Pacific bridge, which withstood the flood, is a very heavy, double-track bridge, and was loaded from end to end with locomotives. Some idea can be formed of the débris which came down the river from the amount which was lodged against the piers and abutments of this bridge. (See Pl. V, B.) The damaged bridges were nearly all steel structures of about 200 feet span, resting on masonry or metal piers. Several of them were double-track structures. The cost of replacing them is estimated to be from one and a quarter to one and a half million dollars. One of the bridges destroyed carried a 36-inch watersupply pipe for supplying Kansas City, Mo., and a part of Kansas City, Kans., with water. As a result of its failure, the whole city was without water for twelve days, and the electric-light company, gas company, and street railways were compelled to shut down for lack of water.

The high

The highway bridge at Eudora was partly washed away. way bridge at Lawrence had one span washed away. The river at this point made a new channel around the north end of the bridge, washing away the Union Pacific freight station and several other structures. In September the total flow of the river was passing through this new channel.

The highway bridge at Lecompton was uninjured, but a channel was scoured around the north end of it. All the bridges across the Kansas at Topeka were destroyed except the Melan arch bridge, and the approaches of that were so badly damaged that for several days the only means of access between the north and south parts of the city was by boat.

By scouring action.-The damage due to the scouring action of the flood was very great, the railroad companies being the heaviest losers in this respect. Many miles of railway track located near Kansas River were washed away or badly undermined.

It can be shown mathematically that the increase in the scouring action of water and its transporting power is proportional to the sixth power of the velocity. If, for example, the velocity along the bed of a stream at a given point is 2 feet per second at ordinary stage, and during the flood the velocity is found to be 4 feet per second, then the cutting or scouring action of the water for the 4 feet velocity during flood is sixty-four times that of the 2 feet velocity at ordinary stage, and bowlders will be carried along during the flood that are sixty-four times as heavy as those carried at ordinary stage.

However, the power of a stream in flood to cut river banks and make new channels, as compared with its action at ordinary flow, varies at a much larger rate than as the sixth power of its velocity, because the toughness of a bank of alluvial material and its ability to resist scour decreases very rapidly from the bottom toward the top. Take, for example, the case of a stream flowing in a channel with banks 10 feet high. When the water is 2 feet deep it comes in contact

with only the lower 2 feet of the bank, which is tough and firm. When the river rises 3 feet, the water flows more rapidly and comes in contact with a part of the bank which is 5 feet up from the bed, and which is less tough and more readily scoured. When water rises to 8 feet or more, the velocity is several times greater than at the shallow depth and the water comes in contact with a part of the bank much more easily eroded than the portion near the bottom; hence the wear is very rapid during a flood, and in a few hours deep channels" are cut and acres of land washed away. This cutting action is greatest just below a bend in the stream. Here water tends to continue moving in a straight course, and hence strikes the concave surface of the bank just below the bend. When, as during the recent flood, the river rises high above its banks, it takes a straight course, regardless of its banks, and often does much damage where it was supposed the water could never reach. The new channel through North Lawrence' around the dam is 200 feet wide and so deep that the whole flow of the river passes through it. The bed of the Kansas at Lecompton Bridge was scoured to a depth of from 3 to 6 feet during the flood; a depth of several feet was scoured also for several hundred feet in width north of the north abutment. A large amount of material was scoured from the left bank of Republican River at the gaging station at Junction, and, in fact, in many places along the stream there is evidence of a very considerable amount of material having been carried away. In many places material has been deposited as well. Some of this deposit is fine silt which will enrich the land, but often it is sand which will injure it to a considerable extent.

HYDROGRAPHIC DATA OF KANSAS RIVERS.

METHOD OF OBTAINING DATA.

The United States Geological Survey has at present eight gaging stations in the Kansas River basin. Four of these are in the Republican River basin, two at Benkelman, Nebr., one at Superior, Nebr., near the State line, and one at the mouth of the river near Junction, Kans. There is one on the Smoky Hill River at Ellsworth, one on the Saline near its mouth, one on the Solomon near its mouth, one on the Blue near its mouth, and one on the Kansas at Lecompton. Six of these stations have been in operation about eight years. At each of these stations there is a gage for measuring the rise and fall of the water surface. This gage is read twice a day by a person living near by, and a copy of the reading is sent at the end of each week to a resident hydrographer who has charge of all the stations in that State. The resident hydrographer visits each station several times a year to measure the volume of water flowing and inspect the station. He measures the depth at 5-foot intervals across the stream and computes the area of the prism of water flowing.