Brunel decided that a viaduct would be the optimal means of crossing the river and designed such a structure. Possessing eleven spans and stretching to a length of 1,200 ft, this viaduct was largely composed of timber, which was treated with creosote under pressure as to sufficiently weather-proof them against the prevailing conditions of the location. Construction work commenced during 1846.
The total cost of the viaduct's construction reportedly exceeded £20,000. However, its extensive use of wood heavily contributed to the bridge's destruction just prior to completion. On 31 May 1848, as the final arch was being put into place, a heated bolt used to rivet a beam together ignited the flammable creosote; within the space of six minutes, a catastrophic fire had spread across the whole structure, setting the opening back by years.