pizzutoGeomorph.ppt

8/14/2019 pizzutoGeomorph.ppt

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U.S. EPA: NCEA/Global Change

Research Program

Jim Pizzuto and students

University of Delaware

Changing Climate and Land Use in

the Mid-Atlantic:Modeling Drivers

and ConsequencesGEOMORPHOLOGY


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Outline

EPA STAR Water & Watersheds projectgoals and some selected results

EPA NCEA/GCRP Effects of Jointly

Changing Climate and Land Use 1: This

Project goals and proposed products


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EPA STAR Water & Watersheds

projectgoals To develop and calibrate a model that

forecasts, conditional on land use changes

through time, stream morphology andsediment characteristics at decadal time scales

throughout a watershed.

To collect observations at a fine spatial grain

within watersheds to determine how spatialpattern and history of watershed development

influence stream morphology


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A Watershed Scale Geomorphic Model for

a Network of Gravel-bed Rivers

FORECAST changes in bed elevation

(slope), depth, width, bed mobility, the

grain size distribution of the bed and banksediment throughout a watershed over

decadal timescales.


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COMPONENTS OF A WATERSHED

SCALE RIVER EVOLUTION MODEL

Governing Equations (sub-models that represent

important processes)

Boundary Conditions (sediment flux boundarycondition a focus for this project (EPANCEA/GCRP Effects of Jointly Changing Climate and Land

Use)

Initial Conditions Spatial Discretization

Temporal Discretization


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Submodels of Important Processes

Thehydraulic sub-modelwill be used to predict water depthand

from discharge and channel characteristics.

The bedload transport sub-modelwill quantify bedload transport

ratesfor each grain size fraction. The sediment continuity sub-model will employ a modified Exner

equation for mixtures of sand and gravel to predict changes in bed

elevation.

The washload sub-modelwill route suspended silt and clay through

channel networks, accounting for deposition on the floodplain, bed,and banks, and for erosion from the bed and banks.

The channel cross-section submodelwill account for bank erosion

and deposition and lateral channel migration.


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Some Preliminary Modeling Results

A Test CaseGood Hope Tributaryof Paint Branch, Maryland

Try to reproduce changes in width andextent of channel migration 1951-1996.

Try to compute measured sediment budget.


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Estimate Changes in Morphology,

1952-1996 Using Regression Equations

Based on Land Use

0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15 20

Horizontal Distance (meters)

Depth(meters)

Good Hope Tributary - 1998

Hollywood Tributary - 1998

Good Hope Tributary - 1952


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Model Computations of Width

versus Time


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FIELD DATA

Measurements of Channel Morphology,

Sediment Characteristics, Post-Settlement

Allluviation at 62 sites

Needed to determine initial conditions for

forecasting channel change, model

calibration, etc.


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Field Sites


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Paint Branch Site 6 (19)

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Width

Depth

6/15/01 1/26/96

Cross Sectional Geometry Survey: an example

Width determined from location of

post settlement paleosol

depth

paleosol


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Slope is Determined from

Longitudinal Profiles at Each Site


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Other activities

Mapping thickness of overbank

sedimentation post European settlement

Evaluating sediment budgets

Historical observations of channel

morphology

Calibrating bedload transport functions

using bucket samplers


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Grain Size Data: an example

PB6

0

20

40

60

80

100

1 10 100 1000

D

%

2001 pointcount+weight 1996 pointcount 2001 pointcount


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EPA NCEA/GCRP Effects of Jointly Changing Climate

and Land Use 1: This Project goals and products

Produce preliminary model predictionsshowing interactions between climate/land

use change on a typical Maryland Piedmontwatershed .

Developa convincingmethodology forforecasting sediment delivery to 1storder

streams


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Preliminary Model Predictions

for a Typical Watershed

Clarify key processes and parameters that

are either likely to be particularly importantor where our understanding is insufficient

Produce some generalized "scenario"

forecasts that will provide the basis forsubsequent detailed predictions of the

effects of climate change.


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Some Questions to Answer

1) What are the nature and magnitudes of geomorphic

changes to stream channels that are likely to occur under

reasonable scenarios of land use and climate changes in

the watershed?

2) What parameters in the model have the strongest

influence on forecasted changes?

3) How does uncertainty in model parameters influence

uncertainty in model forecasts?

4) Do specific spatial patterns of development either

amplify or dampen the effects of climate changes?


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Sediment Supply to First-order

Streams The upstream boundary condition needed to

route sediment through a network of stream

channels. No established method exists for

urban/suburban watersheds


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Approach

L iterature reviewof relevant studies on sediment

supply in urban/suburban piedmont watersheds.

Analysis of existing l i teratureand data to suggest

the most significant sources and how these sourcesare likely to change under different climate

scenarios.

Evaluatecurrent models for predicting changes in

sediment supply in the context of changingclimate and land use.


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The Product

Identify HOW to model changes in

sediment supply,

Determine what field data are needed tocalibrate realistic models for sediment

production under changing land uses and

climate.


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Existing Data

Historical observations

Ongoing data collection (many sources)

New initiatives just being established


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Historical Observations (Yorke

and Herb, 1978)


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Historical Observations

Regression equations relating sediment

yield to % of the basin under construction

(Yorke and Herb, 1978) % construction only explains 50% of

variance.


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Combine Regression Equations

with Historical GIS dataFraction of the Watershed Under Construction, 1952-1998

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

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52

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Year

Fraction

UnderConstruction


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Evaluate Existing Strategies

RUSLE, WEPP, etc.

Chesapeake Bay Program HSPF based model

Ongoing and new initiatives (Johns Hopkins/Stateof MD Patuxent Watershed study, Gwynns Falls

Watershed urban LTER, etc.)


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