Compilation of GIS Data Sets for Flood Control Alternatives in California. A Final Report. Submitted to

Transcription

1 Compilation of GIS Data Sets for Flood Control Alternatives in California A Final Report Submitted to Faculty Fellows Program California State University, Sacramento Sacramento, CA By Hong-lie Qiu Marcos Luna Todd Zagurski Department of Geography and Urban Analysis California State University, Los Angeles Los Angeles, CA November 15, 1997

2 TABLE OF CONTENTS Table of Contents.. 2 Table of Figures 3 1. Executive Summary 4 2. Recommendations Background Data Acquisition Flooded Areas Year Floodplain Boundaries Drainage Basin Reach Files Vegetation Reservoir Agricultural Landuse TM Imagery Preprocessing Decompression of Raw Data Conversion of Map Projection Extraction Mosaicing Map Generation California Vegetation Flooded Areas FEMA Special Flood Hazard Areas Agricultural Land Use Landsat Thematic Mapper Image and Hydrological Units California Dams and Reservoirs Data Dissemination References

3 TABLE OF FIGURES 1. California Vegetation Flooded Areas 3. FEMA Special Flood Hazard Areas 4. Agricultural Land Use Landsat Thematic Mapper and Hydrological Units 6. California Dams and Reservoirs

4 1. EXECUTIVE SUMMARY The objective of this project was to identify, acquire, and compile flood and floodplain related map data that could be used as background information for state legislators to make sound land use and flood control policies in California. Relevant data sets were acquired and processed for the entire state of California. The end product was a GIS data CD-ROM that is ready for use by most popular GIS packages together with sample hardcopy maps representing the selected map attributes. A considerable amount of digital map data related to floodplain management exists among different government organizations and agencies. These data sets were originally developed by different organizations for different purposes, at different time. They vary considerably in terms of map content, geographic coverage, spatial accuracy, map projection, and timeliness. To make meaningful use of them for developing policies for floodplain land use and flood control issues remains a challenge. The desired data layers are not readily available most of the time and they have to be extracted and assembled from multiple sources. Accurate digital data on flooded areas of individual floods are extremely rare and compilation of such a data set for the entire state has proved to be difficult. We did compile a GIS data layer that shows the river segments that were flooded during the 1997 flood season based on government reports and stories from newspapers. Ten statewide GIS data sets are included in the data CD-ROM. This data CD- ROM contains 1) flooded river reaches in 1997, 2) areas subject to the 100 year flood events, 3) drainage basin boundaries, 4) hydrological features (reach files), 5) vegetation, 6) reservoirs, 7) agricultural land use, 8) TM imagery, 9) highway, and 10) county boundaries. All of these are stored in ArcView shapefile format. A subset of the compiled data is available for on-line access on the Internet at 4

5 2. RECOMMENDATIONS This four-month project has focused on statewide data that are available from existing sources. It is impossible to encompass all the data sets that are needed for tackling floodplain and flood control problems in California. The most valuable data would be the boundaries of the areas that actually flooded and the dates those floods occurred. The best source for this type of data is most probably aerial photo and satellite imagery archives. With proper registration, flooded areas delineated from remote sensing source can be assembled into a statewide GIS data layer for identifying flood-prone areas in the past. Flooding is a phenomenon limited to its drainage basin. Land use and flood control policies are going to be drainage basin specific. Therefore, we should use drainage basin boundaries, instead of county boundaries to partition the statewide data into sub-areas. The purpose of mosaicing the county-based data into a statewide GIS data layer is to allow potential users to extract information by drainage basins without having to go through the mosaicing steps. A digital map of existing flood easements and levee systems is currently not available to our knowledge. It would be extremely useful for evaluating the existing flood control system. In addition, generalized land ownership data (public or private) and land value assessment information would be useful for cost-benefit analysis. Continued support of the Internet data dissemination will be a good way of increasing public awareness of policy development as well as to facilitate public access in several fundamental ways. The state should designate a web server as a repository for all digital data sets that can be used for tackling the flood control issues. Most of these data sets are map oriented and they tend to be large in terms of file size. Specialized software network software (e.g. JAVA based application downloadable to client computers) is required in order to deliver map or image-related data sets for meaningful uses. We are currently experimenting this approach at for disseminating data through interactive maps. 5

6 3. BACKGROUND Flood control efforts in California have been focused on the construction of dams and levies. This approach has proved to be costly and sometimes inadequate. Some members of the legislature are now interested in shifting flood control efforts from building dams and levies to acquiring appropriate agricultural lands to serve as flood easements or levee setbacks. A comprehensive database on where and when floods have occurred and where the undeveloped agricultural lands suitable for this purpose exist is essentail. The objective of this project was to compile GIS data sets related to flood and floodplain management to support this new legislative effort. More specifically, digital map data which exist in different government organizations and agencies were acquired and processed to produce a GIS data CD-ROM that is ready to use by popular GIS packages. A subset of the compiled GIS data will be made available for Internet access. These data are intended as background information for developing sound flood control and land use policies. Existing digital maps related to floodplain and flood control were produced and maintained by different government organizations and agencies for different purposes. Data acquired from these sources vary in terms of map type, coverage, accuracy, projection, and file format. Extensive preprocessing work is usually required before they can be integrated into a GIS environment for performing analyses and data queries. Furthermore, not every desired data set exists. For this project, we have focused our efforts on the data sets that are available to us. Development of original data sets was not attempted. 6

7 This report describes (1) the methodology and procedure used in compiling the data sets, (2) content and coverage of the individual data sets, and (3) presentation and dissemination of the end products. 4. DATA ACQUISITION Our first task was to find the desired data sets by contacting relevant government agencies and conducting searches on the Internet. We contacted the California Department of Water Resources, the California Department of Conservation, the U.S. Environmental Protection Agency, the Federal Emergency Management Agency, and the U.S. Army Corps of Engineers for data. We also visited web sites of the relevant government agencies for finding the desired data sets. Web sites that contain information useful for this project include: California Gap Analysis ( We derived vegetation, county boundaries, freeways, and TM imagery from this site. USGS ( We derived reservoirs and hydrological unit boundaries from this site. Federal Emergency Management Agency ( This web site contains descriptive information about environmental database products, including Q3 Flood Data. California Department of Conservation ( This web site contains descriptive information about Farmland Mapping and Monitoring Program products and farmland map categories. 7

8 Environmental Protection Agency ( This site contains descriptive information about the Reach File 3.0 Alpha data and appropriate contact personnel. California Department of Fish and Game ( This site contains information about California Central Valley Wetlands and Riparian GIS data. NASA AMES ( This site contains ER-2 photos of flooding around Marysville in northern California from early January California Governor's Office of Emergency Services ( This web site has an online version of the Final Report of the Flood Emergency Action Team. We have identified some ten relevant data sets for this flood plan mapping project. Some of these were free for download, while others needed to be ordered and paid for. Different levels of preprocessing were required to assemble the desired data themes. A brief description on the individual data sets is included below: Flooded Areas This data layer consists of selected river segments from the EPA Reach File Version 3.0 data and identifies segments of rivers that were reportedly flooded during the January 1997 floods, primarily in northern California. Information regarding the flooded rivers was extracted from excerpted news stories posted on the Sacramento Bee s The Floods of 97 web. 8

9 Year Floodplain Boundaries This data layer displays areas that have been determined to be subject to 100-year flood events (1% annual chance of occurrence) for fifty four counties in California. This information was extracted from the Federal Emergency Management Agency s Q3 Flood Data CD-ROM. 4.3 Drainage Basin This data layer represents boundaries corresponding to river basins and based upon Hydrologic Unit Maps by the U.S. Geological Survey Office of Water Data Coordination. This data layer lists descriptions and names of regions, subregions, accounting units, and cataloging units. This information was downloaded via the Internet from the USGS National Geospatial Data Clearinghouse. 4.4 Reach Files This data layer shows all surface water features (streams, canals, lakes, etc.) for the state of California and contains attributes regarding feature identity, connectivity, flow direction, stream level, and other attributes. 4.5 Vegetation This data layer contains vegetation attributes for landscape scale map units, including canopy dominant species, canopy density, presence of regional endemic species, inclusion of wetland habitats, type of disturbance, and general narrative comments. This data layer was downloaded via the Internet from the California GAP Analysis web site 9

10 and is a composite of what were originally ten separate layers covering the state of California. 4.6 Reservoir This data layer is a point coverage of dams in California which was extracted from a larger coverage that included the entire United States and Puerto Rico. The coverage includes locations and selected characteristics of reservoirs and controlled natural lakes that have normal capacities of at least 5,000 acre feet or maximum capacities of at least 25,000 acre feet and that were completed as of January 1, This information was downloaded via the Internet from the USGS Water Resources web site. 4.7 Agricultural Landuse This data layer displays farmland categories by county for selected areas of California based upon Important Farmland and Interim Farmland maps produced by the California Department of Conservation in its Farmland Mapping and Monitoring Program. 4.8 TM Imagery This data set is a mosaic of 1993 Landsat Thematic Mapper (TM) data (bands 3, 4, and 5) for the state of California. These images were downloaded via the Internet from the California GAP Analysis web site. 5. PREPROCESSING As mentioned earlier, digital map data derived from existing sources vary in terms of map type (vegetation, transportation, hydrology, land use), spatial accuracy, geographic 10

11 coverage (city, county, state), map projection, and file format. Data acquired from these sources have to be converted into a common format before they can be analyzed and overlaid. This task proved to be difficult and time consuming. First of all, we received data in various formats. Most of the acquired data sets were delivered to us in compressed GIS format and they needed to be decompressed and then imported into their original formats in order to maintain their data structures. Second, the acquired data sets were organized in different geographic units, some of them by county and others by specialized units like vegetation region or hydrological units. Map projection conversion had to be performed in order to merge county or region based maps to assemble statewide coverage. Third, many of the acquired data sets contained significant irrelevant data that had to be filtered or removed. Finally, most of the acquired data were partitioned by county or region and not easily integrated with each other. This necessitated a mosaicing process to assemble a statewide data coverage. 5.1 Decompression of Raw Data Some of the data sets came in standard Arc/Info Export files while others came in tarred or zipped files. We had to decompress and import them into Arc/Info before we could view the contents of the data sets to determine their relevancy. We decided to maintain all of the compiled data sets in ArcView shapefile format because ArcView is the most popular and affordable desktop GIS software. 5.2 Conversion of Map Projections Acquired data came in various map projections (e.g. standard and custom Albers Equal-Area, UTM, California State Plane, and Geographic Coordinate System). To 11

12 allow cross-referencing across data layers, all the data layers had to be projected onto a common map projection. We decided to convert all data layers to Geographic because the Geographic Coordinate System is the only projection in ArcView that will allow users to view the maps correctly in other provided projections. ArcView users can display maps that are stored in different projections if no projection is defined for the view environment. These maps will not be displayed or displayed correctly if the view's projection is set to a projection other than geographic. Since no projection conversion utilities are included in the standard ArcView software, ArcView users will not be able to overlay two maps of identical coverage if they are stored in different map projections. 5.3 Extraction Some data sets came with many attribute or graphic data that are of no use to this project. For performance reasons, we have dropped the irrelevant attribute fields or unimportant map features. For example, EPA Reach Files contain very detailed coverage of hydrological features. We extracted only major rivers from the original reach files to assemble a simplified version for representing the major river systems in California. 5.4 Mosaicing This process was performed for data sets that were partitioned by county or other area units. We realized that it is important to be able to integrate data in order to make meaningful analyses. One of the approaches is to assemble all data layers into a common coverage. We chose a statewide coverage for all our data layers. 12

13 6. MAP GENERATION The processed data are stored in standard ArcView shapefiles on a data CD- ROM. We have generated several large format hardcopy maps to accompany it for highlighting the key data themes of the compiled data. The bridge between data and information is an appropriate medium of communication. Maps provide this medium by representing data in a way that is understandable and digestable. The following sections describe the contents of the compiled data layers and procedures we use to generate the submitted maps. 6.1 "California Vegetation" This is a statewide map of California at a scale of 1:13,000,000 which displays eleven generalized categories of vegetation. These categories are gross and somewhat arbitrary classifications that were aggregated based upon grouping of species within the original metadata. The data for this map were acquired from the California GAP Analysis web site. The original data were in ARC/INFO export file format and consisted of ten separate files that divided the state according to Jepson Flora regions. Attribute data includes dominant species distribution, canopy cover, vegetation classification to Holland Natural Communities and WHR habitat types, vegetation series, riparian and wetland types, disturbance, and special interest species distribution. These layers were developed for the California GAP Analysis project to determine the distribution and current management status of the state's vegetation and habitats. Polygon boundaries were derived from photointerpretation of 1990 Landsat Thematic Mapper digital images, supplemented by 13

14 1990 HAP photography and large scale vegetation maps. Attribute data came from the 1990 HAP photography, the 1930's VTM Survey Maps, field visits, and large scale vegetation maps. The minimum mapping unit (MMU) for upland sites is 250 acres and 100 acres for wetland sites. Some sites were mapped at a finer resolution, though no polygon less than 25 acres was retained. These data layers were developed with state and regional level analysis in mind. They do not provide spatial resolution of individual stands of vegetation. In order to present a uniform statewide coverage, it was necessary to merge these ten data layers into a single layer. The original ARC/INFO export files were imported back into ARC/INFO coverages and then appended together one coverage at a time using the PUT command. Because there was significant overlap along the boundaries of these coverages, it was necessary to remove overlapping arcs before actually appending any two coverages. As each coverage was appended, so was its corresponding attribute data. Although some of the original coverages contained unique attribute fields, the final statewide coverage contained only those attributes that were common to all ten data layers. Once the state-wide coverage was complete, it was reprojected from Albers Equal-Area Conic into Geographic in order to make it properly usable within the ArcView environment. In order to plot a map it was necessary to create a more generalized categorization of vegetation. Existing fields would require hundreds of classifications which would be impractical for a hardcopy map due to limitations of the printer and the capacity of the human brain to perceive so many color gradations. Using ArcView, a new field was added to the database file and an arbitrary numbering classification was added based 14

15 upon grouping of species within the original metadata: (1) Non-native vegetation (includes urban areas, water, farmland, barren land, etc.); (2) Coastal scrub; (3) Scrub; (4) Chaparral; (5) Grassland; (6) Meadow; (7) Marsh; (8) Riparian forest; (9) Forest; (10) Woodland; and (11) Dunes. 6.2 "1997 Flooded Areas" This is a statewide map of California at a scale of 1:13,000,000 which displays selected rivers and waterways in blue and highlights segments of these in red which were reportedly flooded during early January These particular waterways were selected for display based on a relative classification of size and importance, as well as reports of flooding in the Sacramento Bee. The waterways are framed by county boundaries. The surface water feature data for this map were acquired from the Environmental Protection Agency's Reach File Version 3.0 Alpha coverages and the county boundaries from the California GAP Analysis web site. The U.S. Environmental Protection Agency's Reach Files are a series of hydrographic databases of the surface waters of the continental United States and Hawaii. For the purposes of this project, only those Reach Files for California were acquired. The structure and content of the Reach File databases were created expressly to establish hydrologic ordering, to perform hydrologic navigation for modeling applications, and to provide a unique identifier for each surface water feature. The files were acquired via the Internet after permission had been granted by the EPA's Office of Water. The files were received in ARC/INFO export format and grouped by over one hundred hydrologic cataloging unit based subsets. Reach file data were constructed from four data sources: EPA Reach File, Version 2.0; USGS 15

16 1:2,000,000 Catalog Unit Boundaries; USGS Geographic Names Information System, Version I; and USGS 1:100,000 Scale Digital Line Graph, Version 3.0. In order to compose a statewide map, it was necessary to select only certain significant surface hydrographic features because the full coverage is extremely detailed and too large to manipulate for practical purposes. The export Reach Files were imported into ARC/INFO coverages in an ARC environment. Additional INFO files were joined to the coverages using the JOINITEM $recno command. In order to select significant hydrographic features, arcs were selected based upon the Stream Level attribute. Each reach is assigned a stream level which defines the hierarchical relationship between streams and tributaries in a given drainage network. A tributary to a given stream is always one level higher than the stream into which it flows. For instance, the Mississippi River is a level-one stream, the Ohio River is a level-two stream, and Tennessee River is a level-three stream. Because stream level is a relative classification, it was necessary to use subjective judgment in deciding which of the selected reaches would be kept. Initial criteria were stream levels of 1 to 3, although this was expanded or reduced depending upon the results. Selected streams were appended to a new coverage using the PUT command. Once all selected streams or waterways were included, the new coverage was reprojected from Albers Equal-Area Conic into Geographic in order to make it properly usable within the ArcView environment. In order to plot a map of significant streams and waterways with regard to flooding, it was necessary to highlight those streams that flooded in early Information regarding flooded areas was acquired from the Sacramento Bee's "Floods of '97" web page which contains selected news stories from the Sacramento Bee about floods in 16

17 northern California in early January Using ArcView, a new field was added to the database file and an arbitrary numbering classification was added to distinguish those segments which had flooded. Flooded segments were classified as 97 and the rest were left with a default 0 classification. Because of the general nature of the descriptions of floods in the news stories, and the difficulty of isolating certain streams based upon stream level, the map of flooded streams and waterways is necessarily generalized and incomplete. 6.3 FEMA Special Flood Hazard Areas This is a statewide map of California at a scale of 1:13,000,000 which displays five categories of areas that are potentially subject to 100 year flood events (1% annual chance of occurrence) for all counties except for Alpine, Butte, and San Diego counties for which no data was available. The data for this map were acquired from the Federal Emergency Management Agency's Q3 Flood Data CD-ROM which was purchased from FEMA for $ The original data were in ARC/INFO export file format and consisted of fifty four separate files that divided the state by county. The Q3 Flood Data are developed by scanning existing hardcopy Flood Insurance Rate Maps (FIRM) to create a raster product suitable for viewing and vectorizing a thematic overlay of flood risks. Vector data contain only certain features. The features contained in the vector Q3 Flood Data files include the following: 1% and 0.2% annual chance floodplain areas, including Zone V areas, certain floodway areas, and zone designations; Coastal Barrier Resources Act (COBRA) areas; political areas, including community identification number; FIRM panel areas, including 17

18 panel number and suffix; 7.5-minute quadrangle areas; and mappable Letters of Map Change (LOMCs). The flood risk data presented in the FIRM are developed only for communities participating in the National Flood Insurance Program (NFIP) for use in insurance rating and for floodplain management. Flood hazard areas are determined using the following sources: statistical analyses of records of river flow, storm tides, and rainfall; information obtained through consultation with the communities; floodplain topographic surveys; and hydrologic and hydraulic analyses. For undeveloped areas where little or no development is expected to occur, FEMA uses approximate analyses to generate flood risk data. Typically, only drainage areas that are greater than one square mile are studied. The Q3 Flood Data do not replace the existing hardcopy FIRMs. The product has been designed to support planning activities, some Community Rating System (CRS) activities, insurance marketing, and mortgage portfolio review. It does not provide base flood elevation information; thus, it has limited application for engineering analysis, particularly for site design or rating of flood insurance policies for properties located within Special Flood Hazard Areas (SFHA). Q3 Flood Data are not tied to a base map, are not used to produce a new version of the hardcopy FIRM, and are not subjected to community review. Q3 Flood Data are intended to provide users with automated flood risk data suitable for determining whether features are within or outside the SFHA. In order to plot a map of areas subject to 100 year flood events, it was necessary to extract only those areas which fell into this category. Because these files are already in the Geographic projection, the ARC/INFO export files were imported as coverages directly into ArcView and then converted into shapefiles. These shapefiles were then displayed by the SFHA category (either IN or OUT) and those areas that were IN were 18

19 selected and converted to a new shapefile. For lack of adequate time, these new shapefiles were maintained as separate files by county and not merged into a single statewide layer. However, the presence of 7.5-minute quadrangle boundary lines within the data caused a problem of segmented and discontinuous polygons. In order to remedy this, each polygon was painstakingly reconnected using the UNION command in the ArcView environment. Once this was completed, the resulting shapefiles were displayed according to sub-categories of SFHA and plotted. 6.4 Agricultural Land Use This is a statewide map of California at a scale of 1:13,000,000 which displays ten general categories of land use areas with emphasis on agriculture or grazing land. The data include all but eleven counties for which no data was available. The land use data are framed by California GAP Analysis county boundaries. The data for this map were acquired from the California Department of Conservation's Farmland Mapping and Monitoring Program via the Internet after permission had been granted. The original data were in ARC/INFO export file format and consisted of forty six separate files that divided the state by county. The relevant category for land use is Agcode. Important Farmland maps for California are compiled from USDA-NRCS Soil Surveys and current land use information using eight mapping categories generally explained below. The minimum mapping unit is 10 acres. Units of land smaller than 10 acres are incorporated into the surrounding map categories. Prime Farmland (P) - Land with the best combination of physical and chemical features able to sustain long term production of agricultural crops. This land has the 19

20 soil quality, growing season, and moisture supply needed to produce sustained high yields. Land must have been used for production of irrigated crops at some time during the two update cycles prior to the mapping date. Farmland of Statewide Importance (S) - Land similar to Prime Farmland that has a good combination of physical and chemical characteristics for the production of agricultural crops. This land has minor shortcomings, such as greater slopes or less ability to store soil moisture than Prime Farmland. Land must have been used for production of irrigated crops at some time during the two update cycles prior to the mapping date. Unique Farmland (U) - Lesser quality soils used for the production of the state's leading agricultural crops. This land is usually irrigated, but may include nonirrigated orchards or vineyards as found in some climatic zones in California. Land must have been cropped at some time during the two update cycles prior to the mapping date. Farmland of Local Importance (L) - Land of importance to the local agricultural economy as determined by each county's board of supervisors and a local advisory committee. See either "A Guide to the Farmland Mapping and Monitoring Program", or the latest copy of the "Farmland Conversion Report" for each county's definition of Farmland of Local Importance. Grazing Land (G) - Land on which the existing vegetation is suited to the grazing of livestock. This category is used only in California and was developed in cooperation with the California Cattlemen's Association, University of California Cooperative 20

21 Extension, and other groups interested in the extent of grazing activities. The minimum mapping unit for Grazing Land is 40 acres. Urban and Built Up Land (D) - Land occupied by structures with a building density of at least 1 unit to 1.5 acres, or approximately 6 structures to a 10-acre parcel. Other Land (X) - Land which does not meet the criteria of any other category. Water (W) - Water areas with an extent of at least 40 acres. Interim Farmland Map Categories - Interim Farmland maps are prepared for specific agricultural counties lacking modern soil surveys. The use of an interim mapping methodology provides a benchmark, or point in time, by which agricultural land use and urbanization can be tracked. Two categories of Interim Farmland are mapped in lieu of Prime Farmland, Farmland of Statewide Importance, Unique Farmland, and Farmland of Local Importance. The categories of Irrigated Farmland and Non- Irrigated Farmland are designed to be easily upgraded as the USDA-NRCS completes modern soil survey mapping as the technical soil information becomes available. The Interim Farmland maps also utilize the categories of Grazing Land, Urban and Builtup Land, Other Land, and Water as defined under the section 'Important Farmland Map Categories'. Irrigated Farmland (I) - Cropped land with a developed irrigation water supply that is dependable and of adequate quality. Land must have been used for production of irrigated crops at some time during the two update cycles prior to the mapping date. 21

22 Non-irrigated Farmland (N) - Land on which agricultural commodities are produced on a continuing or cyclic basis utilizing stored soil moisture. In order to present a uniform statewide coverage, it was necessary to merge these data layers into a single layer. The original ARC/INFO export files were imported back into ARC/INFO coverages and then appended one coverage at a time using the PUT command. Once the statewide coverage was complete, it was reprojected from Albers Equal-Area Conic into Geographic in order to make it properly usable within the ArcView environment. Finally, this coverage was converted to a shapefile and brought into ArcView. The map was plotted using the native Agcode categories appropriately labeled Landsat Thematic Mapper Image and Hydrological Units This is a statewide map of California at a scale of 1:13,000,000 which displays a mosaic of Landsat Thematic Mapper (TM) data (bands 3, 4, and 5), overlaid by USGS Hydrological Units. The TM image data were acquired from the California GAP Analysis web site as ten separate files which roughly corresponded to Jepson Flora regions. The ten TM images were decompressed from a TAR.GZIP compression format and then mosaiced using the ENVI image processing software from Systems Research Inc. The pixel size of the TM imagery is 100X100 meters and are detailed enough to distinguish different land use patterns and major surface features for the entire state. 22

23 The USGS Hydrological Units were downloaded from the USGS Data Clearinghouse web site. The original file was an ARC/INFO export file for the entire U.S. This file was imported as an ARC/INFO coverage in an ARC environment and then reprojected from the Albers Equal-Area Conic projection into the Geographic projection. This reprojected file was then converted into a shapefile. Finally, the shapefile was brought into ArcView and those hydrological units within California were selected and converted to a new shapefile. Plotting the map was a simple process of overlaying the hydrological units on the TM image. 6.6 California Dams and Reservoirs 1988 This is a statewide map of California at a scale of 1:13,000,000 which displays the locations and names of dams in California with reservoirs or controlled natural lakes that have normal capacities of at least 5,000 acre-feet or maximum capacities of at least 25,000 acre-feet and that were completed as of January 1, These point features are framed by county boundaries. The dam and reservoir data was downloaded from the USGS Water Resources web site. The original file was an ARC/INFO export file for the entire U.S. This file was imported as an ARC/INFO coverage in an ARC environment and then reprojected from the Albers Equal-Area Conic projection into the Geographic projection. This reprojected file was then converted into a shapefile. Finally, the shapefile was brought into ArcView and those points within California were selected and converted to a new shapefile. Plotting the map was a simple process of overlaying the point coverage on the county boundaries. 23

24 7. DATA DISSEMINATION Data dissemination has been carried out in two different ways. We have assembled the compiled GIS data sets into a GIS data CD-ROM for delivery of the entire data set to interested users. All data sets are maintained in ArcView shapefile format, and ArcView GIS software from ESRI is required in order to view and analyze the CD-ROM data. We realized that not every interested user can access to a GIS package which is now required for accessing to the compiled GIS data CD-ROM. This is especially true for the general public and concerned citizens. To allow wider public access, the compiled GIS data sets should be improved to allow viewing by popular network browsers such as Netscape Navigator or Microsoft Internet Explorer. One of the improvements is the development of a JAVA-based application that will utilize the CPU power and memory of client machines to display intensive graphics and allow fast computer response. We also realized that updates to the compiled data sets is inevitable and it is going to be more frequent as more and more flood related data become available. We also set up a web server for on-line access to a subset of the compiled GIS data through the Internet. Under current network bandwidth, it is extremely difficult to allow on-line access to the entire compiled data set. We have extracted a subset of the compiled data for Internet users. One of the major advantages of using the Internet for disseminating GIS data is that users can always have access to timely data. 24

25 8. REFERENCES Governor s Flood Emergency Action Team (1997) Final Report of the Flood Emergency Action Team Donley, Michael W. et al. (1979) Atlas of California U.S. Environmental Protection Agency Office of Water (1994) EPA Reach File Version 3.0 Alpha Release (RF3-Alpha) Technical Reference Environmental Systems Research Institute (1990) Understanding GIS: The ARC/INFO Method Federal Emergency Management Agency (1996) Q3 Flood Data User s Guide California GAP Analysis (1993) California GAP Analysis Data Dictionary 25