(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.
(2) If the value of any work, calculated in accordance with sub-paragraph (1) above, exceeds the actual value to an incoming tenant, in any case where—
(a)plans on a suitable scale, made at the time when the work was done, and showing the position of all moles, mains and outfalls, are not made available to the landlord; or
(b)moles were not drawn at a proper depth, having regard to the nature of the soil and subsoil; or
(c)any ditches into which the outfalls discharge have not been maintained clean, free from obstruction and at a proper depth since the work was done; or
(d)deep cultivation or other work interfering with the efficient functioning of the drains has been done on the land since the drainage work was completed; or
(e)the land is not of consistently suitable slope or soil texture for mole drainage to be effective; or
(f)the drainage scheme was not a proper one, having regard to all the conditions, or was not efficiently carried out; or
(g)for any other reason, the drainage system does not function efficiently,
the value so calculated shall be reduced so as not to exceed such actual value.