722 



PRACTICE OF AGRICULTURE. 



Part III. 



old channel For the current of floods, by carrying off the earthy particles with which they come in 

 contact, will soon enlarge it. It is nevertheless right to give ample room in the new channel, lest the 

 first flood should prove high, and, by bursting its bounds, force its way back to its former course. 



4375. A neiv river course requires to be carefully attended to, during a few years after it is opened, to 

 see that its channel preserves its straightness, and that no breaches are made or threatened in its banks. 

 Considering the uncertainty of extraordinary floods, it cannot be said to be out of danger in less than 

 three years : hence it becomes prudent, when a work of this nature is contracted for, or undertaken to 

 be done by measurement at an estimated price or prices previously agreed upon (as it generally ought), 

 that the undertaker should agree to preserve the straightness of the channel, and uphold its banks during 

 that or some other time fixed upon ; and to deliver them up, at the end of the term, in the state and 

 condition specified in the contract. 



4376. A case of straightening the course of a river is given in The Code of Agriculture. The waters, 

 which in their crooked course were formerly almost stagnated, now run at the ordinary rate of the 

 declivity given them. They never overflow their banks. Cattle can now pasture upon those grounds in 

 which they would formerly have been swamped. The surface of the water being now in general four, 

 and sometimes six feet below that of the adjacent fields, this cut serves as a general drain to the whole 

 valley ; so that three hundred acres of meadow may be converted into arable land ; sixty acres of moss 

 may be improved into meadow ; and five hundred acres of arable land are rendered of double their 

 former value, (p. 319.) 



4377. Raising rivers to a higher level. As rivers and streams may require to be 



674 



deepened for the purpose of drainage, 

 so may their waters require to be 

 raised for the purpose of irrigation, 

 impelling machinery, or producing 

 cascades or waterfalls for the purpose 

 of ornament. Dams or wears for 

 this purpose should be constructed 

 so as to form a segment of a circle 

 across the bed of the stream, with the 

 convex side pointing up the stream, 

 and the ends abutting against a na- 

 tural or artificial bank (Jig. 674. ) By 

 this construction, the force of the 

 water, however great, will be effectually resisted, and the structure remains secure. The 

 greater the slope towards the upper side, the better, but the lower side should be nearly 

 perpendicular, that the water may fall over it without coming in contact with the face 



of the building. {Jig. 675.) 

 675 The wall (a) should be 



built of regularly hewn 

 stone, as should the abut- 

 ments (b); next the wall 

 there should be a mass of 

 = clay as a puddle (c), and 

 above that gravel or earthy 

 matter of any kind to a considerable slope (rf). Beneath the dam a considerable por- 

 tion ought to be paved (e). {Gen. Rep. Scot. vol. ii. p. 669.) 



4378. Heads, or banks of earth, for the confinement of water in artificial lakes or 

 ponds, are often constructed at great expense, and, not being properly formed, often break 

 out, and occasion considerable damage. The error in their construction is commonly 

 owing to the want of breadth at the base in proportion to their height, and their not 

 having a sufficient slope towards the water, nor a proper section of puddle in the 

 centre. (Ibid.) 



4379. Heads of loose stones of a large size (Jig. 676.) may be had recourse to in slow 



running rivers not subject to 



g7g high floods, and where there is 



such a superabundance of water 

 that no loss is sustained by the 

 quantity which flows through 

 the stones. Where it is re- 

 quired to retain the whole of 

 the water, a puddle bank should be carried up the middle of the dam. (Ibid.) 



Chap. III. 

 Irrigation, or the Improvement ofCidturable Lands and Farmeries by the means of Water. 



4380. The improvement of lands by water is of three kinds : irrigation, or the appli- 

 cation of water to the surface of the soil, and especially of grass lands, as a species of 

 culture ; warping, or the covering of the soil with water to receive a deposition of earthy 

 matter ; and the procuring or preserving of water by wells, reservoirs, and other means, 

 for the use of farmeries, live stock in the fields, or the domestic purposes of the fanner or 

 cottager. 



