Riparian Land Acquisition and Management

Pima County's watersheds have changed dramatically during the last 150 years. To get a sense for how things have changed over time, check out historic photographs in Pima County's Withdrawal from Its Past (PDF format). In general, watersheds today are capable of generating larger floods, faster than before.

Acquiring flood- and erosion-prone land is a cost-effective strategy for minimizing flood damages.  Through its award-winning Floodprone Land Acquisition Program (FLAP) the District has purchased over 8,500 acres of flood- and erosion-hazard areas throughout Pima County and relocated many families out of harm’s way.  FLAP is funded through general obligation bonds and the District tax levy.  Additional floodplain areas have been acquired using grants, donations, trades and dedications of land during the rezoning process.

Land acquisition reduces costs for disaster and post-disaster assistance, and has helped to create a more flood-resilient community.  The program also helps to reduce flood insurance premiums for homeowners.

Appropriate management of acquired lands is an important component in achieving the biological and riparian goals of the Sonoran Desert Conservation Plan (PDF format).   Acquired lands maintain ecosystem functions such as groundwater recharge, natural overbank flood storage, and regeneration of floodplain vegetation.   Several areas now owned by the District have outstanding wildlife habitat values, and are managed specifically to protect ecological values.

The largest of these is the Cienega Creek Natural Preserve.  Located east of Vail, this Preserve shelters a likeness of what the Santa Cruz River at Tucson once possessed: a precious year-round flow with numerous riparian trees and abundant wildlife.  Establishment of the Preserve in 1986 marked Pima County's first major flood control effort that included riparian habitat preservation. Management of this area resulted in an award from the American Fisheries Society (PDF format) for the “protection, enhancement and overall management of riparian zones within the Cienega Creek watershed.”

Perennial flow in the Cienega Creek is currently diverted at Pantano Dam to a golf course near Colossal Cave Road. A geophysical and well drilling program (PDF Format) was completed to assess effects of acquisition of the in-holding and water right. The District’s objective is to evaluate the potential for recovery of water levels downstream of the dam should surface-water diversions cease, and to monitor impacts to groundwater levels from regional pumping.

Pima Association of Governments has been working with the Arizona Department of Environmental Quality (ADEQ) to have Davidson Canyon (PDF format) added to the Outstanding Waters list.  The Outstanding Waters classification provides the state’s highest level of protection against water quality degradation. The flows are estimated to provide 8-24% of the stream flow in Cienega Creek (PDF format) and are especially important during periods of low flow in Cienega Creek.  The flows also have a higher water quality than is provided by Cienega Creek alone.

The Science Technical Advisory Team for the Sonoran Desert Conservation Plan identified the Santa Cruz River at Canoa Ranch as a critical landscape connection, impaired by Interstate 19 and the loss of habitat due to vegetation removal and groundwater pumping.  Pima County purchased part of Canoa Ranch in 2001. The District manages the floodplain.  As part of the Canoa Ranch acquisition, Pima County and the developer agreed that the Santa Cruz River, as well as Madera and Escondido washes shall remain in their natural states.  Several studies have been undertaken since Pima County acquired Canoa Ranch including baseline vegetation monitoring (PDF format). 

Tanque Verde Creek is one of the county’s most imperiled river systems, where habitat losses are high and where continued or increased groundwater pumping (PDF format) impairs streamflow and shallow groundwater conditions.  The Flood Control District has acquired lands along the Creek to remove people from hazardous areas, and protect riparian habitat for wildlife.  The area at the confluence of Agua Caliente Creek with Tanque Verde Creek is particularly valuable for infiltration, recharge and floodwater storage. The District has attempted to curb off-road vehicular use along Tanque Verde Creek in cooperation with City of Tucson and neighbors.

The West Branch of the Santa Cruz River is, by contrast, an urban refuge for types of plants and wildlife now rare (PDF format) within the city limits.  Parts of the West Branch were acquired as mitigation (PDF format) for bank protection, and must remain in a natural state.  The West Branch is the focus of various efforts by the District to stem erosion and maintain native biodiversity in cooperation with scientists and various community organizations.

In 1989, Pima County Regional Flood Control District acquired lands along the San Pedro River to preserve a spring-fed marsh known as Bingham Cienega.  Because of the site’s remote location and sensitive environment, the District entered into a long-term agreement with the Nature Conservancy to manage the property.  Conservancy volunteers fenced out livestock, and once vegetation began to fill in drainage channels, the marsh vegetation began to spread.  The District installed a small check dam that has arrested erosion that threatened the marsh.  More recently, the Conservancy restored sacaton (PDF format) and other native floodplain vegetation types to the remaining fields.