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

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

3. Test site Gau island, central Fiji

4. 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

5. 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

6. Need to do some cleaning first...

7. Completed DEM

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

9. Flow directions

10. Flow accumulation

11. Stream segment

12. Catchment boundary

13. 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

14. Stream segments

15. Catchment polygons

16. Network junctions

17. Flow tracing using the model

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

19. Amount of rainfall WorldClim climate raster

20. 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)

21. Vegetation + soils

22. Curve number

23. Curve number x rainfall = runoff

24. Clip runoff to a catchment

25. 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