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 Instream Flow
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 Criterion GIS RMA2 Biological Sampling Instream
Flow
Decision Making
Hydrodynamic
Model
Habitat
Descriptions
GIS
RMA2
Biological Sampling
Depth & velocity
Species groups
Criterion

7. Data Requirement Hydrodynamic Modeling Biological Studies
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) Input Data
(Environmental Modeling Systems, Inc.)
RMA2
(US Army Corps of Engineers)
SMS (Surface Water Modeling System)
RMA2 Interface
Input Data
Bathymetry Data
Substrate Materials
Boundary Conditions
Calibration Data

15. Finite element mesh and bathymetric data
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)
Depth [feet]
Run
Fast Riffle
Slow Riffle
Deep Pool
Medium Pool
Shallow
Pool
Mesohabitat Criteria: V, D, V/D, FR
(Vadas & Orth, 1998)

19. Micro Habitat Table Species 50% MinD 50% MaxD 50% MinV 50% MaxV
Group 1
1.5
2.7
2.9
Group 2
0.9
1.7
2.3
Group 3
0.5
1.2
0.6 2
Group 4
1.6
Group 5
1.8
4.6
0.3
Group 6
4.3
6.5
Group 7
3.3
0.1
Group 8
1.1 10
0.01
Group 9
2.0
0.4
Group 10
0.8

20. Hydraulic and Biological Data
Attribute Table
Bathymetry Points
Habitat Descriptions

21. Habitat Modeling using ArcGIS

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
Thalweg
Cross-sections
ProfileLines
3D Network
Measurement points
Surface
Develop generic ways to create all the channel features from measurement points.

28. Data analysis Start with points Create surface from points
Centerline/Thalweg
Cross-sections
ProfileLines
Start with points
Create surface from points
Extract all the necessary information
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.

32. (s,n,z) coordinate systemP Q
Centerlin e
Bankline s
(s = 0, n = 0)
P(n1, s1)
Q(n2, s2) n2 s1 s2
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 3, 4 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

34. (x,y,z) (s,n,z) x y o - n + s
(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
Spatial Interpolation Method
RMSE (m)
Rank
Inverse Distance Weighting
0.53 5
Elliptical Inverse Distance Weighting
0.32 2
Regularized Spline
0.59 6
Tension Spline
0.45 4
Ordinary Kriging
0.44 3
Anisotropic Kriging
0.31 1
Anisotropic kriging gave the least RMSE

37. FishNet in (s,n,z) is flow-oriented!
FishNet (x,y,z) to (s,n,z) s n x y
FishNet in (s,n,z) is flow-oriented!

38. FishNet comparison
Hydraulic FishNet
Regular FishNet

39. Profile Lines and Cross Sections in 3D
Bird’s eye view!

40. Instream flow studies in Texas
Priority segments are 100s of miles long
Study area is only few miles long
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 Meandering shape Thalweg location Cross-section formB C
Cross-section form

44. Deterministic Component
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 Model4 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
@ 30 miles
@ 5 miles
The data for Site 1 and Site 2 are available as (x,y,z) points.

47. Step 1: Normalizing the datanL nR - + Zd
P(ni, zi)
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) becomes Pnew(0.5, 0.5)

48. Original cross-section Modified cross-section
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
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
Y = 0.076*log(x)
Y = 0.087*log(x) – 0.32
0.5
1.0

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
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

53. Cross-sections as Beta pdf
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 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

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
3D Channel
XML
HEC-RAS
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
Cross-section identifier
Hydraulic attributes
Reach identifier

64. Questions