Details as to location, layout or arrangement of plant are so involved with the topographical and other conditions peculiar to any particular dam that it is almost useless to lay down any but a few of the most general rules. However, kind and amount of plant are susceptible of more definite treatment. The following discussion is intended to be of assistance to constructors who are engaged in working out actual problems as well as to furnish an intelligent basis for rapid preliminary estimates. Roughly speaking the necessary and advisable investment in plant for the construction of a masonry dam of some magnitude may be assumed as from 75 cents to $1 per cu. yd. of masonry. The salvage on plant at the end of a job, while a more variable quantity, may be assumed as from 20 per cent, to 50 per cent, of the original cost.
Plant as discussed here is held to include in addition to actual cost of machinery, the freight, handling, wagon haul and erection; also the materials (as lumber and cement) entering into machinery foundations and housing; also any necessary roads or railroads built to reduce cost of haul or to provide access to or communication between different parts of the work.
The first question is the distance from the work to the nearest point on the railroad, and the advisable amount to spend in reducing cost of haul. If a wagon road exists it may be desirable to spend some money surfacing it or to reduce grades. If it is necessary to build the road it may cost anywhere from $1000 per mile in easy country to $25,000 per mile for heavy rock work in mountainous, inaccessible country. With a good road, with grades generally not over 6 per cent., with a length of haul such that loading and unloading take but a small percentage of the time of the teams engaged, with freight coming along with good regularity so that a regular force of teams can be organized and employed without much lost time, a widely applicable and fair rule for cost of hauling ordinary freight like cement, fuel, hardware, supplies, etc., is 25 cents per ton mile. Special or heavy pieces of machinery which require special trucks or which involve much labor loading and unloading may cost twice that.
However, such pieces form but a small part of the total tonnage. The above price might be reduced somewhat by using motor trucks.
In considering how much saving in cost of haul might result from building a railroad, the following actual experience is pertinent. The Reclamation Record for February, 1914, gives the construction and operating costs for such an industrial road at the Arrowrock dam. The distance from Barberton (the nearest railroad station) to the dam was 17 miles. The cost of hauling freight over the rough wagon road was $8 per ton, or about 47 cents per ton mile. Seventeen miles of main line and 2 miles of spur track required the excavation of nearly 250,000 cu. yd. of material, which was done by contract. Culvert and bridge building, track laying and ballasting was done by Government forces working an eight-hour day. The maximum grades on the main line are 1 1/2 per cent, and on the spur tracks 3 per cent. There are three wooden truss bridges on the main line, one 442 ft. long, one 166 ft. and one 366 ft. The total cost of construction was about $20,000 per mile. The rolling stock consists of two locomotives, two passenger cars, four flat cars, three box cars, miscellaneous hand cars, speeders, etc., and cost about $35,000. One train is run each way each week day, with double trips Saturday.
During two years operation by the Government January 1, 1912, to December 31, 1913, 30,337 train miles have averaged a cost of $2.34 per train mile, the minimum for one month being $1.53 per train mile. The total ton miles of freight amounted to more than three-quarters of a million, and 45,000 passengers were carried. Thus in this case the cost of haul was reduced from 47 cents per ton mile to about 9 cents, a saving of $6.46 per ton over the 17 miles. Assume charged against this saving the entire cost of 19 miles at $20,000 or $380,000, plus say $20,000 depreciation on rolling stock, making a total of $400,000. Then for a total volume of freight of about 61,900 tons the investment in the railroad is justified to say nothing of the values attaching to prompt delivery of freight and to good passenger service. Only surveys and a careful examination could determine the feasibility and cost of such a railroad. Allowable grades might be obtainable only at prohibitive expense and the cost of grading and bridging might vary widely from the above example. In addition to the grading and bridging the cost for ties, rails and laying would be $8,000 to $10,000 per mile.
In connection with a possible railroad consider the question of quarry location, and whether, if the quarry be at some distance from the dam, one railroad will not serve to transport stone as well as other freight and thereby furnish a further economic justification for the railroad. It might be that the choice between two or more possible quarry sites might be influenced by the possibility of combining the two reasons for building a railroad. As the total tonnage bears on the question of road or railroad, so does the yardage to be handled influence the amount and kind of plant at the site of the work. Other considerations are the manner of doing the work, which in turn depends upon the general design, the amount of water to be handled during construction, the length of the working season between interrupting floods or winter weather, the total time allowable for the work, etc. Generally speaking it would be silly to put as much plant upon a 50,000-cu. yd. dam as would be advisable upon a 300,-ooo-cu. yd. dam. On the other hand if there were but two months in spring and two months in fall between severe winter weather and a summer season of floods, it might well be necessary to put on a plant of many times the capacity that would be advisable if there were no interruptions from winter or from floods.
Another question which might affect the amount of advisable expenditure for plant is the amount of salvage to be reasonably expected in the particular case, considered in connection with the reduced operating cost which might follow from certain proposed additional equipment. Before discussing this question, however, let us briefly examine the principles governing depreciation and net plant account chargeable to similar jobs under different conditions of location and accessibility.