Concept Course on Spatial Dr. A.K.M. Saiful Islam Application of GIS in Watershed Analysis Dr. A.K.M. Saiful Islam Institute of Water and Flood Management (IWFM) Bangladesh University of Engineering and Technology (BUET)

Concept Course on Spatial Dr. A.K.M. Saiful Islam Watershed analysis using ArcGIS This training will be on: 1.Digital Elevation Model (DEM) 2.Flow direction 3.Flow accumulation 4.Identify and removing sink 5.Stream Network 6.Stream Links 7.Watershed analysis Input Data DEM data of Bangladesh (Resolution 900m)

Concept Course on Spatial Dr. A.K.M. Saiful Islam How to turn on Hydrologic Modeling 1.First turn on Spatial Analyst

Concept Course on Spatial Dr. A.K.M. Saiful Islam Hydrology Tools  Activate ArcToolbox from window menu  Expand “Hydrology” from “Spatial Analyst” Tools

Concept Course on Spatial Dr. A.K.M. Saiful Islam 1.Digital Elevation Model Add digital elevation model of Bangladesh Click on + icon and select bgd900dem

Concept Course on Spatial Dr. A.K.M. Saiful Islam DEM of Bangladesh (Resolution 900m) This DEM will be used To calculate Flow direction

Concept Course on Spatial Dr. A.K.M. Saiful Islam 2. Flow direction  Flow directions simplified: “Dump a bucket of water on your surface and see which of way it flows!”  Shows the direction water will flow out of each cell of a filled elevation raster. WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamDr. Akm Saiful Islam

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow Direction for cell Cell ElevationElevation differenceDistance weight Distance weight Gradient Flow direction Flow direction Number

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow direction using ArcToolbox Click flow direction and select bgd900dem as input surface raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow direction raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam 3. Flow accumulation  Flow accumulation simplified: “Accumulate flow for each cell considering ALL uphill cells!”  Used to estimate rainfall volume within a watershed and delineates drainage.  A flow accumulation raster tabulates for each cell the number of cells that will flow to it.  A flow accumulation raster records how many upstream cells will contribute drainage to each cell ( the cell itself is not counted).

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow Accumulation in cell Cell Elevation Flow direction Flow accumulation From To

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow accumulation using Arc Toolbox Click flow accumulation and select flowdir_bgd91 as input surface raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow accumulation raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam 4. Identify and removing sink Sink is surrounded by higher cell. It can artificially terminate streams by trapping flow. It is caused by possible error in the elevation data and need to be removed before attempting hydrology analysis. Sink

Concept Course on Spatial Dr. A.K.M. Saiful Islam Filling Sinks Filling sinks is an iterative process. Sink cell values are changed to equal neighboring elevation cell values. Lowest value is used. Use Merge to put new sink values in the elevation theme. Test again for more sinks. Fill to lowest Neighboring cell

Concept Course on Spatial Dr. A.K.M. Saiful Islam Identify sink using Arc Toolbox Click on Sink from hydrology Select flowdir_bgd91 as input flow direction raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Sink raster A total of 4621 sinks found

Concept Course on Spatial Dr. A.K.M. Saiful Islam Fill Sink using Arc Toolbox Click on Fill from hydrology Select bgd900dem as input flow direction raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Filled sink DEM

Concept Course on Spatial Dr. A.K.M. Saiful Islam Use filled sink DEM  Now create Flow direction raster aging using this filled sink DEM.  Create Flow Accumulation raster using this new Flow direction raster.

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow Direction raster using filled sink DEM

Concept Course on Spatial Dr. A.K.M. Saiful Islam Flow Accumulation raster using filled sink DEM

Concept Course on Spatial Dr. A.K.M. Saiful Islam 5. Stream network You can use the flow accumulation grid to identify drainage courses by extracting those cells with the highest accumulated flow values ( cell contains the most water are stream channel). You can create a drainage network of any detail by choosing the appropriate volume values (300 is used for this data). Choice of threshold value can be arbitrary. It should be corresponding to high resolution topographic maps of filed maps.

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream Network using ArcToolbox Select Flow accumulation as input conditional raster Set 1 as constant value Expression: Value > 300

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream Network raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream network on Flow accumulation raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam 6. Stream Links After a stream network is derived from a flow accumulation raster, each section of the stream raster line is assigned a unique value and is associated with a flow direction Arbitrarily assign unique values to each link of the stream networks.

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream link using Arc Toolbox Select Stream network as input stream raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream Link

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream Order Assign a numeric order to stream link. Use either Shreve (true) or Strahler (false) ordering methods.

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream order using Arc Toolbox Select streaml_con_1 as input stream raster. Stream ordering method is STRAHLER

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream Order raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Steam as Shape object The stream link raster file can be converted into line feature class. Streams can be represented as shape file.

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream to Feature using Arc Toolbox Select Streaml_con_1 as input stream raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Stream as Shape file

Concept Course on Spatial Dr. A.K.M. Saiful Islam 7. Watershed Analysis Watersheds delineate a drainage area. Drainage basin, water sheds, basin, catchments area, and contributing area are synonymous terms referring to an area of drainage that contributes water to a common outlets (pour points). Pour Point Water sheds

Concept Course on Spatial Dr. A.K.M. Saiful Islam Water shed using Arc Toolbox Select stream link as input raster

Concept Course on Spatial Dr. A.K.M. Saiful Islam Watershed

Concept Course on Spatial Dr. A.K.M. Saiful Islam Change symbology of watershed Double click and change as Unique values

Concept Course on Spatial Dr. A.K.M. Saiful Islam Unique Basins