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.
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River Channels in GIS
Venkatesh Merwade, Center for Research in Water Resources, University of Texas at Austin
Criterion
Depth & velocity
Species groups
Habitat
Hydrodynamic
Habitat
Model
Model
Descriptions
RMA2
Biological Sampling
GIS
Instream
Flow
DecisionMaking
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!
GPS Antenna
Computer and power setup
Depth Sounder
Surface Water Modeling System
(Environmental Modeling Systems, Inc.)
RMA2
(US Army Corps of Engineers)
Finite element mesh and bathymetric data
Deep Pool
Run
Depth [feet]
Medium Pool
Shallow
Pool
Fast Riffle
Slow Riffle
Mesohabitat Criteria: V, D, V/D, FR
(Vadas & Orth, 1998)
Attribute Table
Bathymetry Points
Habitat Descriptions
Source: RMA2 reference manual, 2002
Channel
River channels are represented as a set of crosssections and profilelines in Arc Hydro
Thalweg
Crosssections
ProfileLines
3D Network
Measurement points
Surface
Develop generic ways to create all the channel features from measurement points.
Centerline/Thalweg
Crosssections
ProfileLines
Start with points
Extract all the necessary information
Create surface from points
How can we do this…….
Thought Process:
Regular FishNet
A PolylineMZ can store m and z at each vertex along with x and y coordinates.
112.3213
64.0056
0
P
s1
Centerlin
e
s2
n1
(s = 0, n = 0)
n2
Bankline
s
P(n1, s1)
Q(n2, s2)
Q
Input
Output
Steps 3, 4
Step 2
Steps 5,6,7
Step 8
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
Old vertices
New vertices
n
+
o
n

y
n
s
n
+
x
s
o
(x,y,z)
n

s
(s,n,z)
Bathymetry Points
Interpolated Raster
Anisotropic kriging gave the least RMSE
y
n
x
s
FishNet in (s,n,z) is floworiented!
Hydraulic FishNet
Regular FishNet
Bird’s eye view!
Priority segments are 100s of miles long
Study area is only few miles long
Instream flow studies in Texas
Results from small studies are extrapolated
Are the results valid?? Can we crosscheck??
Meandering shape
Thalweg location
Crosssection form
C
C
C
C
B
B
B
B
A
A
A
A
=
+
Channel Bathymetry
Deterministic Component
Stochastic Component
4
1
2
3
@ 5 miles
@ 30 miles
The data for Site 1 and Site 2 are available as (x,y,z) points.
nL
nR
0

+
Z
P(ni, zi)
d
Zd
w = nL + nR
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)
Original crosssection
Modified crosssection
Depth and width going from zero to unity makes life easier without changing the shape of the original crosssection
r1
r3
r2
Y = 0.076*log(x) + 1.21
0
0.5
1.0
Y = 0.087*log(x) – 0.32
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 crosssections for different thalweg locations
Single pdf
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 crosssectional 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.
http://waterdata.usgs.gov/nwis/measurements
Crosssections
Profilelines
3D Mesh of crosssections and profilelines
Set of Volume objects
3D Channel Model
Blue Line
XML
HECRAS
3D Channel
GIS / Hydraulic Model Data Exchange
HydroID of Reach is ReachID of CrossSections
Hydraulic attributes
Reach identifier
Crosssection identifier