Powerline Plan and Environ. Assessment Jan. 2013 - Flood Control ...
Powerline Plan and Environ. Assessment Jan. 2013 - Flood Control ...
Powerline Plan and Environ. Assessment Jan. 2013 - Flood Control ...
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<strong>Powerline</strong> <strong>Flood</strong> Retarding Structure<br />
Pinal County, AZ<br />
Draft Supplemental Watershed <strong>Plan</strong><br />
<strong>and</strong> <strong>Environ</strong>mental <strong>Assessment</strong><br />
combined with another alternative, <strong>and</strong>/or did not meet the purpose <strong>and</strong> need for the project. Note<br />
that the alternatives are formulated on a system wide approach (integrated system) such that all<br />
three dams were included in an alternative rather than a separate alternative developed for each<br />
dam. This system approach was taken to maintain the functional <strong>and</strong> operational relationship of the<br />
three PVR structures. Full descriptions of the alternatives noted below are provided in the “Level I<br />
Final Alternatives Summary Report” (KHA, February 2011), the “Level II Final Alternatives<br />
Summary Report” (KHA, June 2012), <strong>and</strong> the (Level III Final Alternatives Summary Report – KHA<br />
September 2012). The alternatives eliminated from further detailed study were screened in the<br />
alternatives workshops <strong>and</strong> documented in the workshop notes (see Appendix C in Level II Final<br />
Report for workshop notes <strong>and</strong> ranking matrices).<br />
The “ Level II Final Alternatives Summary Report” (KHA, June 2012) identified five structural<br />
alternatives for plan formulation based on technical analyses <strong>and</strong> input from the NRCS, the<br />
Sponsor, <strong>and</strong> the Consulting team. These alternatives (alternative numbers are as provided in the<br />
Level II report) are listed below for the PVR project:<br />
• Rehabilitation (Alternative 1): Raise <strong>and</strong> Rehabilitate the <strong>Powerline</strong>, Vineyard Road, <strong>and</strong><br />
Rittenhouse FRS structures<br />
• Combination (Alternative 6): Replace <strong>Powerline</strong> FRS <strong>and</strong> Northern 1/3 of Vineyard Road<br />
FRS with Basins <strong>and</strong> Channels, Raise <strong>and</strong> Rehabilitate the Southern 2/3 of Vineyard Road<br />
FRS <strong>and</strong> Rittenhouse FRS<br />
• Combination (Alternative 6A): Replace <strong>Powerline</strong> FRS <strong>and</strong> Northern 1/3 of Vineyard Road<br />
FRS with Basins <strong>and</strong> Channels, Raise <strong>and</strong> Rehabilitate the Southern 2/3 of Vineyard Road<br />
FRS <strong>and</strong> Convert Rittenhouse FRS to a Levee<br />
• Combination (Alternative 8): Replace <strong>Powerline</strong> <strong>and</strong> Rittenhouse FRSs with Channels,<br />
Raise <strong>and</strong> Rehabilitate Vineyard Road FRS<br />
• Combination (Alternative 8A): Replace <strong>Powerline</strong> FRSs with Channels, Raise <strong>and</strong><br />
Rehabilitate Vineyard Road FRS, <strong>and</strong> Convert Rittenhouse FRS to a Levee<br />
• No Action Alternative: Also known as No Action Alternative/Future Without Project<br />
Rehabilitation is defined as modification <strong>and</strong> improvements of the existing dams to meet current<br />
State <strong>and</strong> Federal dam-safety st<strong>and</strong>ards. Rehabilitation would include raising the dams to safely<br />
pass the inflow design flood (IDF) through the auxiliary spillways, providing new filters to address<br />
potential embankment cracking, providing a hardened dam or channel sections within moderate<br />
earth fissure risk zones, modification of auxiliary spillways, <strong>and</strong> replacing the existing principal<br />
spillways.<br />
A combination alternative combines structural measures to replace an individual dam or dam<br />
segment with a channel or levee with rehabilitation of the remaining dam structures/embankments.<br />
A decommissioning alternative (decommissioning of all three dams) was not selected to be<br />
evaluated <strong>and</strong> nor carried further in the Level II report.<br />
The Level III Analysis included analysis of another alternative – Alternative 8B. Alternatives 8A<br />
<strong>and</strong> 8B were carried forward into the Level III analysis (Level III Final Alternatives Summary<br />
Report – KHA September 2012). The Level III analysis conducted further evaluations of<br />
Alternatives 8A <strong>and</strong> 8B including refined earthwork quantity <strong>and</strong> construction cost estimates. Both<br />
USDA- NRCS Page 5-2 <strong>Jan</strong>uary <strong>2013</strong><br />
Kimley-Horn <strong>and</strong> Associates, Inc.