land use change and effects on water quality in the lake tahoe basin applications of gis
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Land Use Change and Effects on Water Quality in the Lake Tahoe Basin: Applications of GIS. Christian Raumann Research and Technology Team USGS Western Geographic Science Center, Menlo Park, California. Project Background 3-year project funded by a Geographic Research

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land use change and effects on water quality in the lake tahoe basin applications of gis

Land Use Change and Effects onWater Quality in the Lake Tahoe Basin:Applications of GIS

Christian RaumannResearch and Technology TeamUSGS Western Geographic Science Center, Menlo Park, California


Project Background

  • 3-year project funded by a Geographic Research
  • Application Prospectus Grant (now in second year)
  • Multi-agency collaboration:
  • USGS Menlo Park: Principle investigators
  • Desert Research Institute, Reno:
  • Remote sensing specialist and geomorphologist
  • USGS Water Resources, Carson City:
  • GIS analyst and hydrologist

Lake Tahoe Basin

  • Located on the California-Nevada border
  • in the central Sierra Nevada.
  • Permanent population of 60,000
  • Transient population over 300,000
  • 22 million visitors per year.
  • Destination for snow sports, hiking,
  • camping, gambling, water sports, and
  • general tourism.
  • Significant development during the
  • past 70 years.
consequences of growth
Consequences of Growth

Land use change contributes to a highly disturbed ecosystem.

Increase in impervious surfaces: any material that prevents the infiltration of water into soil and thereby changing the flow dynamics, sedimentation load, and pollution profile of storm water runoff (roofs, roads, parking lots, sidewalks, etc.).

Major issue: Decrease in Lake Tahoe water quality (~1.5 feet/year) due to increased nutrient and pollutant loading.


Pilot Study Area

Upper Truckee River and

Trout Creek Watersheds

Develop methods and test hypothesis,

then apply them to the entire basin.

Representative of all land use/land cover

types in the Tahoe Basin.

Contains the most developed area of the

Basin: City of South Lake Tahoe.

Many agencies (TRPA, USFS), private

companies (Sierra Pacific), and

community groups (UTWFG) involved

in related projects.

currently available digital data

Currently Available Digital Data

Must have GIS data before performing analysis.

Much GIS data is available for the Tahoe Basin: elevation, orthophotography, soils, fire, wildlife, forestry…

…evenland cover!

data collection
Data Collection
  • High-resolution historical land cover and impervious cover (IC) data is unavailable, so a comprehensive data collection effort is necessary to produce data for analysis in a GIS.
  • Case with many GIS projects: a need for specific data =

time + $$$

Mapping historical land use change and increase in IC:

  • Derive land use data with IC estimates from historical orthophotography using traditional interpretation techniques (labor intensive!).
  • For present day coverage, derive land use and IC from IKONOS multispectral satellite imagery using remote sensing software employing semi-automated routines (T.Minor).
what is remote sensing
What is Remote Sensing?

"...the science of acquiring, processing, and interpreting images, and related data, obtained from aircraft and satellites that record the interaction between matter and electromagnetic radiation." -- F.Sabins, 1997


Collecting information about an object

without being in physical contact with it.


Satellite Imagery

Reflected/scattered/emitted energy can be measured using various kinds of remote sensing instruments. Thankfully, many earth materials have very unique spectral signatures, almost like fingerprints.

remote sensing of impervious surfaces
Remote Sensing of Impervious Surfaces

IKONOS high-resolution multispectral imagery

  • Collected by satellite that “scans” the earth rather

than using a camera to photograph it.

  • 4 spectral bands:

visible RED, GREEN, and BLUE


  • 4-meter ground pixel resolution.
  • Current scene within pilot study area

is approximately 25 km2. Acquiring

entire basin coverage this summer.

satellite imagery vs aerial photography
Satellite Imagery vs. Aerial Photography

2000 IKONOS Imagery

False natural color composite,

bands 3-2-1 (RGB)

1987 Digital Orthophoto

True natural color

cover variety in the tahoe basin
Cover Variety in the Tahoe Basin

Forest canopy cover and shadow is a major concern.

Commercial area around the “Y” intersectionLow canopy cover

Black Bart neighborhoodHigh-density canopy cover

step 1
Step 1

Mask out areas in the IKONOS

scene known not to have any

impervious cover using other

data sources and visual


Infrared false color composite,

bands 4-2-1.

step 2
Step 2

Impervious cover layer generated

using image classification

processing techniques (PCA).

Impervious cover in red,

natural cover in black.

However, forest canopy cover is

still an issue…

step 3
Step 3

Looking through the trees:

Use logical operations to fill

gaps where forest canopy likely

covers IC.

road detected
Road detected!

Canopy covering road

Road detected undercanopy shadow

accuracy assessment








Cover (96)




Natural Cover (74)









Accuracy Assessment

In the field, 170 “random” points were surveyed using GPS.

Labeled points as “impervious cover” or “natural cover”, then compared

to corresponding points in IKONOS-derived IC layer.

IC Layer Points

Surveyed Points

Overall Accuracy = 158/170 = 92.94%

what s next
What’s Next?
  • Derive IC for the entire pilot study area.
  • Compile historical land cover data using aerial photography.
  • Quantify change and analyze in a GIS.

Contact:[email protected](650) 329-5648