what are some techniques used in determining the depth at which a jig or bait is placed below a float? do you just start short and increase length each cast until you feel bottom??

First I just guess. If it's a real snaggy area I always go a bit on the conservative side, if its sandy or small rocks it's ok to bounce it along the bottom for a cast or two (some fish seem to like this). Unless you know the river your fishing well it's almost impossible to judge depths, especially if your covering alot of water. The best advice I can give is to carry extra bobbers and plan on loosing atleast one.

Make a guess as to depth and then set the depth at 1 to 2 feet above the bottom. Drift it through. If nothing happens, lower the jig a foot or two and do it again. Repeat this until you either tap bottom or hook-up. I keep the jig 1 foot above the bottom if I know the depth and sometimes two feet if it's snaggy.

I typically don't go deeper than 6 feet under. Even in deep holes, the fish will rise to get jigs. I've caught steelies out of a 12 foot hole with my jig only 5 feet under my float.

Jacon if the hole was deep for the river the fish might be suspended in the water column. If the water is clear then I bet they will move for the jig when they see it.

~ Dr Pepper

If your float is riding straight up and down or even angled back into the current then your jig is not on the bottom and you can adjust it until the top of your float is pointing down stream ( the jig is now touching bottom) when that happens you'll want to adjust it back up, to get into the right position.

Steelhead, salmon and trout don't grub around in the muck, they always look up to the side or straight ahead.
Watch the angle of your float, as simple as that.

Steelhead don't grub in the muck, but they're not going to rise four feet for a jig all the time either. There are days they'll only move a few inches, and if you're hanging only 5 feet in a 12-foot deep hole, you're going to go home disappointed. Set your jig mid-depth and work it to the bottom otherwise you're not fishing effectively.

In clear water I plumb the depth using nothing but a 1/4 oz. split shot on my line,under the float. I cast as I normally would if I had a jig on, and watch the float, looking for tapping the bottom etc. watch where the float stops tapping, starts tapping etc... I make three or four casts this way with no hook,no jig. covering the hole. when I determine the depth,(dropoffs, ledges etc..) I put on a jig that will contrast with the bottom, and fish below the fish, summer time, I will put on a darker jig, and fish above the fish. about 3 feet. true, sometimes steelhead will suspend, but if the flow is constant, I have found that winter runs especialy will be within a foot of the bottom, summer runs suspend alot more.
this method eliminated alot of guesswork. and I also find that winter fish will not be in the 10-12 foot deep holes, unless they are dark fish or have to pass thruough this area to travel upstream. look for winter fish to be in the typical 2-6 foot range under optimum river levels, if the water is high, well then, 18 inches to 2 feet.

Fuzzy

Silent Approach Jigs they're always there....the trick is to find them