Not sure where you are located, but .... if you are in a part of the country where there are "boom & bust" cycles (chaparral terrain), then river/beach hunting is normally worthless (for old coins, that is).
The reason is: The sand that you are looking at NOW, is NOT the sand that was there 20 or 30 yrs. ago. It will have been "washed out" (downstream) or silted back-in beaches. After each gully-wash rain event.
Perhaps some mid-west states, where the water-table-level never fluctuates beyond a foot or two in any direction, this isn't the case. But for example, here in CA: The beaches that front creeks and rivers is NOT the same "beach" that was there 20 or 30 yrs. ago. Thus .... no matter how colorful the usage/recreational history might have been .... it doesn't pork out old coins.