Hydrologic cycle & groundwater

Geotechnics & Applied Geology

• Prepare by :• Rashmik Diwani

• Tushar Pokar• Nikul Vasani

• Hardik Chaudhari• Setul Paravadiya

• Guidance by:• Kaustubh sane

• HJD Institute Of Technical Education & Research

HYDROLOGIC CYCLE & GROUND WATER

Topic

• Hydrologic Cycle

• Sources Of Ground water

• Occurance of Ground water

• Terms related to Ground water

• Types of Aquifers

• Different Rocks as Aquifers

• Artificial Recharge

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 water cycle is crucial to the existence of life on our planet.

Evaporation

• During part of the water cycle, the sun heats up liquid water and changes it to a gas by the process of evaporation. Water that evaporates from Earth’s oceans, lakes, rivers, and moist soil rises up into the atmosphere.

Transpiration

• The process of evaporation from plants is called transpiration. (In other words, it’s like plants sweating.)

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.

Precipitation

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

Runoff

• When rain falls on the land, some of the water is absorbed into the ground forming pockets of water called groundwater. Most groundwater eventually returns to the ocean. Other precipitation runs directly into streams or rivers. Water that collects in rivers, streams, and oceans is called runoff.

Meteorological factors affecting surface (over soil) runoff

- Type of precipitation

- Rainfall intensity

- Rainfall amount

- Rainfall duration

- Distribution of rainfall over the drainage basin

- Direction of storm movement

- Precipitation that occurred earlier and resulting soil moisture

- Meteorological conditions that affect evapotranspiration

Physical characteristics affecting surface runoff

- Land use

- Vegetation

- Soil type

- Drainage area

- Basin shape

- Elevation

- Topography, especially the slope of the land

- Drainage network patterns

- Ponds, lakes, reservoirs, sinks, etc. in the basin, which prevent or delay runoff from continuing downstream

Groundwater begins as INFILTRATION

Precipitation falls and infiltrates into the subsurface soil and rock

•Can remain in shallow soil layer•Might seep into a stream bank•May infiltrate deeper, recharging an aquifer•May travel long distances•May stay in storage as ground water

Factors affecting infiltration• Precipitation (greatest factor)

• Magnitude, intensity, duration

• Characteristics (rain, snow)

• Soil Characteristics– Clay absorbs less water at a slower rate than sand

• Soil Saturation – Higher saturation leads to more runoff instead

• Land Cover

• Slope of the Land – Hills enhance runoff velocity

• Evapotranspiration– Plants use soil moisture to grow and transpire

Source of Ground Water

• springs

• Infiltration Galleries

• Well

• Karez

• Springs :– A spring is a flow of

ground water at the ground surface.

– A pervious layer, sandwiched between two impervious layers, give rice to a natural spring.

• Infiltration Galleries :– An infiltration gallery is a

horizontal conduit having permeable boundaries so that ground water can infiltrate into the same. It is generally provided in highly permeable aquifers with high water table so that adequate head is available for gravity flow of ground water into the gallery.

Occurance of Ground Water

• The rainfall that percolates below the ground surface, passes through the voids of the rocks, and joints the water table. This voids are generally interconnected, permitting the movement of the ground water.

• Occurance of ground water mainly depends upon two geological features :

– The porosity of the rocks

– The permeability of the rocks

Porosity

• Porosity: Percent of volume that is void space.

– Sediment: Determined by how tightly packed and how clean (silt and clay), (usually between 20 and 40%)

– Rock: Determined by size and number of fractures (most often very low, <5%) 1%

5%

30%

Zone of Aeration

Water Table

Saturated Zone

Permeability

• Permeability: Ease with which water will flow through a porous material– Sediment: Proportional to

sediment size• GravelExcellent

• SandGood

• SiltModerate

• ClayPoor

– Rock: Proportional to fracture size and number. Can be good to excellent (even with low porosity)

Excellent

Poor

Zone of Aeration

Water Table

Saturated Zone

Terms Related to Ground Water

• Aquifer• Aquiclude• Aquitard• Aquifuge• Porosity• Specific yield• Specific retention• Storage co-efficient• Co-efficient of permeability• Co-efficient of transmissibility• Water table

• Aquifer: Saturated sediment or porous rock that is sufficiently permeable to supply useable amounts of water

• Aquiclude :

– An aquiclude may be define as a geological formation of relatively in permeable material which permits storage of water but it is not capable of transmitting water in sufficient quantity.

– For example,

• Clay

• Aquitard :

– A geological formation that as poor permeability, but through which seepage is possible, and hence, it does not yield water freely to wells.

– It may be transmit vertically appreciable quantities of water to or from adjacent aquifers.

– For example,

• Sandy clay

• Water table: the surface separating the vadose zone from the saturated zone.

• Measured using water level in well

The Water Table

Types of Aquifers

• Unconfined aquifer

• Confined aquifer

Unconfined and Confined Aquifer

• Unconfined Aquifer: open to atmosphere e.g., overlain by permeable rocks and soils

• Confined aquifer: sandwiched between aquitards

–Artesian System: Water rises above the level in aquifer because of hydrostatic pressure

Different Rocks as Aquifers

• Igneous rocks :

– It are either intrusive or extrusive in nature.

– The intrusive igneous rocks like Granites, Syenites. etc.

• Sedimentary rocks :

– Among sedimentary rocks, the most common ones are shales, sandstones and limestone shales are impermeable rocks, though considerably porous.

– Clay may have 50-60% porosity.

– For example,

• Gravels

• Sand beds

• Sandstones

• limestones

• Metamorphic rocks :

–Non-foliated metamorphic rocks like marble and quartzite are generally impermeable.

–These rocks, thus behave as aquicludes.

Artificial Recharge

• Due to rapid industrialisation, population increase, intensive agriculture, etc. the use of water has been considerably increased.

• For these purpose water is pumped from the ground water sources.

Methods of Recharging

• Recharging of open wells

• Infiltration bore well

• Hidden dam

• Infiltration tank

• Infiltration tank in river bed

• Infiltration borewell or tube well in river bed

• Recharging of lost rivers

• Check dam