Finding the Distance Across a River

This isn't directly related to orienteering, but if you are hiking, camping, or whatever adventurous outdoor activity you like, you may need to find it necessary to figure out the distance across a river so you can throw a rope to someone or place a log to cross it. This can be done with a neat little geometry trick that won't even get your feet wet. Look at the diagram below...

Here is the step by step of how to do this. First choose an object close to the river or stream on the opposite side. In the diagram I used a tree. Stand close to the stream so that you are directly across the river from that tree. Place a rock or some object on the ground so you can find this spot again. Now. Walk along the river in either direction. I chose to go left in the diagram. Make sure you move square to the line formed between the rock you placed and the tree on the other side. This will ensure that the angle formed is 90 degrees. The dashed orange line represents this walking. As you are walking , stop every once in a while and do the following. Turn around so that you are looking straight towards the rock that you placed on the ground. Turn the degrees on your compass so that 45 is on the direction arrow. Now find 0 on the degrees and see where it is pointing. Your goal should be to get it so that the 45 degrees mark is pointing right at the tree you picked at the beginning. Once you have found this spot, place another object here.

Now, what you will notice is that you have made a 45-45-90 triangle or an isosceles right triangle. In geometry the two legs of an isosceles right triangle are the same length. So you now have two lengths you can measure. Since the whole reason for doing this is to avoid going in the river, lets measure the leg of the triangle that is formed by the two objects you placed on this side of the river. This distance is equal to the distance across the river. Measure it out or just use it to compare your rope or log to see if it is long enough.