Construction began once the necessary land had been purchased, but it soon became apparent that the original surveys were inadequate. The canal engineer John Rennie was asked to advise the proprietors, and proposed three options, for boats of , for boats of , and for barges which were wide. The first was ruled out on cost, the third because of the need to transship all goods at Highbridge, and the second was adopted because it allowed the coasters that worked the Bristol Channel to use the canal. This option required locks of by , and was costed at £28,720. The route would be as authorised, but a single lock was required on the upper section to simplify the water supply. Work resumed in July 1828.