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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. Re-evaluate the recommendations made in the 1993 document 'Flash Flood
Warning Planning for Douglas County Meteorological and Hydrological
Support' to expand the existing Douglas County flood detection network and
make new recommendations if needed.

. Determine basin average rainfall criteria, specific to individual major drainage
basins for the 2-year, 5-year, 1D-year, 25-year, 50-year, 1 DO-year, and 500-
year recurrence intervals for durations of 1-hour, 3-hours, 6-hours, 12-hours
and 24-hours.

. Determine drainage basin hydrologic characteristics such as soil types, time
of concentration, percent of imperviousness, area, and slope. Determine
antecedent moisture affects on basin time of concentration.

. Determine watercourse discharge, velocities, and depths.

. Determine stream gage information that is consistent with National Weather
Service E-19 procedures for the stream gages owned and maintained by the
Urban Drainage and Flood Control District and the United States Geological
Survey.

. Develop Flood Warning Templates which are currently used by the Urban
Drainage and Flood Control District to provide real-time assessment of
streamflow.

. Develop GIS-based flood maps that depict water inundation and water depths
associated with a 25-year, 50-year, 1 DO-year, and 5DD-year recurrence
interval.

. Determine flood risk and vulnerability to residents, business, County and local
jurisdiction infrastructure and critical facilities in and around the East Plum
Creek, Plum Creek, East Cherry Creek, West Cherry Creek and Cherry
Creek watercourses.

. Determine depth and duration rainfall criteria that if predicted would prompt
flood advisories watches and warnings.

. Develop Flood Threat Recognition criteria (rain gage rainfall depth/time and
stream gage criteria water discharge, water stage height), which if reached or
exceeded would prompt information dissemination to key personnel.

. Develop levels or preparedness (Modes) based on potential flood depths
and/or time until potential flooding. Develop actions for
departments/agencies to perform with regard to flood response for each level
of preparedness. Incorporate this information into the Douglas County,
Castle Rock and Parker Emergency Operation Plans (EOP's).

. Develop evacuation procedures and policies based on the levels of
preparedness. Develop specific actions for departments/agencies to perform
with regard to evacuations. Incorporate this information into the Douglas
County, Castle Rock and Parker EOP's.

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