GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

 NITROGEN AND PHOSPHORUS DELIVERY FROM SMALL WATERSHEDS TO
2010-NH-Watershed-Managers_Roundtable-notes
ARIZONA WATERSHED MAP FY 2022 TITLE OF PROJECT LOCATION

BOOKS ABOUT SALMON & WATERSHEDS (MOSTLY FOR KIDS) COMPILED
DATA EVALUATIONDOCUMENTATION FORM NAME OF WATERSHED NAME OF ORGANIZATIONTRIBE
DESIGN AND DEVELOPMENT OF SOFTWARE FOR TRAINING THE WATERSHED

Slope calculation using ArcGIS


GIS for Watershed Modeling Exercise


Slope calculation using ArcGIS


Save the following to a text file ‘elev.txt’


ncols 5

nrows 4

xllcorner 0

yllcorner 0

cellsize 100

NODATA_value -9999

57 55 47 48 48

53 67 56 49 52

53 52 45 42 43

51 58 40 41 40


Based on the elevation grid:

  1. Manually assign eight direction pour point model grid

  2. Draw flow direction grid

  3. Hand calculate flow accumulation grid

  4. Hand draw drainage line


Open ArcMap and ArcToolbox. Use the tool Conversion Tools à To Raster à ASCII to Raster to import this grid file into ArcMap. Specify a name and location for the Output raster (such as “elev”) and specify the Output data type as FLOAT.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Use the Identify button on the grid created to verify that the numbers correspond to the values in the table above.

Open Tools à Extensions and verify that the Spatial Analyst function is available and checked.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Select Spatial Analyst à Surface Analysis à Slope on the Spatial Analyst toolbar.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


At the dialog that appears select your output raster (elev )as the input surface and select the output in Degree or Percent. You will get something like the following:

GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


You can make the slop raster permanent by right click the layer slope of elev, then select Make Permanet:


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Calculating Aspect:


Select Spatial Analyst à Surface Analysis à Aspect on the Spatial Analyst toolbar. At the dialog that appears select elev as the input surface.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Calculate Flow Direction


-- Assign a flow direction to each grid cell based on the neighboring cell with the lowest elevation

Open the Toolbox (not the spatial Analysis tool bar). Open ArcToolbox, select Spatial Analyst Tools à Hydrology à Flow Direction, double click on Flow Direction

GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Select elev as the input raster and specify names for output rasters (e.g. FlowDir).


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Here is the Flow Direction grid:

GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Compare the result with your hand drawing on the flow direction grid.


Calculate Flow Accumulation




With ArcToolbox open, select Spatial Analyst Tools à Hydrology à Flow Accumulation, double click on Flow Accumulation


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Use FlowDir as the input flow direction raster, save flow accumulation raster as FlowAcc.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS



GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Compare the result with your manually calculated flow accumulation grid.


Drainage line processing

Now we will use ArcHydro to generate drainage line


  1. Stream Definition

This step generates stream grid from stream accumulation grid.


From ArcHydro tool bar, select Tarrain Preprocessing – Stream Definition. Use FlowAcc as flow accumulation grid, Str as stream grid to be generated


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


About threshold:


Cell size = 100 x 100 m

Each cell represents 10,000 m2 in area.

If delineate the streams for a 10,000 cell flow accumulation threshold, the minimum drainage area upstream will be:

10,000 x 10,000 = 100,000,000 m2 or 100 km2


Use the default value (0.15) for this example.


Stream Segmentation


Stream segmentation generate a grid of stream segments from flow direction grid and stream grid created from stream definition processing. Input the dialog as following. FlowDir as the flow direction grid and Str as the Stream Grid. Output link grid will be Lnk.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


You will get something similar to the following:

GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

Drainage line processing


This process converts the stream link grid into a drainage line feature class that we are familiar with (we normally represent rivers, streams as line features).


Select Terrain Preprocessing – Drainage Line Processing. Input the dialog as following:


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Does the drainage line feature look the same as your hand calculated one?


Catchment Grid & Catchment Polygon


Catchment area is the region of land whose water drains into a specified drainage line.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Select Terrain Preprocessing – Catchment Grid Delineation


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

Use FlowDir and Lnk grids as input.

GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


The catchment grid will be automatically added to the table of content.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

From catchment grid (Cat), we can derive catchment polygon. From Terrain Preprocessing menu, select Catchment Polygon Processing:


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

Drainage Points

Next, we need to generate drainage point feature class from Catchment and flow accumulation.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


Hydro Network Generation


We have already created drainage features – drainage lines, drainage points and catchment polygons. Select Network Tools – Hydro Network Generation, keep the default input as following:



GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


This process generates two feature classes – hydro junction feature class and hydro edge feature class. It also establish connectivity between the drainage and network feature classes.


Set Flow Direction


This function set flow direction for the hydro network based on FlowDir grid.

GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS


To view the flow direction, go to “view – Tool bars – Utility Network Analyst”. Make sure Utility Network Analyst is checked.


On the Network toolbar, select Flow – Display Arrows. You should see:


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

Use the Add Junction Flag tool GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS on the Utility Network Analyst to place a flag on the basins outlet junction. This will place a green square (representing a flag) on the junction.


GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

GIS FOR WATERSHED MODELING EXERCISE SLOPE CALCULATION USING ARCGIS

36



DEVELOPMENT OF A SYSTEMSBASED APPROACH TO INTEGRATED WATERSHED MONITORING
DRAFT FOR REVIEW BY THE WRIA 9 WATERSHED ECOSYSTEM
EAST BRANCH FISHING CREEK WATERSHED ATMOSPHERIC DEPOSITION TMDL SULLIVAN


Tags: arcgis save, modeling, exercise, watershed, arcgis, using, calculation, slope