1.1 Hydrology and fluvial geomorphology: the drainage basin system

Question 1

What is a drainage basin

Answer 1

A drainage basin is the area drained by a river and its tributaries.

Question 2

What are inputs to a drainage basin

Answer 2

Inputs are the addition of water to a drainage basin in the form of precipitation. It can occur in a number of forms (rain, snow, hail, etc.)

Question 3

What are stores in a drainage basin

Answer 3

Stores are where water is held in some part of the drainage basin for any length of time.

Question 4

What are flows in a drainage basin

Answer 4

Flows refer to the movement/transfer of moisture in a drainage basin

Question 5

What are outputs in a drainage basin

Answer 5

Outputs are the losses of water from a drainage basin

Question 6

Define precipitation

Answer 6

Precipitation is any liquid or frozen water that forms in the atmosphere and falls back to the Earth.

Question 7

Define evapotranspiration

Answer 7

Evapotranspiration refers to the combined loss from both evaporation and transpiration.

Question 8

Define evaporation

Answer 8

Evaporation is the loss of water from the land surface and bodies of water as it transfers from a liquid to a gaseous sate (water vapour) by application of heat.

Question 9

Define transpiration

Answer 9

Transpiration is the loss of water vapour from the stomata in the leaves of plants and trees.

Question 10

Define river discharge

Answer 10

River discharge is the volume of water being discharged by a river.

Normally expressed as the volume of water passing a point in the river channel in a given unit of time. This is commonly the number of cubic metres per second – “cumecs”

Question 11

Define interception

Answer 11

Interception is the precipitation which is intercepted on its way to the land surface by leaves, plants, and trees

Question 12

Define soil water

Answer 12

Soil water is water retained within the gaps and pore spaces in the soil.

Question 13

Define antecedent moisture

Answer 13

Antecedent moisture is the moisture retained in the soil before a rainfall event

Question 14

Define surface water

Answer 14

Surface water is water that is stored on the surface in the form of puddles, streams, and lakes – often above impermeable surface or saturated ground

Question 15

Define groundwater stores

Answer 15

Groundwater stores is water that has percolated downwards and is held in gaps such as cracks, joints, bedding planes, fault lines, and pore spaces in rocks in the underground aquifer.

Question 16

Define channel store

Answer 16

Channel store is the volume of water contained in the river channel.

Question 17

Define throughfall

Answer 17

Throughfall is precipitation that makes it directly to the land surface without being intercepted by the plant canopy. Some of this throughfall may be intercepted by leaves and this water may then flow off the leaves and drip to the ground as dripflow – some plants have developed shiny surfaces on their leaf surface to get water off the leaf surface quickly.

Question 18

Define stemflow

Answer 18

Stemflow is the flow of water from precipitation down the stems of plants. If they reach the trunks of larger trees the water will flow down the trunks of trees, termed trunk flow, to reach the land surface.

Question 19

Define overland flow

Answer 19

Overland flow is when water flows over the land surface… 2 types: channel flow and sheet flow

Question 20

Define channel flow

Answer 20

Channel flow is when the water if flowing in small channels, rills, which are less than 30cm in width/depth, in a defined stream of in a river channel.

Question 21

Define sheet flow

Answer 21

Sheet flow is normally a relatively rare event and takes place when there is a layer/sheet of water on the ground surface. It may occur in two ways:
o Firstly when there is excess overland flow, when rainfall or water arrives too quickly on the land surface and does not have enough time to infiltrate the soil.
o Secondly, it may occur when water flows onto a relatively impermeable surface, such as a clay soil.

Question 22

Define infiltration

Answer 22

Infiltration is when water enters small openings and pores in the ground from the surface

Question 23

Define percolation

Answer 23

Percolation is when water flows down through the soil and underlying rock pulled down by gravity

Question 24

Define throughflow

Answer 24

Throughflow is the lateral movement in soil of infiltrated water. It occurs when water that has infiltrated the surface is retained in the soil. The water then moves horizontally through the soil, down a slope towards a river channel, usually along well-defined lines of seepage (called percolines) that have been formed in the soil or above an impermeable layer.

Question 25

Define baseflow (groundwater flow)

Answer 25

Baseflow (groundwater flow) is water that has infiltrated and percolated into the bed rock below the soil that then moves laterally under gravity or hydrostatic pressure in a downslope direction to feed springs and river channels.

Question 26

Define recharge

Answer 26

Recharge of the groundwater takes place when water is added to the aquifer. Recharge takes place when precipitation on the land surface exceeds evapotranspiration and water then infiltrates the ground and percolates down to the aquifer.

Question 27

Define aquifer

Answer 27

An aquifer is a body of porous rock or sediment saturated with groundwater.

Question 28

Define water table

Answer 28

Water table is the top of the saturated zone (TF the top of the aquifer = water table)

Question 29

Define phreatic zone

Answer 29

Phreatic zone is a zone of permanent saturation within an aquifer.

Question 30

Define spring

Answer 30

Spring is a place where water naturally flows out of the ground.