Mississippi River
Interpreting river levels on the Mississippi.
Overview
RiverSat's Mississippi River System (including tributaries) data follows the methodology established by U.S. federal agencies: the U.S. Geological Survey (USGS) for stream gauge data, the U.S. Army Corps of Engineers (USACE) for channel maintenance and navigation infrastructure, the National Oceanic and Atmospheric Administration (NOAA) for river forecasting, and the U.S. Coast Guard (USCG) for navigation safety regulations.
This page explains how gauge readings relate to navigation conditions, including the critical low water thresholds that trigger draft restrictions under the USCG Waterways Action Plan.
Key differences from the Rhine: Unlike the Rhine River's standardized GlW/TUGLW system, the Mississippi River system uses a simpler "zero gauge" reference that varies by station. The relationship between gauge readings and actual channel depth is more dynamic and regionally dependent.
Note: On official USGS webpages or other documentation, you may see the spelling "gage" instead of "gauge". This is for idiosyncratic historical reasons specific to the USGS and does not indicate any actual difference between a "gage" and a "gauge".
The U.S. River Level System
Gauge Stage vs. Channel Depth
In the United States, river levels are reported as stage (also called "gauge height")—the height of the water surface above an established gauge datum at that specific location.
Critical concept: The gauge datum (zero point) is an arbitrary reference elevation set when the gauge was installed. It is NOT at the riverbed, and a reading of "0 feet" does not mean the river is empty—it simply means water is at the gauge's zero reference mark.
Gauge readings can be and regularly are negative, indicating water below the historical zero reference. During the 2022 and 2023 droughts, the Memphis gauge dropped below -10 feet, meaning water was more than 10 feet below the gauge's zero mark—yet the river still contained significant water depth.
Agencies and Data Sources
USGS (U.S. Geological Survey)
Primary data collection; operates stream gauges nationwide
USACE (U.S. Army Corps of Engineers)
Channel maintenance, dredging, lock/dam operations, navigation infrastructure
NOAA/NWS (National Weather Service)
River forecasting via River Forecast Centers (RFC); issues flood warnings
USCG (U.S. Coast Guard)
Navigation safety regulations; issues draft restrictions and tow-size limits
Understanding Gauge Readings
What the Numbers Mean
When you see a river gauge reading like "15 feet" or "-8 feet," this represents:
Example at Memphis:
Gauge datum was set at a historically low reference point when installed
A reading of 10 feet means water is 10 feet above that reference
A reading of -10 feet means water is 10 feet below that reference
In both cases, there is still navigable water in the channel
Why Gauges Can Show Negative Values
The Memphis gauge datum was established based on historical observations. When conditions become drier than the reference period used to set that datum, water levels fall below the zero mark. This has become increasingly common:
July 1988
-10.70 ft
Previous record low
October 22, 2022
-10.81 ft
New record low
October 17, 2023
-11.91 ft
Current record low
Navigation Reference Levels
NWS Stage Categories
The National Weather Service defines standard stage categories for each gauge:
Major Flood
Extensive inundation of structures and roads
Evacuations; navigation suspended
Moderate Flood
Some inundation; evacuations possible
Significant restrictions
Minor Flood
Minimal property damage; some road flooding
Speed restrictions; caution required
Action Stage
Preparation for significant hydrologic activity
Monitoring intensified
Normal
Between action stage and low water threshold
Unrestricted navigation
Low Water Threshold
Negative impacts on navigation begin
Draft restrictions initiated
Low Water Thresholds — Mississippi River
These are the critical levels for navigation operations, as defined in the USCG Waterways Action Plan (Lower Mississippi, Upper Mississippi):
Watch
0 ft
5 ft
20 ft
10 ft
Action
-2 ft
0 ft
15 ft
7 ft
Extreme
-3.5 ft
-8 ft
10 ft
5 ft
Note: The different absolute values (negative vs. positive) reflect different gauge datum settings, not different water depths.
High Water Thresholds — Mississippi River (St. Louis and below)
For flood conditions, the USCG Waterways Action Plan activates restrictions at these levels:
Level 1
20 ft
25 ft
45 ft
36 ft
Level 2
25 ft
35 ft
50 ft
40 ft
Level 3
30 ft
40 ft
55 ft
50 ft
Flood Stage
30 ft
34 ft
48 ft
43 ft
Channel Depth and Draft Restrictions
Authorized Channel Depths
The USACE is authorized to maintain minimum channel depths:
Upper Mississippi (Minneapolis to St. Louis)
9 feet
300 ft
Controlled by 29 locks & dams
Middle Mississippi (St. Louis to Cairo)
9 feet
300 ft
Free-flowing; no locks
Lower Mississippi (Cairo to Baton Rouge)
9 feet
300 ft
Free-flowing; 12-ft depth authorized but not funded
Lower Mississippi (Baton Rouge to New Orleans)
45 feet
500 ft
Deep-draft ship channel
Lower Mississippi (New Orleans to Gulf)
45 feet
750 ft
Deep-draft ship channel
Low Water Reference Plane (LWRP)
For the Lower Mississippi River, the USACE uses a Low Water Reference Plane (LWRP) as the engineering datum for channel maintenance and navigation charts.
Definition: The LWRP is a hydraulic datum representing a statistically-derived low water elevation, typically based on the 97% flow duration (water levels exceeded 97% of the time over the period of record).
Navigation charts show:
0 ft LWRP — Surface water course area
9 ft LWRP — Shallow draft channel boundary (barge navigation)
45 ft LWRP — Deep draft channel boundary (ocean-going vessels)
Important: LWRP is NOT the same as the gauge datum. They serve different purposes—gauge readings are for real-time monitoring, while LWRP is an engineering reference for channel surveys and maintenance.
Draft Restrictions During Low Water
When gauge levels fall below low water thresholds, the USCG mandates draft restrictions:
Normal water
12 ft
—
1,500 tons/barge
Low water threshold
—
10.5 ft
~1,150 tons/barge
Extreme low water
—
9 ft
~900 tons/barge
Impact formula: Each 1-foot reduction in draft = ~200 tons less cargo per barge = ~7,000 fewer bushels of soybeans
RiverSat Station Coverage
Station by River Section
RiverSat provides forecasts aligned with USCG Waterways Action Plan (WAP) zones:
Upper Mississippi
Pool-controlled section with 29 locks & dams from Minneapolis to Missouri River confluence.
St. Paul, MN
839
Lock & Dam 2 area
Winona, MN
725
Lock & Dam 5A area
Camanche, IA
511
Lock & Dam 13 area
Grafton, IL
218
Last station before Missouri confluence
Middle Mississippi
Free-flowing section from Missouri confluence to Ohio confluence; 195 river miles.
St. Louis, MO
180
Missouri confluence; highest traffic volume
Chain of Rocks/L&D 27
—
Critical chokepoint
Thebes, IL
109
Last gauge before Ohio confluence at Cairo
Illinois Waterway
Major grain feeder connecting Great Lakes to Mississippi; 8 locks.
Valley City, IL
61
Near Mississippi confluence
Peoria, IL
158
Major grain terminal
Lower Mississippi WAP Zone 1
Cairo/Ohio confluence to Memphis; free-flowing.
Cairo, IL
954
Reference
Ohio confluence; 90% of LMR flow enters here
Memphis, TN
737
PRIMARY
WAP Zone 1 trigger; record -10.81 ft (Oct 2022)
Ohio River
Pittsburgh to Cairo; 20 locks & dams; 2nd highest barge traffic in U.S.
Sewickley, PA
14
Pittsburgh area; steel industry hub
Greenup, KY
341
Greenup L&D; Appalachian coal corridor
Louisville, KY
531
McAlpine L&D; major navigation hub
Cannelton, IN
721
Near Wabash confluence
Lower Mississippi WAP Zone 2
Memphis to Greenville; free-flowing.
Helena, AR
663
Secondary
Arkansas River influence zone
Greenville, MS
537
PRIMARY
WAP Zone 2 trigger
Lower Mississippi WAP Zone 3
Greenville to Natchez; free-flowing.
Vicksburg, MS
437
PRIMARY
WAP Zone 3 trigger; VIC activated at 40 ft high water
Natchez, MS
363
Secondary
Levee protection zone at 55 ft
Missouri River
Sioux City to Mississippi confluence; 6 mainstem dams.
Sioux City, IA
732
Below Gavins Point Dam
Omaha, NE
616
Major metro; significant ag shipping
Kansas City, MO
366
Kansas River confluence
Boonville/Hermann, MO
197
Near Mississippi confluence
Note: USACE reservoir releases significantly impact downstream Mississippi levels.
Lower Mississippi Zone 4
Natchez to Gulf; tidal influence.
Baton Rouge, LA
230
Refinery corridor; Old River Control upstream
New Orleans (Carrollton), LA
103
Gulf export terminals; Bonnet Carré spillway
Note: Tidal influence dominates this section; requires different modeling approach.
What RiverSat Forecasts Represent
Historical Data
RiverSat historical water level data comes from USGS stream gauges, accessed via USGS Water Services. Values represent:
Parameter: Gauge height (stage) in feet
Reference: Height above the gauge datum at each station
Frequency: Typically 15-minute intervals
Quality: Real-time provisional data (subject to later quality control)
Forecast Methodology
RiverSat forecasts are generated through:
Input: Historical discharge and stage data from USGS, as well as recent weather and weather forecasts
Model: Machine learning model forecasting target variables
Conversion: Station-specific rating curves translate discharge to river levels
NOAA Forecast Integration
RiverSat also displays NOAA Lower Mississippi River Forecast Center (LMRFC) forecasts for comparison:
NOAA Operational Forecasts: Use 2-day rainfall forecasts; considered reliable
NOAA Experimental Models
Using Forecasts for Operational Decisions
Navigation Planning
To use a RiverSat forecast for barge operations:
Check the forecast stage for your target date and critical gauges (Memphis, Greenville, Vicksburg)
Compare to low water thresholds:
Memphis: Watch at 5 ft, Action at 0 ft, Extreme at -8 ft
Greenville: Watch at 20 ft, Action at 15 ft, Extreme at 10 ft
Vicksburg: Watch at 10 ft, Action at 7 ft, Extreme at 5 ft
Anticipate draft restrictions if levels approach or fall below thresholds
Plan cargo loading based on expected available draft
Example: Barge Loading Decision
Scenario: Planning grain shipment from St. Louis to New Orleans; RiverSat forecasts Memphis gauge at -6 ft in 10 days.
Analysis:
Memphis at -6 ft is below the 0 ft Action threshold
USCG will likely have 9-foot draft restrictions in effect
Barges normally loaded to 12-ft draft (1,500 tons) must reduce to 9-ft draft (~900 tons)
Need ~67% more barges to move same tonnage
Freight rates will be elevated
Decision: Either accelerate shipment before restrictions intensify, or budget for increased transportation costs.
High Water Planning
For flood conditions, check forecasts against high water thresholds:
Level 1 restrictions: Tow size limits, horsepower requirements
Level 2 restrictions: Further tow reductions, no night transit at certain bridges
Level 3 restrictions: Severe limitations on tow size and configuration
Navigation suspended above flood stage at many locations
Terminology Reference
U.S. River Terms
Stage
Water surface height above gauge datum (in feet)
Gauge Datum
The zero reference elevation for a specific gauge
Discharge (Q)
Volume of water flowing past a point, typically in cubic feet per second (cfs)
Rating Curve
Mathematical relationship between stage and discharge at a gauge
LWRP
Low Water Reference Plane; engineering datum for channel surveys
Draft
Vertical distance from waterline to bottom of vessel hull
Tow
Group of barges pushed by a single towboat
River Mile (RM)
Distance marker measured upstream from a reference point
AHP
Above Head of Passes (Gulf of Mexico reference)
WAP
Waterways Action Plan (USCG operational protocols)
Flood Stage Categories
Action Stage
Level at which mitigation actions begin
Bankfull Stage
Level at which water begins overtopping natural banks
Flood Stage
Level at which flooding causes damage or public safety concern
Minor Flood
Minimal property damage; some road flooding
Moderate Flood
Some structural inundation; evacuations possible
Major Flood
Extensive inundation; significant evacuations
Key Station Profiles
Memphis, TN — The Critical Indicator
Location: Mississippi River Mile 737 (WAP Zone 1)
Why it matters: Memphis is the primary trigger gauge for the Cairo-Memphis corridor, the narrowest bottleneck on the Lower Mississippi. All barge traffic between the Gulf and the Midwest must pass this point.
Low Water Watch
5 ft
Low Water Action
0 ft
Low Water Extreme
-8 ft
Flood Stage
34 ft
Record Low
-11.91 ft (October 17, 2023)
Record High
48.7 ft (1937 flood)
Navigation Impact by Gauge Level:
20 to 5 ft
Normal
None (12 ft)
Full 42-barge tows
5 to 0 ft
Watch
10.5 ft
Monitoring; possible reductions
0 to -8 ft
Action
9 ft
Reduced to 25-36 barges
< -8 ft
Extreme
9 ft or less
Severe reductions; groundings likely
Cairo, IL — The Confluence
Location: Mississippi River Mile 954 (Ohio/Mississippi confluence)
Why it matters: Approximately two-thirds of the Lower Mississippi River flow enters at Cairo from the Ohio River with the other third entering from the Upper Mississippi. Immediately below Cairo, the flow is typically 90% of its maximum flow in Natchez, MS (before part of the flow diverts to the Atchafalaya River). Therefore, Ohio River conditions upstream significantly impact Lower Mississippi conditions downstream.
Low Water Threshold
9.2 ft
Record Low
4.5 ft (October 2023)
St. Louis, MO — The Gateway
Location: Mississippi River Mile 180 (below Missouri confluence)
Why it matters: Highest lock volume on the river (Lock 27); transition point between pool-controlled Upper Mississippi and free-flowing Middle Mississippi.
Flood Stage
30 ft
Normal Range
0-20 ft
Vicksburg, MS — Zone 3 Trigger
Location: Mississippi River Mile 437
Why it matters: Primary trigger gauge for WAP Zone 3; site of critical highway bridges with navigation constraints.
Low Water Watch
10 ft
Low Water Action
7 ft
Low Water Extreme
5 ft
High Water Restrictions
Begin at 40 ft
Flood Stage
43 ft
Differences from Rhine River System
If you're familiar with RiverSat's Rhine documentation, note these key differences:
Reference datum
Equivalent Water Level (GlW) — standardized across stations
Gauge datum — varies by station
Channel depth formula
Measured Level − GlW + TUGLW = Channel Depth
No direct formula; channel depth varies with flow
Regulatory framework
CCNR (international)
USACE/USCG (U.S. federal)
Channel guarantee
TUGLW defines guaranteed depth below GlW
9-ft channel authorized but not guaranteed during low water
Negative readings
Rare (GlW set near practical minimum)
Common during drought
Low water prohibition
No hard cutoff
No hard cutoff (skipper's judgment)
High water prohibition
HSW II = navigation prohibited
Varies by location; flood stage closures
Forecast responsibility
Federal Institute for Hydrology (BfG)
NOAA River Forecast Centers
Data Sources
Official Sources
USGS Water Services (waterservices.usgs.gov): Real-time and historical gauge data
NOAA National Water Prediction Service (water.noaa.gov): Forecasts, flood categories
USACE RiverGages (rivergages.mvr.usace.army.mil): Corps-operated gauges and reservoir data
USCG Waterways Action Plan: Navigation restriction protocols
Quick Reference
WAP Primary Trigger Gauges
Memphis
Zone 1
5 / 0 / -8 ft
Greenville
Zone 2
20 / 15 / 10 ft
Vicksburg
Zone 3
10 / 7 / 5 ft
Draft Impact Reference
12 ft → 11 ft
-200 tons
-7,000 bu
12 ft → 10 ft
-400 tons
-14,000 bu
12 ft → 9 ft
-600 tons
-20,000 bu
Recent Record Lows (Memphis Gauge)
1988
-10.70 ft
July 10
2022
-10.81 ft
October 22
2023
-11.91 ft
October 17
Last updated: February 2026 Source data: USGS, NOAA LMRFC, USACE, USCG Waterways Action Plan
Last updated