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Cobalt blue, deeply clear, surrounded entirely by the mountains of the Sierra NevadaÖ
Lake Tahoe is a National Treasure.
Itís the largest alpine lake in North America.
People from near and afar feel keenly passionate about its protection.
Now, close to three million visitors a year.
After the 1960 Winter Olympics at Squaw Valley, Tahoe became a major tourist attraction.
Damage to the lake soon became noticeable. Decline in the lakes clarity raised the alarm.
Dr. Charles Goldman of UC Davis used secchi disks to quantify the problem.
This catalyzed a movement to use science and regional planning to reduce human impacts on the lake.
Contributing to this effort, the US Geological Survey is delivering a range of science through its hydrologists, geologists, geographers, biologists computer modeling experts and others.
The USGS provides a wide range of consistent, reliable, long-term data and maps that are crucial for evaluating and managing the lake and basin.
Since the 1980ís, in cooperation with its partners, the USGS has been doing repeated sampling of 10 of 63 streams entering the lake.
Nancy Alvarez: Well, one of the big concerns up at Tahoe is what are the amounts of nutrients and suspended sediment entering the lake from the streams. So, by monitoring the ten streams weíre able to come up with estimates for the amount of nutrients and suspended sediment that enters Lake Tahoe from all the streams.
Itís a longterm effort to understand exactly whatís entering the lake.
Samples are collected and quickly delivered to labs at the Tahoe Environmental Research Center for analysis.
When it became clear that two stroke jet skis were dumping polluting organic compounds into the lake they were banned in 1999.
Now in cooperation with the Tahoe Regional Planning Agency regular samples are collected during boating season and shipped to the USGS water analysis lab in Denver. Theyíre analyzed for extremely low levels of boat fuel components.
Tim Rowe: Today weíre sampling for Benzene all gasoline related compounds that come off from boating. Weíre out here for the pre-boating season to give a baseline of whatís here during most of the off boating season then weíll come out here six more times during the boating season and major holiday periods to see whatís going on. And weíve been doing this since they banned the jet skis in 1999. And following the concentrations of volatile organic compounds in the lake and they have come way down from what they were before the ban so we do see a slight increase during the major boating season like the major holidays but then it comes right back down in October and things are back clean as can be.
Delivering round-the-clock data are USGS streamgages on several streams entering Lake Tahoe and on the Truckee River leaving Tahoe ---- and a gage in the lake itself. These are essential to water management in Tahoe and downstream.
The streamgages record the vertical rise or drop of water levels and deliver their data via satellite.
And it has some intakes plumbed into the creek so it brings the water from the creek into the gauge, into the stealing well, and I have a float inside the well that goes up and down with the water level and is attached to some equipment that gives us readings and the gauge records it every fifteen minutes.
This oneís mainly used for the alert for any sort of flood issues and itís also used for the amount of water thatís entering Truckee so the Federal Water Master can gauge how much water he needs to allocate.
Chad blanchard-water master:
We have to have uUSGS data to do what we do. I am Chad Blanchard and Iím the Chief Deputy Water Master for the United States District court Water Masterís office. From six in the morning till about midnight when I go to bed Iím constantly looking at it, at work and at home. The Truckee River iis one of the most litigated rivers in the country or possibly the world. We are created to enforce two Federal Court decrees that basically divied up the water rights, and we need the USGS data to be able to meet those requirements.
Many of the USGS streamgages measure and record water quality information. Things like turbidity, specific conductance, ph, and temperature. Combined, the streamgage data keeps the region informed on its most precious and potentially hazardous resource, water.
We have urban and suburban use here and the network of gauges really gives us a good view of whatís going on. What happens in Incline Village on the gauges is a lot different than what happens on the west shore and what happens on the east shore and the timingís different the flows are different and it really gives us a good view of whatís coming into the lake.
Itís longterm data with a real and immediate impact.
One of the great visual and scientific products developed for the basin over the past 15 years is the USGS map of the lake floor. Until this no one knew what the lake bottom looked like.
The bathymetry involved sixty million soundings, or individual depth measurements of the deep parts of the lake.
We used a system called a multi-beam echosounder. In lake Tahoe it was about every four seconds as the boat moved along we sent out a ping we call it, send out the sound and then listen and then four seconds later we send sound out again and we just kept moving back and forth like youíd mow the lawn making sure we overlapped it so we didnít have gaps and it took about ten days and we had the whole thing mapped. And you can put it all together into a surface and actually begin to understand the processes that are going on on the lake floor. And so one of the great things about multibeam bathymetry or multibeam technology is that itís three dimensional that you have a latitude and a longitude and you have a depth and so with those three values you can generate three dimensional images on a computer screen. Generate fly throughs, you can interrogate the data. Its not just a pretty picture itís an analytical tool. No one expected what I found. What I found was this astounding landslide where half of the west side of the lake had caved in in the past and was scattered, debris was scattered all over the bottom of the lake .
The blinders were suddenly removed, and there now is the lake bed in three D.
More recently USGS scientists have spearheaded the effort to use aerial LIDAR to map the ground surface over the entire basin.
Using a computer program we can strip out that vegetative cover and reveal the bare earth. This is very clearly an active fault and for many years these faults have been debated whether they even exist and using this new LIDAR technology weíre able to clearly show that yes there are active faults on the west side of Lake Tahoe.
Aerial photographs taken over the past century have been the focus of USGS geographers Ė their work provides an instructive history lesson on Tahoeís past.
Aerial photography really gives you the power to go back in time. We took old aerial photos for 1940, 1969 and 1987. We can actually scroll through from 1940 to the present time and you can see the data that we actually created and see how much change has actually occurred from 1940 on.
The dramatic data is so easy to access Ė not just for land managers but for anybody, that Google Earth used it as their fist historical imagery sample. Then it was featured in the New York Times.
Thatís a view of the past to present, what about the future?
Over 80% of land in the basin is owned by the US Forest Service and will never be developed. But what about the rest? There are 6,000 parcels available for some form of development or planned use. But, what is the best use?
USGS geographers have developed the novel new tahoe land use simulation model for the Tahoe Basin. Itís being implemented by the Tahoe Regional Planning Agency.
The model can project out fates, of different land uses over time. Whether thereís a house, whether thereís a hotel, whether there is a park or open space. It can help inform what the future landscape might look like. And then you can take that outcome and relate it to other things like fire modeling or areas that are sensitive for water quality. So, you can do some post analysis from the output of the tool.
It can project 20 years into the future, results of choices made today.
Whatís interesting is that most of the private land ownership is down closer towards the lake where things are more sensitive and the uses are more important in terms of the overall concern for the Lake Tahoe Basin which is the water clarity of the lake. So in the decision support tool itís really trying to address this balance of well, where is it ok to develop and where is it not so ok to develop?
The goal? To make better choices for Tahoeís future.
This future does hold real threats from the continued human presence in the basin and from looming factors such as climate change. Science will remain an essential part of decision-making here.
Claire Fortier (Mayor pro tem, South Lake Tahoe, Ca):
At tahoe weíre dependant on science as the driver for decisions we make for policy.
Andrea Parra (Resident, Tahoe City, Ca):
Policy informed by science can really go a long way in protecting the quality of the environment that we have here.
Whether itís streamgaging to assist with water choices. Or monitoring of the lake and streams to quantify change, or mapping of the lake floor and mountains, or modeling to better shape the future, USGS researchers are working to rapidly deliver the best science possible in the on-going effort to protect, preserve and restore the spectacular National Treasure, Lake Tahoe.
Title: Lake of the Sky: USGS Tahoe Basin Science
A documentary film highlighting recent and past USGS research in the Lake Tahoe Basin. The program was produced for screening and release at the 2011 Lake Tahoe Summit. It features USGS science activities conducted by hydrologists, geologists, geographers, computer modelers, and biologists, among others. The story is told through the use of narration, expert interviews, graphics, animations, incredible video imagery and time-lapse video. USGS science detailed in the story includes water quality monitoring, streamgaging, Lake Tahoe bathymetry, aerial LiDAR, historic use of aerial photography, and the Tahoe Land Use Simulation Model. This wide range of consistent, reliable, long-term data and maps are crucial for evaluating and maintaining the lake and basin. The films concluding message is: "USGS researchers are working to rapidly deliver the best science possible in the on-going effort to protect, preserve and restore the spectacular National Treasure, Lake Tahoe".
Date Taken: 8/11/2011
Video Producer: Stephen M. Wessells , U.S. Geological Survey
Note: This video has been released into the public domain by the U.S. Geological Survey for use in its entirety. Some videos may contain pieces of copyrighted material. If you wish to use a portion of the video for any purpose, other than for resharing/reposting the video in its entirety, please contact the Video Producer/Videographer listed with this video. Please refer to the USGS Copyright section for how to credit this video.
Additional Video Credits:
Department of the Interior, U.S. Geological Survey
Directed & Produced by
A Production of:California Water Science Center
Nevada Water Science Center
Office of Communications & Publishing
Pacific Coastal & Marine Science Center
Pacific Southwest Regional Area
Western Ecological Research Center
Western Geographic Science Center
Camera & Editor
Graphics & Sonar Animations
Lake Floor Animations
Snow and Ski Footage Courtesy of
On Camera Interviews
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