Surface Water, Rivers and Floods Lab

1. On a worldwide basis, has more water evaporated into the atmosphere from oceans or from land?

2. Approximately what percent of the total water evaporated into the atmosphere comes from the oceans?

Percent from oceans = (ocean evaporation ÷ total evaporation) x 100

= _______________ %

Notice in the figure that more water evaporates from the oceans than is returned directly to them by precipitation.

3. Since sea level is not dropping, what are the other sources of water for the oceans in addition to precipitation?

Over most of Earth, the quantity of precipitation that falls on the land must eventually be accounted for by the sum total of evaporation, transpiration (the release of water vapor by vegetation), runoff, and infiltration.

4. Define each of the following four variables.

Evaporation:

Transpiration:

Runoff:

Infiltration:

5. On a worldwide basis, about (37, 58, 79) percent of the precipitation that falls on the land becomes runoff. Select what you think is the correct answer.

6. At high elevations or high latitudes, some of the water that falls on the land does not immediately soak in, run off, evaporate, or transpire. Where is this water being temporarily stored?

7. Based on Figure 2, does urbanization increase or decrease the peak, or maximum, stream flow?

8. What is the effect that urbanization has on the lag time between the time of the rainfall and the time of peak stream discharge?

9. Does total runoff occur over a longer or shorter period of time in an area that has been urbanized?

10. Based on what you have learned from the hydrographs, explain why urban areas often experience flash-flooding during intense rainfalls.

11. Rank the peak flood discharges for Data Set 1 in order of magnitude, starting with 1 for the largest and ending with 11 for the smallest. Write these results in the "Rank" column.

12. Use the formula T = (n+ 1) / m and determine the recurrence interval of each of the 11 floods in Data Set 1. Write the results for each year in the "Recurrence Interval (RI)" column.

13. Plot the discharge and recurrence interval for each of your 11 floods in Data Set 1 using the graph show in Figure 3. Then draw a best-fit straight line, not a dot-to-dot curve, through the data points and extend your line to the right side of the graph. This is your flood frequency curve.

14. Based on your flood frequency curve, what is the predicted discharge for a 100-year flood for Data Set 1?

15. Rank the peak flood discharges for Data Set 2 in order of magnitude, starting with 1 for the largest and ending with 11 for the smallest. Write these results in the "Rank" column.

16. Use the formula T = (n+ 1) / m and determine the recurrence interval of each of the 11 floods in Data Set 2. Write the results for each year in the "Recurrence Interval (RI)" column.

17. Plot the discharge and recurrence interval for each of your 11 floods in Data Set 2 using the graph show in Figure 3. Then draw a best-fit straight line, not a dot-to-dot curve, through the data points and extend your line to the right side of the graph. This is your flood frequency curve.

18. Based on your flood frequency curve, what is the predicted discharge for a 100-year flood for Data Set 2?

19. How do the two predicted discharges for a 100-year flood compare.

20. Suggest possible human activities in the watershed that could have caused the differences in predicted floods that result from the two sets of data.