The Bristol line was immaculately done over the levels by Brunel, unlike what his successor Grierson did 60 years later with the Somerton cutoff just to the south. The line has substantial longitudinal drainage ditches each side (still visible, just outside the trackside bushes), with the formation thus isolated from the adjacent waterlogged lands. The excavated material was used in part for the approach ramps for the various road bridges across the line.
Described to me, at a notably young age, by the Taunton ganger, who looked after both lines.