Nearly a decade ago, Gabriel Lozada, a man with a wiry frame and waves of steel-gray hair who looks exactly like the mathematician he is, set out to answer what he thought was a relatively simple question: Could Utah’s proposed Lake Powell Pipeline — a plan to ferry Colorado River water to southern Utah — live up to the state’s rosy forecasts of growth and prosperity? Or was it more likely to tank the economy of a small but lively retirement community in the southwestern Utah desert?