Water, the elixir of life, flows seamlessly through the intricate tapestry of our landscape. Its movement is governed by nature’s rules, and understanding this dance is vital for numerous domains, from managing water resources to preserving the environment, constructing robust infrastructure, and preparing for disaster scenarios. In the realm of hydrology and Geographic Information Systems (GIS), two fundamental tools hold the key to unraveling this mystery: watershed delineation and drainage density mapping.

The Power of Water Behavior Mapping

The core of responsible land use practices and effective water resource management lies in comprehending how water behaves across our terrain. This article will guide you through the process of harnessing the capabilities of GIS and Remote Sensing, specifically using ArcGIS Pro, to create a drainage density map and delineate watersheds. These techniques are indispensable for anyone vested in the sustainable management of Earth’s precious water resources.

Raster To Polygone

Before we embark on this journey, let’s familiarize ourselves with the essential geoprocessing tools that will be our guiding companions in this GIS tutorial. Our toolkit includes:

Fill: Filling in the gaps and preparing the terrain for analysis.

1. 1. Flow Direction: Determining the path water takes as it flows downhill.

1. 1. Flow Accumulation: Quantifying the amount of water that accumulates at any given point.

1. 1. Raster Calculator: Performing complex calculations on raster data.

1. 1. Basin: Identifying individual drainage basins.

1. 1. Line Density: Measuring the density of linear features.

1. 1. Raster to Polyline: Converting raster data into vector format. Raster to Polygon: Transforming raster representations into

Gathering DEM Data

Our journey commences with obtaining Digital Elevation Models (DEMs). These invaluable datasets can be sourced from the United States Geological Survey (USGS)’s EarthExplorer website, available after a straightforward sign-up process. Alternatively, you can generate DEMs by synergizing tools from Google Earth Pro and GPS Visualizer’s website. Here’s how:

1. 1. Open Google Earth Pro.

1. 1. Create a new folder (working directory) in the “Places” tab by right-clicking on “Temporary places.”

1. 1. Select “Add Path” from the tool icons above the visualization pane.

1. 1. Draw random lines to cover your study area.

1. 1. Specify a name for the digitized lines.

1. 1. Click OK.

1. 1. To save your work, right-click on the working folder and choose “save place as.”

1. 1. Specify the desired output name and location.

1. 1. Visit GPS Visualizer’s website.

1. 1. Set the input to the output file from Google Earth.

1. 1. Select “convert and add elevation.

1. 1. Export the output file in .gpx format.

To import and process the gpx file in ArcGIS Pro:

Now that we have our DEM data, it’s time to bring it into ArcGIS Pro and set the stage for watershed delineation and drainage density mapping. Follow these steps:

1. 1. Open ArcGIS Pro and create a new project.

1. 1. In the geoprocessing toolbox’s search bar, select “gpx to features.”

1. 1. Set the input to the gpx file.

1. 1. Specify the “output feature class” name and location.

1. 1. Click Run.

1. 1. In the geoprocessing toolbox’s search bar, type and search for “IDW.”

1. 1. Set “input point features” to the output feature file.

1. 1. Configure “Z value field” to elevation.

1. 1. Define the “Output raster” name and location.

1. 1. Click Run.

Unveiling Watersheds and Drainage from Elevation Data

To focus on the exact geographic area of interest, we may need to extract a subset of our DEM. This can be achieved using the “clip” or “extract by mask” tool. Here’s how to utilize “extract by mask”:

1. 1. Type and search for “Extract by mask” in the search bar.

1. 1. Set the input raster to the downloaded DEM data.

1. 1. Specify the feature mask data for your region of interest.

1. 1. Define the output raster’s name and location.

1. 1. Click Run.

For extracting watersheds or basins from the DEM, follow these steps:

1. 1. Type and search for “fill” in the geoprocessing toolbox’s search bar.

1. 1. Set “input surface raster” to the DEM.

1. 1. Specify the “Output surface raster” name and location.

1. 1. Click Run.

1. 1. After using the Fill tool, type and search for “flow direction” in the search bar.

1. 1. Set “input surface raster” to the result obtained from the Fill tool.

1. 1. Configure “output flow direction raster” to your preferred name and location.

1. 1. Click Run.

1. 1. Now, type and search for “Basin” in the geoprocessing toolbox.

1. 1. Set “input D8 flow direction raster” to the output of the flow direction process.

1. 1. Ensure the output raster is named and located as per your needs.

1. 1. Click Run.

These basins or watersheds are initially in raster format, but we can transform them into vectors using the “raster to polygon” tool:

1. 1. Type and search raster to polygon from the search bar. 

1. 1. Set input raster to the watershed raster file. 

1. 1. Set output polygon features to desired output name and location. 

1. 1. Click Run.

Crafting a Drainage Density Map

Now that we have delineated our watersheds, let’s turn our attention to creating a drainage density map from the generated drainage network:

1. 1. Type and search for “Line Density” in the geoprocessing toolbox’s search bar.

1. 1. Set the input polyline features to the generated drainage network.

1. 1. Configure the Population field to grid_code.

1. 1. Define the output raster’s name and location.

1. 1. Click Run.

1. 1. After finishing the flow accumulation process, proceed to the “Raster Calculator” option within the “Spatial Analyst tools” located in the geoprocessing toolbox.

1. 1. Next, choose “flow accumulation>1000” from the calculation bar

1. 1.  Click the “Run” button.

 

This process ensures that your drainage network reflects the level of detail specified during the calculation in the raster calculator. However, it’s essential to note that the output still appears in raster format. To further enhance the utility of your drainage data, we will proceed to vectorize it.

Vectorization: Converting Raster to Polyline

The “Raster to Polyline” tool is your key to transforming the drainage network into a vectorized format. Follow these steps:

1. 1. Type and search for “Raster to Polyline” in the geoprocessing toolbox’s search bar.

1. 1. Set the input raster to your drainage network (raster file).

1. 1. Specify the output raster with your desired name and location.

1. 1. Click “Run.”

By performing these actions, you will have successfully converted your drainage network into a polyline format, making it more versatile and suitable for various GIS applications.

Creating a Drainage Density Map

Now that you have a vectorized drainage network, you can create a drainage density map using ArcGIS Pro. Here’s how:

1. 1. Type and search for “Line Density” in the geoprocessing toolbox’s search bar.

1. 1. Set the input polyline features to the generated drainage network.

1. 1. Specify the Population field as “grid_code.”

1. 1. Configure the Population field to “grid_code.”

1. 1. Set the output raster with your desired name and location.

1. 1. Click “Run.”

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