Supplemental Modeling Studies Modeling Studies

Housatonic River Project

SupplementalModeling StudiesSupplementalModeling Studies

Earl HayterNational Exposure Research Lab

Athens, GA

Earl Hayter National Exposure Research Lab

Athens, GA

scs1

scs1 Please add name and affiliation susan, 4/6/2005

Housatonic River Project pg 2

OutlineOutline

One-Dimensional (1D) modeling

– EFDC1D – GSTARS-1D– HEC-6

Tests of the applicability of EFDC for the Housatonic River

– Benchmark tests of EFDC hydrodynamics and sediment transport

– Evaluation of alternative grid configurations

One-Dimensional (1D) modeling

– EFDC1D – GSTARS-1D – HEC-6

Tests of the applicability of EFDC for the Housatonic River

– Benchmark tests of EFDC hydrodynamics and sediment transport

– Evaluation of alternative grid configurations


One-Dimensional Modeling - EFDC1DOne-Dimensional Modeling - EFDC1D EFDC1D (Hamrick 2001)– 1D hydrodynamic and sediment transport model – Capable of simulating flow and both cohesive and noncohesive

sediment transport – Applicable to streams, low-order rivers, and non-stratified tidal rivers

Features/capabilities of EFDC1D– Box- or reach-based spatial data structure (compatible with HSPF),

for representing 1D channel networks– Fully dynamic 1D equation solver for 1D momentum and continuity

equations, and generic 1D transport solver for salinity, temperature, multiple sediment and contaminant classes. Sources and sinks are represented.

EFDC1D (Hamrick 2001)EFDC1D (Hamrick 2001) – 1D hydrodynamic and sediment transport model – Capable of simulating flow and both cohesive and noncohesive

sediment transport – Applicable to streams, low-order rivers, and non-stratified tidal rivers

Features/capabilities of EFDC1DFeatures/capabilities of EFDC1D – Box- or reach-based spatial data structure (compatible with HSPF),

for representing 1D channel networks – Fully dynamic 1D equation solver for 1D momentum and continuity

equations, and generic 1D transport solver for salinity, temperature, multiple sediment and contaminant classes. Sources and sinks are represented.


One-Dimensional Modeling - EFDC1DOne-Dimensional Modeling - EFDC1D

Features/capabilities of EFDC1D (continued)

– Time-varying upstream and lateral inflows and withdrawals, including corresponding sediment loads and rainfall

– Time varying downstream boundary conditions for stage – Uses water surface elevation-dependent descriptions of channel

cross-section area, surface width, and wetted perimeter– Representation of hydraulic structures such as dams and culverts – Includes settling, deposition and resuspension of multiple size

classes of cohesive and noncohesive sediments– Bed represented by multiple layers of mixed sediment classes – Sediment bed dynamically coupled to the cross-sectional area,

accounting for area changes due to deposition and resuspension

Features/capabilities of EFDC1D (continued)Features/capabilities of EFDC1D (continued)

– Time-varying upstream and lateral inflows and withdrawals, including corresponding sediment loads and rainfall

– Time varying downstream boundary conditions for stage – Uses water surface elevation-dependent descriptions of channel

cross-section area, surface width, and wetted perimeter – Representation of hydraulic structures such as dams and culverts – Includes settling, deposition and resuspension of multiple size

classes of cohesive and noncohesive sediments – Bed represented by multiple layers of mixed sediment classes – Sediment bed dynamically coupled to the cross-sectional area,

accounting for area changes due to deposition and resuspension


One-Dimensional Modeling - GSTARSOne-Dimensional Modeling - GSTARS GSTARS-1D (Generalized Sediment Transport model for Alluvial River Simulation One Dimensional) (Yang et al. 2004)

– Hydraulic and sediment transport model

– Simulates steady or unsteady flows (with lateral inflows) in a singlechannel or channel network, and simulates cohesive and noncohesive sediment transport

GSTAR-1D’s capabilities– Simulates subcritical and supercritical flows and sediment transport

under unsteady conditions

– Simulates cohesive sediment settling, deposition, erosion, and consolidation processes

– Includes several noncohesive sediment transport equations, applicable to a wide range of hydraulic and sediment conditions

GSTARS-1D (Generalized Sediment Transport model for Alluvial River Simulation - One Dimensional) (Yang et al. 2004)

– Hydraulic and sediment transport model

– Simulates steady or unsteady flows (with lateral inflows) in a singlechannel or channel network, and simulates cohesive and noncohesive sediment transport

GSTAR-1D’s capabilities – Simulates subcritical and supercritical flows and sediment transport

under unsteady conditions

– Simulates cohesive sediment settling, deposition, erosion, and consolidation processes

– Includes several noncohesive sediment transport equations, applicable to a wide range of hydraulic and sediment conditions


One-Dimensional Modeling - GSTARSOne-Dimensional Modeling - GSTARS

GSTAR-1D’s capabilities (continued)

– Simulates exchange of water and sediment between main channel and floodplain

– Simulates fractional sediment transport, bed sorting, and bedarmoring

– Computes channel width changes using theory of stream powerminimization

– Can simulate both point and nonpoint sources of flow and sediments

– Can simulate internal boundary conditions (e.g., time-stage tables,rating curves, weirs, bridges, and radial gates)

GSTAR-1D’s capabilities (continued)

– Simulates exchange of water and sediment between main channel and floodplain

– Simulates fractional sediment transport, bed sorting, and bedarmoring

– Computes channel width changes using theory of stream powerminimization

– Can simulate both point and nonpoint sources of flow and sediments

– Can simulate internal boundary conditions (e.g., time-stage tables, rating curves, weirs, bridges, and radial gates)


One-Dimensional Modeling - SetupOne-Dimensional Modeling - Setup

Setup of 1D models– Model domain was represented with 203 surveyed cross

sections– Upstream flow boundary condition was the:

• measured 5-day hydrograph (starting at 2200 hours on 19 September 1999)

• sediment-discharge rating curve (used to specify sediment load time series)

– Downstream boundary condition used stage-discharge rating curve at Woods Pond Outlet

– Spatially-varying initial bed properties were specified using the measured grain size distributions and the cohesive sedimentproperties estimated from the Sedflume study

Setup of 1D models – Model domain was represented with 203 surveyed cross-

sections – Upstream flow boundary condition was the:

• measured 5-day hydrograph (starting at 2200 hours on 19September 1999)

• sediment-discharge rating curve (used to specify sedimentload time series)

– Downstream boundary condition used stage-discharge ratingcurve at Woods Pond Outlet

– Spatially-varying initial bed properties were specified using themeasured grain size distributions and the cohesive sedimentproperties estimated from the Sedflume study


One-Dimensional Modeling - SetupOne-Dimensional Modeling - Setup

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One-Dimensional Modeling - ResultsOne-Dimensional Modeling - Results

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One-Dimensional ModelingOne-Dimensional Modeling

Conclusions– 1D models not suitable for simulating a major (e.g., 100

year flood) out-of-bank event

– Not possible to simulate meandering river with floodplain inundated with water (see next slide)

– During out-of-bank event, water flows across the floodplain (more or less orthogonally to the river channel) between meanders

– 1D model cannot represent this condition (simulation of wetting and drying) in a meandering river

ConclusionsConclusions – 1D models not suitable for simulating a major (e.g., 100

year flood) out-of-bank event

– Not possible to simulate meandering river with floodplain inundated with water (see next slide)

– During out-of-bank event, water flows across the floodplain (more or less orthogonally to the river channel) between meanders

– 1D model cannot represent this condition (simulation of wetting and drying) in a meandering river


ExampleExample


Tests of the Applicability of EFDC to theHousatonic River

Tests of the Applicability of EFDC to theHousatonic River

I. Benchmark tests of EFDC hydrodynamics and sedimenttransport

– Performed tests to confirm that EFDC accurately represents physicalprocesses controlling flow and sediment transport in the HousatonicRiver

– Two of the more important hydrodynamic processes in the river are: • the impact of meandering on in-channel flow • flow onto the floodplain

Three evaluations were performed, comparing model simulations toexperimental data for in-channel and out-of-bank flow conditions:• Case 1 – Out-of-bank flow: straight channel and overbank flow onto

vegetated floodplain (Thornton et al., 2000)

• Case 2 – Out-of-bank flow: meandering channels and overbank flow ontofloodplain (Shiono and Muto, 1998)

• Case 3 – In-channel flow: 180-degree horseshoe bend (Yen and Lee, 1995)

I. Benchmark tests of EFDC hydrodynamics and sedimenttransport

– Performed tests to confirm that EFDC accurately represents physicalprocesses controlling flow and sediment transport in the HousatonicRiver

– Two of the more important hydrodynamic processes in the river are: • the impact of meandering on in-channel flow • flow onto the floodplain

Three evaluations were performed, comparing model simulations toexperimental data for in-channel and out-of-bank flow conditions: • Case 1 – Out-of-bank flow: straight channel and overbank flow onto

vegetated floodplain (Thornton et al., 2000)

• Case 2 – Out-of-bank flow: meandering channels and overbank flow ontofloodplain (Shiono and Muto, 1998)

• Case 3 – In-channel flow: 180-degree horseshoe bend (Yen and Lee, 1995)


Tests of the Applicability of EFDC to theHousatonic River – Case 2


Case 2 – Out-of-bank flow: meandering channels and overbank flow onto floodplain (Shiono and Muto, 1998)

– Shiono and Muto (1998) designed flume experiments to describe thedistributions of shear stresses and turbulence in meander channels for in-channel and out-of-bank flows

– Constructed hydraulic flume (10.8-m long, 1.2-m wide, and 0.33-mdeep) as a rectangular cross-section representation of a river valleywith a bottom slope of 0.001

– Constructed a series of meander waves with varying sinuositycharacteristics in the floodplain

– Measured flow velocities at sections w/in ½ meander wavelength of the fourth and fifth meanders using a laser-Doppler anemometer

– Using this experimental setup, they conducted detailed measurementsof secondary flow and shear stresses in the meander channel for a range of out-of-bank flows.


– Shiono and Muto (1998) designed flume experiments to describe thedistributions of shear stresses and turbulence in meander channels for in-channel and out-of-bank flows

– Constructed hydraulic flume (10.8-m long, 1.2-m wide, and 0.33-mdeep) as a rectangular cross-section representation of a river valleywith a bottom slope of 0.001

– Constructed a series of meander waves with varying sinuositycharacteristics in the floodplain

– Measured flow velocities at sections w/in ½ meander wavelength of the fourth and fifth meanders using a laser-Doppler anemometer

– Using this experimental setup, they conducted detailed measurementsof secondary flow and shear stresses in the meander channel for a range of out-of-bank flows.





EFDC Setup

• Curvilinear-orthogonal grid used to represent the hydraulic flume • The main channel width of 0.15-m was defined using five lateral cells

with a width of 0.03-m each. Vertical resolution of the floodplain and channel was defined using four layers.

• Bottom roughness was assigned a uniform value of 0.1 mm• The bottom slope of the floodplain and river channel was set at 0.001

m/m, the same slope used in the flume• The depth of flow in the flume was controlled by a tailgate. In EFDC, a

simulated weir was used to control depth as a function of the discharge rate.


EFDC Setup

• Curvilinear-orthogonal grid used to represent the hydraulic flume • The main channel width of 0.15-m was defined using five lateral cells

with a width of 0.03-m each. Vertical resolution of the floodplain and channel was defined using four layers.

• Bottom roughness was assigned a uniform value of 0.1 mm • The bottom slope of the floodplain and river channel was set at 0.001

m/m, the same slope used in the flume • The depth of flow in the flume was controlled by a tailgate. In EFDC, a

simulated weir was used to control depth as a function of the discharge rate.





Conclusions– Magnitude and direction of simulated flow demonstrated good agreement

with the experiments both for flow within the river channel and onto the floodplain

– Reproduced the shift in alignment of the surface layer flow from the channel meander toward the floodplain as the depth of flow increased

– Simulated flow in the channel bottom layer was consistent with the magnitude and direction of the measured velocities

– The 4-layer EFDC model was able to represent the characteristic secondary circulation resulting from channel meanders

– These comparisons confirm the ability of EFDC to properly represent flow in a meandering channel and the transition from the channel to out-of-bank flow onto a floodplain


Conclusions – Magnitude and direction of simulated flow demonstrated good agreement

with the experiments both for flow within the river channel and onto the floodplain

– Reproduced the shift in alignment of the surface layer flow from the channel meander toward the floodplain as the depth of flow increased

– Simulated flow in the channel bottom layer was consistent with the magnitude and direction of the measured velocities

– The 4-layer EFDC model was able to represent the characteristic secondary circulation resulting from channel meanders

– These comparisons confirm the ability of EFDC to properly represent flow in a meandering channel and the transition from the channel to out-ofbank flow onto a floodplain


Tests of the Applicability of EFDCto the Housatonic River - Grid


II. Evaluation of alternative grid configurations

– Systematically tested different Cartesian and curvilinear-orthogonal grids

– Purpose - to evaluate how the grid structure affects:• simulation of in-channel river flow and transport of solids • computational speed

– Selected a 1 km long section of the river just upstream of New Lenox Road as a “Test Reach”

– Performed velocity measurements using an ADCP for comparison between simulated and measured velocities

II. Evaluation of alternative grid configurations

– Systematically tested different Cartesian and curvilinear-orthogonal grids

– Purpose - to evaluate how the grid structure affects: • simulation of in-channel river flow and transport of solids • computational speed

– Selected a 1 km long section of the river just upstream of New Lenox Road as a “Test Reach”

– Performed velocity measurements using an ADCP for comparison between simulated and measured velocities




II. Evaluation of alternative grid schemes CONCLUSIONS

– Decision of final grid configuration based on: • Representation of the physics of in-channel and out-of-bank flow

and transport of sediment • Computational efficiency – need to conduct long-term simulations

of baseline conditions and remedial alternatives– Final Grid

• A curvilinear-orthogonal grid of resolution similar to the tested 20m Cartesian grid

• Designed to conform to the topography of the floodplain and theshoreline of the river channel

• Eliminated unneeded grid cells that would have been presentusing a Cartesian grid

• Allowed for the design of an efficient and computationally time-effective modeling framework

II. Evaluation of alternative grid schemes CONCLUSIONS

– Decision of final grid configuration based on: • Representation of the physics of in-channel and out-of-bank flow

and transport of sediment • Computational efficiency – need to conduct long-term simulations

of baseline conditions and remedial alternatives – Final Grid

• A curvilinear-orthogonal grid of resolution similar to the tested 20m Cartesian grid

• Designed to conform to the topography of the floodplain and theshoreline of the river channel

• Eliminated unneeded grid cells that would have been presentusing a Cartesian grid

• Allowed for the design of an efficient and computationally time-effective modeling framework


Model LinkageModel Linkage Hydrodynamic,

Sediment Transport, &

PCB Fate Model EFDC

Dissolved and sorbed PCBs in water column and sediment

PCB Bioaccumulation

Model FCM

(QEAFDCHN V1.0)

PCBs in Biota

Temperature

Flow (and

Solids*)

Watershed Model

HSPF


• Models are approximations of reality; they can not preciselyrepresent natural systems

• There is no single, accepted statistic or test that determines whether or not a model is valid

• Both graphical comparisons and statistical tests are required inmodel calibration and validation

• Models cannot be expected to be more accurate than the errors (confidence intervals) in the input and observed data

• A ‘weight-of-evidence’ approach was used in calibration of PSA models

• Models are approximations of reality; they can not preciselyrepresent natural systems

• There is no single, accepted statistic or test that determines whether or not a model is valid

• Both graphical comparisons and statistical tests are required inmodel calibration and validation

• Models cannot be expected to be more accurate than the errors (confidence intervals) in the input and observed data

• A ‘weight-of-evidence’ approach was used in calibration of PSA models

CALIBRATION RATIONALE ‘Basic Truths’ in Modeling Natural Systems

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