GEOLOGICAL SURVEY 

CIRCULAR 601-C 

Flood-Hazard 

Mapping in 

Metropolitan Chicago 

Flood-Hazard Mapping 

in Metropolitan Chicago 

By John R. Sheaffer, Davis W. Ellis, 

and Andrew M. Spieker 

WATER IN THE URBAN ENVIRONMENT 

G E 0 L 0 G I C A L S U R V E Y C I R C U LA R 601-C 

Washington 1970 
United States Department of the Interior 

THOMAS S. KLEPPE, Secretary 

Geological Survey 

V. E. McKelvey, Director 

First printing 1970 

Second printing 1972 

Third printing 1976 

Free on application to Branch of Distribution, U.S. Geological Survey 

1200 South Eads Street, Arlington, Va. 22202 
FOREWORD 

Urbanization-the concentration of people in urban areas and the 

consequent expansion of these areas-is a characteristic of our time. It has 

brought with it a host of new or aggravated problems that often make new 

demands on our natural resources and our physical environment. Problems 

involving water as a vital resource and a powerful environmental agent are 

among the most critical. These problems include the maintenance of both 

the quantity and quality of our water supply for consumption, for 

recreation, and general welfare and the alleviation of hazards caused by 

floods, drainage, erosion, and sedimentation. 

A prerequisite to anticipating, recognizing, and coping intelligently with 

these problems is an adequate base of information. This series of reports is 

intended to show the relevance of water facts to water problems of urban 

areas and to examine the adequacy of the existing base of water information. 

6 ;( ./~ut/'t~k__ I 

E. L. Hendricks, 

Chief Hydrologist 

III 

CONTENTS 

Page 

Foreword . . . . . . . . . . . . . . . . . . . . . . . III 

Introduction . . . . . . . . . . . . . . . . . . . . . C I 

Flooding in Metropolitan Chicago . . . . . . . I 

The concept of flood-hazard mapping . . . . 3 

What is a flood-hazard rna p? . . . . . . . . . 3 · 

Profiles and probabilities . . . . . . . . . . . 3 

How to use a flood-hazard map . . . . . . . 3 

The Metropolitan Chicago flood-mapping 

program . . . . . . . . . . . . . . . . . . . . . 6 

Phase I . . . . . . . . . . . . . . . . . . . . . . . 7 

Phase 2 . . . . . . . . . . . . . . . . . . . . . . . 8 

The formulation of phase 3 . . . . . . . . . . 8 

The Metropolitan Chicago flood-mapping 

program --Continued 

Page 

The crest-stage gage network. . . . . . . . . . C 9 

Usefulness of flood-hazard maps in 

urban development . . . . . . . . . . . . . . II 

Regulation of private development . . . . . 12 

Purchase of property for public use .. : . 13 

Development of public facilities . . . . . . . 13 

Guidelines (planning) for future 

development . . . . . . . . . . . . . . . . . . 13 

Selected references . . . . . . . . . . . . . . . . 13 

ILLUSTRATIONS 

Page 

Figure I. Map of the Chicago metropolitan area showing location of quadrangles included 

in flood-hazard mapping program ................................. C2 

2. Flood-hazard map of part of the Elmhurst quadrangle . . . . . . . . . . . . . . . . . . . . . . 4 

3. Graph showing profiles of floods on Salt Creek . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

4. Graph showing frequency of floods on Salt Creek at Addison (Lake Street) . . . . . . . 6 

5. Map showing location of crest-stage gages in the Chicago metropolitan area . . . . . . . . I 0 

6. Sketch of a typical crest-stage gage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

TABLES 

Table 1. Scope of phase 1 of flood-mapping program, July 1961 to June 1966 

2. Scope of phase 2 of flood-mapping program, July 1966 to June 1969 

Page 

C7 

8 

v 

Water 1n the Urban Environment 

Flood-Hazard Mapping in Metropolitan Chicago 

By John R. Sheaffer1

, Davis W. Ellis, and Andrew M. Spieker 

INTRODUCTION 

The effective management of flood plains 

consists of more than building detention 

reservoirs and levees. As urban pressures are 

forcing more and more developments on flood 

plains, such devices as flood-plain regulations 

and flood proofing are coming into wider use. 

These devices, however, require information as 

to what areas are likely to be flooded. The need 

for flood-plain information is further intensified 

by Federal legislation such as the National Flood 

Insurance Act of 1968 (Title XIII, Public Law 

90-448) and recent Federal policies on use of 

flood plains (U.S. Congress, 1966; Executive 

Order 11296). 

The present report describes how these needs 

are being met in the Chicago SMSA (Standard 

Metropolitan Statistical Area) by a cooperative 

program involving the six counties of the 

metropolitan area-Cook, Du Page, Kane, 

Lake, McHenry, and Will-the Northeastern 

Illinois Planning Commission, the State of 

Illinois, and the U.S. Geological Survey. This 

unique flood-mapping program, in progress since 

1961, has resulted in coverage of nearly the 

entire six-county metropolitan area by maps 

showing the flood hazard. Figure 1 is a map of 

the area showing the extent of coverage in June 

1969. Quadrangles showing an HA (U.S. 

lcenter for Urban Studies, The University of Chicago; 

formerly with the Northeastern Illinois Planning 

Commission. 

Geological Survey Hydrologic Investigations 

Atlas) number are published and available for 

sale at the Northeastern Illinois Planning 

Commission, 400 West Madison Street, Chicago, 

Ill. 60606, or the U.S. Geological Survey, 

Washington, D.C. 20242. (Price is 75 cents 

each.) Quadrangles without an HA designation 

are in progress or are scheduled for future 

mapping. At present this coverage is about 85 

percent complete. Metropolitan Chicago is the 

only large metropolitan area in the United States 

for which this information is so widely available. 

The purpose of this report is to describe how 

the program originated and is being carried out, 

the outlook for improving this program to meet 

the changing needs of the rapidly urbanizing 

metropolitan area, and the various ways flood 

maps can be used by individuals and public and 

private institutions. 

FLOODING IN METROPOLITAN CHICAGO 

Floodflows in the rivers and waterways of 

Metropolitan Chicago have periodically spilled 

from their chanJlels and inundated the adjacent 

lowlands or flood plains. The earliest recorded 

flood in the Chicago area occurred on March 29, 

1674, when the explorer priest Marquette and 

his companions were driven from their camp 

near Damen Avenue by high water coming 

through Mud Lake, from the Des Plaines River. 

However, such overflows did not become 

hazards, except possibly to navigation, until 

Cl 
4 2'30' 88'00' 

EXPLANATION 

D 

Mapped in phase 1 

D 

Mapped in phase 2 

To be mapped in phase 3 

Not included ~ in mapping program 

Figure 1.- The Chicago metropolitan area showing location of quadrangles included in flood-hazard mapping program. 

development of the flood plains gave the floods 

something to damage. 

In retrospect, it is conceivable that if 

adequate land-use planning, based on sound 

hydrologic data in conjunction with regulatory 

and flood-proofing measures, had guided the 

development of our flood plains, there would be 

little, if any, improper use today and no major 

flood problems would exist. 

Flood damages have been steadily increasing 

as urban sprawl has engulfed many flood plains 

C2 

and subdivisions have been located on sites 

subject to flooding . The absence of accurate 

information on these areas subject to flooding 

has bee n a limitation on efforts to formulate a 

comprehensive flood damage reduction program. 

The need for this information is particularly 

acute in Metropolitan Chicago and other 

topographically similar regions of flat terrain 

and poorly developed drainage, where the flood 

plains are not readily perceptible to the human 

eye. 
THE CONCEPT OF 

FLOOD-HAZARD MAPPING 

Flood-hazard mapping is a means of providing 

flood-plain information for planning and 

management programs. Such information should 

be designed to assist officials and private 

interests in making decisions and alternative 

plans concerning the development of specific 

lands subject to flooding. Proper use of 

flood-hazard mapping will help to: 

1. Prevent improper land development in 

flood-plain areas. 

2. Restrict uses that would be hazardous to 

health and welfare and which would lead to 

undue claims upon public agencies for remedy. 

3. Encourage adequate stream channel 

cross-section maintenance. 

4. Protect prospective home buyers from 

locating in tlood-prone areas. 

5. Preserve potential for natural ground-water 

recharge during flood events. 

6. Guide the purchase of public open space. 

7. Avoid water pollution resulting from the 

.flooding of sewage treatment plants and solid 

waste disposal sites that were located on flood 

plains. 

WHAT IS A FLOOD-HAZARD MAP? 

A flood-hazard map uses as its base a standard 

U.S. Geological Survey topographic quadrangle 

which includes contours that define the ground 

elevation at stated intervals. Each of the 

quadrangles covers an area 7% minutes of 

longitude wide by 7% minutes of latitude deep, 

or approximately 57 square miles. The scale of 

the tlood maps is 1:24,000, or 1 inch equals 

2,000 feet. The area inundated by a particular 

"flood of record" is superimposed in light blue 

on the map to designate the "flood-hazard 

area." Also marked on the flood-hazard rna p are 

distances (at Yz-mile intervals) along and above 

the mouth of each stream and the locations of 

gaging stations, crest-stage gages, and drainage 

divides. Figure 2 shows part of the Elmhurst 

quadrangle, a typical flood map, reproduced at 

the original scale. 

469-471 0- 72 - 2 

PROFILES AND PROBABILITIES 

Accompanying the flood-hazard map are 

explanatory texts, tables, and graphs, which 

facilitate their use. One set of graphs shows the 

linear flood profiles (see fig. 3) of the major 

streams in the quadrangle; from them, the user 

can tell how high the water rose at any given 

point during one or more floods. 

Another valuable tool (fig. 4) is a set of 

graphs showing probable frequency of flooding 

at selected gaging stations. These charts indicate 

the average interval (in years) between floods 

that are expected to exceed a given elevation. 

Frequencies can also be expressed as 

probabilities which make it possible to express 

the flood risk or "flood hazard" for a particular 

property; for example, a given area may have a 

5-percent chance of being inundated by flood 

waters in each year. 

HOW TO USE A FLOOD-HAZARD MAP 

To illustrate the use of a flood-hazard map, 

assume that you own property along Salt Creek, 

near Elmhurst and about half a mile south of 

Lake Street. Perhaps you plan to build there, 

and you want to know the risk of being flooded. 

You examine the Elmhurst quadrangle 

flood-hazard map (fig. 2) and note that your 

property is located at a point 23.5 miles above 

the mouth of Salt Creek. (The river miles are 

shown on the map.) 

One of the graphs accompanying the map is a 

flood-frequency curve for Salt Creek (fig. 4). 

This curve, however, is for a particular point on 

Salt Creek-the Lake Street Bridge. To apply 

the flood-frequency relationship to your own 

property will require an adjustment for the 

water-surface slope between the two points. So 

you consult another graph, the one which shows 

profiles or high-water elevations, of floods along 

Salt Creek (fig. 3). There, you find that at the 

Lake Street Bridge (river mile 24) the 1 9 54 

flood crested at 671.5 feet, while at the point 

you are interested in (river mile 23.5) the crest 

was at 671 feet. 

C3 
SCALE 1:24 000 

t======== /2~=======1 MILE 

A PPROXI MATE MEAN 

DEC LINATION. 1963 

CONTOUR INTERVAL 5 FEET 

DATUM IS MEAN SEA LEVEL 

EXPLANATION 

Area flooded 1954, 1957 

Boundary of 1954 flood 

Boundary of 1957 flood 

Drainage divide 

River mile measured 

along stream channel 

, .........

.... ........

............ ... .. ! ..... .............. .... ... .... .... .... ···· ······· ······· · 

1954 

----1-%-7----

Figure 2.-- Flood-hazard map of part of the Elmhurs1 quadrangle. Adapt ed from Ellis, All en. and Nuehre ( 1963 ). 

C4 
~---~N 

Q) 

3l8N""HO""nO 

3 Nll""l""d 

----------ro--------------~r-------------------

0 318N""Ha""no 'tJ 

~--------~ ~ ~ ----r---~r----------N_O __ l_8_N_I_l_H_"" __ 

anua/\"" a:lUaJM~l 

'- ::::lCIJCOO 

~~;::g ----~-gj, ~ 0 ~ 

~ ~ E ~ 

gj,~ ~ \\ ~ ~ 0 

I\ \ ..!. 

I\ ~ 

\

\ '-

\ 0 

\ \ 

a. 

CIJ 

E 

c 

§ 

CIJ 

E 

£ 

0 

z 

w I- ....I (f) C) 

o::z 

::J<( 

IO:: 

~0 

....1<( 

w::J 0 

p~OJI!eH :JIJI:Jed pue 

'1ned lS'aa'>1neMIIIIIJ o~e:JILI:) 

,, 

\\. (61 1\~MLI~IH awlS) 

,-p~OH '>1J~d ~UIIUI \, 

\ \ 

\' \ 

z 

0 

I-

<{ 

z 

<{ 

_] 

0... 

X 

w 'tJ 

0 

0 

G:: 

,..._ 

l!) 

0'1 

1:?; ::::l 

-, 

'tJ 

0 

0 

G:: 

0 

\!) 

0'1 

...... 

c 

§a. 

CIJ CIJ 

E E 

133~ NI '13A31 V3S NV3W 3AOSV NOI!VA313 

LLI 

I- ....I (f) C) 

0:: z ::J<( 

IO:: 

~0 

....1<( 

w::J 0 

LLI 

w ....1 

....10 

<CZ 

o<e 

(f)O:: 

~~ I::J 

0 

M 

00 

...... 

~ 

w 

w 

a:= 

u ...:.:: 

0 

1- ~ _J u 

c:::C _. V) :::i 

C/) 

LL.. .- 0 0 

:::c r/J 

"0 

1- :) 

::::> Q 

0 >::;::::: 

::E ·-0 

w r/J 

> cu 

0 '-+-

c:a c c:::C 0: 

I V) I 

w rr-, _J 

1-1 ~ ::E :::; 

M 

a:= ~ w 

> 

1-1 

a:= 

cs 
....J 

w 

> w 

....J 

I 

I 

z 

0 

t-

< 

> 

w 

....J 

w I . I, I 

670 3':---__J4L__-----!_5 l 

_ _J_6_7L-8L-9"------Ll0-------,"-15=-------::2:'-:-0-----:2:'=-5-- i 30 j 

40 

I 

50 

RECURRENCE INTERVAL, IN YEARS 

Figure 4.-Frequency of floods on Salt Creek at Addison (Lake Street). 

Returning now to the flood-frequency curve, 

you find that the 1954 flood has an 8-year 

"recurrence interval," meaning that, over a long 

period of time, floods can be expected to reach 

or exceed that level on an average of once every 

8 years. That level, you have already found, is 

6 71.5 feet at Lake Street and 671 feet at your 

property. Another way of thinking of it is this: 

if you were to erect a building on your property 

at 671-foot elevation, the chances of a flood 

reaching the structure in any given year would 

be approximately one in eight. These are only 

odds-probabilities-and the actuality may be 

better or worse. But the odds are poorer than 

most property owners are willing to accept, so 

you will probably want to seek better odds at 

higher ground. 

Suppose you were willing to accept a flood 

risk of one every 25 years: What is the ground 

elevation at which a building should be situated 

to enjoy that much security? 

The flood-frequency curve indicates that, at 

the Lake Street Bridge, an elevation of 672.3 

feet corresponds to the 25-year recurrence 

interval. You now plot this elevation at river 

mile 24 on the flood-profile chart and draw a 

straight line through the point you have plotted 

C6 

and parallel to the 1954 flood profile. You now 

have the profile for a flood witl' a 25-year 

recurrence interval, and it shows that the 

elevation reached by such a flood at your 

property would be 671.8 feet. Using the line 

you have drawn, you can determine 

corresponding elevations (for the same 

recurrence interval) at other points along Salt 

Creek. And, of course, you can use the method 

outlined to approximate the elevation at your 

property for other recurrence intervals-up to 

50 years. 

THE METROPOLITAN CHICAGO 

FLOOD-MAPPING PROGRAM 

It was determined that flood-hazard mapping 

could meet some of the needs that had become 

evident in Metropolitan Chicago. However, it 

was also recognized that flood-hazard mapping 

of such a large area could not be accomplished 

overnight. It would require financing, time, 

careful planning, and data. The flo')d-mapping 

program is a cooperative effort, financed jointly 

by the six counties of Metropolitan Chicago, the 

Northeastern Illinois Planning Commission, the 

State of Illinois, and the U.S. Geological Survey. 

Funds offered by the six counties through the 

Planning Commission which serves in an 
administrative and coordinating role, are 

matched on a one-to-one basis with Federal 

funds. The actual mapping is done by personnel 

of the U.S. Geological Survey. In 1968 the State 

of Illinois entered into a separate, though 

similar. cooperative agreement with the U.S. 

Geological Survey to assist with part of the 

financing. The flood-mapping program was 

carried out in phases. The first phase extended 

from July l, 1961 to June 30, 1966. Phase 2 

extended from July 1, 1966 to June 30, 1969. 

The formulation of a phase 3 is currently ( 1969) 

being discussed among the principal agencies 

involved. 

PHASE l 

In phase 1 of the program, flood maps were 

prepared for 43 ?Y2-minute quadrangles in the 

six-county area. One flood atlas, U.S. Geological 

Survey Hydrologic Investigations Atlas HA-39, 

"Floods in the Little Calumet River basin near 

Chicago Heights, Ill.," had been prepared 

previously by the Geological Survey as a 

prototype for the program. Each quadrangle is 

given the name of a principal city or prominent 

geographic feature located on the map. The 

location of these quadrangles is shown in figure 

1. 

The scope of phase 1 is shown in table 1 and 

figure 1. The average cost of preparing a flood 

map initially was estimated as $6,250, or a cost 

to the local agencies of $3, 125, and the initial 

agreements between local agencies and the 

Planning Commission were prepared on this 

basis. Early in the program, however, it was 

found that, for several quadrangles, particularly 

in Lake County, there was need for 

supplemental contours on the flood-plain areas. 

These were provided under a supplemental 

agreement among the appropriate agencies. 

Partly because of this change, and partly because 

of steadily rising costs throughout the 5-year 

period of the program, the total expenditure 

for phase 1, including the supplemental 

contours, the preparation of inundation maps 

for 43 quadrangles, and the installation and 

operation to June 30, 1966, of the initi~l 229 

crest-stage gages, was $299,860, or about $6,975 

per quadrangle. 

Table 1.-Scope of phase 1 of flood-mapping 

program, July 1961 to June 1966 

Counties 

c 0 0 k ---------------------------------------

Du Page ----------------------------------

Kane ----------------------------------------

Lake ----------------------------------------

McHenry --------------------------------

Will ------------------------------------------

Total .................................... . 

Quadrangles 

mapped 

113 

6 

6 

10 

I 

8 

44 

1

1ncludes Calumet City quadrangle. Chiczgo Heights, 

which was prepared as a pilot project, was not included 

as part of program. 

Another item of possible intere<'t to those 

who may plan similar programs is the 

expenditure of manpower. All operations were 

conducted from the Survey subdistrict office at 

Oak Park, near the geographic center of the area. 

A total of 37,372 direct man-.llours were 

required to complete phase I~ this indicates an 

average of 869 direct man-hours per quadrangle. 

There was, however, considerable variation for 

the individual quadrangles, ranging from a 

maximum of 1 ,45 5 man-hours to a minimum of 

5 20 man-hours. Man-hours required for 

providing the supplemental contours are not 

included in these figures, as this part of the work 

was performed under a contractual arrangement 

with the Topographic Division of the Geological 

Survey. 

Because of insufficient hydrolo~ic data in 

much of the area, it was necessary to establish 

229 crest-stage gages to record irstantaneous 

flood peaks so that flood r,.ofiles and 

flood-plain limits could be better defined along 

the approximately 1 ,000 miles of streams 

located in the 43 quadrangles. 

Preparation for phase 2 of the flc')d-mapping 

program involved the installation of an 

additional I 65 crest-stage gages in McHenry, 

Kane, and Will Counties in 1963. The 

installation of these gages was neces~ary because 

C7 
the hydrologic events on many of the streams in 

southern Will County and western Kane and 

McHenry Counties had never been recorded. 

These gages are located in 19 quadrangles which 

were scheduled for mapping during phase 2. The 

costs were covered by supplementary 

cooperative agreements with the affected 

counties. 

A flood-hazard mapping program can lead to 

other related hydrologic studies. A study of the 

role of flood-plain information and related water 

r e s o u r c e m a n age m e n t c o n c e p t s in 

comprehensive land-use planning (Spieker, 

1969) was made by the Geological Survey, at 

the request of the Planning Commission, in 

1965-67. This study used the Salt Creek basin 

in Cook and Du Page Counties as a 

demonstration area to illustrate principles which 

govern the effects of alternative land-use 

practices, particularly uses of the flood plains, 

on the overall water resources of the area. 

Emphasis was placed on the interrelationship of 

the various components of the hydrologic 

system, particularly the interrelationship 

between surface water and ground water. 

PHASE 2 

Phase 2 involved the preparation of 19 

additional flood maps. (See fig. 1.) In addition, 

the 394 crest-stage gages, including those located 

in areas already mapped, were kept in operation 

as part of phase 2 to extend the hydrologic 

records. The completion of phase 2 will make 

flood maps available for the entire metropolitan 

area with the exception of the western part of 

McHenry County and the completely urbanized 

area of Chicago and the close-in suburbs in Cook 

County. This area, which comprises four 

quadrangles, was not mapped because 

urbanization has obliterated nearly all the 

natural flood plains and overbank flooding is 

generally not a problem. 

The scope of phase 2 is presented in table 2. 

A proportionally larger share of the local cost 

was allocated to McHenry and Will Counties 

because a major part of the work was done in 

those two counties. In 1967, the State of 

C8 

Table 2.-Scope of phase 2 of floo1.-mapping 

program, July 1966 to June 1969 

Quad- Total Gages having 

Counties rangles number peak discharge 

mapped of gages data 

Cook ------------ 2 70 8 

Du Page------- --------------- 36 12 

Kane ------------ 3 58 11 

Lake·------------ ----------- 40 11 

McHenry------ 6 52 8 

will -------------- 8 138 19 

Total --------- 19 394 69 

Illinois, through the Division of Waterways of 

the Department of Public Works and Buildings, 

entered into a separate cooperative agreement 

with the Geological Survey to assume part of 

Will County's share of phase 2 mapping. The 

cost of mapping in phase 2 was $174,600, of 

which $86,200 was provided by lo~al agencies 

and $88,400, by the Geological Survey. (The 

difference of $2,200 was due to supplemental 

allotments of Survey funds, unmatcl'~d by local 

funds, to partially cover interim increases in 

Federal salary rates.) At the completi<1n of phase 

2, the total cost of flood mapping in the 

metropolitan area was $474,460. (This cost 

includes operation of the entire nety.-ork of 394 

crest-stage gages to June 30, 1969.) 

THE FORMULATION OF PHASE 3 

Providing adequate flood information in an 

urban area is a continuing activity. Floods will 

continue to occur and will provid~ new and 

additional information. Spreading urbanization 

can alter both the frequency and the patterns of 

flooding. Paving and covering of the land tends 

to accelerate storm runoff and inc.·ease flood 

peaks. Manmade changes in the ch~nnel cross 

section can alter flooding patterns. Examples of 

such changes are bridges, culverts, fill on the 

flood plain, and building on the flood plain. 

These changes take place at a rapid pace in a fast 

growing area such as Metropolitan Chicago. 
To keep up with these changes will require 

periodic revision of the flood-hazard rna ps. 

Many of the maps are based on information 

which is 8 years old. Additional flooding and a 

great deal of urbanization has taken place during 

these ,8 years. The crest-stage gage network has 

provided a wealth of data to document these 

flood events and to help in analyzing the 

changes resulting from urbanization. 

Phase 2 of the flood-mapping program 

terminated in 1969. In continuing the program 

into its third phase, the following four activities 

should be considered. 

I. Continued operation of the existing 

network of crest-stage gages. The crest-stage gage 

network is believed to be the densest such 

network in the country. About 8 years of record 

will be available at the completion of phase 2 of 

the program. As urban development continues, 

the continued availability of flood-stage 

information will be increasingly important. Such 

data would be valuable in determining rates if a 

flood-insurance program became operational. 

2. Evaluation of the crest-stage gage network 

for adequacy and relevance. Although the 

e x is t in g n e t work i s o n e o f t he m o st 

comprehensive in the country, there exists a 

need for its review to eliminate redundant gages 

and to add new ones where needed. The 8 years 

of record would be useful in this evaluation. 

3. Extension of the program to unmapped 

areas. At the completion of phase 2 all of the 

six-county metropolitan areas except the 

completely urbanized central city and the 

western 40 percent of McHenry County will be 

mapped. The remainder of McHenry County is 

already planned for inclusion in phase 3. Before 

the metropolitan area expands into Kankakee 

and Kendall Counties, the flood-mapping 

program should be extended there to provide a 

part of the basis for orderly growth. 

4. Periodic and systematic revision of the 

flood rna ps prepared in phases 1 and 2. All 

existing maps should be evaluated as to their 

adequacy and a systematic program should be 

planned for updating the maps where 

urbanization and additional flood data warrant 

it. This should be a continuing process. 

Exarnples of maps greatly in need of revision are 

the Calumet City (HA-39) and Arlington 

Heights (HA·-··-6 7) quadrangles. In addition to 

mapping floods of record, consideration should 

be given to defining floods of given frequencies: 

for example, at 25-, 50-, and 100-year 

recurrence intervals. Even though the cost of 

such a mapping program would be considerably 

greater than that of mapping historical floods, 

the maps would provide a more sound and 

consistent basis for considering the element of 

risk in planning and decision making. Profiles at 

the selected frequencies also should be included 

in future mapping. This kind of flood 

information would be especially useful in 

determining premium rates under the National 

Flood Insurance Act of 1968. It has been 

agreed 2 for example, that the area inundated by 

the I 00-year flood should define the regulatory 

area under the Flood Insurance Act. 

Continuation of the cooperative flood-hazard 

rna pping program along these line5' will assure 

that local governmental bodies, industries, 

utilities, developers, and citizens of l\fetropolitan 

Chicago will have more and b~tter flood 

information which can be used in furthering the 

region's orderly development. 

THE CREST-STAGE GAGE NETWORK 

The Northeastern Illinois Planning 

Cotnmission and the U.S. Geological Survey's 

cooperative flood-mapping program required the 

establishment of a network of crest-stage gaging 

stations. Figure 5 shows the locathn of these 

gaging stations along with the locations of other 

gaging stations in the area which are operated 

under other cooperative programs. 

A crest-stage gage is a rather simple device 

that records the maximum elevation of floods. 

These gages are mounted on wingwalls or piers 

of highway bridges and culverts or anchored in 

concrete along stream banks. After the gages are 

2consensus of Seminar on Flood Plain Managenent held at the 

Center for Urban Studies, University of Chicago, December 16-

18, 1968, at the request of the U.S. Department of Housing and 

Urban Development. 

C9 
CIO 

I I c ••• 

I 

I 

I L ____ _ 

Figure 5 .-Location of crest-stage gages in the Chicago metropolitan area. 
mounted, levels are run from nearby 

benchmarks to establish datum (zero) of the 

gages referred to mean sea level, datum of 1929. 

The base of these gages is set above normal 

water levels so that they record only flood 

elevations. The sketch in figure 6 illustrates how 

the gage functions. Water enters the gage 

through specially designed holes at the bottom 

of the pipe. Finely ground cork at the bottom of 

the gage floats on the water surface and comes 

in contact with the wooden staff located inside 

of the pipe. As the water recedes, the cork 

adheres to the staff and provides a record of the 

maximum stage of the flood. 

After a flood, the crest-stage gage is serviced 

by opening the gage, withdrawing the staff, and 

measuring the distance from the base of the staff 

to the top of the cork line. After the 

measurements are made, the cork is removed 

from the staff, any debris that has collected is 

removed from the holes at the base of the gage, 

new cork is added, and the gage is reassembled. 

It is then ready to record the elevation of the 

2

11 PIPE 

STAFF 

--·r~ .... DERED CORK 

--!!!!!--WATER 

LEVEL 

OPENINGS FOR WATER 

TO ENTER 

D~M~If!9·--GAGE DATUM 

Figure 6.--Typical crest-stage gage. 

next flood. By adding the depth of water 

recorded on the staff (gage height) to the gage 

daturn, the elevation of the flood in feet above 

mean sea level is determined. 

USEFULNESS OF FLOOD-HAZARD 

MAPS IN URBAN DEVELOPMENT 

The main purpose of flood-hazard mapping, 

as stated previously, is to make available 

information which can be used to bring about 

the orderly and beneficial use of areas subject to 

flooding. A wide range of institutions and 

devices exists through which this irformation 

can be put to use. The following outline presents 

the general categories of flood-plain irformation 

use: 

1. Regulation of private development: 

a. By public institutions: 

(I) Building, subdivision, and 

zoning regulations. 

(2) Sewer connection permits. 

( 3) Public financial institutions 

(that is, Federal Housing 

Adtninistration, Veterans 

Administration). 

( 4) Land management and use 

criteria of the flood insuranc~ program. 

b. By private institutions: 

(I) Financial institution~. 

(2) Private utilities (that is, gas, 

electric). 

2. Purchase of property for public use: 

a. Forest preserve districts (county). 

b. Parks and recreation facilities. 

c. Municipal parking lots. 

3. Development of public facilities: 

a. Highways and streets. 

b. Sewer extensions, treatnent plant 

locations. 

4. Guidelines (planning) fer future 

development. 

Following is a resume of how the 

flood-hazard maps have actually be,~n used to 

give direction to urban developmr.nt in the 

Chicago metropolitan area. 

Cll 
REGULATION OF PRIVATE DEVELOPMENT 

One of the n1ost frequently employed devices 

of flood-plain management is flood-plain zoning. 

The zoning authority is usually delegated to 

local governments, villages, and cities. County 

governments may exercise zoning powers in the 

unincorporated areas. 

The Northeastern Illinois Planning 

Com m is~ ion ( 1 964) has prepared a model 

flood-plain zoning ordinance for the assistance 

of county and local governments. This model is 

the basis for many of the flood-plain zoning 

ordinances that have been adopted by 

Metropolitan Chicago communities. 

Progress in the adoption of flood-plain zoning 

ordinances by county and municipal 

governments has been varied. As of late 1968 

three of the six metropolitan counties-Cook. 

Du Page, and Lake-had adopted such 

ordinances. Kane County does not have a 

flood-plain zoning ordinance as such, although 

its zoning ordinance and subdivision regula-tions 

set forth conditions for subdivision development 

in flood-hazard areas. As of October 1968. 94 of 

the 11 7 Cook County municipalities located in 

the. Metropolitan Sanitary District had adopted 

flood-plain zoning ordinances. There arc 20 

Cook County municipalities within the Sanitary 

District which do not have recognized flood 

hazards. An additional three are revising 

ordinances which have been rejected as 

unsatisfactory. Outside of Cook County, only a 

few municipalities have adopted flood-plain 

zoning ordinances. 

One of the reasons for the large number of 

Cook County municipalities taking action is the 

policy adopted in 1967 by the Metropolitan 

Sanitary District regarding the issuance of sewer 

permits. The policy states that: "'No permits 

shall be issued by the Metropolitan Sanitary 

District for sewers to be constructed within a 

flood-hazard area. as delineated on the maps 

prepared by the United States Geological Survey 

in cooperation with the Northeastern Illinois 

C12 

Planning Commission, until the local 

municipality has adopted a flood-plain zoning 

ordinance which meets the approval of the 

Sanitary District." 

""Permits in undeveloped areas will not be 

approved until Cook County adopts flood-plain 

zoning regulations." 

'"The ordinance shall include hut not be 

limited to the following: 

1. Restriction on residential development. 

2. Provisions for establishing permanent 

flood way channels through acquisition of 

rights-of-way, including easements for 

maintenance and improvements. 

3. Requirements for flood proofing buildings 

within the flood-hazard areas. Tte ordinance 

shall be adopted before September 1, 1 96 7.." 

This policy has proved highly effective in 

encouraging municipalities to adopt flood-plain 

zoning ordinances. In addition, Cook County 

has adopted a flood-plain ordinance which 

applies to all its unincorporated areas. 

Financial institutions, public and private, can 

exert a powerful influence over the location of 

private urban development. Where flood-plain 

information is available, these institutions are 

generally reluctant to finance housing 

development in flood-hazard areas. The 

financing of housing in flood-prore areas is a 

risk that financial institutions would rather not 

assume, provided that there exists a knowledge 

of this risk. In the Chicago metropolitan area, 

the Veterans Administration and the Federal 

Housing Administration routinely check the 

location on the U.S. Geological Survey's 

flood-hazard maps of any new housing 

deve lo pmen ts which they are considering 

financing. These agencies as a matter of policy 

will not finance developments in areas known to 

be subject to flooding. A large numb<~r of private 

financial institutions (banks, savings and loan 

companies) make similar usc of the flood-hazard 

maps. 
Private utility companies can influence urban 

d eve I o p m en t b y w here t hey choose to 

extend-or not to extend-gas and electric 

lines. By recognizing that development on flood 

plains is not wise, utility companies are in an 

excellent position to prevent their development 

by refusing to service them. Flood-hazard maps 

thus can be useful to utility companies by 

helping them to identify those areas where they 

might wish to discourage development. 

PURCHASE OF PROPERTY FOR PUBLIC USE 

The public development of flood-hazard areas 

for recreation or aesthetic purposes has long 

been recognized as a technique of flood-plain 

management. Green belts, or undeveloped areas 

along streams, can provide breaks in the 

monotony of urban sprawl. The construction of 

municipal parking lots is another example of 

public use of flood plains. Identification on 

flood-hazard maps of those areas subject to 

flooding can assist public officials in acquiring 

these lands at a reasonable price. 

The Du Page County For est Preserve District 

is now engaged in a long-range program of land 

acquisition whose purpose is to develop a major 

green belt along the West Branch of the Du Page 

River. The U.S. Geological Survey's flood-hazard 

maps have been extremely useful in providing 

guidelines for land purchase. Also, they have 

been helpful in negotiations for public open 

space acquisition in Cook and Lake Counties. 

DEVELOPMENT OF PUBLIC FACILITIES 

Public facilities frequently lead urban 

development into flood-hazard areas. The State 

Division of Highways has made frequent use of 

the flood-plain maps in their highway planning 

process. Proper planning of access can tend to 

discourage improper flood-plain development. 

The location of sewage treatment plants and 

sanitary landfills is also influenced by 

flood-plain information. An example of such use 

is found in "Rules and Regulations for Refuse 

D i s p o sa 1 S it e s a n d F a c i I it i e s " ( Illinois 

Department of Public Health, 1966. p. 1 ). This 

document states that: "sites subject to flooding 

should be avoided*.* *or protected by 

impervious dikes and pumping facilities 

provided.'' Thus, flood-plain information 

becomes involved in all decisions regarding the 

establishment of disposal sites and facilities and 

is cited by the State Geological Survey in their 

site-evaluation reports. 

GUIDELINES (PLANNING) FOR FUTURE DEVELOPMENT 

Planning. or the formulation of gui1elines for 

future d evcl o pm ent. provides the overall 

framework in which the previously discussed 

uses of flood-hazard maps are impiemented. It is 

in the planning process that the broad, 

long-range goals and objectives are set out. These 

objectives can be attained by alternate tactics. 

The importance of wise management of the 

flood plains has been recognized by the Regional 

Planning Agency for Metropolitan Chicago, 

Northeastern Illinois Planning Commission, 

almost from its inception. Examples of how the 

flood-hazard maps arc influencing lvng-range 

planning can be found in the two following 

policy statements taken from the Northeastern 

Illinois Planning Commission's comprehensive 

general plan for Metropolitar Chicago 

(Northeastern Illinois Planning Commission, 

1968, p. 7): "Lands unsuited for intensive 

development due to flooding. un~table soil 

conditions, or where the provision of essential 

public services and facilities is difficult, should 

be maintained in suitable open space use." And 

on page 11 : "Intensive urban development 

should be directed so as to avoid fl')od plains, 

protect ground water deposits. an1 preserve 

lands particularly suited for multi-purpose 

resources management programs." 

SELECTED REFERENCEf 

Bue, C.D., 1967. Flood infornation for 

flood-plain planning: U.S. Geolog:cal Survey 

Circular 539, 10 p. 

Ellis, D.W .. Allen, H.E., and Noe.hre, A.W., 

1963, Floods in Elmhurst quadrangle. Illinois: 

U.S. Geol. Survey Hydro I. lnv. Atlas HA --68. 

Cl3 
Illinois Department of Public Health, 1966, 

Rules and Regulations for Refuse Disposal 

Sites and Facilities: Illinois Dept. Public 

Health, Springfield, Ill., 7 p. 

Mitchell, W.D., 1964, Some problems in flood 

mapping in Illinois: Natl. Acad. Sci.-Natl. 

Research Council Highway Research Board, 

Highway Research Rec. 58, p. 42-43. 

Northeastern Illinois Planning Commission, 

1964, Suggested flood damage prevention 

ordinance with commenta·ry: Northeastern 

Illinois Planning Comm., Chicago, Ill., 28 p. 

---196_8, A regional armature for the 

future: The comprehensive general plan for 

the development of the northeastern Illinois 

counties: Northeastern Illinois Planning 

Comm., Chicago, Ill., 12 p. 

Cl4 

Sheaffer, J.R., 1964, The use of flood maps in 

northeastern Illinois: Natl. Acad. Sci.-Natl. 

Research Council Highway Res<>arch Board, 

Highway Research Rec. 58, p. 44-46. 

Sheaffer, J.R., Zeizel, A.J., and others, 1966, 

The water resources in rortheastern 

Illinois-Planning its use: Northeastern 

Illinois Planning Comm. Tech. Rept. 4, 182 p. 

Spieker, A. M., 1970, Water in urb:m planning, 

Salt Creek Basin, Illinois: U.S. Geological 

Survey Water-Supply Paper 2002, 147 p. 

U.S. Congress, 1965, A unified national program 

for managing flood losses: U.S. 89th Cong., 

2 d sess., House Doc. 465, 47 p. 

U. S. GOVERNMENT PRINTING OFFICE: 1972 0- 469-471