Complex sentence: There it was agreed that it should be replaced with a more appropriate structure, and so in September 1837 it was closed (a temporary wooden crossing was provided for pedestrians) and over the following six months, demolished.
Split into simpler sentences: There it was agreed that it should be replaced with a more appropriate structure. Therefore, in September 1837 the bridge was closed (a temporary wooden crossing was provided for pedestrians) and over the following six months, demolished.