Basic Hydrology

Creating hydrologic models of small watersheds for conservation bmps, leveraging the power of GIS.
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Instructed by Tim Clark Academics / Math & Science
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  • Lectures 20
  • Length 2.5 hours
  • Skill Level Beginner Level
  • Languages English
  • Includes Lifetime access
    30 day money back guarantee!
    Available on iOS and Android
    Certificate of Completion
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About This Course

Published 9/2015 English

Course Description

This course teaches soil and water district technicians and junior engineers how to model small watersheds for conservation and stormwater management structures. Three hydrological models are presented: EFH2, TR-20/TR-55, and the rational method. The course includes a blend of GIS and by-hand analysis methods. For the GIS portions, parallel workflows are presented for ArcGIS (Spatial Analyst extension), and for QGIS. The EFH2 software is presented for rural hydrology while HydroCAD (Free Sampler edition) is used for urban projects. The course culminates in two design examples to allow students to implement what they've learned.

What are the requirements?

  • Need to be able to download and install NRCS software
  • Need to be able to download and install the HydroCAD Sampler
  • Have either ArcGIS Desktop Advanced with Spatial Analyst Extension, or the open source QGIS

What am I going to get from this course?

  • Compute peak runoff rates for rural watersheds
  • Compute peak runoff rates for urban watersheds
  • Delineate watersheds using maps and ground truthing
  • Understand the differences between the 3 most widely used hydrology models

Who is the target audience?

  • Soil and Water District technicians with 0-2 years of experience
  • Entry level engineers working in transportation, civil/site, and agricultural disciplines

What you get with this course?

Not for you? No problem.
30 day money back guarantee.

Forever yours.
Lifetime access.

Learn on the go.
Desktop, iOS and Android.

Get rewarded.
Certificate of completion.


Section 1: Hydrologic Modelling workflow

Start here if you're not really sure what hydrology is or why you would use it. We'll also cover relevant documents for further study. Since we're using NRCS derived techniques, here are the links to NEH Part 630, which is described in the lecture.

Main Page:

Direct Link to Title 210:Part 630:

Section 2: What is my drainage area?

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.

Section 3: How much water flows off the land?

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.

Section 4: How long does the water take to get to here?

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.

Section 5: Software

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.

Section 6: Example Problems

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.

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Instructor Biography

Tim Clark, Conservation Planning, Design & Implementation across NY!

Tim is a NY State Registered Professional Engineer with a diverse background in agricultural conservation, civil/site design, railway design, aviation design, and highway design. He is currently the State Engineer for the New York State Soil and Water Conservation Committee housed at the NY State Department of Agriculture and Markets, where he is dedicated to improving the planning, design, and construction of conservation practices across New York State.

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