US Army Corps of Engineers Los Angeles District Paseo de las Iglesias Ecosystem Restoration Draft Environmental Impact Statement (EIS) SANTA CRUZ RIVER PIMA COUNTY, ARIZONA July 2004 Cover Sheet Responsible Agency and Lead Federal Agency: U.S. Army Corps of Engineers Title: Paseo de las Iglesias Ecosystem Restoration, Draft Environmental Impact Statement (EIS) Contact: For information on the DEIS and the related public hearings and meetings: Michael J. Fink, Environmental Coordinator, U.S. Army Corps of Engineers, Los Angeles District, Arizona/Nevada Area Office 3636 North Central Avenue, Suite 900, Phoenix, AZ 85012-1936 Phone: 602.640.2001 extension 252 Via E-mail to: [email protected] For information on the overall Feasibility Study: Mr. Kim Gavigan, Study Manager U.S. Army Corps of Engineers, Los Angeles District, Arizona/Nevada Area Office 3636 North Central Avenue, Suite 900, Phoenix, AZ 85012-1936 Phone: 602.640. 2001 extension 251 Via E-mail to: [email protected] Abstract: This Paseo de las Iglesias Ecosystem Restoration Draft EIS analyzes the potential environmental consequences of implementing alternatives for riparian habitat restoration on the Santa Cruz River. Mesquite bosque creation is the dominant feature of Alternative 3E, the Preferred Alternative. Alternative 3E provides a nearly uniform mesoriparian hydrologic regime (through various means of supplemental irrigation) to all geomorphic positions in the floodplain above the low flow channel. This alternative creates approximately 718 acres of mesquite, 356 acres of mixed mesoriparian shrub-scrub acres, 18 acres of cottonwood-willow and almost 6 acres of emergent marsh. Alternative 4A is characterized by creating an intermittent flow environment and channel to support adjacent growth of emergent wetlands and cottonwood-willow gallery forest. Additional areas on terraces above the channels and in the historic floodplain would be irrigated to sustain mesquite bosques interspersed with riparian shrub. Alternative 2A uses basic dry-land restoration practices of water harvesting, soil patterning, mulch and fertilizer amendment, surface grading, a low flow diversion and construction of subsurface water harvesting basins. Implementation of these measures will allow creation of new habitat as well as enhancement of existing habitat with plantings in mesquite, scrub/shrub, and river bottom community types. The No Action alternative is also assessed and presented. Public Comments: In preparing the Draft EIS, the Corps of Engineers considered comments received by letter and formal statements made at public scoping meetings. A 45-day comment period on the Paseo de las Iglesias Ecosystem Restoration, Draft Environmental Impact Statement (EIS) begins with the publication of the U.S. Environmental Protection Agency Notice of Availability in the Federal Register. A public hearing to discuss and receive comments on the Draft EIS will be held at a time and location to be announced in the Notice of Availability. Individuals and agencies may present written comments relevant to the DEIS or request to be placed on the mailing list for announcements and for the Final EIS by sending the information to Mr. Michael J. Fink at the address above. The comments received during the comment period will be considered in the preparation of the Final EIS. Late comments will be considered to the extent practicable. Unless otherwise requested, copies of the Final EIS will be provided on CD-ROM. Summary The Arizona/Nevada Area Office of the Los Angeles District of U.S. Army Corps of Engineers is conducting a feasibility study to assess opportunities for riverine ecosystem restoration for the seven-mile Paseo de las Iglesias reach of the Santa Cruz River in Tucson, Arizona. The study is being conducted in partnership with the Pima County Flood Control District, the non-Federal sponsor. The Study Area, as identified in the accompanying feasibility study, includes the Paseo de las Iglesias reach of the Santa Cruz River channel its tributary channels; the New and Old West Branch tributaries, and lands between and adjacent to these channels between Los Reales Road on the south to West Congress Street on the north, encompassing approximately 5000 acres. The Study Area is located entirely within the City of Tucson, Pima County, Arizona. The primary process within the Study Area is systematic and severe ecosystem degradation and loss of riparian habitat that has persisted since the early 20th century. Before 1900, the Santa Cruz channel maintained perennial water flow that supported dense growths of native riparian trees such as cottonwood, willow, and mesquite. Historical accounts of conditions on the Santa Cruz River (circa 1900) describe a tree-lined, river, with dense vegetation, winding throughout a wide flood plain. The river channel formerly provided sufficient water to support rapidly increasing European settlement, increasing uses of the Santa Cruz waters for agricultural irrigation and sustained surface flow. Sustained surface flow has not existed in the Paseo de las Iglesias reach for more than half a century. The once verdant Santa Cruz riparian corridor has been transformed into a deeply incised, ephemeral ditch with either artificially hardened or unstable and eroding banks, that supports flow only briefly in response to storm runoff. These changes came about as a result of the uncontrolled appropriation of surface and groundwater to support expansion of agriculture and nascent industry, acceleration of head cutting resulting from human manipulation of the channel, and transformation of large areas of the landscape to increasingly urban land uses. As a result, native riparian habitat is nearly absent in the Study Area. Historically comprising about 1% of the landscape historically, over 95% of riparian habitat has been destroyed in Arizona. This type of river-connected riparian and fringe habitat is of an extremely high value; a large percentage of wildlife in the arid southwest is riparian-dependent during some part of its life cycle. As a consequence of the loss or degradation of riparian habitat, the area has suffered a concomitant reduction in species abundance and diversity with non-native (exotic) vegetation dominant in the Study Area. 3 Flood damage reduction opportunities were analyzed for the Without-Project Conditions (No Action Alternative). Based on the results of environmental, hydrologic/hydraulic, and economic analyses, flood damage reduction, as a project purpose could not be justified. While the majority of lands in the Study Area are dedicated to residential land use, the majority of lands immediately adjacent to the Santa Cruz River channel are undeveloped. This condition offers an opportunity to accomplish important ecosystem restoration in the Study Area. The Federal planning objective for ecosystem restoration studies is to contribute to National Ecosystem Restoration (NER) through increasing the net quality and/or quantity of desired ecosystem resources. The specific objectives for environmental restoration within the Study Area have been identified as follows: • Increase the acreage of functional riparian and floodplain habitat within the Study Area. • Increase wildlife habitat diversity by providing a mix of riparian habitats within the river corridor, riparian fringe and historic floodplain. • Provide passive recreation opportunities. • Provide incidental benefits of flood damage reduction, reduced bank erosion and sedimentation, and improved surface water quality consistent with ecosystem restoration goal. • Integrate desires of local stakeholders consistent with Federal policy and local planning efforts. A number of ecosystem restoration measures have been developed based upon those originally identified in Reconnaissance Phase of the study, with additional restoration measures added based upon the results of public input and on other similar studies in the region. Once compiled, potential restoration approaches were evaluated for feasibility, with some screened out and others refined. The initial conceptual alternatives presented in the draft Feasibility Study document (USACE, 2002) were recombined with new restoration approaches and expanded into an array of 14 alternatives that were subjected to more detailed analyses. Through this process, a final array of alternatives was produced consisting of the two “best buy” alternatives (Alternative 2A and 4F), a mid-point water use alternative (Alternative 3E), and the no action alternative. Alternative 2A Alternative 2A uses the basic dry-land restoration practices of water harvesting, soil patterning, mulch and fertilizer amendment, surface grading, a low flow diversion and construction of subsurface water harvesting basins. Implementation of these measures will allow creation of new habitat as well as enhancement of existing habitat with plantings in mesquite, scrub/shrub, and river bottom community types. The alternative would require irrigation for establishment and periodic irrigation during periods of prolonged drought. 4 The channel features for this alternative consist of two measures; construction of water harvesting basins on the upstream side of five existing grade structures and construction of a low flow diversion to direct water from the New West Branch back into the Old West Branch. The water harvesting basin features would involve excavating upstream of each grade control structure to a depth of approximately four feet, placing a liner membrane, and filling the excavated