River channels
Venkatesh Merwade, University of Texas at Austin
Data for channels
• Bathymetry data for channels mainly include points with (x,y,z) attributes.
• Data can be collected using– Traditional methods (surveying) – Depth sounder (using a boat)– LIDAR ( Light Detection and Ranging)
– SAR (Synthetic Aperture Radar), etc.
Data analysis
Start with points Create surface from points
Centerline/Thalweg
Cross-sections
ProfileLines
Extract all the necessary information
How do we do this…….
Defining a Thalweg
Input Step 1 Step 3 Step 4 Output
User defines an arbitrary centerline over the measurement points
Thalweg tool creates a surface using the measurement points
Normals are drawn at each vertex of the centerline to locate deepest points
All the deepest points replace the vertices of the old centerline
Final result is a 3D polyline defining the thalweg
Densify the initial centerline to get more points
Old vertices
New vertices
Step 2
Measure in ArcGIS
A PolylineMZ can store m and z at each vertex along with x and y coordinates.
0 64.0056 112.3213
Coordinate Transformation
m is measure along the centerline
r is distance across the river from the centerline
Sinuous river becomes straight when transformed into (m,r) co-ordinates.x
y
m
r
FishNet
Points are interpolated in ArcMap to produce a continuous surface.
FishNet is generated in ArcMap using the FishNet tool.
3D Visualization in ArcScene
Surface in transformed co-ordiantes
Sinuous river
Profile line and cross-sections
Straightened river
Straightened River in 3D
Data back to x,y coordinates
Original river in X,Y Profile lines and cross-sections in (x,y) created using FishNet in (m,r).
FishNet comparison
Regular FishNet FishNet created in (r,m)
Profile Lines and Cross Sections in 3D
Bird’s eye view!
Measurement points Surface
Thalweg/Centerline Cross-sections
ProfileLines Fishnet
GIS for River Channels
Develop generic ways to create all the channel features from measurement points.
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