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

Powerline Flood Retarding Structure
Pinal County, AZ
Draft Supplemental Watershed Plan
and Environmental Assessment
5. GEOHAZARD
This section provides a summary of the geohazard reviews, investigations and analyses for the
PVR project. The reader is referred to the full geohazard reports for further details and
information in regards to the PVR structures.
The geohazard studies are documented in the following reports
• “Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures Rehabilitation or
Replacement Project Final Initial Subsidence and Earth Fissure Report”. (AMEC August,
2010).
• “Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures Rehabilitation or
Replacement Project Final Earth Fissure Risk Zoning Memorandum”. (AMEC May,
2012)
5.1. Final Initial Subsidence and Earth Fissure Report (GeoHazard Study)
The purpose of the geohazards investigation was to evaluate potential impacts of ground
subsidence and earth fissuring on the selection and subsequent development of rehabilitation
designs and/or replacement alternatives for flood protection afforded by the Powerline, Vineyard
Road and Rittenhouse Flood Retarding Structures (FRS). The results, findings and conclusion of
the report were used by the project team in its development and evaluation of dam rehabilitation
and/or replacement alternatives.
The geohazard study and assessment involved the compilation, review and interpretation of
existing technical data. This data included review of aerial photography and interferometric
satellite-based synthetic aperture radar (InSAR) data, ground reconnaissance of the study area,
surface resistivity surveys, development of subsidence predictions, and a preliminary delineation
of earth fissure risks.
Existing Data Collection & Review
Available groundwater data were reviewed and a summary of historical groundwater decline in
the project area was prepared. Included in this effort was review of the East Valley Water Forum
scenarios for the east Salt River Valley sub-basin application of the Regional Groundwater Flow
Model and the impact of the proposed Superstition Mountains Recharge Project on the Central
Arizona Water Conservation District.
InSAR Review and Analysis
InSAR was used in this study to detect the rate and distribution of subsidence occurring in the
study area over the time periods covered. This information was then further utilized in the
characterization of bedrock/alluvial interface and deep alluvium and for the FRZ delineation
ADWR is currently applying InSAR as part of a long-range study of basin subsidence in
Arizona. Recent interferograms developed by ADWR on the basis of 2000 to 2009 synthetic
aperture radar data were compiled and analyzed for the project area. InSAR images previously
provided by ADWR were also reviewed as part of this assessment.
Photogeologic Interpretations
High-resolution aerial digital imagery previously provided by the District was reviewed, and it
proved to be an equivalent substitute for low-sun-angle afternoon photography. Lineament
USDA- NRCS January 2013
Kimley-Horn and Associates, Inc. Page 28