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.