Basic Hydrology

Mapping, or delineating a drainage area is the crucial next step once your design point is known. We'll start with some easy examples.

Students will need an ArcMap basic license to follow along with this lesson. They will load a USGS topographic basemap and practice delineating drainage areas on it.

We'll add a USGS Topographic web map service to our map, and then create a new shapefile to represent a watershed.

The course is targeted at Conservation District Employees in NY state, so let's look at getting LiDAR within the state.

If you're fortunate enough to have and ArcGIS advanced license and spatial analyst extension, you can follow along with these instructions and generate contours from lidar raster files.

QGIS has surface tools built in, so you'll be able to manipulate Lidar files right out of the box if you're going this route.

Curve numbers approximate how much rainfall will end up as runoff. They are determined by the land use and hydrologic group of the soil profile. Students will be able to determine CN values using their best judgment and published sources.

Soil data is tricky to set up but definitely worth it. We'll cover all the steps needed to get it up and running.

Lets digitize land use areas in ArcMap, then intersect them with the hydrologic soil groups layer. Then we'll calculate areas and export the attribute table to excel. A simple pivot table in excel produces our results.

Lets digitize land use areas in QGIS, then intersect them with the hydrologic soil groups layer. Then we'll calculate areas and add them up using Group Stats QGIS plugin.

We need 3 variables to compute time of concentration for rural watersheds. Let's find out what they are!

Here we'll learn how to compute the average watershed slope using the Advanced ArcMap Spatial Analyst extension.

Here we'll learn how to compute the average watershed slope using QGIS built-in tools.

This lecture shows how to compute the TC for urban watersheds, for use in HydroCAD.

EFH2 is a great free program for computing rural watershed hydrology. This lecture shows how to download, install, and use the program.

HydroCAD is a multi-purpose runoff and stormwater modelling platform. We'll just be scratching the surface of its capabilities by looking at the watershed hydrology portion.

We'll still be using HydroCAD but with an alternative hydrology model called the rational method. Nearly everything we've learned so far also applies to the rational method, but it uses different runoff coefficients and rainfall data, as well as a different governing formula.

This short video introduces an example project. Written project instructions are included as supplemental material, as well as a pdf with answers and discussion.

"Rural Areas Export" is an excel spreadsheet with my areas aggregated by land use and hydrologic soil group.

The file, "EFH2 Rural Example.xml" needs to be renamed with a .efm extension. Udemy limits the allowed file extensions for lecture resources.

This short video introduces the project site. We'll be using the same site for a TR-20 analysis and Rational Method Analysis. Written project instructions and answers are included for both methods. There are 2 zipped shapefiles which contain the inlet and pipe locations. You will need to unzip them to load each shapefile into QGIS. There area also two HydroCAD files that contain completed models. These HydroCAD files have been uploaded as .xml files, because Udemy has strict limits on file types. You will need to change their extensions back to .hcp in order to run them in HydroCAD.