Chrome -
It is really pretty common to see coho spawning in so-called "ditches", especially after a heavy rain. Coho natural move well up into the small creeks to spawn on big rise - their way of taking advantage of all the habitat. This strategy work very well for 1,000s of years. Of course today it often fails due to man's impacts on that habitat.

Mike -
There chances of making is really dependent on a couple of factors. Many of those so-called "ditches" were historically function creeks that we have just put into ditch form for our benefits. The survival of the eggs and resulting fry will depend on the stability of the flows - will they stay wet?, and the quality of any rearing habitat for the juveniles - is there pools etc to provide "homes" for the young fish over the next year or so after hatching? Another fact often is how frequently the owner fo the road (County, State, or private) "cleans" the "ditch".

Happy holidays and may the New Year bring you all tight lines
S malma