Complex sentence: In addition an act was proposed to dredge the Avon to make it navigable for larger vessels and although this came to nothing, Hyde started work on the new entrance; laying down a line of ironstone doggers.
Split into simpler sentences: In addition an act was proposed to dredge the Avon to make it navigable for larger vessels but this came to nothing. Despite this, Hyde started work on the new entrance, laying down a line of ironstone doggers.