GIS and River Channels. By Venkatesh Merwade Center for Research in Water Resources, University of Texas, Austin. Instream flow studies. How do we quantify the impact of changing the naturalized flow of a river on species habitat?
By Venkatesh Merwade
Center for Research in Water Resources,
University of Texas, Austin
1/2 meter Digital Ortho Photography
The electronic depth sounder operates in a similar way to radar It sends out an electronic pulse which echoes back from the bed. The echo is timed electronically and transposed into a reading of the depth of water.
Provides full profiles of water current speed and direction in the ocean, rivers, and lakes. Also used for discharge, scour and river bed topography.
Tells you where you are on the earth!
Computer and power setup
A boat is moving along a River and bathymetry is recorded as set of points with (x,y,z) attributes.
Finite element mesh and bathymetric data
Mesohabitat Criteria: V, D, V/D, FR
(Vadas & Orth, 1998)
A PolylineMZ can store m and z at each vertex along with x and y coordinates.
User defines an arbitrary centerline over the measurement points
Thalweg tool creates a surface using the measurement points
Densify the initial centerline to get more 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
Profile line and cross-sections
Bird’s eye view!
3D form is not a problem, what about the dimensions?? They are different everywhere..
Work in a normalized domain where everything is Unity (one). We can re-scale the results using additional information..
Depth and width going from zero to unity makes life easier without changing the shape of the original cross-section
r2Shape characterization through radius of curvature
beta c/s = (beta1 + beta2) * factor
a1=5, b1=2, a2=3, b2=3, factor = 0.5
a1=2, b1=2, a2=3, b2=7, factor = 0.6
Thalweg = 0.20
Thalweg = 0.40
a1=3.75, b1=5, a2 =1.75, b2 =1.75, f=0.25
a1=2.25, b1=7.5, a2 =2.25, b2 =2.25, f=0.225
a2 =2, b2 =2, f=0.24
Thalweg = 0.70