CIVE 445 - ENGINEERING HYDROLOGY SPRING 2004 - MIDTERM 1 - SOLUTION

PROBLEM 4

a. What four types of mathematical models are used in hydrology?

Deterministic, probabilistic, conceptual, and parametric.

b. What four types of lifting cause the cooling of air masses enough to produce precipitation?

Horizontal convergence lifting, frontal lifting, orographic lifting, and long-wave radiation lifting.

c. What is the Bowen ratio?

The ratio between sensible (nonevaporative) heat and latent (evaporative) heat (long-wave terrestrial radiation).

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

e. What is a gully?

A gully is a self-formed channel (formed by erosion) which, due to its large size, cannot be obliterated by farming practices.

f. What do the Creager curves depict?

They depict the diffusion that is present in streamflow. The Creager curves state that the greater the catchment area, the smaller the peak flow per unit of catchment area.

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.