Transcript Document

U.S. EPA: NCEA/Global Change
Research Program
Changing Climate and Land Use in
the Mid-Atlantic: Modeling Drivers
and Consequences –
GEOMORPHOLOGY
Jim Pizzuto and students
University of Delaware
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
Horizontal Distance (meters)
0
5
10
15
0
Depth (meters)
0.5
1
1.5
2
2.5
3
3.5
Good Hope Tributary - 1998
Hollywood Tributary - 1998
Good Hope Tributary - 1952
20
“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
Cross Sectional Geometry Survey: an example
Paint Branch Site 6 (19)
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18
-0.5
-1
Depth
-1.5
-2
Width determined from location of
post settlement paleosol
paleosol
-2.5
-3
depth
-3.5
Width
6/15/01
1/26/96
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
100
%
80
60
40
20
0
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
0.035
0.03
0.02
0.015
0.01
0.005
0
19
52
19
54
19
56
19
58
19
60
19
62
19
64
19
66
19
68
19
70
19
72
19
74
19
76
19
78
19
80
19
82
19
84
19
86
19
88
19
90
19
92
19
94
19
96
19
98
Fraction Under Construction
0.025
Year
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.