--- title: "Measure across a creek without crossing it" published: "2026-10-15" updated: "2026-10-15" author: "Dad Field Manual editors (drafted with AI help)" time: "45 min" cost: "$0" ages: "8 and up" where: "Flat, dry ground with a tree or post on the far side: a yard, an empty field, or a level path well back from a creek." topics: ["classic-skills","outdoors"] print: "https://dadfieldmanual.com/print?p=measure-across-a-creek" url: "https://dadfieldmanual.com/plans/measure-across-a-creek/" --- # 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. ## What you need - A rope or string about 13 feet long, with knots at 0, 3, 7 and 12 feet (have / $5) - 4 to 6 sticks or tent pegs for markers (free) - A square sheet of paper and a book or clipboard to hold it flat (have) - A tape measure, or count heel-to-toe steps (have) - A child's life jacket, for the creek version (have / $30) ## 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** (Dad shows, Kid copies) Peg the rope's first and last knots together. Pull it into a triangle with sides of 3, 4 and 5 feet and peg the corners. The corner between the 3 and 4 sides is a true square corner. The 1911 book uses 6, 8 and 10: the same shape, twice as big. 2. **Pick a landmark across** (Together) Choose a tree, post or big rock right on the far side and call it X. On dry ground well back from your edge, put peg B straight across from it. Set the rope's square corner at B, with the 4-foot side pointing at X. The 3-foot side now runs along your bank. 3. **Fold a sighting triangle** (Kid) Fold the square sheet corner to corner. That gives a triangle with two equal short sides, like the 1911 book's six-by-six triangle. Its two pointed corners are half a square corner each. 4. **Walk along until X lines up** (Kid) Walk from B along the line of the 3-foot side, staying the same distance from the water. Stop now and then, hold the triangle flat on the book with a pointed corner toward you, point the short edge back at peg B and look along the fold. When the fold points straight at X, put in peg C. 5. **Measure B to C** (Together) Measure from peg B to peg C with the tape or by steps. That is the distance from B straight across to X. Take off the distance from B to your edge, and roughly how far X sits back from the far edge, and you have the water's width. 6. **Check it on the yard** (Together) Repeat with a tree across the yard as X. This time walk a tape straight from B to the tree and compare. Ask: "How close did the triangle get?" ## 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. - No creek nearby? Lay two ropes on the lawn as a pretend river and use a tree beyond them. ## Variations - **Ages 6–7:** Do the yard version only. Kids lay the rope and pegs; Dad does the sighting and the subtraction. - **Ages 8–11:** The full plan, starting on the yard and moving to a creek once it works. - **Ages 12+:** Try the 1911 method on p. 66 for the distance between two trees on the far side, using two square-cornered triangles. - **After rain:** Creeks run higher and banks get slick. Do the yard version and save the creek for a dry day. - **Cold:** Stay off ice on any creek or pond. The yard version works in any season. ## Sources - **1911 scouting handbook, pp. 64–66.** The 1911 book says a triangle with sides of six, eight and ten feet or inches makes a true right angle opposite the ten. It describes measuring across a river without crossing by setting a right-angled triangle with two equal sides on the bank in line with a mark across, moving it along the bank until its long side lines up with the mark, and measuring the base. It also shows how to measure between two distant objects with right triangles. (checked 2026-10-15) - **Supervision and life jackets near water.** The CDC says to designate a responsible adult to supervise closely and constantly when children are in or near water, that children should use life jackets for all activities in and around natural water, and that lakes and rivers have hidden hazards such as currents, rocks and limited visibility. (checked 2026-10-15) - **Arm's-length supervision for young children.** The American Academy of Pediatrics recommends staying within arm's length of young children with constant touch supervision around water, says children should wear life jackets in, on or near lakes and rivers, and lists drainage ditches as a water hazard. (checked 2026-10-15)