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 onWater Quality in
the Lake Tahoe BasinApplications of GIS

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

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• 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

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• 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.

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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.

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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.
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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 even land cover!
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2000 National Land Cover Data
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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).

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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 OR MORE
GENERALLY Collecting information about an
object without being in physical contact with it.

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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.
Satellite Imagery
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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
• plus NEAR INFRARED
• 4-meter ground pixel resolution.
• Current scene within pilot study area
• is approximately 25 km2. Acquiring
• entire basin coverage this summer.

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Satellite Imagery vs. Aerial Photography
2000 IKONOS Imagery False natural color
composite, bands 3-2-1 (RGB)
1987 Digital Orthophoto True natural color
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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
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Step 1

• Mask out areas in the IKONOS
• scene known not to have any
• impervious cover using other
• data sources and visual
• inspection.
• Infrared false color composite,
• bands 4-2-1.

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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

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Step 3

• Looking through the trees
• Use logical operations to fill
• gaps where forest canopy likely
• covers IC.

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Road detected!
Canopy covering road
Road detected undercanopy shadow
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Final Impervious Cover Layer
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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
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Final Process for Deriving Impervious Cover Layer
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Whats Next?

• Derive IC for the entire pilot study area.
• Compile historical land cover data using aerial
  photography.
• Quantify change and analyze in a GIS.

Contactcraumann_at_usgs.gov(650) 329-5648