Data Collection Report - Flood Control District of Maricopa County

V. ENVIRONMENTAL OVERVIEWA. Ecological AssessmentIntroductionThe objectives of this ecological assessment are to identify, evaluate, andmap vegetation communities in the Durango drainage area, to determinewhether such vegetation communities may support special interestspecies, and to identify sensitive biological resources. A special interestspecies is any species of interest to any regulatory or managementagency of the federal, state or local government. The list of specialinterest species considered in this assessment was developed from listsprovided by the U.S. Fish and Wildlife Service (FWS) and the ArizonaGame and Fish Department (AGFD), included in the Appendix.A reconnaissance survey of vegetation communities in the project area,except for extremely disturbed, industrial, and urbanized portions, wasconducted between 20 and 23 December, 1999. The survey wasconducted from a vehicle along major roads in the project area, and onfoot in and adjacent to the Agua Fria, Gila, and Salt rivers. Thisecological assessment is general and does not include comprehensivelists of plant and animal species that may occur in or near, or be affectedby the proposed project.Historical Ecological ConditionsPrehistoric Hohokam inhabited and farmed central Arizona until the1400s. The Hohokam built an extensive network of hundreds of milesof canals to convey water from the Salt and Gila rivers and delivered itto fields up to 20 miles into the surrounding desert for crop irrigation.The canals measured up to 30 feet wide and 10 feet deep, and wereabandoned by the time Father Kino arrived in the late 1600s. Littlelarge-scale irrigation was built until Camp McDowell was establishednortheast of Phoenix in 1865.Soon after, the potential for reconstructing the Hohokam irrigationsystem was recognized and prompted the settlement of Phoenix (Rogge,Keane and McWatters 1994). Rainfall in the Sonoran Desert isunpredictable, and the reliable water source from reservoirs anddiversions attracted farmers and ranchers to the area. During the periodfrom 1867 to 1877, eleven or more irrigation canal companies operatedwhile some twenty-one new companies formed (Rogge et al. 1994).By 1885, the Arizona Diversion Dam was built on the Salt River, and theArizona Canal was under construction some 25 miles east of Phoenix -representing the first extension of the Hohokam canal network. TheArizona Diversion Dam was replaced with the Granite Reef Diversion,constructed from 1906 to 1908 in conjunction with the Roosevelt Dam.The Lake Pleasant Dam on the Agua Fria River was complete by 1920,and the reservoir was full by 1941. By 1950, 14 dams and diversionswere built upstream of the Durango drainage area on the Gila, AguaFria, Salt, and Verde rivers to reclaim the arid lands of Arizona (Roggeet al. 1994). Such a magnitude of water diversion reduces the naturalwater table and subsequently changes the composition of vegetation andanimal communities.Local channeling of the Gila, Salt, and Agua Fria rivers predominantlyfor agricultural purposes likely represents the first major fragmentationof the cottonwood-willow gallery forests along these floodplains.Construction of fences to contain livestock obstructed travel by nativewildlife, and diversion of water for mining, livestock, and crops impactednative fish populations (Minckley1991).Existing Ecological ConditionsVegetation CommunitiesApproximately ninety to ninety-five percent of the Durango drainagearea has been disturbed as a result of past and current activities relatedto industrial, urban, and agricultural development. The project areacontains three types of communities: highly disturbed, agriculture fields,and Sonoran Desert (Figure V-1). The highly disturbed areas in the eastportion of the project area have been industrially, commercially, orresidentially developed. Agricultural areas are fairly contiguousthroughout the central and west portions (Photo V-1), while relativelyundisturbed areas are chiefly in and adjacent to riverine floodplains(Photo V-2). Vegetation in highly disturbed areas, and areas adjacentto agricultural fields, is often dominated by invading species such asRussian thistle (Salsola kali) and desert broom (Baccharis sarothroides).Urban and industrial areas have relatively little biological resource valuefor species other than pigeons (Columba livia), pests, and vermin, whileagricultural areas provide more resources for rodents, granivorous birds,and raptors.DIBBLE & ASSOCIATES 35 DURANGO ADMPDATA COLLECTION REPORT