Introduction

In a valley, the water often gets lost through cracks and fissures in the bed. These are known as sinking creek and if their tops are open, they are called bogas.

What is sinking creek?

It is an erosional landform of karst topography.

The surface of the karst plain looks like a sieve because of the development of closely spaced sinkholes. These sinkholes act as funnels because surface water disappears through numerous sinkholes located in the line, the resultant feature is called a sinking creek. The point through which the water goes downward is called a “sink”. The water of short rivers disappears through a single sink while that of large streams disappears through many “sinks”.

Phenomenon for sinking creeks

As has been mentioned, sinking creeks are a part of karst topography, hence they occur in areas where thick beds of massive limestone lie just below the surface.

How sinking creeks defy gravity?

Disappearing streams are surface streams that flow underground into solution cavities. These numerous small disappearing streamlets in sinkholes known as sinking creeks defy the natural law of gravity (1).

Karst topography

In areas of limestone and dolomite rocks, the solution action of underground water gives rise to highly distinctive landforms on and below the surface which are collectively known as topography. There are various landforms related to karst, A few of them are:

1. Caves

Caves or caverns are voids of large dimensions below the ground surface. The cavern is characterized by horizontal passages at the junction of tunnels.

2. Sinkholes

Chemically active rainwater charged with atmospheric carbon dioxide dissolves limestones and other carbonate rocks along with their joints and thus numerous types of sinkholes are formed (2).

Formation of sinking creeks

The sinking creeks disappear after a certain point of time on a karst topography, few forming points are

1. Underground channels

Karst terrain is largely supported by rocks such as limestone or dolomite that are highly porous. As water from streams or rainfall dissolves the bedrock, fractures occur. Over time these fractures are enlarged and an underground drainage channel/system begins to form allowing more water to pass through the system (3).

2. Swallow holes

Also known as sinkholes, are depressions or holes in the ground caused by the collapse of surface layers.

Ecosystem and biodiversity

1. Ecosystem in the subterranean

It refers to the underground environment. The most evident features in these types of karst topography are caves, fissures, cracks, etc.

2. Streams

Underground streams, also known as subterranean rivers, flow at least partly beneath the surface of the earth. Underground streams emerge at sinkholes or above ground, as the karst landscape gives way to soil (4).

3. Adaptation in the dark

There is no particular problem related to sinking creeks and their adaptation in the dark, as it is a karst topography where streams appear and disappear which does not need any particular arrangement of light.

Urbanization toll on sinking creeks

Rampant clearing of land resources to support the population is disturbing the karst regions.
Rocky desertification of land is depleting the streams in karst topography.
The dumping of urban wastes into the karst landforms creates pollution.
Continuous use of groundwater in depleting the water-based sources of areas related to karst topography.

Conservation

Large-scale quarrying of limestone and dolomite from karst regions must be minimized.
Mining of phosphate in karst caves where sinking creeks appear and disappear should be reduced.
Touristic and land use practices must be controlled.
Treatment of sewage from urban areas affecting the nearby karst landforms must be checked.
Farming in karst regions must be prohibited.
The usage of underground water must be done in a controlled way.

Geological significance

The dissolution of soluble rocks results in the formation of a complex underground drainage system, which can lead to the creation of a vast river system.
The sinking creeks that pass through caves contain important geological formations such as stalactites, and stalagmites which provide insight into the earth’s geological history (5).

Hydrological mysteries

Groundwater percolating through cracks removes the soluble rock while leaving an enlarged channel for a further (and progressively more efficient) flow of water. If there is a thick cover of soil above the soluble rock, surface streams may flow above the subterranean karst drainage system. But more commonly, dissolution features occur at the surface, and hence there are few continuous surface streams because runoff encounters sinkholes or is otherwise routed underground.

In some cases, the flow of a surface stream may be diverted underground when subterranean caves collapse and breakthrough beneath the streambed in a process known as stream piracy. Usually, this is a gradual process, with only part of the surface stream being diverted through small cracks in the rock just below the soil cover. The amount of surface water diverted grows larger with time, and the cave also grows with time until the entire surface stream disappears into the ground. Sometimes these disappearing, or sinking, streams provide access to the caves beneath (6).

Cultural significance

The sinking creeks have always been an intriguing topic for researchers for centuries.
Caves formed in karst topography are used for shelter and burial sites.
Karst springs developing from sinking holes have special properties.
The large trees produced in karst regions are important sources of construction materials.
The karst sites and springs are used for shrubs, and herbs with medicinal and food values.

Climate change impact on sinking creeks

The extreme rise in temperature is slowly affecting the underground streams in karst regions.
Due to pollution, the precipitation is often acidic in nature which after getting dissolved underground forms a toxic water system in karst regions.
Desertification is slowly drying up the underground streams i.e. sinking creeks.
Because of the lower amount of rainfall occurrence due to high-temperature rise, the underground streams are vanishing at a faster rate.
Because of extreme urbanization and resource depletion, the recharge of groundwater is happening at a slower rate, which is affecting the karst streams.

Examples of sinking creeks

The different regions where sinking creeks developing in karst topography are found are pointed out below

Causes region of Southern France
Northern Puerto Rico
Southern Indiana
Central Florida of the United States
Carlsbad area of USA
Chalk region of England
Chalk region of France

Summary

When limestone interacts with underground water, the water dissolves the limestone to form karst topography.
In a valley, the water often gets lost through cracks and fissures in the bed. These are known as sinking creeks and if their tops are open, they are called bogas
Sinking creeks are erosional landforms of karst topography
Sinking creeks occur in areas where thick beds of massive limestone lie just below the surface.
There are various other erosional landforms in karst topography like- caves, waterfalls, gorges, canyons, etc.
Sinking creeks are a system of disappearing streams in karst plains, finally making their way to sinking holes.
Sinking creeks are a natural phenomenon, hence they are facing a few problems because of rapid urbanization and climate change.
They have huge cultural significance, the caves are used for burial spaces, and they have been a source of scientific discussion for centuries.
Sinking creeks and karst topography must be conserved by taking steps like preserving karst sites, less usage of polluted materials, etc.
A few notable sinking creeks are karst regions of France and England etc.

References

Savindra Singh. Geomorphology. Pravalika publications, Allahabad. Chapter 22: Fluvial geomorphology. Page no: 437-440
S. Lal. Physical geography. Sharda pustak bhawan, Allahabad. Chapter 14: The dynamics of river systems and their landforms. Page no-214-218
Rajiv Ahir. Spectrums Geography.Spectrum Books Pvt.Ltd, New Delhi. Chapter 18: Karst landforms and cycle of erosion. Page no: 85-87.