River Channels in GIS

1
River Channels in GIS

• Venkatesh Merwade, Center for Research in Water
  Resources, University of Texas at Austin

2
Overview

• Fish Habitat Modeling using GIS
• Standardized 3D representation of river channels
• River Channel Morphology Model
• RCMM and Hydraulic Modeling

3
Instream flow studies

• How do we quantify the impact of changing the
  naturalized flow of a river on species habitat?
• How do we set the minimum reservoir releases that
  would satisfy the instream flow requirement?

4
Objective

• Objective
• To model species habitat as a function of flow
  conditions and help decision making
• Instream Flow
• Flow necessary to maintain habitat in natural
  channel.

5
Methodology

• Species habitat are dependent on channel
  hydrodynamics hydrodynamic modeling
• Criteria to classify species depending on the
  conditions in the river channel biological
  studies
• Combine hydrodynamics and biological studies to
  make decisions ArcGIS

6
Fish Habitat Modeling
7
Data Requirement

• Hydrodynamic Modeling
• Bathymetry Data (to define the channel bed)
• Substrate Materials (to find the roughness)
• Boundary Conditions (for hydrodynamic model)
• Calibration Data (to check the model)
• Biological Studies
• Fish Sampling (for classification of different
  species)
• Velocity and depth at sampling points

8
Study Area (Guadalupe river near Seguin, TX)
1/2 meter Digital Ortho Photography
9
Depth Sounder (Echo Sounder)
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.
10
Acoustic Doppler Current Profiler
Provides full profiles of water current speed and
direction in the ocean, rivers, and lakes. Also
used for discharge, scour and river bed
topography.
11
Global Positioning System (GPS)
Tells you where you are on the earth!
12
Final Setup
GPS Antenna
Computer and power setup
Depth Sounder
13
Final Data View
14
2D Hydrodynamic Model

• SMS (Surface Water Modeling System)
• RMA2 Interface
• Input Data
• Bathymetry Data
• Substrate Materials
• Boundary Conditions
• Calibration Data

15
SMS mesh
Finite element mesh and bathymetric data
16
SMS Results
17
Biological Studies (TAMU)

• Meso Habitat and Micro Habitat
• Use Vadas Orth (1998) criterion for Meso
  Habitats
• Electrofishing or seining to collect fish samples
  for Micro Habitat analysis
• Sample at several flow rates and seasons
• Measure Velocity and depth at seining points
• Statistical analysis to get a table for Micro
  Habitats classification.

18

• Mesohabitat Criteria V, D, V/D, FR
• (Vadas Orth, 1998)

19
Micro Habitat Table
20
Hydraulic and Biological Data
Attribute Table
Bathymetry Points
Habitat Descriptions
21
Habitat Modeling using ArcGIS
22
(No Transcript)
23
Results
24
Overview

• Fish Habitat Modeling using GIS
• Standardized 3D representation of river channels
• River Channel Morphology Model
• RCMM and Hydraulic Modeling

25
Channel bathymetry in Hydraulic Modeling
Source RMA2 reference manual, 2002
26
Channel Representation in Arc Hydro
River channels are represented as a set of
cross-sections and profile-lines in Arc Hydro
27
GIS database for river channels
Measurement points
Surface
Develop generic ways to create all the channel
features from measurement points.
28
Data analysis
Start with points
Extract all the necessary information
Create surface from points
How can we do this.
29
Development of Geospatial Structure for River
Channels
Thought Process

• Regular FishNet in ArcGIS provides a network of
  3D lines, which are not flow oriented
• If the data are plotted in a flow-oriented
  system, the regular FishNet becomes
  flow-oriented.
• Flow-oriented coordinate system is useful for
  getting cross-sections and profile-lines.

Regular FishNet
30
Geospatial Structure for River Channels -
Methodology

• Plot the data in a flow-oriented coordinate
  system (s,n,z).
• Interpolate the data to create a surface.
• Create a FishNet from the interpolated surface.
• Transform the FishNet to (x,y,z).

31
Measure in ArcGIS
A PolylineMZ can store m and z at each vertex
along with x and y coordinates.
112.3213
64.0056
0
32
(s,n,z) coordinate system

• s-coordinate is the flow length along the river
  channel
• n-coordinate is the perpendicular distance from
  the centerline
• n-coordinate is negative to the LHS and positive
  to the RHS of the centerline

33
Defining a Thalweg
Input
Output
Step 2
Steps 5,6,7
Step 8
Steps 3, 4
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
34
(x,y,z)?? (s,n,z)
35
Spatial interpolation
Bathymetry Points

• IDW
• EIDW
• Splines
• Tension
• Regularized
• Kriging
• Ordinary
• Anisotropic

Interpolated Raster
36
Spatial Interpolation Results
Anisotropic kriging gave the least RMSE
37
FishNet (x,y,z) to (s,n,z)
FishNet in (s,n,z) is flow-oriented!
38
FishNet comparison
Hydraulic FishNet
Regular FishNet
39
Profile Lines and Cross Sections in 3D
Birds eye view!
40
Instream flow studies in Texas
Results from small studies are extrapolated
Are the results valid?? Can we cross-check??
41
Overview

• Fish Habitat Modeling using GIS
• Standardized 3D representation of river channels
• River Channel Morphology Model
• RCMM and Hydraulic Modeling

42
Goal

• Based on the knowledge gained from a detailed
  dataset collected for a reach of river, develop a
  model for describing the 3D river channel form at
  regional scale.

43
Conceptual Model
44
Channel Bathymetry


Channel Bathymetry
Deterministic Component
Stochastic Component

• Channel bathymetry is complex
• This research is focused on the deterministic
  component only

45
River Channel Morphology Model
1
2
3

• Get the shape (blue line or DOQ)
• Using the shape, locate the thalweg
• Using thalweg location, create cross-sections
• Network of cross-sections and profile lines

46
Site1 and Site2 on Brazos River
The data for Site 1 and Site 2 are available as
(x,y,z) points.
47
Step 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, Z10 P (10, 7.5)
becomes Pnew(0.5, 0.5)
48
Normalized Data
Original cross-section
Modified cross-section
Depth and width going from zero to unity makes
life easier without changing the shape of the
original cross-section
49
Shape characterization through radius of curvature
r1
r3
r2

• If radius of curvature is small, the thalweg is
  close to the bank and as it increases the thalweg
  moves towards the center of the channel.
• If the channel meanders to left, the center of
  curvature is to the right hand side of the
  centerline and vice versa.
• When the center of curvature is to the right, the
  radius of curvature is considered positive and
  vice versa

50
Step 2 locate thalweg using shape
51
Thalweg and cross-section

• Cross-section should have an analytical form to
  relate it to the thalweg location
• Many probability density functions (pdf) have
  shapes similar to the cross-section
• Beta pdf is found feasible
• its domain is from zero to one
• it has only two parameters (a,b)

52
Step 3 cross-sections as beta pdfs
beta c/s (beta1 beta2) k
a15, b12, a23, b23, factor 0.5
a12, b12, a23, b27, factor 0.6
Create beta cross-sections for different thalweg
locations
53
Cross-sections as Beta pdf
Single pdf
Combination of two pdfs
a15, b12, a23, b23, factor 0.5
Simple, only two parameters, 0 lt x lt 1 A single
pdf has a flat tail, which is undesirable. The
condition of unit area under the pdf makes it
difficult to maintain zlt 1.
A combination of two beta pdfs offers flexibility
to fit any form of cross-sectional shape.
54
Hydraulic Geometry Relationships
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.
55
USGS Measurements
http//waterdata.usgs.gov/nwis/measurements
56
The final framework

• Start with a blue line (s), locate the thalweg
  (t) using the relationship, t f(s).
• Using t, describe cross-sections (c) using the
  relationship, c(a,b) f(t).
• The resulting cross-sections have a unit width
  and unit depth.
• Rescale the normalized cross-sections using width
  and depth (hydraulic geometry)

57
Results
58
Lower Brazos in Texas
59
3D Channel Representation
Cross-sections
Profile-lines
3D Mesh of cross-sections and profile-lines
Set of Volume objects
60
Overview

• Fish Habitat Modeling using GIS
• Standardized 3D representation of river channels
• River Channel Morphology Model
• RCMM and Hydraulic Modeling

61
RCMM and Hydraulic Modeling
3D Channel Model

• Blue line to 3D channel using the shape and
  hydraulic geometry
• Interaction with external hydraulic models
  (HEC-RAS) via XML

Blue Line
XML
HEC-RAS
3D Channel
GIS / Hydraulic Model Data Exchange
62
Hydraulic Model Attributes

• Relationships ReachHasCrossSection
• HydroID of Reach is ReachID of CrossSections

63
FTable

• Linking of 3D channel and hydraulic model can be
  used to run hydraulic simulations and create
  FTable in GIS
• FTable contains useful information on water
  surface elevations, velocity, volume, residence
  times

Reach identifier
Hydraulic attributes
Cross-section identifier
64
Questions