Monday, November 12, 2007

Gray Creek nr Oakridge

The title and image don't match? Well, let me explain, as this photo, taken in 1979 shortly after I started working for the USGS in Eugene, Oregon, has a connection to my work and my life. We installed the gage and stated collecting data on Gray Creek in July 1978 and operated it to October 1986. The gage was part of my field trip in 1978-79 and 1981-82.

The gage was on a small creek on the south side of the Willamette River along Highway 58 a few miles west of Oakridge (map). Access was on a one lane logging road off Highway 58 used by log trucks hauling logs out of the Willamette National Forest. The gage was just below a one lane bridge made entirely of large logs. We parked at the turnout for the bridge and serviced the gage on the left bank.

We made our measurements by wading at the gage. It was a fairly good cross-section about 6-8 feet wide and <1-2 feet deep for most measurements. Highwater measurements could be made from the log bridge when log trucks weren't using it, but you could usually wade the creek anywhere from a few feet to a few hundred feet downstream where the creek went around a bend and spread out into a wider creek.

The creek above the gage made a 90-degree bend and went almost due south into the headwaters. About a few hundred feet above the bend a giant (about 4 foot diameter) Douglas Fir tree had fallen across the creek, leaving an 8 foot gap between the creek and the lowest part of the tree. Over time, storms had washed other trees downstream which got caught into a logjam, along with rocks that rolled along the bed. It was a small, naturally made dam.

When I first saw and explored it one summer day there wasn't a lake behind it, it had filled with rocks, trees and debris collected over the years and the creek level was at the top of the debris and over the Douglas Fir tree holding everything up. All the storms up until then hadn't managed to dislodge anything and just kept adding to the debris in the logjam behind the tree. And so we thought our gage, protected by the log bridge, was safe.

In December 1981 we experienced several major storms in the Willamette River valley and the tributary basins. Then we got a phone call from the Forest Service folks asking if we had been to the gage. They hadn't been to the gage to check their sediment gage, but residents in the area heard a number of really loud sounds overnight coming from the upper creek valley. And being my gage, it was my job to check it out.

When I drove around the last bend I knew something was terribly wrong. The log truck bridge was severly damaged. The length of the creek and creek bed from the upstream bend past the downstream bend was filled with lots of rocks. Not small cobbles. Big and really big rocks. And while the gage was there, protected by the bridge, it was leaning downstream, had some dents in it, and was surrounded by the those big rocks with all the dirt gone.

There weren't any highwater marks to do an indirect there, and two weeks later, in the middle of a snowstorm we did an indirect a few hundred feet upstream of the highway some distance downstream from the gage. That was also an experience I won't forget (try finding a white survey level rod in a snowstorm through a surveyor's level/scope). But the real story was upstream of the gage.

After servicing the gage and make a new measurement, I hiked upstream around the bend. And not much to my surprise but really to my amazement, the entire logjam was gone. Completely. And the creek was then in the original channel before the logjam began to collect material and debris. It was a normal creek again. And the giant Douglas Fir was also gone, presumably broken into pieces and gone downstream. Such is the real world of hydrology. It's not sitting in the office, but in the field standing in creeks and rivers.

The other thing this gage taught me was measuring a creek. Making wading measurements is fairly straight forward, but there is one basic rule to judge when you're in over your head, really over your chest waders, or under your feet. The rule is that the maximum velocity times the deepest depth should not exceed 10, and you adjust it according to your experience. Most streamgagers can wade a factor 7-8 easily but over 9, it's becomes difficult for most normal size men, and above 10-11, you either better be big or tall.

This factor is adjusted when the maximum velocity and deepest depth in the same place, same vertical profile, in the creek, meaning the creek is at its highest energy at that point in the cross-section, which means during storms events, the energy is moving the bed material. You normally lower the factor by one or two to be safe. But sometimes you're faced with the choice of trying or not getting a critical measurements.

Well, one winter storm on Gray Creek I was faced with this issue. I really wanted to make a measurement but the flow was high for the creek. And being a new streamgager wanted to show I could do it. When you make a wading measurement, you have to first wade across the creek to set the tagline, then wade back, and then get the equipment to make the measurement, wading across and back again.

Well, about halfway across to set the tagline, I got stuck. I simply could not move. I was standing parallel to the flow using my wading rod for support as I tried to move each foot. The flow was so fast I had a standing wave on the front (upstream) side of my body like the bow of a ship. The velocity was so fast the rocks on the bed were moving and taking my feet downstream. I knew if i lost my balance, I would be gone downstream, part of floating debris in the flow.

Well, while standing in the middle of the creek with storm water flowing swiftly by and using my wading rod to just stand there while slowly sliding downstream, I thought of John Muir. And this is a really big, "Huh?" Well, John Muir wrote about hiking up a canyon in the Sierra Mountains once when he faced a vertical rock wall with the choice to climb it using a gap in the rock to the top or hike back down.

He chose the gap and began climbing, until he suddenly found the crack just as wide as the length his body from his shoulders to his feet. If it got wider he would fall, and he couldn't use his body to go back down. He was stuck with several hundred feet of air between him and the base of the rock face. He paused for sometime before he continued upward as the gap didn't widen. He realized his luck and his stupidity.

Anyway, I decided to waddle my way across, thinking if it got worse I could simply let go and float downstream or it would get better. It got easier to make it to the other bank. I set the tagline and waded back across, very slowly, sliding and waddling with my feet. And then I did it all over to get the measurement and release the tagline. I finished the day servicing the gage and calculating the measurement to drive home. Except two things.

One the measurement had a factor 12 and at the same point in the cross-section. I just sat there wondering what the hell I was thinking. And two, the photo. While I was catching my life again, I walked around the area. Since I often took my camera with me to take photos of the gages, work and just being in places few people go. I saw the leaf on the rock and took the photo. It was dark (overcast sky and deep in the creek valley), and had to use a slow shutter speed without a tripod.

I forgot about it until I got the slides back. Somehow it touched me as it still does. I had a print made then and another about 10 years ago with a professional print lab. It hangs by my desk as a reminder of our life. And so the photo became a personal story and feeling. The ephemeral and the eternal. Aren't we all the sum of each?

No comments:

Post a Comment