The width of drainage gullies should not be less than 18 inches, thus allowing easy use of brushes issued. With these brushes and adequate gullies, very long stretches of trench can be kept in excellent condition when the trench is wide enough to allow the drying effect of wind and sun to reach the bottom. The time spent in making these gullies is saved over and over again. If there be no natural valley or dip, a sump-pit is generally dug, the size depending on the energy of the troops digging it, but generally it is about 10 feet below the level of the trench it drains, and anything from 8 feet on in diameter. It is dug some fair distance from the trenches and in a position that will allow the maximum amount of gullies to be led to it from that particular section of the trench.
After having this system worked out, the next thing is to ascertain what parts of the rest of the trench system will not be affected by this drainage, and there to dig similar sump-pits just to the side of the trenches drained, small gullies leading to them. These need only be about 6 feet deep below the trench level and 4 feet in diameter. A short gulley, 12 to 15 inches wide and 2 feet long, should lead from the trench to the sump-pit, as shown in sketch of trench system.
Sometimes the sump-pit may be semi-circular and cut into the side of the trench, but in this case some barrier must be put across it to prevent men falling in while traveling at night. The former system is far more satisfactory, and especially so when the trench is hardly wide enough to allow the passing of traffic without touching the sides of the trench.
Entrances to these sump-pits must always be kept clear of all obstructions. Very often a ridge of mud from a man’s foot-mark is enough to put a sump-pit out of action. They should be continually emptied by pumping the contents over the parapet, or carrying in pails to the nearest gulley.
The side sump-pits must never be cut under the wall of a trench. On very short notice the roof will take the place of the excavated soil and there will be no sump-pit.
It is not always that pumps are available, and the few of those which are, are of no practical use for a length of time sufficient to be of any value; in fact, they hardly repay the fatigue entailed in getting them to the trenches. For ordinary trench drainage several small pumps are of far more use than one large one, as the range’s limited by the difficulties of removing it or by the length of pipe attached. These pumps, whether large or small, must be given a large and substantial platform, placed in some central position among a number of sump-pits. Each pump must have not only a discharge pipe, but a suction pipe, the latter being movable from one pit to another in the pump’s area without moving the pump. The placing of these pumps must be thorough and systematic, and those sump-pits not reached by pumps must be kept empty by means of pails.