Whoever encroaches upon, or obstructs or commits any nuisance in, a public road or wilfully obstructs or injures a public bridge shall be fined not less than $15 nor more than $50. In case of a continuing nuisance, the judge shall order the person to abate the nuisance within a given time, and, on failure to do so, a writ of execution shall be issued to the sheriff commanding the person to abate the same. The sheriff's fee for executing the writ shall be $3.00 a day and all expenses, to be paid by the defendant, which payment may be enforced by attachment and imprisonment.