San Diego — The Tijuana River has always been a problem for its namesake city. With a watershed covering hundreds of square miles in

California and Baja, the normally creek-sized river transmogrifies into an aquatic monster after heavy rain. The channelization of the river in the 1970s solved the annual flooding problem and freed up the floodplain land now occupied by Zona Rio, Tijuana's toniest business district. But the concrete channel caused other problems. Difficult for police to patrol, it became a hangout for drug dealers and a home for migrant squatters. And without natural obstructions, the storm waters moved more swiftly, more dangerously through the heart of Mexico's fifth-largest city.

Though the water still roars through the city after rains, Operation Gatekeeper has solved the migrant-squatter problem and the Tijuana Police Department has rid the river of the drug scene. Now the municipal government is looking to the concrete channel to solve another problem that ails the border city: a lack of recreation space.

Néstor Alejandro Arianza, whose lengthy title of Regidor Presidente de las Comisiones de Obras y Servicios Públicos y Reguladora de Bebidas Alcohólicas translates roughly to official in charge of public works and services and regulator of alcoholic beverages, is the point man on a new proposal to use the river bottom for sports courts and recreation. "It was considered in the last administration, but it only got to be a proposal," Arianza explains. "We are now working on the project, and we think that it is possible. We know that there aren't enough places in Tijuana where people can go for sports and recreation. And we think that with a minimum of investment we can use the river as a recreational area and also a place for families where there would be less drug addiction, alcoholism, loitering, and homelessness than in some of our neighborhoods."

A big man in his mid-40s with a thick brush mustache and intense eyes, Arianza leans his elbows on his desk in his third-floor office in Zona Rio's municipal government building. He wears the top button of his pressed white dress shirt open. On the wall behind him hangs a red banner with a Soviet-style gold star and the letters PT in the middle. They stand for Partido del Trabajo, Mexico's leftist Work Party. As he talks, two of his subordinates nod their agreement and whisper to each other. Asked if he plans to tear up the channel's concrete floor to make grass fields, Arianza shakes his head. "No, we will be using the existing concrete bottom," he explains. "And it will only be used during the dry season of the year."

He flips open a large portfolio to display an artist's rendering of the proposed recreation area, which will be built in Colonia Buena Vista, about four miles upstream from the Zona Rio. "Up here on the top of the bank," he says, "we have a trotapista, a jogging track. And on the opposite bank would be a ciclopista, a bicycle track. They're not for speed or racing but more for exercise or recreational riding and running."

In the drawing, the bike and jogging tracks occupy parallel kilometers on the tops of the riverbanks. They're the shape of rubber bands stretched from both ends.

Arianza points to the river bottom in the drawing. "There are volleyball courts, basketball courts, and arena soccer courts with walls to hold the ball in. We envision 24 courts in all, taking up about a kilometer of the river channel. This little building here will also be a security area. And there will be four restrooms. And there are other features contemplated, such as stairways up the banks to the jogging and bicycle tracks. We would even like to have a car ramp and a parking area in the channel."

The first objection to building a park in the river bottom is, What happens when it rains and the river starts flowing? Not a worry, Arianza responds. The courts will be used only from April through November. "All of the equipment," he explains, "the basketball hoops, the soccer goals and walls, and the volleyball nets, it will all be portable. Even the security building and the restrooms will be portable. We will remove it all before the first rain."

And what about surprise rainstorms during the dry season? Won't it be dangerous to have people in the river channel if it rains?

"Our experience has been," Arianza responds, "that only in the heavy winter rains does the water fill the whole channel and begin to rise up the banks. There is a central channel in the middle of the river bottom, and normally all of the water concentrates in it and doesn't spread to the areas on either side where the courts will be. And the other thing is that the materials we will be using will be able to withstand the rain for a couple of days without a big problem. They're made to be out in the weather."

The preliminary cost estimate for the project is 55.4 million pesos, about $520,000. "Most of that will be the construction costs of the stairways and bridges, and the cleaning," Arianza says.

The city will not recover the expenditure by charging users of the recreation area. "It will be free," Arianza says.

Tijuana, a city of nearly two million, features only 75 parks. Its 1.87 square meters of park space per resident is less than a quarter of the amount the United Nations deems healthy. Arianza says the city administration is aware of that problem, but he doesn't foresee using the river bottom to replace neighborhood parks. "Right now, we're only looking at the river for sports uses. But the administration is looking to build green parks where families and children can play."

That's not going to happen by removing the concrete from the river bottom. "For the time being it will remain a concrete channel," Arianza says. "There is no other way to get the water through the city except through that river channel."