Complex sentence: The Hokitika River, and it's eastern tributary, the Kokatahi River, have formed the Kowhitirangi-Kokatahi alluvial plain; a fertile and productive land extensively used for dairy farming.
Split into simpler sentences: The Hokitika River, and it's eastern tributary, the Kokatahi River, have formed the Kowhitirangi-Kokatahi alluvial plain. A fertile and productive land extensively used for dairy farming.