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River Channels in GIS

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  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. Criterion Depth & velocity Species groups Habitat Hydrodynamic Habitat Model Model Descriptions RMA2 Biological Sampling GIS Instream Flow DecisionMaking 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. Surface Water Modeling System (Environmental Modeling Systems, Inc.) RMA2 (US Army Corps of Engineers) 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. Deep Pool Run Depth [feet] Medium Pool Shallow Pool Fast Riffle Slow Riffle 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. Results

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

  24. Channel bathymetry in Hydraulic Modeling Source: RMA2 reference manual, 2002

  25. Channel Channel Representation in Arc Hydro River channels are represented as a set of cross-sections and profile-lines in Arc Hydro

  26. Thalweg Cross-sections ProfileLines 3D Network GIS database for river channels Measurement points Surface Develop generic ways to create all the channel features from measurement points.

  27. Centerline/Thalweg Cross-sections ProfileLines Data analysis Start with points Extract all the necessary information Create surface from points How can we do this…….

  28. 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

  29. 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).

  30. Measure in ArcGIS A PolylineMZ can store m and z at each vertex along with x and y coordinates. 112.3213 64.0056 0

  31. P s1 Centerlin e s2 n1 (s = 0, n = 0) n2 Bankline s P(n1, s1) Q(n2, s2) Q (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

  32. Defining a Thalweg 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

  33. n + o n - y n s n + x s o (x,y,z) n - s (s,n,z) (x,y,z) (s,n,z)

  34. Spatial interpolation Bathymetry Points • IDW • EIDW • Splines • Tension • Regularized • Kriging • Ordinary • Anisotropic Interpolated Raster

  35. Spatial Interpolation Results Anisotropic kriging gave the least RMSE

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

  37. FishNet comparison Hydraulic FishNet Regular FishNet

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

  39. 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 cross-check??

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

  41. 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.

  42. Meandering shape Thalweg location Cross-section form C C C C B B B B A A A A Conceptual Model

  43. Channel Bathymetry = + • Channel bathymetry is complex • This research is focused on the deterministic component only Channel Bathymetry Deterministic Component Stochastic Component

  44. 4 River Channel Morphology Model • 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 1 2 3

  45. @ 5 miles @ 30 miles Site1 and Site2 on Brazos River The data for Site 1 and Site 2 are available as (x,y,z) points.

  46. nL nR 0 - + Z P(ni, zi) d Zd w = nL + nR 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, Z=10 P (10, 7.5) becomesPnew(0.5, 0.5)

  47. 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

  48. Shape characterization through radius of curvature • Ifradius 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 r1 r3 r2

  49. Y = 0.076*log(x) + 1.21 0 0.5 1.0 Y = 0.087*log(x) – 0.32 Step 2: locate thalweg using shape