Home → Field Trip Reviews by the Society → GSOC Field Trip to Mt. Hood, 2007

GSOC Field Trip to Mt. Hood, 2007

by Tara Schoffstall and Ken Cameron

Editor's note: I have included Ken Cameron's field trip guide in this review. Ken's portion will be in boldface type, and Tara's in normal.

Stop One:

Mileage: Cumulative Miles

0.0: 0.0

Starting point at Welches. Head east on Hwy 26

1.0: 1.0

Intersection with Lolo Pass Road in Zigzag. Turn left. This intersection is across from the Zigzag Inn and before the Ranger Station.

0.3: 1.3

The bridge over the Zigzag River. There are no places to park here, but slow down and look at the river, especially near the water’s edge. There is no erosion, no debris caught in the brush, no evidence of high water at all.

4.0: 5.3

Turn off to Old Maid’s Flat. Due to storm damage, there are no signs. The turn off is just beyond the National Forest Boundary sign.

Park in the area just beyond the turnoff on the right. We will be walking upstream along the road (there is no parking available farther up) for about half a mile to where we can see the Sandy River. The river was incredibly erosive during the storm, wandering back and forth, taking the bank and trees with it. Note, however, that at least in this reach there is no deposition at all.

On Saturday, June 30, 2007, Ken Cameron led a field trip around the Zigzag, Sandy, and White Rivers to show us the damage the rain storms last November caused to the area. To start the day, we met in Welches at 9am. Ken then took us to our first stop at the Sandy River Bridge on Lolo Pass Road. On the way, we compared the damage between the Zigzag and the Sandy Rivers. The Zigzag River was completely unaffected. Ken was very eager to point out that even the moss on the rocks wasn’t touched.

However, when we reached the Sandy river, this is what we saw: The bridge was washed out!

And check out the other damage: This is the upstream view. Notice the trees and debris all over the place, as well as the erosion.

The downstream view shows even more damage.

The question Ken posed to us was: why did the Zigzag River get no damage, while the Sandy River got pummeled? He then showed us an overview map of the Mt. Hood area with the drainage basins for each river outlined. One thing he pointed out was that the Sandy River basin covers about 31 square miles, whereas the Zigzag basin only covers about 17 square miles. More area equals more water captured. So because the Sandy River basin is bigger, it gathered more water, and caused more erosion.

Another factor Ken pointed out was the orientation of the drainage basin with respect to the movement of the storm. The storm was out of the northwest and the Sandy basin is oriented northwest to southeast, parallel to the storm track. The storm traveled up the basin and was able to drop a lot of rain, creating a long storm surge. The Zigzag basin, on the other hand, is oriented southwest to northeast, perpendicular to the direction of the storm track. The storm passed over the basin quickly and didn't drop as much rain.

Stop Two:

4.0: 9.3

Back to the intersection of Lolo Pass Road and Hwy 26. We will need to turn left and head east. This can be a problem with traffic, take your time, we are not in a hurry. Head east, going past Government Camp to the Hwy 35 junction.

13.7: 23.0

Junction with Hwy 35, you will take the exit to the right, Hood River and Mt. Hood Meadows.

9.4: 32.4

Pocket Creek Snow Park, parking is on the right.

Here Newton Creek burst out and ran along the side of the highway. While the flow was not large, the effects to the road were. It was mostly erosive, but did bring down some large boulders and deposit them in the trees. In the eroded cuts you can see the evidence of at least three previous events of about the same size, complete with buried soil horizons and logs. Turn around and head back west on Hwy 35. You will have to cross the highway. Again, take your time and be careful, we have plenty of time.

After viewing the bridge on Lolo Pass, we returned back to Hwy 26 and turned onto Hwy 35, heading towards Pocket Creek Snow Park.

This is a view upstream of the damage Newton Creek caused when it left its banks and ran along the side of Hwy. 35. A surge came down Newton Creek, which the culvert for the creek could not handle. Because of that, the creek jumped into the ditch that ran alongside the highway, basically widening the pre-existing ditch.

This picture shows the size of some of the debris the surge was able to carry. Note the size of many of the boulders. Looking at the lack of bark on the left sides of the trees on the right also show the scars from the event. The red is oxidized iron. Reduced iron was brought up and exposed to the air, causing it to turn red.

There are at least 2-3 other flood deposits exposed here.

This is a better picture showing how logs were once covered by a previous flow, and then later uncovered when Newton Creek eroded the material.

Stop Three:

5.5: 37.9

White River Snow Park. Cross the bridge over the White River and take the first road to the right and pull into the far parking area.

This is the last stop of the day and the most dramatic. It is also where we will have lunch and there are restrooms available. The White River flow was completely unlike the other sites we have visited. Here a sudden burst of water from the glacier created a debris flow which deposited many feet of rocks in the valley, plugging the channel by ODOT as their “cure” to the problem and talk about the difference between debris flows and clear-water floods and how they react to channelization. We may walk back to the bridge to see the down stream work that was done.

Our last stop of the day was the White River Snow Park.

This is a view downstream, showing the damage the storm caused. The picture is taken standing on the west berm that ODOT created to help channel the White River towards the Hwy 35 bridge. During the November 2006 event, the White River had jumped its channel to the east. This is a picture of the river back in its normal channel. Please note that the part of the bridge that you see is not the whole bridge. It is only the part that covers the White River. The bridge and the White River channel actually extend at least ¼ mile further on each side. ODOT has filled under the bridge, only allowing the White River to go under the bridge at this one narrow point.

The view upstream shows the debris flow more clearly.

The question here is why is the damage so extensive? The drainage area is actually less than that of the Zig Zag River, yet the Zigzag was untouched compared to the Sandy – possibly because the Sandy has a larger basin and therefore collected more water. The answer here, is that while the Sandy was only a storm surge event, the White River experienced a glacial flood outburst (jokulhlaup). Therefore, the damage was more extensive. This area is prone to frequent jokulhlaups. Ken discussed the advantages and disadvantages to Oregon Department of Transportation’s engineering solutions to the outbursts, including whether which is more cost effective: building an entirely new bridge to span the entire river channel, or merely fixing the bridge every time the jokulhlaups bring down enough debris to destroy it.

The day ended with lunch at the White River Snow Park, and we returned back to Welches.