ArcGIS Assignment 1
Geospatial Data Analysis for Hydrological Modelling

Var Catchment Analysis using GIS

Pages: Assignment - StepByStep - Results

Step By Step Tutorial

Step 1: Preparation of ArcGIS

• activate the extensions (if not yet done):
  -> start ArcMap (any default map), Menu Customize -> Submenu Extensions
  -> select all available extensions
• optional: please install the Arc Hydro Tools:
  -> Esri-Webpage
  Arc Hydro Tools integrates several basic steps in combined funtcions and might be useful esp. for the final working steps of this assignement.

Step 2: create a new project folder and a new map

Please create a new folder on your computer with a suitbale folder name.
This folder is used to store all GIS project related files,
in this tutorial it will be called GISProjectFolder.

Please start ArcMap and create a new map (e.g. A0 size).

• please start ArcMap and create a new map (e.g. A0 size)
• change the default properties of the data frame -> Layers -> Properties
  -> General: name (e.g. "Var_Catchment" map)
  -> Data Frame: Automatic or Fixed Scale
  -> Coordinate System: NTF_Paris_France_III (projected CS; National Grids, France, France III)
• store/save the map in GISProjectFolder
• add a north arrow: Insert->North Arrow
  add a legend: Insert->Legend (items can be defined later)
  add a scale bar: Insert->Scale bar (please us the meter system)

Step 3: download DEM raster files and add this to your map

Let's start with 75 m or 300 m resolution DEM:

• download topo075.asc (5 MB) 75 m resolution or topo300.asc (0.8 MB) 300 m resolution, raster data in ASCII format
• store the raster data file in your folder GISProjectFolder
• import the raster data to the map:
  ArcToolBox -> Conversion Tools -> To Raster -> ASCII to Raster
• define the coordinate reference system (CRS) for the new dataset:
  ArcToolBox -> Data Management Tools -> Projections and ... -> Define Projection
• change the visualization: Properties -> Symbology -> Stretched ->
  Stretch Type Minimum - Maximum -> choose a suitable Color Ramp

Step 4: Flow Direction Operation

Calculate the flow direction for every cell:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Flow Direction
  select the imported DEM as surface input raster
  update the visualization in a suitable way
  analyze the result in comparison to the theory of flow direction analysis
  if the flow direction result is showing no sinks, continue with Step 7

Step 5: Fill-Sink Operation

Check sinks in the DEM and fill the DEM towards a depressionless DEM (only if sinks are existing!):

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Sink
  update the visualization in a suitable way
  analyze the result (location of sinks) in comparison to the DEM
• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Fill
  use the original DEM as input raster
  update the visualization in a suitable way
  analyze the result (depressionless DEM) in comparison to the original DEM (e.g. difference)

Step 6: Flow Direction Operation for Depressionless DEM

Recalculate the flow direction for every cell:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Flow Direction
  select the new depressionless (Fill) DEM as surface input raster
  update the visualization in a suitable way
  analyze the result in comparison to the theory of flow direction analysis

Step 7: Flow Accumulation

Calculate the flow accumulation for every cell:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Flow Accumulation
  select the result of step 6 in case of sinks or step 4 in case of no sinks as input raster
  update the visualization in a suitable way
  analyze the result in comparison to the theory of flow accumulation analysis

Step 8: Identification of Streams

Selection of cells with minimum flow accumulation:

• ArcToolBox -> Spatial Analyst Tools -> Map Algebra -> Raster Calculator
  expression: Con ("result of step 7" > XX ,1)    XX -> threshold: minimum cell value, e.g. (16*50)=800
  update the visualization in a suitable way
  do a variation of the XX values and select a suitable one

Step 9: Stream Link (optional)

This method assigns unique values to the sections of the raster linear network between intersections:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Stream Link
  select the result of step 8 as input raster
  update the visualization in a suitable way
  analyze the result

Step 10: Stream Order (optional)

This method results in a representation of the order of each of the segments in a network:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Stream Order
  select the result of step 9 as input raster
  update the visualization in a suitable way
  analyze the result

Step 11: Stream to Feature (optional)

This method converts the stream raster to vector data line features representing the linear network:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Stream to Feature
  select the result of step 8 or 9 as input raster
  analyze the result

Step 12: Flow Length

This method converts the stream raster to vector data line features representing the linear network:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Flow Length
  select the result of step 6 (flow direction) as input raster
  analyze the result

Step 13: Sub-Catchment Pour Points

Pour points (outflow/outlet points) of the five sub catchments has to be defined:

• create a new, empty point vector data layer e.g. with ArcCatalog
  Please consider the coordinate reference system!
• add the point vector data layer to your map
• start the Editor (activate related Toolbar) and
  create new suitable pour points for the five subcatchments,
  you can use the stream network raster map as background
• maybe optimize the location by ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Snap Pour Points
• in case Step 14 did not produce the expected sub-catchments,
  you can iterate between Step 13 and 14
  to optimize the location of the five pour points

In case of problems with finding good locations for the five pour points,
you can use a prepared PourPoint set as shape file: PourPoint_300.zip or PourPoint_75.zip.

Step 14: Sub-Catchment Specification

Watershed (sub-catchment) delineation based on the defined pour points:

• ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Watershed
  select the result of step 6 (flow direction) and step 13 as input
  important: specify the Extent under Environment Settings in the bottom of the operation window
            Environment Settings -> Processing Extent -> Extent to Same as layer for a layer with the whole catchment
• analyze the result, optimize the pour point location if needed

Step 15: Sub-Catchment Analysis

Geometrical analysis of the five sub-catchments.

• convert the raster data to vector data (polygons):
  ArcToolBox -> Conversion Tools -> From Raster -> Raster to Polygon
• select/split the sub-catchments on both types raster data or vector data:
  Raster: ArcToolBox -> Spatial Analyst Tools -> Extraction -> Extract by Attribute
  Vector: ArcToolBox -> Analysis Tools -> Extract -> Select or
               ArcToolBox -> Analysis Tools -> Extract -> Split By Attribute
• extract sub-DEM by the sub-catchment polygon vector data:
  ArcToolBox -> Spatial Analyst Tools -> Extraction -> Extract by Mask
• analyze the sub-catchments by GIS raster data methods individually for
  • area
    can be done on raster data level (number of cells * cell area)
    or on vector level from the shape size in attribute table
  • length of longest flow path
    can be calculated for every sub-catchment individually (see step 5,6 and 12)
    ArcToolBox -> Spatial Analyst Tools -> Hydrology -> Flow Length
  • slope analysis: ArcToolBox -> Spatial Analyst Tools -> Surface -> Slope
    Please use as output measurement PERCENT_RICE.
    The mean value of the resulting slope raster data slope can be found under Properties Tab Source - Statistics Properties

Step 16: Land Use Distribution

Analyse the five sub-catchments by GIS in respect to land use.

• download landuse.asc (773 kB) 300 m resolution, raster data ASCII
  and landuse_legend.dbf (5 kB) table, converted to DBase-File dbf
• store the landuse.asc raster data and the legend in your folder GISProjectFolder
• import the raster data to the map:
  ArcToolBox -> Conversion Tools -> To Raster -> ASCII to Raster
• define the coordinate reference system (CRS) for the new dataset:
  ArcToolBox -> Data Management Tools -> Projections and ... -> Define Projection
• join the landuse_legend to the land use:
  Joins and Relates -> Join
  join the land use Value to the ID from the landuse_legend table
  the new attribute landuse_legend.LABEL_LEVE can be used to classify the land use for the required six categories:
  • Artificial surfaces
  • Agricultural areas
  • Forests
  • Semi natural areas
  • Wetlands
  • Water bodies
  update the visualization in a suitable way using the six categories
• analyse the five sub-catchments (area) for the six categories:
  • convert the land use to polygons using landuse_legend.LABEL_LEVE as field
    ArcToolBox -> Conversion Tools -> From Raster -> Raster to Polygon
  • dissolve landuse polygons by
    ArcToolBox -> Data Management Tools -> Generalization -> Dissolve using field LABEL_LEVE
    the result are the 6 polygons for the 6 land use classes
    
  • overlay land use polygons with sub-catchment polygons
    ArcToolBox -> Analysis Tools -> Overlay -> Intersect
    the result are the 30 polygons combinations of 5 sub-catchment and 6 land use classes,
    
  • area calculation:
    Open Attribute Table
    you can get the area by the shape areas column in m**2,
    you can add a new field and use Calculate Geometry to calculate the area in km**2

Step 17: Soil Type Distribution

Analyze the five sub-catchments by GIS in respect to soil type.

• download soiltype.asc 2000 m resolution, raster data ASCII
  and soiltype_legend.txt table
• store the soiltype.asc raster data and the legend in your folder GISProjectFolder
• import the raster data to the map:
  ArcToolBox -> Conversion Tools -> To Raster -> ASCII to Raster
• define the coordinate reference system (CRS) for the new dataset:
  ArcToolBox -> Data Management Tools -> Projections and ... -> Define Projection
• join the soiltype_legend to the soil type:
  Joins and Relates -> Join
  join the soil type Value to the ID from the soiltype_legend table
  soil_type can be used to classify the soil type for the required six categories:
  • Loam
  • SandyLoam
  • SiltyClayLoam
  • SiltLoam
  • SandyClayLoam
  • ClayLoam
  update the visualization in a suitable way using the six categories
• analyse the five sub-catchments (area) for the six categories:
  • convert the soiltype to polygons using soiltype_legend.txt.ID as field
    ArcToolBox -> Conversion Tools -> From Raster -> Raster to Polygon
  • dissolve soiltype polygons using field soiltype_legend.txt.soil type as dissolve field
    ArcToolBox -> Generalization -> Dissolve using field soiltype_legend.txt.soil type
    the result are the 6 polygons combinations for the 6 soil type classes,
    
  • overlay soiltype polygons with sub-catchment polygons
    ArcToolBox -> Analysis Tools -> Overlay -> Intersect
    the result are the 30 polygons combinations of 5 sub-catchment and 6 soil type classes
    
  • area calculation:
    Open Attribute Table you can get the area by the shape areas column in m**2,
    you can add a new field and use Calculate Geometry to calculate the area in km**2

Step 18: Rainfall Distribution

Analyse the sub-catchments by GIS in respect to the rainfall distribution.

• download rainfall_stations.txt (1 kB) x y z and name as data ASCII
• store the file in your folder GISProjectFolder
• import the ASCII station point data file to the map as point layer:
  ArcToolBox -> 3D Analyst Tools -> Conversion -> From File -> ASCII 3D to feature class
  update the visualization in a suitable way, you can use the legend table for this purpose
• update the coordinate reference system:
  ArcToolBox -> Data Management Tools -> Projections and ... -> Define Projection
• create the Thiessen polygons for the rainfall gauge stations:
  ArcToolBox -> Analysis Tools -> Proximity -> Create Thiessen Polygons
     select a suitable catchment layer (e.g. basic DEM)to define the extent and the snap raster
     in Processing Extent of Environment Settings
• intersect the Thiessen polygons with the sub-catchments polygon:
  ArcToolBox -> Analysis Tools -> Overlay -> Intersect
  the result are the polygons of each sub-catchment related to each rainfall gauge station Thiessen polygon