rest simply on mudsills. Suitable drains and wings must be provided at both ends of the flume. Where bench flumes are constructed it is best to make the bench twice as wide as the flume in order that there may be a footway alongside. In such flumes the foundation is simply mudsills and crossbeams.

In sheathing a wooden flume it is best to use large wire nails or cut spikes for the floor, but the sides should be fastened with bolts through inside cleats at the joints. If nails are used in the side planking they will rot out and it will be found impossible to keep the planks on.

The weak spot in every flume is at either end where the woodwork joins upon the earth or terreplein, as the case may be. There the earth should be carefully puddled at the apron and the whole surface from side to side of the ditch, and the sides as well, should be tamped and retamped. Retaining walls or riprap at the sides. and embracing the flaring wings may be employed, but in any event the tamping must be thoroughly done and the work gone over time and again if needs be in order to prevent the possibility of washing out. This tamping will be necessary if either the drop box or the inclined apron be used.

The bracing of a flume is an important matter, especially with deep flumes. A good system of side bracing is depicted in the bridge flume across a stream, and shown in Figure 30.

Cross-section braces are often made with iron rods running through the side posts and tightened with nuts and washers. Any builder can arrange the matter of the bracing to suit himself.

In very high flumes a lofty trestle work may be required. If this is the case it is better to build the bents in sections on the ground and then raise them into position by means of tackle blocks and a windlass, or by using a steam hoisting drum if the same may be readily ob

tained without much expense. The modus operandi of hoisting these great trestle sections is clearly illustrated in Figure 31, which is a scene taken by photograph during the construction of a high flume near San Diego, California. As a general rule such structures as this are not practicable.

The great bench flume on the High-line canal in Colorado is illustrated in Figure 32. This flume is twenty-eight feet wide, seven feet deep, and is set on a grade of from five to eight feet to the mile, its total length being 2640 feet and its capacity 1184 second feet. The timbers supporting the flooring are sufficiently heavy and abundant to render the work substantial, while the sills supporting it are well braced and framed. The side braces supporting the uprights are peculiarly and expensively housed by letting them into iron castings or shoes at either end. These shoes, bolted to the wood work of the flume, cannot be said to have increased the life of the structure, as they have caught rain or leakage water and have thus added greatly to the deterioration of the wood.

River. Another notable

Fluming Across a flume is shown in Figure 33. It is the wooden flume across the Pecos river in New Mexico. The bottom of this great flume is 40 feet above the river bed, it is 25 feet wide in the clear, 8 feet deep, 475 feet long, and rests on substantial trestle work with spans 16 feet in length. Across the river bed this flume is founded on cribs drift-bolted to the solid bed rock of the river and filled with rock. The abutments of this flume at its junction with the canal, which runs on top of the terreplein, consists of wooden wings set back a distance of 12 feet into the earth, well braced, and supported on anchor piling and filled with earth. The planking of these wings is two inches in thickness. The flume rests on five sets of 12x12 timbers forming each bent of the tres