River Channels in GIS - PowerPoint PPT Presentation

River Channels in GIS

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

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

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

• 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

Criterion

Depth & velocity

Species groups

Habitat

Hydrodynamic

Habitat

Model

Model

Descriptions

RMA2

Biological Sampling

GIS

Instream

Flow

DecisionMaking

• 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

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)

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

Finite element mesh and bathymetric data

• 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

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

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

Source: RMA2 reference manual, 2002

Channel

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

Thalweg

Cross-sections

ProfileLines

3D Network

Measurement points

Surface

Develop generic ways to create all the channel features from measurement points.

Centerline/Thalweg

Cross-sections

ProfileLines

Start with points

Extract all the necessary information

Create surface from points

How can we do this…….

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

• 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).

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

• 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

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

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

Interpolated Raster

Anisotropic kriging gave the least RMSE

y

n

x

s

FishNet in (s,n,z) is flow-oriented!

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 cross-check??

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

• 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.

Meandering shape

Thalweg location

Cross-section form

C

C

C

C

B

B

B

B

A

A

A

A

=

+

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

Channel Bathymetry

Deterministic Component

Stochastic Component

4

• 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

@ 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 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

• 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

Y = 0.076*log(x) + 1.21

0

0.5

1.0

Y = 0.087*log(x) – 0.32

• 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)

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

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.

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

• 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)

Cross-sections

Profile-lines

3D Mesh of cross-sections and profile-lines

Set of Volume objects

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

• Relationships – ReachHasCrossSection

HydroID of Reach is ReachID of CrossSections

• 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

Hydraulic attributes

Reach identifier

Cross-section identifier