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GIS Data Base and Stream Network Analysis for The Chagres River Basin

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GIS Data Base and Stream Network Analysis for The Chagres River Basin ... Upper Chico. study area. Lower Chagres: good fit with the field data. 10m DEM: black areas ... – PowerPoint PPT presentation

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Title: GIS Data Base and Stream Network Analysis for The Chagres River Basin


1
GIS Data Base and Stream Network Analysis for The
Chagres River Basin David Kinner, USGS WRD,
Boulder CO, Helena Mitasova, NCSU, Raleigh, NC,
Russell Harmon, US ARO, Durham, NC, Robert
Stallard, USGS WRD, Boulder C, Laura Toma, Duke
University http//www.skagit.meas.ncsu.edu/helena
/measwork/panama/panama.html
2
Mapping Chagres
- until the mid-1990s topography was mapped at
a coarse resolution (12,000,000). -
inaccessibility of the upper Chagres, cloud
cover have made mapping difficult - recent
radar survey by the U. S. Army, new LANDSAT
imagery and field investigations new data
for more detailed and accurate maps
3
Primary digital data
- digitized maps geology, streams, topography
at 1250,000 scale -Interferometric
Synthetic Aperture Radar -
Elevation (IFSARE) 10m resolution DEM
-LANDSAT imagery 30m resolution -GPS-georeferenc
ed locations of field sites, rain gauges
and weather stations
4
Data integration
  • Integration of all available spatial data within
    a common GIS data base enables the participating
    researchers to analyze spatial relationships
    between different landscape phenomena and
    features and gain new knowledge about the studied
    landscape interactions.
  • Challenges
  • different coordinate systems and datums (ll,
    UTM)
  • different scales - field data to regional scale
    maps
  • different data models and formats (points,
    vector raster, shape files to spreadsheets)

H. Mitasova
5
Chagres River Basin GIS
Coordinate system Panama Canal Zone coordinate
system (UTM projection, zone 17, and NAS_O
datum) Data models and formats Raster 10, 25,
30 and 50m resolution used for DEM, stream
networks, basins and imagery Vector geology,
streams (old and new), contours Points field
sites, rain gauges, weather stations available in
ESRI and GRASS formats all data are clipped to
the watershed with 5km buffer Distribution
CDROM, Web site http//skagit.meas.ncsu.edu/hele
na/measwork/panama/panama.html
6
Chagres River Basin GISelevation
Derived from IFSARE
H. Mitasova
7
Derived from LANDSAT
H. Mitasova
8
Chagres River Basin GISgeology
Clipped from 1250,000 Panama geology map
9
Chagres River Basin GISfield sites
Measured by GPS
10
Basin analysis parameters
  • Basin analysis includes derivation of basin
    parameters
  • from a DEM based on flow routing. The following
  • map layers and quantitative characteristics
  • were derived
  • basin and sub-basin boundaries and areas
  • stream networks
  • flow accumulation and flow direction

H. Mitasova
11
Basin analysis tools
Basin analysis was performed using the following
raster-based tools
RivertoolsTM - a commercially-available
terrain analysis system for analyzing DEM-derived
river basin characteristics. It has multiple
flow direction algorithms,visualization tools and
tools for extracting statistical properties of
river networks (ie., bifurcation ratio,
statistical similarity, fractal dimension, etc.).
GRASS GIS - an Open Source/Free software
general purpose GIS. It includes a number of
modules for basin analysis, r.watershed was used
in this work.
12
Basin analysis methods
The basic D-8 flow routing algorithm is used by
the tools that were applied in the analysis.
The principle behind the D-8 is that water is
routed in the flow direction with the greatest
slope. The left image shows a hypothetical elevat
ion neighborhood on a DEM. The right shows the
corresponding slopes and the routing of water
from cell (I,J) to cell (I,J-1).
13
Sink filling is used by Rivertools as a precursor
to computing flow direction
The average filling necessary to route water
through the reach in this figure is 7.68 m - this
is magnitude larger than the filling typically
required for bare earth USGS DEM.
14
Flow is routed from one end of the flat to the
other by iteratively and arbitrarily defining
flow direction for each cell (iterative linking
red-line) or by projecting the surrounding
topography into the flat area (imposed
gradients blue line).
H. Mitasova
15
Basin analysis results
Sub-basins and stream network derived at 25m
resolution using r.watershed and threshold
62500m2 upslope area
16
Basin analysis results
Stream networks derived at low resolutions with
threshold 100xcell area
100m
200m
300m
400m
17
Basin analysis results
Stream networks derived at 50m resolution with
threshold for stream origin at 100 x cell area
comparison with field data for entire watershed
18
Stream networks derived at 10m and 25mresolutions
difference between iterative linking and
results from r.watershed
Rivertools iterative linking
r.watershed
19
Stream networks derived at 10m and 25mresolutions
difference between iterative linking and
results from r.watershed, 2D map
Rivertools iterative linking
r.watershed
20
The flat area isn't really flat, it was created
by DEM filling
3D view of the original DEM with streams derived
by Rivertools and field sites
Upper Chico study area
21
Lower Chagres good fit with the field data
10m DEM black areas are filled
Overlayed stream network and field sites
22
Detailed comparison of results 10m(black line),
25m (colored pixels) resolution and field sites
(green points)
23
Panama Stream Network r.terraflow
r.watershed 12 hours for 10m resolution Chagres
basin r.terraflow 3 hours for 10m resolution
entire Panama Flow accumulation using MFD option
for central Chagres
24
Conclusions
In spite of the impact of canopy on the DEM it
was possible to derive stream networks consistent
with the field data, probably due to significant
relief and relatively homogeneous vegetation
cover. In steeper areas the results from
different algorithms are practically the same,
however, there are differences in depressions,
flood plain and flat areas, where algorithms that
do not perform filling and iterative linking
provide better results. Field data are needed
for sound selection of threshold defining the
stream origin
H. Mitasova
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