
where, C is the discharge coefficient, D is the
shortest distance between the gate lip and the
spillway crest curve, L is the net length of the
spillway crest, and H is the vertical difference
between the total head just upstream of the gate
(including the velocity head of approach) and the
center of the gate opening. The relevant figure in [1]
gives C as a function of the angle (Ɵ) between the
tangent to the gate lip and the tangent to the crest
curve at the point closest to the gate lip.
Computation of this angle Ɵ and of D is fairly
complicated and requires involved trigonometric
and geometric analyses. A long numerical and
analytical algorithm is suggested in [6] for
computations of both Ɵ and D, which requires (1)
manually plotting both the crest coordinates and the
slope function of the analytical ogee profile in a log-
log scale millimetric graph paper and visually
reading the numerical values out of this chart, (2)
replacing the analytical expression of the
downstream part of the ogee profile by arcs of three
circles of different center points and radius lengths,
(3) doing computations on a numerical table
comprising 20 columns for the gate opening D and
of the angle Ɵ, and (4) doing computations on
another table having 15 columns for ultimately
determining the discharge Q, [6]. This manual
method, which is advocated by [1] also, presents an
archaic approach as if we were in 1950s and 1960s
and it will definitely take a long time and a large
effort improper to the current age of computers.
Another deficiency of this method is that it does not
present any algorithm for a possible case where the
closest point between a partially open gate lip and
the spillway crest lies on the part of the crest curve
upstream from the spillway apex which is part of a
circle and not the curve depicted by the analytical
expression defining the downstream face of an ogee
spillway. A real-life example to such a case is the
radial gate of Yellowtail after Bay Dam in Montana
USA when the gate opening is 6 ft, [7].
There should exist many ogee spillways
equipped with radial gates in the world, and
controlled releases of floods of moderate
magnitudes through partially open radial gates
should be a common practice. Hence, accurate
computation of discharges under partially open
radial gates is an important problem. There are two
issues about the computation of discharge passing
under a partially open radial gate over an ogee
spillway. First, the curve proposed in [1] is not
sufficient for a general application because it is
developed using the measurements on three actual-
size spillways and two laboratory models only.
Besides, even in its present form, the observed
points have large noises around the fitted curve,
especially for values of angle Ɵ smaller than 73º,
[6]. Secondly, the method advocated in [1] for
computing the flow rate is too cumbersome,
intricate, and time-consuming as explained in the
previous paragraph. To remediate the old-fashioned
and winding method of computation for Q in
equation 1, a novel analytical and numerical
algorithm was proposed in [7], and unfortunately, it
has gone unnoticed so far although it presented a
modern method which is executed in a split second
in an ordinary computer requiring neither initially
prepared manually-drawn graphs nor numerical
tables with many columns, [7].
To probe into the apparent problem of doubt for
the relevant figure in [1] about its being a general
chart applicable to any spillway in the world, a
study was performed whose details and results are in
[8]. In that study, using data from 6 reports of
laboratory model studies done by the United States
Bureau of Reclamation, 9 such reports done by the
United States Army Corps of Engineers, 6 such
reports, and one report of measurements directly on
the flood spillway of Seyhan Dam done by the
Technical Research and Quality Control Department
of the State Water Works of Turkey, all having
radial-gated ogee spillways, the experimentally
determined discharge coefficients for partially open
gates were compared with those given by the
method of [1], whose results revealed large
differences between the two and there did not seem
to have a generalizable chart. In that study it is
concluded that a general chart is not possible, and
the best thing to do is to obtain the chart for the
discharge coefficient peculiar to each spillway by
doing laboratory measurements of all relevant
quantities on not too small a model [8]. It is further
recommended that measurements in the approach
channel of actual spillways during days of incoming
floods should be taken because recent technology
would allow such measurements at reasonable costs
with no danger to life, [8].
Recently, we have had an open channel setup
built by a professional laboratory equipment
manufacturing company with dimensions of 5 m
length, 10 cm width, and 30 cm wall height. The
channel is rectangular and it has a self-circulating
water flow provided by a bottom storage tank and a
pump of suitable capacities. On the pipe supplying
the flow to the upstream entrance of the channel,
there is a high-precision flow meter for measuring
the circulating discharge. Figure 1 shows the
photograph of this open channel model. Recently,
we did experiments for a partially open radial gate
in this laboratory setup on an ogee-profile spillway
WSEAS TRANSACTIONS on FLUID MECHANICS
DOI: 10.37394/232013.2024.19.29
Tefaruk Haktanir, Erol Bor