Wide Hydraulic engineering in its practical application thus calls into play almost the entire range of civil engineering activities and requires co-operation at one time or another with the chemist, physicist, electrician, topog rapher, geologist, meteorologist and with other students of natural phenomena. Its distinguish ing feature is that fundamentally it deals with water in its various phases and has for its special province the practical application of the three distinct sets of laws or principles, namely, (a) hydrostatics, which relates to liquids at rest and has application in particular to the pressure of water against a dam or other re straining body; (b) hydraulics which con siders liquid in motion, as, for example, the action which takes place through an orifice in the dam or restraining wall; and (c) hydro dynamics or hydro-mechanics, which discusses the effect of a stream in motion issuing, for example, from an orifice and acting upon a water wheel or other mechanical device.
Historically hydraulic engineering is among the most ancient of the recorded activities of men. The Egyptian engineers are known to have largely controlled the flow of the Nile and to have built canals and reservoirs whose magnitude caused them to be mistaken for works of nature. Almost innumerable works for storage and distribution of water to agri cultural lands have been built in India and Mesopotamia. Aqueducts, the remains of which still exist, were built by the Romans and other people of antiquity. Although a high de gree of mechanical skill was developed in dis tributing the water supply to houses, baths and fountains, the principles of water measurement were not understood until within comparatively recent times. There is now a steady advance in experimentation to discover the laws which govern the movements of water under varying conditions, such as the form and character of material composing the channels or orifices along or through which the movements occur. The fundamental formula now accepted is that suggested by Chezy in 1775, v Vrs, hi which v represents the mean velocity of the fluid, r represents the hydraulic radius and s the slope of the surface. The value of c is determined by experiments. Kiitter, a German scientist in 1868, from the results of data then available de veloped the formula, expressed in feet per second, The factor n termed the coefficient of rough ness varies with the nature of the channel and its degree of smoothness. The values of ti for channels of various types are as follows: 0.010 Planed lumber or plaster.
0.012 Smooth cement lined section.
0.015 Smooth brick or vitrified surface. 0.017 Rubble.
020 Firm trimmed soil.
0225 Canals in good condition.
0.25 Canals in average condition.
0275 Canals below average condition.
0.030 Canals in defective condition or rivers. 0.035 Very defective channels.
Municipal Supply.— At the present time the greatest activity in 'hydraulic engineering is in connection with procuring water, suitable in quality as well as quantity, for municipalities or similar communities. It is no longer con sidered advisable to take water directly from the flowing streams because of the widespread pollution of these due to increase of population. In most localities the treatment of the water by filtration must be undertaken, necessitating ex= tensive works. The ideal condition for obtain ing water for drinking and related purposes is from some elevated watershed which can be protected from intrusion and where the erosion of the soil may be prevented by the mainte nance of forests or other suitable vegetation. Such conditions are found, for example, in the water supply of Portland, Ore., which ob tains its water from a national forest. These favorable surroundings, however, are rare and N in case of large cities such as ew York and Boston it has been necessary to purchase large areas of land near the head water of small streams and build storage reservoirs, in some cases removing towns and factories in order to secure the necessary land and to the purity of the supply. Among the more notable works are those of the city of Los Angeles, Cal., which brings its water supply from Owens Valley, a distance of upwards of 240 miles. As contrasted with this is the abundant supply of the city of Chicago, pumped from Lake Michi gan, being obtained through tunnels extending out for several miles under the margin of the lake to avoid the pollution. This city dis charges its sewage inland through the Illinois River which empties into the Mississippi near the intake of the Saint Louis waterworks, which utilizes, after filtration, the muddy and polluted waters received from the vast drain age area above.
There has been steady progress in the art of supplying water to towns during the past century and now the questions which the hy draulic engineer is required to consider in the design and construction of any waterworks em brace a great variety of subjects. It is neces sary to consider: 1. The quantity of water likely to be needed. There is not yet any consensus of opinion among engineers on this point, the estimates varying from 100 to 150 gallons per day for each resident of the district to be supplied, at the expiration of 20 ears from the inauguration of the supply. The prospective population is estimated from the records of past growth of die district and the growth of districts of simi lar character of occupation.