I've written an algorithm to try and detect rivers in paragraphs and it actually detects quite a lot when I run it. Some of them are clearly false positives, but there are others that are indeed aligned spaces on consecutive lines. Here are some, colored in green in the following picture:
When are rivers really problematic and/or ugly? Are there rivers in this example that are worth fixing?
What are the parameters (and their importance) to qualify the "badness" of a river, and how could they be calculated?
As an additional question, there doesn't seem to be a standard definition of a river. Defining a river properly would surely help to define the parameters that make it bad. How would you define a river?