šŸŒŠ

CEE514 Great Lakes Datum Converter

v3.4 Interactive

Coastal Engineering ā€¢ Water Level Vertical Datum Transformations & IGLD 2020 Framework

Quick Presets:
Simulate Epoch: 2026.0
Historic Chart Datum

IGLD 1955

600.00 ft
182.880 m
Ī” LWD: -1.00 ft
Orthometric Datum

NAVD 1988

601.00 ft
183.185 m
Ī” LWD: +0.00 ft
Dynamic Height System

IGLD 1985

601.10 ft
183.215 m
Ī” LWD: +0.10 ft
Geopotential Datum
Modernized

IGLD 2020

601.23 ft
183.255 m
Ī” LWD: +0.23 ft

šŸ“Š Interactive Vertical Datum Relative Profile

Drag Water Surface
Scale:
ā†•ļø Drag water surface line or click SVG canvas to adjust water level elevation

Dynamic vs. Orthometric Formula

Hdyn = (gĢ„ / Ī³45) Ā· Hortho

Ī³45 = 980.619 cm/sĀ² (Normal gravity at 45Ā° latitude)

IGLD 85 & 2020 use Dynamic Heights (Hdyn) representing hydraulic potential surfaces so water remains level across the entire lake basin.

NAVD 88 uses Orthometric Heights (Hortho) measured along the physical gravity plumb line.

Great Lakes Water Level Reference & Permitting Matrix

Low Water Datum (LWD) and Official USACE Ordinary High Water Mark (OHWM) Equivalents

Lake Body NGVD 29 (ft) NAVD 88 (ft) IGLD 55 (ft) IGLD 85 (ft) IGLD 85 (m) IGLD 2020 (m) USACE OHWM (ft / m)
šŸ“

Ordinary High Water Mark (OHWM / OHWL) Permitting & Regulatory Framework

Federal Section 10/404 Jurisdiction & State Coastal Zone Management Rules

1. Fixed Statutory Elevations (e.g. Michigan & New York) Codified Law

States like Michigan (EGLE) use specific historical numbers codified under the Natural Resources and Environmental Protection Act (NREPA). Michigan state numbers are consistently lower than federal USACE limits:

  • Lake Superior: 602.6 ft (vs. Federal 603.1 ft)
  • Lakes Michigan & Huron: 580.5 ft (vs. Federal 581.5 ft)
  • Lake Erie: 572.2 ft (vs. Federal 574.1 ft)

New York (DEC): Shoreline rules generally adopt the federal 247.3 ft baseline for Lake Ontario and 573.4 ft for Lake Erie.

2. Natural / Field-Determined Boundary Physical Field Marking

States such as Wisconsin, Minnesota, Indiana, Ohio, Pennsylvania, and Illinois reject fixed elevation constants for state jurisdiction. Agency staff conduct on-site evaluations to spot the Natural Ordinary High Water Mark (NOHWM) using:

  • Vegetation Shifts: Transition from terrestrial trees/grasses to aquatic plants.
  • Soil & Substrate Changes: Lines showing shelving, erosion, or organic soil to bare lakebed transitions.
  • Physical Staining: Water lines naturally etched or stained onto cliffs, seawalls, and boulders.