Complex sentence: The upper basin of the St. Johns was significantly lowered in the 1920s with the establishment of the Melbourne Tillman drainage project which drained the St. Johns' headwaters eastward to the Indian River through canals dug across the Ten-Mile Ridge near Palm Bay.
Split into simpler sentences: The upper basin of the St. Johns was significantly lowered in the 1920s with the establishment of the Melbourne Tillman drainage project. This drained the St. Johns' headwaters eastward to the Indian River through canals dug across the Ten-Mile Ridge near Palm Bay.