A. Statement of the Problem/Need/Relevance

The Cañada Joe Bill is a key component of Campo-Tecate Creek, a major tributary of the Tijuana river watershed, which straddles the U.S.-Mexico border in California and Baja California. Campo Creek originates in eastern San Diego County and flows into Mexico at A (Fig. 1), where it changes its name to Cañada Joe Bill. The latter joins San Pablo Creek at B (Fig. 1) to form Tecate Creek. West of the city of Tecate, Tecate Creek flows back into the United States and joins Cottonwood Creek in Marron valley, San Diego County, to form the Tijuana River. The latter flows back into Mexico, crosses the city of Tijuana, and eventually flows back into the United States exiting into the Pacific Ocean at Imperial Beach. The Cañada Joe Bill flows for a distance of 6,268 m, entirely in Baja California, east of the city of Tecate (Fig. 1).

Due to its close proximity to the United States, the Cañada Joe Bill has strategic binational importance. It the past few years, the bottom of the canyon has been mined at C (Fig. 1) for sand and gravel, which was exported to the United States by rail, entering at D. The existing binational railroad line is administered in Mexico by Ferrocarriles Nacional Mexicanos, and in the United States by Carrizo Gorge Railway.

The sand-and-gravel mining operation was carried out in the period 1989-2000, largely without regulation, leaving a scarred landscape with 8-m deep borrow pits and little resemblance to natural conditions. The current situation is worsened by a flood hazard, since the existing railroad crosses the creek through an earthen embankment at E (Fig. 1). The latter, dating back to 1914, is in a state of disrepair and may breach under an infrequent flood. The postulated breach is likely to cause substantial damage to downstream sites, including the city of Tecate proper.

C. Research Method/Approach

The research method/approach consists of the following steps:

1. Hydrologic watershed modeling using the U.S. Army Corps of Engineers HEC-HMS to calculate flood discharges for return periods of 2-yr to 1000-yr. The SDSU RAINFLO model will be used for comparison purposes. The watershed model uses established hydrologic methods to convert rainfall to runoff, using spatially distributed watershed data encompassing soils, vegetation, terrain topography, stream slopes, channel cross-sectional data, and streambed soils and hydraulic data. Event precipitation is determined using NOAA National Weather Service methodologies (Ponce, 1989). Hydrologic abstraction is performed using the standard NRCS runoff curve number method (Ponce and Hawkins, 1996). Hydrograph generation is performed using the Modified Clark method (Kull and Feldman, 1998). Stream channel routing is accomplished with the Muskingum-Cunge method (Ponce and Yevyevich, 1978).

2. Hydraulic gradually varied flow modeling using the U.S. Army Corps of Engineers HEC-RAS model to determine flood stages, depth, and velocities throughout the study reach (U.S. Army Corps of Engineers, 2003b). SDSU BACKWATER's model will be used for comparison purposes. The gradually varied flow model calculates flood stages, depths, and velocities, when presented with appropriate initial and boundary conditions. The boundary conditions consists of: (1) a flood discharge upstream, which is determined by the hydrology, and (2) a stage or flow depth at the downstream point, which is determined from an assumption of equilibrium (normal) flow downstream of the study reach. The HEC-RAS model uses the iterative standard-step method for backwater/drawdown computation (Chow, 1959). This method requires the flood discharge, detailed cross-sectional data, and the downstream slope. It provides flood depths and stages throughout the study reach. The cross sections will be determined at appropriate distances, up to 200 m per computational reach (at least 32 cross sections).

3. A stream restoration or hydroecological study to determine the most appropriate way to restore Cañada Joe Bill to its former state of productive stability. The study includes a vegetation survey, determination of design velocities, streambank stabilization with gabions and other vegetative methods, and spatial design of the 6.268-km reach.

4. The environmental climatic study will examine historic data on local precipitation and temperature, correlating the variation with known El Niño and La Niña events. The study will compare aerial photography prior to and after the mining intervention, with aim to ascertain possible cause-and-effect relations.

5. The sociological study will review the census statistics from 1970 to 2000, to determine the population growth rates in the canyon's vicinity. Interviews with local actors will be conducted to determine perceptions regarding the future use and development of the canyon. A stakeholder map will be produced, in which the local actors and institutions will be identified and classified. A attitudinal survey will be carried out, seeking to determine local perceptions regarding the restoration of Cañada Joe Bill.

6. The geotechnical study will consist of a review of the embankment's history and an analysis of the embankment safety under (a) existing static loads, and (b) infrequent flood conditions. The embankment's history will be sought in records of the Ferrocarriles Nacionales Mexicanos. The analysis will be performed using Fellenius' method of slices, complemented with a finite-element model of slope stability under seepage (GEOSLOPE). The analysis will include soil sampling and tests to determine permeability and shear strength (direct shear and/or triaxial). Reservoir routing will be used to model the filling of the reservoir and possible overtopping of the embankment under an infrequent flood. The topographic characteristics of the reservoir and the hydraulic characteristics of the existing outlet structure will be determined prior to reservoir routing. The study will include recommendations either to increase the safety of the embankment, or to replace the embankment with a safer structure.

7. The risk-analysis study will carry out an impact assessment and a risk assessment, representing both qualitative and quantitative parts of the analysis. The impact assessment considers several key potential impacts, along with a measure of the potential loss of life resulting from dam failure (Graham, 1998). Combining all measures of impact allows for a single impact score to be calculated, upon which the level of risk assessment may be determined. The risk-assesment methodology is based on a failure mode, effect, and criticality analysis approach (CIRIA, 2000). This offers a single framework in which engineering judgment may be applied through consideration of the various components of the embankment. Components are scored according to their consequence of failure, likelihood of failure, and confidence. The outcome of the risk-analysis study will outline the current situation of the embankment in terms of risks and losses caused by a probable failure.

8. The dam-breach study will include an analysis of a postulated failure of the railway embankment, following an infrequent flood that fills the reservoir and overtops the dam. The breach flood hydrograph will be estimated following established empirical techniques (Taher-Shamsi et al., 2003). The flood hydrograph will be routed downstream, through Tecate Creek, to determine the extent of inundation and the possible damages to existing urban dwellings on the creek's banks. The National Weather Service DAMBRK model and the dimensionless approach to dam-breach flood wave propagation (Ponce et al., 2003) will be used for the purposes of routing the dam-breach flood wave through Tecate Creek.

D. Qualifications/Appropriateness of Research Team

1. Victor Miguel Ponce, project coordinator, hydrologist, professor of civil and environmental engineering, San Diego State University. Dr. Ponce has 36 years of experience in surface water hydrology, hydroecology, environmental hydrology, and computational hydrology. He has extensive experience in the United States, Mexico, and Latin America, in academic, research, and consulting roles. He was the principal investigator of the recently completed SCERP-funded project, which dealt with the sustainable architecture of Arroyo Alamar. He is fluent in both English and Spanish, and has in-depth knowledge and experience of technical and cultural issues on both sides of the border.

2. Dr. Julio Valdes, assistant professor of civil and environment engineering, San Diego State University. Dr. Valdes' expertise is in environmental geomechanics, focusing on novel experimental applications in seepage and pressing geomechanical problems in Latin America. He will be responsible for coordinating the geotechnical aspects of the study, which involve the stability of the railroad embankment, as well as its performance during postulated floods. He is fluent in both English and Spanish, which should facilitate interaction with local counterparts.

3. Mr. Jose Rodriguez Rogero, Associate Director, School of Engineering, Universidad Autonoma de Baja California (UABC), Unidad Tecate. Mr. Rodriguez will coordinate the work of UABC-Tecate students working on the project.

4. Mr. Pablo Andres Rousseau, Associate Director and professor of civil engineering, School of Engineering, Universidad Autonoma de Baja California (UABC), Unidad Ensenada. Mr. Rousseau holds and M.S. in hydraulic engineering and has 13 years of experience with various engineering projects in Baja California. He will provide expertise in hydraulic and geotechnical engineering and will coordinate the work of UABC-Ensenada engineering students working on the project.

5. Dr. Pedro María Sánchez, professor of civil engineering, Faculty of Engineering, Universidad Autonoma de Baja California (UABC), Unidad Ensenada. Dr. María holds a Master of Science degree in Construction Management from the University of Nottingham, United Kingdom, and a Doctorate in Engineering (cum laude) in Risk Analysis from the Technische Universität Dresden, Germany. Dr. María will be in-charge of the risk assessment component of the study.

6. Mr. Walter Zuñiga, adjunct professor, Faculty of Sciences, Universidad Autonoma de Baja California (UABC), Unidad Ensenada. Mr. Zuñiga holds a Masters degree in Ecosystem Management in Arid Zones from the Universidad Autonoma de Baja California. He recently held the post of Director, Forests and Fauna, Secretaria de Fomento Agropecuario, Baja California. He has participated in several SCERP-funded research projects dealing with the sustainable management of water and natural resources in the Ojos Negros valley, Baja California. Mr. Zúñiga will provide the academic expertise in ecosystem survey, riparian assessment, and climate and habitat dynamics, and will coordinate the work of the Ensenada team.

7. Dr. Guillermo Aramburo, professor, Faculty of Administrative and Social Sciences, Universidad Autonoma de Baja California (UABC), Unidad Ensenada. Dr. Aramburo has more than 20 years of experience in research and teaching. As a social scientist, he has participated in several interdisciplinary projects dealing with technology and society and natural resources. Recently, he participated in the SCERP-funded project dealing with the sustainable management of water in the Ojos Negros valley, Baja California. Dr. Aramburo will formulate the sociological component of the study and coordinate the work of UABC-Ensenada social-science students working on the project.

8. Chemist Alfredo Angulo, Tecate environmental consultant. Mr. Angulo is very knowledgeable about the problems facing the Cañada Joe Bill. Mr. Angulo will coordinate the work of the local consultants and students in Tecate.

9. Mr. Cosme Cázares Burgueño, Cañada Joe Bill stakeholder and organizer. Mr. Cázares has substantial local experience in the problems facing the Cañada Joe Bill. He will assist with local logistics and involvement of the local population.

10. Mr. Alberto Castro Garcia, Tijuana hydrological consultant. Mr. Castro is a recognized expert in the hydrology of the Tijuana river basin. He has 30 years of experience in hydrological and hydroecological engineering in Tijuana and Baja California, including the design and construction of several channel-improvement projects in the basin. Mr. Castro will provide expertise in channel rehabilitation and will assist with field work in the Cañada Joe Bill watershed.