Kan. Admin. Regs. § 5-40-24 - Dam breach analysis
A
(a) To determine the appropriate water
surface elevation in the reservoir when the breach begins, the breach analysis
shall route the appropriate design duration one percent-chance storm determined
by K.A.R. 5-40-31 through the reservoir . The routing shall begin by assuming
that the water surface elevation is at the elevation of the lowest uncontrolled
spillway inlet, not including any low-flow augmentation works. The antecedent
moisture condition (AMC) used to determine the runoff shall be determined
according to K.A.R. 5-40-32. The minimum water surface elevation used to begin
the breach analysis shall be the greater of the following:
(1) The water surface elevation determined by
routing the required design duration one percent-chance storm through the
reservoir ; or
(2) the elevation of
the crest of the auxiliary spillway.
Routing the storm through the
(b) The breach discharge shall be determined
by using the peak breach discharge criteria section on pages 1-1 through 1-2 in
"earth dams and reservoirs," TR-60, dated July 2005, published by the
conservation engineering division of the natural resources conservation
service, and hereby adopted by reference, unless the applicant receives written
approval of the chief engineer to use a model that is more appropriate for a
particular dam . The breach discharge hydrograph shall be determined by methods
in NRCS TR-66, third edition, "simplified dambreach routing procedure," dated
September 1985, which is hereby adopted by reference, including the appendices.
If another model is used, the following breach modeling assumptions shall be
used, unless the applicant demonstrates to the chief engineer that more
appropriate assumptions should be used:
(1)
The parameters shall support the assumption of a rapidly developing breach that
is either an overtopping failure or a spillway failure caused by intense,
localized erosion beginning at the downstream end of the auxiliary spillway or
service spillway and working its way upstream.
(2) If the breach model has breach width as a
variable, the minimum bottom width of the breach shall be twice the height of
the dam . If there is a well -defined physical floodplain, the height of the dam
may be measured from the top of the low bank of the stream to the top of the
dam for the purpose of determining the minimum breach width.
(3) If the side slopes of the breach are a
parameter of the model, vertical side slopes shall be used.
(4) If the breach model has breach time as a
variable, the maximum breach time shall be one minute per foot of height of the
dam .
(c) The breach
discharge shall be routed downstream using a hydraulic flow model in accordance
with sound engineering principles and commonly accepted engineering practices.
An unsteady state hydraulic flow model shall be used if it is necessary to
model existing hydraulic structures in the inundation area. In all other
instances, a steady state hydraulic flow model may be used.
(d) The inundation area analyzed shall meet
both of the following requirements:
(1) Be
from the downstream toe of the dam and the control section of any open-channel
section of any openchannel spillway, downstream to the point where the crest of
the breach wave intersects the flood level of the peak discharge of the one
percent-chance storm, assuming that the dam was not in place; and
(2) be analyzed to the point at which there
are no more hazards downstream.
The peak discharge of the one percent-chance storm may be
determined by any of the methods provided in K.A.R. 5-42-5 or the appropriate
published flood insurance study for the
(e) If there is more than one dam on a
stream, it shall be assumed that the most upstream dam is breached first and
that the peak flow of that breach arrives at the next downstream dam at the
same time the peak water surface elevation from the inflow of the one
percent-chance storm from the uncontrolled portion of the lower dam 's drainage
area occurs. An appropriate model may be used to demonstrate when the peaks
will occur for an entire system of dams, in which case the water surface
elevation modeled shall be used.
(f) If there are dams on separate tributaries
above the dam being analyzed, the modeling assumption specified in subsection
(e) shall be applied only to the tributary that has the upstream dam whose
breach results in the greatest computed breach discharge at the dam being
analyzed.
(g) If digital elevation
data is used in the analysis of the breach, the data used shall have a root
mean square error of 2.5 meters or less.
(h) Cross sections for modeling purposes
shall be taken at appropriate locations, but in no case shall the intervals be
greater than 2,640 feet measured along the floodplain of the watercourse. Cross
sections shall be generally perpendicular to the direction of flow and the
contour lines that the cross sections intersect. Cross sections may be broken
into several connected segments as needed to meet the requirements of this
subsection.
(i) Each bridge and
any other hydraulic structure that has a significant hydraulic effect shall be
included in the analysis.
(j)
(1) The applicant shall submit a contour map
of the valley with contour intervals of 10 feet or less and a scale of not less
than 1:24,000, which shall show the following:
(A) The inundation area determined from the
breach;
(B) the location of each
existing hazard; and
(C) each
cross section entered in the hydraulic flow model with a label identifying the
cross section.
(2) The
following items shall be shown on the contour map or on separate documentation:
(A) The elevation of each existing hazard;
(B) the water surface elevation at
each existing hazard;
(C) the
elevation of the streambed at the point nearest each existing hazard; and
(D) a tabular report including the
following information for each cross section:
(i) The label identifying each cross section
shown on the map;
(ii) the
elevation of the maximum water surface attained during the breach;
(iii) the peak discharge; and
(iv) the computed width of the water surface.
(3) If there
are more than 10 hazards in any 2,640-foot reach in the flood inundation area,
the information required in paragraph (j)(2) may be noted only for the hazard
in that reach that is closest to the maximum water surface elevation measured
vertically and the hazard in that reach that is farthest from the maximum water
surface elevation measured vertically.
(k) The applicant shall submit one copy of
each data file used to perform each analysis in electronic form along with
identification of the computer programs used to perform the analysis and any
model documentation needed for the chief engineer to review the analysis.
Notes
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