Boulder Creek applies flood modeling approach for emergency response planning

PORTLAND, OR, Jan. 23, 2007 -- Predicting inundated areas and response time is critical for planning emergency response in the case of flash flooding. To this end, the Urban Drainage and Flood Control District, in conjunction with the City of Boulder and DHI Water & Environment prepared a 2-dimensional (2D) model of overland flooding in the Boulder Creek drainage basin using the MIKE 21 modeling software developed by DHI Water & Environment. A 2D model was chosen for the ease of development and results presentation capabilities.

Purpose of Modeling
"A 2D model can be developed rapidly and with much less effort than a 1D model, given that appropriate topographic data is available," said Chad Kudym from UDFCD.

The objective of the modeling was to provide Urban Drainage and Flood Control District (UDFCD) with static inundation maps, travel times for the flood wave propagation and flood animations for Boulder Creek, based on MIKE 21 model results. The inundation maps and flood animations were used for illustrative purposes during an emergency preparedness exercise in Boulder, CO.

Approach
The project consisted of two main tasks, hydraulic modeling and result presentation.

The model bathymetry was developed from existing USGS 10m DEM data while the model extents were developed based on delineation of the area of interest provided by UDFCD. The model domain extends from approximately half a mile upstream of Orodell to Canyon Park. This represents a stream channel length of approximately 10 miles. The model extents are shown in Figure 1 above. Six inflow locations and corresponding dynamic flood hydrographs were used. The flood flow hydrographs, and inflow locations were specified and provided by UDFCD.

Based on the hydraulic modeling result files, flood hazard maps were prepared delineating the maximum flood depths based on the simulation results, and 2D animations of the flood inundation were prepared. These maps and animations were used to aid in developing and testing an emergency response plan (see Figure 2 below).

"The animations and prepared mapping were extremely useful in understanding the areas at
risk to flood and the travel time of the front of the flood" said Chad Kudym.
Results

Mr. Kudym continues "Flood modeling for emergency response planning is quite different than flood mapping for insurance purposes. The main modeling goals for emergency response planning are a reasonable estimate of inundation areas and response times, while keeping the model development costs to a minimum. Using a 2D model precluded the need to spend a lot of man-hours developing model geometry, and defining flow paths and flow splits. All of these were taken directly from the specified topography. By using a tool like MIKE 21 we were able to quickly develop representative flood models for emergency response planning at low cost."

For more information on this project, or to discuss how MIKE 21 can be applied to your flood modeling or emergency response planning needs, please contact Eric Fontenot, DHI Water & Environment ([email protected]).

Based in Portland, OR, DHI Inc. (www.dhi.us) is the North American subsidiary of DHI Water & Environment, a world leader in the research, development and application of technologies and solutions for water-related issues. With over 30 years of experience, DHI has established a worldwide reputation for excellence and innovation in the field of water science and engineering, and today we continue to push the envelop in search of better solutions for our clients, for our environment, and for our future.

DHI (www.dhigroup.com) is an independent research and consultancy organization, formed by merging the Danish Hydraulic Institute, VKI - Institute for the Water Environment, and Danish Toxicology Centre. Its headquarters are in Horsholm, Denmark, with offices in Australia, Bulgaria, China, Czech Republic, Denmark, France, Germany, India, Italy, Malaysia, New Zealand, Norway, Singapore, Slovak Republic, Spain, Sweden, United Arab Emirates and the United States. DHI has representative offices in Brazil, Japan, Thailand and Vietnam and an extensive agents network.

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