Module 2

Groundwater Quantity

After completing this module, you should be able to…

  1. Identify three basic components that compose the water balance of a groundwater system
  2. Identify how water enters and leaves the groundwater system
  3. Use data to determine how water entering and leaving the groundwater system affects water balance

Pretest

Check your knowledge… To get warmed up, please answer this question to check your understanding. If you are not familiar with some of the terms used, don’t worry! We will define these terms in the module.

Monitoring Groundwater Levels

As you examine issues impacting your Natural Resource District, one important aspect of water resource management is maintaining adequate groundwater levels. The map below shows groundwater level changes in Nebraska

This map shows groundwater level changes in Nebraska

To make informed decisions about this issue, it is important to understand how water moves into and out of a groundwater system.

Let's begin by exploring groundwater levels in a Nebraska location.

Description of the above chart

Why Groundwater Levels Change

Now that you know what is happening to groundwater levels in this location, you can begin to think about why levels are declining

To understand this change, it is helpful to thing of groundwater as a system. While system interactions are complex, three basic components determine groundwater levels in your area. The video below explains these three components.

Under natural conditions, the average amount of water recharged into the system is equal to the amount of water discharged. The volume of water in storage generally does not change and the groundwater system is in balance.

However, if the system has unequal amounts of recharge and discharge, the system is out of balance and a change in groundwater levels will result.

When a system has more inputs than outputs, water storage will increase. When a system has more outputs than inputs, water storage will decrease.

Specific Groundwater Inputs & Outputs

Surface Water Seepage

Rivers, lakes, streams, and irrigation canals are all examples of surface water bodies. In some areas, surface water can “leak” down through sediments to recharge the groundwater system.

Deep Drainage

Sometimes plants are unable to utilize all irrigation water that is applied. Some excess irrigation water may run into surface waters, while some excess water may drain below crop roots (“deep drainage”) and eventually recharge groundwater.

Precipitation

Most groundwater recharge comes from precipitation. Some precipitation will run off the land surface and into surface water bodies. Other precipitation that is not utilized by plants or evaporated will infiltrate below the plant roots and may eventually recharge groundwater.

Groundwater Outputs

Groundwater outputs include pumping for irrigation, drinking water, and industrial uses. Groundwater may also discharge to surface water bodies such as streams.

Post Test

Table 1

Water Sources Amounts of Water
Discharge to Surface Water 40 units
Deep Drainage 10 units
Precipitation 50 units
Surface Water Seepage 30 units
Pumping 70 units