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An integrated hydro-topographic model for Viti Levu Gau Conway Pene 2012 Pacific GIS&RS Conference 27-30 November 2012, Suva

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Hydro-topo integration Water flows downhill... Hydro surface water, stream network... plus... Topo surface shape, slope and aspect... equals... A catchment model

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Test site Gau island, central Fiji

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The big picture 1.Create a Digital Elevation Model (DEM) 2.Process the DEM to find breaklines Streams and ridges 3.Create hydro network Logical network junctions, streams, catchments 4.Integrated model for hydro flow analysis

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Step 1 - DEM using terrain-specific tools Traditional terrain data Contours, spot heights, cliffs PLUS Hydrological data Streams, lakes, sinkholes Hydrology easy to follow on air photos, thus higher accuracy hydrology enforce the terrain shape i.e. breakline

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Need to do some cleaning first...

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Completed DEM

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Step 2 Process DEM DEM Flow direction from each cell to next (slope) Flow accumulation Stream segments (accumulation threshold) Catchment boundary

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Flow directions

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Flow accumulation

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Stream segment

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Catchment boundary

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Step 3 Hydro network Convert raster from DEM processing Stream segment to vector line network Catchment boundary to vector polygons Points created at stream junctions

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Stream segments

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Catchment polygons

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Network junctions

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Flow tracing using the model

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Runoff calculation Predict volume of water at end of catchment Amount of rainfall Size, shape, slope of catchment Surface characteristics (vegetation, soil)

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Amount of rainfall WorldClim climate raster

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Catchment characteristic Curve number hydrological parameter 0 100% of rainfall runoff Function of land cover and soil type Land cover vegetation layer Soil type made up (no soils layer for this island)

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Vegetation + soils

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Curve number

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Curve number x rainfall = runoff

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Clip runoff to a catchment

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What next?... Apply to larger island (Viti Levu) Heavy data load for desktop computer Calculate realistic curve numbers Make dynamic runoff query tool Hover over map and pop-up runoff value