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 onWater Quality in the Lake Tahoe Basin:Applications of GIS
Christian RaumannResearch and Technology TeamUSGS Western Geographic Science Center, Menlo Park, California
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
Must have GIS data before performing analysis.
Much GIS data is available for the Tahoe Basin: elevation, orthophotography, soils, fire, wildlife, forestry…
2000 National Land Cover Data
time + $$$
Mapping historical land use change and increase in IC:
"...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.
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.
IKONOS high-resolution multispectral imagery
than using a camera to photograph it.
visible RED, GREEN, and BLUE
plus NEAR INFRARED
is approximately 25 km2. Acquiring
entire basin coverage this summer.
2000 IKONOS Imagery
False natural color composite,
bands 3-2-1 (RGB)
1987 Digital Orthophoto
True natural color
Forest canopy cover and shadow is a major concern.
Commercial area around the “Y” intersectionLow canopy cover
Black Bart neighborhoodHigh-density canopy cover
Mask out areas in the IKONOS
scene known not to have any
impervious cover using other
data sources and visual
Infrared false color composite,
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…
Looking through the trees:
Use logical operations to fill
gaps where forest canopy likely
Canopy covering road
Road detected undercanopy shadow
Natural Cover (74)
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
Overall Accuracy = 158/170 = 92.94%