CALIFORNIA’S LEVEE EVALUATIONS PROGRAM

California's Levee Evaluations Program 1

CALIFORNIA’S LEVEE EVALUATIONS PROGRAM

Mike Inamine1 Sujan Punyamurthula2 Hamid Bonakdar3 Steve Mahnke4 Richard Millet5 Pat Dell6

ABSTRACT California’s Central Valley is the country’s most productive farmland and a rapidly growing region in the country’s most populous state. The Central Valley faces significant flood risks from California’s two largest river systems and other watercourses. Flood control in the Central Valley is carried out jointly by the State of California and the federal government though an extensive network of levees stretching throughout the valley. The California Department of Water Resources (DWR) is conducting a comprehensive and unprecedented evaluation of 2,100 miles of levees comprising the Central Valley Flood Control System. Most of these levees are non-engineered structures originally intended to protect mostly rural farmland. DWR is conducting geotechnical exploration, testing, analyses and preliminary design studies on levees that protect highly populated urban areas on a fast-track basis, while non-urban levee evaluations are conducted through a risk-based approach. These studies will inform the financial strategy to improve the Central Valley Flood Control System as well as State and local design and construction projects. This paper presents the strategic and technical approach to geotechnical evaluations.

INTRODUCTION The California Central Valley (Figure 1) is an important part of California’s economy and home to a rapidly increasing urban population. The Central Valley also poses the State’s greatest flood risk and associated liability. The DWR is midway through an ambitious geotechnical evaluation of approximately 1,600 miles of State/federal levees that comprise the Central Valley Flood Control System, as well as an additional evaluation of 520 miles of appurtenant private levees. Evaluation results will provide foundational data for the Central Valley Flood Protection Plan, and interim results currently inform ongoing construction projects, operations and maintenance practices, floodplain risk assessments, Federal Emergency Management Agency (FEMA)

1 FloodSAFE Levee Evaluations/Repairs Program Manager, California Department of Water Resources, 3464 El Camino Avenue, Suite 200, Sacramento, CA 95821, [email protected] 2 Vice President, Non-Urban Levee Evaluations Deputy Program Manager, URS Corporation, 2870 Gateway Oaks Dr, Suite 150, Sacramento, CA 95833, [email protected] 3 Project Manager, Non-Urban Levee Evaluations, Division of Flood Management, Department of Water Resources, 2825 3464 El Camino Avenue, Sacramento, CA 95821, [email protected] 4 Project Manager, Urban Levee Evaluations, Division of Flood Management, Department of Water Resources, 3464 El Camino Avenue, Sacramento, CA 95821, [email protected] 5 Vice President, Levee Evaluations Program Manager, URS Corporation, 2870 Gateway Oaks Dr, Suite 150, Sacramento, CA 95833, [email protected] 6 Principal/Senior Geotechnical Engineer, Neil O. Anderson & Associates, 902 Industrial Way, Lodi, CA 95240, [email protected]

Collaborative Management of Integrated Watersheds 2

accreditation efforts and other flood management activities. This paper describes the importance of the Central Valley Flood Control System, the risks posed by aging levees and distinguishes the differences between urban and non-urban levee evaluation processes. While there are a number of technical research and policy issues encompassed by DWR’s Levee Evaluations Program (LEP), this paper focuses on the geotechnical exploration, testing, analysis and preliminary design studies that comprise the bulk of the program’s components.

BACKGROUND Central Valley Flood Control System California's Central Valley stretches from Shasta County in the north to Kern County in the south, covering an area approximately 450 miles long and 40 to 60 miles wide. The valley is drained by California’s largest river systems: the Sacramento River flowing from the north, and the San Joaquin River flowing from the south. The two rivers converge with the Mokelumne, Calaveras and Cosumnes rivers in the Sacramento-San Joaquin Delta before flowing to the Pacific Ocean. The Central Valley is one of the most productive agricultural regions in the world, comprising approximately one-sixth of the nation’s irrigated land and producing approximately one-fourth of the nation’s food supply. The Central Valley is also home to a rapidly expanding urban population of the nation’s most populous state. Since 1980, the population of the Central Valley has nearly doubled from 2 million to 3.8 million people, and the Census Bureau projects that this number will increase to 6 million people by 2020 (Reference 1). Currently, 1.8 million people rely on levees for flood protection in the Central Valley. At current growth rates, this number will rise to more than 2.3 million by 2020 (Reference 2).

Figure 1. California Central Valley


The outlet to the Central Valley, the Sacramento-San Joaquin Delta, is the largest estuary on the west coast of North and South America, encompassing about 700,000 acres of waterways, wildlife habitat, reclaimed farmland, and agricultural towns. The Delta is also the heart of the federal Central Valley Project and the State Water Project that supports much of California’s economy. At the southern end of the Delta, these two massive systems pump water south to southern California. The Central Valley Flood Control System protects people, property and infrastructure from flooding on the Sacramento and San Joaquin rivers. Over 1 million people and 1.9 million acres of cultivated land with an annual production value of over $2 billion are protected behind project levees. Approximately 200,000 structures with an estimated value of $64 billion rely on this system, as well as the last remnants of extensive riparian forests and wetlands that once flourished along California’s rivers prior to European settlement. Finally, the water supply for 23 million people, farms and industry relies on a vast network of 1,100 miles of Delta levees that are susceptible to earthquake damage and flooding. The economic losses resulting from a catastrophic failure of Delta levees would be measured in the tens of billions of dollars. Before European settlement, the Central Valley was often an immense inland sea subject to seasonal, valley-wide flooding. During winter storms and spring snowmelt, the Sacramento River overflowed its banks into large, low-lying basins that slowly drained back into the rivers or Delta sloughs. The San Joaquin River waters spread into broad floodplains and wetlands adjacent to the river. Flooding of the basins and floodplains provided water storage that attenuated peak flows to downstream areas, encouraged percolation into groundwater, and supported diverse riparian and extensive tule/emergent wetland communities. Over the course of a century of reclamation work, the rivers were gradually contained behind levees that kept flows from flooding rural communities and farmland. The resulting construction of the modern Central Valley Flood Control System enabled the rapid expansion of the agricultural economy that dominates the landscape today and enabled urbanization of rural communities. Initially, attempts to contain flows year-round within single channels met with catastrophic failure as flood flows repeatedly overwhelmed non-engineered and poorly constructed levees. On the Sacramento River system, flooding was exacerbated by hydraulic mining, a method of extracting gold invented in the mountains of the Yuba River Basin in 1853. This technology delivered an estimated 1.4 billion cubic yards of sediment into Sacramento River basins by 1905 (Reference 4). Impacts to channels that already lacked sufficient capacity to contain flood flows included raised riverbeds (by as much as 20 feet), repeated bank and levee failures, and severe flooding. A historic decision was made to route flood flows through the natural basins via multiple channels, and beginning in the early 1900s, the current system of bypasses was constructed. An equally historic decision was the practice of aligning Sacramento River levees close to the channel, producing high velocity flows that scoured the channels of sediment from hydraulic mining.


Today, the Central Valley Flood Control System includes reservoirs with flood detention space, approximately 1,600 miles of levees, and a series of overflow weirs and bypass channels. These facilities were originally constructed by or incorporated into a federally designated flood control project (Figure 2). The State of California is the non-federal sponsor of the system and accepted the assurances of operating and maintaining these federal projects under the authority of the Flood Control Act of 1944. In accordance with State law, most of the operation and maintenance responsibilities have been delegated to local reclamation districts. These 1,600 miles of State/federal project levees are referred to as project levees. In addition, project levees are augmented by approximately 520 miles of appurtenant non-project levees (sometimes referred to as private or local levees) that directly impact basins protected by project levees.

Figure 2. Central Valley Flood Control System


Challenges Over the years, major storms and flooding have taken many California lives, caused significant property losses and resulted in extensive damage to public infrastructure. Moreover, a combination of factors described below has put public safety and the State’s financial stability at risk for an even greater calamity in the future. Land Use: Escalating development in floodplains increases the potential for flood damage to homes, businesses and communities. The original flood protection system was successfully designed to protect pioneer farms. Today this system also protects thousands of homes, businesses and other structures. Inadequate Design and Construction: Early levee design and construction are inadequate by modern standards (Figure 3). Construction was often accomplished with dredges and horse-drawn equipment with little consideration for material properties or placement procedures. Many of these non-engineered levees were simply grandfathered into the flood control system without adequate investigation or analyses of their condition.

Figure 3. Levee Construction in the 1920s

Deferred Maintenance: California’s flood protection system, comprised of aging infrastructure, has been further weakened by deferred maintenance. Sedimentation of channels and erosion damage are the results of maintenance that has been deferred due to financial, physical, environmental and regulatory obstacles. Erosion: The historic decision to scour out Sacramento River channels of mining debris by setting levees close to the channel was successful; much of the sediment has now been flushed from the system. However, an unintended consequence is that high velocity flows continue to scour not just sediment, but channel banks and levees. As a result, many levees have been critically damaged and many more will continue to erode. State and Federal Financial Roles: Federal funding for effective flood prevention and management programs has been reduced. Between 2006 and 2009, California spent over $300 million on projects that are normally funded by the federal government. Liability: Court decisions have resulted in greater State flood damage liability. The November 2003 Paterno vs. State of California decision found that when a public entity


operates a flood control system built by someone else, it accepts liability as though the State had planned and built the system. The Paterno ruling held the State responsible for defects in a Yuba County levee foundation that existed when the levee was constructed by local agricultural interests in the 1930s. Not surprisingly, flood risk for the Central Valley ranks as among the highest for any developed country. And within the U.S., the greater Sacramento area is subject to the lowest level of protection for major cities, including pre-Katrina New Orleans (Figure 4).

Figure 4. Flood Protection for Major U.S. Cities

FloodSAFE To meet these challenges, DWR launched FloodSAFE California, a multi-faceted program to improve public safety through integrated flood management. FloodSAFE improves integrated flood management in California through a system-wide approach while reducing flood risk at regional and local levels. FloodSAFE is funded by almost $5 billion in bond measures approved in 2006. System Analysis A major deliverable of FloodSAFE is the Central Valley Flood Protection Plan (CVFPP). This document will describe a sustainable, integrated flood management plan that reflects a system-wide approach for protecting areas of the Central Valley currently receiving flood protection via existing facilities in the Central Valley Flood Control System. DWR is preparing the CVFPP for adoption by the Central Valley Flood Protection Board by July 1, 2012, and plans to update the plan every five years thereafter. This system-wide approach includes the hydrologic, hydraulic, economic, ecosystem and geotechnical elements (Figure5) of flood management in the Central Valley. Key to this approach is an understanding of the geotechnical reliability of the levee system. The LEP provides this important input. A flurry of recent legislation has defined specific outcomes for the CVFPP; notable among these laws is the mandate that urban communities (populations greater than 10,000 people) achieve 200-year level of flood protection by 2025. Begun in late 2006, the LEP is approximately 50 percent complete and is targeted to conclude in early 2012.


Figure 5. System Evaluation

PURPOSE AND GOALS

The purpose of the LEP is to evaluate State/federal project levees and appurtenant non-project levees, to determine if they meet defined geotechnical criteria and, if appropriate, identify remedial measure(s) to meet those criteria. Goals of the program are to: • Support the CVFPP and Central Valley Floodplain Evaluation and Delineation

(floodplain mapping) projects, federal and local flood management projects, local FEMA certification efforts and the legislative mandate of urban, 200-year flood protection by 2025.

• Provide geotechnical data, analyses results and conceptual alternatives for remediating levees in-place to local, State and federal stakeholders.

• Improve geotechnical information exchange methods among State, local and federal flood management agencies.

• Identify levees that require immediate, critical repairs. An outcome of this study will be the prioritization of remediation necessary to improve levees in-place; this will inform the system-wide analysis and provide important input to the financial strategy to improve the flood control system. Levee remediation will be considered along with bypasses, flood corridors, setback levees, reservoir re-operation and non-structural alternatives in the system-wide analysis. Environmental mitigation strategies for these measures also rely on these studies. Although many LEP deliverables are being used for ongoing design and construction projects on many levees, this program provides screening-level analysis intended for planning purposes only. Additional design-level geotechnical investigations and studies are necessary prior to implementing any site-specific remedial measures.


IMPLEMENTATION STRATEGY Work Breakdown Figure 6 shows the overall work breakdown of the LEP. The first two elements, the Urban Levee Evaluations (ULE) project and the Non-Urban Levee Evaluations (NULE) project are the primary subject of this paper and produce the major deliverables of the LEP. Given the magnitude of levee reaches covered by the LEP, limited budget and the challenging schedule, a number of strategies were employed to leverage existing data and concurrent work performed by others. The implementation strategy for ULE and NULE is described in detail below, followed by brief descriptions of the LEP’s Technical Review and Technical Policy sub-elements.

Figure 6. Levee Evaluations Program

Levee Systems As discussed above, DWR is evaluating levees as systems; as a result, levees are evaluated with respect to the entire basin they protect rather than discrete reaches. Although the State has liability only for project levees, the LEP is also evaluating appurtenant, non-project levees that meet at least one of three criteria: • The non-project levee is directly contiguous with a project levee • The non-project levee protects the same basin as a project levee, or • The non-project levee directly impacts the performance of a project levee Table 1 presents the breakdown of urban, non-urban, project and non-project levee miles under study.


Table 1. Approximate Levee Mileage Summary Project Levees

(miles) Non-Project Levees

(miles) Urban 350 120 Non-Urban 1,250 400

Total 1,600 520 Levee Performance Deficient geotechnical performance of a levee is typically caused by: • Inadequate freeboard, resulting in overtopping and erosion. • Underseepage due to the presence of pervious foundation soils beneath the levee. • Through seepage due to the presence of pervious soils in the levee embankment. • Instability on a levee’s waterside or landside slopes due to the presence of soft or

weak soils and/or high seepage forces. • Seismically-induced deformations and/or liquefaction. • Significant erosion of a levee’s waterside slope and undercutting of the waterside toe,

leading to instability and a breach of the levee embankment. • Undetected animal or man-made defects (e.g., penetrations or animal burrows,

construction problems) generating uncontrolled, concentrated seepage, internal erosion and eventual levee breach.

Levee Criteria The U. S. Army Corps of Engineers (USACE) is an important LEP participant and reviewer of technical deliverables. Local experts and levee maintenance agencies also review findings and supply critical local knowledge, particularly with regard to levee performance history. A key strategy of the LEP is to follow existing USACE levee design criteria closely for two primary reasons: USACE criteria are the most comprehensive and widely-accepted criteria available, and projects identified for federal funding must meet USACE criteria. There are exceptions to this policy, such as seismic criteria where applicable USACE design criteria does not exist. Water Surface Elevations Water surface elevations (WSE) define important loading conditions for the ULE and NULE projects; however, due to ongoing changes in hydrologic models, input data and climate change, WSE will always be a moving target. As a result, levee performance is evaluated at a range of WSE, resulting in a rating curve of levee performance that will help planners and designers irrespective of future changes in hydraulic analyses. The four WSE used to evaluate urban and non-urban levees are described below. In addition, some background is given as to why some WSE are not used for evaluations. 55/57 Profile: When California took over federal levees, the State made assurances to operate and maintain levees at the design WSE. This WSE is referred to as the 55/57


profile, a shorthand term to describe the 1957 water surface profile for the Sacramento River Flood Control System and the 1955 profile for the San Joaquin Flood Control System. Both of these water surface profiles are commonly accepted as the liability limit for the State, following the legal principle that State assurances produced an expectation that levees would perform at the 55/57 WSE. The LEP evaluates levee performance at the 55/57 profile for both urban and non-urban levees. 100-year WSE: The 100-year WSE is the minimum standard set by FEMA that will not incur development restrictions or mandatory flood insurance; this 100-year WSE is widely regarded as inadequate in urban areas. Although important for FEMA accreditation, the LEP does not explicitly evaluate levee performance at this elevation. 200-year WSE: The 200-year WSE is the legally mandated standard for urban levees. Urban areas must achieve protection from a 200-year flood event by 2025. Geotechnical performance is evaluated at this WSE, which is based on the best available hydrologic and hydraulic information. Top-of-Levee: A brittle failure of a levee can cause extensive loss of life in an urban setting. Urban levee evaluations were conducted from the standpoint that levee failure should only occur due to overtopping. Under this approach, sudden, high-head failures would be avoided, allowing a high percentage of an affected population to get out of harm’s way. Urban levees are therefore evaluated at the WSE corresponding to the levee crest, 200-year WSE plus 3 feet, whichever is lower. Non-urban levees are also evaluated at this elevation to provide a range of expected performance. Urban Levee Evaluations (ULE) Figure 7 shows the approximately 470 miles of project and appurtenant non-project levees that comprise the group of urban levee systems in the Central Valley. The overall strategy for urban levee evaluations is impacted by two legislative and executive actions. California Senate Bill 5, signed in 2007, mandates that communities with populations of 10,000 people or more must be protected by levees that provide a minimum of 200-year protection. This mandate necessitates a relatively high standard of care for urban levee evaluations. In addition, the Governor’s 2006 Emergency Order S-18-06 fast-tracked this study with the goal of quickly identifying geotechnical deficiencies for repair.


Figure 7. ULE Study Areas

As shown in the work flow chart (Figure 8), the LEP’s phased evaluations are implemented in five major steps. 1. Historical Data Collection. Available levee data is collected, and local, State and

USACE experts are interviewed. Geomorphology studies are also conducted. For each study area, results are documented in a Technical Review Memorandum (TRM) which generally assesses known and unknown conditions as well as levee performance during past flood events. Based on the results of the TRM, Steps 2 and 3 may not be performed in study areas that have already undergone significant investigation by the USACE and/or local stakeholders; in this case, screening efforts proceed to Steps 4 and 5.

2. Initial Field Investigation. Initial field exploration (limited to the levee crown) and laboratory testing programs are conducted and documented in a Phase 1 Geotechnical Data Report (P1GDR).

3. Preliminary Analysis. Based on the results of the TRM and P1GDR, locations for supplemental evaluation are identified by performing preliminary geotechnical analysis of seepage and stability conditions.

4. Supplemental Investigation. Based on the results of analyses performed during Step 3, and particularly its correlation with past performance, a supplemental field and laboratory exploration program is developed and implemented to address any


significant data gaps. This work is documented in a Supplemental Geotechnical Data Report (SGDR).

5. Final Screening. Additional analyses are conducted to evaluate levee conditions based on available data. As necessary, conceptual remediation and corresponding costs are identified on a reach-by-reach basis for each study area. Analyses and conceptual remediation are documented in a Geotechnical Evaluation Report (GER).

Figure 8. ULE Process


Non-Urban Levee Evaluations (NULE) Figure 9 shows the approximately 1,650 miles of project and appurtenant non-project levees comprising the non-urban levee systems in the Central Valley. Given the extent of levees under study and limited funding, NULE evaluations are implemented in a phased approach (Figure 10). All levees are evaluated utilizing existing data in Phase 1. Selected levees are then analyzed in Phase 2 by conducting field investigations and more detailed analyses. This phased, risk-based approach is tactically dissimilar from ULE, in which all urban levees are evaluated to a single, defined standard mandated by law. In contrast, non-urban levees will be evaluated to varying standards with respect to a broad range of actions that are under consideration. Thus, local stakeholders are included in the decision-making process by validating historic levee performance and conditions, providing input on field exploration locations and providing input on high priority areas. This process is facilitated by the overarching Central Valley Flood Management Planning Program, which conducts workshops that provide local stakeholders an important role in prioritizing levees that impact regional flood planning efforts. This approach takes a great deal of time and process, but is essential to leverage the most benefit from available funding. Levees are analyzed under two hydraulic loading conditions: the 55/57 WSE and the top of levee (as described above).

Figure 9. NULE Study Areas


The goal of the NULE Project is to group levees into one of four categories: • Levees that are clearly deficient or have critical performance problems • Levees that have moderate performance problems • Levees that have no apparent deficiencies • Levees that cannot be categorized due to a lack of sufficient information This categorization approach prioritizes further analyses or remedial action based on estimated risk or hazard. This is dissimilar to the ULE approach in that all urban levees are mandated by law to achieve a defined level of protection. Figure 10 describes the NULE phased approach, the steps involved to complete each phase, and key deliverables.

Figure 10. Phased NULE Project Evaluation Process

Phase 1 consists of a hazard assessment followed by a remedial alternative and cost estimate analysis. Tasks include the identification of levees, collection of historical data including past performance, historical archive research, inspections, interviews of local experts, and preparation of a surficial geomorphic study followed by detailed geomorphology in selected reaches. Remedial alternatives are then considered to provide a conceptual estimate of the costs to correct identified deficiencies. Key deliverables are a Geotechnical Assessment Report (GAR) and a Remedial Alternatives and Cost Estimate Report (RACER). A GAR and a RACER will be prepared for all NULE Project levees and appurtenant non-project levees. An important analytical component of Phase 1 is the Levee Assessment Tool, or LAT, which enables analysis of limited data using a systematic, repeatable procedure. The NULE Phase 2 consists of exploration, testing, analyses and refinement of the RACER, and is similar to the ULE analysis process. Levees that receive this higher level of study include those that protect communities of at least 5,000 people, in addition to


smaller rural towns and levees that protect critical infrastructure. Selection of levees for Phase 2 study is facilitated through the Central Valley Flood Management Planning process. Key deliverables include a Geotechnical Data Report (GDR) containing results of exploration and testing, and a Geotechnical Evaluation Report (GER) that documents analyses and the updated RACER. Technical Review and Policy As shown in Figure 6, the LEP also includes technical review and policy components; these are described briefly below. Technical Review: Due to recent legislation, availability of State and local funding, and the potentially negative economic impacts of FEMA regulatory mapping, an increasing number of levees are being repaired and improved through accelerated design and construction projects. As the construction of remedial designs is considered imminent, these designs are being reviewed as “existing levees.” Levee projects are also reviewed by the Central Valley Flood Protection Board. The ULE Program and NULE Project provide technical support for this regulatory function on an as-needed basis. Technical Policy: Three research and policy projects are underway that have immediate and long-term impacts on levee evaluations. Seismic Research and Policy. There is no formal or well-defined seismic policy for California levees. International levee research and seismic vulnerability studies are being conducted to: • Gain a greater understanding of seismic risks posed by levees • Research seismic risk reduction measures undertaken in other countries • Develop California-specific risk reduction measures • Develop technical policy that will reduce flood risk The goal of this research is a statewide policy for levee performance, and emergency and long-term remediation that will mitigate seismic impacts on levees and associated consequences. Interim Levee Design Criteria. Many local and state-funded projects are going forward with construction projects in advance of defined 200-year criteria in urban areas. The LEP, while ongoing, provides interim design guidance that provides reasonable certainty and conservatism that levee construction will meet as-yet undefined 200-year criteria. Vegetation Research. Peer-reviewed scientific research is being conducted to support development of a technically defensible vegetation management policy in support of California’s FloodSAFE initiative. Research considers both beneficial and harmful impacts of levee vegetation on Central Valley levees.


URBAN LEVEE EVALUATIONS As discussed earlier and presented in Figure 8 above, urban levee evaluations are being implemented in five major steps. The 470 miles of levees under study by the ULE Program were subdivided into 12 major study areas as shown in Figure 7. In general, each area represented an independent basin and was evaluated separately. Given the amount of attention focused on urban levees over the past few years, historical levee performance and the nature of fixes at selected locations have been reasonably well documented. However, as most of repair efforts focused on selected locations with historical performance issues, a comprehensive database containing the full extent of urban levee issues has never existed. The ULE Project was tasked with evaluating all urban levees using a system-wide approach to collect and evaluate data for 470 miles of levees. Also, given the extent of levees under study and the relatively limited budget for performing detailed intrusive investigations, a number of methodologies were developed to employ new technologies to efficiently collect and analyze data on a large scale. The following sections discuss some of these methodologies implemented for the ULE Project. Historical Data Collection and Storage A significant amount of data about past levee performance, investigations, and repairs was available from different sources. This data was collected by initially conducting comprehensive research of existing data stored with DWR and USACE, and supplementing it with transcribed interviews with local agency personnel. All of the collected documents were digitally scanned and distilled into Adobe Acrobat’s portable document format (.pdf) and stored in a project database. At a later date this data will be incorporated in the California Levee Database and portions will be included in the National Levee Database (maintained by USACE). Collecting Topographic Data Helicopter-borne light and detection ranging (LiDAR) survey equipment collected data along the majority (about 370 miles) of urban levees. LiDAR data collected via helicopter provided some significant advantages over other methods of data collection, including: • Ability to focus the survey along a levee alignment • Higher data accuracy than with traditional fixed-wing LiDAR surveys • Video and aerial photographic imagery collected simultaneously with topographic

data • Participation of project personnel on helicopter flights to direct surveys and ensure

appropriate data was collected • Collection of a large amount of topographic data in a limited period of time • Smooth transition to GIS-based digital terrain models (DTM) with minimal ground

truthing requirements due to the high density of survey points (90 per square meter) • No right-of-entry issues


As shown in Figure 11, LiDAR data was supplemented with bathymetric data to produce a complete model of a levee’s prism and channel in selected reaches. Bathymetric data was collected using multi-beam sonar technology, which facilitated collection of shallow water data and production of three-dimensional models. A key aspect of LiDAR and bathymetric surveys is the seasonal timing of data collection. LiDAR data was collected in early spring to minimize impacts of new leaf growth and to take advantage of low water levels prior to spring melt. Bathymetric survey data was collected in the fall when water levels were high enough to ensure sufficient overlap between LiDAR and bathymetric survey data. These two survey methods help to prevent data gaps, especially on a levee’s waterside slope.

Figure 11. Topographic data collection from LIDAR and bathymetric surveys

Collecting Subsurface data Subsurface data was collected using a combination of non-intrusive and intrusive investigation methods. Non-intrusive investigations consisted of geomorphic and geophysical surveys. Geomorphic and geophysical surveys were conducted in all urban study areas to develop an initial understanding of geologic setting and to identify potential locations of anomalies. The objective of the geomorphic study was to prepare surficial geologic maps (Figure 12) of site-specific conditions and provide a framework for understanding geomorphic processes in each study area. The approach to developing a surficial geologic map consists of review and research of the following selected sources: • Vintage aerial photography (1937, 1958) • Historical topographic maps • Historical geologic maps • Soil survey maps


• Field reconnaissance observations Vintage aerial photos were compared with vintage topographic maps to help evaluate land features prior to substantial agricultural and flood-control modification of the Central Valley’s land surfaces. A stratigraphic model was also produced from available field investigation data. This geomorphic model was then evaluated for stratigraphic discontinuities, particularly with respect to buried subsurface channels that can significantly increase susceptibility to underseepage.

Figure 12. Typical Surficial Geologic Map

Geophysical studies consisted of Helicopter Electromagnetic (HEM) and ground-based galvanic studies. Both technologies measure differences in electrical properties of soils to infer soil variability. The HEM studies were conducted to provide rapid assessment of subsurface conditions at a macro scale. As the HEM studies involved a helicopter carrying a large sensor, Federal Aviation Administration (FAA) and other safety restrictions limited the extent of survey coverage to about 300 miles of levee reaches. Areas not covered by HEM surveys were supplemented with surface galvanic studies. Figure 13 and Figure 14 present sample results from HEM and galvanic studies.


Figure 13. HEM Survey and HEM Survey Equipment

Figure 14. Galvanic Survey Results

The results of geomorphic and geophysical investigations were evaluated to identify areas of potential anomalies that needed further investigation through intrusive field investigations. Intrusive investigations consisted of soil borings and cone penetrometer test (CPT) soundings. Soil boring samples were obtained using punch-core (mud-rotary) and sonic drilling methods. Punch-core sampling provided a means of obtaining continuous core samples from borings. Soil samples obtained from borings were stored in core boxes and transported to a warehouse for longer term storage. In general, mud-rotary borings were separated about 1 mile apart. CPT soundings or sonic borings were spaced at about 1,000 foot intervals, providing a signature of subsurface conditions between mud-rotary borings, and CPT exploration was correlated with borings approximately every mile. Selected soil samples from mud-rotary borings were then tested in a laboratory for a suite of geotechnical properties, ranging from index to strength tests. Subsurface data collected from intrusive and non-intrusive field investigations provided sufficient information to develop an understanding of subsurface conditions in the ULE study areas for further analyses and development of conceptual remedial alternatives.


Geotechnical Analyses As discussed earlier, geotechnical analyses were conducted for multiple failure modes, consisting of underseepage, through seepage, stability (static and seismic) and erosion. Seepage analyses were conducted using SEEP/W and slope stability analyses were performed using UTEXAS4 and SLOPE/W software. To maintain consistency across multiple project teams performing analyses, the ULE Project developed a guidance document. The Guidance Document for Geotechnical Analyses also provided specific methodology for erosion and seismic analyses that are not currently defined by USACE analyses criteria. Analyses results will then be used to develop conceptual repair alternatives for reaches not meeting criteria. A design alternative and cost estimating manual and an associated cost estimating spreadsheet tool was developed to facilitate quick identification of remedial alternatives and serve as a consistent basis for cost estimates. The final results of analyses are documented in a Geotechnical Evaluation Report (GER) that is specific to each study area.

NON-URBAN LEVEE EVALUATIONS As discussed earlier and presented in Figure 10, NULE is conducted in two major phases. Phase 1 studies are based on a review of existing data without performing any intrusive investigations and Phase 2 involves field investigations and refinement of evaluations for selected locations. Many of the tools and methodologies developed for ULE were adopted by NULE where applicable. However, given the vast quantity of non-urban levees under study, additional tools were developed to perform a prioritized, systematic assessment of levees based on available information. Moreover, the large extent of levees and the need for maintaining consistent data formats among various State, federal and regional programs required evaluation of non-urban levees according to levee segment rather than by study area as in urban evaluations. Levee segments are based on existing unit numbers documented in USACE O&M manuals. NULE Phase 1 Assessments Given the extent of non-urban levees under study, emphasis was placed on maximizing the use of existing information before spending limited funding on more costly components of the project. This was particularly challenging; unlike urban levees, there is limited or sparsely distributed documentation about non-urban levee construction history, levee performance and subsurface conditions. To address these challenges, a systematic data collection and assessment procedure consistent with the following elements was developed for Phase 1 assessment: • Data collection • Geomorphic study


• Data analyses and levee segment classification Data Collection A comprehensive data collection effort was developed to collect information from multiple sources consisting of State, federal, and local agencies. Sources of levee information included: • Existing reports and documents • Existing databases • Interviews with local agencies and experts • Site reconnaissance studies Topographic and water surface elevation data were obtained from other programs within DWR, including the Central Valley Floodplain Evaluation and Delineation project. The NULE Project team reviewed documents obtained from DWR, USACE, levee maintenance authorities, reclamation districts and other local agencies. Specialty research consultants also conducted extensive historical records research on behalf of the project. To date, over 8,000 database records have been collected. The documents have been scanned and archived utilizing hundreds of gigabytes of storage space. To manage this large amount of data and also provide the NULE team with an efficient tool for accessing these files, a Levee Evaluations Database was developed. Levee Evaluations Database: Review was initiated by developing a project specific Levee Evaluations Database (Figure 15) to catalog available levee segment records and related documents. Key features of the database include: 1. A Microsoft Access-based format 2. A portable file that can be used by office or field personnel 3. Database search and output capabilities 4. Compatibility with the California Levee Database (CLD). 5. A hyperlink of each document listed in the database with a digitally scanned file of

the document residing on a separate external hard drive The Levee Evaluations Database was populated by importing or entering key information about documents and records provided by DWR. The NULE Project team also developed systematic database updates and quality control processes to maintain database integrity while allowing additional entries as documents become available. Documents were initially screened to create a set of documents pertinent to Phase 1 assessments. As documents were screened, pertinent levee segment information was collected and stored in a GIS database to capture points of interest (POI) and create a POI map. The points on this map hyperlink to pertinent documents in the Levee Evaluations Database and can be retrieved in full. The POI map also demarcates and labels points and linear features where levee data is available and/or performance events were reported.


Figure 15. Levee Evaluations Database

Geomorphic Studies Geomorphic analyses for the NULE Project were conducted using a stepwise refinement approach by starting with a large-scale map and refining it as needed. Analyses were primarily segregated into two main levels (Level 1 and Level 2). Level 1 geomorphic analysis is completed, and provides a reconnaissance-level (scale 1:100,000) assessment of geomorphic characteristics and domains within the NULE Project area. Level 2-I analyses and mapping covers the entire NULE Project area, and were designed to provide additional technical detail to improve and refine Level 1 analysis results. Level 2-I mapping also provides a technical basis for recommending locations for more detailed geomorphic analysis and assessment (i.e., Level 2-II analysis). Level 2-I mapping was based primarily on the compilation and analysis of existing regional geologic and geomorphic information (e.g., soil survey maps, geologic maps), typically mapped at 1:62,500 scale. Upon completion of Level 2-I studies, additional areas will be selected for the more detailed surficial geomorphic analyses of Level 2-II based on the following goals: • Reducing uncertainty when applying the levee assessment tool (LAT, described

below) and when categorizing levees. • Providing a geomorphic framework for subsurface exploration work plans. • Refining and reducing uncertainty when developing remedial alternatives and cost

estimates. • Providing a better understanding of areas in which historical performance issues were

documented during data collection.


Level 2-II studies are sequenced to match the schedule of studies conducted during Phase 1 geotechnical assessment. Level 2-II analyses includes the preparation of maps at 1:24,000-scale using original surficial geologic maps and vintage photographs consistent with the geomorphic studies conducted under the ULE Project. Data Analyses and Levee Segment Classification In the next step of Phase 1, collected data was analyzed and correlated with geomorphic studies to categorize levees into one of the four assessment categories discussed earlier. Since limited data precluded the use of traditional geotechnical analyses, a levee assessment tool (LAT) was developed to: • Assess limited data using a systematic, repeatable procedure • Maintain consistency among several implementation teams • Document the basis for levee categorizations • Maximize evaluation efficiency The four major modes of failure considered in the LAT include through seepage, underseepage, landside slope stability and erosion. For each mode of failure, available data was reviewed to develop a list of applicable hazard indicators (such as steepness of slope for slope stability, permeable subsurface soils for underseepage). These indicators were then weighted to develop a weighted hazard indicator score (WHIS) for each failure mode. The WHIS and performance characterization were then plotted as best estimate values, minimum credible values, and maximum credible values to capture a confidence interval and a range of likely performance results. The LAT does not produce levee condition categorizations; instead, this tool provides a means for repeatable assessments that are consistent across multiple project teams and provides a basis of characterizing levee segments using engineering judgment. The LAT process described above includes a significant component of engineering judgment, as the tool only uses available performance and geologic data without other traditional geotechnical analyses. This is a key difference between NULE and ULE assessments; NULE Project data is not sufficient to perform the more deterministic analyses performed in the ULE Project. Each NULE Project levee segment is then categorized for each of the four different failure modes. This helps develop a consolidated categorization for each levee segment. Categorization results are documented in a GAR. Conceptual cost estimates for repair of each segment are then estimated using the procedures similar to those employed in the ULE Project. Upon completion of Phase 1 Assessments, selected levee reaches are then evaluated through field investigation and geotechnical analyses. These results will then be documented in a GER as discussed earlier.


CLOSING The DWR Levee Evaluation Program is an unprecedented effort to assess and improve a vast network of Central Valley levees that protect a rapidly growing population, the nation’s most productive farmland, Southern California’s water supply and the last remnants of once-thriving riparian forests and wetlands. In addition to many technical issues, this program faces a number of financial, legal and institutional challenges. These challenges are being met with a comprehensive and innovative approach that differentiates risks posed by urban and non-urban levees. When completed, this program will provide a legacy of foundational data for strategic improvements to the Central Valley Flood Control System.

REFERENCES

1. Faunt, C.C., ed., 2009, Groundwater Availability of the Central Valley Aquifer, California: U.S. Geological Survey Professional Paper 1766, 225 p.

2. Galloway, Gerald E., Jr. Chair, Independent Review Panel. A California Challenge – Flooding in the Central Valley: A Report from an Independent Review Panel to the Department of Water Resources, State of California. CA: October 15, 2007, 65 pages.

3. Kelly, Robert L., Battling the Inland Sea: Floods, Public Policy, and the Sacramento Valley, University of California Press, 1989.

4. Singer, Michael Bliss and James L. Allan, Development of the Lower Sacramento River Flood-Control System: Historical Perspective, Natural Hazards Review, ASCE, Volume 9, Issue 3, August, 2008.

5. State of California, Department of Water Resources, Flood Warnings: Responding to California’s Flood Crisis, January 2005.

6. U.S. Army Corps of Engineers, Sacramento and San Joaquin River Basins Comprehensive Study, California, Interim Report, December 2002.