an integrated hydro-topographic model for viti levu gau
DESCRIPTION
An integrated hydro-topographic model for Viti Levu Gau. Conway Pene 2012 Pacific GIS&RS Conference 27-30 November 2012, Suva. Hydro- topo integration. Water flows downhill... Hydro – surface water, stream network ... plus ... Topo – surface shape, slope and aspect ... equals ... - PowerPoint PPT PresentationTRANSCRIPT
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An integrated hydro-topographic model for Viti Levu Gau
Conway Pene
2012 Pacific GIS&RS Conference27-30 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