The Hard Stuff

The bridges are being manufactured and the poured-in-place concrete abutments for the 5 new bridges have been approved by the City.  The longer the concrete allowed to sit, the stronger the abutment will be.  So the contractor is taking advantage of the holiday lull to get ready to pour concrete.  The photo above shows crew members marking out where the abutments will go.

The point bar is starting to take shape as cobbles are brought in and placed.

There are a few places along the stream where we want to let visitors get right up to the water, but we also need to provide some extra-strong protection for the bank.  In those places, the contractor has placed large, angular boulders that lock together to form a solid structure.  There is no grout or concrete holding the boulders together, just gravity and friction--two things that will outlast the strongest grout.

Bioengineering 101

On Friday (12/18/09), Drew Goetting, Principal designer at Restoration Design Group, came down from Berkeley to give us all a lesson in bioengineering.  First, dig a 3-4" deep trench at the toe of the bank slope.  Toss the dirt from the trench upslope to make it easier to fill the wattle.

Next, lay out the coir fabric so the edge extends a few inches upslope past the lip of the trench.  Secure the fabric to the soil with biodegradable staples (in this case, Bio-Stakes made from corn).

Shovel some of the soil from the trench over the coir fabric, then place willow pieces (branches, twigs, and leaves) over the soil.  Add more willows and more soil, making sure that the willows are generally oriented along the streambank and no branches are sticking out perpendicular to the direction of the water flow.  More willows and more soil, until the whole thing is the right height (see below for what "right" means).

Next, imagine that you are making a giant California roll, using the coir fabric as your sushi mat and the willows and dirt as your rice, crab (or krab), and avocado.  Kick and push the mixture into place--it is pretty rugged and will withstand some rough treatment.  The goal is an evenly compacted roll whose top is fairly level.  The finished top of the willow wattle should be above the water surface when the stream is flowing.

Pull the coir fabric fairly tightly over the soil and willows.  Secure the edge of the coir fabric with more biodegradable staples.

Pound some willow stakes straight through the entire thing.  The stakes should go at least a couple of feet into the ground under the wattle. 

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The result is a willow wattle.  The fabric will hold the soil and protect the bank on a temporary basis.  Meanwhile, some of the willows inside the wattle and some of the willow stakes will sprout and their roots will grow to hold the streambank.   After a while, the coir fabric and the staples will biodegrade and all that will be left will be willows, creating a sustainable streambank and a vegetative screen of riparian habitat.

Fine Grading

About half of the stream has dried out enough so that heavy equipment can go back in.  The contractor is doing the fine grading, getting the elevation of the streambed just right and contouring the banks so they are ready for installation of the bioengineering bank strengthening.  The contractor has also installed a couple of areas of boulder reinforcement like what is shown in the photo above.  The stream restoration consultants will come in tomorrow to look at this boulder reinforcement to make sure it is properly done.  Once the restoration consultant is satisfied with the contractor's work, this bank treatment will be replicated at a few more locations along the stream.  The boulder treatment is being used at spots where erosion potential is greatest--immediately upstream and downstream of the pedestrian bridges, and at a couple of places where the walking trail comes very close to the stream.  The restoration consultant will also be giving the contractor detailed instructions in planting willow poles and stakes, installing coir logs, and building willow wattles.  Some of the willows will even be harvested from within the Nature Center itself.

And the rains came...

The weekend rains put quite a bit of water into the streambed.  The contractor's crew was wading through water and mud today pumping the water out.  Once the water is gone, it will take another couple of days for the streambed to dry out enough to take equipment back in.  Hopefully, we won't lose too many more days to rain.

In Spite of the Rain

It's been a rainy week at the Nature Center, but work continues on the stream.  Last week I posted a photo of the point bar cobble mock-up.  You can see the mock-up in the center-right of this photo.  This week the exact location for the cobbles was defined and graded.  The cobbles will be about one foot deep, so the slope needs to be lowered by that amount to allow for a smooth transition between the surrounding grade and the cobbles. 

The stream grading is almost finished, with just a small area upstream of the south lake remaining.  When the muck was dredged out of the stream, the contractor spread it in an unused part of the Nature Center south of Willow Street.  The material was turned periodically, enabling it to dry out.  The contractor has used that dried out dredge material mixed with clean soil (yes, we tested it) to build up the streambed to the specifications on the plans.  The photos below show the big pile of material that was taken out of the streambed in October (left) and what that pile looks like now (right).  The woman with the muck in her hand is Jessica Hall from Restoration Design Group.

Mocking up the Point Bar

The contractor mocked up a small section of cobbles so we could get an idea of how the point bar area will look.  The area will use cobbles that are approximately 6" in diameter, with coarse sand spread between them for stability.  The mock-up shown above used materials on hand rather than the materials we want in the final product, so is has road sub-base instead of sand.  This worked well enough, but didn't look very good.  Even with the larger sub-base material, the field of cobbles was quite stable.  The area will be uneven to maintain a natural look, but will be fairly easy to walk on (though not for those in high heels or toddlers just learning to walk).

Field Design

Because the exact condition of the stream could not be determined in advance, this project is being done as a design-build. The contractor is working from 30% construction plans with frequent input from the designers and City staff. Here, the project team is discussing when and how to remove willows that lean over the trail.  These willows will be cut where the orange line has been painted across the trunk.  The trunks, branches, and leaves will be used for staking and in willow wattles; the root ball will be used for further bank stabilization and to give the stream a more natural look.

Surveying

The surveyors are out today, establishing the elevations for the stream from the north lake to the south lake. In concert with the stream restoration consultants, we will determine exactly how much to raise the elevation of the north lake. The decision will balance improving the stream flow with innundating the edges of the north lake.

Entwined No More

On Nov. 5, I posted a photo of a sycamore and pepper tree twisted together and seemingly forming a single hybrid tree. Above is another "before" shot, and below is the same tree today. You can see a small bit of the pepper that was left attached to the sycamore -- to have removed that would have damaged the sycamore unnecessarily. The sycamore is kind of spindly and leggy right now, but it likely will fill out and regain a more healthy shape now that the pepper has been removed and the sycamore has access to light and air.

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.

Wow!

The contractor has started removing vegetation from the sides of the stream and the effect is stunning. Removing a patch of overgrown shrubs opens up a whole area to sunlight and opens vistas that no one has seen in years (maybe decades). In consultation with City staff and the project landscape architect, non-native and selected native vegetation is being removed. As you can see in the photo, natives to be preserved in the midst of exotics to be removed are tagged so the heavy equipment operators can easily see what is what. Some natives have to be removed due to their condition or location, but the vast majority of removals are exotic invasives (privet and pepper). We will be re-using all of the vegetation that is being removed--some tree trunks will be used in or around the stream and everything else is being chipped to use as mulch around the Nature Center.

Getting Ready to Remove Vegetation

Today City staff, the contractor, and the construction manager walked the reach of the stream between the weir and the first place the trail crosses the stream downstream of the weir, talking in detail about vegetation removal. The contractor now knows what vegetation is to be removed and what is to remain. To let the equipment operators easily see what is to be done, bright paint was sprayed on trees that are coming out. In addition to removing a lot of non-natives (mostly Brazilian pepper and privet), these removals will open up the stream to sunlight, making it possible to grow shrubs below the tree canopy and further strengthening the stream banks.

Getting the Muck Out

I promised to write more about the muck, so today's post is all about muck. The first order of business in restoring the stream is to remove all the material that has accumulated on the bottom so we can create a more natural stream bed. If you have pulled out a branch that was stuck in this muck, you know that the stuff is sticky, gooey, and often smelly. The smell is from the decomposition that happens in an environment without oxygen (anaerobic decomposition). While there is some oxygen in the water, there wasn't much in the muck. But as I mentioned the other day, the muck doesn't smell. We let it dry out for a few days before we started removing it, and it appears that the drying got enough oxygen into the material to stop the anaerobic decomposition. This was really good news and has made this phase much more pleasant than it otherwise might have been.

We are spreading the muck in the undeveloped part of the Nature Center south of Willow Street. You can see it as you drive by from the eastbound lanes. The pile is about 4 feet high and covers about a half of an acre (as of this writing). Unless my math is bad, that's nearly 1,000 cubic yards. Later on, some of this might be mixed with sandy soil and recycled into the new stream banks.

What does the streambed look like without the water?

Now that the water has been drained out, a lot of the streambed looks like a wide, flat road. As the silt and muck has accumulated over the years, it has filled in all the nooks and crannies that were once there. What is left has almost no variation--no places for water to eddy or swirl, no places for fish to hide, no places where the water can speed up, no places for anything other than the shallow and slow flow from the north lake to the south lake. With no water covering it up, the evenness of the bed is remarkable.

I'm surprised that the muck doesn't smell really bad. After 30 years of anaerobic decomposition under the water, I was prepared for some pretty nasty odors. So far, the material that is being dredged out of the streambed just smells like mud. That's a relief!

Calling all mycologists

Here are some more examples of fungus found near the stream restoration construction site. Post IDs if you know what these are.

Name that Fungus

What is this? I assume it is a fungus of some sort. This photo was taken inside the construction area, downstream from the dam separating the stream from the lake, on the streamward side of the walking trail. The whole thing is about 1 foot in diameter.

Please Respect the Trail Closures

After years of planning and preparation, the Nature Center Stream Restoration is finally under construction. That means that the stream is now a construction site, and, as such, must be closed to the public. Rather than closing the entire Nature Center for the duration, we have closed only those trails that are within the construction area. We have put fencing across the trails at the closure points and put up maps showing which trails are open during construction. For everyone's safety, please respect these closures. When you are out walking the trails and you see a fence blocking the trail, please don't work your way around the fence to continue on the trail, even if other people clearly have done so. It costs us time and money to keep putting the fences back when patrons move them.

We can't put a fence all the way around the stream to cordon off the entire zone--too difficult, too expensive, and would damage too much of the vegetation. Instead, we are counting on every Nature Center visitor to cooperate with the trail closures and stay out of the construction zone.

So when you are out enjoying the beautiful natural environment, please keep your eyes open for construction signs and help us complete the stream restoration on time and within budget.

Critter Patrol

The stream has been draining since Monday. As it drains, we are doing everything that we can to make sure that no wildlife gets trapped by the receding waters. City of Long Beach staff, construction staff, and Nature Center volunteers have kept sharp eyes on the streambed for the telltale signs that animals may be in danger of getting stuck. A ripple on the water's surface might indicate a fish in a shallow pool. A small movement in the mud could be a crawfish working its way out. A tiny, muddy flip-flop could be a pollywog. All of these signs send the watchers reaching for their nets and buckets, to catch the animals and deliver them to the nearest lake. Hundreds of fish have been rescued, along with dozens of pollywogs, quite a few crawfish, and one turtle.

The rest of the stream water should be out by the end of the day on Friday. Then we will let the muck dry for a few days before the contractor begins taking it out. More about the muck in a future post.

Construction has begun!

Bright and early on the morning of Monday, October 5, 2009, the crew from Mike Bubalo Construction and PRM staff gathered at the Nature Center to start construction. The first order of business was to identify exactly where the trail closure fencing would go. Once those locations had been determined, Bubalo sandbagged the weir at the north end of the stream and built a dam at the south end to keep water from the lakes out of the stream. Later in the afternoon, Bubalo began pumping water out of the stream, over the dam, and into the south lake.