Planning of Watershed Development Using Geospatial Techniques
Tutorial May 29, 2015(Georefenecing, Database Creation and Watershed Characterisation)
Short Term Training Programme Organised forthe Engineers of
Department of Watershed Development and Soil ConservationGovt. of Rajasthan
Programme CoordinatorDr. Mahesh Kumar Jat
Email [email protected] 01412713412; 09549654186
Department of Civil EngineeringMalaviya National Institute of Technology Jaipur
Malaviya National Institute of Technology JaipurTutorial Exercise: May 29, 2015Objective of this laboratory exercise is to revise what we have learned in 1st Training programme during April 17 21, 2015. This lab exercise includes revision of Georefencing, GIS database creation, Making queries and automatic watershed characterization in GIS.Scope of this tutorial includes Exercise 1: Georeferencing of Given Survey of India Topo-sheet (D:/dwdsc_training/May29_lab/Georeferencing/topo8.JPG)Exercise 2: GIS database creation from geometrically corrected SOI toposheed (topo8). This exercise includes creation of a point, line and polygon feature class (namely spot_height, drainage and water_body) and joining attributes from xreated tables.Exercise 3: Automatic characterization of watershed using DEM layer given folder (D:/dwdsc_training/May29_lab/hydrology/DEM.img).
Exercise 1: Geo-Referencing 1. At first we will open the toposheet which we want to geo-reference in a desired coordinate system.
2. The toposheet is in geographic (Lat/Long) coordinate system but we want this toposheet in UTM-WGS coordinate system which will represents all the units in meter. So for this at first we will calculate the coordinates which are in degree, we will convert these coordinates in meters by the following process.
3. We will use the tools option from the menu bar. And choose coordinate calculator.4. Tools Coordinate Calculator5. A new window will get open:
6. In this window we will define the input and output coordinate system. For input coordinate system selection we will go to projection menu bar and select set input coordinate system.7. Projection Set input projection and units
8. The new window will look like this and then we will set input projection by clicking on the input projection button on the window.
9. Then we will choose Custom and set the projection type as geographic (Lat/Long) and datum as Everest 1969 and click OK
10. Then we will select output projection system.11. Projectionset output projection and units
12. Then we will set output projection system by clicking on Set Output Projection button. The following window will get appear:
13. Again we will choose Custom and we will set projection information as follows:
14. Then in a particular order we will put longitude and latitude information on the calculator and it will calculate the output projection in meter. But the main thing which we will take care of is the order of coordinates we have given to the calculator. The output will be as follows:
15. Then we will note down all the output coordinates for respective input coordinate. 16. Now we will start geo-referencing process:17. We will go on data preparation icon and then we will choose image geometric correction option
18. It will open a new window. In this window we will select from Image File option
19. Now we will select the toposheet which we want to geo-reference by using icon.
20. Then clock OK. Two windows will get open. One is viewer, which will open the toposheet and the other window is Set Geometric Model Window.
21. In set Geometric Model Window we will set polynomial and then click OK.
22. Again two window will get open. One in polynomial model properties and the other is Geo Correction Tool.
23. In polynomial Model properties window we will select polynomial order as 1 and close this window. A new window will get appeared. Then we will select option Key Board Only and clock OK.
24. A new window will get appeared.
25. In this window we will add/change Map Projection.
26. We will select Custom setting. And set the projection values as follows then click OK.
27. Then we will select GCP in the same order as we have calculated the coordinates earlier.28. WE will use option for GCP selection. And we will enter the Reference X and Reference Y value through keyboard which we have calculated earlier.
29. In the same way will select minimum four GCPs in each corner of the toposheet.
30. After fourth point selection it will calculate the reference by itself but we will not use these reference point. We will enter our calculated reference point. Now we will see that our selected GCP has been shifted from its location. We will readjust this point and if the error will be less than 1 we will proceed further.31. Now in Geo-Metric Correction Tool we will select Display Resample Image Dialog tool
32. In this resample box we will give the output file name and tick the ignore Zero in Stats, then click OK.33. Now in a new viewer we can open referenced image. Now this image is correctly geo-referenced and we can see the units in meter and in UTM/WGS84.
Exercise 2: GIS Database Creation
Objective: GIS database creation from geometrically corrected SOI toposheed (topo8). This exercise includes creation of a point, line and polygon feature class (namely spot_height, drainage and water_body) and joining attributes from xreated tables.
Data: topo8 already georeferenced image. Use already georeferenced image (exercise 1) as base map and create database in folder D:/training_dwdsc/May29_lab/Dbase_creationLayers to be created: 1. point : spot_height (name of layer), attribute to be recorded is RL of these points.2. polyline layer of drainage (from given base map , at least 15-20 drains)3. polygon layer of water_body (water bodies available in given base map
Step 1: open the topo.img map available in D:/training_dwdsc/May29_lab/Georeferencing folder in the GIS software. This file is already georeferenced and is in the WGS-1984, UTM 43N Zone projection system. Step 2: Check the projection system to ensure it is in WGS-1984, UTM 43N Zone.Step 3: Create a new layer with following properties: Many software automatically create Id field to uniquely identify each object of the layer, though they may not automatically generate unique Id number (some software do that). Check to ensure that Id field exists, if not you can create a field with name Id.Name: spot_heightFeature type: pointProjection system: WGS-1984, UTM 43N Zone (import from already georeferenced image topo8Step 4: Similarly create two more layers with following properties:Name: drainageFeature type: polylineProjection system: WGS-1984, UTM 43N Zone (import from already georeferenced image topo8
Water bodies available in base map (topo8) should be located and a polygon layer be created.Name: water_bodyFeature type: polygonProjection system: WGS-1984, UTM 43N Zone (import from already georeferenced image topo8Step 5: Create these files one by one. Procedure to be followed in all layers will be Go in Start/all programmes/ArcGIS/ArcCatalog and select Go to AcrCatalog connect with required folder (D:/training_dwdsc/May29_lab/Dbase_creation). Select the folder in content list then go in folder write click and new/shapefile Create new feature layers i.e., spot_height, drainage and water_body one be one. Specify project and coordinate system by importing information from base map (already geoferenced map i.e., topo8). Open ArcMap and add base map Add spot_height feature layer in ArcMap. Then go to contents and write click on spot_height layer, open attribute table and add one field (column) to record RL of spot heights to be digitized. Go to editor and click on start editing. Then select spot heights from the base map degitise them and record RL of ponts in attribute Table. After completing the digitization save and stop the editing.Step 6: Similarly using appropriate tools and ensuring selection of proper layer, create drainge shown in thick blue lines on the map.
Exercise 3: Automatic watershed characterization
1.0 Purpose The purpose of this exercise to demonstrate the steps involved in delineating a stream network and watershed boundaries from a digital elevation model (DEM) using the Spatial Analyst Hydrology Tools in ArcGIS.
2.0 Computer Requirements You must have a computer with windows operating system, and the following programs (extensions) installed: 1. ArcGIS 10.0 2. Spatial Analyst Extension
3.0 Data Requirements and Description The data files used in the exercise consist of Digital Elevation Model (DEM.img) and other datasets like stream network and micro-watershed points for Reodar Block in Sirohi District of the Rajasthan State. The datasets are given in Tutorial_Hydrology folder. The ArcCatalog view of the data folder is shown below:
DEM.img is a DEM prepared from the stereo image of the area captured from CARTOSAT-1 satellite and obtained from NRCS, Hyderabad. Images are geometrically corrected using WGS-84 coordinate system and UTM projection system with a 43rd Zone.
4.0 Getting Started First of all Open the ArcMap and add the DEM.img dataset to the ArcMap. Further save it as hydrology.mxd. This is the only dataset you will need to get started with the process. We will add other datasets later in the tutorial.
All spatial analyst tools that are used for delineating stream network and watershed boundaries are available in ArcToolbox. If ArcToolbox is not activated within the map document, click on the ArcToolbox button to access the tools. Hydrology tools can be found by selecting Spatial Analyst Tools. Hydrology within ArcToolbox as shown below:
5.0 Filling Sinks This function fills the sinks in a grid. If cells with higher elevation surround a cell, the water is trapped in that cell and cannot flow. The Fill Sinks function modifies the elevation value to eliminate this problem. Double click on the Fill tool. Provide Dem.img as the input surface raster, and save the output raster as fill_dem in your working directory. The main function of this tool is to remove imperfections in the DEM to enable water flow to the watershed outlet. However, if there are natural sinks in the data (e.g, 10m deep lake or pond), you can use the Z limit to retain these natural sinks. For example, if you specify Z limit as 6 m, the program will not fill any sinks that are deeper than 6 m. The default is to fill all sinks (do not provide any input for Z limit). Click OK.
After the process is complete a filled DEM (fill_dem) will be added to the map document.
6.0 Flow Direction This function computes the flow direction for a given grid. The value in any given cell of the flow direction grid indicates the direction of the steepest descent from that cell to one of its neighboring cells using the eight direction pour point (D8) method. Double click on Flow Direction tool in Tool Box in ArcMap. Select fill_dem as the input surface raster, and name the output raster as flowdir. Leave the other optional inputs unchanged. Click OK. After the process is complete, a flow direction grid with cells having one of the eight flow direction values (1,2,4,8,16,32,64,128) will be added to the map document. Save the map document.
7.0 Flow Accumulation The function uses the flow direction grid to compute the accumulated number of cells that are draining to any particular cell in the DEM. Double click on Flow Accumulation tool in Tool Box in ArcMap. Select flowdir as the input flow direction raster, and save the output flow accumulation raster as flowacc. Leave the default options for input weight raster and output data type (float) unchanged. Click OK.
After the process is complete, a flow accumulation grid will be added to the map document. You will clearly see a stream network in this output, and if you check the pixel value (by using the identifier tool), the values along the cells that appear to form a stream network will have much higher values compared to the surrounding cells. Save the map document.
8.0 Stream Network Because the flow accumulation gives the number of cells (or area) that drain to a particular cell, it can be used to define a stream. It is assumed that a stream is formed when a certain area (threshold) drains to a point. This threshold can be defined by using the number of cells in the flow accumulation grid. If we assume an area of 0.50 km2 as the threshold to create a stream, the number of cells corresponding to this threshold area is 5000 (0.5 x 1000000/(10*10)). To create a raster, that will have stream cells corresponding to a threshold area of 0.5 km2, select spatial analyst. Using Con function in Conditional tool create a raster from flowacc dataset such that it only includes cells that have pixel value greater than 5000 as shown below, and click Evaluate. Double click on Stream Network Tool in Tool Box in ArcMap. Here input raster is flowacc and Input value raster or constant value as 1. Write down Output raster as Stream and click ok. Note : while putting condition expression should be - Value >= 5000 ; here first letter of Value should be capital and there shuld be space between Value >= and 5000.
This will create a calculation raster where all the cells with value greater than or equal to 5000 in flowacc will have a value of 1, and all other cells are set to Null. Save raster as stream in your working directory. Remove calculation, and add stream to your map document. Save the map document.
9.0 Stream Link This tool assigns a unique number to each link (or segment) in the stream raster. Double click on Stream Link in Tool Box in ArcMap. Provide stream as the input stream raster, flowdir as the flow direction raster, and name the output raster as stream_link.
10.0 Stream Order This tool creates stream order for the stream network. Double click on stream order in Tool Box in ArcMap. Provide stream as the input for stream raster, flowdir as the input for flow direction raster and name the output raster as Stream_order as shown below. Two methods are available for estimating stream order. Choose anyone you like (Strahler in this case), and click OK.
After the process is complete, stream_order will be added to the map document. Can you tell the order of the Reodar Macro watershed?
11.0 Stream to Feature Double click on Stream to Feature Tool in Tool Box in ArcMap. This tool converts stream raster to a polyline feature class. Provide stream_order as the input for stream raster, flowdir as input for the flow direction raster and save the output as stream.shp in your working directory. Click OK.
After the process is complete, a shapefile named stream.shp will be added to the map document. Save the map document. You can use this tool to create features from other stream related rasters such as stream order and stream link.
12.0 Flow Length This tool uses the flow direction to compute the flow distance or length from each cell to the most downstream or upstream cell in the DEM. Double click on Flow Length tool in the Toolbox of the ArcMap. Provide flowdir as the input flow direction raster and save the output as stream_len in your working directory as show below. Use downstream to compute the flow length to the watershed outlet. Click OK.
After the process is complete, stream_len will be added to the map document. What is the maximum distance any water drop has to travel over the Reodar Macro watershed to reach the outlet?
13.0 Basin This tool uses the flow direction grid to find all sets of connected cells that belong to the same drainage basin, and assigns the number of cells that belong to a basin to all the cells within that basin. Double click on Basin tool of the Tool Box in ArcMap. Provide flowdir as the input flow direction raster, and name the output raster as basin as shown below. Click OK.
After the process is complete, basin raster will be added to the map document. Although you will see a big drainage basin that gives the drainage boundary for Reodar Macro Watershed output, there are some small drainage areas that do not drain to the Macro watershed.
14.0 Creating Watershed Boundary
To get the boundary of for Reodar Macro watershed, convert basin raster to polygon features by selecting from Raster function in Conversion Tools of the Tool Box in ArcMap. Convert Raster to Features. Provide basin as the input raster, choose output geometry type as polygon (or polyline if you want), and save the output as basin_boundary.shp in your working directory as shown below. Click OK.
After the process is complete, basin_boundary shapefile will be added to the map document. Besides the main Reodar Macro Watershed Boundary, this shapefile also has small polygons that do not belong to the Macro watershed. You can delete these polygons if you want.
15.0 Delineating Sub-watersheds
In order to delineate sub-watersheds, add the point shapefile in your map document. Although these points are snapped to the stream, it is a good idea to use the Snap Pour Point function to create grid of snapped points, and then use this grid to delineate sub watersheds. Double click on Snap Pour Point function in Tool Box of ArcMap. Use the point shapefile as input for the feature pour point data, leave the default Id field unchanged for pour point field, use flowacc as input for the flow accumulation raster and name the output raster as snap_pt. Use a snap distance of 10m (this may change for different datasets and resolutions). Click OK.
After the process is complete, a raster named snap_pt will be added to the map document. Zoom-in to the points to make sure that they align with the stream or flow accumulation grid.
Next, double click on Watershed function in the Hydrology tool of the Tool Box of the ArcMap. Use flowdir as input for flow direction, snap_pt for input pour point raster, leave the default pour point field unchanged, and name the output raster as watershed. Click OK.
After the process is successfully completed, you should get a raster showing watersheds at these points as shown.
