Drainage basin systems definitions

Question 1

Evapotranspiration

Answer 1

(output)
the combined process evaporation and transpiration causing water to move from the Earth’s surface into the atmosphere.

Question 2

evaporation

Answer 2

(output)
liquid changes into water vapour, from puddles and streams. Rate of evaporation increases in hot, dry and windy conditions and with larger soil surface area.

Question 3

Transpiration

Answer 3

(output) water is drawn from soil by the plant and leaves the plant as water vapour through the stomata.

Question 4

Potential Evapotranspiration:

Answer 4

(output)
the amount of evaporation that would occur if an unlimited water source were available.

Question 5

River Discharge:

Answer 5

(output)
water that flows into the sea, or that moves in channels (streams/rivers). Water enters the channel as direct channel precipitation or other flows.

Question 6

The equation for river discharge

Answer 6

(output)
Q=AV (Q = Discharge, A = Cross Sectional Area, V = Velocity). Measured in m3/second – Cumecs.

Question 7

Interception

Answer 7

(stores)
precipitation is caught and stored by vegetation before it reaches the ground.

Question 8

Surface Water:

Answer 8

(stores)
when the infiltration capacity is exceeded, water builds upon the surface.

Question 9

Example of temporary stores

Answer 9

puddles and turloughs.

Question 10

Example of Permanent stores

Answer 10

lakes and wetlands

Question 11

Ground Water

Answer 11

(stores)
water that has percolated into bedrock. Is a store of freshwater - wells and boreholes can be dug below water table to access.

Question 12

Ground Water Recharge

Answer 12

(stores)
refilling of rock pores as water moves downwards. Occurs when rate of recharge > rate of abstraction.

Question 13

Channel Storage

Answer 13

(Stores)
all water stored in rivers streams and drainage channels.

Question 14

Soil Moisture:

Answer 14

(stores)
water held sub-surface in soil pores. Sandy soils have many large pores, so is permeable, and has quick infiltration rates. Clays are hygroscopic – clay minerals swell when in contact with water, making it impermeable and unstable.

Question 15

SM Deficit:

Answer 15

(stores)
available water is being used up.

Question 16

SM Recharge

Answer 16

(stores)
precipitation > potential evaporation. Some dry pores refill.

Question 17

SM Surplus

Answer 17

(stores)
soil is saturated, water cannot enter, so flows over the surface.

Question 18

SM Utilisation

Answer 18

(stores)
evapotranspiration (and other water uses) > precipitation.

Question 19

Field Capacity

Answer 19

(stores)
amount of water held once excess has drained away – saturation point.

Question 20

Wilting Point

Answer 20

(stores)
the range of soil moisture content at which permanent plant wilting occurs.

Question 21

Throughfall

Answer 21

(Above ground flows)
Water that either falls through gaps in the vegetation or which drops from leaves, twigs or stems

Question 22

Stemflow:

Answer 22

(Above ground flow)
precipitation is intercepted by vegetation, then runs down the branches and main trunk.

Question 23

Overland Flow

Answer 23

(Above ground flow)
when soil is saturated, or precipitation exceeds infiltration rate, surface runoff occurs – where water flows over the surface.

Question 24

Hortonian Flow

Answer 24

(Above ground flow)
shallow, laminar, fast moving water that causes severe soil erosion when precipitation exceeds the infiltration capacity and depression soil capacity.

Question 25

Channel Flow

Answer 25

(Above ground flow)
movement of water in channels such as streams and rivers.

Question 26

Infiltration

Answer 26

(Below ground flow)
precipitation soaks/is absorbed into soil

Question 27

Infiltration Capacity

Answer 27

(Below ground flow)
maximum rate that precipitation can be absorbed by soil in given conditions.

Question 28

Infiltration is __________ proportional to overland runoff.

Answer 28

Infiltration is inversely proportional to overland runoff. Depends on: rainfall duration, antecedent soil moisture, porosity, slope angle, vegetation.

Question 29

Percolation

Answer 29

(Below ground flow)
slow movement of water downwards through the soil into bedrock under gravity. Fast in Carboniferous Limestone.

Question 30

Rate of Percolation depends on….

Answer 30

(Below ground flow)
Rate depends on permeability and porosity of bedrock. Chalk and sandstones are porous, spaces allow water to percolate.

Question 31

Throughflow

Answer 31

(Below ground flow)
water flows through the soil in natural pipes or percolines. Occurs above bedrock.

Question 32

Groundwater

Answer 32

water that has infiltrated the ground, entered the phreatic zone and discharged into the channel.

Question 33

Phreatic zone:

Answer 33

(Below ground)
part of an aquifer (permeable rocks and sediments that can hold groundwater or allow it to pass through) below the water table where all pores are permanently saturated.

Question 34

Baseflow:

Answer 34

(Below ground flow)
where groundwater seeps into the river’s bed and contributes to discharge. Very slow transfer from bedrock and very deep throughflow. Takes months/years.

Question 35

Water table

Answer 35

(Underground water)
upper layer of the phreatic zone. It will rise and fall depending on the amount of rainfall percolating downwards, and the amount of baseflow from lower rocks. The aeration zone is seasonally wetted and seasonally dries.

Question 36

Ground water Recharge occurs with…

Answer 36

Recharge occurs with:
- Infiltration (from precipitation)
- Seepage (through banks/bed of rivers,
lakes, puddles and ditches)
- Leakage and inflow (from adjacent rocks,
aquifers)
- Artificially from irrigation, reservoirs

Question 37

Groundwater loss occurs with:

Answer 37

• Evapotranspiration (mainly low areas)
• Natural discharge (seepage and spring flow)
• Leakage and outflow (into aquicludes from
  aquifers)
• Artificial abstraction

Question 38

Aquifers

Answer 38

permeable rocks (sandstone, limestone, chalk) that contain significant quantities of water. Water inside moves slowly and maintains streamflow – by absorbing or releasing water in wet/dry periods.

Question 39

Springs

Answer 39

water flow reaches the surface, making a spring. Might be substantial enough to become a source. Usually where percolating water reaches an impermeable layer or the saturated zone.

Question 40

Water budget equation

Answer 40

S=P−Q−E

Soil Storage, Precipitation, QChannel Flow, Evapotranspiration