The water flow in the Grand Canyon is temporarily changing and it could reveal some surprises, geologists said. The U.S. Geological Survey said Sunday that an 11-day “spring disturbance” flow will start Monday and will drop water levels in parts of the Grand Canyon. … While dam maintenance may not seem exciting, the drop in water could reveal parts of the Colorado riverbed that hasn’t been seen in decades, USGS said. It could also impact in the Colorado River ecosystem. The change in water levels will also mimic what the Colorado River was like before the dam was built, USGS said.