Kevin G. Stewart, P. E.
Project Engineer, Floodplain Management Program
The District's ALERT base station logged more than 3500 connections in 1996. This base is one of eight currently used within the District's Flash Flood Prediction Program (F2P2). Four other base stations located in Aurora, Boulder and Denver also have modems which are routinely accessed. In addition, Aurora provides ALERT data via their Internet home page.
The District provides its local government partners and certain other cooperators with free access to the base station. In addition to ALERT data displays from 130 gaging stations (113 rain gages, 62 water level sensors and 8 weather stations), a full suite of weather products is available including watches, warnings and advisories from the National Weather Service; and heavy precipitation outlooks, quantitative precipitation forecasts and internal message status reports from the F2P2 meteorologist, Henz Meteorological Services. Recent system enhancements have contributed to the increased usage by allowing remote users to more easily interpret data using graphics communication software. Warning areas can be displayed using shaded maps. Emergency managers will find tools like these increasingly useful in directing early public safety actions.
Dedicated phone lines were added to the District base station in 1996 to accommodate KCNC-Channel 4 and KMGH-Channel 7, the Evergreen Fire
Protection District (FPD) and the National Center for Atmospheric Research (NCAR). With no
direct cost to the District, ALERT system access was approved by recognizing the public
safety contributions each of these organizations provide. The media lines were used by
weather news teams headed by Larry Green at KCNC and Pam Daale at KMGH. An excellent
working relationship has developed from this interaction and the viewers were well served.
The Evergreen FPD logged daily calls to obtain ALERT data from two weather stations. This,
along with other weather data, was used to develop a more representative fire weather
reporting system for the Jefferson County mountains. The additional stations permitted
dividing the county into three regions to better assist fire districts with their
activities. NCAR's dedicated access to the ALERT system was devoted to Doppler radar
research through the summer months. Their study dealt with improving radar precipitation
estimates using Doppler radar technology. ALERT rain data was used to help validate their
models and identify deficiencies.
The District's ongoing weather information dissemination project with NOAA's Forecast Systems Laboratory (FSL) has evolved in 1996
to include a surveillance component and a LAN link ALERT data ingest. This project is
serving as a model and testing ground for how NWS offices will interact with emergency
managers and other local agencies in the future.
The Program for Regional Observing and Forecasting Systems (PROFS) at NOAA's Environmental Research Laboratories (ERL) in Boulder recently discontinued a 22-station mesoscale network (or Mesonet) of weather stations which has been operating in northeast Colorado since the mid-1980s. This system has been available to the F2P2 and many others at no charge and its loss will be felt. For flash flood forecasting the Mesonet allowed meteorologists to observe changing weather conditions every 5 minutes; display wind fields and convergence lines; identify moisture sources; plot vertical profiles of temperature, wind and moisture up to mountain top levels; and predict storm development and movement.
The District is taking some steps in 1997 to offset this loss by relocating ALERT
weather stations in Boulder County and cooperating
with Douglas County to develop three new sites there. The District is also planning to
evaluate which Mesonet sites have proven to be most useful for flash flood prediction over
the past decade and may consider replacing a few of these stations with ALERT equipment.
ERL also has an ongoing project which may eventually lead to a cooperative of data
providers contributing weather information to be assimilated in a common database and
shared among the contributors.
Between 10 and 11 PM on July 12, a 30-foot wall of water roared down the North Fork South Platte River causing two deaths and damages exceeding $5 million. The flood resulted from a thunderstorm beginning at approximately 9:40 PM which produced an estimated 2 to 3.5-inches of rain within 30 to 90 minutes over a 10 to 30 square mile area. Sand Draw and the lower portion of Buffalo Creek, both running through the small Jefferson County community of Buffalo Creek, were hard hit. Estimated peak discharges (17,000 cfs maximum) exceeded FEMA's 100-year flood estimates by 10 to 20 times.
The storm was centered over a steep-sloped fire-scorched area just south of Buffalo
Creek. A 13,000-acre forest fire, which occurred less than two months prior to the flood,
clearly contributed to the flood's destruction. The intense fire significantly changed the
runoff characteristics of the watershed by causing not only a near total loss of
vegetation but also by altering the physical, chemical, and biological properties of the
soil, producing "hydrophobic" conditions. Essentially the watershed became the
hydrologic equivalent of a parking lot.
The F2P2 activated a record number of 51 days this year. The program has been serving the District since 1979.
During 1996 the ALERT network measured one-hour rainfall amounts exceeding an inch on
eight days. The station at Morrison reported the heaviest amount with of 2.32" on
September 11. Even though we experienced a very active season, all flooding that occurred
within the District this year may be categorized as nuisance events.
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