Pick the route for the season: use river fords and low-lying roads in the dry season, ridgelines and gravel roads in the wet season with 30-50% more time allowed, and frozen ground or tested ice in winter, switching to sleds when snow passes 30 cm. Clear ice of 10 cm bears a person and 20 cm a horse, and the 30 cm often quoted for a loaded wagon leaves a margin of only 1.6 for a 2,000 kg wagon by Gold’s formula, which wants about 40 cm. White or snow ice needs double the thickness.
Part of Logistics & Load Planning
How dry, wet and winter conditions change which routes a loaded convoy can use, and how to judge ice crossings.
Each Season Opens Some Routes And Closes Others
The parent article describes three cases. In the dry season, river fords become passable and low-lying roads that flood in the wet season are open; dust and heat are the problems, so travel early and late and rest in the hottest hours. In the wet season, avoid bottomlands and clay soils, which become impassable mud; use ridgeline routes, which are drier and better drained; gravel roads keep their traction and dirt roads fail; and allow 30-50% more travel time. In winter, frozen ground can carry heavier loads than summer roads; ice crossings must be tested; snow deeper than 30 cm stops wheeled vehicles, so switch to sleds; and shorter days reduce travel hours.
For the parent’s ice thresholds, it says 10 cm of clear ice supports a person, 20 cm supports a horse and 30 cm supports a loaded wagon. Ice Thickness Requirements explains where such figures come from.
What You Need
- Route knowledge for each season — which fords, which low roads, which ridges.
- An ice auger or an axe to drill and measure.
- A pole or rope for rescue.
- A timetable allowance for the season. See Timing & Daily Schedule.
Method: Select And Test A Seasonal Route
Step 1: Match the route to the season Dry: fords and low roads. Wet: ridges and gravel. Winter: frozen ground, tested ice or sleds.
Step 2: Add the time Wet season: multiply the dry-season time by 1.3 to 1.5.
Step 3: Test the ice at many points Drill or chop holes across the crossing, not just at the shore, and measure.
Step 4: Judge the colour and condition White, snow-formed, cracked or refrozen ice is weaker. Do not rely on the number if the ice has been thawed and refrozen, covered with water or slush.
Step 5: Spread the load Cross one vehicle at a time with wide gaps, and never stop on the ice.
Worked Example: Wet-Season Time And A Loaded Wagon On Ice
Wet season. A 120 km trip by horse cart on a fair track at 15-25 km a day takes 120 / 25 = 4.8 to 120 / 15 = 8 days in the dry season. In the wet season: 4.8 × 1.3 = 6.2 days to 8 × 1.5 = 12 days. Plan for 6-12 days.
Ice. Gold’s formula as given in Ice Thickness Requirements is P = 3.5 × h², with P in kilograms and h in centimetres, for clear ice in good condition. That article marks the formula as recalled and not checked against the original paper, so use it for comparison, not as a design value.
| Clear ice | P = 3.5 × h² |
|---|---|
| 10 cm | 350 kg |
| 20 cm | 1,400 kg |
| 30 cm | 3,150 kg |
| 40 cm | 5,600 kg |
- A horse of about 500 kg (an assumption) on 20 cm of ice: margin 1,400 / 500 = 2.8, the same margin the ice article uses for a working crew.
- A wagon of 2,000 kg gross on 30 cm of ice: margin 3,150 / 2,000 = 1.6. For 3,000 kg gross the margin is 3,150 / 3,000 = 1.05, almost none.
- To keep a margin of 2.8: h = √(2.8 × 2,000 / 3.5) = √1,600 = 40 cm for 2,000 kg, and h = √(2.8 × 3,000 / 3.5) = √2,400 = 49 cm for 3,000 kg.
- At a margin of 2.8, 30 cm clear ice carries 3,150 / 2.8 = 1,125 kg gross.
- White ice needs double the thickness of clear ice according to the ice article, so 30 cm of clear-ice thickness becomes 60 cm.
Result: the parent’s 30 cm is adequate for a light cart and thin for a loaded wagon. Treat it as a minimum for sound, cold, clear ice, and add thickness for heavier loads.
Common Mistakes
- Testing only at the shore — ice is thinnest where currents run, near inlets and over springs.
- Trusting an old number — a warm spell cuts ice strength quickly.
- Planning dry-season time in the wet season — add 30-50%.
- Using bottomland roads in the wet season — they become impassable.
- Parking a loaded sled on the ice to rest — a static load is the worst case.
Safety
Falling through ice
A vehicle and team can go through ice without warning, and the team may drown. Test at many points, carry ice picks, a rope and a pole, keep gaps between vehicles, cross early in the cold part of the day, and avoid any crossing with running water, slush or cracks. If in doubt, go around.
What’s Next
- Learn next: Route Optimization — choosing among seasonal options
- Combine with: Terrain Assessment — grades and surfaces