Gis Watershed Application

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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