My recent trip to Illinois and Missouri afforded me an opprtunity to do something I've been wanting to do for a long time: see the confluence of the Mississippi and Missouri Rivers. And almost as an afterthought, I witnessed the confluence of the Mississippi and Ohio Rivers, a far more impressive spectacle than the former (perhaps without the cachet): the Ohio River contributes 38% of the mean annual flow of the Mississippi River, three times that of the Missouri River (see reference). The Arkansas and Red Rivers contribute 10% and 7%, respectively.
So why is Missouri's discharge so much lower than the Ohio's? After all, the Ohio River's watershed area is about 154, 200 square miles (400,000 square kilometers); that of the Missouri River is about 530,000 square miles (1,400,000 square kilometers). Despite its smaller watershed the Ohio's discharge is much greater than the Missouri's because it drains a far more humid region. And I suspect that the Missouri River basin has far more consumptive diversions (irrigation) than the Ohio River basin. That'll do wonders for a stream's discharge.
I've noted this kind of discrapancy before: where I live, the Willamette River drains an area about 5% of the Colorado River's, yet its mean annual discharge os about 60% greater than the Colorado's. And the watersheds of the Colorado and Columbia Rivers are about the same size, yet the latter's mean annual discharge is about 13 times that of the former.
The MS-MO confluence is about 12 miles (20 km) north of downtown St. Louis. Here it is - in all its glory. The Missouri is in the foreground, flowing to the right; the Mississippi is on the right, flowing towards me. I took this picture standing in Missouri; the little spit of land you see is actually a park, also in Missouri. The land way in the right background is Illinois.
Here is a shot of me standing where I snapped the photo. The area is nice; it is actually a state wetland preserve. Right in front of me are four engraved stone markers with quotes about the two rivers (see the bottom of the post).
The MS-OH confluence is about 4 miles (7 km) southeast of downtown (?) Cairo (pronounced 'care-roe'), IL, at the intersection of Highways 51 and 60-62. It's not easy to find - look for Ft. Defiance State Park.
An aside: Cairo has certainly fallen upon hard times. Its population has dropped from about 20,000 to under 4,000 in 100 years. I remember it from the late 1960s, when strife over civil rights and segregation brought in the National Guard. I don't think I've ever seen a place with so many abandoned buildings. But I did leave the main drag to drive through some neighborhoods and saw quite a few well-kept homes.
So here it is. I took this from on an observation deck (with a flagpole inconveniently placed right in the middle) on the Illinois side; the land in the left background is Kentucky: almost out of view to the right center is Missouri. The Ohio River is on the left, flowing to the right into the Mississippi, which bends around to the right (south) in the background. The tug pushing the barge is just about where the two rivers join.
This highway tunnel actually is a massive gate that can be closed to protect Cairo from floods. The picture is from the Wikipedia entry.
I say that my visit to the MS-OH confluence was almost an afterthought because I did not realize I would be so close to it. My meeting was actually in Vienna, IL,maybe 45 minutes from the confluence. So I headed there after my meeting. Glad I did. It was impressive.
Read about my adventures in St. Louis at the Gateway Arch. Pictures, too!