Drainage Basin Hydrological Cycle

Question 1

Define transpiration

Answer 1

The transport of water through an actual, vegetated plant into the atmosphere.

Question 2

Define evaporation

Answer 2

The process by which liquid water is transformed into water vapour, which is a gas. A large amount of energy is required for this to occur. The energy is usually provided by heat from the sun or by the movement of air (wind).

Question 3

Define interception

Answer 3

The process by which raindrops are prevented from directly reaching the soil surface. Leaves, stems and branches on trees, and herbaceous plants and grasses growing close to the surface, intercept water. Evaporation removes some of this moisture from the system and it does not reach the water as run off.

Question 4

Define through flow

Answer 4

The water that moves down-slope through the subsoil, pulled by gravity. It is particularly effective when underlying impermeable rock prevents percolation.

Question 5

Define stemflow

Answer 5

The water that runs down the stems and branches of plants and trees during and after rain to reach the ground. It takes place after interception has occurred.

Question 6

Define surface storage

Answer 6

Part of precipitation retained on ground surface.

Question 7

Define precipitation

Answer 7

Water in any form that falls from the atmosphere to the surface of the Earth. It includes rain, snow, sleet and hail.

Question 8

Define overland flow

Answer 8

When water flows over the surface due to impermeable or frozen ground.

Question 9

Define vegetation storage

Answer 9

Water stored in vegetation.

Question 10

Define infiltration

Answer 10

The passage of water into the soil. Infiltration takes place relatively quickly at the beginning of a storm, but as the soil becomes saturated the infiltration rate falls rapidly. Infiltration rates are affected by the nature of the soil itself. Sandy soils let more water pass through than clay soils.

Question 11

Define soil water storage

Answer 11

The water stored in soil.

Question 12

Define throughflow

Answer 12

The water that moves downslope through the subsoil, pulled by gravity. It is particularly effective when underlying impermeable rock prevents percolation.

Question 13

Define channel storage

Answer 13

A volume of water in a channel (river of stream).

Question 14

Define percolation

Answer 14

The downward movement of water within the rock under the soil surface. The rate of percolation depends on the nature of the rock. Some rocks, particularly those of an igneous or metamorphic nature, are impermeable so there is no percolation or groundwater flow.

Question 15

Define groundwater storage

Answer 15

Water that is stored in the ground.

Question 16

Define groundwater flow (base flow)

Answer 16

The slowest transfer of water within the drainage basin. It provides the main input of water into a river during drought or dry seasons. Groundwater flows at a slow but steady rate through bands of sedimentary rock. It can take thousands of years for moisture that seeps into permeable rocks deep under the surface to be returned to the drainage basin hydrological cycle as groundwater flow.

Question 17

How do you calculate drainage basin discharge?

Answer 17

Precipitation - Evapotranspiration +/- Changes in storage

Question 18

How can discharge be illustrated?

Answer 18

Using hydrographs

Question 19

What are the features of a storm hydrograph?

Answer 19

Base flow, rising limb, peak discharge, receding limb, lag time