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 ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
<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 />
delineations do not anticipate recharge from the proposed Superstition Mountains Recharge<br />
Facility. Recharge from the proposed facility would likely not affect the risk delineation in the<br />
vicinity of <strong>Powerline</strong> FRS, but it may have an effect on the risk delineation at Vineyard Road<br />
FRS.<br />
5.1.5. Conclusions <strong>and</strong> Recommendations<br />
The major concern relating to subsidence <strong>and</strong> earth fissuring is focused on the <strong>Powerline</strong> FRS.<br />
There is a known earth fissure immediately downstream of about <strong>Powerline</strong> FRS Station<br />
115+45, <strong>and</strong> there is a high probability that the earth fissure is also present beneath the FRS<br />
embankment. The earth fissure risk is highest in the area around the <strong>Powerline</strong> FRS <strong>and</strong> the<br />
portion of the Vineyard Road FRS located in FRZ 3.<br />
Predicted future subsidence is greatest in the area of the <strong>Powerline</strong> FRS, particularly portions to<br />
the north of the bend at about <strong>Powerline</strong> Station 110+00. Subsidence is predicted to continue in<br />
this area <strong>and</strong> will complicate future plans regarding the <strong>Powerline</strong> Diversion as it could<br />
potentially impact the grade of the channel <strong>and</strong> make draining water to the south challenging.<br />
Any future alternative options that require moving water from north to south in this area will also<br />
have to address the potential that future subsidence will impact the grade of channels or other<br />
infrastructure. Future subsidence predictions indicate that the potential for 1 to 2 feet of<br />
additional subsidence is likely in area north of about <strong>Powerline</strong> Station 110+00 <strong>and</strong> along the<br />
proposed IDSM alignment.<br />
Other portions of the project are not anticipated to experience large amounts of subsidence in the<br />
future, <strong>and</strong> are anticipated to have a low risk for development of earth fissures. Results of this<br />
study indicate that the portion of the Vineyard Road FRS located in FRZ 3 may have a lower risk<br />
for earth fissures than previously thought. It is recommended that the District consider<br />
performing a future investigation to determine if the earth fissure risk in this zone is less than<br />
currently classified. It is recommended that any future investigation performed include close<br />
evaluation of available monitoring data, additional InSAR analysis, additional geophysical<br />
profiling, additional subsidence prediction, <strong>and</strong> updating the stress-strain model in this area.<br />
5.2. Final Earth Fissure Risk Zoning Memor<strong>and</strong>um<br />
The purpose of this memor<strong>and</strong>um was to address NRCs comments about subsidence <strong>and</strong> earth<br />
fissure risk zoning at the <strong>Powerline</strong>, Vineyard Road <strong>and</strong> Rittenhouse (PVR) <strong>Flood</strong> Retarding<br />
Structures (FRSs) as they relate to the PVR FRS Rehabilitation or Replacement Project. This<br />
memor<strong>and</strong>um starts with a general discussion of ground subsidence <strong>and</strong> earth fissuring due to<br />
groundwater withdrawals. This is followed by discussions of the investigative <strong>and</strong> modeling<br />
methods used to predict future subsidence <strong>and</strong> the risk of earth fissuring, <strong>and</strong> the history of earth<br />
fissure risk zoning at flood control structures in the Phoenix area. The memor<strong>and</strong>um culminates<br />
with a discussion of earth fissure risk zoning at PVR <strong>and</strong> responses to specific questions that<br />
NRCS has posed regarding PVR earth fissure risk zoning.<br />
5.2.1. Subsidence <strong>and</strong> Earth Fissuring Due To Groundwater Withdrawal<br />
L<strong>and</strong> subsidence <strong>and</strong> the development of earth fissures at the PVR FRSs, <strong>and</strong> at other flood<br />
control structures in the Phoenix area, are primarily a result of groundwater level declines..<br />
USDA- NRCS <strong>Jan</strong>uary <strong>2013</strong><br />
Kimley-Horn <strong>and</strong> Associates, Inc. Page 38