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 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 Try to compute measured sediment budget.

Estimate Changes in Morphology, Using Regression Equations Based on Land Use

“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 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

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 1 st 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

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.