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1994

Flood Insurance Study, City of South Jordan, Utah, Salt Lake Flood Insurance Study, City of South Jordan, Utah, Salt Lake

County County

Federal Emergency Management Agency

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Recommended Citation Recommended Citation Federal Emergency Management Agency, "Flood Insurance Study, City of South Jordan, Utah, Salt Lake County" (1994). All U.S. Government Documents (Utah Regional Depository). Paper 201. https://digitalcommons.usu.edu/govdocs/201

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FLOOD INSURANC STUDY

CITY OF SOUTH JORDAN, UTAH ,SALT LAKE COUNTY

REVISED : SEPTEMBER 30.1994

Federal Emergency Management Agency COMMUNITY NUMBER · 490107

IIOTIC! 10 VLOOD IBSUlABCB STUDY USBRS

Co~iti •• partlclpatinl in the If.tiona1 Plood In.urane. Proar .. have e.t.blbbed repo.itorie. of flood hazard data for floodplain JUnaaeMDt and flood in.urane. purpo.... !hh Plood In.urane. Study _y not contain aU data available within the repolitory. It i •• elvil.bt. to contact the co.tuDity repolitory for &oy additional data.

Part or .U of thi. PLood In.uranel Study .. ,. be reviled and republi.hed at aoy ti.. ,In addition, part of tbi. Flood la.urane. Study .. y be reviled by tbe Letter of Map aevilioD proc ••• , ¥bieb doe. not involve republication or rediltribution of tbe PLood In.urane. Study . It ia, tberefore, tbe re.ponlibility of tbe uaer to conault with cO.r\UDity officiala aad to cbeck tbe c.~ity repoaitory to obtain the moat current 'lood Inauranc. Study caponenu.

Tbi. publication incorporate a reviaiona to tbe ori,inal 'lood In.tlraDce Study. Tb.ae reviaiona are pre.ented in Section 9.0 .

Thic preUainary reviaed 'lood In.uraace Study containa only profilea added or revhed aa part of tbe renudy. All profilea will be included in the final publiabed report.

r. '~ //1. / Ii",·/-

TABLE or CO!!'U!!TI

1.0 ImoDVCIIOM

1.1 Purpo •• of Stud,. t.2 Authority and AckDovled ... nu 1 . 3 Coordination ••••••••

2.0 AlIA SDIDIED

2.1 Scope of Btudy 2.2 COCDUDity De.cription 2.3 Principal 'load Probl._ 2.4 Plood Protection "ea,urea

3.0 QCIRRIMC I!Bl!!OPS

3.1 Hydrololic Analy ••• 3.2 Hydraulic Analy •••

4.0 PLQop P!.\I' IWMCIIIIRT APPLICATIO!S

4.1 Flood IoUDclari •• 4.2 Pl"oct_,..

s. C IlSl/I6IICl AlPLICAIIO!

5.1 .each Det.rwin.tion. S.2 Flood a.&ard 'actor. (PHP,) 5.3 .10od In.uunce Zone. 5.4 Plood Io.urance ht. Map De.cription

Pale

2 4 6 6

7 8

10

10 11

14

14 is 1S 16

6.0 rnA ID1DUS ••••••••••• • •••••••••••• 16

7.0 LQCAUO! or DATA . . . . . . . . . . . . . . . . . . . . . . 17

8 . 0 8I1LIOCIAPIX A!!!l urlll!!C!I .•.••...••. • .• • .. 17

9. 0 1E'fI1I0! DIIClInIOIS 26

9. 1 'int levhion 26

TABLE 9. cotrmITS (Cont'd)

Pilure Pigure

- Vicinity Map - 'loadw., Scheaatic

Table 1 - SWIID4ry of Discharg •• T.ble 2 - Ploodway Oeta Table 3 - Jordan liver Proposed De,iln Di.charlel

Ezhibit 1 - Plood Profile.

Dry Creek Willow Creek Jordan River

PUBLISHED IBPAIATILY'

Flood Insurance late Map Indes Flood Insurance late Map

i i

Panels OIP-OJP Panels 04P-05P Panels 06P-07P

Page

3 14

9 12 18

. I

1.0 IR'fIOJOC'rI(II

1 . 1 Purpo .. of Study

'!bt. Flood Inlurance Study inv •• tigate. the exiatence and aeverity of flCXJd haaard. in th. City of South Jordan, Salt r..k. County, tJtab, and ala in tba IldainiaUation of the National Flood Insurance Act of 196. and the Flood Di ... ter Protection Act of 1913. '1'hh Itudy wl11 be UHd to oon .. rt South Jor dan to the regular prograa of flood inaurance by the Pederal _'ganey Managuent Agency. LocaIl and regional planner. wl1l u .. thi. study in their efforte to pr~ eound flood plain __ g_nt.

In eo.e atate. OE ~nltl •• , flood plain .ana~nt crlteria or regulaU0n8 _y I.lat that are ~1'. r •• trictive or ecaprehenllve than tboM em which tile .. federally lupported .tueU •• are baaed. '!be .. criteria ute preee4ence ewer the .lnt.. Pederal criterla for purpoal of legulatlng ctt".los-nt 1n the flood plAlln, •• Nt forth in the c::ode of ,..,81 Ragulationtl at U CPR, 60.3. In IIucb ca ... , howe .. " it -.11 be underltc:lo4 that the State (01' other juriadlctional agency) ahall be able to explaln the .. requlr~ta and criteria.

'l'he 8OU1'ce of authority for thi. Plood Inaurance Study i. the Rational Flood Inaurance Act of 1968, a. _nded. 'lb. bydrologic and hydraulic analYH. for thia .tudy ver. perfor-.d by RDUina, Brown and Gunnell, Inc., for th. Pederal _rg.nc:y lIaM~t Agency, under Contract Ro. &-"593. 'lbi. work, which wa. COIIIPlete4 in lII.y 1982, C09.red aU .ignificant flooding aources affecting South Jordan.

1.3 CoordinaUon

8tre_ de.ignated for detailed and approxiaat. study were identified at a .. Ung in Sept __ r 1977 attended by repre.entative. of the I tucty oontractor, the Pederal ... rgency llana~nt Agency, kIt r..te County, and the City of South Jordan. ...ulte of the hydrologic and hydrauUc analyae. wre coordinated with repr •• enta­U ... of the S.lt r..te County Public WOrk. Depart:.ent, Plood Control and "tel' Quality Di.i.ion, the 0.8. ArIlY C»rpe of lIngi,,"r., anLt the 1ncorpcxated ~nit1e. of kIt Lake County.

An inter-.diat. ~uni ty coordination ... ting was held on February 18, 1982, to allow ~nity repre.entaUve. to review the draft .tudy. Repre.entative. of the Pederal Bllergency Manage .. nt Agency, the .tudy contractor, the U.S. ArllY Corps of Engineer., Salt Lake County, and the CiU •• of Sandy City, Riv.rton, Bluffdale, Draper • .... t Jordan, and South Jordan attended the Meting. Representatives trOW! sever al of the ~niUe. west of the Jordan River expressed concern that only approxiJlate atudies had been perforJlied on the .phe_ral atre_ that drain the Oquirrh Mountain.. It was explained that this .a. done because of the li_ited developaent on that side of the valley.

A final ~unity coordination Meting for Salt Lake County and the CiUe. of Riverton and South Jordan .as held on Deceaber It, 1983. In attendance were repre.entativ.s of the Pederal Ellergency Manag_nt Agency, the study contractor, the county, al'd the incorporated ~nit1es. 'J'Wo .. jar concerns raised at the Meting vere that the studies did not reflect flows frc. the 1983 flood, and the conversion of the detailed study r.aches of the Jordan Riv.r between 2100 South Street and the North Jordan Canal Diversion Daa to approx1aate study. It .a. agr.ed that these probl •• would be addreuec1 during the appeal. period along with other aincr concerns raiNd by the individual co.aunities and the rounty. All requesta were considered and, where appropriate, were acted upon in the preparation of this study.

2. 0 _ STIlDIBD

2.1 Scope of Study

'l'tlia Plood Insurance Study cov.rs the incorporated areas of the City of SOuth Jordan, Salt Lake County, Utah . The area of study ie ehown on the Vicinity Map (Figure I).

'l'tle Jordan Riv.r and Dry and .. illow Creeks were studied in detan for their entire length within the ~unity.

'1'he cJetalled study reach of the Jordan Riv.r within South Jordan wa. converted to approxillllte study. 'l'tlia change r.sulted froa unc.rtainti.a in frequency analysis of the hydrologic data and frOli uncertaintiea in hydraulic .adeling caused by COIIpleted and ongoing .o4it1cationa to the river channel initiated atter the oc.pletion date ot thi •• tudy. In addition, downstre .. of the WOrth Jordan Canal Diveraion 0.., proble. were encountered with elevation data on the orthophoto topographic .. pe used for the detailed flood boundary delineationa, th.re were alllo di.crepanci.s between the re.ult. of the step-backwater analyaie and the detailed flood boundary delineation. . Down.tre .. of the diveraion du, approxillate flood boundar ies vere taken fro. the Flood Basard Boundary Map ( .. ferenee 1) . Up.tre .. of the diversion duI, approxi­.. te flood boundaries were adopted fro. the atudy contractor'. detailed 100-year flood boundary delineations .

, .---.. ' ,

.-

I ,.' oJ' --.. .. ...' -,- , ----

fl"111

thOle area •• tudied by detailed methods were chosen with considera­tion ,iven to all propoaed construction and forec.,ted development tbrou&h 1987.

Mid .. and Bingham. Creek. were studied by approximate methods . Preliminat'y hydrologic and hydraulic analyses for these !Creams revealed tbat tbe approzimate 100-year flood boundaries shown on tbe Plood aazard Boundary Hap (aeference 1) were accunte; tberefore , the Flood Hazard Boundary Hap was cho.en .s the source of .pprozimate flood boundari .. for these stream ••

Approai .. te .naly.e. were u.ed to .tudy tho.e are., having a low develo~nt potential or minimal flood hazards. The scope and _tbods of study were propo.ed to and a,reed upon by the Federal !Mr,ency KaDa,_nt Agency and tbe City of South Jordan.

2.2 C~it,. De.eription

Soutb Jordan i. located alon, the west bank of the Jordan River in .outbwe.tern. Salt Lake County, in north-central Utah. The city has an .ver.le elevation of 4,SOO feet and i. surrounded by .everal distinct terrain feature.. To tbe i_di.t. west are the Oquirrh Mountains, wo.e pe.k. ri.e to 10,000 feet. Twenty-five mile. to tbe nortb is tbe Great Salt Lake. To tbe e.st, .pproxilDately 15 _il •• aerO .. tbe v.lley floor, the W •• atch Mountains ri.e to beiahts of 11,000 feet. Finally, Ut .. h Lake is located to the .outh in nearby Utab Count,.. Tbis lake i. tbe source of the Jordan River aDd ..,tie. into tbe Gr •• t Salt Lake.

Soutb Jordan i. ~rd.r.d by the City of West Jordan on the north, tbe Cities of Sandy City and Drap.r on tbe easc, the City of liverton on tbe soutb, .nd unincorporated areas of Salt Lake County on tbe 'Outb and west. Soutb Jordan cover. an area of approai .. tely 26.0 .quare _ile., 16.0 square miles of which are u.ed for alriculture (.-o.tly in the we.tern portion of the city). Anotber 9.4 .quare .ile. are u.ed for re.idential area.. The r ... inin. are. i. u.ed for cOCllllN!rcial purpo.es.

Ia the Salt Lake V.lley, the Jordan River flood plains .re largely undeveloped . They do, however, cont.in some •• ricultural develop­.. ntt and a fev residence • • Recently, residential, indu.trial, and c~rci.l developeent h ••• hifted from the den.ely developed areas near Salt Lake City tovard the le .. er developed are.s of the • outhern and ve.t.rn portion. of the valley.

The Jor dan River is the .. jor vat.rway in Salt Lake County and the pr incipal .ource of vater for South Jordan. PrOli it. oriain at Utah t.ke, the Jordan liver flov. 55 river mil.s northward to the ereat Salt Lake . The Jordan River .r.dient i. approximately 5.2 fee t per .il.. There ar. no .. jor tdbut.rie. to the Jord. n River i a South Jord", bowever, a •• ries of diveraioa. and irri.ation canale act to deplete the river voluate durin. the s~r. South Jordan it loc.ted n.ar the ar.a wh.r. tbe Jord.n River belin. to

4

flow .lIOothly. This point coincide. with a gradual deterioration of river quality a. it proce.d. downstream.

The County ... terplan use. the canals to carry .torm runoff to the natural cb.nnels. The eace .. from the canal would be discharged to the natural channel. Hany improvements to the canals and the cbannele are required before this system can fully function.

Dry and Willow Creek. are intermittent stream. that drain the .outhea.tern part of the valley. These stream. have fairly steep gradient. a. they era .. the terraces, but become quite flat as they reach the valley floor.

Two intermittent .tre .... originate from the Oquirrh Mountains and traverse the terrace. between tb. mountain. and the valley floor. Binlb .. Creek cuts tbroulh the northwe.tern COrner of the city, and Hida. Creek nearly p.r.llels the .outbern corporate limits. These .tre ... u.ually flow duri:al .no .... lt and storm runoff. Irri.ation company policy allow. storm draiaa,e from new subdivisions to be cbannel.d into the canal .y.t.... Con.equently, durinl periods of beavy runoff, tb. intermittent .tre .... will carry the v~lume that tb. canal .y.t ... are incapable of hendling. This prOcess ha. been adopted by Salt Lake County a. a flood-control .... ur ••

South Jordan h ••• n.twork of five major canale or ditche. flowing i n tbe .outh-nortb direction. This aetwork con.i.ts of Provo R •• ervoir C.nal, Utah Lake Distributin& C.nal, Ut.b and Salt Lake C.n.l, Soutb Jordan Can.l, and Beck.tead Ditch. Th •• e canals and ditcbe. divert water directly frota the Jord.n Riv.r ead .ad at various point. in Salt Lak. County. Tbi. w.ter i. uled to fulfill w.ter rilbt. and alricultural needs. A. IIIOre agricultural land in the valle,. i. developed into urban l.nd, len water vill ne.d to be diverted fro. tb. river for farming.

South Jordan i •• n area of mo.tly confined and shallow unconfined .quifer.. Ground water occurs in the uncon.olid.ted depo.its of the Salt Lak. Valle,. under natural w.ter table and .rtesian condition.. In the lDOuntain area., so .. Iround vat.r seep. into str ... channels .nd flow. to t t. .!. Jordan River, and the remaining ground water move. throulh op.ning. in the b.drock, ev.ntuaLly re.ching the Jordan liver. • •

Soils typically found in the terrace. are granular, while the vall.,. floor i. priIMrily compo.ed of cl.y. or clayey gravels •

V ••• tation r.nle, from conifer, a'pen, and oak. in the hilher .-ountaia elevation. to .crub oak t lale t .nd underbru.h in t he lower .-ountain elevation.. Re.idential valley area. are v •• etated lUinly with lawn .r ••• e., Orn ..... nt.l Ihrubbery , and shade tree •• Undevelop.d valley are.s .re atO.tly cov.r.d by Ir ... e •• nd •••• bru.h. A.pen and cottonwood tree. grov alonl the .tream cour ••••

South Jordan ba •• t..,erate, s .. i.rid climate wi th four distin­,uisbable •••• on.. T .. p.rature. lenerally ranle from 10·' in the

/1

winter to 102°p in the l!Iun.er. Precipitation tends to vary directly with elevation, fro. 16 inches annually on the valley floor t o 40 inchea annually in the high lIIOuntains (Reference 2).

2.3 Principal Plood Problea

Plooding in the Salt Lake Valley generally occurs due to three typea of eventa, anow.elt runoff, cloudburst rainstorms. and general rainator_. S~lt flooda usually occur in April. May. and June. Cloudburet rainstor. are high-intensity, short-duration storms that uaually occur over a relatively aaall area. Theae storms are cbuacterhed by high runoff peaka, but low volWDe8. They generally occur fro. June through October. General rainator ... are caused by low-intenaity, rainfall occurring over a longer period of time . Theae atoru can have a higher peak than the 8nowwtelt flood and a higher volu. than the cloudburat events. General rainstorms can OCCUr a t any tiJle. The history of Salt Lake County indicates that flooding can occur fro. any of these events. However, the most dr_tic and extenaive flooding baa been due to anotnlelt and cloud­bur at flooda.

Significant s~lt flowa occurred in the area in 1909, 1912, 1921, 1949, 1952, 1953, and: 1975. In the 1921 flood, the Jordan River had a ..an daily flow of 1,020 cubic feet per second (cfs) at the Jordan Marrowa O.S. Geological Survey atre .. gage (No . 10167000), with an eatt.ated return interval of 20 yeara. The .,.t notable flood on record in the Salt Lake Valley occurred during April and May 1952. Thia flood waa cauaed by the rapid .. ltin~ of an unuau.lly l.rge anowpack 01"1 the W-!la.tch Mountains . The_an daily flow for thia flood waa 1,410 cfa, with an eatt.ated return inter.al of SO yeara, and was alao recorded at the Jordan Narrows atre .. gage.

2.4 Plood Protection Meaaurea

Otah r..ke, at the head of the Jordan River, afforda a reduction of floodflowe along the Jordan River above 2100 Street South. This lake h • natural water body that has been artificially -=>4ified .a that the water-aurface elevation can be controlled through the u .. of .. veral large radial gates and. a puaping atation. The ability to rai .. and lower the lake elevation caused conflicts between the .ater u.s.re and the property owners adjac.nt to the lake. To reeolye the conflicts, a -cc.proai •• level,- on elevation of 4,489.34 feet, wa. agr.ed on in 1885. Whenev.r runoff forecaats indi cate that the •• tar aurface .Ul exceed the co.pro.ise level, the lake 18 drawn down to per.it diecharg •• co.parable to natural Conditions .

A nu.ber of irri9ation diverdona alon9 tha Jordan River near the south.r", boundary of Salt Lake County, .uch a. Turner DaJI at Jordan .. rrowe, can eub.tantially reduce floodflowa. Mo.t outflow fro. Otah X.k., ezcept &lri"9 perioda of high flow, can be diverted to th ... canolle .

6

Several roadway and railroad fill. on Dry and Willow Creeks afford U.Ilited detention atorage and reduced down.tre_ discharges a. conduit capaciti •• are exceeded.

Officials of salt Lake County have estabUahed a Plood Control and Water Quality Diviaion in their Public Works OepartJlent. It is the r.eponaibility of thi. office to ..,.age and enforce develo~nt and flood-control ordinance. in the unincorporated areas of the county. 'lb. 4epartMnt alao works with the incorporated ~nties within th'.1 county, a. requ.eted, to .. nage and review flood-control projects. Salt r..ke County alao baa a countywide flood-eontrol tax that enable. it to obtain fund. for use in construction of new flood control project. and .. intenanee of exiating facilitiea.

3.0 IIIIGINBllRIHG JIIITIIalS

Por the flooding source. atudied in detail in the ~nity, atandard hydrologic and hydraulic atudy _tbOCSS were used to deter.ioe the flood haaard data required for thi. study. Plood events of a _9"itude which ar. expected to be equalled. or exceeded .!!!5!. on the avera9. during any 10-, 50-, 100-, or 500-year period (recurrence interval) have been selected a. having epeeial .ignificance for flood plain .. nage .. nt and for flood inaurance pre.iUII rate.. 'l'he.e event., ~ly terMcS the 10-, 50-, 100-, and 500-y.ar flood., bay. a 10, 2, 1, and 0.2 percent chance, r .. poct1va1y, of being equalled or e.-..s during any year. Although the r.currence interval r.pr •• enta the long ter. averase period between flooda of • specific ugnitude. rcre flooda could occur at abort int.rvale or even within the ... year. '!'be r18k of experiencing a rare flood incr •••••• en period. 9r.at.r than 1 year ate con.idered. Por eXUlPl., the riak of baving a flood which equals or exceecSa the 100-year flood (1 percent diance of annual occurrence) in any 50-year period ia approxi­ately 40 percent (4 in 10), and, for any 90-year period, the ri.k in­cr.aae. to approxiaat.ly 60 percent (6 in 10). '!'he analyses reported h.re r.flect flooding pot.ntiala baaed on conditions exiating in the ~uni ty at the tiM of oc.pletion of thi. atudy. Mape and flood eleva­tiona .ill be .. oded periodically to refl.ct futUre changee •

3.1 Bydrologic Analy ...

Bydrologic analye.a were carr ied out to eatabUah the peak diacharge­frequency relat10nahipe for flood. of the .elected recurr.nce intervals for each flc:oding source etudied in detail affecting the ~nity.

Several etre .. gage. have been operated by the City of salt r..ke City and the O.S. Geological Survey on count}" .tr .... dnc. the begiMlr'9 of the century (Refer.nce. 3 and 4). 'J'b. O.S. Geological Survey baa operated .tre_ 9ag. Ro. 10167000 at Jordan Marrawa dnce 1913 and alao ran a .tre .. gage at 9400 South Street (Mo. 10167200) frOli 1965 to 1968.

Bxisting atreaallow information is not adequate to predict cloudburst runoff values downstream of the canyon mouths, vhere flows depend on inflow tra. the urban area. To obtain flow values for Dry and Willow Creeks, the u.s. Army Corps of Engineers HEC-l computer runoff .ade l vas used (Reference S). This model uses a kinema tic vave calculation to produce runoff due to rainfall . The model ~tes and routes flows based on physical characteristics of the ba.in (such as percentage of imperviousness, infiltration rates , basin area, and slope) and storm characteristics (such as precipitation depths and rainfall distribution and duration). Rainfall depths were obtained frc. Precipitation Frequency Atlas of the western United States, Volume VI, prepared by the National Oceanic and At.ospheric Aa.inistration (Reference 6). Because of the lack of available rainfall-runoff data, it was not possible to calibrate the oo.puter model.

Peak d1echarge-drainage area relationships for each stream studied in detail are shown in Table 1.

3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of the flooding sources studied 1n the oo..unity vere carried out to provide estt.8tes of the elevations of floods of the selected recurrence intervals along each of these flooding sources.

water-surface elevations of floods of the selected recurrence intervals for the detailed studied strea.. vere oo.puted using the O.S. Ar8y Corps of Engineers BEC-2 step-backvater ~ter prograa (Reference 7).

Cros. section data for Dry and Willow Creeks were developed by the O.S. At., Corpe of Engineer. for the 1974 Flood Plain Infor .. tion report (Reference 8). Cros. sections vere taken fra. topographic asps at a scale of It600, vith a contour interval of 4 feet (Reference 9), suppl ... nted bf additional survey data provided bf the county. SUpple .. ntal cro .. section. to define new bridges or chang.s in topography vere -.de as a part of this Plood In.urance Study. All bridg •• , da .. , and culverts vere field checked to obtain infor .. tion to de.cribe their structural 9eo~try.

Location. of sel.cted cro .. section. u.ed in the hydraulic analyses are 8hown on the Flood Profiles (Exhibit l). POr strea. s~nt8 foe which. floodway i. ~ted (Section 4.2), .elected cross ..etion location. are also ahown on the Plood Boundary and Floodway Map (Bxblblt 2).

Channel roughnes8 factor. (Manning's -n-) used in the hydraulic oo.putation. vere cho.en by engineering jud~ent and ba.ed on field obeerv.tion. of the .tr .... and flood plain area.. Roughness values ranged fra. 0. 030 to 0.040 for .. in channel. and fra. 0. 040 to 0.060 for overbank ar ••••

B

!y

~ \

Table 1. Summary of Discharges

Ploodina Source and Location Drainage Area

(SQuare miles)

Dry Creek. At 700 Eaat Street (upatream of South Jordan)

At 300 West Street

Willow Creek At 12300 South Street (weat of Interltate Highway 1S, uPltream of South Jordan)

Jordan liver Marrovs 9000 Soutb Street saoo South Street Lit t!.e Cottonwood Creek Confluence Iii Cottonwood Creek Confluence Mill Creek Confluence 2100 Soutb Street

1Dilcbarle Qedu~tion. are due to Overbank Storase and/or Loaael to Canal a and Irrigation Syatema

2o.ta Mot Available

13 14

17

2,1S5 2,905 2,985 __ 2

__ 2

__ 2

3,1653

(generally,

Peak Dischargea (cubic feet per second) 10-Year SO-Year 100-Year SOO-Year

lSI no1 2761 9221

1,260 2,400 3,000 4,800 1,170 2,230 2,790 4,465 1,200 2,280 2,850 4,560 1,585 3,010 3,740 5,925 1,930 3,665 4,535 7,145 2,000 3,800 4,700 7,400 2,000 3,800 4,700 7,400

a result of construction 1n the floodplain)

lvalue Eatimated Baaed on Publiabed Draina.e Area for Caae at 1100 South Street

Stllrting vater-aurface elevations for all atreaas were determined by nor_I depth e.lculati~a.

Plood profiles were drawn showing c:::c:.p.lted water-surface elevations to an accuracy of 0.5 foot for floods of the selected recurrence iDterval. (B:dIibit 1).

fte hydraulic analyses for thi. study were based on unobstructed flow. It ahould be noted that flood elevations shown on the profiles are ocnsidere4 valid only if hydraulic .tructures reuin unobstructed, operate properly, and 60 not fail.

Approxiaate flood depth. for the Jordan River, upstre .. of the IIOrth Jordan canal Diversion Daa, were deterained using the O.S. Array COrps of Engineer. BBC-2 step-backwater COIIpUter prograJI (Referenee 7) .

All el.vationa are r.f.renced to the National Geodetic V.rtical D1ta of 1'2' (lCVD). nevation refer.nce .. rks uaed in the study are shown on the .. pe.

4.0 rLOOD PLAIR _ APPLICMIOIIB

'!'he Rational Ploodi Inauranoe Progr .. encourag.s Stat. and local goverMlenta to adopt .ound flood plain aanag ... nt progra.. 'l'tler.fore, each Plood Inaurance Study include. a flood boundary up designed to .. stat ~ni­tie. in developing 80Und flood plain aanag ... nt .. aaures.

4.1 Plood Boundarie.

In order to provide a national standard vithout regional d1acri.ina­tion, th. lOa-year flood has been adopted by the Ped.ral Eaergency Mana~nt Aqency a. the ba •• flood for purpoa •• of flood plain Mnag_nt .... ur... 'l'tle SaO-year flood is etlPloyed to indicate a&Utional area. of flood ri.k in the oo.aunity. Pol' each atrea • • tudied in detail, the boundar i •• of th. 100- and 500-y.ar floods have been delineated u.ing the flood .levation. deter.ioed at each cro .. section, tt.bteen cro .. aection., the toundari •• vere int.r­polated u.ing topographic ups at SCIIl •• of 1 124,000 and 112,400, with a contour int.rval of 5 feet (Ref.renc •• 10 and 11).

Approxiaat. flood boundaries for the Jordan River, uPlltr ... of the IIOrtb Jordan Canal Di"'.raion DaJI , weI'. d.lin •• ted udng the 1 ~ 24,000 SCIIl. topogr.phic .. ps diacu •• ed pr • .,.iou.ly (Referenoe 10) .

Approxiat. flood boundar i •• in ~ portion. of the .tudy a rea wre tIIt.n fro. the Plood liliAI'd Boundary ... p ,lIef.rence 1) .

Plood boundar i •• foe the 100- And 500-y .. r flood. are shown on the .lood Boundary and Pl.oodway ... p (bhibit 2). In ca ••• where the 100- and 500-year flood boundaries ar. l,.. l OH tog.th.r, only the

10

4.2

100-year flood boundary haa been abown. s.all area. within the flood boundaries _y lie above the flood .l.vationa and, th.re­for., not be .ubject to flooding, owing to Iblitation. of the _p sca1., auch ar.aa ar. not shown.

Ploodw.y.

Bncroacm-nt an flood plain., aucb a. artificial fill, reducea the flood-carrying capacity, incr ••••• the flood heights of strea., and incr ••••• flood baarda in ar.aa tt.y0n4 the .ncroacm.ent itaelf. One a.pect of flood plain UM9_nt Involv •• balancing the econo.io gain fro. flood plain develos-ent againat the re.ulting increase in flood haaard. Por purpoaea of the Rational Plood In.urance PeogrD, th. concept of a flooc!way is u.ed aa a tool to a •• ist local ~nitie. in thia aapeot of flood plain aanag ... nt. Onder this concept, the ar.a of the 100-y.ar flood ia divided into a floodway and a floodway fr inge. 'l'tle floodvay is the Ch.M.l of a att ... plus any adjacent flood plain ar.aa that .... t be k.pt fr.e of .ncroachMnt 1n order th.t the 100-y.ar flood _y be carried without aubatantial incr ••••• in flood height.. Kinbl_ standards of the Pederal _rgency Manag_nt Ag.ncy lia1t .uch incr .. s.s In flood beight. to 1.0 foot, provIded th.t hasar60us v.locitiea ar. not produced. '1'be floodvay. in this r.port are preaented to local agencie ••• ainiaua .tand.rd. that can be adopted or that can be used a. a baai. for additional .tudi •••

All tloodw.ya orlIIPUted aa a part of this .tudy were deter.ioed on the baat. of equal-conveyance reduction fra. .ach aide of the flood plain. 1'he r •• ulta of th ... cc.putation. wer. tabul.ted at Hl.cted cro .. Motions for each .tr ... aegMnt for which a fl.oodway vas c:c.pute4 (Table 2).

As shown on the Plood Boundary and Ploodway Map (BlEhibit 2), the floodway width. were det.r.ined at cro .. sectiona, between ero •• aection., the boundar i •• were int.rpolated. In caa •• wh.r. the boundaries of the floodway and the lOa-year flood are either cloae tog.ther or collinear, only the f100dway boundary hal been shown .

'l'be ar .. tt.breen the floodway and the boundary of the laO-year flood is t.raed the floodway fring.. 'l'he floodvay fringe thua enoc:.pa .... the portion of the flood pl.in that cou14 'be cc.pletely ob.tructed without increaaing the wat.r-surfac. elevation of the lOO-year flood .,re than 1.0 foot .t any point. Typical reletion­abipai tt.twHn the floodw.y and the floodvay fr i nge and their signif­lcance to flood plain dev.lo~nt are shown in Pigure 2.

11

17

FLOODING SOURCE F!.OOOWAY BASE FLOOD

WATER SURFACE ELEVATION

DIST....d-SECTION KEAII r I WITHOUT J WITH I

CROSS SECTION WIDTH AREA VELOCITY REGULATORY FLOODWAY FLCX)OWAY INCREASE (FEET) (~ (FEET p~

SE<'ONO (FEET NGVD)

Dry Creek A 5,325 48 151 2.8 4,340.6 4,340 . 6 4.341.3 0.7 8 5,830 35 126 3.3 4,3U.6 4,344 . 6 4,344.8 0.2 C 6,290 60 166 2.5 4,346.2 4,346.2 4,346.7 0.5 0 6,700 36 91 4.6 4,346.7 4,346.7 4,347.5 0.8 B 7,330 36 96 4.4 4,351.4 4,351 . 4 4,352.2 0.8 F 7,818 160 939 0.4 4,358.9 4,358.9 4,359.8 0. 9 G 7,920 57 256 1.6 4.358.9 4,358.9 4.359 .8 0. 9 B 8,760 92 201 2.1 4,360.5 4,360.5 4,361.2 0. 7 I 10,130 38 107 3.9 4,369.3 4,369.3 4,370 . 1 0.8

Willow Creek A 1,000 16 35 7. 8 4,317.9 4,317.9 4,318.2 0.3 8 2,260 5 26 10.7 4.339.1 4,339.1 4,340.1 1.0 C 2,560 30 67 4.1 4.344.4 4,344.4 4,345.2 0.8 0 3,360 60 190 1.5 4,351.3 4,351. 3 4.352.2 0.9

1 Peet Above Mouth

... ,. FEDERAL EMERGENCY MANAGEMENT AGENCY FLOOOWAY DATA - CITY OF SOUTH JORDAN. UT ... ... ISALT LAKE CO.) N 1;2...

DRY CREEK·WILLOW CREEK

FLOODING SOURCE FLOOOWAY BASE FLOOD WATER SURFACE ELEVATION

Krnoo .... IIlGUlA I QIIY I WITHOUT

I M" I IfrK!UAY (M)5S WOfON OISTAI<K!' Wl01H .... VU OC/TV HOOOWA' HOOOWAY

(fEET) ''''''''' IflET PlII

"'" SlCOHO) (fEEl "(iVO)

Jordan Ri ver A 67,856 79 569 5.3 4,303.0 4 , 303.0 4,303.0 0.0 B 68,516 68 447 6.7 4,303.4 4,303.4 4,303.6 0.2 C 69,226 83 785 3.8 4,304.1 4 , 304.1 4 , 304.5 0 . 4 D 70,426 76 564 5.3 4,304 .8 4,304.8 4 , 305.1 0.3 E 70,726 89 533 5.6 4,305.1 4,30).1 4,305.4 0.3 p 71 ,616 362 926 3.2 4,306.5 4,306.5 4,306.7 0.2 C 73,086 310 994 3.0 4,308 . 4 4 , 308.4 4,309.4 1.0 H 74,396 367 1, 272 2. 4 4,310.6 4,310.6 4,311 . 5 0.9 I 74,926 317 1,266 2.4 4 , 310.9 4,310.9 4,311.8 0.9 J 75,706 92 736 4.1 4,311.2 4,311 . 2 4,312.1 0.9 ~ 16,066 74 625 4.8 4,311.5 4 , 311.5 4,312.3 0.8 L 77 ,342 96 537 5.6 4,313.3 4,313 . 3 4,313.9 0.6

" 77,632 144 1 , 017 3.0 4 , 313.9 4,313.9 4,314.5 0.6

• 78,542 108 517 5.8 4, 314 .8 4,314.8 4,315.3 0.5 0 79,652 104 718 4.2 4 , 316. 4 4 , 316 . 4 4,317 . 1 0.7 p 80,902 105 763 3. 9 4 , 317 . 5 4,317 . 5 4 , 318 . 4 0. 9 Q 82,032 128 913 3. 3 4,318 . 5 4,318.5 4,319.5 1.0 a 82,502 86 654 4.6 4,319.1 4 , 319.1 4,320 . 0 0.9 S 82,892 87 559 5.4 4,320 . 0 4 , 320 . 0 4,320.7 0.7 T 83,957 88 527 5.7 4, 321 . 7 4,321.7 4,322.3 0 .6 u 84,777 67 536 5.6 4,322.5 4,322 . 5 4 , 323.2 0.7

Ipeet Above Surplus Canal Diver. i on

T FEDERAL EMERGENCY MANAGEMENT AGENCY A FLOODWAY DATA • l CITY OF SOUTH JORDAN, UT E , (SALT LAKE CO.) JORDAN RiVeR

13

fl ... -------- tOO,Y EAR F LO OD PLAIN --------....,,1

LINE "'8" THE FLOOD ELEV ATION BE FOR I! ENCROACHMENT. LINE CD IS THE FLOOD ELEVATION AFTEA ENCROACHMENT. .SU~HAAGE IS NOT TO E X CEED 1.0 FOOT 'FEM ... AEDUIAEMENTI OR L.ESSEA A MOUNT If ' ,"l e .FIED BV STA TE .

I'igure 2. Ploodway Scb_tlc

5 . 0 xaUM*Z APPLICM'ICB

In «del' to •• tabl1* actuarial iMUrance rat •• , the Pedel'al _rgency lIane9~t Aqency hae ct.v.loped • proce .. to tranaforll the data fro. the 4Ift91neering atudy into flood inauranoe criteria. '!'hi. proce •• includ •• the 4eteraination of reach •• , Flood HaUird Pactor., and flood insurance :10M & .. lgnationa to!: eacb flClOding IlQUrc;:e atudied in detail affecting Sooth Jordan, UUb.

... eb •• are cSefl"!1'd .. length. of watercour ••• having relatively the __ flood baArd , baaed on the a.erage weighted difference in water-llUrface ele.ationa between the 10- and lOO-y •• r floods. '!'hi. difference cIoit. not have • variation greater than ~t indicated in the following table for .,re than 2:0 percent of the re.ch I

A.erage Difference Between 10- end lOO-Y .. r rloo4.

Le .. than 2: f .. t 2: to 7 f .. t 7.1 to 12 f .. t lIOre than 12 feet

14

0.5 foot 1.0 foot 2:.0 f .. t 3.0 f .. t

_'0

5.2 P100d a..erd P.cton (PHP.)

5.3

The PIlI' h tbe reelera1 a..r.eacy MeDa .... nt Aaency device u.ed to correlate flood inforaation 'lith in.urane. nte table •• Corr.lation. bet .... n property cl .... e frCHI flood. and their PHP are u.ed to .et actuarial inlurane. preaium rate t.ble. based on PBP. fr .. 005 to 200.

The PIIP for a r .. ch i. tbe av.ra.e wei,btld difference between the 10- ead 100-year flooel vater-Iurface e l • .,ation •• aprelled to tbe roea .... t one-balf foot, and ,boWD a. a three-digit code. Por ....,11, if the differece bet .... n vater-Iurface elevationl of the 10- eael 100-year floodl h 0 . 7 foot, tbe PHP il 005; if the difference it 1.4 feet, tbe PHP it 015; if the differenc:! i . 5 . 0 feet, tbe FRP i. 050. When the difference between the 10- and 100-year vater- .urflce elevation. it ,reater than 10.0 feet accuracy for the PHP i. to tbe n.are.t foot. '

.ut~r tbe detemination of reache. and their ra.pectiva PHP., the entue incorporated area of tbe City of South Jordan va. divided into zone., eacb havin, a lpacific flood potential or bazard. lach zone val •• liped ODe of the foUovin, flood in.urance aone de.ipation.,

Zone Al

Zone. A.3 and AS I

Zone 8 1

Special Plood aa.ard Areal inunelated by tbe 100-,..ar flood, detemined by approaiute _tbod., no ba.e flood elevation •• hOVD or PHP, deterllined .

Special Plood Haaard Area. i nundated by tbe 100-year flood, deterllined by detailed _tboel., ba.e flood elevationl IhoWD, Ind aone •• ubctivided Iccordin, to PH".

Ar.a. between the Special Flood a.aard Ar.a. and the liaitl of the 500-y.ar flood, includin. a rea. of the 5!J0-y.ar flood plain that ar. protected frCMI tbe 100-year flood by dike, levee, or oth.r vater control Itructure; aho ar ••• lubject to certain type. of 100-y.ar .haUov flood in. where depth I are le .. than 1.0 foot; and Ir.a •• ubject to 100-y •• r floodin. Eroa .ource. vi tb dra i na •• areal l e .. than 1 I quare aile. Zone B i. not .ubd i vided .

6.0

lOne C. Are •• of .lniu1 flooding.

5.4 Flood Insurance Rate llap Deacr ipUon

'lb. nood Inaurance Rate Map for South Jordan is, for inBurance purpo ... , the ~lnclP11 r •• ult of the Plood Insurance Study. 'Dlis _p (publ1 .. ., .. parataly, contain. the official delineation of flood tnaurance .one. and be •• flood elevation linea. Baae flood el ••• tion 11 ... 1Ib0lf the location. of the expected whole-foot water­wrface ele.ationa of the bea. (lOO-year) flood. 'D\ia up is developed In accordance with the lat.at flood inaurance up preparation guideline. published by the Pederal z.erqenc::y Management Agency.

0'l'IIIIIt 82001_

Flood Jnauranoe StueU •• ue being prepared for the adjacent Cl tiea of 8aJxIy City ( .. ference 12), Draper (Reference 13), and the unincorporated ar ••• of Salt Lake County ( .. ference 14). '1'hia study ia In agre_.nt with tile .. Flood Insurance Studi •••

A r •• teed I'lood saurd Boundary IIIIp i. being prepared for the adjacent. City of .. at Jordan ("fe['ence 15'. A Flood Insurance Rate Map 1e being prepel'ed for tbe a4j.aent City of Riverton (Reference 16'. Flood boundal'ie. MCMl an tho .. _~ an in agrHlleftt with flood. boundariea mown in thi. Flood In.urance Study.

!trie D.S. Arwty Cor~ of Bngineer. rlood Plain Infor_tion report for Midvale­Draper, utah (Reference 8) included analyses of Jordan abel' and Dry and willow erHk.. Becau .. of the reviaed hydrology and additional topographic infor_tian ueed in thi •• tudy, it supersedes the Pl00d. Plain Infor_tion report.

Di.cbarge. fro. a .tudy by the U.S. Al'1IY Corpe of Bngineer. (Reference 17) weI'. utiUaed for the Jordan River durift9 the couree of thi •• tudy.

'!be recs.ral _rgency lIana~t Agency previously publhhed • Plood a. .. r4 Boundary Rap f« the City of South Jordan (Rllf.rence 1). This _p ... ueed a. the KlUrce for ... approxiaate flood boundarie. for thi. nood In.urtlftCe Study. 'l'bla atudy repre.enta a .,re recent and ~eben.i .. analy.i., ther.for., it auper..se. the Plood aaurd Boundary Mop.

I'ollc.ing the di ... trou. flooding alOl19 Dtah Lake and the Jordan River in 1983 and 1984, Salt Laka COunty and Utah COunty official. co.Iis.ioned an in".1;igatic. by CII2Il BILL, Inc., of r • .edial .... ur •• to .iUgate

16

future floo~ ~O"~I. The reaultinl report (Reference 18) propoaed cbannel IDOdLflcauoDI on the Jordan River, a flow control Itructure for Utah Lake, and a plan for reaulatina Utah Lak~ outflows. The.e propol~h ver~ b&1~d on delian diacharle valuel eltablished through an analynl of h~ltot'1~al Jordan liver and tributary floodflow record. and a .yn~be81~ of Lllpactl of controlled retea.es froll Utah Lake. The.e de81~ duchar.e~ are .hown in Table 3. The design diacharles vere u.e~ Ln a ?ydt'auhc nap-backwater IDOdel (aeierence 7) of the Jordan RLv~r wbLCh ~"UM.d all propo.ed channel IDOdification. to be in pl~ee. Tb.1I analY811 re.ulted in a water-.urface profile shown in thu Plood Inauranee Study aa tbe Utah Lakel Jordan liver Flood Mana~ .. nt Plan Profil.a. Vo Cotiparieon or correlation between theae ~rofLle. and the data pre •• nted in thia nudy can be IUde or ia Lntended. Moat of the Jordan liver channel IDOdification. and the Utah Lake Outflow con~rol .tructure bave not been completed. The proposed plan for regulating outflows frOil Utah Lake is not being used at preaent.

Tbie study ia autboritative for the purpoaes of the aational Plood Inluranee Progr ... ; data presented herein ei ther supersede or are coepatible with aU previoul deterainationa.

7.0 LOCATIO!! OP DATA

Info!'lll.tion conee~inl the perthent data uled in preparation of thia study can. ~ ~btaLned by contacting the aatural and Technololical HaEards D1VU10D, Pdderal s..r.ency Mana.etMnt Agency, Buildinl 710, Denver Federal Center, Lakewood, Colorado 80225.

8.0 BIBLIOGWHX A!ID MPIRB!!CBS

1.

2.

3.

4.

U.s. Depart_nt of Housina and Urban Developatent Federal Insurance AUiniltration, Plood Ha,.rd Boundary Map. City of South Jordln. ~, Scale h 12 000 July 26 1974 R . d January 30. 1976 "" evue

City of South JardIn, Utah, aaaie PIt. COUee:tion, undated

U.9. Depart~nt of the Interior, Ceological Survey, Water Supply Paperl, Kaapltude and ~re9u.ncy of Plooda in the United State •• Part 10. The Creat Ballg, tbroulh 1963

U.s. Depart_Dt of the Interior, Ceololical Survey, !Y1s.I. aesourclI Ott. for Utah, 1961-1975

U.S: De~rt .. nt of the Ar!Dy, Corp. of Kngin,era, Hydrololic KnlLneerLnl Center, CoeDuter ProlrllD 123-X6-L2010. HKC-l Flood Hxclro'raph lKYu, Davia, CAlifornia, 1979

17

Table 3. Jordan River Propo.ed De.ign Di.cbargel

Loc.tion De,i.n Di,eb.rl. (cf,)l

saoo Soutb Street (Bullion Street) to 9400 Soutb Street

9400 Soutb Street to Jord.n Harrow.

lSource of Di.cblrae Data: Utab Loke/Jordln River Flood Htn,,'!!nt Pl.n. Pb •• e I Report (I.f.r.ne. 18)

I~

3,330

3,260

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

U.S. Depart_ot of Co-.erce, National Oceanic and Atmo.pheric AdIIinhtratioa, Precipitation 'regueae! Atla. of the Western lIIIll.U. lliW. Vol .... VI. 1973

U.S. Depart_at of the "f"IDY, Corp. of Engineer!l , Hydrologic I!nlineeriol Center, Co_outer Proar_,. 72J-X6-L202A. H~C-2 Water ~ EI..e.filn, Davis , California, November 1976 w1th Updates

U.S. Depart_at of the "f'1DY, Corp. of Engineers, FLoodplain Info!'1lltion. Jordan River Complex II. Midvale-Draper. Utah, 1974

Caldwell, Richard. and Soren.on, Inc. , Topographic H.p •• Jordan River. Dry. Willow •• ad Corner Canyon Creeks, Scale 1:600, Contour Interval 4 feet, Kay 1972

U.S. DepartlHDt of the Interior, Geological Survey, 7.'-Minute Serie. Topographic Map., Scale 1:24,000, Contour Interval 5 feet: Midvale, Utah (1963), Photorevi,ed (1969 acd 1915)

Aerograpbics, Inc., Ortbophoto Topolt'aphic Maps. Dry Creek and Willow Creek, Scale 1:2,400, Contour Interval 5 feet, March 1916

Federal Emer •• ney Mana._nt Aaency, Plood Insurance Study. City of SADdy City. utah, unpublished

'ederal "-rl!Dey KaIlaI_nt Aaency, Flood In.urance Study. City of Dranr. UtM, unpub1hhed

Federal r..erl.ncy Mana._nt Aaency, Flood Insurance Study. Salt Lake Coupty. Utlh (Unipcorporated Ar, •• >, 1985

,.d.rll e-rlency Manal_nt Aaency, Flood Hazard Boundlry Map. City of W.1t. Jorde. Ut.h, Scale 1:12,000, unpublished

Federal "-rl.ncy Man'lellent Aaency, flood In.urlnc, Rate Hap. City of Riverton. Utah, Scde 1:6,000, unpubli.hed

U.S. Depart..nt of the Army, Corp. of Enlin.en, JardIn River Ipveuicltion. utah, 1980

ca2M HILL, Inc., utah Lake/Jordln River flood Mana • .,nt PrOlra •• Ph.a. I R'port, .ubaitted to Salt Lake and Utah Countlet , 1984

U.S. Depart .. nt of the Interior, Geological Survey, Interagency Advi.ory Coc.ittee on W.ter Data, Bulletin 178 of the Hydrology Subc.o..ittee, Cyidelipe. for Dtterllinin. Flood Flow Frequency, aevi .. d Septaber 1981, Editorial corr.ction March 1982

calM HILL, Inc., Hydrololy leport of • Dtt.il.d Flood In.ur.nce StudT for the Jord.p liv'r in Salt Lak. Coynty. Ut.h, prepared for rDCA, 1991

19

21.

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23.

24.

25.

U.S. Depart_nt of tbe Araty, Corp" of !nlin •• rs, HydrololY. (I.vie.d) Jordap liv.r Inveltil.ti" n. UQP'r Jordan River tnterim ~. 1984

Aero-C-r.pbic., Inc., Orthophoto Topolraphic M.p.. Jordan River fr. 2100 Sout.h t.o tbl Ut..b CountY 1.ine. Sc.le 1:4.800. Contour IDt.rval 4 fe.t witb 2-foot .upRl .... mtal sontour., November 1990

U.S: Dep~rt_nt of tbe Aray, Corps of Engineer., Hydrololic KnIID •• nn, C.nter, HlC-2 Water Surf.ce Profi le. CO!!put.r lI2&ua, V.rtiOD 4.6.2, Kay 1991, Witb Pull Micro-Ca.puter IlIpl ... ntation by H'eatad Method., HMVerlion 6.41

U.S: Dep.rt_nt ~f the Int.rior, Ceololic.l Surv.y, 1.5-Minute Sen •• Topo'rapble MlP', Scale 1:24,000, Contour Interv.h 5 and 20 feet: Sa~t Lak. City South, Utah (1963), Pbotcrevised (1969 and 1915); Mldvalt, Ut.h (1963), Photor.via.d (1969 and 1915); JordAD .. arrow., Utah (1951), Photor.vi.ed (1969 and 1975)

,!ro-Craphics, Inc., Orthopboto TOP9'tlphie Mlp. of W •• t hU.! CUT' Utlh , Seal. 1:6,000, Contour Int.rval 5 fe.t prepared for W.1t. Vall.y City, April 1985 '

Barn.tt, J.A., Croupdyettr 8ydro10ly of l!ilJ:ltion Cagyon. SIlt 14'" Coupty. utah, Utah State !alin •• rs Office, Jun. 1966

Biallhal Inliae.rinl, lugoff !atiMtI. in !!Iilration Canyon, 1979

Borlquiat, I.S., Utah 4'" - Jorde liv'r I'port, 1947

Caldwell, .ic~rda and Soran.oD, Inc., Ortbophoto Topolr'phic tIIaL. JordlA bytr, Seal. 1:1,200, Contour IDterval 2 Peet Decaber 1966 '

Caldwell, lichards and Soren.oD, Inc., Salt. Wk. county Mauer W.t.r. 1..,1' lAd Stom Drain'I' PIM, 1971

ca2M HILL, ~ordM lint SYTYIY MODUMD" 2100 South to 14600 12!!t.Jl, Sut.1tttd to S.lt Lak. County Plood Control S .... t •• ber 1987 • ~

ca2M HILL, UtAh 14k. - JordAn Riv'r Plood NtDa'IMDt Prolr ... Pha~. I R'port, 1984

~ov, V.n T., Iftadbook of AppU,d Hydrolon, N." York: McCraw-8111 80011. Ca.pany, 1964

Chow, Ven T., Optp-CbtnD.l Hydraulic., NIV York: McCraw-Hill Book Ca.pany, 1959

20

Craddock, D.W., Salt Lake City Flood. 1945, Proceedings of the Utah 4cld_y of Scienc •• , Art. a nd Letter., Volume 23, 194~-46,

pp. 51-61

Denver Regional Council of Governments, Urban Storm. Drainage tIImlIl, Volwae. 1 and 2, 1969

Edvard. and Kelley-Western, Con.ulting Engineers, A Haster Plan for Control of Surface Storm W.ter. Salt Lake City, July 1960

Evan., R.W., An Analni. of Salt Lake City's 1952 Flood, University of Utah, 1953

Panter, E.E., and J.E. Pletcher, Distribution of Predpitation in Mount.inou. Areas, World Meteorological Organization, Geilo SyaPOIiWl, Norway, July 31-Aulullt 5, 1912

Forsgren A"ociatet, P .A. , A,rial Target Coordinate and Elev.tion Li.t for JordlD River Aerial Happing Proiect from Jord'g ".rrow, to 2100 South Street, 1991

Cardner, Br.d, 1989 Ut.b Lake - Jordan River COIIIDi"ioners Annual ~. 1990

Cin,et"y A.sociates, Inc., Hydrology Report - Flood In.urance RYsl!u.- 20 Utab COllllUnitie •• FIA Contrast H-4790, October 1979

Cline., W.P., Cloudburn Plood. of Salt Lake'. !aft Bench 1900-1960 (M Anlly.i. of tbe Contributins Factor.>, University of Utab, June 1970

Hoehcber, 1:., and B. Clenne, Salt Lake Valley Intensity -R,yu tion Frequency Curve •• Partial Duration Series, Univenity of Utah, 1979

Houpton, J.G., Cbar.cterittic. of Rainfall in the Gre.t a.sin, University of Nev.d., De.eret Rue.rcb Institute, 1969

Kin" H.W., and !.P. Brater, Itins l• H.ndbook of Hydraulics, 5th

!clit i on, New York: McCraw-Hill Book. Comp.ny, 1976

Linsl.y, R.It. Jr., et.at. Hydrolosy for Enline.r., McGr.w-Hill Book. Co.-pany, 1982

lIiehon and Mazvell, Con.ultinl Engineen, Plood Control Pl.n !lIia& Dtt.ntion a'dns, report prep. red for Salt Lake County Ca..i .. ioners, 1971

Pac~.r, P.!., and B.D. Willi .. s, Loelinl and Pre.cribsd Burnine IUJcts op tbe Htdrologi, and Soil St.bility Behavior of Larch/Doualas Pir Por.stt in the Nortbern Rocky Mountains, 1974

21

'arD.ll, P.!., CO!!put'I Si!Ulation Mod.l - Description and Users tIIIUlIl, gept .. ber 1975

Roberts, 9.H., Ptt'raination of Re,."ion Hydrolraph. and l2u.i2lJ. Applications

Rollins, Brova, .nd Cunell, Inc., Cau". of Floodinl within Salt Lake VaUey. Utah, 1979

Rollin., Brovo, and Cun.ll, Inc., HydroloRY Report of Flood Ip.ur.gce Studi •• for Sel.ct.d COMUQities in. apd the Upincorporat.d Area. of Salt Lake County. Utah, 1980

Salt Lake City Water Department, 1916 y;tah Lake Stas.-Di"hlrce Curve, Drawina 24, Pile 28, Humber 11347

Salt Lake City Water Department, Oiler.s Shovine Pluctuations of Utah Lake, Dr.vina 2, Pile 28W, 1900

Salt Lake City Water Depart_nt, DialEY ShowinR Pluctu.tions of Vt.h Lake, Dravina 49, File 28W, Nuaber 4948, 1915

Salt Lake City W.ter Department, Pluctyations of Utah Lak •• 1900-1920, Dravinl 54, File 28W, NWIlber 6662

Salt Lau County Depart_ftt of Public Work" 'lood Control Division, StnMfloy apd Precipitatiop Oat. Report. Jordan River Tributari'" S.parat. book. for •• ch v.t.r year, 1983-1989

Salt Lake Count,. W.t.r Quality and Water Pollution Control, Salt Lak. County 208 Study, Area-Wide Water Quality Man,cement Phn, 1978

SODDtal, C., and B. Clenn., RAinfall Inunsity - Duration Prequ.ncy ~, University of Utah, 1978

St.t. of Utah, Fifth Bienni.l Report of the State Enline,r of !I1IIl. 1905

State of Utah, Third Biennial Report of the State Enlin,er, 1901 aDd 1902

Svanson, C.L., R.tid.ntiat Floodine in Bench Are •• in Salt Ltk. Coup,y. U,.b, 1968

V.S. Depart_nt of Aariculture, Precipitation Ch.r.curittics of SwatI' 9tom .t; High El.vat;ion 9tations in Utah

22

U.S. Depart_nt of Aariculture, Office of Eltperimental Station!, "POrt. of Irri'ltioo Invelti.ation. in Utah, Bulletin No. 124, 1903

U.S. Depart_nt of qriculture, Forut Service, Re.eareh Paper ~. 1971

U.S. Depart_nt of Aa;riculture, Soil. Conservation Service, "HydroLogy," 1I.tion.l Enlineerinl Handbook, Section 4, 1972

U.S. Deptrt-.a.t of qricu1ture, Soil Conaervation Service, Soil Surv,! of S.lt Lake Arel. Utlh, 1914

U.S. Depart_ot of Ag:riculture, Soil Conservation Service, Soil Survey and Interpretation. of SWlllDit Soil Survey Area. Wasatch Mountain Portion of S.lt Lake County. Utah, 1975

U.S. Department of qriculture, Soil Conservation Service, Technical Rele •• e 110. 55, Urban HydrololY for Small Watersheds, 1915

U.S. Depart_nt of tbe Aray, Corp. of !naineers, Draft featibility Report fDd Draft EnvironMntal Impact Statement. upptr Jorclap liver Interi. Inv,.thation Ut.h, 1987

U.S. Deptrt_nt of the Aray, Corp. of !naineers, Flood Flow 'r'qUlpcy Wly.i., Ce:ner.li&ed Cotaputer Proar .. 72J-X6-L7550, 1982

U.S. DepartMDt of the Aray, Corp. of !nlin.er., UORubli.hed '1004 Pr'q"ency C"rve. of th. Jordan River, 1985

U.S. Departant of the AraIJ, Corp. of Engineer., Interim S"rvey R.port for Flood Cootrol on Jordan River B •• in. Salt Lake County Str ..... Utah. Appendix A-Hydrology, June 1910

U.S. Dep.rt .. nt of the Anay, Corp. of Enaineer., Hydrology De.iln M..arandum 110. J, Little Dell Lok •. Salt Lake City Str ..... Utah, Jaru.lIry 1972 (Ievi"d Augu.t 1972)

U.S . Depart_ot of the Aray, Corp. of EDain.ers, ~ Cloudburst. Salt Lake County. yt.h, Internal Report, Deceaber 1916

U.S. Depart_nt of the Anay, Corp. of Enlin.er., HydroloRic !alineerinR Center, Technical Paper No. 64, Det:'I1Iininl Peak Dilchtrae Freguegcie. io an Urbapiain. Water.hed: A Cal! Study, PaVil, California, 1979

23

u.s. Depart_ot of the Any, Corp. of !nline.n, HydroloRic !alin •• rinl C.ot.r. Training DocUMnt 110. 5, ll9.2A!!n Dtt.raiMdoQ Ulipl cO!!put:.r Prolry HIC-2, May 1974

u.s. DepartMDt of the Army, Corp. of Enlineen, Hydrologic Inlin •• rinl C.nt.r, Trainin; DoCu.8Dt 110. 10, Introduction and Applisatiop of lip_dc Wave Routin. T,sbniqu" Utin. H!C-t Davi., California, 1979 '

u.s. Depart_nt of C~rc., Weather Bur.au, Memorandum, Severe HlihtoA at Salt Lek. City. AUBU't 194), 1945

U.s . Depart_nt of C~rce, 1Iation.l Velther Service, ClilMt. of Salt Lay City. Utah, 110M T.chnical MeatorandWD NWS WR-152, 1989

u.S. Depart_ot of the Interior, Burea" of Recl .... tion, De.iBn of SMU Dam., 1974

u.s. Depart_Dt of tbe 10t.rior, C.ological Surv.y, Water-Supply Paper 994, Cloudburtt: flood. in U,th. 1850-19l8, 1946

U.s. Depart_nt of the Interior, C.olOlical Surv.y, V.ter-Supply P.~t 1314, COIIpilat:ion of Record. of Surface Waten of th. Ua.llI.!l StU" throulh S'Pt:wbtr 1950. PaU 10. The Creat k.in 19S6 •

U.S. Depart_Dt of the Interior, C.oIOlical Surv.y, Water-Supply Pa~r 1714, eovilation of R.eord. of Surfac. WAt:.r. of the llall.U Stat ••• Oct:0ber 1950 to S'Pt:.ber 1960. Patt 10. The Cr.a: kIia. 1963

u.S. Depart_nt of the Interior, C.oloaictl Surv,y, Water-Supply Paper 1260-8, flood. of April - Jun. 17)2. in Ut:ah and Nevada 19S7 •

U.S. Dtpart .. ot of tb. Interior, Ceological Survey, Flood. in ~ KalRityde and FrequeDcy, 1962

u.S. Depa.rt_nt of tbe Int.rior, Geological Survey, Hydroloaic ~6CliMtol0Rie Data Collected t:hroulh 1964. Salt: Lak. Coumy,

u.S. Depan .. nt of the Interior, G.olOlicd Survey, Hydrologie I.IUl Cli.toloRie Dat:a. 1965. Salt: LAke County, 1966

u.S. Depart_Dt of the Ioterior, Geololical Survey, Technical Publication Mo. 31, Vat.r I"oure •• Dat:a of Salt: Lake County, 1911

u.s. Depart_nt of Trtn.portation, p.d.ral Hilhuay Adainittrltioo, BUtololY for Trap'POuat:ioo Inlin.er., 1918

24

U.S. Depart_nt of Tran.port.tion, Pederal Highv.y Adain1.tr.tion, lugoff IUiNt •• fot' SHll Watenhed. and Dlv.lo_pt of a Sound De.iln M'thod, 1977

U.S. !nviroOlllntal Protection Aiency, 2PA-670-75-046, R.infall­lupoff Relatiop. on Urban and Rural Arelt, Cincinnati, Ohio, 1915

U.S. Ceololictl Survey, Surfas, Water Resot'd. of Utah, Separate book. for eacb year, 1961-1964

U.S. Geo10lical Survey, l2tb Annu.l Report, Part II, Irrilation 1890-1891, 1891

U.S. Ctololical Suney, Unpubli,h,d StrellDflow Oat •• Peak. Disch.rle Streaaflov Record. for Miscellaneou. Gaging Statlons fro. uses, Kainfr ... co.-puter file., 1990

u.S. Ceololictl Survey, Wat..r Re,ourc" Data for Ut.h, Part 1, Surf.c' Water Record., Separate book. for eaeb ye.r, 1965-1974

u.S. Ceololieal Survey, Water a •• ourc" D.ta for Utah, Separ.te book. for elcb v.ter ye.r, 1975-1980

U.S. Ceolo,ic.1 Survey, VU,r Ile.ourc" O.ta - Utab, Sepat'ate book. for e.cb v.ter yell', 1981-1989

U.I. Ceololical Survey, W.t'r-Supply Paper 157

U.S. Soii Con •• rvation Service, "tioMl Enlineerina HlDdbook. Sectiop 4. BUro10u, 1972

U.S. W.ter le.ource. Council, Hydrology Co_itte" Flood Plov PreqUlpsy for YDI.,ed W.terlhed.: A Lit.r.ture EvalUAtion, 1977

Utah Dep.rt_nt of •• tur.l I •• ource., technic.l Publication Ho. 21, Sw.aa of Ma"i .. Di.ch.n,. in Ut.h Stre"., G.C. Whit.ke, 1969

Utah Ce.olOlic.l A .. od.tion, CloudbyrU .nd SnoWIDIlt Flood •• Ipvit'ORMPttl Geolo,y of the W ... tch Pront, 1972

Utah Office of Planoinl and 8udl.t, Utab DeItolraphic R,pot't DIM'Xapbic aAd !sopo-is Analyti., 1991

Utah Wat.r R •• earch Labor.tory, Re90rt Ho. Plwe 86-1, Application of • BUrolo'ic Hod.l to the Planpinl .nd DelilP of StOni ~ STat_ or yrbtD Ar ••• , 1976

Utah W.t.r Re.urch Labor.tot'y, R.port No. UVlL/P-80/01, f.l.2.2!l tleeel' "itjc.tiop iq ytAh, 1980

25

Utab Wat.r I •••• rch Laboratory, Report No. PRwe 35-1, Hydroloaic AU., of Utah, 1968

Vi ..... n, W., J.W. ICnapp, C.L. Levi., .nd T.E. H.rbaugh, Int.roduction to Hydr0101Y, Harper .nd Rov, Publi.herl, 1977

We.th.rbtDk, Inc., !.tiyted Return - Period Isopluvitl Maps fot' S.lt 4" 'IIU.y, 1977

9.0 IBYISIQR DESCRIPTIQHS

Tbi. '.CtiOD ba. been .dded to provide information r'lardinl .ilnificant revitionl .. d •• ince th. orilinal Plood In.u,..nce Study V.I printed. Future r.v1.ion. _y be .. d. th.t do not r •• ult in the republilhing of the Flood Inlur.nc. Study report. To "'ure that .ny u •• r i •• wat'e of .U r.vision., it it advillble to cont.ct tbe cOlllllUnity r,po.itot'y of flood haurd d.ta locat.d at the Salt Lake County Department of Public Work., Flood Control and Hipvay Divi.ion, 20001 South St.t. Street, _r .3300, Salt Lake Cit,., Utah 84190-4600.

9.1 Pir.t I.vition

Thi •• tudy v •• r.vi"d on Septeaber lO, 1994, to include the r •• tudy of tb. Jordan liver conducted for PEMA. by CU2M Hill under Contr.ct 10. 1MII-9O-C-3104. The re.tudy va. co.p1.ted in Hovem.ber 1992.

Th. Jordan liv.r v ••• tudied in d.et.il fra. the Utah - Salt Lake COunty lin. to th. Surplus Canal cliv.nion n •• r 2100 Soutb Street. The Itucly .r.a includ •• portion. of th. unincorpor.ted area. of Salt Lake County, al ... 11 •• portion. of the Citie. of Welt V.lley, South Salt Lalte, Murray, Mid.v.le, W •• t Jord.n, South Jord.n, S.ndy, liv.rton, Dr.ptr, Bluffdale, .nd Salt Lak. City.

Hyd.rololic analy ••• vere performed to e.tabli.h ditch.rl,-ft'equency r.l.tion.hip •• t four loc.tion. in the Itudy re.ch of th' Jordan Riv.r . Hittoric .tr.aaflov dat. were analyz.d in accordance vith crit.ri. outlin.d in Bull.tin No. 17B, Cuideline. for D'termininl Plood Plow Fr.qu.ncy (Referenc, 19).

Hittoric Ut.h Lak •• tale r.cord. belinninl in 1884, and a hilh vat.r r.f.renc. of 1862, vere u.ed in conjunction with a Itag'­ditchara' curv, to e.ti .. te bistoric n.tur.l dischar,e. in tbe Jordan liv.r. Th ••• d.t. vel" u.ed to .uppleaent the U.S. Ceololic.l Survey (useS) ttreaaflov data to dev.lop the d i scharle­fr.qulDcy curv •••

Th •• tr.aaflov "Iinl record. for the Jord.n Rivet' con.itt of tvo data population •• 1 • re.ult of tbe op.rational effects of the CoeprOlli •• Aar._nt: natur.l 1'.1' ..... nd pumped t'el ••• e. (I.f.ranc. 20). Th. two d.t. 9Opul.tion. vel" anal1.&.d

26

independent I, to develop Hood flow frequency curve. for Inowa.elt evea.tl, .1 it v •• det.rained tbat flood. caused by .noVMlt event. are len.raUy -are •• vere than tho.e cau.ed by rainfall events. PIOtld peak. eau.ed by rainfall ,venti vere not evaluated with peak. cau.ad by 'DOWIMIlt eventl .0 that the data popuLation. would be ho.tleneou.. The ",t •• vere .nOWIMlt flood. on the Jordan River are aUGei.ted vitb natuul relea ••• and biah levets of Utah L.ake.

Di.ehar •• contribution. to the Jordan liver fro. Mill Creek Big Cottoov004 Cr •• k, and Little Cottonwood Creek were based on' e.tiuted 100-y •• r tributary ditcta..rgea at the canyon lDOuth. developed by the U.S. 4r8y Corp. of EDlineers <USACE) (I.ferenee 21).

Th. peak di.ch.r,e-draina,e are. relationsbip. developed f or the Jordan liver .... r •• dded to Table 1.

The H!C-2 c.o.puter .octe1 d.veloped by the study contr.ctor •• ilart of the Utah ~k.e: iJordaD aiver Plood Han.,e_nt. Prolr .. in 1984 va. u~ed a •• ban. for perfonainl tbe bydr.ulic .n.ly.es of the Jordan R1ver (Ilifer~ce 18). Th • • crall lection. used to develop tbat .odel .... r. held ,,;,rveyed 1n Jun. 1984 durinl tbe pe.k flov period. That .odel. va. c.hbrated to tbe 1984 event. To update the IIIOde1 developed In 1984, 78 additioul crall .ection. vere added to the 1984 lIOdel. Cro ... ection d.t. for .ppro:dlNtely 38 of the .uppl .... t.l era ... ection. vere obt.ined frail. 1987 .urvey where .atII~ted crol' .ection. vere e.tabli.bed between 2100 Soutb and 14600 Soutb to lIOIlitor erolion and depo.itioo. The data for tbe r ... ioinl 40 cro" .ection. ver. field .urveyed in 1990 .nd 1991. ~rbaDk and UDdervater data were obtained by field .urvey for . n channel cro ... ectiOtl.. In.a.e .rea. (Le., betweeo 2100 South and tbe Mill Creek confluence) luppl ... nt.l overbank crall .ection data vere obt.ined fro. tbe 1990 orthopboto topolraphic .. p. pro"ided by Salt Lake County (Reference 22). The portion of the HIC-2 .octal for tbe .tudy re.cb up.tre .. of Turner D .. wa. obtained fra. data developed by tbe USACI. All hydraulic .tructure. were .urveyed to obt.in elevation and .tructural .eo.etry data.

Wat.r-Iurfac. ele"ation. for flood. of the .elect.d recurrence i nt.rv.ls vere coepu.ted u.ial tbe HIC-2 Water Surfac. Profile. coepu.ter prolr .. dev~loped by the USACIt (aeference 23). Startina v.ter-.urface al.v.t10n. vera deterained u.in, tbe dope-area Mthod.

~tural cbanne~ aDd ov.r~nk rouaboe .. f.ctore (Mllnnin,'. "nn) uled 10 tb. hydr.ullc Co.put.t100. vere cho •• n b.,. enaineerin, judament and ba'ed on fiald ob.erv.tionl and of the stre .. and floodplain .r... . louahne .. value. ranaed fra. 0.022 to 0.077 for the n.tural .. in channel and fro. 0.075 to 0.225 for overbank .r.... MIIin channel rouahne .. co.fficienu of 0.0l2 and 0.013 were u .. d to

27

3 3

ltOdel flov tht'ouab two of the eoncrete cHvereion .tructure. on the river.

Ortbopboto topo,r • ..,hic .. p. with •• c.l. of 1:4,800 and a contour int.rval of 4 feet, with 2-foot .uppl.ment.l contour., were provided to th •• tudy contr.ctor by Salt Lake County (Reference 22). The pboto,r.pb date of th •• tudy .rea wa. Hoveaber 11, 1990 .

Pive .hallow floodin, or pondinl zonel (Zone All) .re identified on tb ... pl. Ooe of tbe.e .re •• i. locat.d ju.t downatre .. of the Big Cottonwood Cre.k confluence. Anotber il loc.ted ju.t upstre .. of th. 4500 Soutb Stre.t bridg.. The otber tbree .re located between the aouth .id. of tb. Sb.ron Steel tailinl' pile .nd tbe Hortb Jordan Diversion Itructure.

The All Zone loc.ted ju.t down.tream of the Bil Cottonwood Creek. confluence i. loc.ted in a low area bebind • short levee. Thi. leve. is not a PIMA certified levee, it provide. Ie .. than J feet of freeboard durin, tbe lOO-ye.r flood, and shallow floodinl occa.ionally occur' in tbe area becau •• of in.dequate internal dr.iule f.cHide.. Th. flood elevation in this .re. va •••• WMd to be equal to tbe v.t.r-.urface elevation in the Jord.n River.

Th. otber four All Zone •• r •• hallow floOd in, are.e in low overbank are ••• lon, tbe Jordan River. The flood. elev.tion. in tho.e area • vere e.d .. ted fra. tbe vater .urf.ce in tbe river at the low pointe ¥b.re wat.r .nter. tbo.e area.. .

Flood bound.rie. for tbe .Jordan liver were d.lin •• t.d ulinl orthopboto topoar.pllic ...... t • Icala of 1:4,800 witb a contour interv.l of 4 faat and .u .. pl .... t.l 2-foot contours. Th. contour. on tbe.e .. p. u:taad to • point that is either 1,000 feet froa the ch.nnel or 10 feet above the to .. of the bank, whichever co ... fir.t. In .re •• where tbe floodplain esc.eded contoured area. on the .. pi, USCS quadr.n,le "Pi were u.ed to .upple-.nt the contours on the orthophoto topolrapbic "Pi (aeference 24). In the ve.t overbank ar.a betveen 2100 Soutb Str.et and the Decker Lake Dr.in, tbe ortbopboto topolrapbic .. p contour data vere .uppleeented with contour d.t. fra. 1985 orthopboto topolr.pbic "ppinl vith a contour interval of 5 feet provided by Wa.t Valley City (Refer.nce 2S).

The S.-ary of Di .cb.r,e. T.ble and Ploodv • .,. D.ta Table were r.vised to includ. data for the Jord.n River, and Plood Profile. for the Jordan River vere .dded. In .ddition. Plood Profile Panel 04P for Willow Cr.ek va. revi.ed to abov the backv.ter effect. froll tbe Jordan Ii ver •

A •• part of tbie upd.t., tba Utah Lakel Jordan River Plood Mana,_nt Plan Profil •• (Jordan liver) have been r..aved fro. this report.

28

3'/

Al,o, a' a part of this update, the Flood Insurance aate Hap for tbe City of Soutb Jordan wa, converted to the Map Initiatives for.at. In the .. p initiatives fo~t, all base flood elevations, cro., section" and floodplain and floodway boundaries are ,hown on the Flood Insurance aate Map. The Flood Insurance Zone Designation. were chanaed to reflect the Hap Initiatives format as follows:

Zone A

Zone A i. the flood insurance rate zone that corresponds to the IOO-year floQdplain. that are deterained in the 1100d In Jrance Study by approaiaate .... thod.. Because detailed hydraulic analyses are not perfo~d for such areas, no baae flood elevations or deptb. are .hown within this zone.

Zone A!

Zone A! is tbe flood insurance rate zone that corruponds to the IOO-year flOodplain. tbat are determined in tbe Flood Insurance Study by detailed .. tbods. Whole-foot base flood elevations derived frota tbe detailed bydraulic analyses are sbown at selected interval. witbin tbi. zone.

Zone AS

Zone AS it tbe flood in.urance rate zone that correspond. to the ar'" of laO-year .ballow flo04ina (u.ually areas of pond ina) vbere averaae deptb. are between I &ad 3 feet. Whole-foot base flood elevation. derived frOil the detailed hydraulic analyse. are .bown at .elected interval. within this zone.

Zone X

Zone X is the flood in.urance rate zone that correspond. to areas oUClide tbe SOO-year floodplain, area, wi thiD tbe SaO-year flood­plain, area. of lOO-year flood in, where avera,e depths are 1 ... tban 1 foot, ar .. , of lOO-year floodina vhere tbe contributina draina,e area i. Ie •• than 1 square .ile, and area. protected fro. the IOG-year flood. by leveel. 110 ba .. flood elevation, or depths are ,hoWD witbin tbil zooe.

In addition, tbe Flood In.urADce Zone Data Table va. removed from the. Flood Inlurance Study report, and all zone designationl and reach determination. ware rellOved, fro. tbe profile ••

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