Chad Roberts
Environmental Planner, Oscar Larson & Associates, Eureka, CA
As I write this, the New Year floods of 1997 have not receded in the Central Valley, and the echoes of the November 1996 Western Regional Urban Streams Conference have not died away in my memory. There's this nagging thought that we haven't got it yet, as far as the relationships go among land use and environmental planning, watershed dynamics, and aquatic ecosystem integrity. We can surely count on calls to "fix the flooding problems" with more watercourse alterations based on hydraulic engineering principles. Before we go that way we should consider what we have learned in the past 30 years about designing and living with natural ecosystem dynamics, including watershed processes.
The 1997 California floods have much in common with the Mississippi River floods of 1993. These large events tend to surprise people with their power to damage possessions and to cause psychological misgivings. These events are not (or should not be) unexpected in the floodplains of large rivers; one of the lessons of the 1997 floods is that "small" urban streams also should be expected to reoccupy their floodplains when it rains a lot. As in the Mississippi valley, it may be time to reconsider whether land uses highly sensitive to flood damage (such as homes) should be located in California's floodplains.
The November 1996 Urban Streams Conference reinforced another theme relevant to land use planning in California: watershed dynamics on a local scale are an important determinant of this state's overall environmental quality. There is a clear need for an enhanced local planning focus on, and increased local regulation of, land uses which affect watershed elements. This conclusion is clearly shared by natural resource professionals, water resource regulators, environmentalists, restorationists, and local residents who want a sustainable local environment. The need for a local focus stems from the relationship between land use and watershed impacts, given the fact that land use regulation is largely a matter of local control in California.
According to the USEPA the water quality effects from "point sources" of pollution (such as factory or wastewater treatment plant outfalls) are now a less severe source of water quality degradation than are "nonpoint source" (NPS) pollution sources such as construction sites, street runoff, and agricultural areas. In this decade the EPA has published several excellent informational documents (see end notes) about NPS pollution. Unfortunately the enhanced knowledge about NPS pollution has coincided with decreased federal and state funding for pollution control. I do not see any current regulatory efforts to address NPS pollution worthy of its importance from either the federal or the state government.
In addition to water quality concerns, local land uses affect watershed processes by altering watershed hydrology, modifying the natural land cover near streams, and modifying instream conditions. All four factors contribute directly to the biological and physical integrity of urban stream ecosystems. Intensified local land uses usually reduce the local infiltration of precipitation; instead it is concentrated and rapidly delivered to urban streams, which are usually re-engineered to function as drainage conduits. Sediment and other NPS pollutants are rushed into the streams, and potential "obstructions" such as logs and large rocks are removed from the watercourses to enhance their efficiency as conduits. Riparian vegetation is removed, the land surface is compacted, and the channel is enlarged and straightened. Soon aquatic invertebrate populations are eliminated, the channels carry no flow during the summer, and the aquatic ecosystem is effectively destroyed. In addition, the watershed's ability to detain precipitation is reduced and winter rains swell streamflows to potentially destructive levels on a regular basis.
The effects of development on watershed processes and aquatic/stream ecosystems may be better understood in the Puget Sound Lowlands (PSL) of Washington state than anywhere else in the west. The historical abundance and recent decline of salmonid fish in PSL streams motivated citizens, government regulators, academic personnel, and local government planners to study the effects of development on stream ecosystems and their fish. (It is likely that the listing of coho salmon and steelhead under the federal Endangered Species Act will similarly motivate many Californians.) One result of this decade-long involvement is a truly excellent stormwater management manual for the Puget Sound Basin (see end notes), which should be adapted for and applied to local and regional planning jurisdictions in California.
The 1996 Urban Streams Conference proceedings (see end notes for availability) features a paper by participants (Chris May and others) in the PSL studies, who have identified the percentage of a stream basin covered by impervious surfaces as a primary independent variable in the relationship between development and aquatic ecosystem integrity.
Ecosystem integrity begins to be degraded when as little as five percent of a basin is covered by impervious surfaces. When 45 to 50 percent of the basin is covered by impervious surfaces the basin exhibits very low ecosystem integrity. These authors also established that maintaining natural, uncompacted riparian buffers as narrow as 100 feet wide significantly reduced the degradation associated with increasing impervious cover in the watershed. That is, both the extent and the location of urban development are important in maintaining, enhancing, or restoring aquatic ecosystem functions in urban watersheds.
In my judgement it is necessary and appropriate for California planners to incorporate a greater awareness of these effects into decision-making processes at all levels, especially at local or project-level scales. These effects should not be overlooked in CEQA reviews of project impacts, and mitigation for the effects should be included in project approvals. Residential projects are no less a concern than commercial and industrial projects. Drainage plans should emphasize runoff reduction and onsite infiltration, not a rapid runoff delivery to local streamcourses. Riparian and aquatic ecosystem functions should be maintained, and project reviews should focus on processes rather than mere setting descriptions. Potential aquatic effects may be associated with sites some distance from a stream, and the hydrological and water quality effects of development proposals in the watershed catchment need tobe evaluated. All of these concerns can be addressed under the existing authority granted by local land use regulations. Doing so will better manage the environment in urbanized stream basins, and will help in minimizing the consequences of events like the 1997 New Year floods.
End Notes:
1. The 1996 Urban Streams Conference proceedings may be ordered from the City of Arcata Environmental Services Department; phone 707-822-8184.
2. The stormwater management manual for the Puget Sound Basin may be ordered from the Washington State Department of Ecology; phone 360-407-6614.
3. EPA publications are available in most libraries or may be ordered from EPA. Two recommended publications are those numbered EPA/625/R-95/003 and EPA/840/B-92/002.
