I-10 Twin Peaks Traffic Interchange, Environmental Assessment

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Affected Environment and Environmental Impacts October 2005 year floodplain with sheet flow flooding where average depths are less than 1 foot; in the 100-year floodplain with stream flooding where the contributing drainage is less than one square mile; or, protected from 100-year flood events by levees. The FIRMs for the study area are shown in Figure 4-2. Impacts No Build Alternative Under the no build alternative, no affects to floodplains would occur. Preferred Alternative Based on the information contained in the FIRMs for the study area, the proposed improvements constitute actions within the limits of the base floodplain; therefore, compliance with EO 11988 and 23 CFR 650 must be demonstrated. These actions within the 100-year floodplain include construction of: twin bridges spanning the low flow channel of the Santa Cruz River; bridge and roadway embankments within the high flow Santa Cruz River channel; bridge and roadway embankments on the east side of I-10; a new signalized intersection at Twin Peaks Road/El Camino de Mañana/Linda Vista Boulevard; and, reconstruction of Linda Vista Boulevard. The floodplain analysis conducted for these improvements is discussed in the following paragraphs. The risks associated with the Santa Cruz River bridges described in Chapter 3, Alternatives, were analyzed. Based on the scour analysis, the Town of Marana would design the bridges’ substructures and foundations for these scour depths; therefore, risks to the structures would be minimized. Incompatible use or development within the floodplain would not be facilitated by the proposed project. Any developments within the area must comply with the Town of Marana or Pima County zoning and floodplain ordinances. The area east of the proposed improvements is within the Tortolita Basin as defined by Pima County. The County has designated this area as a critical basin, which requires that developments provide sufficient stormwater detention to reduce predevelopment peak flows. Several improvement alternatives were developed and their associated impacts to the 100-year floodplain were analyzed. Alternatives considered, but eliminated from further consideration, included: 1) the no build alternative; 2) bridges spanning the high flow channel of the Santa Cruz River; and, 3) bridges spanning the low flow channel of the Santa Cruz River. These alternatives were eliminated because they either did not address the stated purpose and need of the proposed improvements (no build alternative) or they would increase flood elevations over the allowable 0.1 foot according to ADOT and Pima County design standards (the two bridge alternatives). Interstate 10 Traffic Interchange at Twin Peaks/Linda Vista 4-16 Project No.: NH-010-D (AIW) TRACS No.: 10 PM 236 H5838 01D
Twin Peaks Rd Interstate 10 Traffic Interchange at Twin Peaks/Linda Vista 4-17 El Camino de Mañana Linda Vista Blvd Figure 4-2 Floodplain Project Number: NH-010-D (AIW) TRACS No.: 10 PM 236 H5838 01D
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Interstate 10 Traffic Interchange a
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Draft Environmental Assessment Octo
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Mitigation Measures October 2005
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Mitigation Measures October 2005 19
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Mitigation Measures October 2005 St
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Introduction October 2005 CHAPTER 1
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AVRA VALLEY RD MARANA I-10 SCENIC D
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Introduction October 2005 Cortaro R
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Conclusion October 2005 Interstate
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Bibliography October 2005 CHAPTER 8
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Bibliography October 2005 Tetra Tec
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