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

Powerline Flood Retarding Structure
Pinal County, AZ
Draft Supplemental Watershed Plan
and Environmental Assessment
occurring at the Superstition Mountains Recharge Facility and Scenario 2 was a projection with
an operational Superstition Mountains Recharge Facility. Presentation of results included
change-in-water-level contours plotted on figures with township boundaries for location
reference; results obtained from these figures were considered to be approximate. For this
evaluation, the modeled water level changes were estimated for five locations along the CAP
Canal and FRS through the study area using the ADWR estimates. These locations are at the
southern end of the Rittenhouse FRS, the southern end of the Vineyard Road FRS, SG-6 along
the Vineyard Road FRS, the northern end of the Vineyard Road FRS, and the Powerline FRS
IDSM alignment Station 20+00. These water level changes are summarized below. Results of the
more recent Superstition Mountain Recharge Facility modeling are also summarized below.
Modeled Groundwater Levels by Others for Future Subsidence Scenarios
Location
Powerline FRS IDSM Station
20+00
Change in Groundwater Level, feet
Base Case Scenario - No
Recharge Facility
Scenario 2 - With
Recharge Facility
2030 2100 2030 2100
-25 -100 +50 +0 (+30)
North Vineyard Road FRS 0 0 +50 +50
Station 350+00
Vineyard Road FRS Station +50 0 +50 +100 (+80)
271+00, Well SG-6
South Vineyard Road FRS +80 0 +50 +150 (+125)
Station 90+00, Well SG-10
South Rittenhouse FRS +100 0 +100 +200
Approximately Station 50+00
Note: Groundwater level changes in parentheses are from more current 2009 modeling.
5.1.4. Discussion
Known Earth Fissures
There are known earth fissures in the Project area near Hawk Rock and one known earth fissure
located immediately downstream of the Powerline FRS embankment at about Station 115+45.
There also is a high probability that the earth fissure near Station 115+45 extends beneath the
existing embankment. It is suspected that subsidence patterns at the Powerline FRS will continue
into the future, potentially causing further development of fissures in this area.
The earth fissures in the vicinity of Powerline FRS and Hawk Rock appear to follow along or
near the crest of buried ridges that radiate from Hawk Rock. The InSAR data show the locations
of the implied buried ridges. Previous investigations have included continuous seismic refraction
profiling for the purpose of identifying concealed earth fissures. Continuous seismic profiling
has occurred along the proposed Powerline IDSM alignment and much of the alignment of
Powerline FRS. Other than the earth fissure at about Powerline FRS Station 115+45, there are no
known earth fissures in close proximity to the components of the project. It is noted that this
earth fissure may be an extension of the known earth fissure located about 700 feet west of the
Powerline FRS embankment on the west side of Ironwood Road.
USDA- NRCS January 2013
Kimley-Horn and Associates, Inc. Page 35