Week 3: Water Flow Pathways and Groundwater Flashcards
Infiltration excess runoff
Hortonian flow
When water enters the soil system faster than the soil can absorb it. i.e. when precipitation exceeds the infiltration capacity of the soil.
Saturation excess runoff
Dunne
When the soil becomes saturated and any additional precipitation or irrigation causes runoff.
Terrain Index
The TI is a physically based indicator of a landscape’s propensity (tendency to behave in a particular way) to develop and maintain steady-state saturation at a given location for a given soil type. Areas within a catchment possessing the same value of the TI are assumed to have the same hydrologic response to rainfall, regardless of their position in the landscape.
Wilting point
The minimal point of soil moisture the plant requires to not wilt.
Capillarity
The additive force of adhesion and cohesion. Can move water against gravity where small pores conduct capillary water.
Water potential
-3 Main Forces
Refers to the tendency of water to flow/move freely in soil. More water in soil = more water potential. At saturation, water potential is near zero. Water will always try to move from a state of high energy to a low energy state.
Main forces:
• Gravitational (positive) – potential energy due to gravity.
• Matric (negative) – effect of soil on water (most common force).
• Osmotic (negative) – special case for salty soils.
Adhesion/Cohesion forces
Adhesion: attraction of water to soil.
Cohesion: attraction of water to water.
These forces result from the shape of the water molecule and sharing of electrons.
Gravitational flow
The movement of water by gravitational forces.
Occurs only under saturated conditions. It is rapid in course soils due to large pores, and usually results in percolation (filtration) through the soil profile.
Aquifer
A body of permeable rock which can contain or transmit groundwater.
Peizometer
A piezometer is either a device used to measure liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity,
or a device which measures the pressure (more precisely, the piezometric head) of groundwater at a specific point.
Soil water
Water that is held in the soil. Important for plants, seed germination, transpiration, moving products, lowers soil strength and drives microbial activity.
Unsaturated zone
An area of soil that has not reached saturation.
Saturated zone
An area of soil that has reached saturation – any additional precipitation or irrigation will result in runoff.
Phreatic surface
Commonly known as the water table. It is a level where the ground below is completely saturated with water.
