DRAINING. 



77 



Drying of 

 spring 



grounds. 



Draining, pletely intercepted ; but, independent of the first cost, 

 the expence of keeping such a drain in order would be 

 very great, the depth in such a case being considera- 

 ble. Another expedient that occurs, is to fill up the 

 trench, thus formed, with a regular puddle wall, or par- 

 tition of clay and gravel, loamy earth, or black raw 

 peat moss, wrought with water to near the surface, be- 

 hind which the water, if properly intercepted, must 

 rise as behind a dam ; and when we have it within two 

 or three feet of the surface, a drain may be formed in 

 the usual way, by which the superfluous water is led to 

 a proper outlet, and which in case of need is easily ac- 

 cessible ; by this means the upper part of the field is 

 so far drained, as to have an outlet two feet lower than 

 before, and we acquire such a command of the water, 

 that it may easily be kept up to its original level, while 

 the lower parts, which were formerly of the nature of 

 quicksand, and covered by morass, are entirely pro- 

 tected from upper waters, and have their proper waters 

 drawn off by the bleeding drain cc, as before. \Yhere 

 the overlying strata EF are of an impervious nature, 

 the wetness of the sand may be, in a great measure, 

 owing to the surface waters of a great extent of sloping 

 ground descending over the surface EF, and being ab- 

 sorbed at F into the sand. In this case it is evident 

 that these surface waters may be intercepted by a shal- 

 low drain, on the retentive soil above F, and led away 

 to an outlet before they descend into the sand. It is 

 equally evident, that we must be careful not to cut the 

 sand in this drain, or, wherever that is unavoidable, 

 that we line the trench, so as to prevent the water from 

 sinking away ; yet in this case, especially if the up- 

 lands be in tillage, the drain will soon puddle itself up, 

 and be sufficiently retentive even over the sand. 



The next case for consideration is, that where the 

 stratum of sand, or other porous matter which conveys 

 the water, dipping faster than the surface of the ground, 

 does not crop out, or appear at the lower edge, but 

 runs forward under the surface, and is covered by a 

 layer of clay or other retentive substance. 



Fig. 10. exhibits a case of this kind, where the watery 

 stratum DC descending from the porous upland DKL, 

 having no outlet at the point c, is covered by the re- 

 tentive clay BEFG, extending back to H. In this si- 

 tuation, the water finding no outlet, will accumulate 

 in the stratum DC, and be pent up as in a vessel, un- 

 til it rise to the upper edge of the covering, and flow 

 over as at H. Now, this level of the outlet being con- 

 siderably higher than the surface of the covering of 

 clay below, it is plain that there must be a strong pres- 

 sure upwards against the bottom of the clay, inso- 

 much that, if a pipe was put down at G or E, to 

 reach the sand, the water ought to rise in it to the le- 

 vel of the fountain H. If the bed of day, as from C 

 to F, be of sufficient depth and tenacity to resist this 

 pressure, the soil on the surface will be no way in- 

 commoded ; but if the covering l>e any where weak 

 or thin, as from G to H, the head of water pressing 

 against it will force some of the weaker places to give 

 way, when it will burst out, and form a spring as at 

 MM, and the water will immediately subside; and 

 should this not be sufficient for the discharge of the 

 whole in wet seasons, the water will again rise, so as 

 to run also at other higher and higher openings, which 

 after some dry weather will cease ngain, though the 

 lower may still continue running. Tin; upper level of 

 the water will never subside so low as the spring MM, 

 though it may remain very little above it, since at 

 least acme force will be required to press the water 



4, 



PLATE 

 CCXXXIII. 

 Fig. 10. 



through the obstructions in the sand. From this Draining, 

 cause, the ground from K to H, though of an absor- 

 bent nature, is frequently retained in a state of wet- 

 ness, similar to that at CG, Fig 9. on account of the 

 moisture standing high in the subsoil, and, if left to na- 

 ture, will be soon covered with moss. Again, where 

 the texture of the clay covering is sufficiently strong to 

 prevent springs from bursting out, yet the water will 

 squeeze through all the pores and crannies, so as to 

 form a field of spouty clay soil, producing only rush- 

 es, or other aquatic herbage, or brushwood, as from 

 H to G. Where the depth of clay is so great as to 

 prevent the oozing from being of much consequence, 

 yet the water standing high in the subsoil, forms a 

 field of cold, damp, clay land, as from M to F, and F 

 to E, liable at the same time to be injured by the sur- 

 face water from the springs above. In this situation, 

 the cure is to form a drain in the neighbourhood of the 

 lowest springs, and at such a level that the water which 

 runs in it may be so much below them, as to leave the 

 land dry. This ditch must be sunk down in various 

 places, so as to tap the inferior watery stratum ; upon 

 doing which, the water lodged there will issue out in 

 abundance, and flow along the drain ; and having now 

 found a lower outlet than the former springs by which 

 it if sued, these will quickly fall away and dry up ; nay, 

 it' the stratum be of great extent, the same effect may 

 extend to several boggy lands in the neighbourhood, 

 and, to appearance altogether unconnected with the 

 first. The height of the confined water being now di 

 minished, the pressure upwards against the cover will 

 cease, and this being the only cause of injury, a radical 

 cure will be effected ; but no hollow subsoil draining 

 could have had this effect, although the land might be 

 somewhat relieved thereby, in many instances, espe- 

 cially if the drains should any where touch the stratum 

 of gravel or sand in which the water was contained ; 

 neither would any benefit be derived from a catch- 

 water drain, made at H or K, as in the last case ; or 

 even if we could sink down through the whole mass of 

 sand, and bring up a puddle wall from the firm clay, 

 would it be effectual, for such a dam exists, in fact, 

 already in the covering of clay, BGH ; and though we 

 cut off most part of the supply thereby, the water in the 

 bed of sand HC is not removed ; the spring M which 

 still delivers the little water that may insinuate itself, 

 may be greatly weakened, or even cease to overflow, 

 but the hydrostatic pressure against all the lower sub- 

 soil will still remain as before. We mention this the 

 rather, that the unexperienced drainer may be on his 

 guard, and not proceed to work until he is well assu- 

 red of the nature of the case before him ; for the mode 

 of proceeding in one of these cases would be altogether 

 useless in any of the others. 



Having brought up the outfall, or tail drain BG, and 

 formed the tap drain gGg along the lower springs, our 

 next operation is to open a communication with the wa- 

 tery stratum below, if that has not already been effected 

 in digging the tap drain. Now, as a few passages will 

 be sufficient to emit all the water, provided their area 

 exceed that of all the springs, there can be no necessi- 

 ty for sinking all the tap drain to that depth. Small 

 pits may be made at convenient distances, and, to pre- 

 vent them from choking, they may be filled with 

 stones, dried peat, or the like, through which the wa- 

 ter will rise freely. But, in general, unless where the 

 stratum to be pierced is very stony, and even in that 

 case if it be deep, it is much easier, and less cxpcn* 

 sive, to make use of the boring auger, with which; 



