Lab 3 – Watershed Analysis

Scroll down to content

Lab 3 – Watershed Analysis

In this lab, we used elevation data to model where streams should be (based on what we know about the topography) and delineate sub-watersheds and catchments. My task was to produce a Model Builder model that other analysts can easily run using their own data, along with a guide to using the model and interpreting the output files. In the last section of the lab, I modeled connectivity along the streams using a geometric network dataset.

Fenske_Lab3_Map1
This is an aspect map of the South Fork Nooksack Watershed. This gives us a general knowledge of how this mountainous territory is shaped, each different color represents which cardinal direction a slope is facing based off of the Aspect tools 360° range.

Click this link to view a larger image of this map

 

Fenske_Lab3_Map2
I used the flow direction grid to compute the accumulated number of cells that are draining to any particular cell in the DEM, this is known as the Flow Accumulation. This map was the output of the Model Builder shown below. Before doing this I had to use the Fill Sinks tool to fill in any raster inconsistencies.

Click this link to view a larger image of this map

 

Fenske_Lab3_ModelBuilder1

Click this link to view the Model Builder image

 

Fenske_Lab3_Map3
This map was made using the Stream Link tool. The Stream Link tool assigns unique values to sections of a raster linear network between intersections. Links are the sections of a stream channel connecting two successive junctions, a junction and the outlet, or a junction and the drainage divide.

Click this link to view a larger image of this map

 

Fenske_Lab3_ModelBuilder2

Click this link to view the Model Builder image

 

Fenske_Lab3_Map4
This is map showing Strahler stream orders in the South Fork Nooksack Watershed. Unfortunately at the scale I was working at and the fact that the streams were raster, there was a problem differentiating color of stream orders which is why I inserted a detail map. I used the Stream Link tool to create stream orders.
350px-Flussordnung_(Strahler).svg
Here’s an example of how Strahler stream orders work.

Click this link to view a larger image of this map

 

Fenske_Lab3_ModelBuilder3
This is the end of the Model Builder model used to create the above map.

Click this link to view the Model Builder image

 

Fenske_Lab3_Map5
This map of Flow Length was created using the next step in the model builder below For this map I calculated flow direction using the “Flow Length” tool, I used SFN_flow as my flow direction raster. “DOWNSTREAM” was my direction of measurement inside the “Flow Length” tool. This measures the distance from each cell to the most downstream cell in the DEM.

Click this link to view a larger image of this map

 

Fenske_Lab3_Map6
Before I made this map. I went into the attribute table of my SFN_Boundary shapefile and deleted all of the streams and boundaries that extended outside of the South Fork Nooksack Watershed. I then clipped the streams to my new boundary shapefile. After this I made a point feature class in my geodatabase and placed a point where on the stream line raster downstream of the confluence of any two Order 4 or higher streams. I then used the “Snap Pour Point” spatial analyst tool, “snap pour” points to the cell of highest flow accumulation within a specified distance. I used my Outlet points shapefile that I made as the input feature pour point data. I used SFN_acc as the input for flow accumulation raster. I chose 30 m as my snap distance, and my output was called “snap_pt.” I then opened the “Watershed” Spatial Analyst tool and used FSN_flow as my flow direction input. I used my newly created “snap_pt” as the input pour raster. I then called the output “Subwatershed”

Click this link to view a larger image of this map

 

Fenske_Lab3_Map7
From the above map to this one, I opened my “Watershed” spatial analyst tool again and used my flow direction raster “SFN_flow” and for the pour point data I used “StreamLink”. This map shows catchments, which is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water. The drainage basin includes all the surface water from rain runoff, snow-melt, and nearby streams that run down slope towards the shared outlet, as well as the groundwater underneath the earth’s surface.

Click this link to view a larger image of this map

%d bloggers like this: