FLOOD05077

• Designation Number: 351
• County: Arapahoe
• Community: Aurora
• Stream Name: Sable Ditch
• Basin: South Platte
• Title: Letter of Map Revision - Request - Sable Ditch at Sable Boulevard and 23rd Avenue, Aurora, Colorado
• Date: 8/1/1993
• Designation Date: 1/1/1994
• Floodplain - Doc Type: Floodplain Report/Masterplan

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I, INTRODUCTIOt{

The location of Sable Ditch at the intersection of Sable
Boulevard and 23rd Avenue is shown on a portion of the City
map on Figure 1, The special flood hazard area at this
intersection is shown on panel 20 of the Flood Insurance Rate
Map,

In 1982, the City of Aurora requested and obtained a revision
to the Flood Insurance Rate Map for the reach of Sable Ditch
from Sable Boulevard to the upstream limit of the Flood
Insurance Study, following the construction of improvements to
Sable Ditch. The letters in Appendix A refer to that
revision.

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At that time, the culverts under Sable Boulevard were left
unimproved. Therefore, although upstream of Sable Boulevard,
the lOa-year flow is confined within the new concrete channel,
the undersized culverts at the Sable Boulevard crossing cause
the water to backup and flood the intersection, especially the
lower northeast corner. Four lots at this northeast corner
are affected by the flooding (lots 1, 2, 11 and 12, block 1 of
Wiley Heights Subdivision amended).

In December of 1992, the two existing 60" RCP culverts were
replaced with two 9' X 6' reinforced concrete box culverts
capable of carrying the lOa-year flow in Sable Ditch. The
purpose of this submittal is to demonstrate that the lOa-year
flow in Sable Ditch can pass through the new culverts without
overtopping and flooding the intersection of Sable Boulevard
and 23rd Avenue.

II. HYDROLOGY

Peak discharges for Sable Ditch at Sable Boulevard, as taken
from the City of Aurora Flood Insurance Study, are as follows:

la-year
870 cfs

.50-Year
1200 cfs

lOa-year
1350 cfs

SOO-year
1690 cfs

It should be noted that the above numbers have not been
updated since the original 1977 Flood Insurance Study despite
all the changes to the drainage basin.

In 1991, Kiowa Engineering Corporation as a consultant for the
city of Aurora and the Urban Drainage and Flood Control
District, completed the study titled "Major Drainageway
Planning - Granby and Sable Drainageways." Their hydrologic
analysis, using the current Colorado Urban Hydrograph
Procedure (CUHP) and the Urban Drainage Storm Water Management

ECS0036

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