Transcript Land Use Change and Effects on Water Quality and Ecosystem

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
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
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…
…even land cover!
2000 National Land Cover Data
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?
"...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.
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
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.
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
Forest canopy cover and shadow is a major concern.
Commercial area around the “Y” intersection
Low canopy cover
Black Bart neighborhood
High-density canopy cover
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.
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
Looking through the trees:
Use logical operations to fill
gaps where forest canopy likely
covers IC.
Road detected!
Canopy covering road
Road detected under
canopy shadow
Final Impervious Cover Layer
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.
Surveyed Points
IC Layer Points
Impervious
Cover
Natural
Cover
Row
Total
Impervious
Cover (96)
92
4
96
Natural
Cover (74)
8
66
74
Column
Total
100
70
170
Overall Accuracy = 158/170 = 92.94%
Final Process for Deriving Impervious Cover Layer
What’s Next?
1. Derive IC for the entire pilot study area.
2. Compile historical land cover data using aerial photography.
3. Quantify change and analyze in a GIS.
Contact:
[email protected]
(650) 329-5648