1.1 Drainage basin system

Inputs, outputs, stores, and flows

drainage basin

an open system - an area which is drained by a river and its tributaries that collects precipitation, surface runoff, and groundwater from the surrounding landscape.

Hydrological cycle

the continuous movement of water within the Earth and atmosphere through processes such as evaporation, condensation, precipitation, and infiltration.

Percipitation

The conversion and transfer of moisture in the atmosphere from the land. Affected by : the total amount of precipitation, intensity (mm/hour), type of precipitation, geographical distribution, and temporal variability (seasonality).

Interception

Water caught and stored by vegetation

Interception loss

water retained by plant surfaces, later evaporated away or absorbed by the plant

Throughfall

water that either falls through gaps in the vegetation or which drops from leaves, twigs or stamps

Stemflow

water that trickles along twigs and branches, finally down the main trunk

Transpiration

water loss from vegetation to the atmosphere.

Evaporation

•  conversion of liquid/solid precipitation to water vapor in the atmosphere. 

• increases in warn dry conditions, decreases under cold calm conditions. 

• affected by temperature, humidity, windspeed, water availability, vegetation and color of surface

Evapotranspiration

The combined effects of transpiration and evaporation

Infiltration

the process by which water soaks into, or is absorbed by the soil.

influenced by : duration of rainfall, antecedent soil moisture, soil porosity, vegetation cover and slope angle.

Runoff

water that flows over the land’s surface

Infiltration capacity

the maximum rate at which a soil can absorb water from its surface under a given set of conditions

Soil moisture

 subsurface water in the soil.

Field capacity

the amount of water held in solid after excess water draws away - through saturation. 

Wilting points

 the range of moisture content in which permanent wilting of plants occurs. They define the approximate limits to plant growth. 

Throughflow

water flowing through the soil in natural pipes and percolines (lines of concentrated water flow between soil horizons).

Groundwater

 permanently saturated zone within solid rocks and sediments

water table

 the upper surface of saturation within permeable rocks. 

Baseflow

 the part of the river’s discharge that is provided by groundwater seeping into the bed of a river.

Recharge

 the filling of water pores where water has dried up or been extracted by human activities - where recharge does not take place, ground water is considered a non-renewable resource. 

• Groundwater recharge occurs due to : 

  • Infiltration of part of the total precipitation at the ground surface

  • Seepage through the banks and bed of the surface water bodies (rivers, lakes etc)

  • Groundwater leakage and inflow from adjacent rocks and aquifers

Aquifers

 rocks that contain quantities of water

Springs

 natural flows of water from the Earth’s surface. It occurs when the water table occurs at the surface