MOVEMENT OF WATER INSIDE LANDMASS (WATERSHED):
OR, HYDRIC CONDUCTIVITY:
The movement of water is divided into five main heading which is discussed as under:
WATER MOVEMENT IN SOIL: –
Movement of water in the soil occurs in the pores as a liquid or in the vapor phase. For movement to occur driving forces required which are may be,
A) For liquid
- Gravitational pull
- Capillary tension for liquid water
- Hydrostatic pressure
B) For Vapor
- Vapour pressure
- Temperature gradients for vapor
MOVEMENT OF WATER /CLASSIFICATION OF SOIL WATER:
Gravitational water: –
The water, which moves in the subsurface profile by gravitational force, is called gravitational water.
The gravitational water is not retained or stored in the soil but drains freely under the influence of gravity in the non-capillary pores either laterally or downward. The water is not utilized by vegetation but it is available for stream flow.
Capillary water: –
The water, which is retained under the influence of surface tension against the force of gravity, is called capillary water.
The water is present in the capillary pores and to a certain extent around soil particles a coherent film and can move under capillary forces. Capillary water is not available for stream flow but constitutes the main source of water for plant growth.
Hygroscopic water: –
The water retained by molecular forces, as a thin film on the soil particles is called hygroscopic water.
This type of water is not mobile except in the vapor phase, and it is neither available for plant growth nor for stream flow. It is the moisture of dry soils and is of least importance is soil water storage.
Water vapor: –
This is the water of saturated soils water, which is present below the soil, and forms water table is called free water. This water is pulled by vegetation through capillary action.
MOMENT OF WATER IN UNSATURATED SOIL:-
In unsaturated soil moisture moves in the capillary pores mainly under the action of capillary tension which act as the boundary between air and water. Water moves from the moist zone of low tension to dry zone of high tension. For the movement of water, the driving force is required but it does not only depend on the driving voices but also on the conductivity of the medium in which the current movement occurs. The conductivity of a soil for water depends both on its texture and structure as these determine the number and size of its pores & the passageways for water. The distances of capillary water movement are inversely proportional to the diameter of the capillaries because if the diameter is small the resistance against water movement is increased, so it extremely slowly.
It can be concluded that the velocity of moisture movement in unsaturated soil depends on a driving force as well as on the conductivity of the medium. For the movement of water in the unsaturated soil, the soil must be wanted to above field capacity before water movement can take place.
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NJMH is working as Deputy Conservator of Forests in Balochistan Forest & Wildlife Department (BFWD). He is the CEO of Tech Urdu (techurdu.net) Forestrypedia (forestrypedia.com), Majestic Pakistan (majesticpakistan.pk), All Pak Notifications (allpaknotifications.com), Essayspedia, etc & their YouTube Channels). He is an Environmentalist, Blogger, YouTuber, Developer & Vlogger.