Illinois Administrative Code › Title 17 - CONSERVATION › Part 3702 - CONSTRUCTION AND MAINTENANCE OF DAMS › Section 3702.40 - Requirements for Approval of Permits for Construction of New Dams and Major Modifications of Existing Dams

Current through Register Vol. 48, No. 28, July 12, 2024
a) The
			 following are OWR requirements which must be met in order to obtain a permit
			 for construction of a new dam or major modification of an existing dam.
			 Applicants are encouraged to submit to OWR a preliminary report for approval of
			 concept prior to completion of the permit application form. The preliminary and
			 all subsequent plans and reports shall be prepared under the direction of an
			 engineer or other qualified personnel. The engineer or qualified personnel may
			 be assisted by other professional personnel applying the disciplines of
			 hydrologic engineering, hydraulic engineering, soil mechanics, structural
			 engineering, or engineering geology.
b) OWR staff will be available for
			 consultation prior to initiation of design studies, and at any time during the
			 development of the permit application if questions should arise.
1) Structural and Geotechnical Design
			 Requirements
The basis for OWR review and approval of the structural and
				geotechnical design requirements of Class I, II and III dams is the Corps
				Guidelines subject to modification as indicated in this Part. The criteria for
				structural and geotechnical design contained in the Corps Guidelines are
				minimum criteria. Variations from the criteria may be required or allowed by
				OWR for special physical conditions at the proposed site as necessary or
				appropriate to meet the interest of the overall structural and geotechnical
				requirements of this Part. Technical publications, other than the Corps
				Guidelines, may be used by OWR to assure the use of current and applicable data
				for the structural and geotechnical review of the dam design.
2) Hydrologic and Hydraulic Design
			 Requirements
The basis for OWR review and approval of the hydrologic and
				hydraulic design requirements for Class I, II and III dams is the Corps
				Guidelines, subject to modifications as indicted herein. Technical publications
				other than the Corps Guidelines may be used to assure the use of current and
				applicable data for the hydrologic and hydraulic review of dam design.
A) Proposed Dams
The following minimum spillway design floods shall be used for
				proposed structures:
i) Principal
			 Spillway Design Flood
CLASSIFICATION
SIZE
PRINCIPAL SPILLWAY
DESIGN
						  FLOOD
Class I
All
100-yr.
Class II
All
50-yr.
Class III
All
25-yr.
ii)
			 Total Spillway Design Flood
CLASSIFICATION
SIZE
PRINCIPAL SPILLWAY
DESIGN
						  FLOOD
Class I
Small
0.5 PMF
Intermediate
1.0 PMF
Large
1.0 PMF
Class II
Small
100-yr.
Intermediate
0.5 PMF
Large
1.0 PMF
Class III
Small
100-yr.*
Intermediate
100-yr.
Large
0.5 PMF
*For proposed Class III dams where the dam height multiplied by
				the impounding capacity is less than or equal to 300, no specific total
				spillway capacity is required.
iii) For all proposed Class II or III dams, a
			 determination of alternatives for increasing the total spillway capacity to
			 accommodate the PMF shall also be submitted to OWR. The initial dam design
			 shall provide for the capability of increasing the spillway capacity. Future
			 downstream land use, land use controls, and growth projections will be
			 considered in the review of the spillway capacity design.
B) Existing Dams
The minimum spillway design flood for modifications to existing
				dams built after September 2, 1980 shall be the same as the criteria for
				proposed dams. The minimum spillway design flood for modifications to existing
				dams that were constructed and in service on or before September 2, 1980, are
				as follows:
i) Principal Spillway
			 Design Flood
CLASSIFICATION
SIZE
TOTAL SPILLWAY
DESIGN
						  FLOOD
Class I
All
100-yr.
Class II
All
50-yr.
Class III
All
No specific requirement.
ii)
			 Total Spillway Design Flood
CLASSIFICATION
SIZE
TOTAL SPILLWAY
DESIGN
						  FLOOD
Class I
Small
0.3 PMF
Intermediate
0.6 PMF
Large
0.6 PMF
Class II
Small
100-yr.
Intermediate
0.3 PMF
Large
0.6 PMF
Class III
Small
100-yr.*
Intermediate
100-yr.
Large
0.3 PMF
*For modifications to existing Class III dams where the height
				multiplied by impounding capacity is less than or equal to 300, no specific
				total spillway capacity is required.
iii) The Department may approve total
			 spillway design capacities for existing dams other than the spillway design
			 floods listed above. A total spillway design capacity less than the 100-yr.
			 flood will only be allowed for small size, Class III structures with dam height
			 multiplied by impounding capacity less than or equal to 300. Any submittal for
			 variation from the above-listed spillway design flood must include a detailed
			 hydraulic risk assessment that shows that additional spillway capacity will not
			 provide a decrease in potential loss of life or property damage or a detailed
			 economic risk assessment that shows that the chosen spillway design alternative
			 provides the minimum rehabilitation costs plus damage losses; a detailed early
			 warning and emergency evacuation plan coordinated with the local ESDA; and a
			 list (with mailing addresses) of all persons living within the dam breach wave
			 inundation area.
iv) All hearings
			 regarding variation from the above-listed spillway design criteria shall be in
			 accordance with Section
			 3702.170
			 of this Part.
C) For
			 Class I and II dams, a dam breach wave analysis for downstream impacts from
			 failure during the total spillway design flood and impoundment initially at
			 normal pool shall be required for:
i) a nearly
			 instantaneous total failure and
ii)
			 should the applicant so desire, a failure to the degree and timing believed
			 reasonable by the applicant.
D) Dewatering Capabilities
i) All new Class I and II dams, all new Class
			 III dams unless exempted by OWR for functional reasons, and existing Class I
			 and II dams requiring major modifications shall have a capability for
			 dewatering the reservoir within a reasonable period of time. In determining a
			 reasonable time period, OWR shall consider the damage potential posed by
			 possible failure, risk and nature of potential failure, purpose of the dam and
			 reservoir, capability and stability of available drainage courses to convey the
			 waters released in the event of an emergency dewatering, and influence of rapid
			 drawdown on stability of the dam. Although each permit must be considered based
			 on its individual circumstances, in general, a reasonable time to dewater 50%
			 of the normal pool storage volume is 7 days for Class I dams, 14 days for Class
			 II dams and 30 days for Class III dams.
ii) No dewatering capability shall be
			 required for any existing Class III dam or for any existing Class I or II dam
			 which OWR determines to require no major modifications thereto under this
			 Part.
E) Specific
			 requirements for minimum freeboard allowances are not appropriate because of
			 the many factors involved in such determinations. The applicant must assess the
			 factors affecting the individual project and develop the appropriate minimum
			 freeboard allowance. Many projects are reasonably safe without freeboard
			 allowance because they are designed for overtopping, or because other factors
			 minimize possible overtopping. Conversely, freeboard allowances of several feet
			 may be necessary to provide a safe condition for some dams. Factors that should
			 be considered include the duration of high water levels in the reservoir during
			 the design flood; the effective wind fetch and reservoir depth available to
			 support wave generation; the probability of high wind speed occurring from a
			 critical direction; the potential wave runup on the dam based on roughness and
			 slope; and the ability of the dam to resist erosion from overtopping
			 waves.
F) The applicant must
			 provide stilling basins or other appropriate structures or devices capable of
			 dissipating the energy created at the outlet of the principal spillway and at
			 dewatering outlets for all flows.
3) Erosion Protection Requirements
A) As a minimum the applicant shall
			 adequately protect by structural or nonstructural means the upstream face of
			 earth embankment dams from an elevation below normal pool of two feet or 0.50
			 times the anticipated wave height (if greater than 2.0 feet) up to the minimum
			 freeboard elevation. In addition, if normal pool water surface varies, the
			 upstream face shall be protected within the range of variation.
B) The applicant shall vegetate or otherwise
			 protect from erosion the downstream face and top of earth embankment dams. The
			 applicant should design earth embankment dams to provide a dam section which
			 can be easily maintained.
C) The
			 applicant shall provide riprap or other appropriate protection as necessary at
			 dam abutments, dam slope toes (the line of the dam embankment slopes where it
			 intersects the natural ground at the upstream or downstream edge), spillways,
			 stilling basins, and at other locations which, if left unprotected, could lead
			 to damage to, or failure of the dam.
D) If the spillway design of the dam requires
			 that an earth emergency spillway pass any portion of the 100-year flood, the
			 applicant shall protect the earth emergency spillway against erosion consistent
			 with the dam classification and physical characteristics of the dam site. The
			 applicant must construct all earth emergency spillways on in situ material or
			 on well compacted cohesive materials that will be stable during design
			 flows.
E) The applicant shall
			 submit plans for control of erosion and water pollution during the anticipated
			 construction or major modifications, including plans for adequate measures to
			 limit the erosion of the soil from exposed slopes after completion of
			 construction. Such plans shall indicate that adequate control measures will be
			 taken during construction to protect the quality of stream flow below the
			 project site, and during the estimated time for filling.
4) Operating Requirements
An applicant for a Class I or II dam shall submit an
				operational plan specifying the method and schedule for the operation of the
				dam and the routine operating procedures to keep the dam in good working order,
				including an emergency warning plan. The emergency warning plan must outline
				the procedures to be followed during major storm events or other emergency
				situations. Under this plan, a person designated by the dam owner would monitor
				dam conditions, and would warn appropriate state and local officials if major
				problems require immediate repairs and would indicate how the owner plans to
				accomplish the needed repairs, and indicate if evacuation of persons in areas
				downstream of the dam may be necessary.
5) Maintenance Requirements
As a condition of each permit, dam owners shall submit a
				maintenance plan detailing the procedures and schedules to be followed to
				maintain the dam and its appurtenances in a reasonable state of repair. The
				maintenance plan shall include but not be limited to the following:
A) Class I and II Dams
The dam owner shall retain an engineer or other qualified
				personnel to make an initial inspection and report and subsequent inspections
				and reports as required by this Part. The owner of a Class I dam shall submit
				the report annually on forms furnished by OWR. The owner of a Class II dam
				shall submit the report every three years on forms furnished by OWR. In the
				intervals between the engineer or other qualified personnel reports on Class II
				dams, the owner shall file with OWR an annual statement on forms furnished by
				OWR stating that he is maintaining the dam in accordance with the maintenance
				plan prepared by his engineer or other qualified personnel and indicating any
				change in land use which may have occurred in the 100-year flood plain within
				the previously accepted limits downstream of the dam. The reports shall outline
				modifications made to the dam, any deficiencies found, detail the remedial
				measures necessary, and the method and time the owner will use to correct the
				deficiencies found. The dam owner may be required to provide additional
				inspections and reports by an engineer or other qualified personnel, following
				unusual storms or seismic events; provided such inspection procedures are
				required as a part of the maintenance plan approved by OWR in issuing a permit.
				A sketch showing land use in the flood plain downstream of the dam shall be
				included in the reports. The extent of downstream land use to be reported is
				dependent upon factors such as slope and width of the 100-year flood plain and
				the density and intensity of downstream development. The extent downstream will
				not exceed 2 miles unless otherwise indicated by OWR. The owner may provide
				information for review by OWR indicating that an extent downstream which is
				shorter than 2 miles may be appropriate.
B) Class III Dams
The owner of a new Class III dam or owner of an existing Class
				III dam qualifying under the provisions of Section
				3702.30 (relating
				to the major modification of existing Class III dams), shall retain an engineer
				or other qualified personnel to make an initial inspection and report and
				subsequent inspections and reports on a 5-year interval, in accordance with
				this Part. The dam owner shall submit to OWR on forms furnished by OWR the
				engineer's initial report and subsequent fifth year reports. The reports shall
				include a description of flood plain land use downstream of the dam. In the
				intervals between the engineer's reports, the owner shall file with OWR an
				annual statement on forms furnished by OWR stating that he is maintaining the
				dam in accordance with the maintenance plan prepared by his engineer or other
				qualified personnel and indicating any change in land use downstream of the
				dam. The extent of downstream land use to be reported is dependent upon factors
				such as slope and width of the 100-year flood plain and the density and
				intensity of downstream development. The extent downstream will not exceed 2
				miles unless otherwise indicated by OWR.
6) Financial Responsibility of Owner
A) For Class I and II dams, the owner shall
			 document that he has the financial capability to adequately maintain or breach
			 his dam in a safe condition. This may be established by showing that the
			 applicant has the resources and the authority to obtain funds in the amount
			 required to safely breach the dam within 10 days of receipt of notice of the
			 need to breach or repair. For public bodies, this may be done by showing taxing
			 power or other revenue generating ability and passage of an appropriate
			 ordinance or resolution indicating the authority to take such action if
			 necessary. If the owner cannot adequately demonstrate this financial
			 capability, OWR may require the applicant to post a performance bond. The
			 amount of the bond will be that estimated by OWR as reasonably necessary to
			 safely breach the dam in an environmentally sound manner if the condition of
			 the dam becomes a threat to life or property. The owners shall notify OWR when
			 each performance bond has been renewed or extended in time.
B) Except in emergencies, should the cost of
			 repair to place the dam in a safe condition be less than the cost of breaching,
			 the performance bond may be used to pay for repair, rather than breach of the
			 dam.
7) Other
			 Requirements
A) The owner shall grant the
			 State the right of access to inspect the dam site and immediate vicinity
			 before, during and after construction and for the life of the dam and
			 appurtenances. Except under emergency conditions, such as when the dam is in
			 imminent danger of failure or is in the process of failing, the State shall
			 notify the owner at least 10 days in advance of any inspection.
B) For Class I and II dams, the owner shall
			 notify OWR prior to initiating foundation preparations, including cut-off
			 trench excavation.
C) For Class I
			 and II dams, OWR will require the owner to have continuous inspection during
			 construction. The construction shall be under the direction of an engineer, or
			 other qualified personnel. For Class III dams, OWR may require the owner to
			 have continuous inspection during construction if foundation conditions have
			 not been completely determined or if the dam has been designed with minimal
			 factors of safety.
D) For Class I
			 and II dams - prior to commencing filling operations, or refilling operations
			 after a drawdown, the applicant shall request OWR inspection of the dam, and
			 must receive authority from OWR before commencing filling. When drawdowns are
			 performed on a frequent basis as a part of the approved operation plan, the
			 authority is not necessary.
E) If
			 OWR has not acted to grant or deny the authorization to fill within 30 days
			 after receipt of request, the owner may proceed with filling or refilling
			 operations.
F) For all new dams, or
			 for major modifications to existing dams, the dam owner shall
i) own or have permanent flood easements for
			 all land that will be inundated in the reservoir up to the proposed 100-year
			 frequency flood pool elevation, or
ii) submit hydraulic computations showing
			 that, for floods up to the 100-year frequency flood, the pool elevation will
			 not be increased above existing conditions.