GROUND WATER || WATER MASSES || WELLS AND BOREHOLES: PART TWO

 

WELLS AND BOREHOLES:

They are deep holes dug in the ground often with the purpose of getting water. A well can be permanent if it has been sunk deep bellow to a zone of permanent water saturation. And it can be temporary if it has been sunk to a zone of intermittent saturation.

ARTESIAN BASIN

Artesian basin is a saucer-shaped like depression which consists of a layer of permeable rock that is sandwiched between two layers of impermeable rock. It forms broad syncline with either ends or one end of the permeable rock exposed onto the surface.

Rain water enters artesian basin through exposed ends of permeable rock layer and saturate to for aquifer.

Artesian well: it is a well which has been sunk into an aquifer of artesian basin where water comes onto the surface due to hydraulic pressure.

NECESSARY CONDITIONS FOR THE FORMATION OF ARTESIAN WELLS.

i.                 The permeable rock layer (aquifer) must be enclosed between two layers of impermeable rock.

ii.               Either one or both sides of the aquifer must be outcropped in region which is a source of water.

iii.             The mouth of artesian well must be lower than the intake area. This allows the water to be forced to the surface by pressure.

iv.             The aquifer must dip from the region of water intake and the rock layers must form a broad syncline or basin.

SIGNIFICANCE OF GROUNDWATER:

a.      Source of rivers. Some rivers originate from springs.

b.     Source of water for domestic and industries.

c.      Used for irrigation agriculture

d.     Settlement attraction. Some of settlements are found around areas with water like in desert region where settlement is found around oasis areas.

e.      Provision of hot water which gives out geothermal energy also used as medicine to cure some diseases.

f.      Tourist attraction. Some hot springs and karst scenery attract tourist to visit the areas.

g.     Source of minerals like salts.

 

 

 

KARST SCENERY

Karst is the region in Dinaric Alps of Croatia where there is limestone rock and where rain water as created unique features on the surface as well as underground.

Karst scenery refers to features which develop in limestone region.

FACTORS INFLUENCING THE DEVELOPMENT OF KARST SCENERY:

1. The surface rock and the rock beneath should be thick limestone, dolomite or chalk.
2. The rock should be hard and well jointed.
3. The climate should be hot and humid to allow rapid chemical weathering.
4. The water table in limestone rocks should be deep below the surface. This allows the rocks above to form conspicuous features. Where the water table is near to the surface lime stones would dissolve without forming features.

SURFACE FEATURES IN LIMESTONE AREAS.

a)     Grikes and Clints

Grikes are irregular gullies that criss-cross limestone surfaces separating various limestone stone block known as Clints. The gullies occur when water actions widens and deepens the joints in the limestone rocks leaving blocks of rock (Clints) standing.

b)     Swallow-holes: Also called sink-holes. Are the vertical holes in the ground through which rainwater or even river water disappears into the ground. It is formed as the results of vertical cracks/faults being opened and widened by water sinking into the ground especially at the at the point of cracks convergence. When river water or surfaces run off disappear through this hole, it is called swallow-holes.

c)     Ponor (ponore): is the vertical shaft from the surface of the swallow-hole down into the ground. Water passes through this shaft from the swallow hole downward.

d)     Dry valley: is a the part of a river valley in which water is no longer flowing .it is formed when the river disappear in a swallow hole living behind the section of river between swallow hole and point of river re-emergence of the river down-hill remains dry.

e)     Doline/Dolina: is a round or elliptical hollow on the surface of limestone region which is formed when several small hollows merge. It is formed when water start acting at the point of convergence of joints on the surface.

f)      Uvala: is the large depression on the surface of limestone which is as wide as one kilometer in diameter. It is formed similar as doline and it is sometimes referred to as enlarged doline.

g)     Polje: it is the largest surface depression formed by solution in limestone regions. The broadening of the depression is outcome of water action and partly tectonic forces which causes it to sink. Its floor is generally flat. During wet seasons polje becomes temporally lakes.

h)     Gorges: is a steep sided trough formed when the roof of an underground huge cave (carven) collapse.

 

Underground features in limestone areas.

1. Phreatic caves: these are cavities or chambers which form within the rocks, but below the water table .it is the consequence of water dissolving limestone rock to make a chamber. Such chamber is called phreatic cave.
2. Underground caves:  it is a cave formed within the ground where by underground river dissolve limestone rock and widens horizontal cracks along which it flows. Over a time a big tunnel is developed. When such cave is widened and enlarged it is called CARVEN.
3. Stalactite: is a mass of calcium bicarbonate hanging on the roof of the cave as the result of carbonation process/chemical weathering by carbonation process.
4. Stalagmite: Is the accumulation of crystals of calcium carbonates at the base /floor of the cave. (Is the mass of calcium carbonate which stands vertically from the floor of the cave. They are formed from accumulation of drops of calcium bicarbonate from the roof of the cave.
5. Natural pillars: is a mass of calcium carbonate rock formed when stalactite and stalagmite joins. It occurs where stalagmite forms directly below stalactite and the two features grows toward each other ending up joining together and form natural pillar.

IMPORTANCE OF LIMESTONE FEATURES.

i.       Source of tourism. Karst scenery provides good attraction for tourists.

• ii.     Limestone blocks provide building materials.

iii.   In ancient time caves were used as settlement for ancient people.

iv.   Karst region provides pasture for sheep, goats and cattle.

 ALSO READ THE FOLLOWING RELATED TOPIC

1. GROUND WATER || WATER MASSES || SOURCES OF GROUND WATER PART ONE
2. GROUND WATER || WATER MASSES || WELLS AND BOREHOLES: PART TWO
3. GROUND WATER || WATER MASSES || FORMATION AND CLASSIFICATION OF LAKES: PART THREE
4. GROUND WATER || WATER MASSES || SIGNIFICANCE OF LAKES. PART FOUR
5. GROUND WATER || WATER MASSES || IMPORTANCE OF WETLANDS PART FIVE
6. GROUND WATER || WATER MASSES || CORAL COASTS PART SIX