Arizona is known for its vast deserts and arid climates—not necessarily torrential rain. But when it does rain in the southwestern state, the combination of the amount and the speed at which it falls can cause flash floods. The shores of Lake Havasu—a valley destination for flash flood waters—are speckled with residential neighborhoods. When it rained, homes and residents were threatened, and as the water rushed to the lake, it caused land erosion and carried sediment runoff into the lake. A detention basin system was required in the area, and it needed to be in a very confined area.
The solution
The detention basin system includes five basins with battered walls and one flood control channel with near-vertical walls. An original plan called for two separate blocks; however, Keystone licensee Oldcastle Superlite had realized the space was too limited to employ a two-block option, so Keystone redesigned the plan. This plan called for Stratagrid and Sleeve-It products—as well as a single block option—to be utilized to save money and space.
210,000 cu yd of soil were excavated to create the basins. Due to the use of geogrid, the same soil could be used for fill, which eliminated the need to haul off or import soil. The basins required battered walls for extra strength and can now hold up to 74 acre-ft of water. The walls extend 2 to 3 ft underground and reach heights above ground ranging from 5 to 25 ft. The flood channel is an 1H:1V wall to save space in the confined area; without the use of geogrid, this would not be possible.
Strata provided the SG200 and SG500 geogrids needed for both applications. Portions of the project required the Stratagrid to be installed on every course along the bottom wall, and then reduced in frequency to every third course higher up the wall. The customer used master rolls for faster production time. Two hundred fourteen Sleeve-It systems (rail integration devices) secured fence posts that were placed 3 ft from the edge of the wall, as prescribed by the plan.
The results
The $4.5-million, 64,000-sq-ft project began in the summer and was finished by January of the following year. The installation of the project was completed by a crew of 6 to 11 people, who installed an average of 760 sq ft per day. The system detains floodwaters quickly in the five basins and then slowly releases into the lake via the control channel, reducing erosion and sediment runoff deposits. The use of geosynthetic products that utilize onsite soils saved time and money by reducing the need to export or import soil.
