How Should a Water Utility Manage Its Forest for Water Quality Protection?

by Betsy Herbert, Ph.D.

From the Loma Prietan,
Newsletter of the Sierra Club, Loma Prieta Chapter
March/April 2006

Most water utilities are not as fortunate as San Jose Water Company, which owns more than 10,000 acres of relatively undisturbed watershed, much of it forested. Most water utilities own very little land, so they have little control over how their watersheds are managed. They must rely on expensive water treatment facilities to ensure that drinking water meets Safe Drinking Water Act standards.

Despite its good fortune, and its public obligation to protect a major local source of drinking water, San Jose Water Company is preparing a commercial logging plan to log 1,000 acres of 100-year old redwoods along Los Gatos Creek. This creek supplies Lexington Reservoir, as well as drinking water to the Chemeketa and Aldercroft communities.

The primary purpose of a commercial logging plan is not to protect water quality--it is to produce timber. State forestry regulations don’t require commercial logging plans to prevent impacts to water quality; they require them only to mitigate or lessen the impacts, such as sediment loading in streams, increased erosion and build-up of understory brush that timber operations will cause. Many scientists have questioned the effectiveness of these mitigations.

Water experts have long recognized the value of protecting drinking-water sources. Water that is clean to start with is cheaper to treat and safer to drink. So, federal law requires every major water utility in the country to inventory potential sources of contamination within their water-supply watersheds.

The Safe Drinking Water Act identifies a range of activities that pose a risk to drinking water and assigns a risk factor to each, ranging from “very high” to “low.” Commercially logged forests are ranked as a “very high” risk when they occur in sensitive stream zones that supply drinking water.

Consider how an unlogged forest functions to provide clean drinking water and flood control. Some large, old trees growing near a stream will eventually fall into and become an integral part of the stream channel. Old growth redwood is so tight-grained and decay-resistant that logs can persist in the stream for many decades. During big storms, these ins-stream logs reduce the storm water’s force, acting as small natural dams. They form pools that trap sediment. Trees growing along the stream help stabilized banks with their vast root systems. Redwoods play a vital role in the hydrological cycle through transpiration. Their canopies buffer raindrops the would otherwise pummel the ground. In the dry season, fog drip from the redwood canopy can fall like rain. Tree canopies keep stream temperatures cool. Even on a hot day, an old growth redwood forest will be relatively cool. Redwood bark is thick, spongy, and very fire resistant.

Now consider how one would manage a redwood forest primarily for water-quality protection. One would work to restore old growth conditions and to prevent ground disturbance in order to minimize erosion.

To manage a forest primarily for timber production, one would adopt a different strategy altogether. Trees would be cut when they reach their maximum growth potential (100 years for redwoods). Logging roads would be built to access the best timber stands. The conflicts between these two management regimes are obvious.

Other municipal water utilities that own large expanses of forestland apparently understand the conflict between managing for timber production and managing for water quality protection. The Marin Municipal Water District, the East Bay Municipa Water District, the Portland Water Bureau, and the City of Seattle all manage their forest primarily for water-quality protection. They do not engage in commercial logging

As California searches for new sources of high-quality water, San Jose Water Company owes it to the public to manage primarily for water quality and preserve the intact forest ecosystem of the Los Gatos Creek watershed.