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

Powerline Flood Retarding Structure
Pinal County, AZ
Draft Supplemental Watershed Plan
and Environmental Assessment
Draft Supplemental Watershed Plan and Environmental Assessment
for the
Powerline Flood Retarding Structure
Pinal County, Arizona
Prepared by:
East Maricopa Natural Resource Conservation District
and
Flood Control District of Maricopa County
2801 W. Durango Street, Phoenix, Arizona 85009
Assisted by:
United States Department of Agriculture
Natural Resources Conservation Service
AUTHORITY
The original watershed work plan was prepared, and works of improvement have been installed, under the authority of
the Watershed Protection and Flood Prevention Act of 1954 (Public Law 83-566) as amended. This Supplemental
Watershed Plan and Environmental Assessment is authorized under Public Law 83-566 (as amended), and as further
amended by Section 313 of Public Law 106-472 and in accordance with Section 102(2)c of the National Environmental
Policy Act of 1969, Public Law 91-190, amended (42 USC 4321 et seq).
ABSTRACT
The Powerline Flood Retarding Structure (FRS) was constructed by the Soil Conservation Service (now the Natural
Resources Conservation Service – NRCS) in 1968 as part of the Apache Junction-Gilbert Watershed Protection and
Flood Prevention Project. The FRS is operated and maintained by the Flood Control District of Maricopa County
(District). The 2.5 mile long, 21 foot high earth dam provides flood protection to downstream residents, structures, and
infrastructure.
The FRS has developed safety deficiencies and is approaching the original 50-year project lifetime. In May 2007, an
earth fissure was identified in close proximity to the downstream toe of the dam. In light of the proximity of this earth
fissure to the Powerline embankment, and the presence of other documented earth fissures in the general vicinity of the
dam, the Arizona Department of Water Resources (ADWR) classifies Powerline FRS as being in an “unsafe, nonemergency,
elevated risk” condition. As such, the Powerline FRS is one of ADWR’s highest priority unsafe dams in
the state. The District is currently constructing the Powerline Interim Dam Safety Measure (IDSM). The IDSM
consists of a new alignment for a portion of the Powerline FRS based on the results of past investigations indicating a
high probability of an earth fissure beneath the existing embankment. In 2009, the District requested Federal planning
and implementation assistance for long-term solutions to the identified dam safety deficiencies. This Supplemental
Watershed Plan and Environmental Assessment (Plan/EA) determines the feasibility of decommissioning the FRS and
replacing the FRS with a constructed channel to provide for continued flood protection while meeting current
applicable local, State, and Federal regulations.
COMMENTS AND INQUIRIES
Comments and inquiries must be received by March 12, 2013. Submit comments and inquiries to: Keisha L. Tatem,
State Conservationist, USDA, Natural Resources Conservation Service, 230 North First Avenue, Suite 509, Phoenix,
Arizona, 85003 (Telephone: (602) 280-8801).
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USDA- NRCS Page ii January 2013
Kimley-Horn and Associates, Inc.