The Water-works at the Hague, Holland.
Similarly to the water-works supplying the city of Amsterdam, those for the Hague collect their water from a piece of sandy foreshore some 1600 acres in extent, and depend entirely on the surface water falling on this ground and percolating to a level at which it can be conveniently collected, carried to the filter beds, and ultimately pumped to its destination. They were first started in 1872, when an open collecting canal was dug out some 18,400 feet, nearly 3^ miles long, with a number of small side branches. An interesting description of these works is given in Engineering.
The ground water level on the line of this collecting canal varied from three feet to three inches above datum to twentysix feet above datum level, the former near the pumping station, the latter in a part of the sandy plain crossing the direction of the canal and about 2000 yards wide. The total length of the canal is divided into five sections, of which particulars are given in the table above.
In the latter part of 1874 these works were ready and able to supply 900,000 gallons daily. In 1880, however, the demands had increased to such an extent that means for a larger supply had to be considered, and in consequence of local conditions it was decided not to extend the length of the collecting canals, but to deepen them, and by this means to gain a larger percentage of the surface water from the same area.
In the first year only the first section of the canal, some 8500 feet in length, was deepened, at a cost of about ^320, and before any further work was done, a departure in the arrangement was settled upon. Up to this time the water had always been pumped out of this open canal, discharged upon filter beds near the pumping station, and then by means of force pumps conveyed to its destination in the distributing system. A largo percentage of the water was thus lost by evaporation, and it appeared to the engineer, Mr. Waldorp, that a considerable saving might be effected by collecting the water in pipes instead of open canals, and in addition by surrounding the pipes with a filtering material, thus avoiding the necessity of surface filtration later on. The whole collecting ground consisting of clean pure sand, the water is naturally filtered, and once collected in closed conduits, might lie thus utilized. It was further decided in the extension to arrange the deepening in such a manner that the bottom of the collecting pipe and canal formed one continuous level, for which purpose the far end of the canal had to be lowered some eight feet.
The system adopted was to lay with partly open joints earthenware pipes of 21-inch diameter for the main, with smaller branch pipes joining into this. To be able to lay these pipes, it was necessary to form a trench by means of planks, to keep this trench dry by pumping it out, and to lay the pipes in the bottom. The mode of erecting the timber sides of tintrench usually adopted in similar ground is to attach a small iron pipe to a plank about seven inches wide and two inches thick ; this pipe is connected at the top by means of a flexible hose with a hand force pump, and as the water issuing at the end washes away tire sand, the plank is lowered into the ground. In this way two men could place from twelve to fifteen planks, eight feet long, in an hour, much time being lost in hauling up the pipe and reattaching it, and the planks had to be suspended from a tripod, which had to be moved frequently. With a view of saving labor and expense the engineer devised a new plan, which proved very satisfactory. An iron pipe as before, but with holes drilled in two rows op|Msite each other, was used, connected to a more powerful force pump, and after this was once vertically forced into tinground, it was dragged along, cutting a trench in its course, into which the planks were placed, so that with this arrangement four men were enabled to plaec from 80 to 100 planks in an hour, while a^ many as 51×1 could lie lifted in an hour. The pumping engine adopted by the engineer was Merryweather and Sons’ “ Valiant ” type as supplied to the British government for use in the Soudan, and which was selected on account of its power and the case with which it could he transported across the sand. Where peaty ground is met w ith, a pipe fitted with teeth in addition to its water nozzles is used, and being dragged up and down against the ]eaty soil, the teeth, in addition to the action of the water, remove the obstacle. The timber sides formed, the trench is cleaned out to within about eighteen inches of the bottom of planks, a layer of shell sand four inches thick is spread over this plank bottom, and upon this the drain pipes are laid About eight inches away from the pipes, longitudinal planks are laid, ami the space 1/etwccn the pipe and the plank is tilled also with shell sand, which latter material also covers them to a depth of about four inches, so that they are completely bedded in shells. A layer of coarse river sand is next placed over the top, and the breach is then completely filled in with the surrounding sand. The planks are then drawn and the collecting pipe is ready for use. The object of so carefully bedding the pipes in shells is to keep the fine drift sand out, which would otherwise enter through the joints.
There is but very slight wear on the planks, and they have been in use for from three to four years for the same purpose. Circular reservoirs are arranged at intervals along the pipe line, where a branch collecting pipe, of which there are seven in all, joins the main. These branch pipes are, if less than 1300 feel long of nine inches in diameter, while for longer lengths they are twelve inches in diameter. The wells consist of rings made of cement concrete, built up to the required height. During the execution of the works a portable engine driving a centrifugal pump was used for keeping the trenches dry. By the method thus employed a very considerable saving has been effected as against the usual inode of working, and the whole arrangement has proved far superior and far cheaper than enlarged and deepened open canals would have done.
An interesting application of this system of water collection was made in providing a water reservoir for fire purposes. The well consists as liefore of concrete rings, and four collecting pipes nine inches in diameter and eighty feet long each supply the same with water. These pipes are bedded in shells as described lieforc at a level of six feet below the subsoil water level, and an iron manhole is provided to enter the well on the street level. The whole is placed in fine drift sand on the Prince Hendrik Plain in the Hague.
One of Merry weather and Sons’ powerful steam fire engines, capable of throwing 330 gallons |er minute, was used to test the efficiency of this arrangement, and while during the first nineteen minutes the water level in the well fell about four feet, it afterwards remained stationary at this level, although pumping was continued at full force for thirty-two minutes. The trial was considered to be thoroughly satisfactory. The cost of this fire well arrangement was only £20.
The inventor of what may be called the improved hydraulic trenching system suggests further, that it might be utilized to remove sand from a wrecked vessel and thus enable the wreck to be towed into some convenient spot. I le proposes to arrange a long perforated pipe around the vessel, charging it with high pressure water by means of a flexible communication ; on being dragged along the issuing water would cut a channel into the sand, forming n road for the vessel to travel on.