# Problem 54750. Find the length of stream affected by a spill

When a contaminant is spilled into a stream, one might want to know how much of the stream is affected—e.g., the length over which the concentration exceeds a specified threshold. The concentration C is often computed as a function of time t and distance x from the spill using the advection-dispersion equation:
where U is the mean velocity of the river and K is a dispersion coefficient, which describes spreading by several mechanisms. For an instantaneous spill of mass M mixed over the cross section (with area A) at , the concentration can be shown—using some of the math needed for Cody Problem 51625—to be
Write a function to compute the length of stream affected by the spill. In other words, find the position (say) beyond which the concentration never exceeds a threshold .

### Solution Stats

70.0% Correct | 30.0% Incorrect
Last Solution submitted on Nov 13, 2022

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