Complex sentence: Vast agricultural areas in the Mehi River floodplain become flooded in large floods and can stay underwater for days even a couple of weeks costing farmers thousands in ruined crops.
Split into simpler sentences: Vast agricultural areas in the Mehi River floodplain become flooded in large floods. Some areas remained underwater for days, and in some cases, as long as a couple of weeks costing farmers thousands of dollars in ruined crops.