The Buried Hazards ToolboxTM-What's in Your Levee?
Sacramento-San Joaquin Delta levees contain hidden hazards, some implicated as causes of levee failure. Our continuously collected electromagnetic induction (EM3 data have located buried encroachments (relict pipes and cables, rodent dens, concrete blocks and pads, saturated areas, and storage tanks) and lateral changes in embankment materials (pervious/non-pervious reaches), and pinpointed locations that are sources of uncertainty for internal erosion.
Argus Technologies (a Tremaine Company) has completed 25 electromagnetic induction surveys on over 300 miles of Delta levees, acquiring over 1000 miles of data with tens of millions of data points. Over 6000 anomalies have been located and classified using specific criteria and hundreds have been remediated with excavation (see below). Excavation results enable us to challenge assumptions and refine models and continually improve interpretations of the data. The material producing the anomaly is usually predicted, the location is pinpointed (using GPS-tagged data), the orientation is determined (fully penetrating levee versus waterside, center, or landside), and the depth is estimated. The customer knows what type of hazard exists and where to excavate to remediate and reduce risk. This extensive experience is the foundation of the Buried Hazards ToolboxTM, a risk analysis tool for buried hazards in levees.
The Buried Hazard ToolboxTM is a potential counterpart to the Erosion Toolbox, the Seepage and Piping Toolbox, and others developing in the Nationwide Levee Risk Assessment Methodology project. With our nation challenged to upgrade its aging infrastructure at a time when the responsible allocation of limited funds is paramount, identifying buried hazards is an indispensable factor in making informed decisions in comprehensive levee risk reduction and improvement projects. Any type of levee improvement project would benefit by the risk reduction gained by removing buried hazards before construction begins. The Buried Hazards ToolboxTM is adaptable to levees worldwide.
This work is the result of a cooperative effort among Argus, members of the individual Reclamation Districts and their District Engineers, and the California Department of Water Resources. It exemplifies a proactive approach to scope for hazards using recommended geophysical methods (1-3) and improve levee integrity. The list of buried hazards found below will be continually updated as the results of future excavations become available.
- Over 100 Forgotten pipes in 84 locations, sized 1/2 to 14 inches
- 43 Pockets of loose sand or peat
- 15 Buried cables of various sizes and materials
- 8 Concrete slabs, walls and/or rubble
- 8 Metallic debris (auto tire, rebar, trash pits)
- 6 Rodent (beaver) burrows and dens
- 3 Electrical conduit
- 8 Buried fuel tanks, 55 gallon drums, and/or stilling wells
- 3 Tree logs and/or roots
A quantitative numerical method, called inversion, allows three dimensional imaging of the levees by inverting the EM3 data into a model of the electrical resistivity structure of the subsurface that can be related to various levee fill materials and changes in moisture content within the levee.
California's Sacramento-San Joaquin Delta levees were originally built 150 years ago (by hand) to protect farmland. They were constructed by individual preferences with local fill materials such as peat blocks, without standardized engineering specifications. Today, these levees not only protect farmland, but also protect vital infrastructure including water aqueducts, highways, railways, bridges and deep water ship channels, electric utilities, oil/hazardous liquid pipelines, and historic and active communities.
The slide show holds photographs from our Delta levee surveys.
- Cyrille Fauchard and Patrice Meriaux, (2008). Geophysical and geotechnical methods for diagnosing flood protection dikes: Guide for implementation and interpretaion.
- Llopis J. L. & Simms J. E., Geophysical Surveys for Assessing Levee Foundation Conditions, Feather River Levees, Marysville/Yuba City, California, US Army Corp of Engineers, September 2007.
- Rutlege, F.A., M. Mauldon, and C.J. Smith, (2005). Geophysical Primer for Geotechnical Engineers. Center for Geotechnical Practice and Research at Virginia Tech, 123pp.