Groundwater from the Researcher Perspective (2-D Processes)

1.Groundwater Calculator.

Click the button below to load the Groundwater Calculator.

The calculator can be resized to fit your screen.
Groundwater flow is a more complex process than surface runoff. Runoff is primarily influenced by the infiltration permitted by a certain land cover with a particular soil. To determine groundwater flow, one also needs to know evapotranspiration (water uptake from plants and evaporation) and groundwater aquifer geology. The plant uptake will change depending on the time of year and the type of plants. Groundwater aquifer geology will not change, but can be extremely difficult to determine.

Unlike the Runoff Calculator, which was designed for a single storm, the Groundwater Calculator estimates values for the selected month. Also notice the outputs are expressed as percentages of precipitation.

2.Effects of Month

Notice how the precipitation for the month of September is separated into the five outputs. About half of the precipitation is lost through plant transpiration and evaporation. About 14% is surface runoff to streams and 29% is groundwater runoff to streams, resulting in 43% of precipitation making it to streams. Finally, the water storage in the groundwater takes the final 7%, since there is no snow pack storage.

Now change the month to December. Be sure to hit calculate each time for new values.

Notice that 34% of the precipitation is now in the snow pack. Also notice that evapotranspiration is only 8%, because there is little plant uptake of water in the winter. None of the storms in December produced runoff. Therefore, all stream flow came from the groundwater flow, which actually took some water from the groundwater storage. Remember that outputs express percent of precipitation.

Try the other months and see what happens. March is similar to December, with no snow pack change. June has a dramatic increase in evapotranspiration due to plant growth. The plant uptake is pulling water from the groundwater storage.

3.Effects of Seasonal Weather

For wet months, there is more runoff, less of the groundwater storage goes to plants, and there is more groundwater flow. For dry months, there is no runoff, more groundwater storage goes to plants, and there is a smaller portion of precipitation becoming groundwater flow.

4.Effects of Land Cover and Soil Texture

Now, see if the groundwater flow always decreases when the runoff increases.

You should notice something different happening. The change in groundwater flow has more to do with the change in evapotranspiration caused by different land covers. Going from forest to row crop to residential to pasture shows the groundwater going down as the evapotranspiration goes up.

Now experiment with the soil textures.

Notice the expected relationship holds, since runoff increases and groundwater flow decreases as the soil texture allow less infiltration. Also notice that evapotranspiration does not change, since the time of year and land cover stays the same.

5.Effects of GW Discharge Rate

Notice that varying these values only change the groundwater flow and storage. A faster discharge rate causes more groundwater water to discharge to the streams and causes a larger storage decrease.

Summary

More Details?

Back for Water Resources	Back for Perspectives	Home	Next for Water Resources	Next for Perspectives