LAND DRAINAGE
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tour, and there is nothing for it but to maintain that artificial frontage.
   Those who are responsible for thus keeping intact dangerous salients are compelled to resort to sea-walls and groyning of so massive a character that they are unassailable. The defences of the town in effect constitute a blockade, which starves the coast-line to leeward and destroys the regular sweep of the shore, a factor setting up the familiar phenomenon of irregular inroads of the sea.
   The distance apart of groynes is a matter which must be dealt with on purely empiric lines. If it were attempted to evolve a formula or general law on the subject such formula would have to be in terms of the angle of inclination of the foreshore to the horizon and the local rise of tide. These are the main factors in determining the point. A rule commonly stated is that of placing the groynes a distance apart equal to their length, but such spacing is purely arbitrary, and is not based upon any physical reason. The average inclination of the foreshore on the English East Coast is about i in 15, the inclination on the English Channel averaging about 1 in 11. Where the foreshore runs down into sandy flats the gradients of these are up to 1 in 100.
   The profile of the foreshore of the Dutch coast is variant, but along its sandy flats the ruling gradient may be probably taken as about 1 in 30 to 1 in 40, and on the sea marge as flat as 1 in 100.
   One matter of serious moment in connection with the conservation of a coast-line is that of land drainage, more especially where high ground or cliffs abut on the seashore. The instances of the North Parade at Scarborough and of the sea front at Frinton may be quoted. In the former case, with the object of diverting land drainage, an expenditure of ,£26,000 was incurred, and in the case of Frinton an intercepting drain was laid for a length of 3860 feet at a cost of £1390. It is probable that by systematic and scientific planting a threatened land slope contiguous to a foreshore may to a large extent be partially unwatered, and the expense of heavy drainage works thus lessened.
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