SAN FRANCISCO – From gauging water levels behind dams, insuring the durability of levees, to working with local communities, the U.S. Army Corps of Engineers in San Francisco has embarked on an extensive effort to prepare the Bay Area and its network of waterways, wetlands and reservoirs for the arrival of an El Nino weather pattern which forecasters warn could bring prolonged periods of heavy rain, mudslides and flooding to a region more accustomed to years of drought.