FLOOD09310

• County: Adams
• Community: Adams County
• Stream Name: Todd Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation
• Date: 12/1/1985
• Prepared For: Adams County
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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- FUTURE FLOODS -

floodplain and the water surface profile. Table V,
F100dway Reference Data," presents the computed
elevations, along with other pertinent floodplain
descriptive data.

"Floodplain and
100-year flood
information and

Flood Frequency and Discharge

The 100-year flood is based upon recorded historical precipitation and
other valid data and, statistically, has a one percent chance of being
equalled or exceeded during anyone year. Likewise, the 10-year flood
has a ten percent chance of being equalled or exceeded during anyone
year. The 100-year flood is also commonly referred to as the base
flood, regulatory flood, and intermediate regional flood.

Present development along the Todd Creek main stem and tributaries is
very light. The majority of land adjacent to the streams is used for
agricultural purposes. Several streamside oil and gas wells are also
present. Very little subdivision type residential development has
occurred within the basin. Instead, many of the residential dwellings
appear to be older farmhouses and scattered rural type development.

The discharge probability profiles in Figures 3 through 5 graphically
represent the rel ati ve magnitude of the major flood events. Thi s
information is useful not only for regulating future floodplain
construction, but also for planning and engineering of channel
improvements, flood protection facilities, and road crossings.

The Todd Creek mai n stem and tri butary channels are generally well
defi ned with adequate conveyance for the 100-year flood. However,
problem areas do exist and are created primarily by inadequate road
crossings, existing reservoir embankments, or breached reservoir
embankments.

The 100-year flood is i dentifi ed by the Urban Drai nage and Flood
Control District, the Colorado Water Conservation Board and the
Federal Emergency Management Agency (FEMA) as the flood magnitude used
for the regulation of floodplains and for the design of improvement
facilities. However, the UDFCD and FEMA differ in their definition of
the 100-year flood. FEMA uses existing basin development for
hydrology calculations, and the UDFCD uses future basin development.
Both agencies use the existing channel facilities to convey flows. In
Colorado, the 100-year floodplain represents an area of state interest
as defined in H.B. 1041.

The fo 11 owi ng
of 100-year
tri butari es.

several pages of narrative
flooding for the Todd

contain a general description
Creek main stem and four

Todd Creek Main Stem: The study reach for the Todd Creek main stem
begins at its projected confluence with the South Platte River (Cross
Section No.8) and ends at Cross Section No. 97, 2500 feet upstream of
Holly Street. Floodplain limits and the water surface profile for
this reach are shown on Plan and Profile Sheets 2 through 13, and
Floodplain Map Sheets 23, 24, and 25.

Flooded Areas

Stream crossings in this reach include Holly Street, Quebec Street,
Yosemite Street, Elmira Drive, Havana Street, and Riverdale Road. An
unnamed private road and the Brantner Ditch Flume also cross Todd
Creek in the lower portion of the study area. The stream gradient for

The Appendix of this report contains the Flood Hazard Area Delineation
plan and profile drawings showing the limits of the 100-year

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