Tuesday, November 7, 2017

External Instrumentation at Calaveras Dam

Typical survey monument

The old and replacement Calaveras Dams are located approximately 1,500 feet from the Calaveras Fault.  This means that we need to make sure that there are devices in place to monitor the movements of both the current and future dams and the area around them. 

The future Calaveras Dam will have a total of seven types of instruments inside it and around it.  Today I will focus only on two types of external instruments that will be placed at Calaveras Dam to help us monitor and protect it -- survey monument and accelerographs.

 I will explain the purpose of each and the role each device plays at Calaveras Dam. 

Survey Monuments

Survey monuments are placed both around the exterior of a dam and later will be placed on the surface of the dam.  They are monitored periodically to determine if they have moved from previous measurements, which would indicate any significant movement of the ground surface has occurred. Survey monuments also track the change in elevation of the ground surface, allowing us to determine the settlement of the new dam embankment. Some of the survey monuments placed at Calaveras Dam have survey prisms permitting the monitoring to be done remotely using a digital theodolite (aka total station).   We will have a total of 65 survey monuments at Calaveras Dam.  

 Survey Monument with Optical prism


Accelerographs are used to detect strong acceleration of the ground due to seismic forces. Accelerographs record the acceleration of the ground with respect to time. An Accelerograph is different than a seismograph. The difference is that an accelerograph doesn’t start working until something moves it.  A seismograph is recording continuously.  An accelerograph is a recorder that uses an accelerometer. Accelerometers are much less sensitive than seismometers, but have a much greater range. There will be 4 accelerographs installed around the new Calaveras Dam. 

These features are just some of the ways in which we are ensuring that the new Calaveras Dam serves our current and future generations of customers.

See you around the Valley!

Monday, October 30, 2017

Creepy Tarantulas and Tarantula Hawks

This week’s blog is about one of Sunol’s creepy crawlers—the tarantula. It lurks in the dark and doesn’t come out until October. It’s furry and looks menacing, but is it?

In Sunol there are two types of tarantulas: the blond and the brown tarantula. Pictured below is a brown tarantula or Aphonopelma smithi. This fellow was spotted by our field engineer, Ryan Dougherty.

If you’ve noticed an increase in spotting them, you’re not alone. In fact, it’s mating season for these giant arachnids. Male tarantulas will spend a lot of time weaving webs just above ground, outside the female’s burrow. If you don’t have a keen and trained eye, it is very difficult to tell the difference between a male and female tarantula. A typical tarantula reaches maturity at around 10 years. Most males die within a year after mating and females can live up to 25 years.

If provoked, the tarantula may inflict a painful bite, about like a bee sting. However, tarantulas tend to have a gentle nature, and rarely uses it’s fangs except to catch prey. If proved, it may raise its front legs and its abdomen to look aggressive. It may also release stinging hairs from its abdomen. These hairs irritate the skin of an attacker by digging themselves in with hundreds of tiny hooks.

They eat a variety of insects and other invertebrates, and their diet sometimes includes lizards, snakes and small rodents. They bite their prey, injecting it with digestive juices. Then they mash it with their strong jaws, and drink the liquid.

The tarantula’s feeding habits are gruesome but it's predator, the tarantula hawk, takes the word “gruesome” to another level. The tarantula hawk is a huge spider wasp. When the female tarantula hawk is ready to lay her eggs, she leaves the flowers behind and goes on the hunt for a tarantula. Once she finds one, she paralyzes it with a sting. Even though the tarantula is several times her own weight, she drags it to a hole, lays her eggs on it, and buries it. The eggs soon hatch into wasp larvae which slowly devour the paralyzed tarantula alive, from the inside out. Below is a picture of a tarantula hawk. Don’t let their beauty deceive you.

Image courtesy of San Antonio Express-News

If you are hiking in or around Sunol be on the lookout for these furry arachnids. Though they have fangs and carry poison, tarantulas are not considered a serious threat to humans. Please try not to step or run over one.

Happy Halloween!

Thursday, October 5, 2017

New Fish Screens at Fish Passage

Last week several members of our Fish Passage project took a trip to Sacramento to examine the project’s fish screens designed by Intake Screen Inc. (ISI). Next week, our team will be installing four of these fish screens at Fish Passage Facilities located in Alameda Creek.

Pictured below is one of the four new fish screens.

Here is Yen Ng, one of our project engineer’s; looking through what is called an internal cylinder brush. The internal cylinder brush is a key component of the fish screen.

Below is a diagram of a fish screen and its significant components.

Image courtesy of http://intakescreensinc.com/

The goal of the Fish Passage Project is to provide for safe passage of fish around the Alameda Creek Diversion Dam to support the restoration of Steelhead trout to the Alameda Creek Watershed. The project is part of the San Francisco Public Utilities Commission’s $4.8 billion Water System Improvement Project (WSIP) to repair, and seismically upgrade portion of the Hetch Hetchy Regional Water System.

Construction is expected to be completed in fall 2018.

See you around the valley!

Friday, September 22, 2017

Photo Friday at the Arroyo Hondo

Happy Photo Friday!

Today's post comes courtesy of watershed keeper Pat Jones.

Recently cloudy skies helped produce some stunning photos. This one shows Calaveras Reservoir and a major tributary into it - the Arroyo Hondo.

Have a great weekend, and we'll see you around the Valley!

Friday, September 15, 2017

Meet Sunol Valley's Natural Garbage Collectors

This week we wanted to highlight some special local inhabitants - turkey vultures.  If you drive anywhere in the Sunol Valley, you will almost always spot a committee of vultures waiting to see what their next meal will be. 

Turkey vultures, like this one spotted near Calaveras Reservoir, like to roost in bare trees to keep an eye (and nose) out for their next meal.

Turkey vultures, also known as turkey buzzards, are the most widespread species of vulture in the New World. They are so named because of their resemblance to the male wild turkey. Their range spreads from Canada all the way to the southernmost tip of South America. We call them nature’s garbage collectors because they feed almost exclusively on carrion and perform a crucial natural function of picking clean disease carrying carcasses.

Vultures are probably one of the most misunderstood birds in the animal kingdom. Here are some fun facts about these creatures:

  • Turkey vultures have one of the best senses of smell in the animal kingdom.
  • It's a misconception that they actually prefer their food rotten.  However, vultures do have a cool adaptation; their stomach acid is almost comparable to battery acid.
  • Nothing goes to waste with a vulture. They even make good use of semi-digested and digested food.

Photo courtesy of WikiCommons

Although few people would call them cute, they do perform a crucial role in natural areas like the Sunol Valley. 

See you around the valley!

Friday, September 8, 2017

The Building Blocks of the Replacement Calaveras Dam

If you are new to the world of dam construction, you might wonder what types of materials are used in building one.  Today’s blog will focus on what types of materials we are using to construct the new Calaveras Dam. Calaveras Dam is an earth embankment dam.  Earth embankment dams tend to be constructed of all types of geologic materials.

Calaveras Dam, July 2017
The picture above was taken recently; from it you can visually see the different materials. Let’s start with the middle and the most important material used in our dam, the core. 

The Core of Calaveras Dam

Zone 1 & 1A—aka…the Core
The core is made up of clay.  Clay is very dense and less permeable than most materials.  Our new dam will have a large core, which will help ensure that the dam withstands a 7.2 magnitude earthquake.  The clay used in our dam has been ‘borrowed’ from the south end of Calaveras Reservoir.

The core is taking shape.

Zone 1A- Core’s foundation
At the bottom of the core, you will find Zone 1A material. This clay is plastic, pliable clay, or another words, clay that has a Play-dohtm like consistency.   Zone 1A material is placed on the foundation’s bedrock and acts as a seal against water flow beneath the dam.

The core is the most important element of the dam and therefore must be protected.  We protect our core by using filters in both the upstream (reservoir side) and the downstream (dry side) of the dam to control the seepage of water and remove it safely from the Dam.

Zone 2 and 2A- Sand
Upstream zones are made of sand  (Zone 2A) and large gravel (Zone 5A)The downstream filters or chimneys are made of sand (Zone 2) and pea gravel (Zone 3).

Zone 5-Rock Fill
Further protection for both the core and filters is provided by rockfill shells. The upstream shell consists of hard durable rock because it will be submerged in the reservoir, Zone 5 material.  This material consists of metamorphic rock known as blue schist.

The downstream shell (Zone 4) consists of onsite material from a geologic formation known as Temblor Sandstone.  While this is a sedimentary rock, it tends to degrade into a gravelly, sandy soil and is best suited for drier conditions than the upstream shell.

Zone 6- Rip Rap
Wave action in the reservoir due to wind can erode most earthen materials.  Large durable rocks are placed on the slopes of the dam at the waterline to prevent this erosion. This is Zone 6 also known as rip rap.

Image courtesy of www.fhwa.dot.gov

See you around the valley!

Friday, September 1, 2017

What is a desmostylus and what is it doing in the Sunol Valley?

Photo courtesy of www.alchetron.com

A Desmostylus was a hippo-like creature that lived about 20 million years ago. It happens to be the only order of marine mammal to have gone extinct. Some individuals lived along the shoreline of an ancient ocean that used to be located where the Sunol Valley is today.

If you stumbled upon this would you know it was a rib cage?  What it looked like prior to Excavation

During excavation of the Calaveras Dam Replacement Project, the project paleontologists found not only a few teeth belonging to these strange creatures, but recently found an entire rib cage. Removing the fossilized rib cage of an animal that likely weighed between 200 and 400 pounds in life is no small task.

First the bone had to be cleaned and separated as much as possible from the surrounding rock on the hillside.

Above is the picture after our fossil was cleaned and ready to be removed.

In order to physically remove it from the hillside, crews used a lift to grab the entire rib cage. Now that the rib cage has been safely removed from the construction site, it awaits further stabilization treatment by project paleontologists. 

See you around the Valley!