Flood Hazard and Risk Assessment Modeling with GIS in the Transborder Tijuana River Watershed
The Tijuana River Watershed (TRW) is a 1,750 square mile drainage system that straddles the California-Baja California section of the United States-Mexico border. In 1998 the watershed was selected by the National Partnership for Reinventing Government and the Federal Geographic Data
Committee as one of six pilot projects nationally to demonstrate the application of the National Spatial Data Infrastructure (NSDI) in a transborder setting and the use of geospatial technologies in helping to solve local problems. The other five sites are the City of Baltimore, Maryland;
Dane County, Wisconsin; Gallatin County, Montana; the Susquehanna-Lackawanna Watersheds, Pennsylvania; and Tillamook County, Oregon. The TRW, the only binational community among the six sites, was given demonstration status because of well documented problems of environmental deterioration
related to rapid urban expansion and the existence of a GIS that was initiated in 1994 with startup funding from the National Oceanic and Atmospheric Administration (NOAA). The database was prepared jointly by San Diego State University (SDSU) and El Colegio De La Frontera Norte (COLEF), under
a memorandum of understanding (MOU) between the two universities. The MOU provides for collaboration between the two universities in the areas of GIS database development, scientific research, watershed education, and public outreach.
This paper has two principal objectives: 1) to describe
the TRW Demonstration Project process and milestones for accomplishing its objectives and 2) to identify hazards and risks associated with flooding in the watershed. The principal partners are SDSU, COLEF, NOAA, and the Tijuana River National Estuarine Research Reserve (TRNERR). Two private
sector firms, Environmental Systems Research Institute, Inc. (ESRI) and Sun Micro Systems, Inc. (Sun), are contributing resources to the project. ESRI is providing software, training, and other assistance. Sun has donated a computer workstation to COLEF to bolster its GIS hardware capability.
project was carried out in several phases. The first involved a process of identifying the specific characteristics of the demonstration project. This was accomplished by engaging stakeholders in two user workshops and a needs assessment survey. For the first workshop, government and academic
organizations engaged in a number of high profile border area projects met in a daylong session to discuss their projects' characteristics and data requirements. Those attending recommended that a mail survey and follow-up workshop involving a larger, more diverse stakeholder group be
conducted to define the nature of the demonstration project more precisely. Two types of written surveys, one on issues and the other on data, were administered. The issue survey was intended to identify critical issues in the TRW and adjacent regions from the perspective of different organizations
that have an interest in the watershed. The data survey was designed to identify available data required to address critical issues. From these surveys the themes of water quality, water quantity, and quality of life were distilled as being the most critical problems in the watershed. Following
the analysis of the surveys, a second workshop was held (1) to identify, through a structured process, which problem within the three themes was the preferred NSDI demonstration and (2) to develop an outline for its content. Participants, who were divided into breakout groups based on the
three themes, were asked to select a priority problem in each theme area based on the severity of the problem, the availability of data for addressing the problem, and the degree to which the problem is cross border in character. After considering recommendations from each focus group, it
was agreed that the NSDI Demonstration Project should focus on flood hazards and risk assessment. Flooding is a source of serious damage to property and life and the primary source of sediments impacting the environment of the Tijuana Estuary. The second phase of the project focused on the
formation of technical and policy advisory committees, project-related hardware and GIS software upgrades at SDSU and COLEF, the generation of a high resolution digital elevation model and other geospatial data to augment the existing TRW GIS, and the development of a methodology for modeling
flood hazards and risk under different flood conditions. The DEM for Goat Canyon-Cañon de los Laureles, a side canyon of the lower TRW, was prepared by SDSU and COLEF students and staff, under the supervision of NOAA photogrammetric specialists, from aerial photography flown in support
of the project. In the third phase, several flood hazard and risk assessment models were evaluated taking into account the physical and cultural characteristics of the study area. In the fourth phase, flood hazard and risk assessments of the lower TRW and Goat Canyon were conducted following
methodologies developed by FEMA and the NOAA Coastal Services Center in their community vulnerability assessment programs. In the fifth and final phase, end users in Mexico and the United States will be trained in the use of GIS software and the application of one or more flood hazard and
risk models to the study area.
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