CIVE 445 - ENGINEERING HYDROLOGY SPRING 2006 - MIDTERM 1 - SOLUTION

PROBLEM 4

1. What is an aquifer?

An aquifer is the volume of groundwater lying within the saturated zone, below the water table.

2. What is the mouth of a catchment?

The mouth of a catchment is its outlet, or lowest point, to which the runoff from the entire catcment flows by gravity.

3. On a global annual basis, what percentage of precipitation is abstracted as deep percolation?

2%.

4. What is albedo? What is the albedo of a mirror? What is the albedo of a black body

Albedo is the reflectivity coefficient of a surface toward short wave radiation.

The albedo of a mirror is 1.

The albedo of a black body is 0.

5. What is the Bowen ratio?

The Bowen ratio is the ratio of sensible (nonevaporative) heat to latent (evaporative) heat.

6. How are the Dalton, Penman, and Penman-Monteith evaporation equations related?

The Penman combination method included the Dalton (conceptual) method to calculate the mass-transfer evaporation rate.

The Penman-Monteith method improved the Penman method by calculating the mass-transfer evaporation rate based on physical principles.

7. What four hydrologic variables influence time of concentration? How many variables does the Kirpich formula have? What are they?

Length L, Slope S, friction n, and effective rainfall intensity i.

The Kirpich formula has only L ans S.

8. What is an ephemeral stream? In what climate is it found

A stream that has flow only in response to precipitation, i,e., it has no baseflow.

It is found in arid and semiarid climates.

g. What is the difference between and evapotranspirometer and a lysimeter?

The evapotranspirometer measures potential evapotranspiration, while the lysimeter measures actual evapotranspiration.

h. To what five factors is to be attributed the recurrence of debris flows in the San Gabriel Mountains of Northeast Los Angeles?

1. The uplift (through tectonism) of the mountain range (reported to be the highest in the U.S.).

2. The type of vegetative ecosystem (mediterranean, chaparral), which has developed adaptations to survive through droughts, including waxed leaf surfaces to minimize evapotranspiration. The mediterranean ecosystem occurs in midlatitudes (30^o-35^o) that have exposure to westerlies (trade winds from the west).

3. The wind storms (Santa Ana), which affects the region.

4. The wildland fires, propelled by drought and wind, which recur approximately every thirty years in chaparral ecosystems. The fires vaporize the waxy substances (in the litter and standing biomass) at the surface, and condense 1-5 cm inside the soil, creating the hydrophobic soil layer.

5. The intense rainfall events, exceeding 1 in/hr, which follow the fire because of enhanced coalescence in the lower atmosphere due to ash particles produced by the fire.