Determination of the 100-Year Flood Plain on Fourmile ... · PDF fileDetermination of the 100-Year Flood Plain on ... In par ticular, cross ... of Aiken and Bamwell Counties and

Determination of the 100-Year Flood Plain on Fourmile Branch at the Savannah River Site, South Carolina, 1996

By TIMOTHY H. LANIER

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 96-4271

Prepared in cooperation with the U.S. DEPARTMENT OF ENERGY

Columbia, South Carolina 1997

U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Government.

For additional information write to:

District Chief U.S. Geological Survey Stephenson Center-Suite 129 720 Gracern Road Columbia, SC 29210-7651

Copies of this report can be purchased from:

U.S. Geological Survey Branch of Information Services Box 25286 Denver, CO 80225-0286

CONTENTS

Abstract.............................................................................................................._^ 1Introduction.......................................................................................................................................................... 1

Purpose and Scope ...................................................................................................................................... 1Description of Study Area........................................................................................................................... 2Acknowledgment........................................................................................................................................ 2

Hydrologic and Hydraulic Data Collection ......................................................................................................... 2Flood Frequency......................................................................................................................... ......................... 5Model Selection and Development...................................................................................................................... 7One-Hundred-Year Flood Plain and Profile......................................................................................................... 9Summary.................................................................................................................................... ......................... 19Selected References ............................................................................................................................................. 19Appendix - List of Elevations Reference Marks.................................................................................................. 21

PLATE

1. Map showing area' extent of the 100-year flood for Fourmile Branch at the Savannah River Site, near Aiken, South Carolina [in pocket]

FIGURES

1. Map showing Savannah River Site with site areas and streams in Aiken, Allendale,and Barnweli Counties, S.C. ............................................................................................................... 3

2. Map showing boundaries, drainage basins, and stream locations at the SavannahRiver Site, S.C..................................................................................................................................... 4

3. Graph showing relation of percentage impervious area and 100-year recurrenceinterval flow for Fourmile Branch at Road A-7, Savannah River Site, S.C........................................ 6

4-7. Graphs showing the flood profile of Fourmile Branch, Savannah River Site, S.C., from:

4. Station 16000 to Station 24000 and Station 24000 to Station 32000.............................................. 10




TABLES

1. Summary of 100-year recurrence-interval flows for Fourmile Branch, Aiken and BarnweliCounties, S.C.............................................................................................................................................. 8

2. Cross-section name, station, location, type, and 100-year flow, flood-plain width, and water-surface elevation for selected cross sections of Fourmile Branch, Aiken and Barnweli Counties, S.C........................................................................................................................ 14

Contents III

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Multiply

foot (ft)

foot per mile (ft/mi)

cubic foot per second (ft /s)

square mile (mi 2 )

By

0.3048

0.1894

0.02832

2.590

To obtain

meter

meter per kilometer

cubic meter per second

square kilometer

Sea Level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.

Acronyms used in this report:

ERM Elevation reference markNRCS Natural Resources Conservation ServiceSRS Savannah River SiteUSDOE U. S. Department of EnergyUSGS U.S. Geological SurveyUSC&GS U.S. Coastal and Geodetic SurveyWSPRO Computer model for Water Surface Profile Computations

In this report, the station number represents the distance in feet upstream from the mouth of the subject stream. For example, Station 37600 on Fourmile Branch is 37,600 feet upstream from the mouth of Fouimile Branch.

In this report, the words "right" and "left" refer to the directions that would be reported by an observer facing downstream.

IV Contents

Determination of the 100-Year Flood Plain on Fourmile Branch at the Savannah River Site, South Carolina, 1996By Timothy H. Lanier

Abstract

A hydrologic analysis was made to estimate the 100-year recurrence-interval flow for Fourmile Branch. The analysis showed the South Carolina upper Coastal Plain regional rural- and urban-regres sion equations were applicable for the Fourmile Branch drainage basin. This was verified by analysis of the flood-frequency data collected from U.S. Geo logical Survey gaging station 02197342 on Fourmile Branch.

Cross sections were surveyed throughout the reach, and other pertinent data such as flow resistance and land use were collected. The surveyed cross sec tions and computed 100-year recurrence-interval flows were used in a step-backwater model to compute the 100-year flood profile for Fourmile Branch. The pro file was used to delineate the 100-year flood plain on a topographic map. Results are also provided in tabular and graphical formats.

reactor in 1991, all of the remaining reactors have been placed on stand-by since the late 198CTs. Other areas on the SRS include reactor materials (area M), separation (areas F and H), waste man agement (areas E, F, H, S, Y, and Z), heavy-water processing (area D), administration (areas A, B, and CS), the Savannah River Ecology Laboratory, and the Savannah Technology Center (Arnett and others, 1992).

In 1992, the U.S. Geological Survey (USGS), in cooperation with the USDOE, initi ated an investigation to determine the areal extent of the inundation caused by the 100-year recur rence-interval flow (100-year flow) for the Savar- nah River along the SRS boundary and for the major streams and their tributaries on the SRS, with the exception of Lower Three Runs. This report describes the inundation caused by the 10C- year flow on Fourmile Branch.

INTRODUCTION

In 1951, the U.S. Department of Energy (USDOE), formerly the Atomic Energy Commis sion, created the Savannah River Site (SRS) to produce nuclear materials for national defense. The SRS is located in parts of Aiken, Barnwell, and Allendale Counties, South Carolina. The operation of the first nuclear production reactor, in area R, began in 1953 (fig. 1). In addition, there are four other nuclear reactors at the SRS, located in areas C, K, L, and P. Reactors in areas R and P were permanently deactivated in 1964 and 1991, respectively, and except for the restart testing of K

Purpose and Scope

This report documents the approximate boundaries of the 100-year flood plain on the SRS for Fourmile Branch (fig. 2). One-hundred-yeer flows at selected locations, graphical and tabular profiles of the 100-year flood are listed in tables. Descriptions and elevations of benchmarks for Fourmile Branch are listed in the appendix.

Less-than-detailed methods, which require less cross-sectional definition, were used to com pute the 100-year flood-plain boundaries. In par ticular, cross sections were surveyed primarily at road crossings or other easily accessible locations.

Introduction 1

Intermediate cross sections were interpolated using these surveyed cross sections and 7.5-minute topographic maps (U.S. Geological Survey, 1963-65b). This method was requested by the USDOE, because greater accuracy was not warranted.

Description of Study Area

The SRS occupies more than 300 mi along the Georgia-South Carolina border in parts of Aiken, Bamwell, and Allendale Counties, South Carolina. The southwestern boundary of the SRS is formed by the Savannah River. The five major streams that drain into the Savannah River from the SRS are Upper Three Runs, Fourmile Branch, Pen Branch, Steel Creek, and Lower Three Runs (fig. 2). The SRS is located in the upper Coastal Plain of South Carolina, which encompasses about 20 percent of the State (fig. 1). The general topography of the upper Coastal Plain consists of rounded hills with gradual slopes; however, some areas of highly irregular terrain exist in the prov ince, and some elevations exceed 700 ft above sea level. The highest elevation on the SRS is approx imately 420 ft above sea level, near Tims Branch and the northwest boundary of SRS (fig. 2). The land-surface elevation at the boundary of the upper and lower Coastal Plains, located southeast of the SRS, is usually less than 200 ft above sea level. Upper Coastal Plain stream slopes range from 5 to 20 ft/mi, and many of the streams are bordered by swamps with wide flood plains rela tive to the size of the stream (Zalants, 1990).

The study area is the Fourmile Branch Basin (pi. 1). Fourmile Branch begins just upstream from Road F (fig. 1; pi. 1), and flows into the Savannah River south of Augusta, Ga., at river mile 150.7 (pi. 1). Fourmile Branch enters the Savannah River Swamp approximately 11,400 ft upstream from its confluence with the Savannah River; downstream from this point, Fourmile Branch becomes braided and mixes with flow from the Savannah River. The down stream study limit is the confluence of Fourmile

Branch and the Savannah River; however, 100- year flood-plain and profile computations begin upstream from where Fourmile Branch enters the Savannah River Swamp because of the effect of backwater from the Savannah River (pi. 1). The drainage area of Fourmile Branch before it enters the Savannah River Swamp is 23.0 mi".

The upstream study limit is located at Road F; this point was selected because the drainage area upstream of Road F is less th?n 1.0 mi2 , and there is no urbanization or road crossings upstream of this point. All of the Fciirmile Branch drainage basin lies within the SRS, and contains significant industrialization, which includes areas C, CS, E, F, and H (fig. 1).

Acknowledgment

The author is grateful to Lee Davis, USDOE, for his logistical and administrative sup port of this project.

HYDROLOGIC AND HYDRAULIC DATA COLLECTION

Hydrologic data, which includes drainage area, soil type, impervious area, and peak-flow records at USGS gaging stations, were used to estimate the 100-year flow for Fourmile Branch. The drainage area for the basin was delineated using 7.5-minute series topographic maps (U.S. Geological Survey, 1963-65b) at selected loca tions along the reach. These locations were selected based on major tributary confluences, changes in drainage-area shape, and changes of imperviousness within the drainage basin. Soil types were determined from the Natural Resources Conservation Service (NRCS) [for merly the Soil Conservation Service] soil reports of Aiken and Bamwell Counties and the Savan nah River Plant Area (Rogers, 1977; 1985; 1990). Urbanized areas in the drainage basin were deter mined from aerial photographs, 7.5-minute series

Determination of the 100-Year Flood Plain on Fourmile Branch at the Savannah River Site, South Carolina, 1996

81°50' 81°40' 81°30'

Site BoundarySouth Caro

Savannah River Site

Savannah Technology Center

Savannah River Ecology Laboratory

Upstream x Study Limit)

DownstreamStudy Limit - -

EXPLANATION

UNITED STATES ROUTE

SOUTH CAROLINA ROUTE

SAVANNAH RIVER SITE ROUTE

USGS GAGING STATION AND NUMBER

012345 KILOMETERS

Figure 1. Savannah River Site with site areas and streams in Aiken, Allendale, and Barnwell Counties, S.C.oQ.0)5T oo

9

I§a o 575' o

5"

CD

io

(D

a?

CO

ff

isoOJ

3

81°50' 81°40' 81°30'

33°20'

33°10'

Site Boundary

EXPLANATION

FOURMILE BRANCH BASIN BOUNDARY

BASIN BOUNDARY

HIGHEST LAND SURFACE ELEVATION OF THE SAVANNAH RIVER SITE , IN FEET ABOVE SEA LEVEL

Figure 2. Boundaries, drainage basins, and stream locations at the Savannah River Site, S.C.

topographic maps (U.S. Geological Survey, 1963-655), the SRS Atlas (Savannah River Site, 1994), and field inspections. Only urbanization in and around the industrial areas of the basin, which include areas C, CS, E, F, and H, were considered. Paved roads outside of these areas were not included. Percent-imperviousness data associated with urbanized areas were obtained from Cron- shey and others (1986). Peak-flow data were obtained from USGS gaging station 02197342, Fourmile Branch at Road A-7 (fig. 1). These peak-flow data were used to verify the methods of regionalization of selected recurrence-interval flows described by Guimaraes and Bohman (1992) and Bohman (1992).

Cross sections for the step-backwater analy sis of Fourmile Branch were taken upstream and (or) downstream from bridge and culvert cross ings, along road grades at these crossings, and at selected locations along the streams, such as natu ral or man-made expansions or contractions and powerline right-of-ways. In addition, elevation data and structural geometry for all bridges and culverts were determined. Synthesized cross sec tions were developed using surveyed cross-sec tional data and 7.5-minute series topographic maps (U.S. Geological Survey, 1963-65b).

Cross-section elevations were referenced to sea level. In areas where no elevation reference marks (ERM) were located, a global positioning system was used to establish temporary ERM's. Standard surveying levels were used to reference the temporary ERM's to more per manent structures.

Manning's roughness coefficients used in the hydraulic computations were estimated for the channels and flood plains using engineering judgement. Coefficient estimates were based on field notes, photographs, and methods docu mented by Arcement and Schneider (1984) and Barnes(1967).

FLOOD FREQUENCY

The regionalized rural- and urban-regres sion equations developed by Guimaraes and Bohman (1992) and Bohman (1992) were used to compute the 100-year flow for Fourmile Branch. The use of these equations was verified by a hydrologic analysis of peak-flow data from gag ing station 02197342, Fourmile Branch at Road A-7 (fig. 1). In the hydrologic analysis, the 100- year flow was computed using the log-Pearson method and 23 years of peak-flow data; this 100- year flow was compared to the 100-year flow computed using the regional rural- and urban- regression equations. This comparison showed that the regional rural- and urban-regression equa tions reasonably describe the 100-year flows of Fourmile Branch.

By using the peak-flow data of gaging sta tion 02197342, a 100-year flow of 1,080 ft3 /s was computed using the log-Pearson method. How ever, the 100-year flow computed with the regional rural-regression equation was 661 ft /s. This large difference in computed flows is proba bly the result of the 5.0-percent imperviousness of the basin. However, the lower limit of impervi ousness used to develop the regional urban- regression equations presented by Bohman (1992) is 10 percent. Therefore, a relation of impervious area to flow was established for the drainage area of station 02197342, using the rural flows which assume no significant imperviousness and the urban-regional flows using 10- to 50-percent imperviousness (fig. 3). The relation and an impervious area of 5.0 percent were used to obtain a 100-year flow of 1,170 ft3/s. This flow was adjusted using methods described in Guima raes and Bohman (1992) for determining flood frequency at or near a gaged site on the same stream. A 100-year flow of 1,110 ft3/s was obtained, compared to 1,080 ft3/s computed by log-Pearson methods. The flows are well within the 95-percent confidence limits of both methods. Therefore, the regionalized rural and urban- regression equations were used to compute the 100-year flows on Fourmile Branch.

Flood Frequency

CD CO I o a> ** (D W Q> i 0) W

O I o a>

2,60

0

2,40

0

2,20

0

2,00

0

1,80

0

Q z g

1,60

0L

U £

1,40

0L

U

LU

L

L O1,

200

O O

81,

170

CU

BIC

FE

ET

PE

R S

EC

ON

D

1,00

0

800

-

600

400

200

O

D

10

0-Y

EA

R F

LO

W B

Y U

RB

AN

-RE

GIO

NA

L

FLO

OD

-FR

EQ

UE

NC

Y M

ET

HO

D (

BO

HM

AN

, 1

99

2)

NO

T V

ALID

BE

LO

W 1

0 P

ER

CE

NT

IM

PE

RV

IOU

SN

ES

S

INT

ER

PO

LA

TE

D 1

00-Y

EA

R F

LO

W B

ELO

W

10 P

ER

CE

NT

IM

PE

RV

IOU

SN

ES

S

10

0-Y

EA

R F

LO

W B

Y R

UR

AL-R

EG

ION

AL F

LO

OD

F

RE

QU

EN

CY

ME

TH

OD

(G

UIM

AR

AE

S A

ND

BO

HM

AN

, 1

99

2)

100-Y

EA

R F

LO

W B

Y L

OG

-PE

AR

SO

N M

ET

HO

D F

OR

S

TA

TIO

N 0

2197342

AD

JUS

TE

D 1

00-Y

EA

R F

LO

W U

SIN

G M

ET

HO

DS

DE

SC

RIB

ED

IN

G

UIM

AR

AE

S A

ND

BO

HM

AN

(1992)

FO

R D

ET

ER

MIN

ING

FL

OO

D

FR

EQ

UE

NC

Y A

T O

R N

EA

R A

GA

GE

D S

ITE

ON

TH

E S

AM

E S

TR

EA

M

2 4

6 8

10

12

PE

RC

EN

TAG

E I

MP

ER

VIO

US

AR

EA

AT

RO

AD

A-7

(G

AG

ING

STA

TIO

N 0

2197

342,

FO

UR

MIL

E B

RA

NC

H A

T R

OA

D A

-7)

14

Figu

re 3

. R

elat

ion

of p

erce

nt im

perv

ious

are

a an

d 10

0-ye

ar r

ecur

renc

e in

terv

al f

low

for

Fou

rmile

Bra

nch

at

Roa

d A

-7,

Sav

anna

h R

iver

Site

, S

.C.

The equations are:

for rural Upper Coastal Plain watersheds (Guima- raes and Bohman, 1992),

RQ inn = 116 (A)0.69

(1)

and for urban watersheds (Bohman, 1992),

TT^ m At AA°- 506 /^T A\°-932 /r>^ s 0.280 ...UQ loo = 10.4(A) (TIA) (RQ 100 ) , (2)

typically less than 10 percent. Therefore, the pre viously described method to adjust flows for urbanization at Station 02197342 was used to compute flows for the subbasins which had an imperviousness of less than 10 percent.

The 100-year flow was computed at 15 loca tions on Fourmile Branch. The drainage area of nine of these sites was within 50 percent of the drainage area of the Station 02197342, therefore the flows were adjusted using the methods described in Guimaraes and Bohman (1992). The results of the hydrologic analysis on Fourmile Branch are presented in table 1.

whereRQioo is me 100-year recurrence-inter

val flow for rural drainage basins, in cubic feet per second;

A is the drainage area, in square miles;

UQjoo is the 100-year recurrence-inter val flow for urban drainage basins, in cubic feet per second; and

TIA is the total impervious area, in per cent of total drainage area.

Equation 1 requires that the drainage areas be greater than 4.4 mi2 and less than 1,720 mi2 . However, the relation was extended downward to 1.04 mi2 , because no other regional-regression equations specific to South Carolina were avail able. This extrapolation seems to be viable, because the logarithmic regional relation is linear. In addition, the relations for other physiographic provinces are generally linear throughout the range of data, and therefore, it is expected that the relation for the upper Coastal Plain could be extrapolated below a drainage area of 4.4 mi2 .

Equation 2 requires that the impervious area be greater than 10 percent, and the drainage area be greater than 0.18 mi2 and less than 41.0 mi2 . The subbasins of Fourmile Branch meet the drain age area requirement for urbanized basins; how ever, the impervious area of the subbasins is

MODEL SELECTION AND DEVELOPMENT

Water-surface elevations for the 100-year flows were computed for Fourmile Branch by using either the USGS/Federal Highways Admin istration step-backwater water-surface profile computer model (WSPRO) (Shearman and others, 1986; Shearman, 1990), or where flow is affected by backwater from the Savannah River, data from Lanier (1996) were used. The WSPRO model can compute backwater caused by bridges without subdividing the reach; however, the reach must be subdivided at culverts and a separate culvert-flow computation must be made to determine the back water caused by the culvert. The culvert backwa ter was calculated using the USGS A-526 culvert- flow model (Bodhaine, 1968). The computed water-surface elevation at the approach to the cul vert was used as the initial water-surface elevation for the WSPRO analysis of the next upstream reach.

The downstream limit of the Fourmile Branch study area was located at the confluence of the Savannah River. Because the drainage area of the Savannah River is much larger than the drainage area of Fourmile Branch, it is assumed that at the time of the 100-year flood, the flow in Fourmile Branch would have peaked and receded before peak flow occurred on the Savannah River.

Model Selection and Development

Table 1.--Summary of 100-year recurrence-interval flows for Fourmile Branch, Aiken and Barnwell Counties, S.C.

[mi~, square miles; ft /s, cubic feet per second; ft, feet; --, cross section not surveyed; *, impervious area les? than 1 percent.]

Location (plate 1)

Station 2 1707; Road A- 12. 2

Station 32057; at Road A

Station 38000; 5,943 ft upstream from Road A and 3,650 ft downstream from Road 3

Station 39950; upstream from the confluence with an unnamed tributary; 1 ,700 ft below Road 3

Station 44888; Road A-7

Station 49750; 4,862 ft upstream from Road A-7 and 5,372 ft downstream from Road C-4

Station 52500; 2,622 ft downstream fromRoad C-4

Station 55350; 228 ft upstream from Road C-4

Station 59623; 3 15 ft upstream from Road C

Station 63813; 340 ft downstream from Road 4

Station 65238; 1,085 ft upstream from Road 4

Station 71750; 3,918 ft upstream from Road E-l

Station 73400; 5,568 ft upstream from Road E-l and 5,320 ft downstream from Road F

Station 76750; 1,970 ft downstream from Road F

Station 78720; at Road F

Drainage area (mi2)

21.9

18.7

17.1

13.3

12.5

11.4

10.7

8.15

6.96

6.08

4.50

3.66

1.91

1.29

1.04

Percentage of

impervious area

3

4

4

5

5

5.5

5.5

5

2

3

*

*

*

*

*

One- hund red- year flow

(tt3/s)

'1,380

1 1 ,400

'1,320

'1,170

'1,110

1 1 ,060

'1,030

'823

'590

570

327

284

181

138

119

Cross- section name

BR30

BR70

S97.5

EMB

SE240

'Flow adjusted using data from gaging station 02197342.

8 Determination of the 100-Year Flood Plain on Fourmile Branch at the Savannah River Site, South Carolina, 1996

The elevation of the 100-year flood on the Savan nah River at the mouth of Fourmile Branch is 106.0 ft, which intersects Fourmile Branch at Sta tion 22625. Therefore, due to the backwater of the Savannah River, the initial Fourmile Branch water-surface elevation was computed by slope conveyance at cross section SEC 10, which is located 18,287 ft upstieam of the confluence of Fourmile Branch and the Savannah River (pi. 1). The 100-year flood elevation on the Savannah River of 106.0 ft intersects the 100-year flood ele vation on Fourmile Branch at Station 19846.

the CSX Railway Bridge. The old road embank ment just upstream of Road 4 causes 1.9 ft of backwater. In addition, Roads A-7, C-4, and E-l are overtopped by a depth of 2.7 ft, 1.2 ft, and 1.0 ft, respectively. Graphical and tabular profiles of Fourmile Branch are shown in figures 4 through 7 and listed in table 2, respectively. The areal extent of the inundation caused by the 100- year flood on Fourmile Branch is shown in plate 1.

ONE-HUNDRED-YEAR FLOOD PLAIN AND PROFILE

Fourmile Branch was analyzed from its con fluence with the Savannah River to Road F (pi. 1). Station 0 is located at the confluence of Fourmile Branch and Savannah River. The 78,800-ft long study segment consists of 49-surveyed and 132-synthetic cross sections. Within the study area, there are 4 highway bridges, 1 railway bridge, 5 culvert crossings, and 10 breached dams or old road beds that cross Fourmile Branch. The highway bridges are located on Roads A-12.2, A, C,"and 4 at Stations 21707, 32057, 59308, and 64153, respectively (pi. 1). The CSX railway bridge crosses Fourmile Branch at Station 25806 (pi. 1). The culverts are located at Roads 3, A-7, C-4, E-l, and F at Stations 41650, 44888, 55122, 67832, and 78720, respectively (pi. 1). The breached dams/road beds are located at Stations 18457, 21885, 24807, 27132, 35870, 36307, 39930, 49654, 59391, and 64218 (pl.l). Roads 6-1, 6-2, 6-3, and A-6 are located at Stations 32650, 33250, 34020, and 46475, respectively, but do not cross Fourmile Branch. In the area of Fourmile Branch affected by backwater from the Savannah River, the 100-year flood-plain widths range from 1,150 ft at Station 15850 to 350 ft at Station 20500 (pi. 1). Outside of this area, the 100-year flood-plain widths range from 900 ft at Station 58025 to 120 ft at Station 68250 (pi. 1). Backwater caused by the road and railway bridges ranges from less than 0.1 ft at Road C to 2.0 ft at

One-hundred-Year Flood Plain and Profile

150

140

- 130

120

OCD

110<

100

9016,000

I100-YEAR WATER-SURFACE ELEVATION

BED ELEVATION

TOP OF ROAD

LOW STEEL OF DRAINAGE STRUCTURE

SURVEYED CROSS SECTION AND IDENTIFIER

(SECIO&DAMIS)

.I,,,,

18,000 20,000 22,000 24,000

DISTANCE UPSTREAM FROM THE CONFLUENCE WITH SAVANNAH RIVER, IN FEET

160

OCD

150-

140

130

8' 120 <

110

100

DC 0)

100-YEAR WATER-SURFACE ELEVATION

BED ELEVATION

TOP OF ROAD


(RDeoa'sEcei) SURVEYED CROSS SECTION AND IDENTIFIER j

(DAM38 & SEC39)

24,000 26,000 28,000 30,000 32,000


Figure 4. Flood profile of Fourmile Branch, Savannah River Site, S.C., from (a) Station 16000 to Station 24000 and (b) Station 24000 to Station 32000.


170

160

- 150

140

130 <

120 -

I


BED ELEVATION

TOP OF ROAD



(JRD90 & SEC92)

^EX69, BR70, & APP7g)

no32,000 34,000 36,000 38,000


40,000

180

170

160

150

140-

130-

(SEC99& SE100)

I


BED ELEVATION

TOP OF ROAD



LOW POINT OF ROAD, 160 FEET TO THE RIGHT OF THE CULVERT AT ROAD A-7

12040,000 42,000 44,000 46,000


48,000


Figures 11

210

200

- 190

180

170 <

160

150

y -L

1 00-YEAR WATER-SURFACE ELEVATION

BED ELEVATION

TOP OF ROAD



I

(DM130. SW131, SE1J2. & SE133)

48,000 50,000 52,000 54,000 56,000


230

OCQ <

z O

220 -

210

200 -

190

180

I


BED ELEVATION

TOP OF ROAD



(SE160 BR170. & AP18(Q

17056,000 58,000 60,000 62,000 64,000




250

240 -

230-

Om

Q<

_ _ _ _ 100-YEAR WATER-SURFACE ELEVATION

BED ELEVATION

TOP OF ROAD


iiTSD SURVEYED CROSS SECTION AND IDENTIFIER

(FV209. SE210, & AP220)

XSE190. BR' 90. & AP200)

220 -

64,000 66,000 68,000 70,000


72,000

~7 270 L

Om

Q - - - - 100-YEAR WATER-SURFACE ELEVATION

BED ELEVATION

T TOP OF ROAD

-1 LOW STEEL OF DRAINAGE STRUCTURE


260-

250-

240-

23072,000 74,000 76,000 78,000


80,000


Selected References 13

o <DTa

ble

2.--

Cro

ss-s

ectio

n na

me,

sta

tion,

loc

atio

n, t

ype,

and

100

-yea

r flo

w,

flood

-pla

in w

idth

, an

d w

ater

-sur

face

ele

vatio

n fo

r se

lect

ed c

ross

sec

tions

of

Four

mile

Bra

nch,

Aik

en a

nd B

arnw

ell C

ount

ies,

S.C

.

ion

of

the

100-

Year -n 0 o Q. o CO 3'

0 -n

o c <D Branch

at tl .j o w CO CO 3 CO 2 0 w p V) o c O m o_ 5' 0) _L tO J)

[11

/t

>,

CU

U1C

ltd

JJC

1

:

Cro

ss-s

ecti

on

nam

e

SEC

10

DA

M 1

5

S17.

3

SYN

19

SEC

20

SYN

21

EX

29

BR

30

S3 1

.5

SEC

32

SYN

37

DA

M38

SEC

39

EX

40

>C

CU

11

VJ,

1

1,

It-S

/lJ

Cro

ss-s

ectio

n st

atio

n

1828

7

1845

7

1900

0

2028

3

2034

0

2039

0

2160

2

2170

7

2188

5

2195

5

2479

0

2480

7

2484

7

2568

0

Cro

ss-s

ectio

n lo

catio

n

170

ft do

wns

trea

m f

rom

a b

reac

hed

dam

Bre

ache

d da

m, 3

,250

ft d

owns

trea

m f

rom

Roa

dA

-12.

2

543

ft up

stre

am f

rom

a b

reac

hed

dam

57 f

t do

wns

trea

m f

rom

an

unna

med

pow

erlin

e

Unn

amed

pow

erlin

e, 1

,367

ft d

owns

trea

m f

rom

R

oad

A- 1

2.2

50 f

t ups

trea

m f

rom

an

unna

med

pow

erlin

e

105

ft do

wns

trea

m f

rom

Roa

d A

-12.

2

Bri

dge

at R

oad

A-1

2.2

Bre

ache

d da

m,

1 78

ft up

stre

am f

rom

Roa

dA

-12.

2

248

ft up

stre

am f

rom

Roa

d A

-l 2

.2

1 7 f

t do

wns

trea

m f

rom

a b

reac

hed

dam

Bre

ache

d da

m.

3,10

0 ft

upst

ream

fro

m R

oad

A-1

2.2

40 f

t up

stre

am f

rom

a b

reac

hed

dam

126

ft do

wns

trea

m f

rom

CSX

rai

lway

bri

dge

Type

of

cros

s se

ctio

n1

surv

eyed

surv

eyed

synt

hetic

synt

hetic

surv

eyed

synt

hetic

synt

hetic

surv

eyed

surv

eyed

surv

eyed

synt

hetic

surv

eyed

surv

eyed

surv

eyed

1 00-

year

flo

w

(ft3/

s)

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1 00-

year

fl

ood-

plai

n w

idth

(«)

636 73 541

318

320

318

523 85 108

548

521

483

526

375

100-

year

w

ater

-sur

face

el

evat

ion

(ft, a

bove

sea

leve

l)

2 1 0

6.0

2 1 0

6.0

2l06

.0

106.

64

106.

74

106.

81

110.

06

31 1

0.09

1 1 1

.25

111.

75

117,

86

117,

85

118.

09

120.

20

Tabl

e 2.

--C

ross

-sec

tion

nam

e, s

tatio

n, l

ocat

ion,

typ

e, a

nd 1

00-y

ear

flow

, flo

od-p

lain

wid

th,

and

wat

er-s

urfa

ce e

leva

tion

for

sele

cted

cro

ss s

ectio

ns o

f Fo

urm

ile B

ranc

h, A

iken

and

Bar

nwel

l Cou

ntie

s, S

.C.--

Con

tinue

d

[ft3

/s, c

ubic

fee

t per

sec

ond;

ft,

feet

]

Cro

ss-s

ectio

n na

me

RB

R50

APP

55

SYN

59

RD

60

SEC

61

EX

69

BR

70

APP

72

SEC

80

S80.

5

SYN

81

SEC

84

DA

M85

SY85

B

SYN

89

BR

D90

SEC

92

Cro

ss-s

ectio

n st

atio

n

2580

6

2593

3

2711

2

2713

2

2715

2

3199

5

3205

7

3211

9

3265

0

3325

0

3402

0

3584

5

3587

0

3589

0

3629

5

3630

7

3631

9

Cro

ss-s

ectio

n lo

catio

n

CSX

rai

lway

brid

ge

1 27

ft up

stre

am f

rom

CSX

rai

lway

bri

dge

20 f

t dow

nstr

eam

fro

m a

n un

nam

ed p

ower

line

Unn

amed

pow

erlin

e ro

ad,

1 ,32

6 ft

upst

ream

fr

om th

e C

SX r

ailw

ay b

ridg

e

20 ft

ups

trea

m fr

om a

n un

nam

ed p

ower

line

62 f

t dow

nstr

eam

fro

m R

oad

A

Bri

dge

at R

oad

A, (

Rou

te S

.C.

125)

62 f

t ups

trea

m f

rom

Roa

d A

Roa

d 6-

1

Roa

d 6-

2

Roa

d 6-

3

25 f

t dow

nstr

eam

fro

m a

bre

ache

d da

m

Bre

ache

d da

m, 3

,813

ft u

pstr

eam

fro

m R

oad

A

20 f

t ups

trea

m f

rom

a b

reac

hed

dam

12 f

t dow

nstr

eam

fro

m a

bre

ache

d ro

ad

Bre

ache

d ro

ad, 4

,250

ft u

pstr

eam

fro

m R

oad

A

1 2 f

t ups

trea

m f

rom

a b

reac

hed

road

Type

of

cros

s se

ctio

n1

surv

eyed

synt

hetic

synt

hetic

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

synt

hetic

synt

hetic

surv

eyed

surv

eyed

synt

hetic

synt

hetic

surv

eyed

surv

eyed

100-

year

flo

w

(ft3/

s)

1,38

0

1,38

0

1,38

0

1,38

0

1,38

0

1,40

0

1,40

0

1,40

0

1,40

0

1,40

0

1,40

0

1,40

0

1,40

0

1,40

0

1,32

0

1,32

0

1,32

0

100-

year

flo

od-p

lain

w

idth

(ft

) 38 474

432

167

443

354 38 374

278

244

221

434 99 436

414

277

414

100-

year

w

ater

-sur

face

el

evat

ion

(ft, a

bove

se

a le

vel)

3120

.50

122.

62

123.

31

5123

.38

123.

66

134.

89

3134

.89

136.

11

5136

.68

5137

.58

5139

.23

143.

56

143.

59

143.

76

144.

42

5 144

.43

144.

46

Tabl

e 2.

-Cro

ss-s

ectio

n na

me,

sta

tion,

loc

atio

n, t

ype,

and

100

-yea

r flo

w, f

lood

-pla

in w

idth

, an

d w

ater

-sur

face

ele

vatio

n fo

r se

lect

ed c

ross

sec

tions

of

Four

mile

Bra

nch,

Aik

en a

nd B

arnw

ell C

ount

ies,

S.C

.-C

ontin

ued

[ft

/s, c

ubic

fee

t per

sec

ond;

ft,

feet

]S srmination

of

tl j (D 0

O (D 0) n o a T

J0) 3' O ^n :ourmi (D 7 3

O 3-

0) (D (/> 0) 0) 3

3

0) 3-

3) i 1 o c o 0) o. 5' 0)

L

7

i

Cro

ss-s

ecti

on

nam

e

S96.

5

DA

M97

S97.

5

SEC

99

SE10

0

APP

99

SE10

9

EM

B

APP

R1

RW

119

RD

120

RW

121

API

22

DM

130

swm

Cro

ss-s

ectio

n st

atio

n

3991

0

3993

0

3995

0

4149

5

4165

0

4171

6

4467

2

4488

8

4492

7

4643

9

4647

5

4651

1

4673

5

4965

4

4Q66

Q

Cro

ss-s

ectio

n lo

catio

n

20 ft

dow

nstr

eam

fro

m a

bre

ache

d da

m

Bre

ache

d da

m,

1 ,72

0 ft

dow

nstr

eam

fro

mR

oad

3

20 f

t ups

trea

m f

rom

a b

reac

hed

dam

1 55

ft do

wns

trea

m f

rom

Roa

d 3

Roa

d 3

66 f

t ups

trea

m f

rom

Roa

d 3

216

ft do

wns

trea

m f

rom

Roa

d A

-7

Roa

d A

-7

39 f

t ups

trea

m f

rom

Roa

d A

-7

36 f

t dow

nstr

eam

fro

m R

oad

A-6

Roa

d A

-6

36 f

t ups

trea

m f

rom

Roa

d A

-6

260

ft up

stre

am f

rom

Roa

d A

-6

Bre

ache

d da

m, 6

6 ft

dow

nstr

eam

fro

m th

edo

wns

trea

m e

dge

of a

n un

nam

ed p

ower

line

5 1

ft d

ow

nst

ream

frr

mi

the d

ow

nst

ream

edoe n

f

Type

of

cros

s se

ctio

n1

synt

hetic

surv

eyed

surv

eyed

surv

eyed

surv

eyed

synt

hetic

surv

eyed

surv

eyed

surv

eyed

synt

hetic

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

ived

100-

year

flo

w

(ft3/

s)

1,32

0

1,32

0

1,32

0

1,17

0

1,17

0

1,17

0

1,11

0

1,11

0

1,11

0

1,06

0

1,06

0

1,06

0

1,06

0

1,06

0

i n^

n

1 00-

year

fl

ood-

plai

n w

idth

/£A

\(f

t)

514

4148 514

369

324

389

404

132

327

281

250

279

422

245

TO

8

100-

year

w

ater

-sur

face

el

evat

ion

(ft, a

bove

sea

leve

l)

151.

16

151.

18

151.

29

155.

08

157.

72

157.

72

161.

05

6163

.37

163.

80

165.

16

5165

.21

165.

28

165.

78

171.

11

171

91

an u

nnam

ed p

ower

line

0> IN)

Tab

le 2

.--C

ross

-sec

tion

nam

e, s

tatio

n, l

ocat

ion,

typ

e, a

nd 1

00-y

ear

flow

, flo

od-p

lain

wid

th,

and

wate

r-su

rface

ele

vatio

n fo

r se

lect

ed c

ross

sec

tions

of

Fou

rmile

Bra

nch,

Aik

en a

nd B

arnw

ell

Cou

ntie

s, S

.C.-

-Con

tinue

d

| IV

/s,

cubi

c fe

el p

er s

econ

d; l

l, fe

el)

Cro

ss-s

ectio

n na

me

Cro

ss-s

ectio

n ^

. .

. ..

Cro

ss-s

ectio

n lo

catio

n st

atio

n

Type

of

cros

s se

ctio

n1

100-

year

flo

w

(ft3

/s)

100-

year

flo

od-p

lain

w

idth

(f

t)

100-

year

w

ater

-sur

face

el

evat

ion

(ft,

abov

e se

a le

vel)

SE13

2

SE13

3

SW13

3

4973

5

4980

4

4981

0

SE13

9

EX 140

RDC4

AP150

SE16

0

BR170

API 80

SE190

BR190

AP20

0

FV209

SE210

AP220

54827

55056

55122

55149

58916

59308

59391

63910

6415

3

64218

6781

3

67832

67868

15 f

t ups

trea

m f

rom

the

dow

nstr

eam

edg

e of

an

unna

med

pow

erlin

e

26 f

t dow

nstr

eam

fro

m t

he u

pstr

eam

edg

e of

an

unna

med

pow

erlin

e

20 f

t dow

nstr

eam

fro

m th

e up

stre

am e

dge

of a

n un

nam

ed p

ower

line

295

ft do

wns

trea

m f

rom

Roa

d C

-4

66 f

t dow

nstr

eam

fro

m R

oad

C-4

Roa

d C

-4

27 f

t ups

trea

m f

rom

Roa

d C

-4

392

ft do

wns

trea

m f

rom

Roa

d C

Bri

dge

at R

oad

C

Old

Roa

d be

d, 8

3 ft

upst

ream

fro

m R

oad

C

243

ft do

wns

trea

m f

rom

Roa

d 4

Bri

dge

at R

oad

4

Old

roa

d be

d, 6

5 ft

upst

ream

fro

m R

oad

4

19 f

t dow

nstr

eam

fro

m R

oad

E-l

Roa

dE-1

36 f

t ups

trea

m f

rom

Roa

d E

-l

surv

eyed

surv

eyed

synt

hetic

1,06

0

1,06

0

1,06

0

391

406

405

171.

31

171.

37

171.

37

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

surv

eyed

1,03

0

1,03

0

1,03

0

1,03

0

590

590

590

570

570

570

327

327

327

326

752

315

378

571 60 37 322 45 54 266 93 315

181.

38

183.

01

6186

.75

186.

98

191.

67

3 192

.70

192.

95

202.

37

3203

.22

203.

61

216.

61

6219

.59

219.

80

Tabl

e 2.

--C

ross

-sec

tion

nam

e, s

tatio

n, lo

catio

n, ty

pe, a

nd 1

00-y

ear f

low

, flo

od-p

lain

wid

th,

and

wat

er-s

urfa

ce e

leva

tion

for

sele

cted

cro

ss s

ectio

ns o

f Fo

urm

ile B

ranc

h, A

iken

and

Bar

nwel

l Cou

ntie

s, S

.C.-C

ontin

ued

3 21

o" 3 a CD _L O -n o 0 ex

o £.3* O

3 51 5"

co i o 3" O 0) 0> 3

" 31 1 O c 5

O 1 j>

Cro

ss-s

ectio

n C

ross

-sec

tion

nam

e st

atio

n

EX

230

7865

9

SE24

0 78

720

APP

F 78

771

Cro

ss-s

ectio

n lo

catio

n

61 f

t dow

nstr

eam

fro

m R

oad

F

Roa

dF

5 1

ft up

stre

am f

rom

Roa

d F

Type

of

100-

year

cr

oss

flow

se

ctio

n1

(ft3/

s)

surv

eyed

1 1

9

surv

eyed

1 1

9

synt

hetic

1 1

9

100-

year

^J

floo

d-pl

ain

wat

er-s

urfa

cew

idth

f'

evaKt

l0n

,m

(ft, a

bove

v ;

sea

leve

l)

176

276.

88

10

3277

.82

183

277.

82

*A11

sur

veye

d cr

oss

sect

ions

are

sho

wn

on p

late

1;

synt

hetic

cro

ss s

ectio

ns a

re n

ot s

how

n on

pla

te 1

. 2B

ackw

ater

fro

m th

e Sa

vann

ah R

iver

. 3R

oad

or r

ailw

ay is

not

ove

rtop

ped.

4D

ue to

mor

e th

an o

ne b

reac

h in

the

dam

, the

flo

od-p

lain

wid

th m

ay n

ot m

atch

pla

te 1

. 5R

oad

does

not

cro

ss F

ourm

ile B

ranc

h.

6Roa

d is

ove

rtop

ped.

7D

ue to

roa

d ov

erfl

ow, t

his

floo

d-pl

ain

wid

th i

s in

crea

sed

to th

e sa

me

floo

d-pl

ain

wid

th a

s cr

oss

sect

ion

RD

C4.

SUMMARY SELECTED REFERENCES

In 1951, the U.S. Department of Energy, formerly the Atomic Energy Commission, created the Savannah River Site to produce nuclear mate rials for national defense. The Savannah River Site occupies approximately 300 square miles along the Georgia-South Carolina border in parts of Aiken, Barnwell, and Allendale Counties, South Carolina. In 1992, the U.S. Geological Sur vey, U.S. Department of the Interior, in coopera tion with the U.S. Department of Energy, initiated an investigation to determine the areal and verti cal extent of inundation caused by the 100-year recurrence-interval flood for the Savannah River along the Savannah River Site southwestern boundary, and for the major streams and their trib utaries on the Savannah River Site, with the exception of Lower Three Runs.

This report includes a map of the 100-year flood plain and flood profile on Fourmile Branch. The results also are provided in tabular format. The 100-year flood-plain map and flood profile provide water-resource managers with a technical basis for making flood-plain management deci sions that could minimize future flood problems and provide a basis for designing and constructing drainage structures along roadways.

A hydrologic analysis was made to estimate the 100-year recurrence-interval flow for Four- mile Branch and its tributaries. This analysis showed the U.S. Geological Survey regional rural- and urban-regression equations for South Carolina reasonably describe the 100-year flows of Fourmile Branch.

Throughout the reach, cross sections were surveyed and other pertinent data such as flow resistance and land-use data were collected. The computed 100-year flows and surveyed cross sec tions were used in a step-backwater model to compute the 100-year flood plain for Fourmile Branch. The profiles computed by the step-back water model were used to delineate the 100-year flood plain on topographic maps.

Arcement, G.J., Jr., and Schneider, V.R.. 1984, Guide for selecting Manning's roughness coefficients for natural channels and flood plains: Federal Highway Administration Pub lication FHWA-TS-84-204, 62 n.

1989, Guide for selecting Manning's roughness coefficients for natural channels and flood plains: U.S. Geological Survey Water-Supply Paper 2339, 38 p.

Arnett, M.W., Karapatakis, L.K., Mamatey, A.R., and Todd, J.L., 1992, Savannah River Site environmental report for 1991: Westinghouse Savannah River Company Publication WSRC-TR-92-186, 562 p.

Barnes, H.H., Jr., 1967, Roughness characteristics of natural channels: U.S Geological Survey Water-Supply Paper 1849, 213 p.

Bodhaine, G.L., 1968, Measurement of peak dis charge at culverts by indirect methods: U.S. Geological Survey Techniques of Water- Resources Investigations, book 3, chap. A3, 60 p.

Bohman, L.R., 1992, Determination of flood hydrographs for streams in South Carolina: Volume 2. Estimation of peak-discharge fre quency, runoff volumes, and flood hydrographs for urban watersheds: U.S Geological Survey Water-Resources Investigations Report 92-4040, 79 p.

Chow, V.T., 1959, Open-Channel Hydraulics: New York, MacMillan Publishing Co., Inc., 522 p.

Cronshey, Roger; McCuen, R.H.; Miller, Norman; Rawls, Walter; Robbins, Sam; and Wood ward, Don, 1986, Urban hydrology for small watersheds: Soil Conservation Service, Tech nical Release 55, Washington D.C., 94 p.

Guimaraes, W.B., and Bohman, L.R., 1992, Tech niques for estimating magnitude and fre quency of floods in South Carolina, 1988: U.S. Geological Survey Water-Resources Investigations Report 91-4157, 174 p.

Hulsing, Harry, 1967, Measurement of peak dis charge at dams by indirect methods: U.S.

Summary 19

Geological Survey Techniques of Water- Resources Investigations, book 3, chap. A5, 29 p.

Lanier, T.H., 1996, Determination of the 100-year flood plain on Upper Three Runs and selected tributaries, and the Savannah River at the Savannah River Site, South Carolina, 1995: U.S. Geological Survey Water-Resources Investigations Report 96-4014.

Matthai, H.F., 1967, Measurement of peak dis charge at width contractions by indirect meth ods: U.S. Geological Survey Techniques of Water-Resources Investigations, book 3, chap. A4, 44 p.

Rogers, V.A., 1977, Soil Survey of Barawell County, South Carolina, Eastern Part: U.S. Department of Agriculture, 52 p.

1985, Soil Survey of Aiken County Area, South Carolina: U.S. Department of Agricul ture, 134 p.

-1990, Soil Survey of Savannah RiverPlant Area, Parts of Aiken, Barawell, and Allendale Counties, South Carolina: U.S. Department of Agriculture, 127 p.

Savannah River Site, 1994, Savannah River Site atlas including off-site locations and index, OSR3-158,40p.

Shearman, J.O., 1990, User's manual for WSPRO a computer model for water surface profile computations: Federal Highway Administration Publication FHWA-IP-89- 027,187 p.

Shearman, J.O., Kirby, W.H., Schneider, V. R., and Flippo, H.N., 1986, Bridge waterways analysis model; research report: Federal Highway Administration Publication FHWA- RD-86-108, 112 p.

U.S. Geological Survey, 1963, New Ellenton SE, S.C., quadrangle: 7.5-minute series topo graphic map, scale 1:24,000.

1964, Girard NW, S.C., quadrangle: 7.5-minute series topographic map, scale 1:24,000.

1965a, New Ellenton SW, S.C., quadran gle: 7.5-minute series topographic map, scale 1:24,000.

1965b, Shell Bluff Landing, Ga.-S.C..quadrangle: 7.5-minute series topographic map, scale 1:24,000.

Zalants, M.G., 1990, Low-flow characteristics of natural streams in the Blue Ridge. Piedmont, and upper Coastal Plain physiographic prov inces of South Carolina: U.S. Geological Sur vey Water-Resources Investigations Report 90-4188, 92 p.


APPENDIX

List of Elevation Reference Marks

Appendix 21

APPENDIX-List of Elevation Reference Marks

[ft, feet; USGS, U.S. Geological Survey; mi. mile; USC&GS, U.S. Coastal and Geodetic Survey] (In this report, the words "right" and "left" refer to directions that would be reported by an

observer facing downstream.)

Benchmark LocationElevation atove sea

level(ft)

FMB30 Chiseled square in the downstream left end of the Road A-12.2bridge crossing Fourmile Branch; 10,326 ft downstream from Road A. Established by the USGS.

112.49

FMB50 Chiseled square in the downstream left abutment headwall of the CSX Railway bridge crossing Fourmile Branch, 6,257 ft down stream from Road A. Established by the USGS.

146.67

FMB70 Chiseled square in the upstream left abutment headwall of theRoad A bridge crossing Fourmile Branch. Established by the USGS.

146.02

FMB170 Chiseled square on the downstream left abutment headwall of theRoad C bridge crossing Fourmile Branch. Established by the USGS.

202.68

R102 Brass tablet located 3.15 mi southwest of the junction of Road C and Road 3, about 0.4 mi northeast of four 6-ft diameter concrete pipes over Fourmile Branch, at the junction of the woods road leading north, 59 ft north of the center line of Road 3, 37 ft west of the center line of the woods road, 2 ft east of the metal witness post, 1.5 ft below the level of the highway. Established by the USC&GS.

200.154

U102 Brass tablet located at the junction of Roads C and 5, set in the junc tion Y of Road 5, 80.5 ft southwest of the centerline of the southwest two of four lanes of Road C north, 77 ft southeast of the center line of Road 5, 71 ft northwest of the centerline of the southeast leg of the junction. Established by the USC&GS.

301.213

22 Determination of the 100-Year Flood Plain on Fourmile Branch at the Savannah River Site, South Carolina, 199f

APPENDIX-List of Elevation Reference Marks-Continued

[ft, feet; USGS, U.S. Geological Survey; mi, mile; USC&GS, U.S. Coastal and Geodetic Survey] (In this report, the words "right" and "left" refer to directions that would be reported by an

observer facing downstream.)

Benchmark LocationElevation above sea

level(ft)

M101 Brass tablet located at crossing of CSX Railway and Road 3, 259 degrees north and across the track from mile post Number 438, 33 ft northeast of northeast rail, 49.5 ft southeast of the centerline of the road, 60.5 ft east of the center of the crossing. Established by the USC&GS.

153.372

L101 Brass tablet located 0.6 mi southeast along the CSX railway from the Road 3 crossing, thence 0.15 mi south on a spur track to Area D, at the crossing of Road A-12 (a black top road), the road passes between the main line track and the Area D, 114 ft southeast of the southeast rail of the spur track, in the top of a concrete block 18 ft wide by 27 ft long by 1 ft high, 188 ft northeast of the center line of the road. Established by USC&GS.

152.218

H101 Brass tablet located 4.75 miles northwest along CSX railway from the railway station at Robbins, at the crossing of Road A-13 and CSX Railway, 24 ft northeast of the northeast rail, 27 ft southwest of the center line of the road, 69 ft north of the center of the crossing, and 1 ft southeast of a metal witness post. Established by the USC&GS.

150.193

X102 Brass tablet located 1.35 mi north on Road 4 from junction of Road C and Road 4, thence 0.9 mi northwest on M Line U.S. Government Railway track, about 0.1 mi northwest of milepost No. 12, 85 ft southwest from the southwest rail of track, 2 ft southeast of the metal witness post, 1 ft above the level of the track. Established by the USC&GS.

249.350

Appendix

Documents

Determination of the 100-Year Flood Plain on Fourmile ... · PDF fileDetermination of the 100-Year Flood Plain on ... In par­ ticular, cross ... of Aiken and Bamwell Counties and

Determination of the 100-Year Flood Plain on Fourmile ... · PDF fileDetermination of the 100-Year Flood Plain on ... In par ticular, cross ... of Aiken and Bamwell Counties and