TOWN OF TONAWANDA, ERIE COUNTY

i,-

FEBRUARY 17, 1981

federal emergency management agency federal insurance administration

COMMUNITY NUMBER • 360260 OF

1., 1 Purpc:se of Study

1 ~ 2 and AcKnowledgements

1. 3 Coordj nation

2

Scope of Study 2

2

2~3 Principal Flood Problems 4

2~4 Flood Protection Measures 6

6

6

3.2 Hyd.raul.ic l\rla 8

10

10

12

Rcacl·, Detenninations 12

Floc;c1 Hazard Factors 14

F'j_ood Insurance Zones 14

oo(:l Insurance" Hate Ylap 16

i TABLE OF CONrrENTS - continued

6 ~ 0 OTHER STUDIES 17

7. 0 LOCATION OF DA1'A 17

q 8.0 BIBLIOGRAPHY AND REFERENCES ''

FIGURES

Figure 1 - Vicinity Map 3

Figure 2 - Potential Flood Elevation, Town of Tonawanda 1 New York 5

Figure 3 - Potential Flood Elevation, Town of Tonawanda, New York 5

Figure 4 - Floodway Schematic 13

'fABLES

Table 1 - Summary of Discharges 8

Table 2 - Floodway Data 11

Table 3 - Flood Insurance Zone Data 15

EXHIBITS

Ex-hibit 1 - Flood Profiles Panel 01P Niagara P~ver - Tonawanda Channel Panel 02P Panel 03P

Exhibit 2 - Flood Boundary and Floodway Map Index

Exhibit 3 - Flood Boundary and Floodv-;ay Ivlap

ii TABLE - continued

PUBLISHED SEPARATELY:

Flood Insurance Rate Map Index

F'lood Insurance Rate f"lap

iii FLOOD INSUP.Ji"NCF: S'l'UDY TOVJN OF TONAVJANDJ\, NF\!J YOHK

1.

1. 1 Purpose of St_udy

This Flood Insurance Study investigates the exist_ence cmd severity of flood hazards in the Town of Tona\vanda, Erie County, New York, and aids in tJ1e administ-ration of the National Flood Insurance Act of 1968 and thr: Flood Disaster Protectior Act of 1973~ This study will be used tc convert rronavJanda to the regular program of flood insurance by the Federal Insurance Administration (FIA}. Local and planners wil_l_ use this s·tudy in their efforts to promote sound flood plain management.

In some states or communities 1 flood manaqement criteria or requlations may exist that are more restrictive or comprehensive than those on which these federally-supported studies are basedc These criteria take precedence over the minimum federal criteria for purposes of requlating in t.he flood plain, as set forth in the Code of Federal ons at 44 CFR, 60~3~ In such cases, ho\o1ever, it shall be unc.h_';rstood that the state (or other jurisdictional agency) shall be able

to n t_hese requirements and criteria~

1 ~ 2 huthor.ity and Acknowledgements

The source of for this Flood Insurance Study is the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973.

The c and hydraull c analyses for this study were prepared by

DeleuvJ, Cather and Company of New York f Inc*, for Federal Insurance Administ:rat_ion, under Contract No. H-4552. This work was in November '1979~

~3 Coordination

Iden"cification s·treams to be studied detailed and approximat:e mt:tJ1ods was made at t.:he initial Consul tat.ion and Coordination Officer's

(CCO} mec'-'t:Lnq on t'1ay 23t 1977 r between the F'I/\ 1 DeLeuw, Cather a'1d Company of Nevi York£ Inc", {the study contractor), and tohn officials.

For tl-1ose :c;treams stuciied in detail, techni ca 1 data were coordinat~ed with the NevJ York St~a-te Department of Environmental conservation (NYSDEC), the

U. S. GeoJ Survey (USGS}, the U0 S~ Army Corps of Engineers (CO£),

the Erie~l'--Eagara Counties Reg:Lona} Board and the ing fj_ rms of Erdman, AntJ:ony Associates and Goodkind O'De-a. OthPr orqanizut_ions contacted for information .included t.he Soil

Conservation Scrv.:i ce ( SCS) 1 t;he New York State Depart.rr.ents of Hiyhv;a_y Planrd ng, Dra:i naqP and Scmitation, Environment.al Quality and Sol 1 s Conservation. Information from the general public was solicited thrcuqh

newspaper announcements in October 1977~

on September 3, 1980, results of this s·tudy were reviewed at a final c-,.-­ meeting attended by representatives of the FIA, the study contractor and the Town. of Tonawanda~

2.0 ARE/\ STUDIED

2~1 Scope of Study

This Flood Insurance Stud.y covers the incorporated area of the Tovm of Tonawanda, Erie County, New York. 'l'he area of study is shO'i"''TI on the Vicinity Map (Figure 1).

li. 2, 500-foot portion of Ellicot·t Creek, centered around Colvin Boulevard, was studied by detailed methods. The -Tonawanda Channel was studied in detail from about: 2, 000 feet upstream of Motor Island to the upstream corporate limits of the Town of Tonawanda~ Tonawanda Creek was studied from the northeastern corporate limits to a point about 1,600 feet upstream. The areas studied by detailed methods were selected with priority given to all known flood hazard areas and areas of projected development and proposed construction for the next five years, through November 1984.

A portion of Ellicott Creek from Niagara Falls Boulevard to 1,000 feet upstrefutt of Colvin Boulvard, and the portion of the Niagara River­ Tonawanda Channel between a point about 2,000 feet upstream of Motor Island tn the upstream corporate limits were studied by approximate methods. A portion of Tonawanda Creek was also studied by approximate

methods~ methods of v;ere used to study t"bose areas hav low development al and minimal flood hazards as identified at the: initiation of the study~ The scope and methods of study were to and aqreed upon the FIA ~

2~2 Comnmnity

Thf:: Town of TcmaHanda is located .in State in the nortJn-vest corner of Erie County and, with the Village of Kenmctre, forms the northern of the of Buffalo. Thf' -r.ov.m is bordered by the: City of North 'Tonawanda to the north, the Town of Amherst

to the east t t.he City of Buffalo to the south, and by the City of Tonawanda and the Niagara River-Tonawanda Channel to the west-

2 I I I ~-r I

'fiI ~ ! I ! I ! I I The Town of Tonawanda was formed from the City of Buffalo on 1\pril 16 1

1836~ It has an area of 19~8 square miles and in 1970 had a population of 107,282. The town is a mix of residential, commercial and industrial land, with some open space areas. , a county

recreational facility 1 .is located vii thin the corporate limits, as are several town parks and golf courses.

Ellicott Creek comprises the major drainage feature in Tonawandao Flowing west through the northern part of town, it joins Tona1danda Creek in the City of Tonawanda, meandering through Ellicott Creek Park. For part of this reach, development along the banks is residential and commercial ..

Surface soils \Vi thin the town reflect the texture of the glacial t.J ll and lake deposts from which they are formed. 'rhe predominant surface soi_ls

are unsorted rock material, forming a thin mantle over the bedrock in tlv~

southern portion of town 1 and interbedded clay, silt and fine sand in the remainder of town. Soils are generally shallow and well-drained. Elevations within the community vary from 570 feet to 620 feet.

Precipitation in the study area averages 33.0 inches annually. The average annual snowfall is 85~0 inches. Average temperatures range from 42 degrees Fahrenheit { °F) to 86°F in summer and from -7°F to 30°F in the winter.

2.3 Principal Flood Problems

The low-lying areas of Tonawanda have been subject to frequent and great depths of flooding~ Floods usually occur in the late winter or early spring and are caused by melting snow coincident with moderate amounts of rainfall~ Flood hazards have been lessened since the construction of a diversion channel from Ellicott Creek to Tonawanda Creek. It was constructed in the summer of 1965 and is located upstream of Niagara Falls Boulevard.. Only minor damages have been sustained within Ellicott Creek Park.

'l'he most recent flood occurred in .0-1arch 1960, inundating parts of the town~ Other arge floods occured in March 1916, January

1929, l>'la:r.-ch 1936, June 1937, March 1940, l'Jiarch 1954 1 Ivlarch 1956, January

1959 and March 1963~

The maximum recorded flood of march 1960 had a discharge determined to be a 20-year event at a location 11 miles upstream of Tonawanda. The greatest knm.,zn flood occurred on march 17, 1936, and was estimated to be a 50-year event~

4 A damage survey of the area flooded by the March 1960 flood was made in the summer of 1962 by the Buffalo District of the COE.. Only minor damages were sustained within the Town of Tonawanda.

Figures 2 and 3 illustrate potential flood elevations within Tonawanda.

Figure 2 - The potential 1 00-year flood \vould be approximately 3 feet lower than the bottom of the Colvin Boulevard bridge over Ellicott Creek.

Figure 3 is approximately 0 .. 5 foot lower than the 9round floor of the bui_ at the Her Road School. 2. 4 Flood Protection Measures

Con;.:;truction of a divnrsion r:hanne-l Jn Ellicott Crc,ek P:1rk from E]i;r:iltt

Cr0('k to Tonawanda Creek, in \:hP i.own, Wd~; (:

Major channelization and diversion channels for Ellicott Creek in the Town of Amherst and widening of the diverionary channel in Ellicott Creek Park between Ellicott Creek and Tonawanda Creek in tl-1e Town of Tonawanda

are planned and funded for construction. However 1 construction may not take place until 1980, and its effects were not considered in this study.

3.0 ENGINEERING METHODS

For the flooding sources studied in detail in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data for this study. Flood events of a magnitude which are expected to be equalled or exceeded~ on the average dur.ing any 10-, 50-, 100-, or 500-year period (recurrence interval) have been select"ed as having special significance for flood plain management and for flood insurance premium rates.

These events 1 commonly termed the 10-, 50-, 100- 1 and 500-year floods, have a 10-, 2-, 1-, and 0.2-percent chance, respectively, of being equalled or exceeded during any year. Although the recurrence interval represents the long-term average period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than one year are considered. For example, the risk of having a flood which equals or exceeds the 100-year flood (one-percent chance of annual occurrence) in any 50-year period is about 40 percent (four in ten) and, for any 90-year period, the risk increases to about 60 percent (six in ten).. The analyses reported here reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes~

3.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish the peak discharge­ frequency and peak elevation-frequency relationships for floods of the st~lected recurrence intervals for each source studied in detail affecting the community~

Hydrologic data on Ellicott Creek were obtained from the Buffalo District of the COE publication dated November 1976 and revised April 1978 (Reference 1). A (statistical) frequency curve was computed from the annual discharges of the since-discontinued

6 Wi.lliamsville gage on Ellicott Creek at ~~~·xJ(? r;ri 1 n t.hc:. of l\mherst. 'ro compensate for the short !W~,- i od of. Beard-type qeneralized discharge information form three stat._i.cr s U:.h basin characteristics similar to Ell:Lcott Creek near Dansville, Little Tonawanda Creek at Linden and Toroavianda

Creek at Alabama~ The resulting discharge-frequency analysis was the data source for flows on Ellicott Creek used in this study¢

The gages mentioned above are a11 USGS qaqeE; ~ ~~e Williarrs~ille gage (no. 04218500) du~vnstrea.rn. of ~Vehrle Dy i V(' \4as ace-d in 19 72 by another USGS gage upsL:ceam of SJ:-H::l Dri.v0 (no. 042185 8). The Canaseraga Creek gage (no. 04225000) is :located west of Dansville, Nev,r

York, in County~ It provl ic records t.o 1919 a_n d continuously from 1919 except '!969~ 'T.'he Linden gage on Lit·tle Tonav;anda

Creek is a partial record s·tation (no~ 042 6500) and has been operating

since 1913. It is located at. L.inden 1 Ne':/ York, in Genesee County. The

Tonawanda Creek gage (no~ 04217500) is located west of 1\.labama 1 New York, in Genesse County {Reference 2)~

The hydrologic information for Tona~,;anda Creek ~-;as obtained from rpqiona1 flood-frequency curves determined by Coodk.Lnd and 0 1 Lie a, Consul tinq Engineers, in their performance of ot.hcr Flood Insurance Studies in Erie and Niagara counties~ 'l'he peak of six USGS gaging stations within the Tonawanda Creek basin were established using the standard log-Pearson Type Ill method and then adjusted for

expected probability~ The re-gional skew value of -0.3 \Vas a computed weighted average considering the natur-al sl

each gage~ A set of curves was t:her~ derived for the basin j graphically discharge and drainage area for the selected return periodsQ These curves provided t.he 'l'ona'tianda Creek

used in this study~ Discharqe val.ut-:;;=:; for Tonav1anda c:n-::ek were also established by Erdman, Anthony Associater; in t.he performance o-f Uv~ .flood Insurance Study for the of Tcmav,randaf Nev; York~

Using information ied by ·the B-uffalo Distxict of the COE and Ontario-Hydro, stage-frequency relation were derived for the

Tonawanda Channel of the Niagara Rivef.' (References 3 anct 4)~

Stage elevations for the-: following gag<::'S on '.f'ona"~dilnda Channel operated the National Oceanic and Administration { NOP-J-1.), National Ocean Survey, LaJ<-e Survt~y Center, 'dETe obt~ained from thE-~ Buffalo District of the COE (Reference 3}~

7 The Black Rock located necn t.he northern end of Squaw Island in the Cit.y of Buffalo, New York, was cc:n-r_ in operation from 1933 until its removal in 1975.

The Huntley Station Gage, locat_ed [301X(hwest of t:he intersectJ_on of Sa'>tJyer !\venue and River Road in the TohT of 'ronawanda, New York, hns been in operation since 1967.

The Tonawanda Island Gage, located on the :;outhwestern side of TonavJanda

Island in the City of North Tonawanda, New York 1 has been continuously in

operation since 1967~

'I'he .Lasalle Gage 1 located near the Lasalle Yacht Club in the City of

Niagara Falls, New York 1 has been continuously in operation since 1965.

From the maximum annual instantaneous peaks, statistical analyses were made for the gages using non-log-Pearson 'rype III distribution (Reference 5) ~ Using a skew of 0. 0 and the standard deviation computed for each gage, stage elevations were computed for the selected recurrence intervals • Profiles for the Niaqara River-Tonawanda Channel were established by connecting the respective stage elevations at the various

gages~

A summary of the drainage area-peak discharge relationships for the streams studied by detailed methods is shovlY1 in Table 1, " Summary of Discharges. 11

TABLE 1 - SUMMAHY OF DISCHARGES

DRAINAGE l\REJ\_ PEAK DISCHARGES (cfs) FLOODING SOURCE AND LOCATION (sq. miles) 10-YEAR 50-YEAR 100-YEAR 500-YEAR

ELLICOTT CREEK

at Colvin Boulevard 3 f 300 4' 400 4,900 6,300

TONA\t.JANDA CREEK At Twin Cities Memorial

Hiqhv;ay 1 about 2, 700 feet down stream of corporate limits S25 11 { 70 0 15,900 17, 150 22,000

3 ~ 2 Hydraulic Analyses

Analyses of the hydraulic characteri sties of the flooding sources studied in detail were carried out to eE->timates of the elevations of

8 floods of the Sfc1ectecl. :t'ecurrcnce i:ntervaJs alon(; each of thrcs::·: flood sources~

flOWll in } 1978 ( Hcof PY."C(JC0 (;). were obtained by field measurernent ~ J\ ll bri r c;ulve:rt.s and dams 1tJe:ccc surveyed to obt.:ain elevation data and structural geometry.

\Vab::,or-surface elevations were using the COE HEC·-2 step- back'.vater computer model (References 7 and 8)- The starting water-surface elevtion for Ellicott Creek was obtained from elt-:vation::o; computed for the Flood Insurance Study of the City of Tona\vanda

(Reference 9) ~

!1 culvert on the south bank of Ellicott Creek about 1, 000 feet upst_·r:-eam of Colvin Boulevard permits flood flmvs from Ellicott Creek to ent~er the area south of Ellicott Creek Road~ The area is inundated by shallow flooding~ Similar floodwaters cominq from the City of Tonawanda at the

western corporate limits also co~1tribubc: to this area of shallow flooding.

Water~surface elevations for the N.iaqara Rive:c-'l'onawanda Channel were taken cU from the Flood Insurance Study for the Town of Grand

Island 1 New York (Reference 10 J. \tJater-surface elevations for Tonawanda Creek v.;ere taken directly from the Flood Insurance Study for the City of

North Tonawanda t New York (Reference 11 ) .

coefficients (Hanning's "n") for Ellicott and Tonawanda Creeks

were determined by field inspection~ The range of roughness values for the overbanks of Ellicott Cret:l<;" \r.Jas between 0. 060 and 0 ~ 075, and the channel ro value was 0.035. For Tona·,..Janda Creek, the overbank 0 n" ranged between 0~065 and 0~100! and thf.:~ channel "n° ranged between 0~020 and 0~035~

Flood water-surface elevations t.o an accuracy of Q.S foot for floods of ·the selected recurrence int,ervalsq Loca.t.i.ons of selected cross sections used in the hydraulic are shown on the Flood Profiles {Exllibit 1 }~ For st.ream ses'Itlents for which a is (Section 4~2), ~1elected cross-section locations are also shovm on the Flood Boundary and F1oodway Map (Exhibit 3).

Al.1 elevations used in this study are referenced to the National Geodet.i c

Vertical Datum of 1929 (NGVD) 1 formerly referred. to as Sea Level Datum of 929~ Loca·tions of the e1evat.ion rE;feren.ce marks used in the are sho\vn on the rnaps.

The l.C for tJ--,j_£.; study are based on t.he effects of unoh- structed flow~ The flood elevat.ions shown on the profiles are valid or,ly if hydraulic st:r:·uctures remain unobstructed and do not. fail.

9 4.0

adopt sound flood plain manaqement. programs# TfH,rrforcc, ,c-~ach Flood Insurr1nce Study includes a flo

4. 1 Flood Boundaries

In order to provide a national standard v-:ithou·t. reqional discrimir,at.ion, the 100-year flood has been lJ}-' the FIA as t.he basEc f load for puy- poses of flood plain management measures~ The 500-year flood is employed to indicate additional areas of flood risk in the community. For each st·ream studied in detail, the boundar.-ir::.s of the 100- and 500-year floods have been delineated using the flood elevat.ions determined at. each cross section; between cross sections, the boundaries were interpolated

topographic maps at a scale of 1:2,400 and at a scale of 1:24 r 000 \IJi-th a

contour interval of 10 feet ( Refe~cences G and 12} In cases where ·the 100- and 500-year flood boundarfes are close together, only the 100-year boundary has been shown~

The 100-year flood boundaries for the ons of Ellicott Creek, 'ronawanda Creek and the Niagara Ri ver-Tonmvanda Channel which were

studied by approximate met~hods were delinea-ted using the Flood Hazard Boundary Map for the Tov./nof Tona'A'anda, which 1das published in ,June 1974 and revised in CJctober 1975 (Reference 13).

The boundaries of t.he 100- and 500-year floods are shovm on the Flood Boundary and Map (Exhibit 3). Small areas within the flood boundaries may lie above the flood (:le"\ations and, thereforer may not be ec-t to flooding. to lirnltat.icns of tJ1e map scale and lack of

detailed topographic (1ata 1 such areas are not shown~

4.2

Encroachment_ on flood such as artif~cial fill, reduces the capacity, increases th:::; flood height.s of streams, and increases flood hazards in areas the t:I1croac::hm.cnt itself~ aspect of f load management involves balancing the economic qain from flood a_j_n increase in flood hazar de For purposes of ·the .Flood Insurance Program, th0 concept of a is used as a tool to assist hKCll communities in this aspect_ of

flood plain management~ Under this concept, the area of the 100-year flood is divided int~o a and a The is the channe-l of a stream plus any acent flooc1 areas that must be free of encroachment in order tJD_t the 100-year flood can be carried without substantial increases in flood Minimum standards of the

10 FLOODING SOUHCE FLOODWAY BASE FlOOD WATER SURFACE ELEVATION SECTION MEAN WITHOUT WITH WiDTH 1 RE• •Tnov !NCR EASE CHOSS SECTION l)!STANCE AREA VELOCITY FLOODWAV (FT J '(;;'~~~)' (FEET) ISO. FT.I IF.P.S.) " (NGVDI (NGVD)

. E:1 icott Creek' 8 6501 * 1, 827 2.7 572.2 572.2 573. 1 0 ~ 1 572.4 572.4 57J $4 1 • [I 9 f 8 "1 * 1' 945 2.5 c 10,81 1 * 1 '520 3~2 572.6 572~6 573~5 0.9

Tonawanda Creek 2002 * 4, 713 3.6 572.0 572.0 572~7 0$7

I '

I

• I 1Feet above mouth above corporat,e limit.s *Floodway coincident. wit~h channel banks

FEDERAL EMERGENCY MANAGEMENT AGENCY Federnt lnsunmce f TO N Of TONA AN It HU 0 REf AND~. Fll\ lim_lt such increases in flood hniqhts to 1~0 foot_, provided UJat

hazardous vE~loc ities ar0 not~ produced. ThE? f 1 r;r>h;ay;; i_n this report arc-

pn:sPnt,ed to local aqcncies as mininmrn ~-:t:andar,·is that can be adopted or that: can be used aE; a basis for addit,.-ionaJ studir:::.::;8

The floodways presented in this study were computed on the basis of equal conveyance reduction from each side of the flood plains. The results of thesEo computations are tabulatl~d at selected cross sections for each stream segment for which a floodway is computed (Table 2).

A floodway is not appropriate in areas such as those that may be inundated by flood'>"laters from the Niaqar a River-'ronawanda Channel, which generally are a result of high-vJater e1E:vationc; on Lake Erie. Thus, no flodway was computed for the Niagara Ri 'Jer-Tonawanda Channel. The floodways computed for Ellicott and 'l'onawanda Creeks v1ere found to be coincident with the channel banks~

As shown on the Flood Boundary and Floodway Map (Exhibit 3), the floodv:ay widths were determined at. cross sections; between cross sections, the

boundaries were interpolated~ In case,s where the boundaries of the flood- way and the 100-year flood are either close ·together or collinear, only the floodway boundary has been shown.

The area between the floodway and the boundary of the 1 00-year flood is termed the floodway fringe. The floodway fringe thus encompasses the portion of the flood plain that could be completely obstructed without increasing the water-surface elevation of the 100-year flood by more than 1.0 foot at any point~ Typical relationships between the floodway and the floodway fringe and their significance to flood plain development are shown in Figure 4.

5. 0 INSURANCE F,PPLICATION

In order to establish actuarial insurance rates, the FIT"- has developed a pro-· cess to transform the data from the engineering study into flood insurance criteria. This process includes the determination of reaches, Flood Hazard

Factors (FHFs) 1 and flood insurance zone designations for each flooding source the Tovm of 'rona wanda.

5.1 Reach Determinations

Reaches are defined as len of watercourses relatively the same flood hazard, based on the average weighted diffet-ence in water-surface elevations between the 10- and 0 floods. This difference does not_

12 ----100 YEAR flOOD PLAIN ------J

FlOODWAY_~+~------FLOOOWAY------f--FLOOOWAYFRINGE ...J' 1--I FR!NGE

r-STREAM -j I CHANNEL I I

FLOOD ElEVATION WHEN I I CONFINED ""I,"'~OODWAY I I I ENCROACHMENT ~ I , ENCRS2~HMENTI r I " I c D --- 1/i?P-==-

AREA OF FLOOD PLAIN THAT COULD FlOOD ElEVATION BE USED FOR DEVELOPMENT BY BEFORE ENCROACHMENT RAISING GROUND ON FLOOD PLAIN

UNE A- BIS THE FLOOD ELEVATION BEFORE ENCROACHMENT UN£ C- 0 IS THE FlOOD ElEVATION AFTER ENCROACHMENT

•SURCHARGE NOT TO EXCEED 1.0 FOOT If lA REQUIREMENT) OR LESSER AMOUNT IF SPECIFIED BY STATE.

FLOOOWAY SCHEMATIC Figure 4

have a variation greater than that indicated in the following tahle for more than 20 percent of the reach.

Average Difference Between 10-· and 100-Year Floods Variation

Less than 2 feet o.s foot 2 to 7 feet 1 • 0 foc·t

7~1 to 12 feet 2.0 feet 0-1ore than 12 feet 350 feet

The locations of the reaches det-ermined for the flooding sources of ·the Town of Tonawanda are shown on the Flood Profiles (Exhibit 1) and are· summarized .in the Flood Insurance Zone Data Table (Table 3).

13 5.2 Flood Hazard Pactors

The FHF .is the F'IA device used to cor-r-elate flood information 1tiit!'1 lnstn--

ance rate tablesQ Correlations bct:\>Vnen l'roperty datn2hJP from flocds z:n~'-1 their FHFs are used to set actuar ia insurance _premi urn rate tables ba.sed on FHFs from 005 to 200.

The FHF for a reach is the average difference between the 10- and 1 00-year flood ~,.. rater-surface elevations expressed to the nearest 0. 5 foot, and shown as a three-digit code~. For example, if the difference between water-surface elevations of the_ 10- and 100-year floods is O. 7 foot, the FHF is 005; if the difference is 1.4 feet, the FHF is 015; if the difference is 5.0 feet, the FHF' is 050. ~Vhen the difference between the 10- and 1 00-year water-surface elevations is greater than 10. 0 feet, accuracy for the FHF is to the nearest foot~

5.3 Flood Insurance Zones

After the determination of reaches and their respective FHFs, the entire incorporated area of the Town of Tonawanda was divided into zones, each having a specific flood potential or hazard. Each zone was assigned one of the following flood insurance zone designations:

Zone A: Special Flood Hazard 1\reas inundated by the 1 00-year flood, determined by approximate methods; no base flood elevations shown or FHFs determined.

Zone AH: Special Flood Hazard Areas inundated by types of 100-year shallow flooding where depths are betvveen 1.0 and 3 .. 0 feet; base flood elevations are shown, but no FHFs are determined.

Zones A2 and A3: Special Flood Hazard Areas inundated by the 100-year flood, determined by detailed methods; base flood ele­ vations shownr and zones subdivided according to FHF.

Zone B: Areas between the Special Flood Hazard 1\rea and the limits of the 500-year flood, including areas of the flood that are protected from the

100-year flood dike 1 levee, or other 'dater control structure; also, areas ect to certain types of 100-year shallow flooding where depths are less than 1. 0 foot; and areas ect to 100-year flooding from sources with areas less than 1 square mile. Zone B is not subdivided.

zone C: Areas of minimal flooding.

14 1

''"' .

!

< -·'"'\ "} -L5 ooQ .. , f ~ _, (} ~ ~'"

Reach ·t '' ' -o ~ 9 -0.2 +0' .5 01

Tona\rVar,da

0! 03 0-1 ,.5 ' ,4 15

rnst map

AGENCY N of

~!' t\. Table: 3~ "Flood Lnsurance ZonE: Data," summariz<'S th0 flood el0vat.ion dif­

ferences~ FHFs, flood insurance zonesi and base flood elevations for thf:,

floodinq sources studied in dt?tail in the Town of 'I'oncnvo.nda~

5.4 Flood Insurance Rate Map Description

The Flood Insurance Rate Map for the Tmiln of Tonawanda is, for insurancE:: purposes, the principal result of t>he Flood Insurance Study~ This m,'lp (published separately) contains the off.icial delineation of flood insurance zones and base flood elevation lines5 Base flood elevation lines show the locations of the expect0d whole-foot water-surface

elevations of the base (100-year) flood~ This map is rleveloped in accordance with the latest flood insurance map preparation guidelines published by the FIA.

6.0 OTHER STUDIES

The USGS Flood Prone Area. Map covering the 'I'ovvn of Tonawanda defines the 100-year flood boundary (Reference 14). 'These flood-prone areas were delineated by the USGS based only on readily available information. Because of the approximate nature of the results, the flood boundaries depicted therein were used to check the accuracy of this study.

The Buffalo District of the COE has issued a series of reports on flood control and allied purposes for the Ellicott Creek Basin. Reports were issued in April 1939, January 1968 (reprinted June 1971), May 1970, October 1972, August 1973 and November 1976 (updated April 1978) (References 15, 16, 17, 18 and 11~ The 1939 report is unavailable. The 1968 report delineated a

100-year flood boundary and profile which scr

1972 and 1973 reports wert~ geared t:.oward fJ ood-contxol solutions. They are also sumrnarized in the November 1976/April 197H rer>ort. This last report was prepared to determine the economic, social and environmental acceptability of a plan for flood control and allied purpose's on Ellicott Creek. The plan has not been implemented.

The USGS has maintained the Wi liamsvillP galJC no~ 04218500 and no. 04218518 on Ellico·tt Creek for 24 years~ *4 miles northwest of

~·hlliamsville and has a area of 77 ~ square miles~ Their Type III flood frequency of field ciata substantiates the accuracy of the discharges obtained from ·the above-mentioned COE reports (References 19 and 20} ~

J\ Counties Regional 11ay 1973 (Reference 21). Its purpose v;a s t_o rccom.."'Ttend solutions to ems common to Erie and Niagara

16 Count~ 'i es. report. The 10- and urbanization witt1 100-year boundaries were detenni 1es usirHJ topoqrapll rrk1J'< with 10-foot and 20-foot contour intet:va1"">• Tbro infonT:ation qenerated 'JiE·s strictly for purposes., l\.s recomrnended in the report i tsrl f, more accurate profiles and flood plain zoning flood insurnace programs~

There are completed and Flood Ins'.n~ancc: ,'3tudies in many of the communities adjacent to the Town of Tonawanda~ Completed studies are avai.lable for the 'l'own of Grand Island and t,he C'i ty of Tonawanda ( Referer~ce.:_~ 10 and 9). Ongoin9 studies are beinq p1:;rfonrec1 for the; City of Buffalo and the Towns of f--:u'Tlherst and Clarence and the' Cj tv of North Tonawanda ( Rcfcorences

2 2, 2 3 , 24 and 11 ) ~ Conti nuJ ·ty of all p-r_:or: t i nent f lond data among ttJe:3(' studies has been maintained~ Flood bounz_k;;ies on Ellicott Creek at the Tovn of Tonawanda and City of Tonawanda corporate ]_ :Lmits do not agree because this study used more detailed topographic rnaps than were used in the previously published study for the City of Tonawanda.

'I'his study is authoritative for purposes of the Flood Insurance Program, and the data presented here either supersede nr are compatible with previous deter­ minations.

7. 0 LOCATION OF DATA

Survey, hydrologic, hydraulic, and otJJt:=T pertinent data used in this study can be obtained by contacting t_he office of t_-_he Insurance and Mitigation Divisior of the Federal Emerqency Ha:na(_Jemen-t Aqcncy; i

8.0 BIBLIOGRAPHY AND REFERENCES

1. 1 Buffalo District, Ellicott Creek, New York, I Plan Formulation ~ Final, Buffalo, New F.pri 1 1978 ~

2. the lnteriorf Geoloqical Survey, .£~ .£:}c>c-ds in t.he United States, Part 4. ~Vashington, D. C~, 1965.

3. Bill Erdell, River Centred Divisionr Uo s .. Army Corps of Engineers, Buffalo District, Persona.l Communication~

17 4~ OntJxrio-Hydro Corporat,i0n, Ci..v:i.l ~Yorks ])(•part:rn(•nt, "Caqe !Ju.ta on Ni<~qnr-a River," ished} ~

5. VJa ter Resources Council; "Guidelinc~s for Determin_i.nq Flood -F'1ow ;_,~rc­

quency," Bulletin 17 1 Washington 1 D~ C., Narch 1976 ~

6. Lockwood ~lapping, Inc~, of Rochester, Nee;..; York, Photomosai c Haps compiled from aerial photos, Scale 1:2,400: Erie and Counties, New York,

flown April 13, 1978~

7. u. s. r~rmy Corps of Engineers I Hydrolog_1 c Engineering Center' HEC-2 Surface Profiles, Davis, California, October 1973, Updatect

November 1977~

8~ U,. S. Army Corps of Engineers, Hydrologic Enqincerinq Center, of the HEC-2 Routines, ~. Davis, California, June 1974.

9.. U, S. Department of Housing and Urban Development, Federal InsurancP

Administration, Flood Study, City of Tonawanda 1 Erie County,

New York, VJashington, D. c. i February 1979~

10. U~ S. Department of Housing and Urban Development, Federal Insurance Admi nistra·tion, Flood New York, Washington, D. c., July 1979.

11 ~ Federal Emergency Management Agency, Federal Insurance Administration, Flood Insurance StudyF of North Tonawanda, Niagara County, New York, Washington, D. C., July 1979.

12. U~ S* Department of tJJe lnt.r:.rior, Geoloqical Survey, 7.5-Ninute Serins Topographic Mans, Scale 1:24,000, Contour Interval 10 Feet: Buffalo Northeast, New York, 1965; Buffalo Northwest, New York, 1965; 'ronawanda East, New York, 1965; Tonawanda VJest_, New York, 1965.

13. U~ S~ Department of Urban Dt;vclopmPnt, Federal Insurance Administration, Flood Map, Tov~ of Tonawanda, Erie New York, Washington, D. C., June 7, 1974, Revised October 24, 1975.

14~ U~ S~ Department of the Interior, Geol cal SuYvey, 7.5-Minute of

Flood Prone~~ Scale 1:24 1 000; Buffalo Northeast, New York, 1970; Buffalo Northwest, New York, 1970; 'Tonawanda East, New York, 1970 i Tonawanda \\lest, New York, Ne1d York, 1970~

18 15. u. S. Army Corps of r;eers, Buffalo Dist,:rict 1 Flood Plain Ellicott in of

Amherst, Ne\.v York, Buffalo 1 Nt'"'w York, January 1968 {

16~ u. S. r--.rmy Corps of Enqineersf Buffalo Dist_rict and the Sta-te of NC\·;

York, Joint Report ~ and Idlie:d Purposes on

Creek, Buffalo, New Yorkr May 1970~

17. S. Army Corps of Enqi.neers: Buffalo D.istrict, Flood Plain Informat~ion

Report 2!!. Ellicott in the anc;2 ?f .:&ancaster and Alden, Buffalo f Nev~ York, October 1972~

18. U.S. Army Corps of B:Jffalo District_, Creek Restudy Reoort Creek Watershed Main Report, and Surrunary Report, Buffalo, New York, August_ 1973.

19. U. s. Department of -the In-ccrior 1 Geolocrical. Survey, Log-Pearson IIl Flood Frequency Resources Bulletin Systematic Record of Vhlliamsville gage no9 04218500 and 04218518 on Ellicott Creek, Albany, New York, 1978.

20. U.s. Departme'nt of the Interior, Ceo} ca Survc~y, Loq-Pear son Flood Frequencz Council Guideline~, Systematic Record; of the \'Jilliamsville gage no$ 04218500 and 04218518 on Ellicott Creek, , New York, 1978~

21. Erie and Niagara Counties Planning Board, Regional Storm Drainaqe Manaaeroent Plan, Amherst., New York, May 1973~

22. Federal Emergency Management, Agency, Federal Insurance hdrni nistration, Flood Insurance of County, ~York, (Unpublished).

23* Federal Emergency Management Agency, Federal Insurance Administration, Flood Tovm of New York

24, Feder a Emergency r.;anaqc:ment AcF-:ncy 1 Fe dc:ral Insurance Administration r ---l''lood Insurance of New York, (Unpublished).

19 Erie and Niagara Counties Regional Planning Boardr Storm Drainage Design Manual, July 1972.

Eric-Niagara Counties Reqional Planning Board, Surface VJater ~ the Basin, !~ew York, Basic Board ENB- 2, 1968.

State of New York, Department of Environmental Conservation - Water Resources

Commission Bulletin No. 67 1 i'-iaximum Known Discharaes of New York Streams, 1970.

U .. s. Army Corps of Engineers, Buffalo District, Buffalo Hetropolitan Area,

Ne~ York f ~ Resources Management in Tonawanda Creek VJatershed, Pinal Feasibility Report, 1976, Updated 1978.

U. s. Department of the Interior, Geological Survey 1 VJater Resources Data for New York, Part l' Surface Water Records, Albany, New York, Published Annually 1963 - 1973.

Water Resources Council, "A Uniform Technique for Determining Flood Flow

Frequency," Bulletin 15, Washington 1 D. C., December 1967.

20 m+ +- I ~ j._ ~~~I _j__ I 'Ht H

+

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~ I ' it + ---+- +t r-t+H z 565 0 r ! ' i= I ' <( • l- w> -+-+ ...1 ! ! w + .u ;- + ! • 560 + ++ -;,LL t

I ' LEGEND -t r-+r I ! I i i 500 YEAR FLOOD +' 100 YEAR FLOOD 50 YEAR FLOOD . ctr --f 10 YEAR FLOOD ! STREAM BED

CRO~ SEf;!ION '' "-'" 8.0 8.5 9.0 9.5 10.5 11.0 STREAM DISTANCE IN THOUSANDS OF FEET ABOVE MOUTH 01P ELEVATION IN FEET (NG\101 m m Ci) m "' " w"

i l

f 0

1- t

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I

t _+ z •+ . ,ttH+++-H ::r:it +; ;t tr , . r' + I - , t +

' ..r+r ::} +- >-u 2 '"'(!) c0 zw 100 VEAR FLOOD 0"' 0- 2 5 w~ 1-- 0: 50 YE ..euq FLOOD <.?E w oc- 14.'-' y'EAR FLOOD w:? c ::;;~ :z STREAM BEO "'"-J"- <{ IX Q CliOSS SECT!Of-4 U! LOCAT!ON 0 1- w "" 0.0 5.0 12.5 15.0 STREAM DISTANCE IN HUNDREDS OF FEET ABOVE CGRPOR/\TE UM!TS 03P