Lab 1: Calculating Areas from Raster Datasets
Here we see how to use the cell size and the linear unit of projected rasters to calculate the area within a raster that meets some criteria.
Hydrologic Analysis Lab Exercise Videos
Module 3 · Watersheds and Basic Hydrological Analysis · 11 videos · 1 h 31 min in all
Lab 2: Problems when creating Watersheds without filling the DEM!
Here we learn the consequences of failing to fill a DEM before running hydrologic analyses on it. This a common mistake we make when trying to generate watersheds, and this lab exercise will help you learn to recognize the signs of trouble!
view the Lab 2: Problems when creating Watersheds without filling the DEM! video lecture on YouTube
Lab 3: Filling Sinks in a DEM
In Lab Exercise 2 we saw what happens when you fail to fill your DEM before you generate your flow direction raster, and how that caused your watershed analysis to fail. If there is a low point in the DEM where all the neighboring cells are higher than that point (and there almost always is), then the algorithm stops at that low point. These low points are called sinks in the DEM. So we just need to fill these sinks in the DEM before calculating the Flow Direction raster. This lab exercise will show you how to do that, using the Fill tool.
Lab 4: Calculating an Accurate Flow Direction Raster
Here we will use the Flow Direction tool to calculate flow direction using the D8 method across the landscape around Picture Canyon. This time the flow direction will allow continuous flow across the entire landscape because we have filled in the sinks in Lab Exercise 3. We will also see why the Flow Direction tool produces the eight specific flow direction values it does (1, 2, 4, 8, 16, 32, 64 and 128).
Lab 5: Generating an Accurate Watershed
Here we will use the correct Flow Direction raster we generated in Lab Exercise 4 to create an accurate watershed that shows the true catchment that drains into the Picture Canyon Preserve. We will also see how to use the Raster to Polygon tool to convert that watershed raster into a polygon feature class, which allows us to more easily calculate spatial relationships with other objects (such as distances to other objects, or whether they intersect, contain, or are contained by other objects, etc. You can also calculate more accurate area and length statistics with vector objects). Finally we will see how to export the map as an image, and how to load that image into Microsoft Word.
Lab 6: Creating a Flow Accumulation Raster
This lab will demonstrate the Flow Accumulation tool in ArcGIS Pro. A Flow Accumulation raster is used to calculate the size of the catchment area that drains into every point on the landscape, and is generated from the Flow Direction raster, which was in turn generated from the filled DEM.
While these Flow Accumulation values are interesting enough in themselves, we can also use them to generate additional interesting and useful data, such as stream flow networks and a topographic wetness index.
Lab 7: Generating a Stream Network using Strahler Stream Orders
Here we will use several ArcGIS Pro raster tools, including the Set Null tool, the Stream Order tool and the Stream to Feature tool to generate a network of stream features on the landscape based on the Flow Accumulation raster we created in Lab Exercise 6. These stream features will all be classified into stream orders using the Strahler method, in which the smallest tributaries have a stream order of 1.
View the Lab 7: Generating a Stream Network using Strahler Stream Orders video lecture on YouTube
Lab 8: Aspect Statistics within Watershed
Back in Lab Exercises 3 through 5 we saw how to generate an accurate watershed that drains into Picture Canyon and to convert that raster to a polygon feature class. A common next step would be to describe conditions in that watershed, so this lab exercise will demonstrate how to calculate the acreages of north- vs. south-facing slopes within the watershed. Whether the landscape faces north or south can make a big difference in the vegetation, habitat types and microclimate on the ground, so this is good information to know.
And we'll also get to practice one of the ArcGIS Pro Surface Analysis tools, plus the Reclass tool and the Extract by Mask tool, and we'll get to try out our method for calculating acreages directly from raster that we learned about in Lab Exercise 1.
Lab 9: Slope Statistics within Watershed
This lab is very similar to Lab Exercise 8, where we calculated the areas within the Picture Canyon Watershed that faced north, south or flat. This exercise will show how to figure out how much of the watershed has shallow vs. steep slopes, which can be important information for land managers. If you plan timber harvests in an area, for example, the slope of the area tells you what kind of equipment and harvesting methods you'll need to use to do the work.
And as before we'll also get to practice one of the ArcGIS Pro Surface Analysis tools, plus the Reclass tool and the Extract by Mask tool, and use our method for calculating acreages directly from raster that we learned about in Lab Exercise 1.
Lab 10: The Topographic Wetness Index (TWI)
Topographic Wetness Index (TWI) is a landscape index that combines two topographic phenomena, slope and catchment area, to describe the tendency of water to collect in an area. Areas with high TWI values may be more likely to have higher soil moistures, different soil pH values and more likely to support water- or moisture-dependent species.
We will look at two ways to calculate TWI in ArcGIS Pro, first using the Raster Calculator tool to perform all calculations in a single function. This method is generally the quickest and easiest way to run the analysis. Then we will use Model Builder to build a model linking several Spatial Analyst Math tools together to run the analysis. This method has the advantage of producing a flexible tool that can be rerun in different areas. This model will use the Spatial Analyst Math tools Plus, Times, Divide and NL (for Natural Log).
Lab 11: Finding the Shortest Path Through the Stream Network
In this lab exercise we will learn how to use the Create Trace Network, Enable Network Topology, and Shortest Path tools to build a trace network from our Streams that we created in Lab Exercise 7, and then to find the distance between two spring locations through that network.
View the Lab 11: Finding the Shortest Path Through the Stream Network video lecture on YouTube