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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. Hydro- topo integration. Water flows downhill... Hydro – surface water, stream network ... plus ... Topo – surface shape, slope and aspect ... equals ... - PowerPoint PPT Presentation
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An integrated hydro-topographic model for Viti Levu Gau
Conway Pene
2012 Pacific GIS&RS Conference27-30 November 2012, Suva
Hydro-topo integration
• Water flows downhill... • Hydro – surface water, stream network• ... plus ...• Topo – surface shape, slope and aspect• ... equals ...• A catchment model
Test site
• Gau island, central Fiji
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
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
Need to do some cleaning first...
Completed DEM
Step 2 – Process DEM
• DEM• Flow direction from each cell to next (slope)• Flow accumulation• Stream segments (accumulation threshold)• Catchment boundary
Flow directions
Flow accumulation
Stream segment
Catchment boundary
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
Stream segments
Catchment polygons
Network junctions
Flow tracing using the model
Runoff calculation
• Predict volume of water at end of catchment– Amount of rainfall– Size, shape, slope of catchment– Surface characteristics (vegetation, soil)
Amount of rainfall
• WorldClim climate raster
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)
Vegetation + soils
Curve number
Curve number x rainfall = runoff
Clip runoff to a catchment
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
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