Flood Control Channel Armoring

In order to facilitate future development within an existing floodplain, the City worked with the Flood Control District to develop a comprehensive Area Drainage Master Plan Report. The study area was approximately 85 square miles located within the Mohave Desert. The Drainage Master Plan was developed to meet four primary objectives:

1. Evaluate and identify flooding hazard and drainage problems within the project area by the implementation of a work plan which includes data collection, review of previous studies, information gathering from public agencies and residents, hydrologic and hydraulic modeling

2. Develop a series of alternatives to either partially or wholly mitigate the hazards identified in the first objective

3. Conduct a desktop cultural and environmental analyses for the conceptual solutions to identify their potential impacts on the drainage problems

4. Provide stakeholder coordination and public outreach of the project through a public meeting and multiple project stakeholder meetings

The results of the study were used as a planning tool and as input to the design of potential future drainage infrastructure and flood mitigation measures that are appropriate for the physical environment for both existing and future development. Based upon this data, a plan was developed to create a flood control channel to open flood plain land for future development. This required a 4800' long channel to be constructed. The Flood District engineers needed permanent erosion control for the channel and sought an alternative to rock rip rap. The engineers did not view rock rip rap as a permanent solution, knowing that the rock would often displace after large rain events and be an ongoing maintenance issue for the Flood District. The project location in the Mojave Desert created unique design challenges, this area is known as one of the harshest climates in the world.

The Mojave Desert is bordered by the Great Basin Desert to its north and the Sonoran Desert to its south and east. The Mojave Desert contains the lowest and hottest place in North America: Death Valley at 282 ft (86 m) below sea level, where the temperature often surpasses 120 °F (49 °C) from late June to early August. The Mojave is a desert of temperature extremes and two distinct seasons. Winter months bring comfortable daytime temperatures, which occasionally drop to around 25 °F (−4 °C) on valley floors, and below 0 °F (−18 °C) at the highest elevations. Storms moving from the Pacific Northwest can bring rain and in some places even snow. Spring weather continues to be influenced by Pacific storms, but rainfall is less widespread. By mid-June, Monsoon Season begins in the Mohave Desert. Monsoonal moisture creates thunderstorms from mid-June through early September.

Due to the extreme climate, Flood District engineers needed a product that would withstand these tough conditions. A cellular confinement system was specified to armor the flood channel from future erosion, also known as geocells. Typical cellular confinement systems are geosynthetics made with ultrasonically welded high-density polyethylene (HDPE) strips or novel polymeric alloy (NPA)—and expanded on-site to form a honeycomb-like structure—and filled with sand, soil, rock, gravel or concrete. The Flood District engineers specified Flexamat 10-NW as an alternative to the cellular confinement/geocell. Flexamat 10-NW is a tied concrete block erosion control mat. This concrete erosion mat includes a 10-ounce non-woven geotextile underlayment.

The low bidding contractor for this project determined Flexamat 10-NW would be a significant labor and time savings compared to installing the cellular confinement/geocell system. The concrete erosion mat was manufactured on the project site, greatly reducing transportation cost.