My map has a mountainous island that's relatively steeply sloped from its center down to it coast. It's ~720 miles long and it's width varies but averages, I'm guessing, 90 miles. I think a close analogy from it to a real world place would be Honshu since it's roughly the same size and is at around the same latitude. Honshu if Honshu was rotated 30 degrees clockwise. I'll say the climate and weather are similar too.

Because of its scale my map can only show features of 88 feet wide or greater (1 pixel = 88 feet).

Its rivers would mostly be small and fast flowing. But I'm not sure how small is "small." I only want to display rivers that are at least 88 feet wide. That is, once they reach that size they stay at least 88 feet wide til they reach the ocean. My question is how many rivers that big should there be? How many miles along the coast should separate them?

A quick look at Google maps of my local region seemed to showed rivers being pretty frequent but it wasn't always possible to tell how wide they were. I tried looking at Honshu on Google Earth but Earth is buggy on my computer and I can't get a clear enough close-up view to estimate river width.