In order to find out how much impervious surface is in the watershed, we use presence/absence sampling. In other words, we pick a lot of random points, count the number that are impervious, and then calculate a percentage.
Below, you can get some practice estimating impervious surface using the presence-absence method. Don't worry, the program will do the actual counting. All you need to do is tell it to take samples, and then decide when enough samples have been taken.
Now consider that the University of Maryland campus has > 60% impervious surfaces. How healthy do you think streams in this area are?
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