Rhine River

Interpreting river levels on the Rhine.

Overview

RiverSat's Rhine River data follows the methodology established by Germany's Federal Waterways and Shipping Administration (WSV) and the Central Commission for Navigation of the Rhine (CCNR). Historical water level data is sourced from the PEGELONLINE portal, while reference levels (GlW, TUGLW) are defined by official CCNR resolutions¹.

This page explains how gauge readings translate to actual navigable water depth in the shipping channel.

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The Core Formula

To convert a gauge reading to actual navigable channel depth:

Actual Channel Depth = Measured Level − GlW + TUGLW

Where:

• Measured Level = The water level reading from the gauge (in cm)

• GlW (Gleichwertiger Wasserstand) = Equivalent Water Level for that station (in cm)

• TUGLW (Tiefe unter GlW) = Guaranteed fairway depth below GlW (in cm)

Example: Kaub Gauge Station

Using the parameters for Kaub (the critical bottleneck on the Middle Rhine):

Parameter	Value
GlW (Equivalent Water Level)	77 cm
TUGLW (Fairway Depth below GlW)	190 cm

If the gauge reads 60 cm:

Actual Channel Depth = 60 − 77 + 190 = 173 cm (1.73 m)

If the gauge reads 150 cm:

Actual Channel Depth = 150 − 77 + 190 = 263 cm (2.63 m)

If the gauge reads 77 cm (exactly at GlW):

Actual Channel Depth = 77 − 77 + 190 = 190 cm (1.90 m)

This last example demonstrates that when water levels are exactly at the Equivalent Water Level, the channel depth equals the guaranteed fairway depth (TUGLW).

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Terminology Reference

German-English Terminology Table

German Abbreviation	German Term	English Equivalent	English Abbreviation	Definition
GlW	Gleichwertiger Wasserstand	Equivalent Water Level	EWL	A reference low water level that, statistically, is only undercut on 20 ice-free days per year over a 100-year average
TUGLW	Tiefe unter GlW	Fairway Depth below EWL	—	The guaranteed minimum channel depth maintained below the Equivalent Water Level
PNP	Pegelnullpunkt	Gauge Zero Point	GZP	The reference elevation (zero point) of the gauge staff, relative to the national height datum
NHN	Normalhöhennull	Normal Height Null	—	German national vertical datum (similar to Mean Sea Level); replaced NN in 1992
HSW	Höchster Schifffahrtswasserstand	Highest Navigable Water Level	HNWL	Maximum water level for safe navigation; shipping prohibited above this level
MHW	Mittleres Hochwasser	Mean High Water	MHW	Average of annual maximum water levels over a reference period
MW	Mittelwasser	Mean Water	MW	Average water level over a reference period
MNW	Mittleres Niedrigwasser	Mean Low Water	MLW	Average of annual minimum water levels over a reference period
HHW	Höchster bekannter Wasserstand	Highest Recorded Water	HRW	Historical maximum water level ever recorded at that gauge
NNW	Niedrigster bekannter Wasserstand	Lowest Recorded Water	LRW	Historical minimum water level ever recorded at that gauge
HW	Hochwasser	High Water	HW	High water event or level
NW	Niedrigwasser	Low Water	LW	Low water event or level

Navigation-Specific Terms

Term	Definition
Available Draught	The maximum depth a vessel can safely draw; calculated as: Actual Channel Depth minus Under-Keel Clearance
Under-Keel Clearance (UKC)	Safety margin between the vessel's keel and the riverbed; accounts for squat effects and bottom irregularities
Squat	The hydrodynamic sinking of a vessel while underway; increases with speed and decreases with water depth
Fairway	The marked navigation channel maintained to guaranteed depth standards

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How Gauge Systems Work

The Gauge Zero Point (PNP)

Every river gauge has a Gauge Zero Point (PNP) — an arbitrary reference elevation from which water levels are measured. Critically:

• The zero point is NOT at the riverbed

• The zero point is typically set well below normal low water to avoid negative readings

• The PNP is surveyed relative to the national height datum (NHN in Germany)

Why Gauge Readings ≠ Water Depth

Because the gauge zero point is arbitrary and not at the riverbed, a gauge reading of "78 cm" does not mean there is 78 cm of water. The actual depth depends on:

1. Where the gauge zero point is relative to the riverbed

2. The profile of the navigation channel at that location

3. The maintained depth of the fairway

This is why the formula exists: it converts the gauge reading into the actual navigable depth by accounting for these factors through the GlW and TUGLW parameters.

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The Equivalent Water Level (GlW/EWL)

Definition

The Equivalent Water Level (GlW) is a standardized reference level defined by the Central Commission for the Navigation of the Rhine (CCNR)¹. It represents:

"The water level occurring along the Rhine at an equivalent low water flow that falls below the long-term average for only 20 ice-free days per year."

In practical terms: water levels drop below GlW approximately 20 days per year under normal conditions. When water falls below GlW, navigation becomes increasingly restricted.

Determination Process

The CCNR determines GlW values every 10 years based on:

• 100 years of historical flow data

• Analysis of equivalent low-water discharge (GlQ) at each gauge

• Conversion of discharge to water level using station-specific rating curves

Current values: EWL 2022 (effective January 1, 2023 through December 31, 2031)

GlW Values for Key Rhine Stations (EWL 2022)

Station	River km	GlW (cm)	TUGLW (cm)
Basel	166.6	501	—
Maxau	362.3	372	210
Speyer	399.5	237	—
Mannheim	424.5	155	—
Worms	443.4	68	—
Mainz	498.5	171	—
Oestrich	519.8	92	190
Bingen	529.1	97	—
Kaub	546.3	77	190
Koblenz	590.3	77	—
Andernach	613.8	91	—
Bonn	654.8	142	—
Cologne	688.0	139	250
Düsseldorf	744.2	91	—
Duisburg-Ruhrort	780.8	227	280
Wesel	814.0	174	—
Rees	837.4	118	—
Emmerich	851.9	74	—

Source: CCNR Resolution 2022-II-19

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Gauge Station Profiles

Kaub — The Critical Bottleneck

Location: Rhine-km 546.3 (Middle Rhine, between Koblenz and Mainz)

Why it matters: Kaub sits at the shallowest, narrowest section of the navigable Middle Rhine. All vessels traveling between the North Sea ports and the industrial southwest (BASF at Ludwigshafen, etc.) must pass through this choke point.

Parameter	Value
GlW (EWL 2022)	77 cm
TUGLW (Fairway Depth)	190 cm
HSW I (High Water Mark I)	460 cm
HSW II (Shipping Prohibited)	640 cm
Historical Minimum (NNW)	24 cm (October 22, 2018)
Historical Maximum (HHW)	825 cm (January 5, 1883)

Navigation Impacts by Gauge Level:

Gauge Level	Channel Depth	Vessel Capacity Impact
250 cm	3.63 m	Full capacity
135 cm	2.48 m	~50% capacity
78 cm (at GlW)	1.91 m	Minimum guaranteed depth
75 cm	1.88 m	~25% capacity (4× vessels needed)
55 cm	1.68 m	~16% capacity
40 cm	1.53 m	Freight navigation impractical
35 cm	1.48 m	Only specialized low-draft vessels

Planned Infrastructure: Works are in the planning approval stage to increase TUGLW from 190 cm to 210 cm between Budenheim and St. Goar (the section including Kaub and Oestrich).²

Maxau — Upper Rhine Gateway

Location: Rhine-km 362.3 (Upper Rhine, near Karlsruhe)

Why it matters: Maxau marks the transition between the canalized Upper Rhine and the free-flowing river. It's the key gauge for traffic to/from Basel and Switzerland.

Parameter	Value
GlW (EWL 2022)	372 cm
TUGLW (Fairway Depth)	210 cm

Note: The higher GlW value (372 cm vs. Kaub's 77 cm) primarily reflects different gauge zero point positions, not deeper water. Always use the formula to calculate actual depth.

Cologne — Lower Rhine Reference

Location: Rhine-km 688.0 (Lower Rhine)

Why it matters: Major industrial and population center; key indicator for traffic between Duisburg/Rotterdam and points south.

Parameter	Value
GlW (EWL 2022)	139 cm
TUGLW (Fairway Depth)	250 cm
Flood Alert Level	830 cm

Cultural note: The Cologne gauge ("Pegel Köln") has measured Rhine levels since 1891 and is a cultural landmark. Water levels are regularly reported in local media.

Duisburg-Ruhrort — Industrial Heart

Location: Rhine-km 780.8 (Lower Rhine, Ruhr confluence)

Why it matters: Europe's largest inland port; gateway to the Ruhr industrial region. Thyssenkrupp's steel operations depend on approximately 10,000 annual barge movements through this point.

Parameter	Value
GlW (EWL 2022)	227 cm
TUGLW (Fairway Depth)	280 cm

Emmerich — Border Gauge

Location: Rhine-km 851.9 (German-Dutch border)

Why it matters: Last German gauge before the Netherlands; reference point for cross-border traffic statistics and coordination with Dutch authorities.

Parameter	Value
GlW (EWL 2022)	74 cm

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What RiverSat Forecasts Represent

Historical Data

RiverSat historical water level data comes from PEGELONLINE, an online service the WSV provides for distribution of river level gauge data and metadata. Values represent:

• Parameter: Water level (Wasserstand) in centimeters

• Reference: Height above the Gauge Zero Point (PNP) at each station

• Frequency: Typically 15-minute intervals

• Quality: Raw (unvalidated) measurements from automatic gauges

Forecast Data

RiverSat forecasts are generated through:

1. Input: Historical discharge and river level data from PEGELONLINE, as well as recent weather conditions and weather forecasts

2. Model: Machine learning model forecasting target variable

3. Conversion: Station-specific rating curves translate discharge to river levels

Output: Predicted water level in centimeters above Gauge Zero Point, daily, for each day in the forecast trajectory.

Converting Forecasts to Operational Decisions

To use a RiverSat forecast for navigation planning:

1. Read the forecast water level for your target date and station

2. Apply the formula: Actual Channel Depth = Forecast Level − GlW + TUGLW

3. Subtract your required Under-Keel Clearance to get Available Draught

4. Compare Available Draught to your vessel's loaded draft requirements

Example: Planning barge loading for arrival at Kaub in 14 days

• RiverSat 14-day forecast for Kaub: 95 cm

• Calculation: 95 − 77 + 190 = 208 cm channel depth

• Minus 30 cm UKC = 178 cm available draught

• Your barge requires 160 cm draft at target load → Sufficient clearance

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Regulatory Context

High Water Restrictions

Unlike low water (which has no hard cutoff), high water triggers mandatory navigation suspensions:

Level	Description	Effect
HSW I (Mark I)	First high water threshold	Speed and traffic restrictions begin
HSW II (Mark II)	Second high water threshold	Navigation prohibited

These thresholds vary by station and river section. At Kaub: HSW I = 460 cm, HSW II = 640 cm.

Low Water — Skipper's Responsibility

There is no regulatory minimum water level that prohibits navigation. It is the skipper's responsibility to determine whether passage is safe given:

• Current water levels

• Vessel draft when loaded

• Channel conditions

• Weather and visibility

However, as a practical matter, freight navigation becomes impractical at Kaub below approximately 40 cm gauge level.

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Understanding "Days Below GlW"

A key metric for assessing navigation conditions is the number of days per year when water levels fall below the Equivalent Water Level. Historical benchmarks:

Year	Days Below GlW at Kaub	Conditions
2017	28	Typical
2018	107	Severe drought
2019	0	Excellent
2020	0	Excellent
2021	10	Good
2022	80+	Significant drought
2023	24	Moderate

Long-term average: Approximately 20 days per year (by definition of GlW)

When days below GlW significantly exceed 20, this indicates a drought year with sustained navigation restrictions.

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Key Differences from Tidal/Maritime Systems

If you're familiar with maritime chart datums, note these important differences for the Rhine:

Aspect	Maritime/Tidal Systems	Rhine (Inland)
Primary reference	Chart Datum (CD) / LAT	Equivalent Water Level (GlW)
Water level variation	Predictable tidal cycles	Weather-driven, irregular
Guaranteed depth reference	Below CD	Below GlW
Navigation prohibition	Rarely (storm events)	Above HSW II only
Forecast challenge	Tidal prediction (deterministic)	Weather-dependent hydrology (probabilistic)

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Data Sources and Standards

Official Sources

• ELWIS (Elektronischer Wasserstraßen-Informationsservice): Primary source for German inland waterway data

• PEGELONLINE: Real-time gauge data from the Federal Waterways and Shipping Administration (WSV)

• CCNR (Central Commission for the Navigation of the Rhine): Sets GlW standards every 10 years

Update Schedule

• GlW values: Updated every 10 years by CCNR (current: EWL 2022, valid 2023-2031)

• TUGLW values: Updated as infrastructure improvements are completed

• Historical data: Available from PEGELONLINE from January 1, 2000 onward

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Quick Reference Card

The Formula

Channel Depth = Measured Level − GlW + TUGLW

Critical Stations at a Glance

Station	GlW	TUGLW	At GlW, Depth =
Kaub	77 cm	190 cm	1.90 m
Maxau	372 cm	210 cm	2.10 m
Cologne	139 cm	250 cm	2.50 m
Duisburg	227 cm	280 cm	2.80 m

Kaub Quick Reference

Gauge Reading	→ Channel Depth	Navigation Status
> 250 cm	> 3.6 m	Optimal conditions
150 cm	2.6 m	Good conditions
78 cm	1.9 m	At GlW (minimum guaranteed)
50 cm	1.6 m	Severely restricted
< 40 cm	< 1.5 m	Freight impractical

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Last updated: February 2026 Source data: CCNR Resolution 2022-II-19, PEGELONLINE, ELWIS