CHAPTER 2

Question 1

That part of atmospheric moisture that falls on the earth surface

Answer 1

PRECIPITATION

Question 2

what are the 10 types of precipitation?

Answer 2

1. rain
2. ice crystals
3. sleet
4. freezing rain
5. snow
6. snow grains
7. graupel
8. hail
9. drizzle
10. freezing fog

Question 3

Water droplets in clouds are formed by nucleation of vapor on aerosols, then go through many condensation evaporation cycles as they circulate in the cloud, until they aggregate into large enough drops to fall through the cloud base.

Answer 3

SUBLIMATION NUCLEI

Question 4

a process of artificially nucleating clouds to induce precipitation

Answer 4

CLOUD SEEDING

Question 5

is a common nucleating agent and is spread from aircraft in which a silver iodide solution is evaporated with a propane flame to produce particles.

Answer 5

SILVER IODINE

Question 6

___________ and ___________are known to co-exist in the atmosphere at sub-freezing temperatures.

Answer 6

ICE CRYSTALS and WATER DROPLETS

Question 7

_________ of water droplets as a result of their coming in contact through the action on them of air movement and
gravitational pull.

Answer 7

COALESENCE

Question 8

air is drawn upwards by convective action, such as in the center of a thunderstorm cell

Answer 8

CONVECTIVE PRECIPITATION

Question 8

where warm air is lifted over cooler air by frontal passage

Answer 8

FRONTAL PRECIPITATION

Question 9

which an air mass rises to pass over a mountain range

Answer 9

OROGRAPHIC PRECIPITATION

Question 10

what are the 4 types of precipitation?

Answer 10

1. CONVECTIVE PRECIPITATION
2. FRONTAL PRECIPITATION
3. OROGRAPHIC PRECIPTATION
4. CYCLONIC PRECIPITATION

Question 11

the simplest method of determining areal average rainfall which involves averaging the rainfall depths recorded at a number of gages

Answer 11

ARITHMETIC AVERAGE

Question 12

This method is satisfactory if the gages are uniformly distributed over the area and the individual gage measurements do not vary greatly about the mean.

Answer 12

ARITHMETIC AVERAGE

Question 13

Assumes that at any point in the watershed the rainfall is the same as that at the nearest gage so the depth recorded at a given gage is applied
out to a distance halfway to the next station in any direction.

Answer 13

THIESSEN METHOD

Question 14

The relative weights for each gage are determined from the corresponding areas of application in a Thiessen polygon network, the boundaries of the polygons being formed by the ____________.

Answer 14

PERPENDICULAR BISECTORS OF THE LINES JOINING ADJACENT GAGES.

Question 15

• Composed of isohyets which are lines of
  equal rainfall magnitude
• Most accurate and more flexible than
  Thiessen method
• Harder to construct for complex storms
  with dense network of gages

Answer 15

ISOHYETAL METHOD

Question 16

The gaging networks in the Philippines

Answer 16

• Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) weather stations and facilities (more or less 500 in total)
• PAGASA Automated Weather Stations (AWS)
• National Irrigation Administration
• Bureau of Forest Development and the
• Bureau of Plant Industry
• State colleges and Universities
• Private entities

Question 17

3 types of estimation of Areal Precipitation

Answer 17

a. ARITHMETIC AVERAGE
b. THIESSAN METHOD
c. ISOHYETAL METHOD

Question 18

2 types of rainfall adjustments

Answer 18

A. Estimation of Missing Rainfall Data
B. Adjustment of Rainfall due to Changes in Locations

Question 19

Complete measured precipitation data are important to many problems in hydrologic analysis and design but there are missing values

Answer 19

ESTIMATION OF MISSING RAINFALL DATA

Question 20

type of Estimation of Missing Rainfall Data that is preferrable for relatively flat areas

Answer 20

STATION-AVERAGE METHOD

Question 21

• A consistent record is one where the characteristics of the record have not changed with time
• An inconsistent record may result from any one of a number of events

Answer 21

ADJUSTMENT OF RAINFALL DUE TO CHANGES IN LOCATION

Question 22

is the method that is used to check for an
inconsistency in a gaged record.

Answer 22

DOUBLE-MASS CURVE ANALYSIS

Question 23

is a graph of the cumulative catch at the rain gage of interest versus the cumulative catch of one or more gages in the regions that have been subjected to similar hydrometeorological occurrences and are known to be consistent

Answer 23

DOUBLE-MASS CURVE

Question 24

If a double- mass curve has a constant slope, the record is ________.

Answer 24

CONSISTENT

Question 25

If a double –mass curve has not a constant slope, the record is ________________.

Answer 25

NOT CONSISTENT AND NEED TO BE ADJUSTED

Question 26

what are the 4 characteristics of a rainstorm?

Answer 26

1. Intensity (mm/hr) 2. Duration (min, hours, days) 3. Areal extent (m2, ha): area over which it is distributed 4. Frequency: once in 5, 10, 15, 20, 25, 50 or 100 years

Question 26

* graph showing the depth or intensity of rainfall with respect to time * useful in determining the maximum intensities of rainfall during a particular storm as is required in land drainage and design of culverts.

Answer 26

HYETOGRAPH

Question 27

3 basic terms in Statistical Hydrology

Answer 27

* Time period of interest (N) * Probability of occurrence (P) * Recurrence interval or return period (T)

Question 28

probability that a T-year storm may occur in any series of N years.

Answer 28

PROBABILITY OF EXCEEDANCE

Question 29

* Enables the hydrologists to develop hydrologic systems that consider worst-case scenarios of rainfall intensity and duration during a given interval of time * It is often used by entering with the duration and frequency to find the intensity. Or * It is used to find the frequency for a measured storm event. The predicted frequency is determined by finding the intersection of the lines defined by the measured intensity and the storm duration.

Answer 29

IDF CURVE (Intensity vs. Duration vs. Frequency)

Question 30

Refers to the probabilistic analysis of hydrologic processes.

Answer 30

HYDROLOGIC FREQUENCY ANALYSIS

Question 30

probability that a T-year storm may NOT occur in any series of N years

Answer 30

PROBBAILITY OF NON-EXCEEDANCE

Question 31

any hydrologic phenomenon which undergoes continuous changes with time.

Answer 31

HYDROLOGIC PROCESS

Question 32

Categories of Hydrologic Process

Answer 32

1. DETERMINISTIC 2. PROBABILISTIC 3. STOCHASTIC

Question 33

- is one in which a definite law of certainty exists - it is one where the chance element is ignored as in the case of flood routing - Commonly used for man-made canals channels

Answer 33

DETERMINISTIC PROCESS

Question 34

* is one governed by chance phenomena, that is, there are so many causes at work that the influence of one cannot be readily identified * Time-series independent

Answer 34

PROBABILISTIC PROCESS

Question 35

* means that the sequence of occurrence of events or the time series is considered in its analysis * Time-series dependent

Answer 35

STOCHASTIC PROCESS

Question 36

what is the objective of Hydrologic Frequency Analysis?

Answer 36

to relate the magnitude of events to their frequency of occurrence through probability distribution, that is, a frequency curve

Question 37

steps in Frequency Analysis

Answer 37

1. Selection of Data 2. Determination of Statistical Parameters 3. Fitting of Data 4. Testing the Significance of Results

Question 38

types of Probability Density Function

Answer 38

1. Normal density function 2. Log-normal function with two parameters 3. Gamma density function with two parameters 4. Kappa density functions with two parameters

Question 38

all data above a given threshold value

Answer 38

PARTIAL DURATION SERIES

Question 38

only one data point per year, usually the maximum

Answer 38

ANNUAL SERIES

Question 39

a hydrologic event is not influenced by another event

Answer 39

INDEPENDENCE

Question 39

events under the same type of conditions or statistical properties are not changing

Answer 39

HOMOGENITY

Question 40

Fitting of data to known statistical distributions

Answer 40

* Normal distribution * Log-normal distribution * Log-Pearson Type III distribution * other applicable density functions