Hydrology

Question 1

What is storm frequency?

Answer 1

The average recurrence interval of a storm of a given intensity or depth.

Question 2

What is a 100-year storm?

Answer 2

A storm that has a 1% chance of occurring in any given year.

Question 3

How is rainfall measured?

Answer 3

Using rain gauges, which record depth over time.

Question 4

What is hyetograph?

Answer 4

A graph showing rainfall intensity versus time.

Question 5

What is areal distribution of rainfall?

Answer 5

The variation of rainfall intensity over a geographic area.

Question 6

What is the Rational Method equation?

Answer 6

Q = CiA, used for estimating peak runoff.

Question 7

What does ‘C’ represent in the Rational Method?

Answer 7

Runoff coefficient, indicating the fraction of rainfall that becomes runoff.

Question 8

What is the SCS Curve Number method used for?

Answer 8

To estimate direct runoff from rainfall.

Question 9

What does a high Curve Number (CN) indicate?

Answer 9

Low infiltration and high runoff potential.

Question 10

What are typical CN values for impervious surfaces?

Answer 10

Between 90 and 98.

Question 11

What is a hydrograph?

Answer 11

A graph of stream discharge versus time after a rainfall event.

Question 12

What is the rising limb of a hydrograph?

Answer 12

The portion where discharge increases due to rainfall input.

Question 13

What is baseflow in a hydrograph?

Answer 13

The portion of streamflow that comes from groundwater.

Question 14

What is a synthetic hydrograph?

Answer 14

An estimated hydrograph derived from watershed characteristics.

Question 15

Name one method used to develop synthetic hydrographs.

Answer 15

The SCS Unit Hydrograph method.

Question 16

What is an IDF curve?

Answer 16

A graph of rainfall Intensity vs. Duration for a given Frequency.

Question 17

What does rainfall exceedance probability mean?

Answer 17

The likelihood that a certain rainfall event will be equaled or exceeded in a given year.

Question 18

What is the relationship between return period and probability?

Answer 18

Probability = 1 / Return Period.

Question 19

How does storm duration affect rainfall intensity?

Answer 19

Longer duration storms generally have lower intensity.

Question 20

What is time of concentration?

Answer 20

The time it takes for runoff to travel from the most distant point in the watershed to the outlet.

Question 21

Why is time of concentration important?

Answer 21

It determines the critical storm duration for peak flow estimation.

Question 22

What factors affect time of concentration?

Answer 22

Slope, surface roughness, land use, and flow path length.

Question 23

What is the Kirpich equation used for?

Answer 23

To estimate time of concentration for small, steep watersheds.

Question 24

What is a stream gauge?

Answer 24

A device that measures water level (stage) in a river or stream.

Question 25

What data is collected at rainfall stations?

Answer 25

Rainfall depth, duration, and intensity over time.

Question 26

What agency maintains a national streamflow network in the US?

Answer 26

The United States Geological Survey (USGS).

Question 27

What is a rating curve?

Answer 27

A graph that relates stream stage to discharge.

Question 28

What are hydrologic depletions?

Answer 28

Losses of water through processes like evaporation, infiltration, or diversion.

Question 29

What is evaporation?

Answer 29

The process by which water changes from liquid to vapor.

Question 30

What is percolation?

Answer 30

The downward movement of water through soil to groundwater.

Question 31

How do detention basins reduce runoff?

Answer 31

By temporarily storing stormwater and releasing it slowly.

Question 32

What is a detention pond?

Answer 32

A basin designed to store stormwater temporarily and reduce peak discharge.

Question 33

What is a retention pond?

Answer 33

A pond that retains water indefinitely and allows infiltration and evaporation.

Question 34

What is the purpose of an infiltration trench?

Answer 34

To promote stormwater infiltration into the ground.

Question 35

How do swales manage stormwater?

Answer 35

They convey and filter runoff through vegetated channels.

Question 36

What is the role of constructed wetlands in stormwater management?

Answer 36

To treat runoff by sedimentation, filtration, and biological uptake.

Question 37

What is first flush in stormwater management?

Answer 37

The initial runoff containing the highest pollutant concentrations.

Question 38

Why are green infrastructure practices important?

Answer 38

They manage stormwater sustainably while providing environmental benefits.