Section 3708.70 Permitting Appropriate Uses of the Regulatory Floodway

Section 3708

Section 3708.70  Permitting

Appropriate Uses of the Regulatory Floodway

a)         The Department will issue permits for appropriate uses of the

regulatory floodway of which

periodic inundation will not pose a danger to

the general health and welfare of the user or require the expenditure of public

funds or the provisions of public resources or disaster relief services

(Section 18g of the Act) or result in increased flood stages due to the

singular or cumulative loss of regulatory floodway storage or regulatory

floodway conveyance or increase in flood velocities.

b)         To receive a permit for work in the regulatory floodway, the

proposed construction shall meet two criteria:

1)         The proposed construction shall be an appropriate use of the

regulatory floodway as defined in subsection (c); and

2)         The proposed construction shall not reduce the regulatory

floodway storage or conveyance and shall not increase regulatory floodway

velocities.

c)         Appropriate uses of the regulatory floodway that will be

considered for permit issuance consist of construction, modification, repair,

or replacement of:

1)

Flood control structures, dikes, dams and other public

works or private improvements relating to the control of drainage, flooding or

erosion

(Section 18g of the Act) or water quality or habitat for fish and

wildlife (e.g. Section 3708.80(a)(3) and(4));

2)

Structures or facilities relating to the use of, or

requiring access to, the water or shoreline, such as pumping and treatment

facilities, and facilities and improvements related to recreational boating,

commercial shipping and other functionally dependent uses

(Section 18g of

the Act);

3)         Storm and sanitary sewer outfalls;

4)         Underground and overhead utilities;

5)         Recreational facilities such as playing fields and trail

systems including any related fencing built parallel to the direction of flood

flows;

6)         Detached

Garages, storage sheds, or other

non-habitable

accessory structu

g and other functionally dependent uses

(Section 18g of

the Act);

3)         Storm and sanitary sewer outfalls;

4)         Underground and overhead utilities;

5)         Recreational facilities such as playing fields and trail

systems including any related fencing built parallel to the direction of flood

flows;

6)         Detached

Garages, storage sheds, or other

non-habitable

accessory structures to existing buildings that will not block flood flows.

This does not include the construction

or placement

of any other new

structures

, (Section 18g of the Act) fill, building additions, buildings on

stilts, fencing (including landscaping or plantings designed to act as a fence)

and the storage of materials;

7)         Bridges, culverts, roadways, sidewalks, railways, runways and

taxiways and any modification thereto;

8)         Parking lots built at or below existing grade where either:

A)        the depth of flooding at the 100-year frequency flood event

will not exceed 1.0 foot; or

B)        the parking lot is for short-term outdoor recreational use

facilities where the applicant agrees to restrict access during overbank

flooding events and agrees to accept liability for all damage caused by

vehicular access during all overbank flooding events;

9)         Aircraft parking aprons built at or below ground elevation

where the depth of flooding at the 100-year frequency flood event will not

exceed 1.0 foot;

10)       Regulatory floodway regrading, without fill, to create a

positive slope toward a watercourse;

11)       Flood proofing activities to protect existing structures such

as, but not limited to, constructing water tight window wells, and elevating;

12)       The replacement, reconstruction or repair of a damaged

building, provided that the outside dimensions of the building are not

increased, and provided that, if the building is damaged to 50% or more of the

building's market value before it was damaged, the building will be protected

from flooding to or above the 100-year frequency flood e

cting water tight window wells, and elevating;

12)       The replacement, reconstruction or repair of a damaged

building, provided that the outside dimensions of the building are not

increased, and provided that, if the building is damaged to 50% or more of the

building's market value before it was damaged, the building will be protected

from flooding to or above the 100-year frequency flood elevation; and

13)       Modifications to an existing building that would not increase

the enclosed floor area of the building below the 100-year frequency flood

elevation, and which will not block flood flows including but not limited to,

fireplaces, bay windows, decks, patios and second story additions.

d)         The construction of an appropriate use below the 100-year

frequency flood elevation will be considered permissible provided the proposed

project meets the following criteria and is so stated in writing with supporting

plans, calculations and data by a registered professional engineer or in the

case of a federal project, by the federal agency:

1)         In the case of the construction of a new bridge or culvert

crossing and roadway approach, the proposed structure shall not result in an

increase of upstream flood stages greater than 0.1 foot  when compared to the

existing conditions for all flood events up to and including the 100-year

frequency event; or the upstream flood stage increases will be contained within

the channel banks (or within existing vertical extensions of the channel banks)

such as within the design protection grade of existing levees or flood walls or

within recorded flood easements; or a flood control project is built to

mitigate the increased backwater due to the structure

to and including the 100-year

frequency event; or the upstream flood stage increases will be contained within

the channel banks (or within existing vertical extensions of the channel banks)

such as within the design protection grade of existing levees or flood walls or

within recorded flood easements; or a flood control project is built to

mitigate the increased backwater due to the structure.

2)         In the case of bridge and culvert reconstruction or

modification, the bridge or culvert and roadway approach reconstruction or

modification shall be constructed with no more than 0.1 foot increase in

backwater over the existing flood profile for all flood frequencies up to and

including the 100-year event, if the existing structure is not a source of

flood damage. The proposed construction shall meet the following criteria:

A)        The proposed structure, including approach roads, does not

result in an increase in upstream stages for normal and flood flows when

compared to the existing structure.

B)        On publicly navigated waterways, the proposed structure is not

an obstruction to navigation.

C)        The determination as to whether the existing structure is a

source of flood damage shall be made according to the following method:

i)          Determine the increase in upstream flood profile due to the

existing bridge or culvert by calculation or from the flood study used to

delineate the regulatory floodway for all reported flood profiles up to and

including the 100-year flood.

ii)         Determine if there are any buildings or structures located in

the 100-year flood plain upstream of the existing bridge or culvert that may be

subjected to flooding.  The upstream flood plain shall be checked for the

length of stream required for the backwater impacts due to the existing bridge

or culvert to be reduced to 0.1 foot or less.

iii)        Collect the low opening elevations or lowest damageable

elevations of the upstream buildings and structures as identified in subsection

am of the existing bridge or culvert that may be

subjected to flooding.  The upstream flood plain shall be checked for the

length of stream required for the backwater impacts due to the existing bridge

or culvert to be reduced to 0.1 foot or less.

iii)        Collect the low opening elevations or lowest damageable

elevations of the upstream buildings and structures as identified in subsection

(d)(2)(c) (ii), above.  Determine if any buildings or structures are subject to

inundation by the 100-year frequency flood event.

3)         In the case of bridge or culvert reconstruction and

modification, if the existing bridge or culvert and roadway approach is a

source of flood damage to buildings or structures in the upstream flood plain,

based on the above review, the applicant's engineer must evaluate the

feasibility of redesigning the structure to reduce the existing backwater,

taking into consideration the effects on flood stages on upstream and

downstream properties.

A)        The applicant's engineer must submit to the Department his or

her evaluation to justify why the proposed structure should be designed to

allow an increase in the upstream flood stage of more than 0.1 foot when

compared to a flood stage without the existing bridge or culvert or roadway

approach in place for all flood events up to and including the 100-year

frequency event.

B)        The evaluation shall also consider the feasibility of

containing the upstream flood stage increases within the channel banks (or

within existing vertical extensions of the channel banks such as within the

design protection grade of existing levees or flood walls), or within recorded

flood easements; or constructing a flood control project to mitigate the

increased backwater due to the structure.

4)         In the case of any other on-stream structure built for the

purpose of backing up water in the stream during normal or flood flows, but not

permitted as a dam according to 17 Ill. Adm

hin the

design protection grade of existing levees or flood walls), or within recorded

flood easements; or constructing a flood control project to mitigate the

increased backwater due to the structure.

4)         In the case of any other on-stream structure built for the

purpose of backing up water in the stream during normal or flood flows, but not

permitted as a dam according to 17 Ill. Adm. Code 3702 (Construction and

Maintenance of Dams), the proposed structure shall not result in an increase of

upstream flood stages greater than 0.0 foot when compared to the existing

conditions, for all flood events up to and including the 100-year frequency

event; or the upstream flood stage increases will be contained within the

channel banks (or within existing vertical extensions of the channel banks)

such as within the design protection grade of existing levees or flood walls or

within recorded flood easements; or a flood control project is built to

mitigate the increased backwater due to the structure.

5)         In the case of the construction of appropriate uses other than

bridge or culvert crossings, on-stream structures or dams, all effective

regulatory floodway conveyance lost due to the project will be replaced for all

flood events up to and including the 100-year frequency flood.  In calculating

effective regulatory floodway conveyance, the following factors must be taken

into consideration:

A)

Regulatory flood way

conveyance,

K

=

1.486 AR (⅔)

n

where "n" is Manning's roughness factor, "A" is the

effective area of the cross-section, and "R" is the ratio of the area

to the wetted perimeter. (See Open Channel Hydraulics, Ven Te Chow, 1959

Edition, McGraw-Hill Book Company, New York, New York.  This incorporation contains

no later editions or amendments)

e taken

into consideration:

A)

Regulatory flood way

conveyance,

K

=

1.486 AR (⅔)

n

where "n" is Manning's roughness factor, "A" is the

effective area of the cross-section, and "R" is the ratio of the area

to the wetted perimeter. (See Open Channel Hydraulics, Ven Te Chow, 1959

Edition, McGraw-Hill Book Company, New York, New York.  This incorporation contains

no later editions or amendments).

B)        The same Manning's "n" value shall be used for both

existing and proposed conditions unless a recorded maintenance agreement with a

federal, state or local unit of government can assure the proposed conditions will

be maintained or the land cover is changing from a vegetative to a

non-vegetative land cover.

C)        Transition sections must be provided and used in calculations

of effective regulatory floodway conveyance.  The following expansion and

contraction ratios shall be used unless an applicant's engineer can prove to

the Department through engineering calculations and model tests that more

abrupt transitions may be used with the same efficiency:

i)          When water is flowing from a narrow section to a wider

section, the water should be assumed to expand no faster than at a rate of one

foot horizontal for every four feet of the flooded stream's length.

ii)         When water is flowing from a wide section to a narrow

section, the water should be assumed to contract no faster than at a rate of

one foot horizontal for every one foot of the flooded stream's length.

iii)        When expanding or contracting flows in a vertical direction,

a minimum of one foot vertical transition for every ten feet of stream length

shall be used.

iv)        Transition sections shall be provided between cross-sections

with rapid expansions and contractions and when meeting the regulatory floodway

delineation on adjacent properties.

v)         All cross-sections used in the calculations must be located

perpendicular to flood flows

cal direction,

a minimum of one foot vertical transition for every ten feet of stream length

shall be used.

iv)        Transition sections shall be provided between cross-sections

with rapid expansions and contractions and when meeting the regulatory floodway

delineation on adjacent properties.

v)         All cross-sections used in the calculations must be located

perpendicular to flood flows.

6)         For all appropriate uses, compensatory storage shall be

provided for any regulatory floodway storage lost due to the proposed work from

the volume of fill or structures placed and the impact of any related flood

control projects.  Artificially created storage lost due to a reduction in head

loss behind a bridge shall not be required to be replaced.  The compensatory

regulatory floodway storage must be placed between the proposed normal water

elevation and the proposed 100-year flood elevation.  All regulatory floodway

storage lost below the existing 10-year flood elevation must be replaced below

the proposed 10-year flood elevation.  All regulatory floodway storage lost

above the existing 10-year flood elevation must be replaced above the proposed

10-year flood elevation.  If the compensatory storage will not be placed at the

location of the proposed construction, the applicant's engineer must

demonstrate to the Department through a determination of flood discharges and

water surface elevations that the compensatory storage is hydraulically

equivalent.

7)         For all appropriate uses, except bridges or culverts or

on-stream structures, the proposed work will not result in an increase in the

average channel or regulatory floodway velocities.  However in the case of

bridges or culverts or on-stream structures built for the purpose of backing up

water in the stream during normal or flood flows, velocities may be increased

at the structure site if scour, erosion and sedimentation will be avoided by

the use of rip-rap or other design measures

ork will not result in an increase in the

average channel or regulatory floodway velocities.  However in the case of

bridges or culverts or on-stream structures built for the purpose of backing up

water in the stream during normal or flood flows, velocities may be increased

at the structure site if scour, erosion and sedimentation will be avoided by

the use of rip-rap or other design measures.

8)         When excavation is proposed in the design of the bridge and

culvert openings, including the modifications to and replacement of existing

bridge and culvert structures, or to compensate for lost conveyance for other

appropriate uses, transition sections must be provided for the excavation. The

following expansion and contraction ratios shall be used unless an applicant's

engineer can prove to the Department through engineering calculations and model

tests that more abrupt transitions may be used with the same efficiency:

A)        When water is flowing from a narrow section to a wider section,

the water should be assumed to expand no faster than at a rate of one foot

horizontal for every four feet of the flooded stream's length;

B)        When water is flowing from a wide section to a narrow section,

the water should be assumed to contract no faster than at a rate of one foot

horizontal for every one foot of the flooded stream's length; and

C)        When expanding or contracting flows in a vertical direction, a

minimum of one foot vertical transition for every ten feet of stream length

shall be used.

9)         If the 100-year regulatory floodway elevation at the site of

the proposed construction is affected by backwater from a downstream receiving stream

with a larger drainage area, the proposed construction shall be shown to meet

the requirements of this section for the 100-year frequency flood elevations of

the regulatory floodway conditions and conditions with the receiving stream at

normal water elevations

ear regulatory floodway elevation at the site of

the proposed construction is affected by backwater from a downstream receiving stream

with a larger drainage area, the proposed construction shall be shown to meet

the requirements of this section for the 100-year frequency flood elevations of

the regulatory floodway conditions and conditions with the receiving stream at

normal water elevations.  However, for bridge and culvert construction or

reconstruction, a smaller bridge or culvert may be built if it can be

demonstrated to the Department that the proposed structure would meet the

requirements of this section for the 100-year frequency flood elevation of the

regulatory floodway flood study profile and would not be a source of flood

damage as determined according to the method described in subsections

(d)(2)(C)(i)-(iii), to any existing upstream building or structure when

analyzed as follows:

The proposed bridge or culvert shall be analyzed for a

100-year flood frequency flow on the tributary stream and for all tailwater

elevations on the receiving stream between and including the normal water

elevation and the 10-year flood frequency elevation.

10)       If an applicant learns from the Department, local government or

a private owner that a downstream restrictive bridge or culvert is scheduled to

be removed, reconstructed, modified, or a public flood control project is

scheduled to be built within the next five years, the proposed construction

shall be analyzed and shown to meet the requirements of this Section for both

the existing conditions and the expected flood profile conditions when the

bridge, culvert or flood control project is built.

11)       In the case of flood proofing activities, if construction is

required beyond the outside dimensions of an existing building, the flood

proofing construction shall be placed as close as possible to the existing

building and be the minimum width necessary to protect the building

itions and the expected flood profile conditions when the

bridge, culvert or flood control project is built.

11)       In the case of flood proofing activities, if construction is

required beyond the outside dimensions of an existing building, the flood

proofing construction shall be placed as close as possible to the existing

building and be the minimum width necessary to protect the building.

Compensation of lost storage and conveyance will not be required for flood

proofing activities.

12)       For public flood control projects (as defined in Section

3708.20), the permitting requirements of this Section will be considered met if

the applicant can demonstrate to the Department through hydraulic and

hydrologic calculations that the proposed project will not singularly or

cumulatively result in increased flood heights outside the project

right-of-way or easements for all flood events up to and including the 100-year

frequency event.

13)       If the appropriate use would result in a change in the

regulatory floodway location or the 100-year frequency flood elevation, the

applicant shall submit to the Department and to FEMA all the information,

calculations and documents necessary to be issued a conditional regulatory

floodway map revision and receive from the Department a conditional approval of

the regulatory floodway change before a permit is issued.  However, the final

regulatory floodway map will not be changed by the Department until as-built

plans are submitted and accepted by FEMA and the Department.  In the case of

non-government projects, the municipality in incorporated areas and the county

in unincorporated areas must concur with the proposed conditional regulatory

floodway map revision before Department approval can be given.

14)       All engineering analyses shall be performed by or under the

supervision of a registered professional engineer, except in the case of a

federal project.

15)       All dams, as defined by 17 Ill. Adm

unicipality in incorporated areas and the county

in unincorporated areas must concur with the proposed conditional regulatory

floodway map revision before Department approval can be given.

14)       All engineering analyses shall be performed by or under the

supervision of a registered professional engineer, except in the case of a

federal project.

15)       All dams, as defined by 17 Ill. Adm. Code 3702, shall meet the

permitting requirements of Part 3702 (Construction and Maintenance of Dams).