Flash Flooding and Rapid Hydrologic Response
Much of the CNRFC area is susceptible to flash floods.
In addition, many of these flash flood prone areas are among the
most heavily populated in the country. The NWS defines a flash flood
as a flood event which occurs within 6 hours of the causative event.
The rapid and often localized development of these events requires
real time assessment and immediate public warning. As such, the
responsibility for public flash flood watches and warnings rests
with the continuously staffed WFOs. In support of their efforts,
the CNRFC provides flash flood guidance based on current watershed
conditions.
The CNRFC contributions to the flash flood threat
dont end there. With the assistance of the CNRFC, numerous
cities and counties have installed and actively maintain an automated
local flood warning system. The CNRFC pioneered the concept, design,
development, and application of ALERT (Automated Local Evaluation
in Real Time). The systems consist of automated event-reporting
rain and river gages and a computer system that analyzes current
and developing hydrologic conditions. Data from the river and rain
gages are generated in response to changing conditions (e.g. 0.04
inches of rain or 0.1 foot change in river level) and transmitted
to the computer base station using line-of-sight radio operated
on the Hydrologic Warning Frequency. Approximately 30 such systems
currently exist within the CNRFC area. Between them, they monitor
in excess of 700 precipitation and 275 river level gages. All data
are automatically passed to the nearest WFO as well as the CNRFC.
Collaboration among the operators of these systems is facilitated
by the ALERT Users Group.
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