5: Surface Runoff

Question 1

What is runoff?

Answer 1

Surface water flow formed by precipitation that doesn’t infiltrate

Question 2

What is depression storage?

Answer 2

Water that is held in puddles or small depressions

Question 3

What is interflow?

Answer 3

The lateral movement of water through shallow surface soils, a.k.a. subsurface lateral flow or throughflow

Question 4

What is interception loss?

Answer 4

Precipitation stored & evaporated due to interaction with vegetation i.e. precipitation that does not contact ground or water surface

Question 5

What is interception store?

Answer 5

Precipitation retained by vegetation, does not contribute to runoff

Question 6

What is throughfall?

Answer 6

Rain that passes through a vegetation canopy, including water that drips from leaves

Question 7

What is stemflow/trunkflow?

Answer 7

Water that originates from precipitation, that travels down tree trunks or plant stems

Question 8

What is Hortonian runoff?

Answer 8

Soil has saturated from rainfall and excess rain moves downslope to the stream as runoff, saturates from ABOVE

Question 9

What is saturated overland flow?

Answer 9

Light precipitation doesn’t saturate soil but causes water table to rise, soil saturates from BELOW

Question 10

What is the water table?

Answer 10

The elevation where groundwater is at atmospheric pressure

Question 11

What is a piezometer?

Answer 11

Vertical pipe placed into ground to measure elevation of water table

Question 12

What is transmission loss?

Answer 12

Loss of water from streamflow when water infiltrates into stream bed or floodplain

Question 13

Describe the shape of a flood wave.

Answer 13

A flood wave is not symmetric; the advancing front is normally steeper than that receding tail

Question 14

What is a rating curve?

Answer 14

Stage vs. discharge
Relationship between river level (stage) and discharge, can change over time depending if flood wave is advancing or receding (results in ‘looped’ rating curve)

Question 15

How is a rating curve determined?

Answer 15

Direct measurement (stage vs. discharge) or theoretically if hydraulic control is available (e.g. weir)

Question 16

Where is ‘average’ velocity occur in a cross section? When is this approximation valid?

Answer 16

Average velocity is taken at 60% depth from the water surface,
Valid for uniform flow in a wide channel

Question 17

What are some flow measurement methods for stage and discharge?

Answer 17

Stage:
- visual, float, pressure sensor, electrical resistance
Discharge:
- flowmeters, weirs/flumes/orifice, floats, dilution

Question 18

How do you estimate the discharge of a wide section using sub-area velocities?

Answer 18

Q = ∑AiVi

Question 19

What is quick flow?

Answer 19

Rapid component of catchment runoff in response to rainfall

Question 20

What is base flow?

Answer 20

Slow component of catchment runoff in response to rainfall, usually result of groundwater discharge to a stream

Question 21

What is recession?

Answer 21

Decline in streamflow that occurs after a flow peak

Question 22

What is a hydrograph?

Answer 22

Graph of flow vs. time

Question 23

What is a hyetograph?

Answer 23

Graph of rainfall per time period vs. time

Question 24

What is the relationship between a hyetograph and a hydrograph?

Answer 24

A hyetograph shows the rainfall per time and the hydrograph shows the resulting flow in response to this rainfall. The peak of the hydrograph occurs after the rainfall peak (lag)

Question 25

What are the St Venant equations used for? What are the assumptions?

Answer 25

Kinematic wave approximation
Assumes: 
- pressure & inertial forces not important
- gravity & friction forces balance
- water surface is parallel to bed

Question 26

In a rating curve (stage vs. discharge) what does the ‘stage’ represent?

Answer 26

Water level (elevation of water surface)