The GG50 America’s Working Waterway Vocabulary - Glossary of Terms

A reference for the America's Working Waterways series

Every post in this series uses the same working vocabulary. Rather than re-explain terms post by post, this page collects them in one place — grouped by category, so you can find what you need without hunting through an alphabetical list. Link back here anytime a term needs more than a one-line definition.

One editorial rule the whole series follows: every figure states its unit — bushels, short tons, metric tonnes, barge loads, or vessel loads. Grain crosses all of them, and conflating them is how basis conversations go sideways.

Infrastructure & channel terms

Authorized depth vs. operating depth

Authorized depth is the project target; operating depth is what carriers can safely use under current river conditions.

Chamber

The individual lock structure a tow passes through. Some lock sites have more than one chamber, often of different lengths (commonly 600 ft or 1,200 ft).

Channel depth

The authorized navigation depth maintained by dredging and river-control work; not necessarily the depth available on a given day.

Cut

A section of a tow separated out to fit through a lock chamber during a double lockage; a 15-barge tow split for a 600-foot chamber typically moves through as two cuts.

Design life

The engineering lifespan a lock or dam component was originally built to serve, commonly 50 years for USACE inland structures; a chamber can keep operating well past it with regular maintenance and rehabilitation.

Dewatering

Pumping a lock chamber dry behind bulkheads so crews can inspect and repair gates, valves, and concrete that sit under water in normal service. A dewatering closes the chamber. At a lock with only one chamber, it closes the river.

Double lockage

Breaking a tow into sections because it's longer than the lock chamber, then passing sections separately.

Dredging

Removing accumulated sediment from a channel to restore or maintain authorized depth.

Drift

Floating debris carried by the river: whole trees, root balls, lumber, and anything else the river picks up on the way. It runs heaviest on spring rises, and on the Middle Mississippi much of it comes down the Missouri. A loaded barge at a dock is a big target. In this series, drift means river debris, not a vessel drifting off course. See also: Kicker barge.

Head of navigation

The farthest point upstream where a commercial channel is maintained. On the Kaskaskia it is Fayetteville. Above that point the river is watershed, not working waterway.

Headwater / tailwater

The water level just above a lock or dam (headwater) and just below it (tailwater). The difference between the two is the lift.

Inland waterway

A navigable river, canal, or connected water route used for commercial transportation.

Lift

The difference in water level a lock raises or lowers a vessel. It changes with river stage; at Locks 27 near St. Louis it runs from a few feet in high water to more than ten feet in low water.

Lock

A water-filled chamber that raises or lowers vessels between different river elevations.

Lockage

The process of moving a vessel or tow through a lock.

Low water dam / fixed crest dam

A dam with no movable gates that holds a minimum pool in low water and lets high water pour over the top. Dam 27 at the Chain of Rocks is a rock low water dam, set more than three miles from its locks and not used as a navigation route.

Main chamber / auxiliary chamber

At lock sites with two chambers, the main chamber handles most commercial traffic and the auxiliary chamber, often shorter, serves as backup and for smaller vessels. When a main chamber closes for repair, tows squeeze into the auxiliary, which can turn a single lockage into a double lockage. At Locks 27, the main chamber is 1,200 feet and the auxiliary 600. When the Corps closed the main chamber from January 1 to April 1, 2025, every 15-barge tow had to lock through the auxiliary in two cuts.

Miter gate

The pair of steel gates at each end of a lock chamber. They swing shut to meet at an angle pointed upstream, so the water pressure holds them closed. The downstream set holds back the full lift whenever the chamber is filled, which is why a cracked hinge there can close a lock.

Mooring cell

A large, rock filled steel cylinder set in the river near a lock, where a tow can tie off to wait its turn instead of holding position in the current.

Navigation pool

The stretch of slack water held back behind a navigation dam, reaching up to the next dam upstream. The Upper Mississippi is a staircase of these pools, each numbered for the dam that forms it; Pool 9 runs from Lock and Dam 8 down to Lock and Dam 9.

Navigation season

The period a route is open to traffic. Ice sets it on the Great Lakes–St. Lawrence system and on the northern Upper Mississippi, where the St. Paul District reach typically closes from about early December to mid March and reopens when the first tow breaks through Lake Pepin. Farther south, the Mississippi system runs year round, with selected locks closed for scheduled winter maintenance.

Open pass

The condition at a wicket dam when the wickets are laid flat on the riverbed, letting tows run right over the dam without locking through. It takes the lock out of the tow cycle in high water. Crews often call this running open river; in this series, open pass is the wicket dam term.

Open river

The condition when high flows force a dam’s gates to be raised completely out of the water, so the pools flatten and the river runs close to its natural state. On the Upper Mississippi, tows still pass through the lock during open river; there is no route over these dams. In a major flood, locks close altogether. The term is also used for a reach with no locks and dams at all, such as the Middle and Lower Mississippi below Locks 27, where tows are sized to the channel's width and depth instead of chamber length. See also: Open pass.

Pinnacles

High points of bedrock in the riverbed that sit under sand and plenty of water in normal stages and reach up into the channel in a drought. On the Middle Mississippi the problem reaches are limestone near Thebes, roughly river miles 46 to 38, and near Grand Tower, around miles 80 to 79. The Corps removes them by blasting, usually in low water when they are exposed, as in 1988–89 and again in 2012–13.

River mile

The standard distance marker on a navigable river. On the Upper Mississippi, miles count upstream from the mouth of the Ohio at Cairo, so Minneapolis sits near mile 854 and Locks 27 at mile 185.5.

River stage

The water level at a river gauge, read in feet. Stage drives draft, tow size, and lift. A falling stage at St. Louis can cut Illinois River drafts even when the Illinois itself looks fine. Stage is read against the gauge's zero point, not the riverbed, so a negative reading, such as the St. Louis record low of minus 6.2 feet in 1940, means low water, not no water. See also: Gauge / river gauge; Crest / flood stage.

Scheduled outage / unscheduled outage

A scheduled outage is planned lock downtime for maintenance, announced ahead of time so shippers can adjust; an unscheduled outage is an unplanned closure, harder and more costly to plan around.

Shoaling

The buildup of sediment that reduces usable channel depth or width, often the direct cause of draft restrictions.

Tainter gate / roller gate

The two main movable gate types on Upper Mississippi dams. A tainter gate is a curved steel gate that pivots upward to release water; a roller gate is a large steel drum that rolls up and down between piers. Both can be raised completely clear of the water in high flows.

Wicket dam

A movable dam made of rows of hinged panels, called wickets, that crews raise to hold pool in low and moderate water and lay flat on the riverbed in high water. LaGrange and Peoria on the Illinois Waterway are wicket dams.

Equipment & operations terms

Barge

A non-self-propelled cargo vessel, commonly moved by a towboat on U.S. inland waterways.

Covered hopper barge

The standard dry-cargo barge for grain and other bulk commodities, with a cover that protects cargo from weather; distinct from an open hopper barge, used for coal, gravel, and similar cargo that doesn't need weather protection.

Downbound / upbound

Direction of barge movement relative to river flow. Downbound generally carries grain toward Gulf export points; upbound generally carries fertilizer and other inputs back to the interior.

Draft

The vertical distance from a vessel's waterline to its lowest point; a deeper draft normally means more cargo but requires more water.

Draft marks / mean draft

Draft marks are the depth scales on a barge hull at the bow and stern, port and starboard. Mean draft is the average of the four readings, but it only means something if the barge is level. The deepest corner is what hangs up on the bottom, so a good loader trims the barge to even marks at all four corners.

Fleeting area

A designated barge staging and storage area — the river equivalent of a rail yard or truck parking/queueing area.

Harbor service

Local boat work that builds/breaks tows, spots barges at terminals, and shifts equipment within a port area.

Harbor, shifting, and fleeting boat

A towboat used for local work: building and breaking tows, spotting barges at terminals, and moving equipment within a fleeting area or harbor, rather than moving a tow over distance.

Jumbo barge

The standard covered hopper on the Mississippi system, about 195 by 35 feet. It carries roughly 1,500 short tons of grain at 9 feet of draft and more at the deeper drafts common on the Lower Mississippi; each inch of draft is worth about 17 to 18 tons.

Light loading

Loading barges below their normal draft because of low water, shoaling, or carrier limits. The river stays open, but each barge carries less, so moving the same grain takes more barges, more boat time, and more freight per ton.

Line-haul movement

Long-distance movement of barges between origin, interchange, and destination areas.

Line-haul towboat

A towboat built and crewed to move an assembled tow over long distances between origin and destination, as distinct from the local vessels described under Harbor, shifting, and fleeting boat.

Make-up / face up

Make-up is rebuilding a tow after a double lockage or in a fleet, putting the barges back in place and lashing them together. Face up is the towboat setting its bow square against the stern of the tow and tying off so it can push.

Rake barge / box barge

Two common hull shapes for inland dry-cargo barges. A rake barge has sloped ends for better handling in a tow; a box barge has squared-off ends, common on larger configurations where that handling edge matters less.

Rolltop

A covered hopper barge whose steel covers roll along tracks on the hatch coaming to open and close, as distinct from lift-top covers that are lifted off. Retired rolltops often find second lives as kicker barges or fleet spares. See also: Covered hopper barge.

Switchboat

A small towboat stationed at a lock to pull the unpowered first cut of a double lockage clear of the chamber, shortening the lockage. NESP includes switchboats among its small navigation improvements. See also: Harbor, shifting, and fleeting boat.

Tow

One or more barges connected and pushed by a towboat.

Tow configuration

The arrangement of barges in a tow, such as 3 wide by 5 long.

Towboat

The powered vessel that pushes a barge tow; “towboat” is more accurate than “tugboat” for most inland grain movements.

Handling & trade terms

Basis / river bid

Basis is the difference between a local cash price and the futures price. The river bid is what a river house pays. For export grain it is built from the Center Gulf price, set at the export elevators on the lower Mississippi, minus barge freight and handling. When barge freight jumps, the river basis weakens.

Crush plant

A processor that crushes soybeans into meal and oil. Crush demand, including oil for renewable diesel, competes with the river for soybeans.

Elevator / terminal

A facility receiving, storing, conditioning, loading, unloading, or transferring grain between modes.

Export elevator

A terminal that receives grain and loads ocean-going vessels for export.

House

Grain trade shorthand for an elevator, as in river house, country house, or shuttle house. “Left the house at 8 feet 6” means the barge was loaded to that draft at the elevator.

Interior elevator

A grain-handling facility away from export gateways — the origin point most barge grain starts its trip at, as distinct from an export elevator.

Modal share

The percentage of a commodity's total export or shipment volume carried by a given transportation mode (barge, rail, truck).

Over-the-bank loader

A barge loading setup without bins on the bank. Trucks dump at a receiving point inland, and a conveyor carries the grain out to the barge.

Shuttle train / unit train / loop track

A unit train is a train of grain cars moving as one shipment from one origin to one destination. A shuttle train is a unit train, commonly 100 cars or more, that cycles repeatedly between the same origin and destination. A loop track lets the whole train load without being cut apart. Shuttle loaders compete directly with river houses for the same grain.

Transload

Transferring grain or other cargo from one mode to another at a terminal, such as rail to barge or truck to barge, through the terminal's receiving and loading equipment. When the river is tight, more grain rides the rail straight to the Gulf or PNW instead of transloading to barge at St. Louis. See also: Transshipment.

Waterfront structures & port operations terms

Berth

The specific, designated space where a vessel or barge ties up to load, unload, or wait — distinct from the larger dock or terminal it's part of.

Bollard

A fixed post on a dock, pier, or wharf that mooring lines are tied off to.

Dock

The general term for a structure or facility where a vessel or barge moors to load or unload; often used loosely to mean the whole berth area, though piers and wharves are more specific structure types within it.

Dolphin

A cluster of piles, or a standalone mooring structure, not physically connected to a wharf or pier. Used to secure a vessel or tow, guide it into a berth, or absorb impact and protect a structure from being struck.

Kicker barge

An old barge, often a retired steel rolltop, moored at an angle off the upstream end of a dock so it throws ice and drift out into the channel and away from the barges working the dock. See also: Drift.

Mooring

The act and the system (lines, bollards, dolphins, or buoys) used to secure a vessel or barge in place.

Pier

A structure that projects out from the shoreline into the water, allowing vessels to moor and work cargo on both sides.

Piling

A vertical support post (wood, steel, or concrete) driven into the riverbed or seabed to carry the structural load of a dock, pier, or wharf.

Pilot / river pilot

A licensed navigator with specialized knowledge of a specific river, channel, or harbor who boards a vessel to guide it through that stretch — required on many U.S. harbor approaches and internationally on rivers like the Mississippi.

Port district / port authority

A local public authority created under state law to develop and run port facilities. Illinois calls them port districts; Missouri calls them port authorities. The Kaskaskia Regional Port District, chartered in 1965, runs the docks on the Kaskaskia. The Southeast Missouri Regional Port Authority (Semo Port), created in 1975, runs the slackwater harbor near Scott City.

Stevedoring / stevedore

The labor and operations of loading and unloading cargo from a vessel; a stevedore is the worker or firm performing that work.

Transshipment

Transferring cargo from one vessel or mode directly to another — barge to ship, barge to barge — rather than moving it through shore-based storage first. Some grain-export operations run mid-river transshipment where a fixed berth isn't practical.

Wharf

A structure built parallel to the shoreline, allowing a vessel to moor alongside a single face rather than project into the channel.

Named waterways, corridors & regional systems

Black Warrior-Tombigbee Waterway

A river system connecting industrial and agricultural areas of Alabama to the port of Mobile, alongside the Tennessee-Tombigbee Waterway.

Brandon Road / invasive carp barrier

The Corps has run electric barriers on the Chicago Sanitary and Ship Canal at Romeoville since 2002 to keep invasive carp out of Lake Michigan. The Brandon Road project near Joliet adds a second layer: a flushing lock, another electric barrier, sound, and a bubble curtain, at about $1.15 billion. Construction started in 2025 and has brought weekday closures.

Cal-Sag Channel

An engineered canal connecting the Calumet River system to the Chicago Sanitary and Ship Canal, forming part of the physical link between Lake Michigan and the Illinois Waterway.

Calumet River

A short river system in the Chicago area that connects Lake Michigan to the Cal-Sag Channel, tying local industrial traffic into the Illinois Waterway and Great Lakes systems. T.J. O’Brien Lock and Dam on the Calumet, 1,000 feet long, is the top lock on the Illinois Waterway.

Chain of Rocks Canal

An 8.4-mile canal on the Illinois side above St. Louis, opened in 1953, that lets tows bypass the Chain of Rocks, a series of rock ledges in the main river. Locks 27 sit at its lower end; Dam 27 is a separate low water dam across the main channel.

Chicago Sanitary and Ship Canal

An engineered waterway connecting the Chicago River system to the Illinois Waterway. It's one of the key junctions where the Great Lakes system physically connects to the Mississippi River system.

Columbia-Snake System

The river system connecting the inland Pacific Northwest, particularly wheat country, to export terminals near Portland and the Pacific Coast. Operates under different rail competition and port geography than the Gulf system.

Great Lakes-St. Lawrence System

The combined Great Lakes and St. Lawrence Seaway system connecting the U.S. and Canadian interior to the Atlantic. Runs on a seasonal calendar and vessel constraints that don't apply to most of the Mississippi system. See also: Navigation season.

Gulf Intracoastal Waterway (GIWW)

A protected, largely sheltered waterway running along the Gulf Coast from Texas to Florida. It functions as a lateral connector, linking river mouths, ports, refineries, fertilizer plants, terminals, and marine service areas rather than running toward one export elevator.

Illinois and Michigan Canal

The first water link between the Great Lakes and the Mississippi basin, opened in 1848 from Chicago to LaSalle. It made Chicago the junction of the two systems and was replaced by the Chicago Sanitary and Ship Canal in 1900.

Illinois Waterway

The 336-mile navigation route from the Calumet River at Chicago to Grafton, where the Illinois meets the Mississippi. It is a built system: Chicago-area canals at the top, the Des Plaines River in the middle, and the Illinois River the rest of the way, dropping about 160 feet through eight locks. Seven chambers are 110 by 600 feet. T.J. O’Brien, on the Calumet, is 1,000 feet. Covered in Post V.

Kaskaskia River

A tributary of the Mississippi that lies entirely within Illinois, joining at Mississippi mile 117, about eight miles above Chester and below Locks 27. Its lower 36 miles are a 9-foot navigation channel to Fayetteville with one lock, the Jerry F. Costello Lock (600 by 84 feet), moving fertilizer, coiled steel, gypsum, and stone, with grain loading at a few docks. Above Fayetteville it isn’t a commercial route: part of the watershed, not the working waterway.

Locks 27

The Corps of Engineers' name for the two-chamber lock at the foot of the Chain of Rocks Canal near Granite City, Upper Mississippi mile 185.5: a 110-by-1,200-foot main chamber and a 110-by-600-foot auxiliary, opened in 1953. Plural because there are two chambers; the separate low water dam across the main river is Dam 27. Often called Lock 27 in conversation, but this series uses Locks 27, matching Corps notices and lock data. It is the last lock on the Mississippi and the only one below the Missouri confluence; everything coming off the Upper Mississippi and the Illinois passes it to reach the open river.

Lower Mississippi River

The open river from the mouth of the Ohio at Cairo to the Gulf, about 950 river miles with no locks or dams. Mileage counts upstream from Head of Passes near the Gulf. Barges commonly load deeper here than on the upper rivers, about 2,100 short tons at a 12-foot draft, and on the lowest reach a deep-draft channel carries ocean-going vessels to the export elevators. Often shortened to the Lower Miss.

McClellan-Kerr Arkansas River Navigation System (MKARNS)

A lock-and-dam navigation system on the Arkansas River connecting Catoosa, Oklahoma, and points across Arkansas to the Mississippi River. Commonly shortened to MKARNS.

Melvin Price Locks and Dam (Mel Price)

The lock and dam at Alton, Illinois, about 17 miles above St. Louis, with a 1,200-foot main chamber and a 600-foot auxiliary. It replaced the old Lock and Dam 26 and is sometimes still called Lock 26. With Locks 27, it is one of the two 1,200-foot locks a tow passes on its way into St. Louis harbor.

Middle Mississippi River

The 195 miles of open river from the mouth of the Missouri to the mouth of the Ohio at Cairo, as the Corps' St. Louis District defines it. Locks 27 sits at the top; there are no locks below it. Technically the lower end of the Upper Mississippi, it operates as the transition to the Lower Mississippi. The Corps holds its 9-by-300-foot channel through the Regulating Works Project rather than dams, and rock, low water, high water, ice, and drift are its main hazards. Often shortened to the Mid Miss. Covered in Post VI.

Missouri River

The longest river in the United States, joining the Mississippi just above St. Louis at the head of the Middle Mississippi. Its commercial channel runs 735 miles from Sioux City, Iowa, to the mouth, with no locks, on a navigation season set by releases from upstream reservoirs. It brings a heavy sediment load, ice, and spring drift into the Mississippi, which is a big part of why dredges stay busy below St. Louis.

Regional gateway

A port or waterway connection that moves less national grain volume than the major export corridors, but remains essential to a specific local market, processor, fertilizer territory, or customer base. Examples include the Sacramento-San Joaquin system, Baltimore, Wilmington in Delaware, and Savannah in Georgia.

Sacramento-San Joaquin System

A California river and delta system supporting regional agricultural and bulk shipping, distinct in geography and market orientation from the Gulf and Pacific Northwest export corridors.

Tennessee-Tombigbee Waterway (Tenn-Tom)

A man-made waterway connecting the Tennessee River to the Tombigbee River and the port of Mobile. It gives shippers on the Tennessee River, a Mississippi system tributary, a Gulf route that bypasses the Lower Mississippi.

Upper Mississippi River

The locking river from Minneapolis to the mouth of the Ohio at Cairo, about 850 river miles. All 29 of its locks and dams, 27 still in service, sit between Minneapolis and Locks 27 at St. Louis; most have 600-foot main chambers. Often shortened to the Upper Miss. Covered in Post IV.

Ohio River

The 981-mile river from Pittsburgh (confluence of the Allegheny and Monongahela) to Cairo, Illinois, where it joins the Mississippi. On average it contributes more water at the confluence than the Upper Mississippi brings past Thebes (roughly 281,000 cubic feet per second versus about 208,000). It helps create the conditions of the Lower Mississippi. The river is largely modernized with 1,200-foot main chambers (most sites also have a 600-foot auxiliary; Smithland and Olmsted have twin 1,200-foot chambers). High-water ranges of 50 feet or more are a normal operating condition on the lower river rather than a closure. Covered in Post VII.

Tennessee River

Navigable for roughly 650 miles from Paducah, Kentucky, to Knoxville, Tennessee. A major transportation system in its own right for grain, fertilizer, aggregates, industrial products, and traffic using the Tennessee-Tombigbee Waterway. Linked to the Cumberland River by a short canal between Kentucky Lake and Lake Barkley. Covered in Post VII.

Cumberland River

Joins the Ohio at Smithland and is navigable through Nashville. Like the Tennessee, a good share of its grain traffic is inbound feed and processing demand for the Southeast. Covered in Post VII.

Green River

Enters the Ohio between Evansville and Henderson. Navigable for a stretch through grain country (and historically coal); feeds traffic directly into the lower Ohio. Covered in Post VII.

Olmsted Locks and Dam

Twin 1,200-foot chamber lock and dam near the mouth of the Ohio River. Replaced two older locks and dams after decades of construction. Provides critical capacity on a high-volume reach. Covered in Post VII.

Smithland Lock and Dam

Lock on the lower Ohio with twin 1,200-foot chambers. One of the three locks (with Myers and Olmsted) between the Evansville/Henderson area and Cairo. Covered in Post VII.

John T. Myers Lock and Dam (Myers Lock)

Lock on the lower Ohio near Evansville. With Smithland and Olmsted, one of the three locks a barge passes between the Evansville area and open river at Cairo. Covered in Post VII.

Kentucky Lock

Lock on the Tennessee River near its mouth. The existing main chamber is 600 feet, so a standard 15-barge tow must be broken into two cuts. Average waits have run around ten hours. A new 1,200-foot chamber has been under construction since 1998; the current target is 2029, with risk-adjusted estimates running into the early 2030s. Until complete, traffic is often pushed to Barkley Lock. Covered in Post VII.

Barkley Lock

Lock on Lake Barkley serving the Cumberland River system. Acts as the practical alternate route for traffic that would otherwise use Kentucky Lock, via the short canal connecting Kentucky Lake and Lake Barkley. Covered in Post VII.

Flood control & channel stabilization terms

Articulated concrete mattress (ACM)

Interlocking concrete panels strung together with cable and sunk against a riverbank to form a flexible, erosion-resistant surface; the standard revetment material used on the Lower Mississippi.

Backwater

Water pushed up a tributary when the river it flows into is running higher. When the Mississippi is high at Grafton it backs up the Illinois, so the Illinois floods from the bottom up.

Dike

A low structure built out from the riverbank, partly submerged, that directs river flow to help maintain channel depth and alignment; distinct from a levee, which runs parallel to the bank to hold back floodwater.

Floodwall

A concrete or steel flood-control structure that does the same job as a levee, typically used where limited space rules out an earthen embankment.

Levee

An engineered embankment built along a riverbank to contain flood flows and keep the river within its channel during high water.

Mat Sinking Unit

The U.S. Army Corps of Engineers’ fleet dedicated to casting and placing articulated concrete mattress on the Lower Mississippi; the largest revetment operation of its kind in the world.

Mississippi River and Tributaries (MR&T) Project

The federal flood-control and navigation program, authorized after the 1927 flood, that built and maintains the mainstem Mississippi’s levees, floodways, channel stabilization, and tributary basin improvements.

Regulating Works Project

The Corps program that holds the Middle Mississippi's 9-foot-deep, 300-foot-wide channel without locks or dams, using river training structures, revetment, dredging, and rock removal. It goes back to Rivers and Harbors Acts in 1910, 1927, and 1930. See also: River training structures.

Revetment

Engineered bank protection, typically articulated concrete mattress placed against a riverbank, that keeps a channel from migrating and protects the levee system behind it.

River training structures

Rock structures that steer the current so the river scours and holds its own channel. They include dikes; bendway weirs, submerged rock sills angled upstream across the outside of a bend that spread the current and widen the usable channel through it; and chevrons, V-shaped rock structures in the channel, open end downstream, that split the flow. Revetment protects the bank rather than steering the flow, but is usually grouped with them. Their effect on flood heights was challenged in court in 2020; the Corps prevailed. See also: Dike, Revetment, Regulating Works Project.

Measurement terms

Barge rate as percent of tariff

The standard way inland barge freight is quoted. Rates are stated as a percentage of a 1976 benchmark tariff for each river segment, so 400 percent of tariff means four times the benchmark rate per ton. USDA publishes weekly rates by segment, including the Illinois River, in the Grain Transportation Report.

Bushel, short ton, and metric tonne

Grain is commonly bought and sold in bushels, while transportation is often measured in short tons or metric tonnes; disclose the unit every time.

Crest / flood stage

A crest is the highest stage a river reaches on a rise before it starts to fall. Flood stage is the gauge reading where the river begins to cause flooding at that location; at St. Louis it is 30 feet. Navigation limits are set separately: traffic through St. Louis harbor stops above 38 feet. The St. Louis record crest is 49.58 feet, on August 1, 1993. See also: River stage, Gauge / river gauge.

Gauge / river gauge

A measured water-level reading at a specific point on a river, used to track flood or low-water conditions and set draft restrictions.

Grain Transportation Report (GTR)

USDA Agricultural Marketing Service’s weekly report on grain movement by barge, rail, truck, and ocean vessel, including downbound barge grain counts at Locks 27 and other points.

Lock Performance Monitoring System (LPMS)

The Corps of Engineers’ database of traffic, tonnage, and delays at each lock; the source behind most published tonnage figures by lock.

Reliability

The probability that a route can move cargo when needed, at expected draft, tow size, transit time, and cost.

Spot freight rate

The current market price to move a barge of grain, often quoted per ton; highly sensitive to draft restrictions and lock outages.

Funding & policy terms

Corps district

The Corps of Engineers’ regional operating units. On the Upper Mississippi, the St. Paul District runs Minneapolis through Lock and Dam 10, the Rock Island District runs Locks 11 through 22, and the St. Louis District runs Lock 24 through Locks 27.

Harbor Maintenance Tax (HMT) / Harbor Maintenance Trust Fund (HMTF)

A tax on imports and certain domestic waterborne cargo that funds harbor and channel dredging.

Inland Waterways Trust Fund (IWTF)

Funded by a per-gallon diesel tax on commercial towing operators; cost-shares construction and major rehabilitation of locks and dams.

Marine highway

A federal program/designation (America's Marine Highway) that treats coastal and inland waterway routes as extensions of the surface transportation network.

Navigation and Ecosystem Sustainability Program (NESP)

A Corps program, first authorized in 2007, that pairs navigation upgrades on the Upper Mississippi and Illinois Waterway with ecosystem restoration. Its navigation plan includes seven new 1,200-foot chambers, at Locks 20, 21, 22, 24, and 25 on the Mississippi and LaGrange and Peoria on the Illinois, plus mooring cells and switchboats. Lock 25 is first, with commissioning targeted for 2034.

Part of the GG50 America's Working Waterways series. New terms will be added here as later posts require them, rather than redefined post by post.

Version 3.4 — adds terms introduced in Post VII: Ohio River, Tennessee River, Cumberland River, Green River, Olmsted Locks and Dam, Smithland Lock and Dam, John T. Myers Lock and Dam (Myers Lock), Kentucky Lock, and Barkley Lock.

Version 3.3 — adds terms introduced in Post VI: kicker barge, drift, rolltop, pinnacles, Regulating Works Project, river training structures (bendway weirs, chevrons), Locks 27, Melvin Price Locks and Dam, Lower Mississippi River, Missouri River, crest / flood stage, and transload. Standardizes Locks 27 as the series name; updates Main chamber / auxiliary chamber, Open river, River stage, Port district (now Port district / port authority), Middle Mississippi River, and Upper Mississippi River.

Version 3.2 — adds terms introduced in Post V: Illinois Waterway, Illinois and Michigan Canal, Brandon Road / invasive carp barrier, river stage, miter gate, head of navigation, dewatering, draft marks / mean draft, make-up / face up, house, over-the-bank loader, shuttle train / unit train / loop track, crush plant, basis / river bid, port district, backwater, and barge rate as percent of tariff. Standardizes LaGrange spelling; updates Open pass, Kaskaskia River, Calumet River, and Switchboat.

Version 3.1 — adds high water and dam terms (open river, wicket dam, open pass, low water dam), navigation pool, lift, river mile, jumbo barge, light loading, switchboat, mooring cell, the Upper and Middle Mississippi and Chain of Rocks Canal, NESP, Corps districts, and data sources introduced in Post IV; updates Navigation season and Kaskaskia River.

Last update after Post VII