U.S. EPA: NCEA/Global Change Research Program

Jim Pizzuto and studentsUniversity of Delaware

Changing Climate and Land Use in the Mid-Atlantic: Modeling Drivers and Consequences –GEOMORPHOLOGY

Changing Climate and Land Use in the Mid-Atlantic: Modeling Drivers and Consequences –GEOMORPHOLOGY

Outline

• EPA STAR Water & Watersheds project – goals and some selected results

• EPA NCEA/GCRP Effects of Jointly Changing Climate and Land Use 1: “This Project” – goals and proposed products

EPA STAR Water & Watersheds project – goals

• To develop and calibrate a model that forecasts, conditional on land use changes through time, stream morphology and sediment characteristics at decadal time scales throughout a watershed.

• To collect observations at a fine spatial grain within watersheds to determine how spatial pattern and history of watershed development influence stream morphology

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 bank sediment throughout a watershed over decadal timescales.

COMPONENTS OF A WATERSHED SCALE RIVER EVOLUTION MODEL

• Governing Equations (sub-models that represent important processes)

• Boundary Conditions (sediment flux boundary condition a focus for “this project” (EPA NCEA/GCRP Effects of Jointly Changing Climate and Land Use)

• Initial Conditions• Spatial Discretization• Temporal Discretization

Submodels of Important Processes

• The hydraulic sub-model will be used to predict water depth and from discharge and channel characteristics.

• The bedload transport sub-model will quantify bedload transport rates for 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-model will 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 submodel will account for bank erosion and deposition and lateral channel migration.

Some Preliminary Modeling Results A Test Case – Good Hope Tributary

of Paint Branch, Maryland

• Try to reproduce changes in width and extent of channel migration 1951-1996.

• Try to compute measured sediment budget.

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)

Dep

th (

met

ers)

Good Hope Tributary - 1998Hollywood Tributary - 1998Good Hope Tributary - 1952

“Model Computations of Width versus Time”

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.

Field Sites

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

Dep

th

6/15/01 1/26/96

Cross Sectional Geometry Survey: an example

Width determined from location of post settlement paleosol

depth

paleosol

Slope is Determined from Longitudinal Profiles at Each Site

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

Grain Size Data: an example

PB6

0

20

40

60

80

100

1 10 100 1000

D

%

2001 pointcount+weight 1996 pointcount 2001 pointcount

EPA NCEA/GCRP Effects of Jointly Changing Climate and Land Use 1: “This Project” – goals and products

• Produce preliminary model predictions showing interactions between climate/land use change on a typical Maryland Piedmont watershed .

• Develop a convincing methodology for forecasting sediment delivery to 1st order streams

Preliminary Model Predictions for a Typical Watershed

• Clarify key processes and parameters that are either likely to be particularly important or where our understanding is insufficient

• Produce some generalized "scenario" forecasts that will provide the basis for subsequent detailed predictions of the effects of climate change.

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?

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

Approach

• Literature review of relevant studies on sediment supply in urban/suburban piedmont watersheds.

• Analysis of existing literature and data to suggest the most significant sources and how these sources are likely to change under different climate scenarios.

• Evaluate current models for predicting changes in sediment supply in the context of changing climate and land use.

The Product

• Identify HOW to model changes in sediment supply,

• Determine what field data are needed to calibrate realistic models for sediment production under changing land uses and climate.

Existing Data

• Historical observations

• Ongoing data collection (many sources)

• New initiatives just being established

Historical Observations (Yorke and Herb, 1978)

Historical Observations

• Regression equations relating sediment yield to % of the basin under construction (Yorke and Herb, 1978)

• % construction only explains 50% of variance.

Combine Regression Equations with Historical GIS data

Fraction of the Watershed Under Construction, 1952-1998

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

1952

1954

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1996

1998

Year

Fra

ctio

n U

nd

er C

on

stru

ctio

n

Montgomery County Water Quality Monitoring Data (and

similar efforts elsewhere)

Evaluate Existing Strategies

• RUSLE, WEPP, etc.• Chesapeake Bay Program HSPF based model• Ongoing and new initiatives (Johns Hopkins/State

of MD Patuxent Watershed study, Gwynn’s Falls Watershed urban LTER, etc.)

SUMMARY

• EPA STAR Water & Watersheds project will produce a watershed scale geomorphic model to forecast decadal timescale changes in stream morphology caused by landuse changes.

• EPA NCEA/GCRP Effects of Jointly Changing Climate and Land Use 1 project will result in– a proposed approach for predicting upland sediment

production to first-order streams.– scenario forecasts of geomorphic changes caused by

changing land use AND climate for a single watershed.