Flood Warning & Preparedness

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

Prediction & Notification

The District’s Flash Flood Prediction Program (F2P2) issued messages on 48 days in 1997 falling three short of last year’s record. The number of flash flood watch (Message 2) days did, however, set a new record this year at 12 days, two of which (July 27 and July 30) resulted in flash flood warnings (Message 3) also being issued in the District. Henz Meteorological Services (HMS) provided the weather forecasting for the F2P2 and were responsible for notifying local governments of impending floods.

As suspected, the October 1, 1996 loss of the FSL Mesonet had an adverse impact on flood forecasting capabilities in 1997 (ref. 1996 Flood Hazard News). By mid-July three Boulder County ALERT weather stations had been strategically relocated which, according to HMS forecasters, had a the very positive net effect as the Colorado monsoon rains began soon thereafter. One additional Boulder County weather station will be relocated by spring of 1998, along with the installation of three new weather stations in Douglas County. The Mesonet Loss Impact Study draft report, completed early in 1997, is being revised to reflect the past year’s operational experience and to revisit the recommendations for locating additional weather stations.

ALERT System News

The District’s ALERT base station logged 5511 modem connections during 1997 representing over 1640 hours of remote use and exceeding the previous year’s "high-water mark" of 3871 logins. This record-setting use year is indicative of the 1997 flood season (see cover story). It should be noted that these statistics do not represent total system usage since the District Base is one of eight existing base stations.

The District provides it’s local government partners and certain other cooperators with free 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.

Having just completed two years of adjusting to a substantial operating system upgrade along with its associated "improved" database management and display software, it is nice to report that system stability has finally been achieved. In other words, the bugs now appear manageable. More custom reports and graphics tools are available then ever, making the interpretation of ALERT data more friendly.

Also, a new windows-based software package known as STORM Watch™ is becoming the system of choice for many. The District’s ALERT system maintenance contractor, DIAD, Inc. of Lyons, Colorado, is the author of this Microsoft Access™ driven program. The District began running STORM Watch as part of their ALERT base station operations this year, having participated with Boulder County in its initial concept development and testing. This parallel utility provides a very nice visual addition to the multiple-PC District Base Station environment as well as providing backup data collection and analysis.

ALERT data requests and local government interests continue to fuel demands for Internet access. The District is currently considering a proposal with the City of Aurora to support a dedicated "Server" for ALERT, making data from the system widely available.

Record Year for Breaking Gage Records

*1997 ALERT Gage Records*
Location	Peak (cfs)	Date & Time
Cherry Creek at Market Street	3200	July 28 at 20:56
Cherry Creek at Steele Street	2350	July 28 at 19:47
Cub Creek above Evergreen	180	June 7 at 18:02
Goldsmith Gulch at Eastman Ave.	2040	July 28 at 18:26
Lena Gulch at US Highway 6	510	July 27 at N/A
No Name Creek at Quincy Ave.	530	July 28 at 19:07
Sand Creek at Brighton Road	4200	July 29 at 02:47
Sand Creek Park near I-225	3480	July 29 at N/A
Toll Gate Creek at E. 6^th Ave.	1760	July 30 at 19:21
Westerly Creek at Montview Blvd.	1200	July 19 at N/A

During 1997 the ALERT system logged a record number of 53 rainfall rate alarms (1"/hr amount exceeded) on 11 days (May 29; June 6; July 19,27,28,30,&31; August 4,5,&11; September 4). The table lists the ALERT stream gages which set new records in 1997.

Gages on three detention basins also measured record levels this year: Granby Ditch on East 6^th Ave. in Aurora (11.0’ on July 30 at 21:47); Holly Dam on Little Dry Creek in Arapahoe County (15.0’ on July 31 at 17:52); and Slaughterhouse Gulch/Grant Street detention basin in Littleton (5.3’ depth on July 31 at 16:34).

ALERT data is currently available from 130 gaging stations comprising 113 rain gages; 62 water level sensors and 8 weather stations. Anyone interested in obtaining ALERT data from the District may contact Kevin Stewart at 303-455-6277.

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