try to look at the highest flood stage (in your mind) try to picture where the water would hold up, slow down the most and also include a current pushing towards it.
then dig there.
Inside curves in the river are your best bet.
top 12 inches will produce flood gold, you can stat at the inner most area of the bend, digging a 12 inch trench outward towards the water classifying bucket after bucket and running it through a lsuice with blak matting (shows gold best) and see where the most gold shows in your pan per bucket.
Then go to the start of the corner and do the same, then at the tail of the corner and also the same.
Then after this, you will have a line where in the three small tranches you got the most color, you make a line through the bank with a stick from the start of the bank to the end where you got the most gold color in each of the three small trenches.
You will have your pay streak line to follow the whole length of the bank.
Then dig up the line in a 3 foot wide trench (more people digging = more gold) the length of the bank, leaving the rest alone as there isnt good color there.