundary of areas of moderate flood hazards. In cases where the 100 and 500-year floodplain boundaries are close together, only the 100-year floodplain boundary has been shown. Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data. For the streams studied by approximate methods, only the l00-year floodplain boundary is shown on the Flood Insurance Rate Map (Exhibit 2). Approximate 100-year floodplain boundaries in some portions of the study area were taken directly from the Flood Hazard Boundary Map (which has since been superseded) for the unincorporated areas of Sheridan County, Wyoming (Reference 18).

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 100-year 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 l00-year 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 that can be used as a basis for

16  

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 3, "Floodway Data"). In cases where the floodway and l00-year floodplain boundaries are either close together or collinear, only the floodway boundary is shown. The area between the floodway and l00-year 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 l00-year flood more than 1 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

483 90 519 7.8 3738.0 3738.0 3738.0 0.02,301 45 395 10.3 3744.1 3744.1 3744.3 0.22,886 70 620 6.6 3746.8 3746.8 3747.1 0.34,292 73 524 7.8 3750.1 3750.7 3750.9 0.24,714 80 461 8.8 3753.2 3753.2 3753.3 0.16,742 76 565 7.2 3760.3 3760.3 3760.8 0.510,828 700 2300 1.8 3766.2 3766.2 3766.7 0.513,874 309 1243 3.3 3772.5 3772.5 3773.3 0.816,980 173 669 6.1 3779.5 3779.5 3779.9 0.420,132 118 513 7.9 3787.3 3787.3 3787.9 0.624,589 91 535 7.6 3800.6 3800.6 3801.5 0.926,904 84 510 8.0 3807.7 3807.7 3808.1 0.430,121 359 1180 3.4 3812.7 3812.7 3813.6 0.933,704 482 959 4.2 3820.2 3820.2 3820.7 0.537,358 150 709 5.7 3831.2 3831.2 3832.1 0.939,366 120 758 5.4 3840.0 3840.0 3840.9 0.943,070 138 518 7.8 3848.4 3848.4 3848.6 0.247,419 272 793 5.1 3860.1 3860.1 3860.8 0.749,457 292 1365 3.0 3866.3 3866.3 3866.8 0.553,442 371 937 4.3 3872.8 3872.8 3873.4 0.655,264 461 1518 2.7 3879.0 3876.9 3877.6 0.758,649 158 566 7.2 3895.3 3891.0 3891.7 0.764,257 245 1473 2.8 3913.7 3913.7 3914.7 1.068,053 422 1165 3.5 3920.4 3920.4 3920.6 0.272,144 161 676 6.0 3930.2 3930.2 3930.7 0.5

1 Feet Above Confluence with Goose Creek

BIG GOOSE CREEK

TABLE3

AB

W

GH

CD

QR

EF

IJKLMNOP

SHERIDAN COUNTY, WY And Incorporated Areas

FEDERAL EMERGENCY MANAGEMENT AGENCY

STUV

YX

FLOODING SOURCE

DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

CROSS SECTION

FLOODWAY

MEAN VELOCITY (FEET PER SECOND)

BASE FLOODWATER-SURFACE ELEVATION

(FEET NAVD)

WITH FLOODWAY INCREASE

FLOODWAY DATA

BIG GOOSE CREEK

REGULATORY WITHOUT FLOODWAY

75,724 150 871 4.7 3948.1 3948.1 3948.2 0.177,278 402 1106 3.7 3953.7 3953.7 3953.9 0.280,749 84 219 9.1 3970.7 3970.7 3971.1 0.483,784 295 880 2.3 3986.0 3986.0 3987.0 1.084,789 81 367 5.5 3992.0 3992.0 3992.4 0.485,254 83 474 4.2 3994.7 3994.7 3994.9 0.288,866 798 1804 1.6 4011.0 4011.0 4011.9 0.992,249 298 684 2.9 4028.5 4028.5 4029.4 0.995,787 250 612 3.3 4045.0 4045.0 4045.9 0.998,780 189 453 4.4 4064.9 4064.9 4065.6 0.799,810 126 638 3.1 4076.1 4076.4 4076.7 0.3103,205 149 354 5.7 4102.8 4102.8 4103.4 0.6106,042 179 350 5.7 4135.6 4135.6 4136.6 1.0109,199 111 241 8.3 4178.4 4178.4 4178.6 0.2112,033 61 227 8.8 4216.2 4216.2 4217.0 0.8115,079 73 213 9.4 4272.3 4272.3 4273.3 1.0118,342 70 208 9.6 4339.8 4339.8 4340.4 0.6121,173 47 181 11.1 4413.5 4413.5 4413.7 0.2122,685 52 195 10.2 4464.9 4464.9 4465.1 0.2124,210 41 173 11.5 4510.2 4510.2 4510.4 0.2125,950 49 182 11.0 4581.1 4581.1 4581.2 0.1126,950 43 175 11.4 4627.5 4627.5 4627.8 0.3

1 Feet Above Confluence with Goose Creek

FLOODING SOURCE FLOODWAY

INCREASEWITHOUT FLOODWAY

WITH FLOODWAY

BIG GOOSE CREEK

WATER-SURFACE ELEVATION(FEET NAVD)

BASE FLOOD

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY

AMAN

AEAF

(cont'd)Z

AAABACAD

AGAHAIAJAKAL

FLOODWAY DATASHERIDAN COUNTY, WY And Incorporated Areas BIG GOOSE CREEK

TABLE3

AQAR

FEDERAL EMERGENCY MANAGEMENT AGENCY

AOAP

ASATAU

39,962 104 711 10.5 3672.9 3672.9 3673.4 0.542,788 415 2699 2.8 3679.0 3679.0 3679.8 0.945,587 414 1591 4.7 3681.3 3681.3 3682.2 0.950,758 416 2437 3.1 3691.0 3691.0 3691.7 0.754,007 175 1199 6.2 3698.8 3698.8 3698.9 0.256,434 93 889 8.4 3701.4 3701.4 3701.5 0.159,115 241 1078 6.9 3706.3 3706.3 3706.4 0.161,405 105 937 8.0 3713.3 3713.3 3713.5 0.261,553 110 981 7.6 3714.0 3714.0 3714.3 0.363,677 99 814 7.3 3717.3 3717.3 3717.6 0.464,414 108 896 6.6 3719.5 3719.5 3719.7 0.265,682 78 696 8.5 3722.4 3721.7 3722.0 0.266,946 108 935 6.4 3726.2 3726.2 3726.5 0.3

1 Feet Above Confluence with Tongue River2 Water-surface elevations without consideration of ice-jam effects

FLOODWAY DATA

GOOSE CREEK

REGULATORY WITHOUT FLOODWAY

BASE FLOODWATER-SURFACE ELEVATION2

(FEET NAVD)

WITH FLOODWAY INCREASE

FLOODING SOURCE

DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

CROSS SECTION

FLOODWAY

MEAN VELOCITY (FEET PER SECOND)

SHERIDAN COUNTY, WY And Incorporated Areas

FEDERAL EMERGENCY MANAGEMENT AGENCYTABLE3

EF

KLM

IJ

GOOSE CREEK

AB

GH

CD

283 54 576 6.1 3,729.9 3,729.9 3,730.2 0.3417 51 538 6.6 3,729.9 3,729.9 3,730.2 0.3824 50 461 7.7 3,730.0 3,730.0 3,730.2 0.2

1,139 50 406 8.7 3,730.1 3,730.1 3,730.3 0.21,433 53 389 9.1 3,730.6 3,730.6 3,730.8 0.21,847 100 358 9.9 3,731.5 3,731.5 3,731.8 0.33,386 69 427 7.7 3,739.2 3,739.2 3,739.2 0.04,625 68 399 8.3 3,743.4 3,743.4 3,743.4 0.05,386 62 415 8.8 3,746.0 3,746.0 3,746.0 0.06,816 73 523 6.5 3,752.4 3,752.4 3,752.4 0.07,561 67 429 7.6 3,753.8 3,753.8 3,753.8 0.09,367 64 411 8.6 3,760.0 3,760.0 3,760.0 0.0

10,201 79 486 7.3 3,763.2 3,763.2 3,763.2 0.011,788 85 526 6.7 3,768.8 3,768.8 3,768.8 0.014,141 61 462 7.7 3,778.9 3,778.9 3,779.0 0.118,451 265 1,268 2.8 3,790.8 3,790.8 3,790.8 0.020,890 186 590 6.0 3,796.4 3,796.4 3,797.2 0.823,637 156 664 5.3 3,803.7 3,803.7 3,804.3 0.626,867 153 675 5.2 3,815.1 3,815.1 3,815.5 0.430,050 123 788 4.5 3,828.9 3,828.9 3,829.9 1.033,202 95 533 6.6 3,836.8 3,836.8 3,837.2 0.437,000 310 1,165 3.0 3,846.4 3,846.4 3,847.4 1.038,858 120 885 4.0 3,857.3 3,857.3 3,858.3 1.041,721 299 1,006 3.5 3,858.8 3,858.8 3,859.7 0.944,705 231 1,145 3.1 3,866.2 3,866.2 3,866.5 0.3

1 Feet Above Confluence with Goose Creek

BASE FLOODWATER-SURFACE ELEVATION

(FEET NAVD)

WITH FLOODWAY INCREASE

FLOODWAY DATA

LITTLE GOOSE CREEK

REGULATORY WITHOUT FLOODWAY

FLOODING SOURCE

DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

CROSS SECTION

FLOODWAY

MEAN VELOCITY (FEET PER SECOND)

R

SHERIDAN COUNTY, WY And Incorporated Areas

FEDERAL EMERGENCY MANAGEMENT AGENCY

STUV

YXW

NOPQ

DEF

L

IJK

M

LITTLE GOOSE CREEK

TABLE3

AB

GH

C

47,275 285 1,188 3.0 3,872.1 3,872.1 3,873.1 1.049,378 301 978 3.6 3,877.4 3,877.4 3,878.0 0.652,049 548 1,253 2.8 3,884.5 3,884.5 3,885.3 0.856,375 446 1,045 3.4 3,892.8 3,892.8 3,892.8 0.059,756 367 937 3.8 3,896.9 3,896.9 3,897.9 1.062,571 293 1,264 2.8 3,906.3 3,906.3 3,907.3 1.065,412 80 443 8.0 3,914.3 3,914.3 3,914.8 0.568,478 246 1,223 2.9 3,927.2 3,927.2 3,927.2 0.071,198 675 574 6.2 3,938.3 3,938.3 3,939.0 0.774,268 205 527 2.7 3,956.5 3,956.5 3,956.9 0.474,986 410 1,100 1.9 3,961.4 3,961.4 3,961.7 0.377,817 461 766 1.9 3,978.9 3,978.9 3,979.3 0.478,298 470 823 3.3 3,984.4 3,984.4 3,984.5 0.181,155 239 414 3.5 4,001.0 4,001.0 4,001.8 0.883,078 475 948 2.0 4,014.1 4,014.1 4,014.1 0.085,306 351 254 5.6 4,021.8 4,021.8 4,022.2 0.488,511 52 253 5.7 4,047.0 4,047.0 4,047.1 0.191,332 73 173 8.3 4,073.0 4,073.0 4,073.2 0.295,091 253 599 2.4 4,108.7 4,108.7 4,108.7 0.098,034 86 246 5.8 4,136.3 4,136.3 4,136.5 0.2

101,162 29 139 10.3 4,172.1 4,172.1 4,172.2 0.1104,386 62 216 6.6 4,214.8 4,214.8 4,215.0 0.2105,360 65 418 3.5 4,228.3 4,228.3 4,228.7 0.4

1 Feet Above Confluence with Goose Creek

AU

FLOODWAY DATASHERIDAN COUNTY, WY And Incorporated Areas LITTLE GOOSE CREEK

AV

TABLE3

FEDERAL EMERGENCY MANAGEMENT AGENCY

AQARASAT

AMANAOAP

AJAKAL

AEAFAGAH

ABACAD

(cont'd)Z

AI

REGULATORYCROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

AA

FLOODING SOURCE FLOODWAY

INCREASE

LITTLE GOOSE CREEK

WATER-SURFACE ELEVATION(FEET NAVD)

BASE FLOOD

WITHOUT FLOODWAY

WITH FLOODWAY

MEAN VELOCITY (FEET PER SECOND)

108,334 137 252 5.7 4,264.7 4,264.7 4,265.0 0.3111,388 90 195 7.3 4,315.9 4,315.9 4,316.0 0.1114,034 49 152 9.4 4,359.6 4,359.6 4,359.8 0.2

1 Feet Above Confluence with Goose Creek

WITHOUT FLOODWAY

FLOODING SOURCE FLOODWAYBASE FLOOD

WATER-SURFACE ELEVATION(FEET NAVD)

SECTION AREA

(SQUARE FEET)

AX

INCREASE

LITTLE GOOSE CREEK(cont'd)

AW

MEAN VELOCITY (FEET PER SECOND)

REGULATORY WITH FLOODWAYCROSS SECTION DISTANCE1 WIDTH

(FEET)

AY

FLOODWAY DATASHERIDAN COUNTY, WY And Incorporated Areas LITTLE GOOSE CREEK

TABLE3

FEDERAL EMERGENCY MANAGEMENT AGENCY

317 62 221 6.0 3,717.8 3,717.8 3,717.9 0.13,555 62 175 7.5 3,731.4 3,731.4 3,731.5 0.16,753 100 261 5.1 3,748.3 3,748.3 3,748.4 0.1

10,014 47 182 7.3 3,766.1 3,766.1 3,766.6 0.513,166 66 192 6.9 3,780.3 3,780.3 3,780.5 0.216,437 200 284 4.6 3,794.7 3,794.7 3,795.2 0.519,000 61 255 5.2 3,811.0 3,811.0 3,811.0 0.019,213 58 334 4.0 3,812.4 3,812.4 3,813.1 0.722,359 136 222 5.9 3,828.2 3,828.2 3,828.3 0.123,950 260 552 2.4 3,836.3 3,836.3 3,836.3 0.027,327 158 290 4.6 3,845.4 3,845.4 3,845.5 0.130,133 40 184 7.2 3,853.9 3,853.9 3,854.7 0.833,543 149 343 3.9 3,865.7 3,865.7 3,866.7 1.035,957 45 347 3.8 3,878.0 3,878.0 3,878.6 0.636,164 45 480 2.9 3,878.9 3,878.9 3,879.7 0.840,120 32 129 10.2 3,893.7 3,893.7 3,893.8 0.143,424 141 385 3.4 3,907.7 3,907.7 3,908.7 1.046,005 98 514 2.6 3,917.1 3,917.1 3,917.9 0.850,348 72 231 5.7 3,927.9 3,927.9 3,928.6 0.753,447 76 279 4.7 3,943.7 3,943.7 3,944.7 1.056,367 215 507 2.6 3,955.0 3,955.0 3,955.4 0.459,330 71 257 5.1 3,967.2 3,967.2 3,968.0 0.862,823 55 231 5.7 3,980.7 3,980.7 3,981.5 0.865,593 40 210 6.3 3,993.8 3,993.8 3,994.5 0.769,178 171 378 3.5 4,010.1 4,010.1 4,011.0 0.972,294 52 190 7.0 4,019.8 4,019.8 4,020.6 0.8

1 Stream Distance in Feet Above Mouth

SOLDIER CREEK

REGULATORY WITHOUT FLOODWAY

BASE FLOODWATER-SURFACE ELEVATION

(FEET NAVD)

WITH FLOODWAY INCREASE

FLOODWAY DATA

FLOODING SOURCE

DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

CROSS SECTION

FLOODWAY

MEAN VELOCITY (FEET PER SECOND)

SHERIDAN COUNTY, WY And Incorporated Areas

FEDERAL EMERGENCY MANAGEMENT AGENCY

TUVW

ZY

TABLE3

X

NOPQRS

LM

JK

HI

DEFG

SOLDIER CREEKABC

24  

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 loo-year floodplains that are determined in the Flood Insurance Study by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no BFEs or depths are shown within this zone. Zone AE Zone AE is the flood insurance rate zone that corresponds to the loo-year floodplains that are determined in the Flood Insurance Study by detailed methods. Whole-foot BFEs derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Zone X Zone X is the flood insurance rate zone that corresponds to areas outside the 500-year floodplain, areas within the 500-year floodplain, areas of loo-year flooding where average depths are less than 1 foot, areas of l00-year flooding where the contributing drainage area is less than 1 square mile, and areas protected from the 100-year flood by levees. No BFEs or depths are shown within this zone.

6.0 FLOOD INSURANCE RATE MAP The Flood Insurance Rate Map is designed for flood insurance and floodplain management applications. For flood insurance applications, the map designates flood insurance rate zones as described in Section 5.0 and, in the 100-year 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 100-and 500-year floodplains, floodways, and the locations of selected cross sections used in hydraulic analyses and floodway computations. The current FIRM presents flooding information for the entire geographic area of Sheridan County. Previously, separate FIRMs were prepared for each identified floodprone incorporated community and for the unincorporated areas of the county. Historical data relating to the maps prepared for each community are presented in Table 4.

25  

 COMMUNITY NAME

INITIAL IDENTIFICATION

FLOOD HAZARD BOUNDARY MAP

REVISION DATE(S)

FLOOD INSURANCE

RATE MAP EFFECTIVE DATE

FLOOD INSURANCE

RATE MAP REVISION DATE(S)

Town of Clearmont Town of Dayton Town of Ranchester City of Sheridan Sheridan County (Unincorporated Areas)

January 16, 2014

September 6, 1974

September 6, 1974

January 4, 1974

July 4, 1978

-

January 16, 1976

March 12, 1976

October 10, 1975 October 1, 1976

December 18, 1979

January 16, 2014

August 1, 2008

April 15, 1988

September 1, 1978

August 1, 1986

- -

January 20, 1999

June 30, 1981 January 19, 2001

March 30, 1998

T A B L E

4

FEDERAL EMERGENCY MANAGEMENT AGENCY

SHERIDAN COUNTY, WY AND INCORPORATED AREAS

COMMUNITY MAP HISTORY

26  

7.0 OTHER STUDIES A Flood Hazard Boundary Map was previously published for the unincorporated areas of Sheridan County (Reference 18) and Flood Insurance Studies were previously published by FEMA for the Town of Ranchester, the City of Sheridan, and the unincorporated areas of Sheridan County (References 19-21). This Flood Insurance Study is more detailed and comprehensive, and therefore, supersedes the previous Flood Hazard Boundary Map and Flood Insurance Studies. This report either supersedes or is compatible with all previous studies published on streams studied in this report and should be considered authoritative for the purposes of the NFIP. 8.0 LOCATION OF DATA Information concerning the pertinent data used in the preparation of this study can be obtained by contacting FEMA, Mitigation Division, Denver Federal Center, Building 710, Box 25267, Denver, Colorado 80225-0267. 9.0 BIBLIOGRAPHY AND REFERENCES

1. Federal Emergency Management Agency, Flood Insurance Study, City of Sheridan, Sheridan County. Wyoming, March 1978.

2. U.S. Water Resources Council, Bulletin No. 17B, Guidelines for

Determining Flood Flow Frequency, 1981. 3. U.S. Department of the Interior, Geological Survey, Water Resources

Investigative Report 88-4045, Streamflows in Wyoming, H. W. Lowham, 1988.

4. U.S. Department of the Interior, Geological Survey, Water Supply Paper

2056, Analysis of Runoff from Small Drainage Basins in Wyoming, G.S. Craig, Jr. and J.G. Rankl, 1978.

5. Federal Emergency Management Agency, Flood Insurance Study, Town

of Ranchester, Sheridan County, Wyoming, April 15, 1988. 6. U.S. Department Of the Army, Corps Of Engineers, Hydrologic

Engineering Center, HECFFA Flood Frequency Analysis, Version 3.0, Davis, California, May 1992.

7. U. S. Department of the Army, Corps of Engineers, Hydrologic

Engineering Center, HEC-1 Flood Hydrograph Package, Generalized Computer Program Version 4.0, Davis, California, September 1990.

27  

8. U.S. Army Corps of Engineers, Omaha District, Hydrologic Engineering Branch, Engineering Division, Goose Creek, Sheridan County & City of Sheridan, Wyoming, Section 22: Planning Assistance to States and Tribes, March 2009.

9. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-SSP

Version 1.0, August 2008. 10. Lowham, H.W. Techniques for Estimating Flow Characteristics of

Wyoming Streams. U.S. Geological Survey; Cheyenne, WY. 1976. 11. Lowham, H.W. Streamflows in Wyoming. U.S. Department of the

Interior; Cheyenne, WY. 1988. 12. Miller, Kirk A. Peak Flow Characteristics of Wyoming Streams. U.S.

Geological Survey; Cheyenne, WY. 2003. 13. U.S. Department of the Army, Corps of Engineers, Hydrologic

Engineering Center, HEC-2 Water-Surface Profiles, Generalized Computer Program Version 4 6 2, Davis, California, February 1991.

14. U.S. Department of the Interior, Geological Survey, 7.5-Minute Series

Topographic Map, Scale 1:24,000, Contour Interval 20 feet, Ranchester, Wyoming, 1964, Photo revised 1980.

15. Federal Highway Administration, FHWA-RD-86/108, Bridge Waterways

Analysis Model/Research Report, by H.N. Flippo, W.H. Kirby, J.O. Shearman, and V.R. Schneider, 1986.

16. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-

RAS Version 4.0.0, March 2008. 17. U.S. Army Corps of Engineers, Omaha District, Hydrologic Engineering

Branch, Engineering Division, Section 22 Study, Soldier Creek and Goose Creek, City of Sheridan and Sheridan County, Wyoming, Hydrologic Report, March 2010.

18. U.S. Department of Housing and Urban Development, Federal Insurance

Administration, Flood Hazard Boundary Map, Sheridan County, Wyoming (Unincorporated Areas), December 18, 1979.

19. Federal Emergency Management Agency, Flood Insurance Study, Town

of Ranchester, Sheridan County, Wyoming, January 20, 1999. 20. Federal Emergency Management Agency, Flood Insurance Study, City of

Sheridan, Sheridan County, Wyoming, January 19, 2001.

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21. Federal Emergency Management Agency, Flood Insurance Study,

Sheridan County, Wyoming (Unincorporated Areas), March 30, 1998. 22. http://quickfacts.census.gov/qfd/states/56/56033.html 23. http://quickfacts.census.gov/qfd/states/56/5669845.html