Multilayered map to battle flash floods in Tijuana

The steep slopes of Laureles Canyon just west of downtown Tijuana are crowded with small homes made of wood and corrugated tin.

Although it's been bone dry this year, winter rains turn these hillsides into torrents of mud that can easily destroy these flimsy homes as well as damage an important wildlife refuge nearby.

To warn residents of the potential dangers, US and Mexican researchers are collaborating on a project using sophisticated mapping, aerial photography, and ground-based sensors.

The Tijuana River Valley project is designed to show the power of geographic information systems (GIS) to improve communities and protect the environment.

"The nice thing about GIS is that it is an integrative technology," says Richard Wright, geography professor at San Diego State University and a coordinator of the project. "It crosses borders."

GIS programs connect information from the computer to aerial photographs and maps. In the Tijuana project, separate sheets of data containing rainfall patterns, soil type, canyon topography, vegetation, and housing density are layered upon each other, resulting in visual trends that would otherwise be missed by looking at many different tables.

In recent years, flash floods and mud slides have killed Tijuana residents and damaged dozens of homes, most recently in February 1998, when seven people died.

Since then, Tijuana municipal officials established a $60,000 network of automated rain gauges at 10 sites around the city that transmit rain levels via modem every five minutes to a command center. The rainfall information is hooked into the GIS network being developed by the researchers.

"Many investigators do reports that end up in the libraries of universities," says Antonio Rosquillas, Tijuana's director of civil protection. "But we want [the information] to be used for some kind of benefit."

In the past few years, GIS has become a vital tool for police and fire departments, conservation groups and companies seeking new customers or markets. This powerful technology has become more widespread as the software to create some GIS systems has become more affordable, costing less than $15,000 and operating on a personal computer.

The Tijuana River project is one of six GIS demonstration projects across the United States funded last year by the Federal Geographic Data Committee, a multi-agency organization.

As a pilot project, researchers here have focused on Laureles Canyon, a 12-square kilometer watershed several miles west of downtown Tijuana. The canyon was originally settled by squatters in the mid-1970s and is now home to an estimated 15,000 to 20,000 people.

Poor land management has worsened the flood risk. Tijuana city officials have allowed residents to build homes on steep slopes and to block a concrete drainage channel with debris and, in some cases, small homes.

As part of the GIS project, the researchers created a computer-generated, 3-D "fly-through" of Laureles Canyon as a tool to show local leaders on both sides of the border high-risk flood zones.

(c) Copyright 2000. The Christian Science Publishing Society

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