What Is Meant By Salt Water Intrusion?
Salt water intrusion, as can be gleaned from its name; means the intrusion of Salt water into freshwater bodies.
Meaning that the salt water moves into freshwater zones and compromises the quality of drinking water. It is most commonly observed when Wells are dug and used for a long period of time.
Both types of water are present underground. Since freshwater is lighter it is present on top. Brackish water (intermediate or mixture of fresh and salt water: generally known as a transitional zone for the mixing of two waters) is present in the midst. Lastly, the densest which is salt water is present at the bottom.
This problem of salt water intrusion occurs since above the salt water reserves, lies the freshwater reserves. And each time freshwater is drawn through Wells or via other means; the overhead pressure is reduced and an imbalance is created. Thus, salt water moves in after freshwater has been exhausted.
Also check out: Dire Need of Sea Water Desalination Plants in Sindh Pakistan
Reasons for Salt Water Intrusion- Causes:
Some of the most common causes include:
- Overdrawing from wells: the reservoirs of fresh underground water sources are generally used by population in the form of Wells and aquifers. When freshwater is drawn sometimes lateral encroachment of water from nearby saltwater/marine sources. Meaning salt water moves up vertically to take up the space left empty by freshwater reserves due to withdrawal. This causes the mixing of freshwater in Wells with salt water sources.
Also read , Aquifer Vulnerability And Groundwater Quality In Pakistan - Groundwater extraction: the main source of drinking water in most areas around the world is groundwater. There is a pressure exerted by the freshwater The extraction of this can reduce underground water tables and when the overlying pressure of freshwater tables is reduced, salt water, which is denser, starts moving towards the surface.
- Construction of Canals/Drains: Constructions of channels, drains, water ways or even digging too deep wells for drinking purposes, may lead to salt water intrusion. In many cases, the search for oil and drilling to extract it from underground sources also leads to the salt water entering the surface level waters where it can degrade the quality of existing freshwater reserves.
Effects of Salt Water Intrusion:
- Depletion of Freshwater: Freshwater sources such as from wells or aquifers are rendered useless as they become unfit for consumption by the general populace in the vicinity. This may lead to abandonment of the wells or aquifer stores once salt water starts to be withdrawn after depletion of freshwater.
Read: Freshwater Ecosystem of Pakistan – Climatic Biome - Salinity Problems: due to salt water intrusion, salinity increases in the area and contaminates not just the freshwater sources but also nearby plants are effected. Due to the increased salinity, soil and land quality are also affected that may lead to problems in crop growth and inability of plants to take up nutrients.
Related: Waterlogging and Salinity in Pakistan - Destruction of Habitats: For many diverse species of flora and fauna; salinity effects them seriously. Such as crocodiles, magpies and geese that are impacted due to loss of vegetation induced by salinity and this leads to destruction of their breeding grounds.
Control Of Salt Water Intrusion:
- Set Limits: This entails that public wells need to be regulated and its monitoring should be carried out to ensure that they are not being overdrawn. This will allow wells and aquifers to have enough time to replenish its freshwater or the underground water tables when it rains.
- Construct Basins: near marine coastal areas where there is a high chance of salt water intrusion by seeping in via bedrock, basins or channels need to be constructed. This is so that any salt water that has managed to escape nearer to the freshwater source, it will be caught in those basins. This water can then be either pumped into a separate space for fishing or providing a habitat for migrating fish. But mostly it is pumped back to the sea. Seawalls, Gyrones, Breakwaters and Small sandbags are also used to prevent salt water intrusion.
- Preserve Wetlands: Preserve and maintenance of natural wetlands and shoreline protection greatly helps against salt water intrusion.
You may also be interested in: Freshwater Wetland Ecosystem of Pakistan – Climatic Biome
I hope you all liked this post! Please comment below if you have any suggestions, comments, or feedback! We at #envpk love hearing from our readers! Thanks!
