Water cycle and water budget

Hydrological Cycle and Water Budget

Dr. Mohsin Siddique

Assistant Professor

Dept. of Civil & Env. Engg

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Outcome of Today’s Lesson

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� The following are the objectives of the lesson:

� 1) To know the principles behind the sources of water,

� 2) To study about hydrologic cycle in general aspect, and

� 3) To further understand the hydrological components like evaporation, precipitation, infiltration, runoff and subsurface flow.

Global Water Resources

3[does not add to 100% due to rounding, numbers differ slightly depending on study used]

Global Water Usage:

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�Types/Categories of water uses

�Domestic water demand

�Public water use

�Commercial water use

�Industrial water use

�Irrigation water demand

�Losses and wastes

Global Water Usage:

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Global Water Usage:

Increasing Population

6More the population more the water usage

Global Water Usage:

Water demand

7http://chartsbin.com/view/1455

Global Water Usage:

Water availability

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Global Water Usage:

Water availability

9http://en.wikipedia.org/wiki/Water_resources

By the year 2025 nearly 2 billion people will live in regions or countries with absolute water scarcity, even allowing for high levels of irrigation efficiency.

Hydrological cycle (Water cycle)

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� Water never leaves the Earth. It is constantly being cycled through the atmosphere, ocean, and land. This process, known as the water cycle, is driven by energy from the sun.

� The hydrologic cycle has a profound effect upon climate prediction.

� Water is vital so we must understand where to find water and how hydrological-cycle supplies water through the Earth.

� Branch of science to study of movements and characteristics of water under of over surface or earth is called Hydrology.

Hydrological Cycle

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Component of Hydrological Cycle

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� Evaporation

� Evapotranspiration

� Condensation

� Precipitation

� Interception

� Infiltration

� Percolation

� Runoff

� Storage

Schematic diagram showing components of hydrological cycle


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� Evaporation: Heat from the sun starts the hydrologic cycle causing water into water vapor that is held in the air of the atmosphere.

� Transpiration occurs when plants take in water through the roots and release it through the leaves, a process that can clean water by removing contaminants and pollution.

� Evapotranspiration is water evaporating from the ground and transpiration by plants. Evapotranspiration is also the way water vapour re-enters the atmosphere

� About 90% of atmospheric water comes from evaporation, while the remaining 10% is from transpiration

� Water is evaporated from lakes, streams, oceans, and plants. In addition, water is released by animals' breathing and perspiration.


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� Evapotranspiration is water evaporating from the ground and transpiration by plants.

� Evapotranspiration is also the way water vapor re-enters the atmosphere


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� Condensation:

� As water (in the form of gas) rises higher in the atmosphere, it starts to cool and become a liquid again. This process is called condensation. When a large amount of water vapor condenses, it results in the formation of clouds.


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� Condensation can form fog, dew, and clouds

� Fog: Fog forms when air near the surface is cold and nearly saturated with water. Now when water from the ground evaporates, it condenses immediately forming tiny water droplets that create a low-lying cloud we call fog.

� Dew: Dew forms at night when air becomes saturated with water vapor. When this saturated air comes in contact with plants or other objects it condenses, leaving tiny water droplets behind on the object.

� Clouds: When the air containing water vapor is heated by the sun, it rises into the atmosphere by convection. The water vapor in the air is then cooled by the colder air higher in the atmosphere causing the relative humidity to increase. As the relative humidity increases, the air eventually becomes saturated. The water vapor then condenses into tiny water droplets around particles of dust or salt in the air. These tiny water droplets make up clouds.

Precipitation

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� When the water in the clouds gets too heavy, the water falls back to the earth. This is called precipitation.

� Types of Precipitation:

� Drizzle

� Rain

� Freezing rain

� Sleet

� Snow

� Hail


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� Types of Precipitation:


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� Interception refers to precipitation that does not reach the soil, but is instead intercepted by the leaves and branches of plants and the forest floor.

� Surface detention

� Depression storage


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� Infiltration: Some precipitation seeps into the groundwater and is stored in layers of rock below the surface of the Earth.

� This water stays there for varying amounts of time. Some water may evaporate into the hydrologic cycle within days, while other water will stay in the ground for centuries or more.

� This process of precipitation seeping into the groundwater is called infiltration.

� Groundwater percolation: It is a part of infiltrated water that percolates into deeper strata and become part of ground water.


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� If the terrain is sloping, infiltrated water starts to flow under gravity. This flow is termed as Subsurface flow. It can be further categorized into

� Interflow: Shallow ground water flow-joins stream within few days of rain

� Base-flow: Deeper ground water flows-becomes part of ground water

Subsurface flow incorporates movement of water within the earth,either within the recharge zone or aquifers. After infiltrating,subsurface water may return to the surface or eventually seep intothe ocean.


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� On hard or frozen ground, most of the precipitation is unable to seep below ground. This precipitation then flows down slopes and hills, eventually stopping in rivers, lakes, streams, and oceans.

� Some of this water will then evaporate and rejoin the hydrologic cycle, while other water will remain in the body of water.

� This process of water traveling over the ground and collecting in a body of water is called surface runoff.


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� Storage:

� Natural lakes or man-made reservoirs or ground water

Lake Geneva or Lake Léman is a lake in Switzerland and France

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Table: Typical Resident time of water found in various reservoirs

Water Budget

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� Water balance equation in its most fundamental form is given by

� Where, P=precipitation, E =evaporation, Q = runoff and ∆S = change in storage

Example Long Term Water Balance

for Estimating Evapotranspiration

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� For the Embarras River at Camargo 1978 to 1998, precipitation (P) = 40in/yr, average stream flow (Q) = 188 ft3/sec, and the watershed area = 186mi2. Estimate the average annual evapotranspiration for this watershed andthis period, assuming net groundwater flows and changes in storage arenegligible, and the density of water is constant. Because water volume ismass divided by density, if density is constant, a volume balance isequivalent to a mass balance.

Solution: We can only add or subtract items of the same type, or items with common units. The depth of annual precipitation input can be converted to a volume by multiplying the depth by the watershed area.

Example Long Term Water Balance

for Estimating Evapotranspiration

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Global Water Cycle

28 Oki, T. and Kanae, S. 2006. Global hydrological cycles and world water resources. Science, 313, 1068-1072.

Typical Hydrological Cycle for UAE

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100%

75%

15%

Infiltration/groundwater recharge

10%

Guess how much is average annual precipitation in UAE ??

Thank you

� Questions….

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Date post:	19-Jul-2015
Category:	Engineering
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Water cycle and water budget

Engineering