River Channels in GIS. Venkatesh Merwade, Center for Research in Water Resources, University of Texas at Austin. Overview. Fish Habitat Modeling using GIS Standardized 3D representation of river channels River Channel Morphology Model RCMM and Hydraulic Modeling. Instream flow studies.
Venkatesh Merwade, Center for Research in Water Resources, University of Texas at Austin
Depth & velocity
DecisionMakingFish Habitat Modeling
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
(Environmental Modeling Systems, Inc.)
(US Army Corps of Engineers)2D Hydrodynamic Model
Finite element mesh and bathymetric data
Mesohabitat Criteria: V, D, V/D, FR
(Vadas & Orth, 1998)
Source: RMA2 reference manual, 2002
River channels are represented as a set of cross-sections and profile-lines in Arc Hydro
3D NetworkGIS database for river channels
Develop generic ways to create all the channel features from measurement points.
Start with points
Extract all the necessary information
Create surface from points
How can we do this…….
A PolylineMZ can store m and z at each vertex along with x and y coordinates.
(s = 0, n = 0)
Q(s,n,z) coordinate system
Steps 3, 4
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
Anisotropic kriging gave the least RMSE
sFishNet (x,y,z) to (s,n,z)
FishNet in (s,n,z) is flow-oriented!
Bird’s eye view!
Study area is only few miles long
Instream flow studies in Texas
Results from small studies are extrapolated
Are the results valid?? Can we cross-check??
@ 30 milesSite1 and Site2 on Brazos River
The data for Site 1 and Site 2 are available as (x,y,z) points.
w = nL + nRStep 1: Normalizing the data
For any point P(ni,zi), the normalized coordinates are:
nnew = (ni – nL)/w
znew = (Z – zi)/d
For nL = -15, nR = 35, d = 5, Z=10
P (10, 7.5) becomesPnew(0.5, 0.5)
Depth and width going from zero to unity makes life easier without changing the shape of the original cross-section
Y = 0.087*log(x) – 0.32Step 2: locate thalweg using shape
beta c/s = (beta1 + beta2) * k
a1=5, b1=2, a2=3, b2=3, factor = 0.5
a1=2, b1=2, a2=3, b2=7, factor = 0.6
Create beta cross-sections for different thalweg locations
Combination of two pdfs
a1=5, b1=2, a2=3, b2=3, factor = 0.5
Simple, only two parameters, 0 < x < 1
A single pdf has a flat tail, which is undesirable.
The condition of unit area under the pdf makes it difficult to maintain z*< 1.
A combination of two beta pdfs offers flexibility to fit any form of cross-sectional shape.
Hydraulic geometry relationships for Brazos River at Richmond.
Hydraulic geometry relationships are developed at USGS gaging stations.
W, d, and v obtained at the gaging stations are then interpolated to get the corresponding values at other locations.
An ideal scenario would be to have gaging stations both upstream and downstream from the point of interest.
3D Mesh of cross-sections and profile-lines
Set of Volume objects
3D Channel Model
GIS / Hydraulic Model Data Exchange
HydroID of Reach is ReachID of CrossSections