# 17 Ill. Adm. Code 3708.60: Section 3708.60 Delineation of the Regulatory Floodway

> Illinois · Regulations · In force

URL: https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_60

## Section

- **Citation:** 17 Ill. Adm. Code 3708.60
- **Heading:** Section 3708.60 Delineation of the Regulatory Floodway
- **Jurisdiction:** Illinois
- **Kind:** Regulations
- **Status:** In force
- **Text as of:** August 14, 2026
- **Source:** Compiled text
- **Location:** Illinois Administrative Code / Title 17 CONSERVATION / CHAPTER I: DEPARTMENT OF NATURAL RESOURCES / Part 3708 FLOODWAY CONSTRUCTION IN NORTHEASTERN ILLINOIS / Section 3708.60 Delineation of the Regulatory Floodway

## Text

Section 3708
Section 3708.60  Delineation
of the Regulatory Floodway
a)         The regulatory floodway is defined based on a flood event that
has a one percent annual chance of exceedence or an expected 100-year
recurrence interval. The Department encourages, but does not require, that the
100-year frequency flood event be determined  based on anticipated future land
use in the watershed.  When utilized,  anticipated future land use should be
based on adopted local or regional land use plans.
b)         The boundary of the regulatory floodway is portrayed on
Department regulatory floodway maps.  To locate the regulatory floodway
boundary on any site, the regulatory floodway boundary should be scaled off the
regulatory floodway map and located on a site plan, using reference marks
common to both maps.  Where interpretation is needed to determine the exact
location of the regulatory floodway boundary, the Office should be contacted
for the interpretation.
c)         The regulatory floodway boundaries are determined by hydraulic
and hydrologic analyses, which calculate that portion of the flood plain which
must be preserved to store and discharge floodwaters without causing damaging
or potentially damaging increases in flood stage and flood velocities or loss
of flood storage which would result singularly or cumulatively in more than a
0.1 foot increase in flood stage or a 10% increase in velocity.
d)         The need to preserve storage when defining the regulatory
floodway will be waived by the Department if all the municipalities and
counties along a hydraulically significant portion of the watershed require
effective compensatory storage for all construction and fill in the 100-year
frequency flood plain.  Effective compensatory storage requires flood plain
storage volumes be replaced at the same flood frequency event as previously
existed
egulatory
floodway will be waived by the Department if all the municipalities and
counties along a hydraulically significant portion of the watershed require
effective compensatory storage for all construction and fill in the 100-year
frequency flood plain.  Effective compensatory storage requires flood plain
storage volumes be replaced at the same flood frequency event as previously
existed.  Additionally, legal assurances such as easements must be provided so
that the compensatory storage site will remain open to the stream system in
order to allow flood waters to reach it.
e)         Determination of the flood elevation at any point along the
stream shall be made from the flood profile.

## Nearby sections

- [17 Ill. Adm. Code 3708.10 Section 3708.10  Purpose](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_10.md)
- [17 Ill. Adm. Code 3708.30 Section 3708.30  Jurisdiction](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_30.md)
- [17 Ill. Adm. Code 3708.40 Section 3708.40  General Provisions](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_40.md)
- [17 Ill. Adm. Code 3708.50 Section 3708.50  Regulatory Floodway Maps](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_50.md)
- [17 Ill. Adm. Code 3708.60 Section 3708.60  Delineation of the Regulatory Floodway](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_60.md)
- [17 Ill. Adm. Code 3708.70 Section 3708.70  Permitting Appropriate Uses of the Regulatory Floodway](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_70.md)
- [17 Ill. Adm. Code 3708.80 Section 3708.80  Changes to the Regulatory Floodway](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_80.md)
- [17 Ill. Adm. Code 3708.90 Section 3708.90  Delegation to Municipalities and Counties](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_90.md)
- [17 Ill. Adm. Code 3708.100 Section 3708.100  Violations](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_100.md)
- [17 Ill. Adm. Code 3708.110 Section 3708.110  Permit Application](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_110.md)
- [17 Ill. Adm. Code 3708.115 Section 3708.115  Permit Application Fee](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_115.md)
- [17 Ill. Adm. Code 3708.120 Section 3708.120  Public Notice](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_120.md)
- [17 Ill. Adm. Code 3708.130 Section 3708.130  Public Hearings](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_130.md)
- [17 Ill. Adm. Code 3708.140 Section 3708.140  Time to Permit Issuance; Emergency Authorizations; Duration; Revisions](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_140.md)

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Source: Frix Law Library, https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T17_P3708_S3708_60. Check the current official text before relying on it. Not legal advice.