FLOOD WARNING &
PREPAREDNESS
by
Kevin G. Stewart, Project Engineer
Floodplain Management Program
ALERT System Usage Increases
The District’s
ALERT base station logged more than 3,500 modem connections during 1996. This
base is only one of eight similar platforms currently used within the
District’s Flash Flood Prediction Program (F2P2). Four other base stations
located in Aurora, Boulder and Denver also have phone modems which are
routinely accessed. In addition, Aurora provides ALERT data to the public via
their Internet homepage.
The District
provides its local government partner agencies 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 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 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 may also be displayed using color-shaded
maps. Emergency managers will find tools like these increasingly useful in
directing early public safety actions.
Dedicated
phone lines were added to District base station in 1996 to accommodate two Denver
television stations (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, conditional 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 the Hiwan and Blue Mountain
weather stations. This, along with other weather data from the Colorado State
Forest Service (CSFS) and the USFS, was used to develop a more representative
fire weather reporting system for the Jefferson County Mountains with daily
information disseminated by the Sheriff’s Department to all county fire
districts. Rather than reporting a single fire danger rating for the entire
county as in the past, the additional weather stations permitted dividing the
county into regions (north, central and south) to better assist fire districts
with their wildland fire prevention and suppression activities. Readers wanting
more information about this program should contact Chuck Dennis at CSFS or Brad
Ruder with the Evergreen FPD.
NCAR’s
dedicated access to the ALERT system was devoted to Doppler radar research
lasting only through the summer months. Their study dealt with improving radar
precipitation estimates using dual-polarity Doppler radar technology. Data was
gathered from a transportable research radar located near the Denver NEXRAD
radar, precipitation algorithms were processed and the results were compared
with NEXRAD precipitation estimates. ALERT rain data was used to help validate
the models and identify deficiencies. Readers wanting more information about
this project may contact Ed Brandis at NCAR or visit their website.
Outside
requests for ALERT data is also increasing. Records are retained of each
request and appropriate disclaimers are attached with each transmittal. Anyone
interested in obtaining ALERT data from the District may contact Kevin Stewart
at kstewart@udfcd.org.
Loss of Mesonet
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. Antiquated equipment, high maintenance
costs and no federal funding were cited as the reasons for ending the project.
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 proved invaluable allowing
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
will be 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.
Local Data Acquisition & Dissemination
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. Readers wanting more information about this
project may contact Rich Jesuroga at NOAA/ERL/FSL or visit their website.
Buffalo Creek Fire/Flood
Within hours
following the closing session of a well-attended international symposium in
Fort Collins marking the 20th anniversary of the Big Thompson Canyon flash
flood, Coloradan’s received a grim reminder of how devastating mountain flash
floods can be. Between 10 and 11 PM a 30-foot wall of water roared down the
North Fork South Platte River causing two deaths and damages exceeding $5
million. Without question, the Buffalo Creek flash flood of July 12, 1996 was
the headline flood news event of the year in Colorado. Buffalo Creek is a small
mountain community in Jefferson County located outside the District
approximately 25 miles southwest of Golden.
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 this
mountain watershed became the hydrologic equivalent of a massive shopping mall
with lots of parking and no stormwater detention.
|
1996 Peak Flows (no records set) |
||
|
Location |
Peak |
Date/ |
|
Cherry Creek at Market St. |
1140 |
May 26 |
|
Cherry Creek at Steele St. |
660 |
Sept. 18 |
|
Goldsmith Gulch at Eastman Ave. |
1100 |
July 12 |
|
Harvard Gulch Park at Logan St. |
650 |
July 12 |
|
Ralston Creek at Carr St. |
1540 |
August 26 |
|
Sand Creek at Brighton Road |
1390 |
May 26 |
|
S. Platte River at Dartmouth Ave. |
1630 |
May 26 |
|
Toll Gate Creek at E. 6th Avenue |
1760 |
July 30 |
|
Westerly Creek at Montview Blvd. |
1200 |
July 19 |
By contrast,
the 1976 Big Thompson flood was caused by a 12-inch storm oven an unburned
forest and claimed 145 lives along US Highway 34 between Estes Park and
Loveland. Fortunately, no major US highways run along the streams affected by
the Buffalo Creek disaster and the population in harm’s way was much smaller on
July 12, 1996 than it was on July 31, 1976.
Other Main Events
The District’s
Flash Flood Prediction Program (F2P2) activated a record a number of 51 days
this year. This program has been serving the Denver/Boulder metropolitan area
since 1979, the same year in which the Boulder Creek early flood detection
network became operational.
During 1996
the ALERT network measured one-hour rainfall amounts exceeding an inch on eight
days (6/13, 7/9&12, 8/22&26, and 9/11, 12&14). The station at
Morrison reported the heaviest amount where a total of 2.32” fell Wednesday
evening, September 11, forcing cancellation of the “Hootie and the Blowfish”
concert at the Red Rocks Park amphitheater.
Even though we
experienced a very active season, all flooding that occurred within the
District this year may be categorized as nuisance events, resulting mainly in
traffic snarls, an occasional flooded basement, more than a few irritated
sports enthusiasts and a small army of disappointed Blowfish fans. The table
summarizes peak flows at locations.
From December 11, 1996 DRAFT of 1996 Flood Hazard
News article…NOT PUBLISHED
Reformatted & edited by KGS 8/12/2020