Water Education Poster - Navigation

Navigation Poster for Elementary School Students

Dredging:

Sediment (gravel, sand, and silt) is deposited naturally in a harbor or river channel when a river slows down. Accumulated sediment reduces the channel depth and can make the waterway unsafe for navigation. Mechanical and hydraulic dredges are used to deepen and widen channels filled with sediment and deposit the sediment in an approved location. Mechanical dredges shovel or scoop up bottom materials and place them on a barge or scow. The two hydraulic dredges shown on this poster use pumps to remove a mixture of water and sediment ("slurry") from the channel bottom. The HOPPER DREDGE is an ocean-going vessel used to dredge sediment from the bottom of a deep-water channel or coastal harbor. Dredged material is stored in "hopper bins" inside the ship before disposal in the open sea or other location.

PIPELINE DREDGE: Vessel commonly used to dredge sediment from the bottom of shallow rivers or calm coastal waters. Dredged material is pumped from the river or ocean bottom and flows through a floating pipeline to shore. The dredged material commonly is used to restore eroded beaches.

Locks and Dams:

Dams are built on shallow rivers to hold back water and form deeper navigation "pools." Most pools in the United States are maintained at a constant minimum water depth of 9 feet for safe navigation. Dams make it necessary for river vessels to use a series of locks to "step" up or down the river from one water level to another. The three steps in the "LOCKING THROUGH" process are shown below.

For a boat going downstream, the lock is first filled by opening the filling valve. The drain valve and upstream and downstream gates are closed, so the level of the water in the chamber rises to the upstream level. The upstream gate opens and the boat moves in.

To lower the boat, the gates are closed behind it, the filling valve is closed, and the drain valve is opened. The higher water in the lock chamber drains to the downstream level within minutes.

The downstream gate is then opened and the boat moves out on the lower water level. The process is reversed for a boat going upstream.