612 PROTECTION AGAINST SWAMPS. 



conveyed it lower down. If such a watercourse does not 

 exist a drain must be dug to receive and drain away the 

 surplus water. The system of drains gave admirable results, 

 and the cost was 12s. per acre, that of the upkeep per acre, 

 2s. annually. 



The cost of open drains in Germany, in 1883, was about 

 8s. per acre, but the extra cost of Kaiser's drainage is incon- 

 siderable when compared with the superior benefits obtained. 



The only objection to the method consists in the fact that 

 the collecting trenches at least in depressions form so many 

 little frost-holes, that increase local danger from frost. 



3. Covered Drains. 



a. Trenches. 

 i. METHOD OF CONSTRUCTION. 



Underground drains are usually made as in Fig. 280. 

 The trenches should be about one foot broad at their base, 

 1J to 2J feet deep, and with a slope as steep as the nature of 



Fig. 280 Section of a drain. 

 a. Layer of stones, b. Layer of branches, c. Layer of earth. 



the soil will allow. The trench is then half filled with stones, 

 which are covered with brushwood, reeds or sods, and the top 

 is filled in with earth. 



Another method is to cover the base of the trench with 

 fascines or tied bundles of green osiers, branches of alder, 

 poplar or shrubs, which are used immediately after they have 

 been cut. The vacant spaces between the fascines along the 

 sides of the trenches are filled up with moss, and the whole 



