Complex sentence: At its widest point in a big flood year, the seasonal swamp stretches to 150 km across from east to west; one of the factors that leads to the ever-changing nature of the delta is the flatness of the area.
Split into simpler sentences: At its widest point in a big flood year the seasonal swamp stretches to 150 km across from east to west. And one of the factors that leads to the ever-changing nature of the Delta is the flatness of the area.