Drainage Basins and Rivers

Question 1

Drainage basin

Answer 1

an area of land drained by a river and its tributaries

Question 2

Watershed

Answer 2

The boundary marked by a ridge of highland beyond which any precipitation will drain into adjacent basins

Question 3

Evaporation

Answer 3

Physical process by which moisture is lost directly into the atmosphere from water surfaces, due to the effects of air movement and the suns heat

Question 4

Transpiration

Answer 4

The biological process by which water is last froma plant throught the minute pores in the leaves

Question 5

Potential evapotranspiration

Answer 5

In theory what could happen based off the different factors

Question 6

Interception storage

Answer 6

First raindrops of a rainfall event fall on vegetation which shelters the underlying ground

Question 7

Throughfall

Answer 7

Water reaches the ground by dropping off the leaves

Question 8

Stemflow

Answer 8

Water reaches the ground by flowing down the trunk

Question 9

Secondary interception

Answer 9

Water reaches the ground by hitting leaves/other and then hitting the undergrowth

Question 10

Surface storage

Answer 10

Due to dryness, when the ground can’t absorb the water and so the water that lies on the surface

Question 11

Surface runoff

Answer 11

When the ground is so saturated that it can’t absorb anymore water, so excess water flows over the surface

Question 12

Infiltration capacity

Answer 12

The maximum rate which water can pass through the soil. The more pores the higher the infiltration capacity

Question 13

Porosity

Answer 13

The space between soil particles (air pockets)

Question 14

Capillary action

Answer 14

System by which water is drawn up to the surface through small air pockets in the soil

Question 15

Groundwater storage

Answer 15

Water collects above an impermeable rock layer under the earths surface (created by percolation)

Question 16

Zone of saturation

Answer 16

The area above the permeable rock which is filled with water

Question 17

Positive water balance

Answer 17

Precipitation input exceeds evapotranspiration loss

Question 18

Negative water balance

Answer 18

When evapotranspiration exceeds precipitation

Question 19

Soil moisture budget

Answer 19

Balance of water in the soil, as a result of precipitation and evapotranspiration

Question 20

Soil moisture surplus

Answer 20

Precipitation exceeds transpiration resulting in considerable surface runoff and rise in water levels

Question 21

Field capacity

Answer 21

The maximum amount of saturation the soil can hold

Question 22

Soil moisture deficit

Answer 22

Plants can only survive at this point if they are either drought resistant or have proper irrigation due to the lack of water in the soil

Question 23

Recharge

Answer 23

When precipitation does exceed potential transpiration after the summer, rain is needed to replace and recharge that taken from the soil

Question 24

Channel precipitation

Answer 24

Rain falls directly into the channel in the river

Question 25

Channel storage

Answer 25

When water reaches the river it becomes channel storage

Question 26

Groundwater flow/baseflow

Answer 26

Water underground that flows laterally against the earths impermeable surface

Question 27

Watertable

Answer 27

Upper boundary of the saturated material that can then be transffered laterally as groundwater

Question 28

Water balance formula

Answer 28

P=Q+E
P - precipitation measured using rain gauges
Q - runoff measured by discharge fumes in the river channel
E - evapotranspiration (far more difficult to measure)

Question 29

Aquifers

Answer 29

Underground layer of water bearing permeable rock, rock fractures of unconsolidated materials from which ground water can be extracted using a water well

Question 30

Hydrograph

Answer 30

Means of showing the discharge of a river at a given point of a short period of time

Question 31

Hydrology

Answer 31

The study of water (precipitation, runoff, evaporation etc

Question 32

Discharge

Answer 32

The amount of water, originating as precipitation which reaches the channel by surface runoff, throughflow and baseflow

Question 33

Discharge formula

Answer 33

Q=AxV
Q - discharge (measured in m)
A - Cross sectional area of the river (measured in m2)
V - Velocity (m3/sec or cumecs)

Question 34

Approach segment

Answer 34

Shows the discharge of the river before the storm (antecedent flow rate)

Question 35

Rising limb

Answer 35

On the hydrograph, the rapid increase in discharge os indicated by the beginning line

Question 36

Lag time

Answer 36

The period between maximum precipitation and peak discharge

Question 37

Several factors that regulate ways a river responds to precipitation

Answer 37

• Types of precipitation
• Temperature
• Tides and storm surge
• Basin shape/size/relief
• Landuse
• Rock type
• Soil type
• drainage density

Question 38

Falling or recession limb

Answer 38

Is the segment of the graph where discharge is decreasing and river levels are falling. This segment is usually less steep than the rising limb because throughflow is being released relatively slowly into the channel

Question 39

Storm flow

Answer 39

The discharge, both surface and subsurface attributed to a single storm

Question 40

Baseflow

Answer 40

Very slow to respond to a storm, but by releasing groundwater, it maintains the rivers flow throughout periods of low precipitation

Question 41

Bankfull discharge

Answer 41

Occurs when a rivers water level reaches the top of its channel and any further increase in discharge will result in the flooding of the surrounding land

Question 42

Types of precipitation (River responds)

Answer 42

Prolonged - When flooding most frequently occurs after. Ground has maximum saturation and surface runoff
Intense storms - Rain intensity may be greater than the infiltration capacity of the snow. Rapid rise in rain levels due to lots of surface runoff (flash floods)
Snowfall - Water is held in storage and rain levels drop. After it warms up ground may stay frozen for a while, surface runoff increases

Question 43

Basin size, shape and relief (River responds)

Answer 43

Size - small basin means that rainfall will reach the main channel more quickly. Lag time is greater in larger basins
Shape - Circular basins are more likely to have a shorter lag time and higher peak flow than an elongated basin
Relief - Steep-sided upland valleys, water is likely to reach the river more quickly than in a gently sloping lowland areas

Question 44

Temperature (River responds)

Answer 44

Extremes of temperature can restrict infiltration and therefore increase surface area runoff. If evapotranspiration rates are high then there will be less water available to flow into the main river

Question 45

Landuse (River responds)

Answer 45

Vegetation can help prevent flooding by intercepting rainfall. Also can reduce through flow by taking up water from the soil.
Urbanization can increase flooding because water can’t infiltrate through the tarmac

Question 46

Rock type (River responds)

Answer 46

Permeable rock (porous or pervious) permit rapid infiltration which means little surface runoff and limited number of surface streams.
Impermeable rocks do not allow water to pass, therefore more surface streams and runoff

Question 47

Soil Type (River responds)

Answer 47

Can control the rate and volume of infiltration, the amount of soil measure storage and rate of throughflow. Sandy soils allow more infiltration and do not encourage flooding. Clays have smaller pore spaces which reduce infiltration rate and encourages runoff

Question 48

Drainage density

Answer 48

Refers to the # of surface streams in a given area. The density is higher on impermeable rocks and clay. The higher the density the greater the probability of flash floods

Question 49

Tides and storm surges

Answer 49

High spring tides prevent river flood water from escaping into the sea, therefore causing floodwater to build up in the valley.
High tides + gale force winds = storm surge