# Geology 127 Hydrogeology Assignment 2

Directions: Show all your work, including any necessary conversions. Label all axis and graphs. Use appropriate number of significant figures. Use short, concise sentences to explain your answer where appropriate.

- A forested watershed has an area of 97 ha. A peak stream flow of 1.9 cubic feet per second (cfs) at the outlet was measured following a 24 hour rainstorm with an average intensity of 1 inch per hour.
- Calculate the total amount of rain that fell during the storm. (4pts)
- Calculate the runoff coefficient using the rational equation. (4pts)
- What assumption must be made to use the rational equation? (4pts)
- Estimate the range of peak stream flows you would expect from a similar storm if the watershed had been developed with single family homes (use Table 2.3 in Fetter). (4 pts)

- The following values were recorded during a double-ring infiltrometer test:

time (min:sec) |
depth (cm) |
Cumulative infiltration (cm) |
infiltration rate (cm/hr) |

0:00 |
15.0 | ||

0:30 |
14.4 | ||

1:00 |
14.0 | ||

2:00 |
13.5 | ||

3:00 |
13.1 | ||

4:00 |
12.8 | ||

5:00 |
12.6 | ||

10:00 |
12.4 | ||

15:00 |
12.3 | ||

20:00 |
12.1 | ||

25:00 |
11.9 | ||

30:00 |
11.8 | ||

35:00 |
11.7 | ||

40:00 |
11.6 |

- Plot the cumulative infiltration (cm) as a function of time (sec) (3pts).
- Plot the infiltration rate (cm/hr) as a function of time (sec) (3pts).
- A rainstorm with an intensity of 2.0 in/hr lasts for 10 minutes. When does

Hortonian overland flow begin? (4pts)

- How much water from the above storm is infiltrated? (6pts)
- How much water from the above storm runs off as infiltration excess? (6pts)

- The following graph shows discharge for the Cosumnes River at Michigan Bar, CA. The watershed area above the gauging station is approximately 536 square miles.
- How long do the surface water effects from the storm last. (2pts)
- Draw the approximate baseflow component of the hydrograph. (3pts)
- Estimate the increase in baseflow (GW) from this storm in cfs. (3pts)

- Derive an expression for porosity in terms of bulk density and solid density using the equation for porosity (n=V
_{v}/V_{t}), bulk density (ρ_{b}=m_{s}/V_{t}), and solid density

(ρ_{s}=m_{s}/V_{s})where V_{v} is the volume of the voids, V_{t} is the total volume, and m_{s} is the mass of the solids. (4pts)