Flood Warning


Flood Warning Program Activities

Kevin G. Stewart, P. E.
Project Engineer, Floodplain Management Program

20 Years of Flood Prediction & Notification


The GRD Weather Center


Henz Kelly and Associates (HKA)


Henz Meteorological Services (HMS)

The District's Flash Flood Prediction Program (F2P2) just completed its 20th year of providing local governments with early forecasts of flood potential, internal alerts and warnings. Congratulations to John Henz who has served as the District's private meteorologist since 1979. John has been involved with three businesses in providing the contract services to the District.

In 1998, messages were issued on 33 days including 3 days in May, 3 in June, 14 in July, 12 in August and 1 in September. Flash flood warnings (Message 3) were issued on four days (July 25, 30, & 31, and August 21). With the arrival of the Denver monsoon beginning July 22, the next two-week period was marked by messages being issued every day except 7/27 and 8/2. What began as a very dry drought-like summer ending wetter than normal with the South Platte River basin receiving the highest rainfall amounts in the State (205% of July average) according to the Natural Resources Conservation Service.

ALERT System Use & Expansion

The District ALERT base station logged over 4900 modem connections during 1998 representing over 3500 hours of connect time. This represents a 113-percent increase in remote use time compared to last year's record-breaker of 1640 hours. It appears that Colorado's 1997 flood disasters may have contributed to this dramatic increased interest in real-time flood data. These numbers do not represent total system usage since seven other base stations are also operating in the service area. Many new users are rapidly becoming aware of the availability of ALERT data on the Internet. The ALERT Web Server may be accessed from the District's home page (http://www.udfcd.org/).

The District provides its local government partners and certain other cooperators with free dial-up access to the base station. In addition to ALERT data displays, a full suite of weather products is also available including watches, warnings and advisories from the National Weather Service; and heavy precipitation outlooks, quantitative precipitation forecasts and internal message status reports from HMS.

The Douglas County flood detection network (FDN) project is nearing completion with 5 of 6 sites fully operational. This FDN consists of 3 weather stations and 3 rain/stream gages. Final site selection for the East Plum Creek gage is one remaining task. It is anticipated that this station will be in the vicinity of Castle Rock. The other two stream gages are located on West Plum Creek at Pine Cliff Road and on Cherry Creek at Castle Oaks Road. The weather stations are located at Highlands Ranch, Parker and Castle Rock. A local flood warning plan will be developed with Douglas County in 1999.

ALERT data is currently available from 143 gaging stations comprising 124 rain gages; 69 water level sensors and 13 weather stations.

A new FDN project is expected to start next year for the Upper Sand Creek basin in Aurora. A preliminary design has been completed with five new ALERT stations proposed. The total expected cost for this expansion is $60,000 with the District and Aurora cost sharing equally in the project. Once completed, the Sand Creek basin will be monitored by a total of 28 rain gages and 19 stream gages combining existing FDNs for Toll Gate Creek and Westerly Creek along with two other main stem gages on Sand Creek downstream of I-225.

1998 Floods

No federal flood disasters were declared in Colorado in 1998, but heavy rains and significant flooding continued to plague the Colorado front range much like the summer of 1997, which will be long remembered for the deadly July 28 flash flood in Fort Collins. Twelve other Colorado counties also received flood disaster declarations in 1997. With last year's events fresh in everyone's mind, flooding concerns in the Denver metropolitan area remained high and the 1998 storm season proved itself worthy of this attention.

Wednesday, July 22:
The monsoon season kicked-off with the heaviest rainfall being reported for Aurora in the vicinity of Mississippi and Chambers (2.59"). The ALERT system measured rainfall amounts exceeding one-inch at a number of locations. The cover story describes what happened on this day in Broomfield along City Park Drainageway. The gage at Broomfield measured 0.83" while other areas received more than twice this amount. The Rocky Mountain News characterized this day as "welcome relief from the recent heat wave."
Friday, July 24:
Heavy rains that occurred during the evening caused problems in Denver with flooded basements, stranded drivers and downed power lines. A forecaster for the NWS measured 3" in 30 minutes at his home near W. 38th Ave. and Federal Blvd. The railroad viaduct near 38th and Fox trapped motorists in water 4 to 5 feet deep. This notorious flood area has been less of a problem in recent years due to drainage improvements completed by Denver and the District, but this storm clearly exceeded the design rainfall amounts.
Saturday, July 25:
The cover story is devoted to this day and describes the benefits of completed drainage and flood control improvements in the City of Broomfield. Impacts to other areas are also described. The annual peak discharges listed in the accompanying table, "1998 Peak Flows" further illustrate the significance of this day District-wide.

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ALERT Record Rainfall July 30, 1998
Salisbury Park Weather Station in Parker
1-min 5-min 10-min 30-min 60-min Total







Thursday, July 30:
In 20-years of measuring heavy rainfall with ALERT gages, this day marks the maximum measurement of rainfall intensity and storm total by the ALERT system. It is also interesting to note that this measurement was made at a new site installed just this year in Parker. The accompanying table shows the duration and corresponding maximum rain amounts measured at the Salisbury Park weather station on July 30. At one point in the storm, rainfall intensities were approaching 20"/hour. According to the ALERT equipment vendor, Panama is the only other location known to have measured rain intensities of this magnitude with an ALERT tipping bucket. The NOAA precipitation frequency atlas estimates the 5-minute, 100-year intensity at 9"/hour.

ALERT rain map for July 30, 1998 storm
                                     Click on BOULDER or DOUGLAS for more maps
    A flash flood warning for the Parker area was issued based on both the precipitation forecast and the real-time rain observations from the Parker gage. HMS and District staff initiated the conversation with the NWS that led to the warning. This represents another landmark event illustrating how local programs in partnership with the NWS benefit the public by enhancing the early warning process. Richard Brandt, Acting Public Works Director for Parker, felt that the July 30 early warning was a very good decision.
    Local streets and small drainageways in Parker were hit hardest by the flooding, while no major damages to private properties occurred. The worst stream flooding was reported along Sulphur Gulch and Tallman Gulch, but damages there were also low since development has been kept outside the floodway and above 100-year levels. Cherry Creek experienced an estimated 5-year event based on a field survey conducted by Leonard Rice Consulting Water Engineers for the District. The USGS stream gage on Cherry Creek at Main Street was damaged by floodwaters. The effluent discharge pipe from the Parker wastewater treatment plant was buried under 4 feet of sand in Sulphur Gulch.
    Coordination with the news media by District staff resulted in excellent coverage and documentation of the flooding at Parker. Video taken from the KCNC-News 4 and KMGH-News 7 helicopters was especially useful.
Parker was not the only area hit on July 30; with Denver street flooding, zodiac boat rescues at "Lake Logan" (Logan Street underpass of I-25) and a kayaker rescue from the S. Platte River at Santa Fe being the lead stories for the evening news.

Friday, July 31:
A flash flood watch was issued by the NWS shortly after 2 p.m. for the entire front range from Colorado Springs to Fort Collins. At approximately 6 p.m., a flash flood warning was issued for western Douglas County. Local authorities considered evacuating homes in the Sedalia area but no action was needed. In Denver, street flooding damaged private property in the vicinity of Evans Ave. and Lipan Street. Buffalo Creek flooding was the top news story. This Jefferson County mountain community has sustained numerous floods since a forest fire ravaged the area in May of 1996. Three inches of rain in one hour was reported to have fallen at Buffalo Creek causing extensive road damage, large debris accumulations, and disrupting electric, phone and water service for the night. Mudslides were a problem for a number of other mountain towns that evening.
Monday, August 10:
While no flash flood warning was issued for the August 10 storm, extensive urban flooding did occur in Lakewood and Denver. Between 4:45 and 5:45 p.m., 3.26 inches of rain was measured in Lakewood near the intersection of W. 1st Ave. and Balsam Street. Rush-hour traffic was at a crawl while many homes had their basements flooded. Vehicles were floating in the Wal-Mart parking lot where the floodwater was 3 to 4 feet deep. This parking lot is located in the floodplain of South Lakewood Gulch near W. 2nd Ave. and Wadsworth Blvd. East of Kipling Street, McIntyre Gulch was out of its banks at a number of locations. Lakewood Gulch in Denver overtopped Wolff St. by at least 3 feet. This event contributed directly to a Lakewood City Council action exactly 2 weeks later endorsing a plan to form a storm water utility and establish a fee of 88 cents a month for each 1000 square feet of impervious area, costing the average home owner $1.98 per month.

1998 Peak Flows: This table lists some of the more notable
peak flows measured by the ALERT System in 1998.



Peak (cfs)

May 6 @ 23:07

Bear Creek above Cold Spring Gulch


July 25 @ 18:54

Broomfield Basin 3207/Pond 6

* 470

July 25 @18:56

Harvard Gulch Park


July 25 @ 19:09

Goldsmith Gulch at DTC/Temple Pond


July 25 @ 19:12

S. Platte River at Dartmouth Ave.


July 25 @ 20:04

S. Platte River at 19th Street


July 25 @ 20:34

Holly Dam


July 25 @ 20:46

Toll Gate Creek at E. 6th Avenue


July 26 @ 00:20

Englewood Dam


July 30 @ 17:46

Lena Gulch below Youngfield Street


Aug 19 @ 21:15

Westerly Creek at Montview Blvd.


Aug 22 @ 04:52

Sand Creek Park near I-225


Oct 16 @ 13:48

Ralston Creek at Carr Street


* Indicates new record.

Friday, August 21:
At 4:19 p.m., the NWS issued a flash flood warning for NW Elbert, south central Arapahoe and extreme NE Douglas Counties. The storm was centered over Coal Creek just outside the District in Elbert County, east of Parker and north of Elizabeth. Newspapers reported that up to six inches of rain fell in Elbert County with two county roads under water much of the evening. Roads in Arapahoe County were also closed. Coal Creek and Murphy Creek join to form Sand Creek near Buckley ANG Base in Aurora. The 1998 peak discharge at the Sand Creek Park ALERT gage below I-225 occurred nearly 12 hours later (see table).


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