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

768 , JULY 1977 H t H~ WHITEWATER CHANNEL 769

6. Provide a whitewater c"""nel that would be safe under all flo"1 conditiom' channel. was modeled in wood, as were the retaining walls of the channel
This means there must be no ','keeper" rollers or holes, and that all s'1lid SUrfa~ and dividing walls of the inlet. The gates were modeled in sheet metal. and
~hat might be hit must be s~ooth and sloping. (The "keeper" is la hydra' were hinged to make them fully operational. In its final form, the model included
Jump ~hlch tends to hold a ;person or object in the turbulent roll~r. A ma esthetic details such as the proposed bicycle-foot path along the west bank.
obJecllve of the model studies was to not lose the effect of jumpl waves. , (ootbridge crossing the river, railings along portions of the left bank, and
instead to design them so they will not hold a boater or swimll/er. This' shrubs and trees (Fig. 5). Photographs and movies showing the final model
accomplished by careful design, such that the. mass flow i~ through the walq hydraulics were made, and the general arrangement of how the Denver white water
and reverse cIrculatIon IS red~ced.) In addlllon, the eddIes for'l'ed bebim\ c","nel would actually appear was apparent. .
obstructIOns should have velOCIties low enough so that swimmers iwill not
trapped but can swim either to shore or continue downstream.' Moos. STUDIES

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Similitude and Hydraulic Model Studies.-Open channel structures such ill. Inlet Control Strueture.-Severe restraints existed. such as the necessity of
the kayak chute generally have gravity forces and inertial forces that f~r outwei maintaining the Public Service Company pool surface within inches of EI. 90.2
viscous and turbulent shear forces. Thus, geometric similitude and equivalenq (except during floods), not creating a significant obstacle to flood flows, the
of Froude number for the model and prototype produce a good approximati""
to dynamic similitude; i.e. v' jg I = v'jg I in which v = velocity' g ,I
. m m m p p p' . I
~ccelerahon due to gravity; and I is some appropriate length. Because graVil!l.
IS the same (8" = 8,), and if one defines a length ratio. A = I / I , tlx .
following is defined: v z v v1:' = velocity; t = t v1:' = ti;;'e' mQ .
p m pm' P
Q"A5i' = flow; F, = F"A = force; and h. = h"A = depth. On the bas.
of the preceding. and in consideration of having adequate flow quantities, deptlu:
and velocities. a model scale ratio. A. of 1-20 was selected. Thus, velociti
in the prototype will be V20 or 4.47 times the velocities measured in t
Diodel. while dimensions of the prototype will be 20 times the model dimension
Laboratory Facililies.- The 1:20 scale model was constructed within an exist'
wooden containment box;. or flume. available in the Bureau of Reclamation' ,
Hydraulic Laboratory in Denver, Colo. Water was supplied by a centrifu
pump and measured by a standard laboratory orifice.venturi meter. Horizon'
rails were attached along the top of the model and a 6-ft-long (1.8-10) transve,
movable aluminum beam rode on the rails and carried the point gage used{
to establish elevations and grades in the model channel. Velocity measuremenUl' :
were made using a standard laboratory Pitot-static tube and a water-filled two_tu~ . ,
manometer. After completing its journey through the model, the water flow
back into the laboratory reservoir for recirculation.
The 3j4-in.-thick (19-1010) plywood channel floor was set at about hip heIgh FIG. 5.-Archltectural Faltu... of Final Modal
on seven pairs of screwjacks and seven adjustable support structures. The latter
provided the needed lateral and longitudinal stability, while permitting easll' ability to regulate the flow entenng the channel, and doing so in a way that
adjustment of the elevation and slope of the channel floor with the screw jacks would let boats pass safely from the pool through the gate mto the channel.
Reinforcing stnps of 2-in. by 2-in. (51-10m by 51-10m) lumber were fastened. In addition. the structure had to be reasonable in cost. capable of wlthstandmg
longitudinally to the underside of the floor to prevent sagging of the PIYWOod'l flood flows. not conducive to sediment deposition and fouling, and generally
The final berms or obstructions were made of commercially available hard plaster trouble-free in operation.
material mixed and poured into wooden forms and allowed to harden. A Sofl Of the inlet designs tested, the most favorable was a 4O-ft-wide (12.2-10)
grade of modeling clay was used to seal lhe joints in the model, to quickl) 'ntrance (Figs. 6 and 7) controlled by a 24,ft-long by 6-ft-high (7.3-m by 1.8-10)
make various shapes and slopes for trial testing in the model, and (0 foro radial (taintor) gate of 6-fl (i .8-m) radius at left side and a l5-ft-wlde (4.6-10)
transition slopes, fillets, architectural details, and the small wave-making humpl boat passage to the right. (The major portion of the existing fabridam will
on the channel floor (Fig. 4). Small bags of sand were helpful in the earl) remain in place and be available for passing floods. The fabndam wIll usually
stages to identify arrangements of obstructions and humps that would produce be used instead of the radial gate, but for large floods. the fabrioom will be
desirable currents. velocities. and depths. The fabridam, at its fully inflated operated jointly with the radial gate and the flap gate.) A I-ft-thick (0.3-10)
height and with its length shortent1tl to provide room for the entrance for th< . divider wall separates the two flow passages. Flows through the boat passage

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