Tempe will need six such dams of various lengths to build Town Lake. Three 300-foot rubber dams will anchor the western side of the lake while three shorter dams will block off the eastern side. The western dams, to be located about 800 yards west of Mill Avenue, will rise to a height of 16 feet, the highest such structures in the world.

The collapsible rubber dam is needed to drain the lake in the event of a major water release from upstream reservoirs. Toward the end of a release, the dam could be reinflated to refill the lake. Such a dam is in use in California's Alameda County Water District, where two water-inflated rubber dams and one air-inflated rubber dam impound water on a flood-control channel that drains into San Francisco Bay.

The Alameda dam is about 250 feet long and 13 feet high. The water district raises and lowers the dam about ten times per year and, to date, it has worked perfectly, according to Bill Blair, the district's design manager.

The air-filled dam is inflated to a very low pressure--about six pounds per square inch--which eliminates the danger of a massive blowout, sending a wall of water downstream. The dams are manufactured by Bridgestone Corporation, a Japan-based tire manufacturer, and are projected to last 30 to 50 years.

Waters impounded by such a dam would be only a marginal source of water for Tempe's fake lake. Other water-supply sources would have to be tapped to replace the huge amount of water lost through irrigation, evaporation and seepage. The city's latest plan, one in a long series of constantly changing scenarios, calls for drilling groundwater supply wells next to the river. The city would then pump treated effluent from its south Tempe reclamation plant into the aquifer to replace the one million gallons of groundwater it would draw from wells for the lake each day.

But the groundwater-recharge option faces a major obstacle. The lake is located just west of a massive groundwater contamination site included on the Superfund list. Tempe will have to show that pumping groundwater beneath Town Lake will have no impact on the contaminated groundwater pool nearby.

With a water source jeopardized by a Superfund site, a lake that is really a glorified Grand Canal and a collapsible rubber dam as the mainstay of the project, it is no wonder that wildlife considerations are far down on the list. Long-range-development plans show nearly every square foot of lakefront property that could support a building will have a building.

The most promising wildlife corridor will be west of the lake, where a 1.5-mile-long riparian band extending to the Hohokam Expressway is planned. A narrow stream will cut through 100 acres of native wildflowers, shrubs and grasses, 14 acres of mesquite stands and about two acres of water vegetation.

This watercourse, however, will be of lower quality than the lake water, because it will also be used to divert Tempe storm water from pouring into the lake. Planners hope to allow catch-and-release fishing in the stream, although it is possible the watercourse will be dry at certain times of the year.

Another area expected to provide a wildlife habitat is land dedicated to the Southwest Center for Education and the Natural Environment, where a 13-acre mesquite grove will be planted. Like the riparian area west of the lake, this project will be located away from the lake's perimeter, and north of Red Mountain Parkway. The area was selected by Tempe as a site to fulfill federal requirements to replace wetlands destroyed by the channelization project.

While Tempe bills Rio Salado as a recreational haven, there is a hitch. Many of the planned activities along the lake will cost money, as the city encourages "commercial-based recreation." In other words, family amusement parks mixed with a golf course, driving range and "pay to play" volleyball and softball fields will stretch along the south bank from Mill Avenue to Priest Drive.

And forget visions of taking a plunge in the cool water on a hot July afternoon. The lake will be off-limits to swimming. Planners do hope to build a swimming pool within the lake to give "an illusion" of swimming in the lake.

As for boating, city officials say there are no plans to charge for launching nonmotorized watercraft from one of several docks. But woe to those who may fall out and be forced to swim to shore. The banks of the lake will be very steep and could be unscalable by exhausted swimmers.

@body:One of the key promises the city has made to sell the project to the public is that the pathways surrounding the lake will remain accessible 24 hours per day. "We will not allow private development to block access to any part," Nielsen says.

This promise is viewed with great skepticism by some, including longtime council observer Art Jacobs. "I have second thoughts about Rio Salado in terms of whether I, John Q. City, along with barefoot children, will be allowed down there. The more I see the plan, the more it is for the people who have bucks to spend."

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