Lesson 1: 
What Happens to Water
When it Reaches the Earth


Welcome to Water Resources Technology!  In this course you will learn about many aspects of watersheds, including how to control erosion, runoff, and stormwater detention.  In addition, you will use the information learned in this course to write a Best Management Plan or stormwater plan for a piece of property. 



In this lesson we will answer the following questions:



Reading Assignment

Along with the online lecture, read chapter 1 in your text. 




Where Does the Water Go?

I’m sure that you have been outside during a thunderstorm.  But have you ever wondered where all of the water goes?


The first step in learning about watersheds is to understand what happens to water when it reaches the earth.  When water falls to the earth as precipitation (rain, snow, hail, etc.), it can either evaporate, become groundwater, or become surface water. 

Unless there is 100% relative humidity, some of the falling water quickly evaporates back into the air.  This water will become collected in clouds and will fall to the earth again the next time it rains. 


Other water percolates down through the soil, becoming part of the groundwater.  Water is able to move through the soil because the soil is permeable – there are spaces between the soil particles through which water can flow.  The groundwater trickles downward until it reaches an impermeable layer of soil or rock.  We use wells and springs to pull groundwater back to the surface to drink.

The rest of the precipitation becomes surface water, the type of water with which this course is primarily concerned.  Surface water includes rivers, lakes, oceans, and even the water which runs down streets during thunderstorms.

Surface Water and Runoff


Surface water, left to its own devices, will flow downhill until it reaches a creek.  The creek will eventually feed a river which will, in turn, flow into the ocean.  Along the way, some water will evaporate back into the sky and will fall back to the earth as rain. 

In this course, we are most concerned with rain which has hit the ground and become surface water but which has not  yet flowed into a creek or other body of water.  This type of surface water is known as runoff.  

On steep slopes, storm water runoff can cause problems.  The quickly flowing water can erode the slope and cause other harm.  In this course, we will learn a variety of methods to prevent damage caused by runoff.  


Storm water runoff can be minimized by planting vegetation on the slope.  When rain falls on plants, a good deal of the surface water is retained by the plants, preventing it from becoming runoff. 

Surface water can also be collected in ponds.  Ponds slow the flow of runoff so that it causes less erosion.


Water falling to the earth as precipitation either evaporates back into the air, becomes groundwater, or becomes surface water.  Surface water on slopes becomes storm water runoff, which can be minimized using vegetation and ponds.


  1. Visualize your yard the last time it rained.  Where did the water go?  Did most of it become groundwater or surface water?  Did water collect in puddles in certain areas? 

  2. Find an eroded area.  Why do you think this region became eroded?  How could the erosion have been prevented?




For extra credit you can take the Quizzes for Chapter 1When you have gotten all the answers correct, print the pages and either mail or fax them to the instructor.