WEEK ONE
Questions and Definitions
1. What is the average annual rainfall in Los Angeles?
2. What’s the least amount of rain we’ve had on record?
3. What’s the most amount of rain we’ve had on record?
4. When does it rain in Los Angeles?
5. Why is it important to understand rainfall seasonality and variability?
6. Water Balance Equation – write the equation and define each of the terms
7. Define Infiltration
8. Define Percolation
9. Define Watershed
10. Give 2 reasons why is it important to be able to delineate a watershed?
WEEK ONE
KEY
Questions and Definitions:
1.
2.
3.
4.
5.
What is the average annual rainfall in Los Angeles? 15 inches
What’s the least amount of rain we’ve had on record? <5 inches
What’s the most amount of rain we’ve had on record? ~38 inches
When does it rain in Los Angeles? Most rain occurs from November to April
Why is it important to understand rainfall seasonality and variability? To plan for
water supply and flood control
6. Water Balance Equation – write the equation and define each of the terms
o Precipitation = ET + GW + Runoff
o Precipitation = rain, snow, sleet, hail, etc.
o ET = Evapotranspiration = the process by which water is transferred from
land to the atmosphere by evaporation from soil and other surfaces and by
transpiration from plants (evaporation of water from plant leaves)
o Groundwater = water that is stored in deep underground in soil pores or
rock crevices
o Runoff = water that flows over the land surface and in creeks, streams, and
rivers
7. Define Infiltration – the process by which water enters the soil surface and moves
downward
8. Define Percolation - the movement of water through the soil. Once rainwater
infiltrates, it can either be evaporated, transpired, or percolated deeper into the soil
to recharge groundwater.
9. Watershed – the area draining to a specific point on a stream is called the watershed
for the stream to that point. Often, the point is where the stream (or creek or river)
reaches the ocean or meets a larger stream, but a watershed can be delineated to
any point on a stream.
10. Give 2 reasons why is it important to be able to delineate a watershed?
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
If you want to know where pollution in a stream is be coming from, you need to
know the area that drains to it, then you look at the land uses (residential, urban,
industrial, agricultural) in that watershed.
You have to know the area of the watershed (acres or square miles) to calculate
the water balance and estimate streamflow for water supply and flood planning.