596 Additions and Correétions

“bank as well as the inner furface; and where the preflure of fiagnant or almoft ftili water is merely to be refifted, the outer flope may be formed of the fame. But in cafes where the force of either waves or currents operate directly upon the banks, the outer flopes fhould be well fecured againft it, with the beft materials that can be conveniently provided, and the bafes or foundations be properly fecured from being undermined; piles, timber, and mafonry being had recourfe to where the founda- tions-are- not fufficiently firm and folid. It is of the utmoft importance in thefe cafes to guard againft accidents.

Befides the conftruétion of the banks, attention is alfo neceflary tothe formiug of the difcharging channels on the outfides of the embankments.‘The pofition of the mouth, or out-fall, fhould conftantly befuch as that the current of the receiving waters may not warp or fill them up, but tendo clear them out, and keep them free. They-thould likewife be fituated as low as they can be conveniently permitted be+

iow the’flood-gates of the banks, the better to induce currents, and thereby keep the flood-gates and the mouths of the channels the more free and open.

In cafes of open feas or other extended waters without any difcharging channels, but where the waves extend to the foot of the banks, two flood-gates may fometimes be neceflary, one on the external fide, to refift the force of the waves, and prevent their Zlowing up the works-on the infide; the otheron the inner fide, to fecure the paflage more fully. Thus, when water is admitted by the outer flood-gate being lifted by the waves, its progrefs is effeually fiopped by the inner valve being in a serfet flate. Where the valves are liable to be choked up, from being fituated below the furface of fand or other fhifting banks through which the water forces its way, and are only capable of being kept clear by conftant trouble and expenfe, the remedy, in difficult cafes of this nature, 1s that of defending the difcharging flood- gates by covered channels carried out into the fea through the line of beach, made fufficiently firong to refilt the force of the waves, This is however an expenfive method, and fhould of courfe be avoided when poffible*.‘In all cafes where ex- ternal valves or gates are required, and liable to be filled up, great care mutt be

-taken to keep them open and free, either by piles, fences, or other contrivances, ron out in fuch a manner‘from the embankments as‘not to interrapt the difcharging water, the earthy materials colle@ed by it being occafionally removed.

In thefe cafes, common Dinge flood-gates may be the moft proper, or fuch as fwing outward, and fall into a rabbetted frame.‘They thould be always made of feafoned oak timber; being made double, by the different planks crofting each other, in order to prevent their warping.‘They fhould be fo contrived as to fit pretty tight, with-

* Marfhall on the Landed Property of England.