Chapter 8 Runoff Discharge

Question 1

Rain and snowmelt water take various paths to streams. Each path contributes differently to;

Answer 1

• peak and timing of storm runoff
• erosion
• transport of chemicals into streams

Question 2

Planners need to understand runoff processes to;

Answer 2

• identify the area contributing to runoff generation
• assess the impact of deforestation, road construction, and other landuse change on runoff characteristics
• evaluate the risk of stream pollution

Question 3

Path 1:

Answer 3

Horton overland flow

Question 4

Path 2:

Answer 4

groundwater flow

Question 5

Path 3

Answer 5

shallow subsurface storm flow

Question 6

Path 4:

Answer 6

Saturation overland flow

Question 7

Infiltration capacity decreases as

Answer 7

the soil gets wet

Question 8

Overland flow occurs when

Answer 8

rainfall intensity exceeds infiltration capacity

Question 9

Infiltration capacity …………………considerably within a ………………depending on ………………………… and ………………………………

Answer 9

varies

catchment

soil types and vegetation cover

Question 10

Horton overland flow may occur in

Answer 10

localized areas within the catchment; partial-area concept.

Question 11

Horton overland flow is rare in

Answer 11

vegetated humid region

Question 12

. Horton overland flow is rare in vegetated humid region. It is common in areas

Answer 12

devoid of vegetation such as;

• semi-arid rangelands
• compacted soil, e.g. logging roads
• paved urban area, e.g. parking lots

Question 13

subsurface storm flow (SSSF)

Answer 13

During the storm, the water table near the stream rises rapidly and increases the volume of groundwater flow.

Question 14

If a low permeability layer exists at some depth,

Answer 14

water accumulates above this layer and flows horizontally toward the stream

Question 15

Subsurface storm flow generates …………………….. than ………………………..

Answer 15

lower volume of runoff than Horton overland flow

Question 16

Runoff to rainfall ratio is usually

Answer 16

less than 20%

Question 17

Most of the rain is stored in ……………………and is …………………..to ……………………………..

Answer 17

the sediments

released slowly

supply steady base flow

Question 18

If the rainstorm is large enough, the water table near the stream

Answer 18

rises to the ground surface

Question 19

return flow (RF).

Answer 19

Groundwater seeps out from the ground surface and generates overland flow.

Question 20

This Groundwater seeps ………..from the ground surface and generates …………………………is called return flow (RF)

Answer 20

out

overland flow

Question 21

The rain falling on the saturated area cannot infiltrate because

Answer 21

groundwater flow direction is upward under the area.

Question 22

Direct precipitation onto ………………………..also generates overland flow.

Answer 22

saturated areas (DPS)

Question 23

The combination of RF and DPS is called

Answer 23

saturation overland flow.

Question 24

Before a storm, saturated areas are limited to

Answer 24

the close vicinity of the stream.

Question 25

Before a storm, saturated areas are limited to the close vicinity of the stream. They …………….during the storm resulting in ……………………………………….

Answer 25

expand

larger rate of runoff generation

Question 26

Before a storm, saturated areas are limited to the close vicinity of the stream. They expand during the storm resulting in larger rate of runoff generation

some areas also ……………. and ………………………………

Answer 26

expand and contract seasonally

Question 27

In arid and semi-arid regions with ………………………and those disturbed by ……………………………

Answer 27

scarce vegetation

humans (urbanization, logging, etc.)

Question 28

In arid and semi-arid regions with scarce vegetation and those disturbed by humans (urbanization, logging, etc.), infiltration capacity is ………………………. and ………………………… is a dominant process

Answer 28

a limiting factor

Horton overland flow

Question 29

infiltration capacity is a limiting factor and Horton overland flow is a dominant process. This also happens when the top soil is

Answer 29

frozen

Question 30

In most humid regions, ………………………………. and …………………………………are dominant processes.

Answer 30

subsurface storm flow and saturation overland flow

Question 31

Where the soils are ………………, ……………and …………………………., the water table is deep and the saturated zone is confined to the………………………

Answer 31

well-drained

deep

very permeable

valley floor

Question 32

Where the soils are well-drained, deep and very permeable, the water table is deep and the saturated zone is confined to the valley floor. …………………………….is less important than ……………………………in this situation.

Answer 32

Saturation overland flow

subsurface storm flow

Question 33

Where the soils ………………………………………………………….., and slope is ………………………………………………………….,the water table is shallow and the saturated zone expand readily.

Answer 33

are thin and only moderately permeable

gentle and concave shaped

Question 34

Where the soils are thin and only moderately permeable, and slope is gentle and concave shaped, the water table is shallow and the saturated zone expand readily. ………………………………….dominates in this situation.

Answer 34

Saturation overland flow

Question 35

Modification of the land surface during urbanization changes

Answer 35

the type and magnitude of runoff processes.

Question 36

Modification of the land surface during urbanization changes the type and magnitude of runoff processes. Covering parts of……………………………. increase …………………………………………………

Answer 36

the catchment with impervious roofs and concrete lots increases the volume and rate of Horton overland flow.

Question 37

Planners have to design……………………….to accommodate increased runoff.

Answer 37

detention ponds

Question 38

…………………….. and…………………….convey runoff rapidly to stream channels.

Answer 38

Gutters and storm sewers

Question 39

The channels are …………………………and……………………. to increase the efficiency, so that they transmit the flood wave ………………………..more quickly.

Answer 39

straightened

lined with concrete

downstream