Dredging and Vegetation Removal Completed

The stream has been dredged and non-native vegetation has been removed. A swath ranging from 10 feet wide to 40+ feet wide has been cleared on either side of the stream bed. This photo is looking downstream from a spot between the 5th bridge and the south lake. The next step is a detailed survey to establish the exact elevation of the stream channel at approximately 35 locations between the north and south lakes. This is a critical step as the flow of the stream depends on the elevation falling between the two lakes. Before this project began, the north lake was only 1 foot higher than the south lake. That meant that the stream only had 1 foot of fall over its entire half-mile length. This project includes replacing the weir where the stream comes out of the north lake. The new weir will raise the elevation of the north lake by approximately 1 foot, effectively doubling the amount of fall as the stream flows to the south lake.

Boulders

Boulders will be placed in strategic locations to protect the stream banks from future erosion. The boulders have to lock together to effectively hold the bank. If they don't, the water will slowly edge the boulders away from each other, slowly gaining access to the soil behind, and eventually washing the soil away, leaving individual boulders where the bank used to be. Previous failed attempts at boulder treatment used rocks that were too round and so didn't lock together. Since we don't have a source for angular boulders, the contractor broke very large round boulders into smaller pieces. As this photo shows, the resulting pieces have lots of sharp edges--perfect for locking.

Last week I posted photos of this spot just upstream of the 4th bridge. This area is going to be a "point bar," where the cobbled bank will slope gently down to the water. The point bar will let visitors get right up to the water. In addition, it will allow the stream to spread out during heavy rains, reducing flooding and erosion along the rest of the stream. To create the space for the point bar, the trail is being realigned farther away from the stream. If you know where this drinking fountain is, you can get an idea of the new trail alignment.

This photo shows the current view from the junction of the one- and two-mile trails. As you can see, the whole area has been dramatically opened up. These beautiful sycamores that used to be almost invisible in the thicket of peppers and privet can now be seen in all their glory. You can see the caution tape that the contractor has tied around the trees that are being preserved. Mike Bubalo Construction Company is doing an excellent job of surgically removing the non-native species and leaving the natives--even in some places where they have to literally untangle the invasive species from around and between the natives. A few non-natives are being preserved, like the large palm in the above photo (only the trunk is visible). Even though it is not native, this palm helps stabilize the streambank and removing it would be difficult and costly. Besides, palms are not particularly invasive, so there is little harm in leaving it.

This is what the area between the 3rd and 4th pedestrian bridges looked like on 10/20/2009. Preliminary clearing had been done to allow equipment access through the stream corridor so the contractor could start removing the muck from the streambed.

And this is what the area looks like today. A tremendous amount of vegetation has been removed from the banks. All debris* is being chipped and the mulch spread on-site. Vegetation has been cleared from the north lake as far downstream as the 4th pedestrian bridge (or rather, where the 4th bridge used to be and will be again). The contractor is being very careful to protect the native vegetation as the exotics and invasives are being removed. The whole stream is being opened up to air and sunlight. The claustrophobic feeling of being choked by the overgrown vegetation is gone.

* One streamside tree was covered with an unknown fungus. As a precaution, that tree was taken to the area south of Willow Street, rather than chipping it up and spreading a fungus that was potentially harmful.

Room to breathe

You can almost hear these sycamores saying "ahhhh" now that the Brazilian peppers and other invasive species that were crowding around them have been removed. With the other vegetation gone, the magnificent structure of these beautiful trees can be seen.

Some of the trees were so crowded together that they had actually grown into and through each other. It almost looks as if these two trees have created a hybrid, a sort of "Western Brazilian sycamore." It will be interesting to see what the sycamore looks like once the pepper is removed.