The following table shows the distribution of the material removed from Gaillard Cut:

Cucaracha slide was very active from July to October, quiet during the dry season and active again with the beginning of the rainy season in April.

Culebra slide, east, has been very active since October 14, 1914, during which time over 4,500,000 cubic yards of material have moved into the canal and approximately 4,000,000 cubic yards additional in

motion.

Culebra slide, west, showed little activity throughout the greater part of the year, but in June, 1915, a general movement of the bank from stations 1771 to 1796 was noticeable, and it was estimated that 5,000,000 cubic yards of material were in motion on June 30, 1915. NOTE. This estimate based on a uniform slope to the canal prism from the farthest cracks, on an approximate 3 feet horizontal to 1 foot vertical slope.

Surveys of the canal in the vicinity of the active slides were made daily, the channel dragged and marked with buoys for the passage of shipping. At times the channel shoaled so rapidly that it was necessary to drag after the passage of each ship. At times such shoals required dredging before following ships could proceed.

All material removed from the Cut by ladder, dipper, and selfpropelling suction dredges was dumped in Gatun Lake, from Gorgona to San Pablo. Material removed by pipe-line dredge was deposited on dump in the Rio Grande Valley with the assistance of a 20-inch relay pump.

Navigation suspended on account of slides October 14 to 20, 1914, October 31 to November 4, 1914, and March 4 to 10, 1915.

Output of dredges was greatly reduced because of necessary daily channel clean-up for the passage of shipping.

SECOND DISTRICT.

Dredges were engaged during the year deepening and maintaining the canal channel at the Atlantic entrance; 1,044,575 cubic yards of material were removed. Of this amount 12,514 cubic yards were chargeable to construction work and 1,032,061 cubic yards to canal

maintenance.

No dredging was done in the Gatun Lake section (Gatun Locks to Gamboa Bridge).

Material excavated in the second district was dumped on Mindi Island, Cristobal Mole, east breakwater, and at sea.

MISCELLANEOUS DREDGING.

PACIFIC TERMINALS.

From the Balboa Inner Harbor 2,718,406 cubic yards of earth and 93,686 cubic yards of rock were removed by pipe-line and ladder dredges. The soft material underneath Pier 18 and the unloader wharf was sluiced out by dredge No. 85 and the hydraulic grader. Material removed by pipe-line dredges was used in reclaiming the swamp areas north of Balboa and in the San Miguel section of Panama City; that removed by ladder dredges was towed to sea and dumped. To maintain depths at berths along the Panama Railroad wharf at Balboa 14,128 cubic yards of earth and 4,434 cubic yards of rock were removed.

To prepare berth for tank ships at the Balboa oil dock 33,366 cubic yards of earth were removed.

ATLANTIC TERMINALS.

From the Cristobal approach channel 709,240 cubic yards of earth and 50,006 cubic yards of rock were removed; 201,240 cubic yards of earth from opposite piers Nos. 11, 13, 14, Cristobal Harbor; 113,659 cubic yards of earth from the turning basin at the entrance to the old coal dock slip; 21,074 cubic yards of earth from the coal dock slip and 5,116 cubic yards of rock at the west end of Pier No. 10.

From the submerged storage basin 132,867 cubic yards of coral rock were removed; 2,129 cubic yards of coral rock from the east berth; 35,711 cubic yards of coral rock from the west berth, and 132,167 cubic yards of coral rock from the berth and turning basin north of the Cristobal Coaling Station. In the government and private storage areas to elevation +2.0 feet 62,668 cubic yards of fill were placed; 26,846 cubic yards of fill placed under the east and 2,086 cubic yards of fill under the west concrete docks inclosing the submerged storage basin.

Around the substation building at Cristobal 6,650 cubic yards of fill were placed.

FORTIFICATION RESERVE.

In fills on the fortification reserve at Toro Point 477,898 cubic yards of material were placed and 407,724 cubic yards at Margarita Island.

EAST BREAKWATER.

In the core of the east breakwater at Coco Solo 252,319 cubic yards of coral sand and fingers were placed; 26,016 cubic yards of coral rock removed from Coco Solo Harbor; 5,074 cubic yards of fill placed in the pile yard; 23,057 cubic yards of fill in the relay station foundations; 35,758 cubic yards of sand and 200 cubic yards of rock fill in dikes.

The core of the breakwater was filled by running the dredge discharge line down the center of the breakwater trestle and discharging overboard. The greater length of discharge line used was 12,150 feet with one relay 4,200 feet from the dredge. Two northers, February 8-10 and April 4, 1915, were experienced. The norther of February 8-10, carried away a large part of the trestle, 13,200 feet of discharge pipe, and the relay pump house; also damaging the motors and

pump.

SAND AND GRAVEL PRODUCTION.

The sand and gravel necessary for construction purposes was excavated by dredges at the Chame sand pit and Chagres River gravel beds, transported in barges to the unloading docks at Balboa and Gamboa, for delivery to the various divisions and outside companies. The dredge Gopher operated in the Chame sand pit from July 1 to October 20, 1914, after which date all sand was supplied from the Chagres River beds. Sixty-seven thousand and seventy-five cubic yards were dredged and delivered to storage piles.

Ladder dredge No. 1 and pipe-line dredge No. 82 were operated in the Chagres River sand and gravel service, delivering 455,686 cubic yards of material to the Gamboa handling plant.

Suction dredge No. 82 was placed in the gravel service because of the demand for sand and screened gravel, it not being practicable to operate the screening plant with ladder-type dredge. Owing to the heavy repairs made necessary to the suction dredge, from the wearing of pumps and pipe lines, it was found to be more economical to retain both the ladder and suction dredges in the service, operating with single crews, the ladder dredge excavating run-of-bank and the suction dredge handling gravel to be screened.

The screen used was of the revolving cylindrical type, 9 by 14 feet, inside plates 2 inches and outside three-eighths-inch mesh, mounted on a barge provided with the necessary chutes for loading barges and delivering sand, and Nos. 1, 2, and 3 gravel.

No. 1 gravel was passed over the 2-inch screen, No. 2 through the 2-inch screen, No. 3 over the three-eighths-inch screen, and sand through the three-eighths-inch screen.

OBISPO DIVERSION.

The Obispo diversion, which carried all the drainage water east of the canal and between the Continental Divide and the Chagres River, was located very near and parallel to the canal from south of Empire to opposite Buena Vista. Where the diversion channel crossed valleys, large earth and rock dikes had been built forming lakes of considerable extent and in some cases 26 feet deep. The elevation of the water in the channel and lakes averaged 90 feet higher than mean water level in the canal and as a result the east bank of the canal was continually saturated with water, causing numerous slips and slides. These lakes and the channel between were drained into the canal by excavating a series of six ditches, one to each lake. The material was removed by hand, crane with clamshell bucket, and by sluicing with the hydraulic grader. A total of 21,700 cubic yards was excavated.

HYDRAULIC FILL NEAR PANAMA.

A gang of men was engaged in digging drainage ditches through the hydraulic fill on the reclaimed swamp lands at San Miguel and north of the Balboa Railroad station, from June 18 to 30, 1915.

DAILY REPORTS ON SLIDES.

A daily inspection and report on the slide conditions at east and west Culebra slides was made from December 18, 1914, to June 30, 1915. A continuous record of the horizontal and vertical movements kept, all new cracks and breaks located, noted, and reported.

REPORT OF RESIDENT ENGINEER, DREDGING DIVISION. 187

MINDI DIKES.

Three permanent rock dikes to replace the temporary dikes were constructed on the south shore of Limon Bay. Work was started in October, 1914, and completed in March, 1915. Dike A is 705 feet long, 800 feet west and parallel to the canal axis; B, 460 feet long and 1,300 feet west of the canal; C, 270 feet long and 1,800 feet west of the canal with a top width of 5 feet and elevation plus 2 feet M. S. L., side slopes of 1 to 1.

The rock was loaded into barges in Gaillard Cut, towed to the side of the dikes, reloaded into pan cars which were run out on the dikes and dumped. Seven thousand two hundred and forty-two cubic yards of rock were used on this work. The norther of February 8-10, 1915, caused some settlement of the dikes and they had to be recrowned, but no settlement was noticeable after the norther of April 4, 1915.

Timber groins, for protection of the beach, were built at intervals of 400 feet from Dike C, around the south shore of Limon Bay, to a point near Kinney's Bluff, also between the rock dikes and between Dike A and the canal, a total of 34 in all. Groins are perpendicular to the beach, 90 to 100 feet long, constructed of 6 by 6 inch posts driven on 6 feet centers and planked on both sides from one-half foot below to 2 feet above ground line, and extend from above wash line to beyond low-water line.

WATER HYACINTHS.

The destruction of water hyacinths in the canal, Gatun Lake and its tributaries, was continued throughout the year. The outfit used and methods employed were the same as described in the annual report for 1914.

One hundred and thirty-five thousand square yards of old hyacinths were killed by poisoning and about 600,000 young plants pulled up and deposited on shore. Very few old plants are now to be found and practically none have been allowed to seed since January, 1915, though the waters of the lake from Gamboa to Bohio and the Chagres Valley had been so thoroughly seeded prior to this, that it requires constant inspection, and a force of men to pull the young plants before they have had time to seed.

An inspection of the waters of Gatun Lake including the Chagres, Trinidad, Gatun, and Siri River Valleys and tributaries was made. No hyacinths were found in the lake north of Bohio or in the Trinidad, Siri, and Gatun River Valleys, although the upper reaches of these valleys are so badly choked with standing trees, snags, and drift, that a complete inspection was impossible.

The water hyacinth as found in the waters of Gatun Lake belongs to the family Pontederiaceae and is known technically as Eichornia azurca. This species is closely related to Eichornia (Piaropus) crassipes, the plant which is known in Florida and Louisiana as the water hyacinth.

The Isthmian species of plant is found in nearly all waters of the Atlantic slope, from Colombia to Costa Rica, especially the shallow lakes and more sluggish streams, and is commonly called "oreja de mula" (ear of the mule) or "buguclito" (little boat) by the natives.

During the year numerous tests and experiments have been made to determine as nearly as possible the habits and conditions under which the plant will grow.

The plant is propagated by stotons and seed, but principally from seed. The seed is very small and hard. After sprouting the young plant becomes attached to the bottom by numerous small threadlike roots. The character of the bottom is apparently immaterial, as they are found growing in either mud or rocky bottoms and in water 1 to 16 feet deep.

Young submerged plants have long narrow leaves, three-sixteenths of an inch wide by about 3 inches long, at intervals of about oneeighth inch, on opposite sides of the stem and are very regular. When the plant reaches the surface of the water the leaves immediately change form and are 3 to 6 inches wide and 5 to 8 inches long, pointed at the outer end and tapering to the stem.

The stem below water, or root, is ropelike and very tough, above water the stem is thicker, tough, and very porous, and follows along the surface of the water sending out branches every 10 inches or so which in turn branch out and eventually form a thick mass or bed, bound together by many small matted roots 2 or 3 feet long which appear along the main stems as the plant grows. Beds of plants 6 months old will support a man on a 6-inch board.

The growth of the young plant while submerged is one-half to threefourths inch per day, but upon reaching the surface it grows 2 to 3 inches a day. One plant, noted when 8 inches out of water, grew to be over 10 feet in length, had 11 branches and 2 stems of flowers in 54 days, covering an area of over 80 square feet.

The young plants are very tender and should not be pulled under three weeks or they are liable to break off below the water; this is especially so where the bottom is hard. If broken off the stem sends out from three to eight shoots, each of which grows to the surface and develops into full-grown plants.

A healthy plant will bloom in about six weeks from the time it appears above the surface, in eight weeks the bloom has died and seed pods formed. Each plant will produce two or more stems of 35 to 45 purple-colored flowers a month, or about 25 a year, a seed pod containing an average of 170 seeds forming at the base of each flower. Each healthy plant will therefore distribute about 170,000 seed each year. The seed ripens in four to six weeks' time and are very small; several pods of seed were counted with the aid of a glass.

Seeds planted in tubs under 10 inches of water sprouted and grew in 25 to 30 days; seed fully formed but not dry was planted but did not grow.

On dump No. 3, at Gamboa, several thousand square yards of old plants were killed in April, 1914. One year later, April, 1915, young plants appeared, grown from the seed deposited the year before in water 8 to 12 feet deep.

On May 19, 1915, about 2 cubic feet of mud was taken from an area where old hyacinths had been growing and deposited in a tank under 12 inches of water. On June 30, 42 days later, 32 young hyacinths had sprouted and were growing, some of which were 7 inches long.

From the distribution of the original beds of hyacinths it is thought that the parent plants which furnished the seed for these beds came on a flood or floods from the upper reaches of the Chagres River and