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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 • 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? 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. 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 Fish Habitat Modeling Criterion Depth & Species Hydrodynamic velocity Habitat groups Habitat Model Model Descriptions RMA2 Biological GIS Sampling Instream Flow Decision Making 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 Study Area (Guadalupe river near Seguin, TX) 1/2 meter Digital Ortho Photography 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. 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. Global Positioning System (GPS) Tells you where you are on the earth! Final Setup GPS Antenna Computer and power setup Depth Sounder Final Data View 2D Hydrodynamic Model • SMS (Surface Water Modeling System) – RMA2 Interface • Input DataWater Modeling System Surface (Environmental Modeling Systems, Inc.) Bathymetry Data Substrate Materials Boundary Conditions RMA2 (US Data Calibration Army Corps of Engineers) SMS mesh Finite element mesh and bathymetric data SMS Results 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. Deep Pool Run Medium Pool Shallow Fast Riffle Pool Slow Riffle Mesohabitat Criteria: V, D, V/D, FR (Vadas & Orth, 1998) Micro Habitat Table Species 50% MinD 50% MaxD 50% MinV 50% MaxV Group 1 1.5 2.7 1.5 2.9 Group 2 0.9 1.7 0.9 2.3 Group 3 0.5 1.2 0.6 2 Group 4 0.6 1.2 1.6 2.3 Group 5 1.8 4.6 0.3 1.6 Group 6 4.3 6.5 0.5 0.9 Group 7 1.5 3.3 0.1 1.2 Group 8 1.1 10 0.01 0.9 Group 9 0.5 2.0 0.4 1.6 Group 10 0.3 1.5 0.01 0.8 Hydraulic and Biological Data Attribute Table Bathymetry Points Habitat Descriptions Habitat Modeling using ArcGIS Results Overview • Fish Habitat Modeling using GIS • Standardized 3D representation of river channels • River Channel Morphology Model • RCMM and Hydraulic Modeling Channel bathymetry in Hydraulic Modeling Other Viscosity 4% 6% Roughness 10% Boundary Geometry Conditions and Study 20% Design 60% Source: RMA2 reference manual, 2002 Channel Representation in Arc Hydro Channel River channels are represented as a set of cross-sections and profile-lines in Arc Hydro GIS database for river channels Thalweg Cross-sections Measurement points Surface 3D Network ProfileLines Develop generic ways to create all the channel features from measurement points. Data analysis Centerline/Thalweg Cross-sections ProfileLines Start with points Create surface Extract all the from points necessary information How can we do this……. 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 Geospatial Structure for River Channels - Methodology 1. Plot the data in a flow- oriented coordinate system (s,n,z). 2. Interpolate the data to create a surface. 3. Create a FishNet from the interpolated surface. 4. Transform the FishNet to (x,y,z). Measure in ArcGIS A PolylineMZ can store 64.0056 112.3213 0 m and z at each vertex along with x and y coordinates. (s,n,z) coordinate system s1 P Centerline s2 n1 (s = 0, n = 0) n2 Q Banklines P(n1, s1) Q(n2, 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 Defining a Thalweg Input Step 2 Steps 3, 4 Steps 5,6,7 Step 8 Output User defines Thalweg tool Densify the Normals are All the Final an arbitrary creates a initial drawn at each deepest result is a centerline surface using centerline to vertex of the points 3D over the the get more centerline to replace the polyline measurement measurement points locate deepest vertices of defining points points Old vertices points the old the New vertices centerline thalweg (x,y,z) (s,n,z) +n o -n y n s +n x o s -n (x,y,z) s (s,n,z) Spatial interpolation Bathymetry Points • IDW • EIDW • Splines – Tension Interpolated Raster – Regularized • Kriging – Ordinary – Anisotropic Spatial Interpolation Results Spatial Interpolation Method RMSE Rank (m) 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 FishNet (x,y,z) to (s,n,z) n s y x FishNet in (s,n,z) is flow-oriented! FishNet comparison Regular FishNet Hydraulic FishNet Profile Lines and Cross Sections in 3D Bird’s eye view! 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?? Overview • Fish Habitat Modeling using GIS • Standardized 3D representation of river channels • River Channel Morphology Model • RCMM and Hydraulic Modeling 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. Conceptual Model C C C C B B B B A A A A Meandering Thalweg Cross-section shape location form Channel Bathymetry z( x, y) = ˆ z ( x , y) + ( x, y) 14 14 8 Elevation (m) Elevation (m) 12 12 Elevation (m) 10 10 0 8 8 6 6 -8 0 25 50 75 100 0 25 50 75 100 0 25 50 75 100 n-coordinate (m) n-coordinate (m) n-coordinate (m) Channel Bathymetry Deterministic Component Stochastic Component • Channel bathymetry is complex • This research is focused on the deterministic component only River Channel Morphology Model 1 2 3 4 1. Get the shape (blue line or DOQ) 2. Using the shape, locate the thalweg 3. Using thalweg location, create cross-sections 4. Network of cross-sections and profile lines Site1 and Site2 on Brazos River @ 5 miles @ 30 miles The data for Site 1 and Site 2 are available as (x,y,z) points. Step 1: Normalizing the data nL 0 nR - For any point P(ni,zi), the + Z normalized coordinates P(ni, zi) are: d nnew = (ni – nL)/w Zd znew = (Z – zi)/d w = nL + nR For nL = -15, nR = 35, d = 5, Z=10 P (10, 7.5) becomes Pnew(0.5, 0.5) Normalized Data Original cross-section Modified cross-section 13 Normalized width 12 0 0.25 0.5 0.75 1 11 0 Elevation (m) Normalized depth 10 0.25 9 8 0.5 7 Bathymetry Points Bathymetry Points 6 0.75 -75 -50 -25 0 25 n-Coordinate (m) 1 Depth and width going from zero to unity makes life easier without changing the shape of the original cross-section 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 Step 2: locate thalweg using shape Y = 0.076*log(x) + 1.21 1.00 Thalweg location 0.75 2 R = 0.8238 0.50 R2 = 0.8717 0.25 0.00 -15000 -10000 -5000 0 5000 10000 15000 Radius of Curvature (m) 0 0.5 1.0 Y = 0.087*log(x) – 0.32 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) Step 3: cross-sections as beta pdfs beta c/s = (beta1 + beta2) * k x x 0.00 0.25 0.50 0.75 1.00 0.00 0.25 0.50 0.75 1.00 beta c/s beta c/s Beta c/s Beta c/s Beta1 Beta1 Beta2 Beta2 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 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 combination of two beta A single pdf has a flat tail, pdfs offers flexibility to fit which is undesirable. any form of cross-sectional shape. The condition of unit area under the pdf makes it difficult to maintain z*< 1. Hydraulic Geometry Relationships W aQ b d cQ f v kQ m 1000 100 10 Average Width, w (feet) Average Depth, d (feet) w = 95.654Q0.1206 a = 95.654 d = 1.4895Q 0.2537 c = 1.4895 y = 0.0094x 0.5894 R2 = 0.8164 b = 0.1206 R2 = 0.8672 f = 0.2537 Velocity, v (fps) R2 = 0.9576 10 1 k = 0.0094 m = 0.5894 100 1 100 1000 10000 100000 0.1 100 1000 10000 100000 Flow, Q(cfs) Flow, Q (cfs) 100 1000 10000 100000 Flow, Q (cfs) 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. USGS Measurements http://waterdata.usgs.gov/nwis/measurements 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) Results Lower Brazos in Texas 3D Channel Representation Cross-sections Profile-lines 3D Mesh of cross-sections and profile- Set of Volume objects lines Overview • Fish Habitat Modeling using GIS • Standardized 3D representation of river channels • River Channel Morphology Model • RCMM and Hydraulic Modeling 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 Hydraulic Model Attributes • Relationships – ReachHasCrossSection HydroID of Reach is ReachID of CrossSections 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 Questions

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posted: | 11/21/2012 |

language: | English |

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