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4/6/2009
1
Watershed ApplicationWatershed Applicationusing ArcGIS
Agus WibowoMSc in IT for NRM
Bogor Agricultural Universitye mail: aw3126@yahoo come-mail: [email protected]
Aplikasi GIS untuk “Watershed”
• Menentukan batas DAS / watershed boundaries
• Menentukan distribusi curah hujan di DASo Polygon Thiesseno Isohyet
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Data Used
• Data Digital Elevation NASA Shuttle Radar Topography Mission (SRTM)
• Dapat di-download di http://srtm.csi.cgiar.org/• Tersedia Data SRTM 90m Version 4
Website Data SRTM
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Search Data SRTM
3. Click untuk mencari data
2. Click lokasi data1. Pilih format data
Download Data
Click untuk download
Data hasil download
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Software: ArcGIS Desktop + Spatial Analyst Tools
Watershed Delineation
• Creating a depressionless DEM• Flow direction• Flow direction• Flow Accumulation• Stream network/line• Stream link• Stream order• Delineating watersheds
Sumber: ArcGIS Desktop Help
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Add Data to ArcMap - 1
• Ekstrak Zip file data hasil downloaddownload
• Start ArcMap• Aktifkan ArcToolbox• Click menuConversion tools → ASCII to raster
Add Data to ArcMap - 2• Input: ..\srtm_58_14\srtm_58_14.ASC• Output: ..\SRTM_v4\jabar_dem• Output data type: INTEGER• Output data type: INTEGER• Click OK
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Add Data to ArcMap - 3
Ubah Symbology Peta
Double Click Layery
Pilih jenis Color Ramp
Click untuk membalik urutan warna
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Cropping Data DEM
• Gunakan ArcToolBox →Spatial Analyst Tools →Spatial Analyst Tools →Extraction
• Untuk ekstraksi berdasar luasan misal poligon batas admin Jawa Barat gunakan Extract by Mask. Buat raster poligon batas admin Jabar terlebih dahulu.
Buat Mask Batas Admin Jabar
• Pilih poligon Jabaro Load batas admino Load batas admin
Indo_prop.shpo Select Jawa Barat
• Konversi Poligon ke rastero Gunakan Arctoolboxo Conversion tools → Too Conversion tools → To
Raster → Polygon to Raster
Atur ukuran sel 0.001 (10 m)
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Extract by Mask / Cropping
• Gunakan menu ArctoolboxArctoolbox
• Spatial Analyst Tools → Extraction → Extract by Mask
Hasil Extract by Mask
•Spatial Analyst Overview of Hydrology Tools
• Basin: Creates a raster delineating all drainage basins within the Analysis window.• Fill: Fills sinks in a surface raster to remove small imperfections in the data.• Flow Accumulation: Creates a raster of accumulated flow to each cell by accumulating the weight
for all cells that flow into each downslope cell.• Flow Direction: Creates a grid of flow direction from each cell to its steepest downslope neighbor.Flow Direction: Creates a grid of flow direction from each cell to its steepest downslope neighbor.• Flow Length: Calculates upstream or downstream distance along a flow path for each cell.• Sink: Creates a grid identifying all sinks or areas of internal drainage.• Snap Pour Point: Snaps selected pour points to the cell of highest flow accumulation within a
specified neighborhood.• SnapPour: Snaps selected pour points to the cell of highest flow accumulation within a specified
neighborhood.• Stream Link: Assigns unique values to sections of a raster linear network between intersections.• Stream Order: Assigns a numeric order to segments of a grid representing branches of a linear
network.• Stream To Feature: Converts a raster representing a raster linear network to a feature class.• StreamShape: Converts a grid representing a raster linear network to a shapefile.• Watershed: Determines the contributing area above a set of cells in a grid• Watershed: Determines the contributing area above a set of cells in a grid.
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Watershed Delineation
• Creating a depressionless DEM• Flow direction• Flow direction• Flow Accumulation• Stream network/line • (Map Algebra)• Stream link• Stream order• Delineating watersheds
Sumber: ArcGIS Desktop Help
•Creating a depressionless DEM - 1
• Sink dan Peak terjadi resolusi data atauresolusi data atau pembuatan nilai integer
• Sink dan peak harus dihilangkan, jika tidak maka delineasi jarinagn drainase tidak kontinyu.
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•Creating a depressionless DEM - 2
• Arctoolbox → Spatial Analyst Tools→Hydrology Fill DEM h ilHydrology → Fill
• Waktu: 4 menit (Core 2 duo 2.33 GHz, RAM 4GB)
DEM hasil
Create Flow Direction
• Menentukan arah aliran air• Evaluasi 3 x 3 cell berhenti
• Nilai cell antara 1-255• Contoh untuk illustrasi
• Evaluasi 3 x 3 cell, berhenti pada tengah cell dan evaluasi dengan nilai cell tetangganya.
• Jika arah aliran ke utara maka nilai cell tengah diganti dengan cell tsb.
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Compute Flow Direction
• ArctoolBox → Spatial Analyst Tools → Flow Direction
• Waktu: 30 detik
Hasil Flow Direction
Compute Flow Accumulation
• Untuk menentukan jaringan sungaijaringan sungai
• Waktu: 1' 6” Hasil Flow Accumulation
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Extract Stream Network - 1
• Ubah symbology peta FlowAccumulation menjadi classified dengan 5 klas secara Natural Breaks.
• Maka akan terlihat angka tresholdangka treshold jaringan sungai.
Extract Stream Network - 2
• ArctoolBox → Spatial Analyst Tools → Map Algebra → Single Output Map ALgebra
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Stream Link
Stream Order
• Metode:
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Watershed Delineation
• Watershed Outlet / “Pour” PointsCreate shapefiles
• Add “pour” point pada pertemua cabang sungai• Create shapefiles
(point) using ArcCatalog
sungai.
Pour Point
• Buat “pour” point sesuai kebutuhan
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Watershed Delineation
• Hasil kurang bagus, perlu pour point yang banyak.
Automatic Basin Delineation• Secara otomatis delineasi
basin / watershed area untuk seluruh data.
• ArctoolBox → Spatial Analyst Tools → Hydrologi → Basin
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Compute Flow Length
• Flow length is the • ArcToolBox → Spatial distance travelled from any cell along the surface flow network to an outlet. This can be used to find areas that are
Analyst Tools →Hydrology → Flow Length
find areas that are closer to headwater locations or closer to stream outlets.
Hasil Flow Length
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Hillshade• Untuk memberi efek tampilan 3D• Arctoolbox → Spatial Analyst Tools → Surface → Hillshade• Overlay dengan Flowlenght dengan transparancy 35%
Referensi
• ArcGIS Desktop Help• Hydrologic Modeling and Watershed y g g
Delineationhttp://courses.washington.edu/esrm590/lessons/hydrology/index.html
• SRTM 90m Digital Elevation Data• http://srtm.csi.cgiar.org/• Data Batas Administrasi, jaringan jalan, lokasi kota, http://neonet.bppt.go.id