Cataloging California's River Levee System
Take an aging system of river levees and other flood control structures in the heart of one of the nation’s most agriculturally rich states. Consider that the river system providing irrigation to those essential farmlands also supplies drinking water to 23 million residents. Then add a fast-growing population with an insatiable demand for housing that encourages developers to build suburban housing directly adjacent to flood-prone rivers.
Now consider the possibility that the “Pineapple Express”—a hypothetical series of wet tropical storms blowing in off the Pacific Ocean, warm enough to melt snow in a nearby snow-capped mountain range—will suddenly generate more water than the rivers can carry away. Then consider the occurrence of an earthquake as severe as that which hit northern California in 1989—a 40% to 60% possibility by 2050, according to some researchers. Consider that both disasters could occur simultaneously.
Next, include the understanding that a legal precedent has been set for state government liability in the case of river-levee breaks, regardless of whether or not the state was responsible for building those levees. Add to that the loss to homeowners and businesses unable to qualify for federally underwritten flood insurance due to new Federal Emergency Management Agency (FEMA) regulations that dictate state and/or local authorities must provide documentation certifying the integrity of levees protecting floodplains.
These circumstances combined with a state- or federal-project levee failure will result in every taxpayer being affected, according to a FloodSAFE California presentation by California’s Department of Water Resources (DWR). FloodSAFE California is a strategic initiative by Governor Arnold Schwarzenegger to improve flood protection for the people of California. The goals of FloodSAFE California are as follows:
- Reduce flood risk to the people of California and to their homes and property.
- Develop a sustainable flood management system for the future.
- Reduce the consequences of floods when they do occur.
Broad and Deep Implications
Levees, flood control, and flood insurance go hand in hand, not only practically but also legally. In August 2005, FEMA, as part of the map modernization program, announced new requirements for levee certification via FEMA Procedure Memorandum 34. To meet the standards of FEMA certification and therefore qualify for coverage under the National Flood Insurance Program, state, county, or local entities must certify the levee system with the submittal of the following:
- As-built drawings of the levees and other freeboard documentation
- Levee-opening protection documentation
- Embankment protection documentation
- Embankment and foundation stability analysis
- Settlement analysis
- Interior drainage analysis
- An operation and maintenance plan
For flood insurance mapping purposes, FEMA considers areas behind a levee protected from flooding only if the levee is certified. If it is not certified, then FEMA considers the levee nonexistent and the entire area behind the levee prone to flooding.
All earthen levees, whether reinforced internally or armored externally, are vulnerable to a wide range of natural events that include channel scouring, vegetation growth, eroding foundation soils, widespread subsidence, surface erosion, seepage, animal burrows, and decaying buried vegetation. Often these will occur unnoticed—until a disastrous levee break occurs.
Property owners in areas behind those levees may be required to purchase flood insurance. Furthermore, a 2003 California court decision found the state liable for $500 million in damages for a 1986 Yuba County levee break, even though the levee was not owned and operated by the state. This court decision opened the door for potential liability suits throughout the entire California river-levee system.
The best way to head off any of these scenarios, according to the DWR’s “Flood Warnings: Responding to California’s Flood Crisis,” a January 2005 white paper, is “an aggressive investment in the flood management system and a new flood management philosophy.” The commitment to this investment was confirmed with voter approval of new bonds and the Governor’s FloodSAFE California initiative. But neither is possible without reliable and detailed information on current levee conditions.
The California DWR Levee Database project, undertaken with assistance from PBS&J, a nationwide engineering firm with expertise in water resources, information system building, and program management, is one part of a larger floodplain-mapping project designed to enhance the DWR’s flood management capability.
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Map: CA DWR |
| The predominance of river levees (shown in blue) in California is in the Central Valley. |
Levee Database Extraordinaire
The DWR’s levee database supported by a geographical information system (GIS) platform was the most appropriate method in which to capture and organize the information concerning levees to support flood management. Using GIS has many advantages to tabular database format. For instance, GIS allows for quick visual reference and a common operational picture of the levee systems with respect to other infrastructure and physical features such as roads, political boundaries, buildings, streams, and parcels. Streams and levees stationing can be accomplished within GIS, and additional data may be added or updated easily. GIS provides an effective means of data management leading to more effective governance and multiobjective management of floodplains in California.
For the California Levee Database project, approximately 14,000 miles of levees, canals, and flood control features were spatially located. A database was developed and populated with a set of attributes that include the following:
- Location
- Stream name
- Left/right bank
- Primary use
- Structure type
- Maintenance agency
- Local authority
- Owner-agency
- County
- Congressional district
- Assembly district
- Senate district
- Hydrologic unit name
- 24k Quad
- 100k Quad
- 250k Quad
- Project/non-project category
Emphasis was placed on locating levees spatially by using US Geological Survey quads and geo-referenced FEMA flood insurance rate maps (FIRMs). This task formed the basis for further attribute development in subsequent tasks.
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Photo: Robert A. Eplett/OES CA |
| A soldier returns to what is left of his home, close to the levee break on the Feather River. |
Levee-Related Data Sources
Base maps provided both a geospatial reference and a primary source of levee centerlines. The base map data includes the National Hydrology Dataset stream centerlines, USGS 1:24,000 quad Digital Raster Graphics (DRGs), USGS Digital Ortho-Quads (DOQs), and FIRMs. The DRGs and FIRMs were primary sources of levee alignments from which levee centerlines could be directly digitized. DOQs were used to verify the geospatial location of the levees.
The base map collection also includes layers with governmental and political boundaries, including California senate and assembly districts; congressional districts; counties; and flood control, levee maintenance, and reclamation districts. Much of the information is available on the California Spatial Information Library Web site.
The first attempt to compile GIS levee data was a joint effort by the US Army Corps of Engineers (USACE), FEMA, and the California Office of Emergency Services after the 1997 floods. Inherent issues in the data were addressed, including duplicate levee segments, incorrect topology, and information on levees that no longer existed or had major changes. Additional sources of existing levee data included the DWR’s Bay-Delta Unit and a joint DWR/USACE Comprehensive Study for the Central Valley.
Contacts were initiated with 147 agencies, including federal and state agencies, counties, cities, and flood control and reclamation districts to identify and obtain required ownership and maintenance information, to identify levees not shown on other maps, and to determine the availability of additional information that may be collected in subsequent phases of the data collection effort.
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Photo: Robert A. Eplett/OES CA |
| 1997 floodwaters rose to window level in many homes in California's Central Valley. |
The California Levee Database represents a state-of-the-art application of GIS technology. Building on the FEMA Levee Information System (FLIS), the California Levee Database not only stores data but also is designed for ease of use by a wide variety of potential users. Whereas FLIS was a simple data storage application, the California Levee Database is built on the latest geodatabase design technologies. It has been designed to be accessed without the need for expensive software or special training. This design promotes integration with other applications. It will enhance the maintenance management of this critical type of infrastructure, permitting communication bridges between multiple organizational sectors, and can be supported and maintained through direct, remote, or disconnected editing.
Current development work includes a prescribed bridging and structuring of the DWR levee database, the USACE levee database, and the FLIS in direct support of a National Levee Policy. Specifically, it will add and develop the functional applications and interfaces necessary enabling the DWR levee database to support a consistent and comprehensive integration of data with the USACE and FEMA levee databases. This will provide for enhanced data sharing of critical information among the databases and will develop the necessary integration for other specific applications currently being developed by related agencies. Ultimately, the levee database program will provide a detailed framework for levee inventories performed by all related agencies. This database will also store and identify information that is critical in determining whether existing levees will meet many of the factors that are required to receive certification meeting FEMA standards.
Strong Commitment
In October 2006, California allocated $500 million for emergency Central Valley repair projects to help prevent a Hurricane Katrina–like flood disaster in California. In November 2006, California voters approved $37.2 billion in bond issues for statewide infrastructure improvements, including $4.09 billion toward river-levee maintenance and repairs. However, DWR officials estimate a comprehensive program of data-mapping, maintenance, rehabilitation, repair, and FEMA compliance for California’s entire river-levee system could cost as much as $12 billion or more. Obviously much work will remain even with the funding provided by the 2006 bonds.
However, by collecting critical data and making it available to a wide range of users for a variety of critical applications, the California DWR Levee Database project represents significant progress on several fronts that will stretch the taxpayer funds provided by the bonds. The database will enhance the state’s ability to address the most pressing needs for maintenance, rehabilitation, and repair. It will also enable meaningful risk analysis and emergency planning. At the same time, it will help deliver the information required to support long-term project planning and large-scale funding strategies. The GIS database can be used to support analysis of spending alternatives, public participation, and ultimately spending decisions that synergistically address multiple objectives in flood management with each capital investment decision. Finally, the information provided by a statewide river-levee database floodplain will allow the State of California to take meaningful steps toward protecting valued resources including critical infrastructure, essential businesses, environmental assets, and the lives and well-being of its residents.
Author's Bio: Ricardo Pineda, P.E., CFM, is the chief of the Floodplain Management Branch of the California Department of Water Resources.