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

Powerline Flood Retarding Structure
Pinal County, AZ
Draft Supplemental Watershed Plan
and Environmental Assessment
4.1.7.1. Soil Profiles Underlying Structures Based on All Geotechnical Investigations ..... 16
4.1.8. Discussions .................................................................................................................. 17
4.1.8.1. Failure modes (with an emphasis on the impacts of the presence of Holocene soils
beneath the dams ................................................................................................. 17
4.1.8.2. Data Gaps and Recommendations for Additional Investigations .......................... 20
4.2. Final Filter Alternatives Memorandum ................................................................................... 20
4.2.1. Project Background ...................................................................................................... 20
4.2.1.1. Embankment Cracking ........................................................................................ 20
4.2.1.2. Installation of Central Filters ............................................................................... 21
4.2.1.3. Presence of Collapsible Holocene Soils ............................................................... 21
4.2.2. Foundation Excavations and Central Filter Construction ............................................... 22
4.2.2.1. Upstream Cutoff Trench ...................................................................................... 22
4.2.2.2. Central Filters ..................................................................................................... 22
4.2.3. Existing Filter Potential Failure Modes ......................................................................... 23
4.2.3.1. Function of Existing Filters ................................................................................. 23
4.2.3.2. Potential Failure Modes ....................................................................................... 23
4.2.3.3. Summary of Failure Modes ................................................................................. 24
4.2.3.4. Mitigation of Failure Modes ................................................................................ 24
4.3. Filter Alternatives ................................................................................................................... 25
4.3.1. Central Filter ................................................................................................................ 25
4.3.2. Upstream Sloping Filter ................................................................................................ 26
4.4. Recommendations .................................................................................................................. 26
5. GEOHAZARD .................................................................................................................. 28
5.1. Final Initial Subsidence and Earth Fissure Report (GeoHazard Study) .................................... 28
5.1.1. Investigative Approach ....................................................Error! Bookmark not defined.
5.1.2. Geological Setting ........................................................................................................ 30
5.1.3. Deep Alluvium Characteristics ..................................................................................... 32
5.1.4. Hydrogeological Conditions ......................................................................................... 33
5.1.5. Discussion .................................................................................................................... 35
5.1.6. Conclusions and Recommendations .............................................................................. 38
5.2. Final Earth Fissure Risk Zoning Memorandum ....................................................................... 38
5.2.1. Subsidence and Earth Fissuring Due To Groundwater Withdrawal ................................ 38
5.2.2. Investigative and Modeling Methods ............................................................................ 40
5.2.3. PVR Earth Fissure Risk Zones ...................................................................................... 41
5.2.4. Recommendations ........................................................................................................ 45
6. ENVIRONMENTAL STUDIES ....................................................................................... 46
6.1. Biological Evaluation ............................................................................................................. 46
USDA- NRCS January 2013
Kimley-Horn and Associates, Inc.
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