(1) (a) Where the moles discharge into a piped main drain, the value shall (subject to sub-paragraph (2) below) be the reasonable cost of the work less one-sixth for each year since the work was completed;
(b)Where the moles discharge direct into an open ditch (whether the outfalls are piped or not), the value shall (subject to sub-paragraph (2) below) be the reasonable cost of the work less one-third for each year since the work was completed.