The launch right above the dam at Independence is really top-notch for an Iowa river launch. Two concrete ramps and a dock (very handy if you’re alone).
I’ve been north from that point about a mile, to the very top of the impoundment above the railroad tracks. The entire impoundment is less than 2 feet deep, but the channel runs 6-12 feet all the way to the top end. We didn’t try to go above that, but we were passed by a Tracker deep-V, probably about a 18′, since it was much larger than my bass boat. He continued up around the next bend and out of sight, doing about 25mph all the way. He didn’t look concerned about hitting anything.
If you’re not in a hurry, I would put in at Independence and head north to where the river narrows above the impoundment. Then tilt up the gas motor and throw down the electric. The current isn’t very fast, and you should be able to keep going without risking your lower unit & prop. It’s not a very effective way to cover a lot of ground, but the first time your electric runs into a rock you’ll be glad you took your time.
If you want to put in with the flat-bottom, the best river launch info I’ve found to date is in the book Iowa Fishing Atlas, Volume 2 – Rivers and Streams. He has a breakdown of every river in Iowa along with all the launches, float sections, portages, yadda yadda. Check to see if your library has a copy.
Oh yeah, and MOST IMPORTANTLY OF ALL: email me or post here to let me know how you do!