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Dad Field Manual · Field card 90 · Classic Field Skills

Measure across a creek without crossing it

Forty-five minutes, a knotted rope, a few sticks and a sheet of paper. Find how wide a creek is from your own side, then try it across the yard where you can check the answer with a tape.

Time
45 min
Cost
$0
Ages
8 and up
Where
Yard, field or creek bank

Since 1911: The 1911 book measured across rivers from the bank. Today the CDC says a responsible adult should supervise closely and constantly whenever children are near water, and that children should wear life jackets around natural water. Work from flat ground well back from the edge, or practice across a yard first. The book's 6-8-10 triangle works the same as a smaller 3-4-5.

What you need

  • A rope or string about 13 feet long, with knots at 0, 3, 7 and 12 feet
  • 4 to 6 sticks or tent pegs for markers
  • A square sheet of paper and a book or clipboard to hold it flat
  • A tape measure, or count heel-to-toe steps
  • A child's life jacket, for the creek version

Water safety: read this first

  • An adult watches the kids closely the whole time near water. No phone, no wandering off.
  • Stay well back from the edge. Every peg goes on dry, flat ground on your side. Nobody wades in to check.
  • Life jackets near natural water. The CDC says children should wear them in and around creeks, rivers and lakes.
  • Any child under 5 who comes along stays within arm's length of an adult, as the AAP advises.

Steps

  1. Make a square corner with the rope. Peg a knotted rope into a 3-4-5 triangle; the corner between the 3 and 4 sides is square.
  2. Pick a landmark across. Pick a landmark X across; put peg B opposite it, with the rope's square corner there.
  3. Fold a sighting triangle. Fold a square sheet corner to corner to make the sighting triangle.
  4. Walk along until X lines up. Walk along the bank line; stop where the fold points at X while a short edge points back to B.
  5. Measure B to C. Measure B to C. That equals B to X; subtract the dry ground on each side.
  6. Check it on the yard. Repeat across a yard and check the answer with a tape.

If it stalls

  • If the answer is far off, peg B probably wasn't straight across from X. Re-sight along the rope's 4-foot side.
  • If the paper flops, tape it to the book cover.
Triangle answer vs. tape answer
Signed off: can do this.Signed by Date