In the operation of the larger canal struc tures mechanical power has almost entirely superseded hand-operation. The great advances made in the development of electrical equip ment render electric power particularly suitable for canal service. Also by its use the best means of lighting for night operation can be obtained. Where water power is available at a lock, a hydro-electric plant may be installed. In some cases, where power may be needed at times when water power is not available, as at movable dams, the electric generators are driven by gasoline engines. Electric power has the advantage of ease in distribution to points where it is needed and also flexibility in the amount employed. In addition, the modern equipment for lock operation is damaged very little by flood water. The equipment is often quite extensive, as on the Panama locks at Gatun, where all the operations are indicated on a board or diagram, which automatically shows the position of all the moving parts of the locks at all times.
Any project for canal construction must necessarily be considered from three stand points — the commercial, the engineering and the financial. From these standpoints there must be considered not only the subjects that have already been discussed, such matters as terminals, power-supply and types of locks, darns and a host of lesser structures, but also the more general problems that arise in canal building, and which remain for discussion.
These problems are so many and so inter dependent that they do not readily lend them selves to brief classification. However, under three main heads— (1) dimensions, (2) route and (3) water-supply—the most important can he considered.
1. Several elements enter into a determina tion of the dimensions for a canal. In general a large boat can carry freight cheaper than a small boat, but unless the traffic is sufficient and of the proper kind to keep the large boat working to capacity, a canal of large size is not economical. A canal often terminates at a large lake or river or at the ocean. The ques tion then arises as to whether it is advisable to make the waterway to fit the boats which navigate these adjacent channels or to use smaller boats and transfer the cargoes. The nature of the territory traversed is also a de termining factor. If natural waterways are available, then a larger channel may be de sirable, since it can be made without excessive cost and will permit greater speeds. The necessity of bridges has a bearing on the sub ject. If they must be fixed bridges, the mini mum clearance tends to limit the boat dimen sions and through them the channel dimensions.
Until recent times the question of speed has not had much bearing on canal dimensions. On the old and small canals the permissible speed did not exceed three and a half or four miles an hour, this limit being necessary because of injury to the banks by wave action. Since larger channels and canalized rivers have come into use, higher speeds are obtainable. Just how high speeds will eventually be attained is hard to say. The economical speed probably has not yet been worked out ; at least it is not generally recognized. Doubtless higher speeds
are attempted than are warranted economically. In a restricted channel, such as most canals must necessarily have, the power required for a speed in excess of about five miles per hour increases much more rapidly than does the resulting speed attained. The necessity for a considerable amount of water under the keel has not been appreciated by canal boatmen of the old order. They have usually crowded the channel dimensions beyond a reasonable limit by the boats they have used, not realizing that they were defeating their own ends by in creased cost for traction. On some of the recently improved canals the allowable speeds change with the locality. For example, on the New York Barge Canal they range from 4 to 10 miles. From this discussion it appears that, if a given speed must be attained on a canal, then the channel dimensions must be planned accordingly.
Closely allied to the question of speed is that of power. In the primitive canals man furnished the motor power, pushing the boats by poles, rowing them or drawing them by ropes from the banks. Then came the use of animals on a towpath. This was the common method until the modern era of improvement. Sometimes locomotives have replaced the ani nals. Steam propulsion has been in use to a limited extent on various canals for many Experiments in electric propulsion have been numerous, but no very successful system has yet been developed.' A cable or a chain along the bottom 'of the canal has been used in some places, especially in Europe. These are either gripped or wound over a drum on the boat. According to modern methods canal boats are self-propelled or move in fleets of one power boat and one or more consorts. The newer canals are not provided with towpaths.
2. The early canals followed the natural contours of the ground much closer than do modern canals. Because of difficulties con nected with stream canalization, preference was usually given to the building of independent channels, which often were close to but slightly above the streams. As previously stated, mod ern practice favors river canalization. After certain general features of location have been determined by commercial and broad topo graphical considerations, the detailed location of a canal is distinctively a technical problem, in which questions of engineering expediency and relative costs play the chief part. The desiderata sought in canal location are short ness of route, minimum of curvature, least num ber of locks, all possible elimination of inter mediate summit levels, minimum of excavation and embankment, avoidance of a channel above surrounding country, greatest ease of excava tion consistent with stability, suitable founda tions for structures, accessibility to water supply, least interference with adjoining private, municipal and industrial interests, utilization of natural water courses, etc. This subject of location, like that of dimensions, is complicated. Only by careful surveys and comparative plans and estimates can the questions be solved.