A towhead is a sandbar that has cottonwoods on it as thick as harrow-teeth.

沙洲是一片沙土岗子，上面长满了白杨，密得象耙齿一般。

As soon as I got started I took out after the raft, hot and heavy, right down the towhead.

船一开动，我就顺着沙洲，朝着木筏，拼命追去。