Research the types of areas that gold likes to gather during flood events (study historical placer deposits covering MANY waterways), then start sampling those kinds of spots first. Keep in mind that the landscape during a major flood event can look quite different from what it may appear the majority of the time. Learn about where gold likes to settle, which side of boulders, how to predict and imagine the water flow and turbulence during a flood event.
Gold isn't found everywhere, and even within the same waterway, gold may be much more prevalent in certain sections while virtually non-existent in others. If you do the research, you can save yourself LOADS of time and effort while at the same time ensuring better future success in your prospecting endeavors.
Anyway, if you find gold, you'll learn how to trace it back more to its point of origin. That isn't always possible, but the closer you can get, the better your chances of getting the most you can. Many old (early and even pre-1900's) books are available for free online, usually in .pdf download. How gold acts in nature hasn't changed, so there is still much great knowledge available there. Also, look to newer technologies, such as Gold Hog matting. Those guys have literally written new chapters in how to recover gold and separate it from the waste material quickly and efficiently.
Placer mining in waterways definitely has its advantages, IF you choose to learn them. And that is, that nature has been depositing gold in certain locations year after year regardless of whether people were out there looking for it or not. So better your chances for success and learn how to read a waterway during flood events! But also keep in mind that waterways can (and do!) change, most commonly during these types of major flood events, so also try to learn how to read the landscape - to see where a waterway might have run in years/decades/centuries past.
Good luck!!
