Should construction-king Bill Williams be allowed to enlarge the mountain-surrounded Harper's Park dam, which sits just upstream from an (unidentified) city apparently somewhere in the Central Southwest? True, the city needs the extra hydro energy. But what about all that pretty land being submerged? The dilemma becomes a more critical one, however, when geophysicist Jay Harper (""Oil is by bag"") visits his ancestral home and, while scuba-diving around the dam, begins to suspect that there'd be danger of flood in enlarging the dam; in fact, there might be danger right now, because of weakness in the supporting rock structure, ""Think of Johnstown in 1889, only this could be worse, much worse . . ."" Persuaded by Williams' feisty daughter to stay and help, Jay brings in a colleague, and they confirm that the dam sits right on a fault line! Their recommendation: drain the lake, divert water upstream, and start planning to evacuate the city's Chicano barrio -- which would be hit hardest by a flood. So Jay is asked to begin this controversial scheme (it will involve destroying some fancy neighborhoods), but before they can finish -- heavy rains, flash floods, looting in the evacuated streets, and . . . ""It's beginning to go! The whole goddamned thing! It's like in the movies . . ."" To an even greater extent than usual with Stern (The Tower, Snowbound Six), the characters here are barely functional; besides Jay & Co., there are those losing or making money on the shifting effects on land values around the dam -- plus a pair of lovers (an ex-football star, a lady Fire Ranger) watching it all from a fire lookout tower (""That is one marvelous pair of knockers you've got, baby . . ."") So the big personality here is the dam itself, and only those readers who can become emotionally involved in diversion tunnels and such will find much interest in this talky, static (the disaster doesn't come till the very end) geological formation.