The United States government has recog nized the necessity of furnishing data of this kind and has instituted through its Weather Bureau and Geological Survey series of obser vations of climatic factors and steam flow, which enable the hydraulic engineer to make his estimates with, a fair degree of accuracy.
Rapid advances have been made throughout the United States, especially in the western or arid portions since 1900 in the construction of large storage reservoirs and distributing canals for bringing water to agricultural lands; so that in 1919 about 15,000,000 acres are under irrigation out of possibly 40,000,000 acres in all which may be watered. Also in other parts of the country drainage works have been provided for say 10,000,000 acres out of 70,000,000 acres needing such treatment to relieve the low lands of an excess of moisture. Large works have been and are being built in arid countries, not ably in Egypt India, South Africa and Aus tralia by the British engineers. In other dry lands, notably in Spain and Italy, there has been a gradual development and in many cases resto ration and enlargement of great works built centuries ago.
Disposal of Waste.— With the rapidly in creasing density of population, the question of disposal of sewage from towns and cities is offering more and more intricate problems to the hydraulic engineer. In this he must call to his assistance the bacteriologist and chemist. Closely connected with the sewage problem is that of disposing of manufacturing or indus trial wastes, especially where the custom has grown up of discharging these into the sewers or natural streams. Water is the universal carrier and solvent and of necessity must be largely employed in removing noxious materials.
The opinion has been advanced that the streams of the country should be preserved in their original purity and that each city or manu facturing establishment should be required to dispose of its sewage or waste in some other way than by using water as a carrier. Prac tically, however, it has been found that the natural streams must be used to a continually Increasing degree in removing sewage, prefer ably of course after its more or less complete purification. The hydraulic engineer and his advisers are becoming expert in reducing the amount of pollution and in maintaining a high degree of purity in the effluent which escapes from the sewage or waste treatment works, and which flows away in the natural stream channels so that it will not be injurious to health or offensive to the senses.
Manufacturing.— The next large use of water with which the hydraulic engineer is concerned is in connection with manufacturing — this coming fourth in the scale of importance to human life, following after drinking water, food production and sewage or waste disposal.
The problems in many respects are similar to those just enumerated as they are concerned with the provision of an adequate quantity and quality. In manufacturing water may be needed either for direct consumption or simply in washing or cooling. Included under this head is the use also of water for steam purposes in which case it must be free from mineral sub stances which would encrust the boiler or cause other deleterious action. For each purpose of manufacture there are certain requirements of purity, such, for example, in paper making where freedom from soluble matter is essential and where the hydraulic engineer and chemist must work together.
Water Power.— Next in importance after manufacturing is the employment of water in the production of power. As compared with other uses, the quality of water —its mineral contents or freedom from bacteriological life— is insignificant. What are required for power production are large volumes with steady flow and an adequate fall. The use of water for power is ordinarily compatible with its later employment for irrigation or in manufacturing —so that development of water power often goes hand in hand with the upbuilding of municipal supplies, irrigation works or other industries.
Through the United States the smaller water powers were sought and developed about a cen tury ago but with the introduction of the steam engine these water powers were abandoned to a large extent and the cities which had origin ally been located near the water power gradu ally came to depend more and more upon the use of steam, while other cities built at more convenient railroad points have surpassed them in size and in manufacturing capacity. The immobility of water power and the former im practicability of transmitting power to any considerable distance from the water fall re sulted in stagnation or even abandonment of the use of the water in power production. The situation was changed, however, by the inven tion of methods of electrical transmission of power. Since 1900 there has been a notable revival of interest in water-power development. Hydraulic engineers are being called upon to a greater extent than in the past to utilize the larger and more inaccessible streams of the country. Similar conditions prevail throughout the world and in localities such as in Norway and Sweden the water falls are now being de veloped and utilized by electrical transmission, the cheap power making possible the manu facture of certain chemicals, particularly the fixation of nitrogen from the air to form the basis of agricultural fertilizers.