496 eozet's plan. 



gravel — wlaicli, by increasing tlie mechanical force of the water, 

 greatly aggravate the damage by floods — much diminished. When 

 the stream has reached that part of its com'se where it is bordered 

 by soil capable of cultivation, and worth the expense of protec- 

 tion, he proposes to place along one or both banks, according to 

 circumstances, a Une of cubical blocks of stone or pillars of 

 masonry three or four feet high and wide, and at the distance of 

 about eleven yards from each other. The space between the two 

 lines, or between a line and the opposite high bank, would, of 

 course, be determined by observation of the width of the swift- 

 water current at high floods. As an auxihary measure, small 

 ditches and banks, or low walls of pebbles, should be constructed 

 from the hue of blocks across the grounds to be protected, nearly 

 at right angles to the current, but shghtly inchning downwards, 

 and at convenient distances from each other. Rozet thinks the 

 proper interval would be 300 yards, and it is evident that, if he 

 is right in his main principle, hedges, rows of trees, or even com- 

 mon fences, would in many cases answer as good a purpose as 

 banks and trenches or low walls. The blocks or pillars of stone 

 would, he contends, check the lateral currents so as to compel 

 them to let fall all their pebbles and gravel in the main channel 

 — where they would be rolled along until ground down to sand 

 or silt — and the transverse obstructions would detain the water 

 upon the soil long enough to secure the deposit of its fertihzing 

 slime. IS^umerous facts are cited in support of the author's views, 

 and I imagine there are few residents of rural districts whose 

 own observation will not furnish testimony confirmatory of their 

 soundness.* 



* The effect of trees and other detached obstructions in checking the flow 

 of water is particularly noticed by Palissy in his essay on Waters and Fount- 

 ains, p. 173, edition of 1844. "There be," says he, "in divers parts of 

 France, and specially at Nantes, wooden bridges, where, to break the force 

 of the waters and of the floating ice, which might endamage the piers of the 

 said bridges, they have driven upright timbers into the bed of the rivers above 

 the said piers, without the which they should abide but little. And in like- 

 wise, the trees which be planted along the mountains do much deaden tha 

 violence of the waters that flow from them." 



Lombardini attaches great importance to the planting of rows of trees trans- 

 versely to the current on grounds subject to overflow. — Esa/me degli Studi ml 

 Tevere, § 53, and Appendice, §§ 33, 34. 



