Flood Control Infrastructure Design

Horizon Six
Lake Havasu City, Ariz.

Project Size:  2-mile channel and detention design, 320-acre community

Project Description: The Horizon Six subdivision is a 320-acre mature residential development near Lake Havasu City in Mohave County.  No provisions were made to control a wash that diagonally bisects the site.  Uncontrolled grading activities by other homeowners had created harmful flooding.  Hillside topography, steep slopes, and the existing wash required significant federal submittals and permitting.

Value Added:  CVL assessed possible drainage improvements after completing a comprehensive analysis of hydrology, hydraulics, and sediment transport.  CVL used the HEC-1 model to determine design event flows from a 3.2-square-mile watershed.  CVL also used the FLO-2D model to define the flood plain.  Based on this analysis, an upstream detention basin and an engineered channel were determined necessary.

Using a cascading system for a detention basin, CVL was able to reduce the upstream design flows by approximately 50%, consequently reducing material costs of the channel.  The selection of the offline basin approach and the reduced engineered channel cross section resulted in a savings of approximately $2 million.

In addition, CVL significantly reduced the engineered channel cross-section and culverts for five road crossings, which led to a more convenient approach for acquiring Right-of Way property for the new, engineered channel. CVL coordinated timely CLOMR/LOMR submittals to the Federal Emergency Management Agency and preliminary jurisdictional determination submittals to the USA COE for construction permitting.

Images: upstream detention basin, Project I (Figure 1), and an engineered channel, Project II (Figure 2).