1. Flow Modeling on Massive Grids Laura Toma, Rajiv Wickremesinghe with Lars Arge, Jeff Chase, Jeff Vitter Pat Halpin, Dean Urban in collaboration with

2. Applications n Automatic estimation of terrain parameters u watersheds u drainage networks u topographic index n Surface saturation n Soil water content n Erosion, Deposition n Forest structure n Species diversity n Sediment transport

3. Modeling Flow n Terrain modeled by grid of elevations n Flow direction u direction water would flow from each cell u what does it mean on flat areas?

4. Massive Data n Remote sensing data available today u NASA-SRTM (whole Earth: 5TB) u USGS (entire US at 10m resolution) n Typical grid u East coast USA u 11,000 x 25,000 grid u 0.5 GB

5. Scalability n Current GIS software minimizes CPU time n I/O is bottleneck n Total time does not scale n ArcInfo u more than 3 days on East coast USA grid n TARDEM u 2 days on 1/4 East coast USA grid

6. Theoretical Results n I/O Model u disk much slower than CPU u count number of I/O operations (rather than CPU time) n I/O Efficient Algorithms u identifying flat areas u assigning flow directions on plateaus u identifying watersheds u filling depressions/sinks u assigning flow directions on terrains u flow accumulation

7. Speedup over ArcInfo ArcInfo runs with 750MB RAM; Our program runs with 512MB or 128MB RAM memory limit