A new groundwater sustainability agency that has struggled to get its footing in recent months is on a fresh trajectory with a new general manager.  Michael Knight, Porterville assistant city manager, is leaving the city to take the reins as manager of the Porterville Groundwater Sustainability Agency. He also will serve as assistant manager for Porterville Irrigation District. His first day is Aug. 4. … Landowners have repeatedly voiced concerns over management and transparency issues since the Porterville ID board voted to break away from the embattled Eastern Tule GSA in February. That move came amidst fallout from a ruling by the state Water Resources Control Board to place the Tule subbasin on probation for its lack of a cohesive groundwater plan that would staunch runaway subsidence in the region and protect domestic wells.