**[Topic List:]{.underline}**

1.  Impervious Cover Estimates for Lake Tahoe -- Tim Minor

2.  Water, Energy and Isotope Budget for Lake Tahoe -- Jim Trask

3.  Short Topics - Various

**[Topic Summaries:]{.underline}**

**Impervious Cover Estimates for Lake Tahoe -- Tim Minor, DRI**

Tim described the tools and some of the methods that he and Mary Cablk
used to make a map and estimates of hard cover in the Lake Tahoe Basin.
The team used IKONOS satellite data with a 1 m resolution from Space
Imaging, Inc. After the data was analyzed, they made a significant
accuracy assessment effort and provided a zonal analysis of coverage by
county, watershed and parcel.

The data included 19 overlapping scenes that covered 1329 Km2 and was
orthorectified to an existing coordinate system. The total information
cost was about \$130K. The data was processed with a combination of
automated and manual techniques in a GIS environment. Several spectral
layers were fused to create images that would allow the team to discern
between natural cover (trees, shadows) and hard cover using Principle
Components Analysis and manual techniques. Roads were manually digitized
using centerline analysis and county road widths. The final product
contained 1.5 Gigs of data in each of the 19 scenes.

The accuracy assessment field checked 500 randomly generated points near
developed areas in the Basin. It eventually determined that the mapping
was 92% accurate, with a significant percentage of errors coming from
roadside materials that are debatably "soft" coverage.

Results indicate that the basin was 3.5% covered at the time of the data
collection (2002). Interestingly, 76% of this coverage is located within
3km of the Lake and roughly half is within 1km. Jim's results have been
submitted to the TRPA and he would encourage further analysis for
management decisions.

**Water, Energy and Isotope Budget for Lake Tahoe - Jim Trask, UC
Davis**

**           ** Jim\'s talk reviewed some of his work from 2000-2001
that was designed to improve on previously reported water budgets for
Lake Tahoe.  This information has great importance for water managers in
our watersheds (South Lake Tahoe,Truckee, Reno) because the Lower
Truckee River is a significant source water for these areas.  Jim\'s
work focused on further constraining previous evaporation estimates for
the Lake.   He compared previous (based on a shadowed evaporation pan)
and new estimates to Sierra lake averages.  He found that Tahoe\'s
evaporation rate averages 36.2 in/year +- 3.6in/year, using new
evaporation pan data and energy balance measurements.  Inter-annual
variation in lake evaporation was also quantified.  He also presented
precipitation and runoff data showing (a)  relative inter-annual
precipitation and runoff is invariant across the Tahoe Basin (b)  the
current year\'s runoff volume is strongly correlated to precipitation
for the current and previous two years.  Jim also mentioned that the
stable isotope mass balance of the lake\'s water supports the water mass
balance results; and shows the lake water balance has not shifted or
trended substantially over the last few hundred years.

            When the audience had the opportunity to ask questions, Jim
was able to provide answers to many interesting management questions. 
He told us that the Lake loses 2/3 of its water from evaporation, and
only 1/3 down the Lower Truckee.    Jim also noted that the water
balance for the Lake is quite sensitive to shifts in climate.  For
example, if average basin  precipitation declines by 20% and lake
evaporation increases by 10% (climate change shift scenario), all flow
down the Lower Truckee would cease and lake level would decline.

            In his conclusion, Jim mentioned that Tahoe Basin air
temperature data indicates a trend of substantial increase of average
air temperature over the last few decades, but that the annual average
lake surface water temperature increase has been much smaller. 
Investigations are needed to help define the relation between air
temperature increase and Lake Tahoe temperature increase, and whether
there may be a lag period in lake warming, on the order of decades or
longer, due to the depth and volume of the lake.  If lake surface
temperature increase catches up with the current recorded increase in
air temperature, this could substantially increase the lake evaporation
rate, and make significant changes to the source water supply in our
watershed.

            Jim has gained a wealth of knowledge from his research and I
would encourage resource managers to contact him with relevant
questions: <jctrask@ucdavis.edu>.

**Short Topics-**

Chris Twomey gave a five minute overview of the recent workshop on
advanced flocculation treatments including electro-flocking and chemical
dosing. The presentations were mostly focused on temporary solutions for
construction projects, but there were presentations from Tahoe
researchers like Phil Bachand. The group consensus from those who
attended the workshop was that the technologies were interesting and
effective, but very expensive.

Rita Whitney described some interesting aspects of a large water quality
research center at Japan's Lake Biwa. This project was recently
publicized by a visiting researcher from the center.

Jack Landy also mentioned that the **TMDL Forum Dec 9-10,2004** will be
held in the Embassy Suites at South Lake Tahoe.

In Attendance:

Nancy Alvarez, USGS\*

Nicole Beck, 2^nd^ Nature

Ivo Bergsohn, STPUD

Mitch Blum, HDR\*

Mike Elam, TRPA

Robert Erlich, Lahontan

Brendan Ferry, TRPA

Michelle Kramer, WET Lab\*

Hamid Hakim, CalTrans

Roger James, WRM

Mark Keisler, CalTrans

Jack Landy, Lahontan\*

Kansas McGahan, Placer Co.\*

Kevin Murphy, CSUS-OWP

Andrea Parra, TRG

Chad Praul, NTCD\*

Lou Regenmorter,- CDM

Rick Susfalk, DRI

Chris Twomey, c2me\*

David Vaccarello, Placer Co.

Debbie Vreeland, Entrix

Rita Witney, TRPA\*

Brent Wolfe, CTC\*

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