Water-Resources Investigations Report 02-4251
Simulation and Internet-Based Delivery of Forecast-Flood Inundation Maps Using
Two-Dimensional Hydraulic Modeling--A Pilot Study for the Snoqualmie River,
system of numerical hydraulic modeling, geographic information system processing,
and Internet map serving, supported by new data sources and application automation,
was developed that generates inundation maps for forecast floods in near real
time and makes them available through the Internet. Forecasts for flooding are
generated by the National Weather Service (NWS) River Forecast Center (RFC);
these forecasts are retrieved automatically by the system and prepared for input
to a hydraulic model. The model, TrimR2D, is a new, robust, two-dimensional
model capable of simulating wide varieties of discharge hydrographs and relatively
long stream reaches. TrimR2D was calibrated for a 28-kilometer reach of the
Snoqualmie River in Washington State, and is used to estimate flood extent,
depth, arrival time, and peak time for the RFC forecast. The results of the
model are processed automatically by a Geographic Information System (GIS) into
maps of flood extent, depth, and arrival and peak times. These maps subsequently
are processed into formats acceptable by an Internet map server (IMS). The IMS
application is a user-friendly interface to access the maps over the Internet;
it allows users to select what information they wish to see presented and allows
the authors to define scale-dependent availability of map layers and their symbology
(appearance of map features). For example, the IMS presents a background of
a digital USGS 1:100,000-scale quadrangle at smaller scales, and automatically
switches to an ortho-rectified aerial photograph (a digital photograph that
has camera angle and tilt distortions removed) at larger scales so viewers can
see ground features that help them identify their area of interest more effectively.
For the user, the option exists to select either background at any scale. Similar
options are provided for both the map creator and the viewer for the various
flood maps. This combination of a robust model, emerging IMS software, and application
interface programming should allow the technology developed in the pilot study
to be applied to other river systems where NWS forecasts are provided routinely.
Two-Dimensional Simulation of Flood Inundation
Automated Processing and Display of Forecast-Flood Information
Internet Map Server Development
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