Book III. 



IRRIGATION OF GRASS LANDS. 



729 



a way as tliat the earthy particles it may contain may be deposited as equally as possible 

 over the whole surface to be irrigated. But it is to be observed, that this mode of applying 

 water must not be exhibited as a perfect model. If it should answer the purpose of a 

 coat of manure, upon such an extent of ground, it is all that can be expected, and will 

 amply repay the expense. Losing fall is wasting water. 



44o5. The drains of a water meadow require no greater declivity than is necessary to carry the water 

 from the surface : therefore the water ought to be collected and used again at every three feet of the fall, 

 if it be not catch-work. It is sometimes difficult to do this in bed-work meads ; but where the upper part 

 of the meadow is catch-work or in level beds, and the lower part not too much elevated, it may be done. 

 By collecting and using the water again in the same piece of ground before it falls into the brook, a 

 set of hatches is saved ; and it is not necessary to be very particular about getting the upper part into 

 high ridges, since that part of the meadow which is near the hatches generally becomes the best, and 

 the lower end of the field, being often the wettest or most boggy in its original state, requires to be 

 thrown up the highest. If the land is of a dry absorbent nature before floating, it is not necessary that 

 it should be thrown up into high beds, but merely as much inclined as will give the water a current. 



4436. Inclined planes are absolutely necessary for the purpose of irrigation. To form these between 

 straight and parallel lines, it is necessary to dig away land where it is too high, and move it to those 

 places where it is too low, to make such a uniformity of surface. The new-made ground will of course 

 settle in hollows proportioned to the depth of loose matter which has been recently put together, but 

 this settlement will not take place until the new soil has been completely soaked and dried again; 

 therefore these defects cannot be remedied before the second or third year of watering : it will there- 

 fore require more skill to manage a water meadow for the first three or four years, than afterwards. 



4437. Properly to construct a water meadoio is much more difficult than is commonly 

 imagined. It is no easy task to give an irregular surface that regular yet various figure 

 which shall be fit for the overflowing of water. It is very necessary for the operator to 

 have just ideas of levels, lines, and angles ; a knowledge of superficial forms will not be 

 sufficient; accurate notions of solid geometry (obtained from theory or practice) are 

 absolutely necessary to put such a surface into the form proper for the reception of 

 water, without the trouble and expense of doing much of the work twice over. {Obs. 

 on Irrigation, ^c.) 



4438. As an example of irrigating a meadow from both sides of a river, we take the following case from 



Boswell's treatise. From tlie upper part of 

 the grounds, two main drains {Jig. 684. a, a) 

 are formed at right angles to the river, one 

 running north, the other south, across the 

 meadow, to within about six yards of the Tence 

 ditches which surround it (b) and are used for 

 tail drains : by means of these fence ditches 

 the water is discharged into the river. A 

 wear erected across the river forces the 

 water into either of the main drains, which 

 is done by shutting the other wear close. 

 When there is not water enough, or it is not 

 convenient to water both parts of the mea- 

 dow at once, by shutting close one of the 



, wears, the current is forced into that main 

 ^ whose wear is open, thence to be conveyed 

 through the trenches over the panes, to water 

 that side of the meadow ; then by shutting 

 that, and opening the other, the opposite main 

 is filled, and by means of the trenches that 

 side of the meadow is watered in the same 

 manner ; and lastly, by shutting them both, 

 and opening the river wear, the water flows 

 in its usual course, and the land on both sides 

 is laid dry. From the main drains (a, a) the 



water flows along the highest part, or crowns of the ridges in the trenches (c), and is carried off" to the 



tail drains by the trench drains (rf). 



4439. As an example qf an irregular surface watered from one side of a river, we shall have recourse 



to the same author. There is a wear 

 (Jig. 685. e) erected across the river, 

 and another across the head-main (a), 

 from which proceed three main and 

 branch trenches {g, g, g, and /, /), 

 which water the whole meadow. 

 There is a tail drain (Z>) for carrying 

 off" the whole of the water by means 

 of the drain trenches {d, d). The 

 water, having thus passed over the 

 field, is returned to the river by the 

 tail drain already mentioned. When 

 it is desired to withhold the water, the 

 wear of the head main () is shut, and 

 that of the river (e) opened. It will 

 be observed, that in this design there 

 are branch trenches (/,/), and vari- 

 ous gutters (A, h), taken out of the 

 ends of some of the trenches, to carry 

 the water to the longest corner of the 

 panes, and sometimes taken out of 

 different parts of the trenches, to water 

 some little irregularities in the panes, 

 which, without such assistance, would 

 not have any water upon them. There 



is a sluice if) erected at the end of one of the small mains, to force the water into the branch trench 

 adjoining ij\ that being the highest ground. 



