FLOOD10402

• County: Douglas
• Basin: South Platte
• Title: Douglas County, Colorado Flood Warning Assessment - Project No. CI03-037
• Date: 9/1/2004
• Prepared For: Douglas County Public Works, CWCB, Parker Stormwater Utilities, Castle Rock Stor
• Prepared By: HDR
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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It should be noted that the NWR continuously distributes forecasVwatch/warning
products on a '24/1' basis. The responsibility of monitoring the information from NWR
lies primarily with the end-user of a NWR receiver. However, in terms of a 'pro-active'
notification, (ex: an audio alert or tone) there are only certain products that triaaer such
alerts. Typically, any NWR receiver should be triggered with the issuance of any watch
or warning in the area of responsibility of the NWSFO-BOU, including Douglas County.
A user can limit the geographical area of interest that triggers an alarm given they have
a NWR receiver that has such programmable features. In regards to the utilization of the
EAS, not every NWS watch and/or warning product is disseminated over the system.
Typically there is some local control and discretion that is exercised over what
information is transmitted through the EAS.

Criteria That Prompts the Issuance of the Advisory, Watch and Warning
Products

Flash Flood Guidance FFGCO (FOUS63 KKRF)
Flash Flood Guidance (FFG) produced by the NWSMRBFC to quantify the amount of
rainfall in various time periods that may initiate flash flooding. This product is utilized
to offer guidance to the potential of flooding in particular basins by quantifying criteria
of critical precipitation amounts to generate such conditions in 1-, 3-, and 6-hour
intervals.

The above information along with some localized alteration of values is merged into a
system called the Flash Flood Monitoring and Prediction product (FFMP). This system
overlays Doppler radar rainfall estimates and real time Doppler radar over a projection of
various sub-basins in an area. The observed/forecast information is used in concert with
the FFG provided by NWSMRBFC. The NWSFO-BOU staff can alter the guidance
locally for individual sub-basins given more specific information (Le. basin
characteristics, local rainfall amounts). The use of the FFMP is driven by the program
utilizing the Doppler radar estimated rainfall with (where applicable) some ground truth
values and the forecast to determine if the precipitation in the basin is or will exceed
FFG.

Hydrological Forecasts

The NWSMRBFC produces both basin-specific quantitative precipitation forecasts (QPF)
and site-specific hydrologic forecast guidance to the NWSFO-BOU.

There is one hydrological forecast point in Douglas County, which is located at a USGS
stream gage on Plum Creek, near Sedalia. The point is identified by the following 5
character ID: LOVC2: Plum Creek near Sed alia

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