REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


canal, which is also the mouth of the Rio Grande estuary, there has been built a wharf or pier of steel 1,000 feet long, carrying two railroad tracks and a platform for the exchange of cargo between ships lying alongside the pier and freight cars on the railroad tracks. The foundation structures of this pier, known as the La lBoca pier, are steel cylinders sunk to bed rock by the pneumatic process and illed with concrete. Mud and rock have been dredged not only alongside the pier, but over an area in front of it to make a turning basin suffcient for the present needs. The depth of water alongside and in the basin varies f rom 22 to 25 feet at low water, but, like the entrance channel, must be frequently dredged to maintain this depth.
 The bottom of the bay of Panama, at the anchorage off the islands of Perico and Naos, consists of mud mixed with sand, shells, and other materials, and forms excellent holding ground. There are no swells to disturb ships at anchor. There is, however, little depth of water near the shore, and the 30-foot contour lies to the westward and southward of those islands. Deep-water channels approach the islands or this anchorage from three directions, that -immediately eastward of the island of Flamenco being probably the best adapted for the approach to the dredged channel leading into the canal.
 .The tides in Panama Bay are of far greater range than those at Colon, although mean sea level is the same in both harbors. They are very regular. During spring tides the water surface may oscillate between 10 feet above mean sea level to 10 below. During neap tides the range from. high to low may not exceed 7.9 feet. Tidal observations have been made at the manigraph station on the island of Naos for many years and they supply data for the statement of the tidal range given above.
 The flood tide passes between Naos and Guinea Point, in a direction north-northwest, with a maximum current exceeding two miles per hour. The tide ascends the Rio Grande to a point nearly f our miles above La B~oca pier and inundates, up to Miraflores, the manglares or low marshes through which the river flows. The period of inflow is short, and after it the water recedes from the swamp with an outgoing current increased by that in the river between two and four hours after high tide. This maximum current is estimated at a little over three miles per hour during the spring tides in. that part of the rainy season in which high freshets occur. Under ordinary conditions the current in the Rio Grande during the dry season, or in those portions of the wet season when the rainfall is small, is too slight to have any effect upon the ebb flow of the tide. Between La Boca and the anchorage ground the ebb follows essetially the direction of the dredged channel, with gradually decreasing current, and then turns to the south and southeast beyond Flamenco.
 The direction of the present dredged change is about N. 600 W. It was originally intended by the old Panama Canal Company to give the channel a depth of 301 feet at low water and a bottom width of about 170 feet, with side slopes of one vertical on three horizontal. The present channel was dredged to a depth of 30 feet below mean tide, and was opened to navigation in December, 1900, since which time it has been in constant service, but this depth has not been maintained. The material taken out in this dredging consisted of mud and silt, some material of vegetable origin, sand, gravel, and, in the vicinity of La Boca pier, a small quantity of rock.
 It has already been observed that a littoral current moves from west to east across the dredged channel, causing considerable sediment to deposit. As a consequence of this condition nearly continuous dredging is required to maintain a depth in the qhbannel of 21 to 22 feet at low water. The volume dredged in this manner is about 150,000 cubic yards annually, and sometimes rises to 20,000 or more cubic yards per month. This dredged material is not, except in comparatively small quantities, brought down by the Rio Grande River, but is moved into the channel by the littoral current. The course of that river is short and the volume of its flow far too small to bear a sensible quantity of sediment, nor does the latter appear to be of the character found along the banks of the Rio Grande or in its bed.
 There are also other small currents existing in the bay in the vicinity of the entrance channel, and under certain conditions of tide and wind there may be even a little westerly current, but all other movements than that from the west are small and probably negligible in their effects upon the maintenance of the entrance, whether in its present location or on a new line between Ancon and Sosa naills.