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Spring 2003
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San Francisco's Peninsula and Alameda Watersheds

Gold in the Water--Watershed Management With GIS

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This series of maps convinced the watershed managers that vegetation management was a worthwhile investment. About 33 percent of the watershed has high fire potential.

The successful design, construction, and management of man-made structures and networks with respect to our natural environment have never been at a greater premium.

Over decades and even centuries in the United States and around the world, people have sought to build cities and environments that maintain the health of both communities of people and the environments in which they live.

The San Francisco, California, Bay Area water supply system is a perfect example. Built with great foresight and ambition, it now delivers 200,000 gallons of water per day to Bay Area users via the Hetch-Hetchy system--from a source 167 miles distant.

The large portion of the water supply of the greater Bay Area passes through the impoundments of the Alameda watershed in the East Bay and the Peninsula watershed in San Mateo County, approximately 20 miles south of San Francisco. The watersheds are maintained by the San Francisco Public Utilities Commission (SFPUC). Approximately 2.4 million residents rely on the health of these watersheds.

ArcInfo was used for an ambitious watershed management project. Researchers and managers captured, analyzed, and shared spatial data and information in new and exciting ways to establish optimum management policies.

"The complexity and comprehensiveness of the watershed management planning effort could not have been handled without GIS as a tool," says Joe Naras, land and resources manager of the San Francisco Public Utilities Commission. "For natural resources management it's a natural. Developing the watershed management plans was done using GIS because preserving the environmental and ecological values of the watersheds is critical to maintaining high water quality for citizens."

The Peninsula watershed covers 23,000 acres of nearly pristine lands. Interstate 280 runs along the ridgeline, which forms the eastern boundary of the watershed. The area east of the ridge is crowded by eight suburban cities extending from San Bruno to Redwood City. The western edge of the watershed is the crest of Montara Mountain, and several intermediate ridges divide the combined watershed. The three primary threats are fire, erosion, and pollution.

photo of the Pulgas Water Temple
The Pulgas Water Temple was built in 1938, marking the terminus of the SFPUC water system that flows 167 miles from the Hetch Hetchy Reservoir in Yosemite. Built as a tribute to the engineering marvels of the Hetch Hetchy system, the Roman Renaissance revival style temple is surrounded by grounds that are a carefully maintained mix of indigenous and cultivated landscaping on the edge of 23,000 acres of watershed owned by the SFPUC (photo courtesy of SFPUC).

The greatest protection is afforded by SFPUC's ownership of most of the watershed. There are three small inholdings, totaling 1,200 acres, but these are well managed and pose little risk to the watershed. There are several overlay districts including the San Francisco State Fish and Game Refuge, a scenic easement, and a scenic and recreation easement. The political mechanisms are in place to protect the watershed; the threats come from natural events or the actions of people.

Spreading across the Alameda and Santa Clara Counties, the Alameda watershed supplies surface water captured and stored in the Calaveras and San Antonio reservoirs. SFPUC manages 36,000 acres of the watershed, consisting of grasslands and native oak woods. In the northern portion of the watershed, highway I-680 meets with Route 84. Down the center of the watershed, Calaveras Road extends in a north-south direction. The cities of Milpitas and Fremont are located to the west of the reservoir and to the northeast lie the cities of Pleasanton and Livermore.

Protect Water Quality Above All Else

In 1992, SFPUC decided to update its watershed management plan. After intensive study, SFPUC chose to work with the environmental design firm of EDAW, an Esri Business Partner, and a team headed by EDAW's San Francisco office was established. To set goals for the project, the team worked with a group of SFPUC staff called the Watershed Planning Committee. The team also met with local communities at three points in the process to establish goals and to review interim and then final results. The primary goal was agreed to by all stakeholders: maintain and improve source water quality to protect public health and safety.

The following six secondary goals were also identified:

  • Maximize the contribution of the watersheds to the water supply.
  • Preserve and enhance the ecological and cultural resources of the watersheds.
  • Protect the watershed, adjacent urban areas, and the public from fire and other hazards.
  • Continue existing compatible uses and provide opportunities for additional compatible uses on watershed lands including educational, recreational, and scientific uses.
  • Provide a balance among financial resources, revenue generation activities, and overall benefits.
  • Enhance public awareness of water quality, water supply, conservation, and watershed protection activities.

GIS Implementation

SFPUC developed a GIS to help guide the resource planning phase and ultimately to manage all the watershed lands. Consequently, EDAW initiated a GIS Needs Evaluation to start the planning process. The evaluation strategy began with interviews of various personnel from all divisions within SFPUC's Water Department to assess existing software and potential future needs for data and management interactions. The next step was to develop a plan for both short- and long-term implementation of the GIS. A UNIX-based ArcInfo Workstation, including the ArcTIN and ArcGrid extensions, digitizing table, and color plotter, was selected for the initial hardware and software configuration.

Using the goals as directives, EDAW's consultant team began developing a basic GIS database and designing a process for evaluating the watershed. The United States Geological Survey (USGS) 7.5-minute quad digital data was established as the basemap, and thematic layers were assembled and registered to the base from various primary and secondary sources. The basic data types included geology and soils, elevation, hydrology, vegetation, rare or endangered plants and animals, habitats (field recorded and potential), fisheries, archaeological and historic features, land status (ownership, leases, and overlay districts), roads, trails, utilities, and recreation facilities. Digitizing and data management were accomplished with ArcInfo software's digitizing and editing capability.

Some of the basic data types were subsequently manipulated by various ArcInfo operations (such as overlay, reselect, recoding, dissolves, buffering, and latticepoly) to derive new layers. Examples of derived maps are slope (derived from elevation), vegetation fuel loads (derived from vegetation communities), and drainage protection zones from buffered hydrologic features.

Along with the basic data, the derived maps formed the building blocks of models to create vulnerability maps. A model is the set of step-by-step instructions given to the computer to combine data in mathematical manipulations or graphic overlays. EDAW developed models in a vector-based data format using ARC Macro Language (AML) routines that incorporated various ArcInfo overlay processes and manipulations of attribute data in tables. Final analyses were generally ranged into high/medium/low categories for more simplified interpretation. The modeling process ultimately resulted in the generation of five vulnerability maps for ecological resources, fire hazard, slope instability, cultural resources, and water quality.

"The real power of GIS is its analytical capabilities and its data integration," says Naras. "Our management project was quite ambitious, because it would guide policy for many, many years. Once we learned what we could do with GIS, it was obvious we needed the technology."

Ecology Model Tells Tale of Sensitivity

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The Composite Ecological Sensitivity Zones map shows three levels of sensitivity. The moderately sensitive areas cover more than half of the watershed. Restriction of new recreation uses is clearly indicated by the ecological sensitivity of the watershed.

Environmental Science Associates (ESA) and its ecology specialist, Diane Renshaw, provided the data and classification systems for the vegetation and wildlife studies. ESA developed the model for the Composite Ecological Sensitivity Zones, which combined the findings of the sensitive vegetation and wildlife communities and maps of special-status species (rare or endangered plants and animals).

Frightening Fire Hazard

Fire hazard is revealed by combining data from the vegetation fuel loads, slope, and dwelling densities maps. The fire hazard data was compiled by ESA, while the fire hazard model was developed by Wildland Resource Management (WRM). WRM followed guidelines set by the California State Assembly's Bates Bill, which was passed in response to the disastrous 1991 fires in Oakland hills. A fire management plan was prepared after the watershed study based on fire simulation models shown on page 20.

Slope Instability

By combining the raw data for soils with the slope maps, then selecting from those resultant soil/slope categories the ones that are rated for severe and very severe erosion potential, the analysts were able to determine slope instability. Maps showing historic landslide sites were then added for predicted landslide potential. The Natural Resources Conservation Service (formerly the Soil Conservation Service) is converting most of its soils maps and ratings into GIS format, which will be available for many counties over the Internet.

Cultural Sensitivity Survey Reveals History

David Chavez and Associates provided the base data for historic structures and prehistoric archaeological sites. Historic features included early water conveyances and an old stage road. The map of cultural sensitivity zones resulted from a comparative ranking of the historical resources. The archaeological basemaps were not released to the public.

Water Quality Model

The ratio of imported water to local runoff dictates the water quality as much as surface conditions in the immediate watershed. The model for water quality, developed by the Montgomery Watson engineering team, was based on a combination of approaches from similar studies throughout the United States. Factors included the size of the contributing watershed and its rainfall intensity, drainage buffer zones, slopes, various soil characteristics, vegetative cover, and wildlife concentrations. Soil attributes particularly were analyzed in great detail for determining water quality vulnerability to potential contaminations from microorganisms, nutrient, turbidity, and various volatile organic compounds.

A Visual Framework

The high-sensitivity areas of four out of the five vulnerability maps were extracted and superimposed on a single map to form the Composite High Sensitivity Zones map within ArcInfo. The cultural sensitivity map was not included because policies were already in place to protect cultural resources.

The comprehensive data map shows that about 10 percent of the watershed have no conditions that receive a high sensitivity rating, and about 35 percent have two or more conditions with high sensitivity ratings. It is not only the proportion of high sensitivity ratings that directed formulation of the management policies but also their physical relationship to one another and to features such as roads and reservoirs. Ease of access, nearness to homes and Businesses, and visibility from the freeway all played a role in developing policies.

"We were successful with the project and that success encouraged increased GIS use," says Naras. "We started as a single shop, and now we're looking at networks with servers and clients throughout our organization."

The GIS configuration based on ArcInfo originally set up by EDAW was eventually turned over to the SFPUC staff, who maintain and continually upgrade the database and service the ongoing watershed management efforts.

"Today, GIS is used to document the health and vitality of the watershed and to continue to direct watershed management policy," says Jeremy Lukins, GIS manager of the SFPUC Land and Resources Section. "One of the biggest benefits today is the efficiency it provides. GIS allows the organization to access all the available environmental data in a very short period of time."

This article is derived from a chapter in the Esri Press book GIS for Landscape Architects (ISBN: 1-879102-64-1) by Karen C. Hanna. Esri Press books are available at better bookstores, online ( or, or by calling 1-800-447-9778. Outside the United States, please contact your local Esri distributor; see for a current distributor list.

For more information, contact Peter Jonas, EDAW (e-mail:, tel.: 415-433-1484).

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