FLOOD00310

• County: Arapahoe
• Stream Name: South Platte
• Title: Union Avenue Boat Drop
• Date: 1/1/1983
• Prepared For: CWCB
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

772 JULY 1977 . T. WHITEWATER CHANNEL 773

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consideratIOn. Another concept was to use a narrow uncontrolled entrance t 'b size and shape. but not for dynamics or mass) passed easily through this
would pass a given flow for the specified upstream pool water surface elevati junp when at or near right angles to it. but were often rolled when entering
[i.e., 60 cfs-IOO cfs (1.7 m' Is-2.8 m' Is) for the Denver channel]. The remaim ... jump sideways. They were not kept in the roll. but quickly passed through
fiver flow would be passed by another control structure such as a tabn ,lito the channel. However. at some nonstabilized operating conditions such
or gate. When low flows were experienced, the entrance would be gated sb .. might occur during abrupt gate position changes. dangerous "keeper" jumps
and the channel would not be used. 'occurred. This was demonstrated by using lumps of wax to represent swimmers.
The first concept tested was an irrigation-type verticaJ.lift sluice gate witt Analysis and further experimentation showed that placement of two "spoilers H
the gate .leaf lifting upward from the sill to pass water underneath. [Fig. 8(0)) 411 :speciaJly-shaped triangular blocks of considerable thickness, one on each
Two sImilar Side gates would provide the flow control needed while boats passt( '* on the downstream panel, overcame any tendency for keeper conditions
through the fully raised central section. Such a gate control section is usei,IFigs. 6 and 7). They also improved the jump pattern so as to make it an
at Augsburg, Germ~ny. The concept was not used because it required a hi8l~lIent surfing wave. On the wave's upstream face, boats could descend and
superstructure that Interfered with flood flows. Also, the underflow from IlK ..,ve from side to side without being caught by the opposing current and carried
two side gates posed a possible safety hazard. A gate in which the leaf woo 'mwnstream. At low flows, the "spoilers" channeJ the water toward the center
rise from a pit below the channel floor to reduce or cut off flows would providt. ellhe chute. thus increasing the depth and creating better hydraulic conditions.
flow regulation, permit passage of boats, and present no obstruction to fI At-high flows, they continue to produce excellent flow conditions and do not
[Fig. 8(b)]. However, the design was rejected because of complications d si811ificantly decrease the discharge coefficient, passing the maximum flow of
to silting tendencies in the pit. and because of the sudden drop Qoats wou 120 cfs (9 10' / s) with only a O.I-ft (0.03-m) increase in required pool depth.
experien~e in passing over the partly raised gate. I No tendencies for vibration, lifting, or "floating" of the downstream part
A fabndam also would provide flow regulation and, when defl~ted, ()uk 01 the gate were detected at any operating condition.s in the model. Not that
offer I,ttle Interference to floods [fig. 8(c)]. It would also produce a sudd,,'no seals were used on the model. e,ther along the hInge hne at the upstream
drop for boats passing over it. Consideration was given to mounting a semiflexiblt MH, the hinge line between the two panels of the gate, or along the sides of
chute onto the downstream face to carry the flows and boats down into tb, tbe gate onto the dividing walls. Such seals are planned for the full,sized gate.
channel, but such a scheme risked unknown stability problems and possible Gravity is expected to be adequate for closing the steel gates, assuming a moderate
premature damage to the fabr~dam. Because there was not enough time to full)' degree of seal drag. It was. anticipated that holes through the downstream panel.
explore the concept, it was discarded. I or some other method of "ventilation," might be necessary to insure stable
Bascule gates. ~re suitable for. flow regulation [Fig. 8(d)], a~d in their operation. Because nQ instabilities were found, no holes were tried in the model
turned-down posillons present, no Interference to flood flow. When rrised, the, panel.
present an abrupt drop for bqats passing over. Possibilities of proViding some Channel Slope Determinations,-Early studies with relatively small berms ~nd
kmd of chute or gUideway to aVOid the sudden drop were examine~. One was humps showed that bottom slopes as low as OJl04 and 0.005 [corresponding
to hinge a grating onto the Bascule leaf to carry boats down to the channel to 2 1t-2.5 It (0.6 10-0.76 m) and total drops in the 500-1t (I5()..m) length of
below w~ile letting part of the water fall through to reduce the hYdrrulic jump channel] would result in high velocities and shallow depths throughout the t~nncl.
and obtam smoother energy .;iissipation. The other was to use a ~olid chute The average slope of the Augsburg Olympic course was about 0.013. Tentatively,
which carried all of the water jiS well as the boats. Neither was cestid because it was decided that slopes from 0.008-0.010 would be appropria.te for the Denver
costs of the Bascule gates wer~ felt to be too high. . recreationaJ channel. and that large berms. humps, and bumps would be needed
The hinged flap gate design!combined the principle of the Bascul~ gate and on the flat floor to control flow depths and velocities. and produce desirable
a downstream chute [Fig. 8(tl)]. Insofar as the flow profile was concerned current and eddy patterns.
it closely resembled the gate used in the Augsburg course where ~he newe; Exploratory studies at a uniform 0.008 bottom slope and using 4.5-f~-high
channel branched from the older one, which was used at times to cu~ off flowl (I.4..m) berms having side slopes and rounded noses lying on ~: J slopes (~i?s.
to the new channel. It differed in that it was raised by overhead caqles rathel 4 and 5) produced good flow depths and patterns. but not quite the veloctlles
than by hydraulic cylinders underneath. With the IO-in-thick (254-mm) flap gat, desired. The channel was then steepened to an average slope of 0.010, but
(with spoilers) fully lowered onto the EI. 81.5 concrete sill, and with:the radial was so arranged as to have three sections lying on 0.008 slopes connected
gate fully opened, the 4()"ft-wide (l2.2-m) inlet passed 320 cfs (9 m' I s) at 'I. with two relatively abrupt drops of I It (0.3 m) each. One drop was at about
pool water surface of EI. 91. J3 ft. At high flood flows, these gates as weU midJength in the channel and the other near the downstream end. Good flow
as the Public Service Company's fabridam would be fully opened. ! patterns, flow depths, and current velocities were obtained through further
Control Gate Spoilers.-Model studies showed that flow over the flap gat,' trial-and-error experimentation with the standardized berm, hump. and wav<-
crest and down the downstream panel was remarkably smooth and that boats making bump shapes for flows from 150 cfs-320 cfs (4.2 m'/s-9 m'/s).
passed through easily at any angle or position. At all stabilized conditions 0/ Channd Configuralion.- The aJinement of the left (west) side of the channel
flow over the gate and water depth in the channel immediately downstream, conforms generally to the slope of the existing left bank of the Platte River.

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