500-YEAR FLOOD EVENT STUDIES

 

    

 

AS&A’s professional engineers routinely perform 500 – Year Flood Event Studies as part of their professional services in Site Selection and/or Planning Phases of Projects. A 500 – Year Study involves investigation of existing runoff records, drainage structure plans, field survey data and structure measurements. The entire watershed above the project is determined and investigated in detail. 

The field measurement for drainage structures follow the procedures prescribed in the AASHTO Manual for Condition Evaluation and Rating of Highway Bridges.  

The 500 – Year Event Studies are performed based on information obtained from Methods for Estimating Magnitude and Frequency for Floods in the Southwestern United States, U.S. Geological Survey Open File Report 93-419.   This report was prepared by the United States Department of Interior with the cooperation of the Colorado Department of Highways, Arizona Department of Transportation, California Department of Transportation, Idaho Department of Transportation, New Mexico State Highway and Transportation Departments, Oregon Department of Transportation, Texas Department of Transportation, and Utah Department of Transportation. 

A high water channel alignment is established using USGS 7 ½ minute quadrangle maps from approximately 3 miles upstream to 3 miles downstream of the selected sites.  After this alignment is established from data obtain in both the field survey and the 7 ½ minute quadrangles. Cross sections were then prepared perpendicular to the channel alignment.  The cross sections are taken at every contour interval crossing the flow-line of the channel. This information is then input into the BOSS INTERNATIONAL version of HEC-RAS River Analysis System version computer program, along with the other pertinent information such as manning “n” values, center and left and right over-bank flow distances between cross sections to generate a watershed model. All data collected is evaluated and a Drainage Study Report is prepared on the Effects of a 500 – Year Flood Event on the Site under study. 

In addition to 500-Year Event Drainage Studies, SHP Professional Engineers have performed the drainage analysis on numerous Bridge Design Projects and Dam/Reservoir Projects.

Example Projects of 500 – Year Event Drainage Studies:

 

•   Drainage Study 500-Year Event (3 sites), Polacca Day School, First Mesa, AZ, Hopi Indian Reservation

•   Drainage Study 500-Year Event, Beclibito Day School, NM

•   Drainage Study 500-Year Event, Rough Rock School, AZ