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.
