Modeling the Effects of Land Use Change on Flooding

Adam Nayak, Cleveland High School

Research Question

How will changes in wetlands and developed land affect future flooding in rivers?

Aim: To predict the effects of changes in land use on flooding to advocate for future land restoration and implementation

Background: Urban Development

● Causes losses of wetlands, forested land, and riparian vegetation● Leads to limitations in native habitat growth, water passage, and water quality● Developed land is mainly impervious, preventing rainfall and snowmelt from

infiltrating the soil● Since human settlement, about 57% of total wetlands area has been lost in the

Willamette River Basin

Background: Wetlands, Basins & Flooding

Wetlands & Basins● Support biodiversity key for rivers and streams● Cleanse polluted waters by retaining sediments and collecting excess

nutrients● Offer a source of baseflow for streams in dry summer months● Provide a floodplain for rivers during the wet season

Flooding● Discharges affected directly by basin topography, land use, precipitation, and

temperature● Urbanization has been shown to have major influence on stream discharge

due to its effects on land use and basin topography

Study Area

Urban Streams Near Portland, OR

● Johnson Creek● Tualatin River● Pudding River● Clackamas River

Methods

● Part I: Historical Evaluation● Part II: Land Use & Changes● Part III: Predictive Modeling

Methods: Part I

Part I: Historical Evaluation1. Investigate wetlands and developed lands historically in four stream basins in

the Portland-Metro Area between 1996 and 2010 (Johnson Creek, Tualatin River, Pudding River, and Clackamas River).

2. Use historical flood records to investigate the relationship between land use and flooding.

Methods: Part IIPart II: Land Use & Changes

1. Track changes in wetlands and developed areas in each watershed using Geographic Information Systems (GIS) and NOAA Coastal Change Analysis Program (C-CAP) Data 1996-2010 (Johnson Creek, Tualatin River, Pudding River and Clackamas River).a. Classify palustrine wetlands in terms of forested, shrub/scrub, and emergent.b. Classify developed land in terms of high intensity, medium intensity, low intensity,

and developed open space.c. Calculate total area of each wetland and developed land type in each basin for

each C-CAP evaluation.d. Track change over time in wetland area and determine percentage change

between periods.e. Use trendline regression to predict future change.

2. Use NOAA’s Impervious Surface Analysis Tool (ISAT) to evaluate changes in imperviousness

Methods: Part IIIPart III: Predictive Modeling

1. Using the Community Hydrologic Prediction System (CHPS) to Predict the Effects of Land Use Changes on Flooding

a. Based on annual percent change, input new percentage impervious constants into the Sacramento Soil Moisture Accounting (SAC-SMA) Model based upon ISAT analysis.

b. Investigate how flooding/discharges would change based upon changes in wetland and developed land coverage using historical data to run the SAC-SMA Model and then CHPS.

2. Applying the GIS Flood Tool (GFT) for Flood Inundation Mappinga. Obtain four raster datasets for desired flood mapping area: Raw & Conditioned Digital Elevation

Maps (DEM), Flow Directions, and Flow Accumulation.b. Map different projected floods to visually represent discharge rates.

3. Suggesting Land Use Changes with Green Infrastructurea. Investigate potential solutions in land use changes to counteract developmentb. Contact local watershed councils and isolate areas for potential renovation based upon community

recommendations and site availabilityc. Use land use and flood maps to prioritize locations for green infrastructure implementation

Model of Experimentation

Tools & Models

● NOAA Historical discharge/flood records● ArcGIS Mapping Software● Impervious Surface Analysis Tool:

○ NOAA ISAT Software

● Remotely Sensed Imagery○ C-CAP-- 30m res○ DEM-- 30m res

● Hydrologic Models○ NWRFC SACSMA & CHPS

● Flood Inundation Mapping○ USGS GIS Flood Tool

Part I: Historical EvaluationJohnson Creek Evaluation:

● Milwaukie Gauge (MIWO3)○ Percent Basin Developed: 62%○ Percent Basin Wetlands: 1.1%

● Sycamore Gauge (SYCO3)○ Percent Basin Developed: 36.5%○ Percent Basin Wetlands: 1.9%

● Historical data in Johnson Creek suggests that basins with larger percentages of wetlands and smaller percentages developed land experienced less severe flooding

● Data suggested a significant relationship between percent basin wetlands and flood chance percentage across basins (p<0.001)

*Outlier due to a broken gauge during evaluation of the flood in 2009

Part II: Land Use & Changes● Each basin investigated experienced significant changes in imperviousness between

1996 and 2010● Overall areas of developed land increased in all basins, and wetlands area decreased

across all basins● Due to overall small percentages of wetlands within basins investigated, losses in

wetlands usually did not change imperviousness significantly● Data availability limited the time period investigated

Part II: Land Use & Changes Cont.Regression Analysis

● Changes in land use from 1996 to 2010 were processed and analyzed● Using regression analysis of 26 different land classifications within all four

basins, predictions were made for future land use changes for developed and wetland areas

● These changes were applied to ISAT, then converted into new impervious percentages for each basin

Land Use Summary: Tualatin River Basin

Part III: Predictive ModelingUsing CHPS to Predict the Effects of Land Use Changes on Flooding● Using the imperviousness percentages calculated with ISAT, new flood responses were modeled with

prior flood data● Outdated impervious percentages in CHPS and SAC-SMA Models were updated using new accurate

percentages calculated with GIS and ISAT in Part II● With increases in imperviousness, discharges increased● Discharges varied depending on the basin and specific flooding event● Factors such as snowmelt and precipitation patterns during each flooding event proved to create

variance in discharge changes between flooding events● The effects of climate change and increased precipitation were not accounted for in modeling, leading

to limitations in flood intensity projections

Part III: Predictive Modeling Cont.Applying GFT for Flood Inundation Mapping● 30m DEM resolution led to limitations in

flood inundation mapping● Due to low resolutions, very little change

was able to be seen visually in flood inundation maps, despite large changes in discharge rates

● Additionally, low resolutions prevented floods from being mapped in smaller basins

● LiDAR DEM was able to be applied within the Johnson Creek Watershed and produced much more accurate results

Conditioned DEM

Pudding River

Pudding River Basin

Flood February 1996

Johnson Creek Prediction, LiDAR DEM

Potential Stormwater Site

Initial Flood 1996

Predicted Flood 2045

ESRI World Imagery

Created Using ArcGIS 10 and USGS GIS Flood Tool

Depicted to the left is the flood inundation map for Johnson Creek created using LiDAR DEM and USGS GIS Flood Tool at the Sycamore Gauge. Changes in flooding between the initial 1996 flood and the 2045 prediction are shown in red based upon land use change prediction analysis.

Part III: Predictive Modeling Cont.Suggesting Land Use Changes with Green Infrastructure● Large land use changes must be implemented to account for urban growth● Wetlands restoration proved to require very large sums of land to counteract developed land

changes across all basins● Data suggests that prevention of future flooding is best mitigated through implementation of pervious

area within impervious regions● Data serves as strong support of green infrastructure and helps to quantify areas of change

necessary to counteract changes in development in each basin

Part III: Predictive Modeling Cont.

Suggesting Land Use Changes with Green Infrastructure Cont.● GIS Mapping serves as strong resource for local watershed councils to isolate locations for

green infrastructure implementation● Potential areas for green infrastructure (stormwater) implementation were isolated based upon

recommendations by the Johnson Creek Watershed Council and impervious surface data● Flood inundation maps within the Johnson Creek Watershed are to be used to advocate for

green infrastructure implementation

Stormwater sites in the Johnson Creek Watershed

Isolating Areas for Green Infrastructure Implementation

To the left, potential areas for green infrastructure implementation (stormwater sites) have been isolated based upon recommendations by the Johnson Creek Watershed Council and impervious land use mapping.

Major Takeaways

● Remote sensing technology serves as a strong tool for land use analysis● Restoration of wetlands would be expensive● Implementation of green infrastructure could mediate wetland loss and urban

development● Impervious surface maps are useful to prioritize areas for future restoration

Future Directions

● Using LiDAR DEM to map floods in other basins● Using ArcMap to isolate open areas for wetland implementation● Approaching other local watershed councils to advocate for land use changes

within various basins● Advocating for green infrastructure implementation using flood inundation

maps

Acknowledgements

I would like to thank first my mentors that have guided me in my scientific research for the past few years: Ronda Royal, Kate Fickas, and Andy Bryant. Additionally, I would like to thank those who directed me through problems we encountered while working with the different software utilized in this study: Bill Eslinger, NOAA (ISAT), James Verdin & Kristine Verdin, USGS (GFT), and James Woolard, NOAA (ASD Field Spectroradiometer options). Lastly I would like to thank the members of the Johnson Creek Watershed Council, in particular Katie Songer and Danielle Miles for their support. Without the direction of these professionals, I could not have completed my work; thanks again to all of these amazing scientists.

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