FLOOD03254

• County: Logan
• Community: Sterling
• Stream Name: Pioneer Ditch
• Basin: South Platte
• Title: Master Drainageway Plan Pioneer Ditch at Sterling
• Date: 12/1/1995
• Prepared For: Sterling
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

3.2.10 The crest of the drop structure
of the weir and extends down below the double
, be turbulent near the top of the structure, and
3.2.11 The detention pond will disch
. pipe. As described previously and shown on PIa
a small collector channel sloped toward Pion
located at the center of the detention basin sout
It is recommended that reinforced concrete pipe
The upstream invert of the pipe will be the floo
downstream invert elevation will depend on the
put in. The pipe should not be placed on the ch
and yet it should have as much of a positive slo
a 0.5-foot drop. Three outfall sizes were an
concrete pipe. Culvert nomographs from the
calculate discharge through the outlet pipes b
of pipe, roughness, and entrance conditions.
peak discharge they can evacuate and the amo
Table 4 summarizes the results of the analysis
T
DETENTION POND
OUTFALL DIAMETER PEAK D
(inches)
30
42
54
· The time to drain the pond spans from the time when 0
above the invert. Flow beginning is marked by the point
the water elevation in the channel. For all of the outlet pi
3.2.12 The final detention pond design
. .

should have a cutoff wall that extends the width
riprap layer and filter at least 1 foot. Flow wilJ
the cutoff wall wilJ help prevent undercutting.

arge flows back into Pioneer Ditch via an outfall
te 3, the basin floor is sloped to the center, and
eer Ditch aids in drainage. The outfall will be
h wall and will be approximately 70 feet long.
be used, but the final choice is up to the City.
r of the detention pond at 3916.0 feet msl. The
Pioneer Ditch channel invert when the pipe is
anne1 bottom because of potential sedimentation,
pe as possible. The calculations were based on
a1yzed for efficiency: 30-, 42-, and 54-inch
reference listed in paragraph 2.9 were used to
ased on headwater and tai1water conditions, length
The basic differences in the three pipes are the
unt of time it will take to draw the pond down.

ABLE 4
OUILET ALTERNATIVES

ISCHARGE
(cfs)

50

90

130

"TIME TO DRAIN POND
(days)

2-3

1-2

1

utflow begins to when the pond is drawn down to 0.5 foot
where the elevation of the water in the pond is higher than
pes, outflow begins 1.6 hours after the peak inflow.

will include the pond itself, an overflow weir
to divert Pioneer Ditch peak flows mto the pond, a berm between the pond and Pioneer Ditch
to prevent flows from entering the pond somewhere other than the weir, and an outfall pipe to
drain the pond. The design of the detention pond and weir should be followed closely if the
pond is constructed because significant modifications could alter the results of this study. The
pond could be deepened if needed, but the method of discharging flows back into the ditch may
get more complicated. The outfall pipe size and slope and drop structure slope are variable,
depending on the resources at hand.

8