Powerline Plan and Environ. Assessment Jan. 2013 - Flood Control ...

Powerline Flood Retarding Structure
Pinal County, AZ
Draft Supplemental Watershed Plan
and Environmental Assessment
FEMA levee certification requirements. FEMA levee certification requirements are located in Title
44 CFR 65.10. Minimal requirements include but are not limited to: a minimum of three feet of
freeboard for the length of the levee above the base flood (100-year) elevation and an additional
one foot on either side of structures (bridges, etc.); provisions for embankment erosion protection,
embankment and foundation stability, and settlement analysis. The levees will also be required to
be designed to meet US Army Corps of Engineers and/or NRCS standards for earthen levees.
Portions of the Powerline Channel would be required to be hardened sections. These channel
segments are located within the moderate fissure risk zones. Typical sections of the hardened
channel sections are provided in Appendix C as Figure C-7.
Alternative 2 would not require additional right-of-way or easements for the Powerline Channel.
The channel would be located within the existing modified easement.
The construction of the Powerline Channel and removal of the Powerline FRS and IDSM
embankment potentially locally impact both environmental and cultural resources. The acres of
existing mesquite bosque vegetation that may be directly affected have been quantified
(approximately 120 acres). ). Mesquite bosque mitigation may include planting tall-pot mesquite
trees (approximately 60 acres) and salvage of some mature mesquite trees and transplanting in
designated areas (e.g., along Powerline Channel and potential mitigation area at north end of
Vineyard Road FRS). The Sponsor and NRCS will coordinate with ASLD regarding trees along
the existing low flow channel along the Powerline FRS. Mitigation plans will be refined during
final design. The estimated cost of mesquite bosque mitigation for the PVR project is
approximately $1,938,000.
Clearing and excavation of the channel and construction of an O&M road on either side of the
channel will disturb or remove existing vegetation. Disturbed areas will be hydroseeded and
restored to a native plant community following construction.
An estimation of the potential for impacting cultural resources has been completed for Alternative
2. The area of potential effect (APE) was determined and an estimate of the mitigation for cultural
resources prepared. Sites in the APE that will not be subject to project-related impacts will be
avoided by project implementation activities. Data recovery studies will be performed to mitigate
impacts to all sites likely to suffer project-related impacts. Based on known sites in the vicinity, the
majority of the cultural resources present would be either prehistoric sites without evidence of
habitation (which might include scatters of artifacts on the surface, or artifacts with remnants of just
one or a few roasting pits, agricultural features, and/or other non-habitation features) or historical
sites (which might include homesteads, farming or ranching features, or simply scatters of historical
artifacts). Most of the remaining sites would be smaller prehistoric habitation sites, with up to two
relatively large prehistoric habitation sites within the total APE (for Powerline, Vineyard Road, and
Rittenhouse FRSs). Based on experience with recent data recovery efforts in central and southern
Arizona, the estimated cost for cultural resources mitigation for the PVR project is $3,010,000.
The total installation cost for Alternative 2 (from NRCS Table 2 in Section 8.0) is $23,893,600.
Total project costs include a contingency of 25%, additional permitting, engineering and
construction management percentages. The Sponsor’s O&M costs are estimated at $212,700.
USDA- NRCS Page 5-12 January 2013
Kimley-Horn and Associates, Inc.