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

1. 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

2. 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

3. 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

4. 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.

5. 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

6. Submodels of Important Processes • Thehydraulic 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.

7. 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.

8. Estimate Changes in Morphology, 1952-1996 Using Regression Equations Based on Land Use

9. “Model Computations of Width versus Time”

10. 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.

11. Field Sites

12. Cross Sectional Geometry Survey: an example Width determined from location of post settlement paleosol paleosol depth

13. Slope is Determined from Longitudinal Profiles at Each Site

14. 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

15. Grain Size Data: an example

16. 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 . • Developa convincingmethodology for forecasting sediment delivery to 1st orderstreams

17. 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.

18. 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?

19. 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

20. 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.

21. 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.

22. Existing Data • Historical observations • Ongoing data collection (many sources) • New initiatives just being established

23. Historical Observations (Yorke and Herb, 1978)

24. Historical Observations • Regression equations relating sediment yield to % of the basin under construction (Yorke and Herb, 1978) • % construction only explains 50% of variance.

25. Combine Regression Equations with Historical GIS data

26. Montgomery County Water Quality Monitoring Data (and similar efforts elsewhere)

27. 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.)

28. 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.