INTRODUCTION
The environmental impact report (EIR) for the Santa Clara Valley Water District (the District) routine sediment and erosion work is a ground breaking effort on many levels.
At the permitting level, it addresses a shift in the US Army Corps of Engineer's approach to regulating wetlands. This shift towards a regional perspective on the effects of cumulative impacts will affect urban water districts throughout Northern California. The following model will benefit districts needing to apply or renew for regional permits as well as those that currently process applications on a site by site basis.
At the analytical level, the EIR required a new approach to integrating data. A model had to be created to maximize the use of data available from many departments within the District.
At the procedural level, the EIR required an innovative approach to implementation. A work protocol was needed that was not burdensome. The steps to be taken while performing maintenance work under the umbrella of the regional permit needed to be as easy as filling out a checklist, sensitive enough to trigger appropriate measures to protect environmental and human resources, and comprehensive enough to provide sufficient data to take the Water District into the 21st century.
THE SETTING
The Santa Clara Valley Water District supplies water and flood control for Santa Clara County. The District is divided into 5 flood control zones -four northern zones that drain into San Francisco Bay and one southern zone that drains into the Monterey Bay via the Pajaro River (Figure 1).
The District has flood control jurisdiction over those sections of creeks and rivers that drain a watershed larger than 320 acres (1/2 sq. mile). The District is committed to maintaining a 1 percent (100 year) flood capacity on more than half of the 700 miles of creeks under its jurisdiction. The District performs routine maintenance work to: a) reduce the accumulation of sediment that decreases the designed flow capacity of stream channels; b) repair and stabilize eroded banks to protect adjoining public and private property; and c) remove sediment from percolation ponds to maintain groundwater recharge capacity.
Sediment removal and bank stabilization undertaken by the District requires regional permits from the US Army Corps of Engineers under Section 404 of the Clean Water Act, a general permit for work at the Bay margin from San Francisco Bay Conservation and Development Commission, State Water Quality Certification from the Regional Water Quality Control Board, and the issuance of Streambed Alteration Agreements from the California Department of Fish and Game.
Although CEQA does not apply to actions by federal agencies, federal agencies can use CEQA for project review and permitting. The EIR being developed by Thomas Reid Associates for the Santa Clara Valley Water District follows CEQA guidelines (section 15168) for a Program EIR, identifying the routine sediment and erosion work as a series of individual actions that are related "geographically, as logical parts in a chain of contemplated actions in connection with ... a continuing program ... carried out under the same statutory or regulatory authority". The EIR covers a 10 year planning horizon.
THE DYNAMIC SEGMENTATION MODEL
The amount of data collected by the many divisions of the Santa Clara Valley Water District in the last few decades is staggering. Judicious use of appropriate data required: a) estimating the contribution the data set would make to the overall project; b) weighing the contribution of the data set relative to the time and effort to integrate it into the ArcInfo analysis; and c) if the data set was necessary but needed significant processing, assessing whether an alternative data source could be used to produce the same result.
The three main challenges to integrating data from the many sources available were:
- creating coincidence between layers. Due in part to the fractal nature of creeks, different data sets had different lineal measures associated with the same creek position.
- converting data. Available data sets spanned several technologicalgenerations and were not equally accessible, accurate or precise.
- filling significant data gaps. Data was collected by each working group within the District for their own particular analytical requirements and provided only a focused subset of variables.
The ArcInfo Dynamic Segmentation route system was used to create a "creek base map" (Note 1) to which all District data would be linked. Creek arcs, 1 percent FEMA floodplain boundary polylines, and annotation were acquired from the District's Drafting department AutoCad drawings. Due to the flood control jurisdictional limit (1/2 sq. mile) used by the District, the AutoCad drawings had to be augmented with 286 hydrology map unit coverages from a county wide, on-going, cadastral based mapping project. These hydrology vectors digitized by Barclays from 1:500 hardcopy maps provided referencing for all layers. Additional layers from the District's Hydrology Department provided watershed boundaries and subboundaries used in various water supply and flow calculations.
The Waterways Management Model (WWMM), a well developed tabular data set describing the channel conditions associated with creek segments was converted from HP 3000 Rbase image files. The District Flood Control Division authored the WWMM 20 years ago to facilitate prioritizing flood control projects. It includes variables such as HEC model inputs, potential flood damage per creek segment and outputs for cross section graphics of stream channels. The database is maintained to show current conditions.
Historical records from the Maintenance Department included hardcopy work orders with on site design sketches, photo documentation and records of all sediment and erosion work for the last 19 years. An extensive tif image file collection was created from this data set, linked geographically in ArcView.
Tabular Data such as the WWMM and maintenance records were processed as event tables. Figure 2 illustrates the dynamic segmentation file structure of one of the workspaces.
ANALYSIS
To create a successful EIR it must be shown that probable impacts likely to occur from the planned project have been reasonably identified. The first step in this process, creating a 10 year projection of the planned, routine sediment and erosion maintenance work, was challenging. A California water district cannot easily predict the maintenance work to be performed because of the unpredictable nature of the climate. Winter rains and summer droughts are punctuated by unforeseen years of drought and extreme winter flooding. As the historical weather data grows over time, even the statistics used to estimate the 1 percent flow change. Historical records, archived aerials (from the District's Surveying department), assessments of current channel conditions and EBGs (expert best guesses) were used by Maintenance staff to predict future work.
Identifying alternatives to the projected work project, in conformance with Section 404(b)1 of the Clean Water Act, was a bit more challenging. To remain tractable the analysis focused on 15 representative types of situations. In addition to the data compiled from the District, other data layers and information used to analyze alternatives were either generated from field work, or digitized and compiled from other sources. Fish habitat, and wetland vegetation were digitized from original field work and previous county projects, out-of-print hardcopy US Geological Survey land stability maps were rasterized and processed, digital data from USGS (surface materials) and Associated Bay Area Government (land use) were recategorized, Landsat imagery was projected into California coordinates and as built drawings and cross-sections were scanned as images. Figure 3. shows a sample visual analysis of historic sediment work (1979-1996) as a function of geologic surface material.
The complexity of the analysis is significantly reduced when graphics and computer demonstrations can be used to explain the patterns found in the data, therefore it might be more practical for the District to submit EIR documents either on-line or on CD. Public review would also be facilitated by an on-line EIR.
ARCVIEW IMPLEMENTATION
Compliance with the Regional Permit is monitored by the Agencies through annual reporting of the Proposed Maintenance Plan and end of the year Activity Report. Both of these documents can be prepared in large part from data input into or accessible through the ArcView projects developed for the District. Documentation at selected steps in the Best Management Protocols shown in the flow chart, 4, would allow the efficient ArcView assisted preparation of both documents.
For the first phase of the process, maintenance planners and field engineers can define the project and maintenance needs using data previously compiled from ArcInfo into ArcView. These would be accessed either at a desktop linked to the enterprise GIS prior to the on site visit or in the field using files downloaded from a CD equipped portable computer. Adding records and photodocumentation with digital cameras and GPS could improve on-site annotation and update the geographic accuracy and precision of the entire data set. Calling up information on sensitive habitat, protocols for anthropological site procedures, as-built channel records, hydrologic flow variables, and assessor parcel records, will inform the decisions that need to be made (Figure 4 flow chart diamonds).
The accumulated historical records and data we have accessed from many District departments has been a rich source from which to increase our understanding of the fluvial and geomorphic processes at work in the Santa Clara County creeks. The challenge now for the District is to use GIS as the backbone for full integration of all their data sets, by using the common denominator of location. With the incremental additions of GPS records, the accuracy of the data set and hence the quality of the staff's work product is being improved. Having an accessible common data base streamlines the interactions between planners and engineers, field crews and staff from various departments. Just as email has enabled the District to increase communication efficiency by providing all necessary staff with the documents pertinent to ongoing issues, GIS can be used to enable effective communication about the work that needs to be done.
NOTES
1. A statistical measure of the accuracy associated with the base map routemeasure system, generated by the Routemeasure command was developed by identifying the delta positional values at different points along the creek system on various layers.
REFERENCES
ArcInfo Version 7.0.2 User Documentation, Dynamic Segmentation.Environmental Systems Research Institute, Redlands, CA
Santa Clara Valley Water District Sediment and Erosion Program EIR, Administrative Draft, April 1996. 5750 Almaden Expwy, San Jose, CA 95118, (408) 265-2600.
Alisya Torregrosa Galo GIS Coordinator, Thomas Reid Associates PO BOX 880 Palo Alto, CA 94301 telephone: 415-327-0429 fax: 415-327-4024 email: lisy@bing.stanford.edu