SIOUX CITY — The president of Briar Cliff University in Sioux City plans to step down at the end of the 2015-16 academic year. Bev Wharton told the university trustees earlier this month about her intention. She’s been president since June 1, 2001, after working for MidAmerican Energy Co. The Roman Catholic institution reported enrollment of nearly 1,150 for this fall’s semester.