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In 1993, the last really wet winter in the border region, 26 people died in Tijuana, and hundreds of horses on a dozen or more ranches in San Diego County were evacuated as floodwaters swamped the Tijuana River Valley. Yet there had been no “storm of the century,” only a series of rainy days followed by a big downpour. Coming after a drought in this semi-arid, very disturbed landscape populated by more than a million humans, that was enough to bring disaster.
Residents of both countries share an interest in improved safety during storms. This winter, for the first time, some of them will at least get timely warning. Thanks to a binational agreement in June 2000, a flood warning system has been developed for the lower Tijuana River watershed, funded by governments on both sides of the border. It is now on-line as part of a cross-border program to cut storm-related losses. This warning system is a result of a two-year project to examine flood risk in the lower watershed using geographic information system (GIS) mapping and modeling capabilities shared by the two countries. It is a tangible product of the many new efforts to cooperate on issues of mutual concern in this binational watershed. Soils in the border area are among the most erosive soils that exist. They fall apart and crumble with human disturbance, then dissolve in heavy rain. In an arid region, even the most extreme impacts to the earth’s surface can occur without many repercussions . . . until it rains. Then a torrent of mud and water cascades to the lowlands in a flash flood. Fast-paced urban development on both sides of the border has resulted in thousands of acres of impermeable surface and increased runoff where, under natural circumstances, water would have been absorbed into the earth. In Tijuana’s poorest colonias, communities sprang up without any provisions for storm runoff. The city’s best efforts to provide stormwater culverts and drains hasn’t kept pace with its burgeoning population. On the north side of the international fence the scarred landscape hints at similar soil impacts from U.S. Border Patrol roads and vehicles. During the 1993 flood disaster, the mesas and cañons of Tijuana were awash with mud and debris as flash floods whipped the area and filled the city’s concrete river channel to the brim. People and animals were swept away in the middle of the night and entire communities were isolated for days. Hundreds of the poorest people were left injured and homeless, and scores of businesses and major transportation arteries were covered in a thick sheet of mud. North of the border, rainwater flowed down mesas and cañons and through gutters and culverts. The Tijuana River floodway flowed full-bore with a thick coffee-colored torrent. Bridges were swept away and the river dug an entirely new channel, erasing productive farms forever. People and livestock were evacuated, some in deep floodwaters laden with sewage. Massive amounts of sediment and debris remain in the valley to this day and everyone is left to wonder what the next big flood will do. Bridges have been replaced, and today the City of San Diego is undertaking a program to remove people and structures from the floodway in a willing-seller land acquisition program. Because of the size of the lower Tijuana River Watershed and its large population, the flood warning project was launched as a pilot project in a high-risk cross-border region to test the feasibility of the new integrated flood warning system. It includes the Rio Alamar corridor and the associated Cottonwood, Tecate, and Campo Creek subbasins. National Weather Service rain and stream gauges were installed in November, and other gauges have been upgraded. Communication equipment was put in place to enable warning system staff in both countries to communicate with other agencies to create a seamless exchange of real-time data on rain and flow throughout the watershed. Researchers in universities in San Diego, Tijuana, and Ensenada will have access to the data for modeling purposes. The real-time weather information will be overlaid with other GIS data on roads, topography, and human population centers. Such information is intended to enable emergency response providers on both sides of the border to use the interactive program for decision-making during flood emergencies. The new system will not prevent flooding, but it should help people to make their way to safe quarters when serious danger arises. The harder work required to reduce flood risk in the Tijuana River watershed has only just begun. —Jim King For more information, Rand Allan Nina Garfield In Mexico: Mario Rodriguez Alberto Castro |
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