Techniques for Estimating Flood-Depth Frequency Relations on Natural Streams in Georgia U.S. GEOLOGICAL SURVEY Water-Resources Investigations 77–90 BIBLIOGRAPHIC DATA 3. Recipient'S' Accession No. r.it 'SHE~T '., .... .. , ~" 4. Title .ndSub~~tle;. ...•. '.> ...:.' .:., . I TECHN!·QU:ES~;:FOR '. ESTiMATIN(t:FL00lhDEI>'J;'li<~QUEiNCYR.I!:J.ATIONS dUM} .. 0NNATlJ1U.LSTREAMSINGEORGIA .' i!il~;~t~~ ............ '1-:,"". ~A-ut"':'h"'o"'r("'s"')."""---"""--"""-----------'-----'-"""""""""---------------'----"""-h--;;-;"""~---:::-~-......'"'::""......--4 7 .McGlone P~ice 9. Performing OrganizatiooNalDe ~d Address . .... '.•..•...•.•.•••..'..•..•••... ,ii 10. Project/Task/Work Unit No. u, S.qeological Survey, WateI' Reaourcea DivisiOn 648lPeaChtree Industrial Boulevard, .... S¢teB porav:l.lle,Georgia 30360 ..... ' ..... '. 12. Sponsoring Organization Name and Address --- 16~ Abstracts Regional relations'are defined forestima.ting>'ri;hed«!pth of.water of floods having I a recurrence interval of 10, 50, and 100ye/:irsfor·streams with natural flow in .-_.~ Georgia.., . ". '. .....•......•... ".."...•..... .' .Multiple-regression .analy~is.;is""9Sedt()de.f..inEirelations~etween floo&-depth frequencystationdataforstreamscix:#IdngltOJ.,OOOsquare miles andlO physical and climatological·basin charact~rist~c~•.... The ari~lysis indicates that the drainage area. of .:the basin is themosts~~~~c.~tvt:lJ::i;ab.~~~. Five regions having distinct flood-de'!pth.·frequency characteris~i~SJJi:r~d~J.~Il~~t~~l~·. ThedevelopedIelat:i;onsareC;()Ils~d~#e4.~~.~1:t~~~ifgI'i~rtuallyany site in Georgia where the drainage .azea is betweeri.~laI1Ci l,.OOO··.~;q~~~.~les and the flow is natural. ,.. -'.' ,,--. -- -.' ;,,:,;:,,' ..:', ,,:.'.::'~.~:..~" ;::.- ::'-':'.:., -:-.>:::'.:::.:>.~_:.- '".' //1> ..-:,~<;,;!\ .- .':~. - -:'·:;·>::<L/;-:::.~':-':.'·:·· 17. KeyWords and Document Analysis. 17a.Descriptors F~oods, Flood depth, Flood data, Frequency analysis, R.egression analysis, Natural flo:w, ProbabiJ,.ity. ~ 17b.Jdeotifiers/Open-Ended Terms I Flood-depth probability, Basincharacteristi.cs. - - 17 c. COSATIField IGroup 18. Availability Statement 19•.SecUrity Class (This 2l.No. of Pages Report) 33 ~ No restriction on distribution. N • SecutityClass (This 22. Price Page •UNCLASSIFIED . .,. FORM NTI5-3!l IREV. 10-73) ENDORSED BY ANSI AND UNESCO. nnSFORM MAYBE REPRODUCED USCOMM-DC 82611· P 7 . TECHNIQUES FOR ESTIMATING FLOOD-DEPTH FREQUENCY RELATIONS ON NATURAL STREAMS IN GEORGIA By McGlone Price U.S. GEOLOGICAL SURVEY Water-Resources Investigations 77-90 =, I .- August 1977 ..._'------------------------------------------- .. - UNITED STATES DEPARTMENT OF THE INTERIOR rIt:~ CECIL D. ANDRUS, Secretary 1r GEOLOGICAL SURVEY Jl V. E. McKelvey, Director r~ J~ ~ .....J , :". I'f-r I ] 1 For additional information write to: U.s. Geological Survey Water Resources Division Suite B 6481 Peachtree Industrial Boulevard Doraville, Georgia 30360 j CONTENTS Page Abs trac t •••••••••••••••••••••••••••••••••••••••••••••••••••••• ., . •. • • • . 1 Int roduc t ion.•...••.•...•.••....•...•.•............•.................. 1 Determination of flood-depth frequency relations •••••••••••••••••••••• 1 Regression analysis ••••••••••••••••••.•••••••••••••••••••••••••••• . 6 Accuracy and limitations.............................................. 10 Use of flood-depth frequency relations •••••••••••••••••••••••••••••••• 13 .:..... Ungaged s1tes..................................................... 13 Gaged sites....................................................... 13 Summary ••••••••••••••••••••••••••.•••••••••••..••••••••••••••••••••••• 19 References ••••••••••••••••••:.......................................... 20 ILLUSTRATIONS Page Figures la - ld. Maps showing: La , Location of gaging stations in northwest Georgia••••••••• 2 lb. Location of gaging stations in northeast Georgia••••••••• 3 Ie. Location of gaging stations in southwest Georgia •••••.•.. 4 ld. Location of gaging stations in southeast Georgia ••••••••• 5 2. Location of regional flood-depth frequency boundaries in Georgia•.••••••••••••••••••••••••••••••••••••. 9 3. Graph showing relation of lOO-year flood depth to drainage area in Regions l-5••••••••••••••••••••••••• ~ 11 iii -. ~ I"~, TECHNIQUES FOR ESTIMATING FLOOD-DEPTH FREQUENCY RELATIONS J ON NATURAL STREAMS IN GEORGIA By McGlone Price :J ABSTRACT ~ Regional relations are defined for estimating the depth of floods having :l recurrence intervals of 10, 50, and 100 years on streams with natural flow in Georgia. ~l Multiple-regression analysis of station data is used to define the rela­ tions between flood depths and frequency for streams draining from 1 to 1,000 .~ square miles, and for 10 climatological and physical basin characteristics. - J The analysis indicates that the drainage area of the basin is the most significant variable. Five regions having distinct flood-depth frequency characteristics are delineated. The developed relations, expressed as equations and graphs, are consid­ ered usable for any site in Georgia where the drainage area is between 1 and 1,000 square miles, and the. flow is natural; exceptions include streams that are urbanized, regulated, tide affected, channelized, or where manmade,struc­ tures significantly affect peak stages. INTRODUCTION When the U.S. Geological Survey began preparing maps of flood-prone areas, a need arose for a quick and easy method of determining flood depths for use in delineating approximate flood-prone areas. Regional flood-depth frequency relationships were developed for this purpose. The purpose of this report is to describe a technique for determining and using these relations for estima­ ting flood depths on most natural streams in Georgia. The flood-depth frequency relations developed herein will be of great value-in preparing flood-prone area maps in Georgia for floods having recur­ SJ rence intervals of '10, 50, and 100 years, and in answering local requests I~ concerning the depth of flooding. J DETERMINATION OF FLOOD-DEPTH FREQUENCY RELATION I, Streamflow and stage records for 217 gaging stations on areal streams I, draining basins frpm 1 to 1,000 square miles were analyzed to provide plan­ I I ners and designers with relations for estimating the depth of floods having , tt~ recurrence intervals of 10, 50, and 100 years on streams with natural "flow in I Georgia. (See figs. la-ld.) The results are valid for natural flow only, J and do not apply to streams that are urbani~ed, regulated, tide affected, channelized, or where other manmade structures significantly affect peak stage or discharge. -1- '] &l h 4 $) Q £4 J6 . ; 8S0 ·1~ 02384000 .-'..... , "~ ··., , . I:"".'. [ 33·--+t'----+----,=-,..,..---'r+--........",)L--'>-..~:jo..33° 8S0 84° o 10 20 30 40 SO MILES I !" I I I I I I EXPLANATION --- Regional boundary 02339000 J.r .. Gaging station and identification number ."" LOCATION OFMAPAREA FIGURE IA.-LOCATION OF GAGING STATIONS IN NORTHWEST GEORGIA.-, '--'- -2- ... <' Jr" I~ I~ I~ "L.. ~T.~ 1\ ~ -""'5. T'~ [ r- I'- l '-:.....;;.;...... r- .b.. rl...;."J-. '1"- !;;.. ";'; rill.I 84· 83· o 10 20 30 40 50 MILES I! II I I IIII .J,-f EXPLANATION ---Regional boundary -r- 02328000 @ LOCATION OF MAP AREA ,1.. • Gaging station and identification number -r- ~ FIGURE I C.-LOCATION OF GAGING STATIONS IN SOUTHWEST GEORGIA. ~ ''Illo f -4- -,i :- __L £ . £ 83° 82° , 33=-°rr=';~/~S:0~~~:s:-,"\:~\-i-33' 't- LOCATION OF MAP AREA 83' EXPLANATION ---Regional boundary I 022.2.6300 ... Gaging station and identification number I· Iu o 10 20 30 40 50 MILES I",,I I I I I I -'" I, i FIGURE I D.-LOCATION OF GAGING STATIONS IN SOUTHEAST GEORGIA. ~ ~ I ! -5- r-­ L~ Depths above the elevation of zero flow at gaging stations were computed for the 10-, 50-, and 100-year floods from elevation-discharge relations. The elevation of zero flow corresponds to the lowest point in the low-water '1 'TIl control, usually a riffle, just downstream from the gage or point of interest. ,c~ The'depths for selected flood frequencies were determined as follows: 1. Discharges were obtained for the 10-, 50-, and 100-year floods at 1: gaging stations using discharge-frequency data from the statewide flood-frequency study now in progress. Guidelines in Water Resources ' ~ " Council Bulletin 17 (1976) for determining flood-flow frequency are 1 being used in this study. ~ 2. The elevation of the 10-, 50-, and 100-year floods and "zero" flow were obtained from the defined elevation-discharge relations at I: gaging stations. ',:.. 3. The flood depth was computed as the difference between the elevation \ of the desired flood (10-, 50-, or 100-year flood) and the elevation ""'" of zero flow. fT- I Several gaging stations were deleted from the analysis because the I""", elevation-discharge relations for the higher frequency floods could not be defined adequately. 1'rw I i if~ Regression Analysis Since flood-depth information is collected at only a few of the many sites where this information is needed, gaging-station information must be transferred to ungaged sites. Regional analysis is a method for doing this. The regression method described by Riggs (1973) is a useful means of region­ alization as the flood depth for a given flood-frequency level can be related to physical and climatological basin characteristics. Th~~egression model used is of the form [ 'Dn = a Ab B c Cd where Dn = flood depth above bottom of channel having a n-year recurrence interval. A, B, C = physical and climatological characteristics of drainage basin. a, b, c, d = constants and coefficients