Monthly Archives: May 2013

A tale of two rivers

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Last Friday on my way back to Rome from Huntsville, I stopped at the Little River Falls overlook to see what had happened to the flow since I saw it three days earlier. The river was down, but not very obviously. Here is the picture from a week ago last Tuesday (April 30) and from last Friday (May 3). You can see some differences. More rock is visible to the left in the second figure, but in general they look pretty similar.

Little River Falls, Tuesday, April 30

Little River Falls, Tuesday, April 30

Little River, May 3, 2013

Little River, May 3, 2013

After I got home, Leah and I went into town to eat. We stopped to get a picture of the Oostanaula River. This is a picture of the river Friday afternoon looking downstream from a pedestrian bridge towards the Second Avenue bridge.

Oostanaula River, May 3

Oostanaula River, May 3

Just downstream from the highway bridge there is an old, abandoned railroad bridge and just downstream from that, the Oostanaula flows into the Etowah River to form the Coosa River. Downtown Rome is to the left in this shot; Broad Street crosses the Etowah just up from the confluence of the two rivers. If you boated down the Coosa into Weiss Lake (watch out for the old Mayo’s Lock and Dam, because you have to portage around that), you could find the mouth of the Little River.

The Oostanaula was muddy, but the color was closer to a murky olive than to the red clay it sometimes shows immediately after heavy rain. The Little River was pretty much clear in both of the shots I took.

When I stopped at the Little River on Friday, I met a National Park Service volunteer who had a clipboard with an interesting figure. The figure showed a week-long history of the water flow in the Little River where it empties into Weiss Lake, not very many miles downstream from the waterfall.

Here is a figure I got from the USGS showing the period from just before the weekend of April 27-28, when we got a lot of rain. It includes last weekend, when we got some more rain. I put red diamonds on the chart showing the levels on Tuesday and Friday when I took the pictures. The Y-axis is on a logarithmic scale, which can be hard to read, so I added some additional numbers.

Streamflow on the Little River

Streamflow on the Little River

You can see that the level on Friday, about 450 cubic feet per second, was roughly half what it had been on the Tuesday before. A cubic foot is about 7.5 gallons, so 450 cubic feet per second is about 3375 gallons per second. An olympic pool is about 660,000 gallons according to Wikipedia, so it would take a little over three minutes to fill at that flow. That doesn’t really sound like that much.

The Park Service volunteer showed me a picture of the falls from a few years ago when the flow was about twice the maximum of the April 27-28 weekend, or over 20,000 cubic feet per second. The photo was impressive. He said the record high flow was about twice that number, which would be really impressive, and probably scary from the overlook.

This is a figure showing streamflow for the Oostanuala River for the same period. I think the flow when I took the picture above was probably around 17,000 cubic feet per second.

Streamflow on the Oostanaula River

Streamflow on the Oostanaula River

As I said in the earlier post, the Little River is a short river with a small watershed compared to the Oostanaula River, so it responds quickly to changes in the local rainfall. The Oostanaula itself is about 50 miles long, about the same as the Little River, but it is formed by two other rivers, the Conasauga, about 93 miles long, and the Coosawattee, about 50 miles. The Little River drains an area of about 200 square miles. The total Oostanaula basin is about 2150 square miles, more than 10 times larger. It’s no wonder it takes longer to respond. The tan colored triangles in the plots show the average stream flow for the two rivers. The Oostanaula is about 3000 cubic feet per second on average during this period, while the Little River is around 200 or 300 cubic feet per second, or about one-tenth as much. It seems reasonable that the stream flow is proportional to the area drained.

But there is another interesting difference between the two rivers. The Little River responds very quickly to rain, and then again when the rain stops. You can see how quickly the river flow drops during the week, when there was no rain. It started raining again late Friday and the river flow jumped up again pretty quickly. You can see a period when the rain stopped for a while over the weekend, and then started up again. Compare that to the flow of the Oostanaula. The Oostanaula began to drop after Friday, May 3, but slowly compared to the Little River. It increased again last weekend when it started to rain again. There is a segment with no data for some reason, but you can follow where the curve would be.

One of the interesting things about these figures is how this kind of behavior shows up in other physical systems. Most people have experience with cast-iron frying pans and also with aluminum foil. You know if you fry eggs in a cast-iron pan, the pan will stay hot for quite a while after you take it off the stove. And you probably also know that if you have a pan covered with aluminum foil in a hot oven, you can touch the aluminum foil almost immediately after you take it out of the oven. If you plotted the temperatures against time, the cast-iron pan would look like the Oostanaula, and the aluminum foil would look like the Little River. In my business, we would say the cast-iron pan is thermally massive, and the aluminum foil is thermally lightweight, or thermally responsive. I think it’s pretty cool stuff, but that’s just me.

I plan to keep my camera handy, and if we have some really heavy rain, I’m heading over to the Little River. I want to see just how scary it can get over there.

Promises, promises

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Partial rainbow

Partial rainbow

We’ve had a lot of rain over the last two weekends. Rome and Floyd County were in flash-flood warning areas both weekends. The heaviest rain was ending Monday evening as I walked the dogs. This partial rainbow appeared right before sunset. According to the Atlanta TV weathermen, it’s supposed to dry up and get warmer this week. And rain again next Saturday.

Friday Felines

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Smokey puts up with a lot

Smokey puts up with a lot

Smokey puts up with a lot, and he seems to love it. He actually seems to enjoy some pretty vigorous brushing to get the knots out of his fur. None of the other cats are anywhere as even tempered as him.

Not so little river

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We had a lot of rain towards the end of last week, and then a little more on the weekend. There were flash flood warnings in the area, and the Oostanaula River was high and muddy. My drive over to Huntsville takes me over the Little River right above a waterfall, so Tuesday morning I thought I would see what the falls looked like.

Little River Falls

Little River Falls

The falls here are somewhere between 45 and 60 feet high, depending on which source you believe. It’s not too high, but high enough to kill people when they are swept over the edge. The end of the Alabama Highway 35 bridge is to the upper right in this shot. I posted another shot of this waterfall a little while ago. (If you click on the link to the previous post, you can tell something about the time of day when I took these two, otherwise similar pictures.)

According to the National Park Service Web site for the Little River Canyon Natural Preserve, the Little River is unique in that it forms and flows for essentially its entire approximately 50-mile length on top of a mountain. It flows generally from northeast to southwest on Lookout Mountain.

Lookout Mountain was the site of a Civil War battle fought on its slopes near Chattanooga, Tennessee. It’s probably better known now for its tourist attractions. If you have driven the backroads in the Southeast, you have probably seen a barn roof with a painted message saying “See Rock City.” There are also signs saying “See Ruby Falls.” Rock City is a tourist attraction near Chattanooga on top of Lookout Mountain. It’s a jumble of sandstone boulders that the fanciful can imagine to look like a city. The owners help that illusion with various elf or gnome figures located here and there. Ruby Falls is an actual waterfall deep inside Lookout Mountain in one of its many, many caves. You can take an elevator down to see it.

Lookout Mountain is very different from Lavender Mountain and the other mountains around Rome. Our mountains are what you expect when you hear the word “mountain”; they have slopes that lead up to a ridge, and on the other side of the ridge, slopes that lead down to a valley. Lookout Mountain and most of the other mountains to the west towards Huntsville, Alabama, are part of the Cumberland Plateau. They have slopes that lead up to a relatively level region that can be miles wide before you reach the downhill slopes on the other side. If you were put down five miles to the west of the Little River bridge, you would not know that you were on top of a mountain. On the other hand, you could probably walk from the Little River bridge to the eastern slope in about fifteen minutes. The width of the mountain makes it possible to contain a river, but the hard sandstone cap also limits the flow of the river. In dry weather, it shrinks to a trickle.

Little River Canyon

Little River Canyon

In this image, the waterfall and the bridge are at the top center. The Little River makes a big loop, with the highway running very close along one side. The edge of the mountain is where the highway curves and runs down along the right side of the image. This is a steep slope.

There is some question about how the Little River ended up on top of the mountain. One theory is that the limestone that lies beneath the sandstone cap was eroded by an underground stream, and eventually collapsed, leaving what we see now as a canyon. The other theory is that some unknown event caused a rift to form, which was eroded over time into the current canyon.

The Little River flows into Weiss Lake, which is formed by a dam on the Coosa River. The Coosa is formed by the confluence of the Oostanaula and Etowah Rivers in Rome. The rivers around Rome flow through wide floodplains, and they pick up a lot of mud during heavy rain. They are normally green, which indicates a good burden of organic material and sandy silt, but they are relatively clear. My father and I paddled a canoe a few times on the Oostanaula when it was flowing normally. When I dipped my paddle into the water, it gradually disappeared into a swirl of faintly glimmering silt. This weekend, the rivers in Rome were rich, red and opaque. On the other hand, the Little River was clear, even though it had a much higher flow than normal, mainly because it flows over rocky land and doesn’t pick up much muddy runoff even in heavy rain.

I think I know what the Little River would look like down at Weiss Lake. The Little River’s water would look dark as it flowed into the lake and gradually extended in tendrils into the muddy water. We used to see something similar where the Oostanaula met the Etowah. When I was growing up, there were mines along the Etowah that made the river muddy all the time. The Oostanaula’s green water and the Etowah’s red water mixed reluctantly at their junction, right at the end of Broad Street in Rome. The red eventually won, and the Coosa was muddy as it left Rome. Some years ago the mining runoff along the Etowah was stopped, and now it’s green like the Oostanaula. But right now, the Etowah and the Oostanaula are both very muddy, and I’m sure the lake is, too.