Salt River Channelization

Channelization of the Salt River was completed in 1996 and recovered 843 acres of developable land from the floodplain. The channelization, which was funded by the Arizona Department of Transportation (ADOT) and Flood Control District of Maricopa County (FCDMC) features eight-foot thick soil cement on a lower 10-year flood levee (extending to the bottom of the channel) and wire mesh-encased rock gabions on a 200-year flood levee. 

These terraces comprise the north and south bank linear parks. The lower terrace features a decomposed granite walking trail around the lake and beyond its edges along the channel. The upper terrace is landscaped to cover the gabions, provide shade for the lower path and enhance the concrete bicycle path on top of the levee. 

Channelization was designed to contain a 250,000 cubic feet per second (cfs), 220-year event flow from dam releases and floods and still have four feet of freeboard (room within the channel before overflowing the edges). 

Recorded floods in the metropolitan Phoenix area date back to 1891 with the largest recorded at 300,000 cfs (this figure may vary due to technological limitations prior to the 1900's and possible errors in recording). The channel varies in width from 800-to-1,200 feet wide. Grade-control structures were built in every mile to control scouring caused by water flows. A 12-foot deep concrete structure is being used as part of the foundation of the inflatable dam at the west end of the lake. This particular grade-control structure can be seen in the river channel. 

Rock gabions consist of wire mesh (like chain link fence) pillows filled with river rock and tied together along the slope of the levee.

Soil cement is a mixture of mostly sandy soil and a little cement. It is combined as a stabilizer along the levee and tests at about 900 psi (pounds per square inch) of force. It is not as strong as concrete, so some erosion can be seen, but it is a much more natural looking material.

After starting construction of the Town Lake, contractors were required to remove the outer layer of this soil cement. However, the equipment being used had difficulty breaking through the material. Material testing proved that the material had the strength of structural concrete (2,500 psi) - much harder than what was called for during the channelization project. A change in equipment and method finally allowed the lake edge contractor to break through the surface and chisel it to the required slope for pouring a hard edge lake treatment that now makes up the edge of Tempe Town Lake.