Government Engineering College, Bhavnagar.

Civil Engineering Department

Design Engineering – I

Topic:-

Salinity Prevention

Guided By,Prof. D.J. Langaliya

Contents

INTRODUCTION SEA WATER INTRUSION CAUSES Of SALINITY EFFECTS OF SEA WATER INTRUSION PREVENTIVE MEASURES GOVERNMENT PROJECTS

INTRODUCTION

India has a dynamic coast line of about 7500 km length, including the main land coast line of about 5400 km.

Nearly 25 percent of the total population of India resides in the coastal tracts of the country.

The State of Gujarat has the longest coastline of 1600 km, which is about one third of the total coastline of India.

INTRODUCTION

• Due to heavy withdrawal of groundwater and very less recharge sources (only rainfall), ingress of sea water has converted the available groundwater resources into a saline belt.

SALINITY

Salinity is the saltiness or dissolved salt content of a body of water or in soil. Salinity is discovered in two physical factors of our earth. They are:-

Soil Water

We will discuss the salinity of water in detail.

SALINITY

SEA WATER INTRUSION

• Sea water intrusion is the migration of saltwater into freshwater aquifers under the influence of groundwater development. (Freeze and Cherry, 1979).

Natural Occurance of Seawater Intrusion

Causes of Sea water intrusion

Ground Water Extraction Canals and Drainage networks Higher seawater density than freshwater

Ground Water Extraction

Groundwater is the portion of the Earth's water cycle that flows underground.

Groundwater extraction is the primary cause of saltwater intrusion.

It is caused by excessive pumping

Ground Water Extraction

Water Table

Ocean

Sea Level

FreshWater

Brackish

Water

Equilibrium

Coastal Aquifer - No Pumping

Ground Water Extraction

Water Table

Ocean

FreshWater

Sea Level

Brackish

Water

Coastal Aquifer - With Pumping

Ground Water Extraction

Water Table

Ocean

Brackish Water

Fresh Water

Sea Level

FreshWater

Brackish

Water

Coastal Aquifer - Intrusion Advancing

Canals and Drainage networks

The construction of canals and drainage networks can lead to saltwater intrusion. Canals provide conduits for saltwater to be carried inland, as does the deepening of  channels for navigation purposes. 

Drainage networks constructed to drain flat coastal areas can lead to intrusion by lowering the freshwater table, reducing the water pressure exerted by the freshwater column.

Higher seawater density than freshwater

f = freshwater density = 1.0g/cm3

s = saltwater density = 1.025g/cm3

  The law of nature is that object with higher density

flows toward the object with lower density. Thus the sea water which has higher density (can reach up to 1050 Kg / m3) than the fresh water (1000 Kg / m3) will flow towards the fresh water area when the water from there is removed because of extraction.

Some Other reasons are:- Mismanagement of ground water due to over-irrigation and water

loss through high run-off.

Inefficient use and wastage of water by farmers.

Cultivation of high water intensive crops like sugarcane, banana etc. resulting in lowered water table and ingress of saline water into groundwater.

Over-exploitation of ground water to meet needs of growing population.

Breaking up of joint family system resulting in fragmentation of land, leading to rampant increase in no. of wells and extensive use of diesel and electrical pumps.

High run off due to improper or inadequate water harvesting.

Recurrent droughts.

Ghyben-Herzberg Relation

The figure shows the Ghyben-Herzberg relation. In the equation,

Effects of Salinity

Agricultural production Water quality Ecological health of streams Infrastructure and fixtures  Irrigation Human Health

Effects of Salinity

Preventive Measures

Salinity Control Techniques:-

1) Tidal Regulators and Bandharas at river

2) Physical barriers

3) Fresh Water barriers

4) Extraction barriers

Barriers

Preventive Measures

Recharge Techniques:-

(1) Check dam

(2) Recharge Tanks

(3) Recharge Reservoir

(4) Recharge Wells at suitable locations

(5) Spreading Channel

Recharge Techniques

(1) Check dam (2) Recharge Wells(3) Spreading Channel

Check dam

Check dam is a structures across the gully / waterway with packed stones or stone masonry structure. This is constructed in the middle reaches of the gully or stream. The upstream stored water is useful for recharge as well as supplemental / life-saving irrigation.

A check dam placed in the ditch, swale, or channel interrupts the flow of water and flattens the gradient of the channel, thereby reducing the velocity. In turn, this obstruction induces infiltration rather than eroding the channel. They can be used not only to slow flow velocity but also to distribute flows across a swale to avoid preferential paths and guide flows toward vegetation. Although some sedimentation may result behind the dam, check dams do not primarily function as sediment trapping devices.

Recharging Techniques

Recharge wells can be of two types –

(a) Injection well, where water is “pumped in” for recharge

(b) Recharge well, where water flows under gravity

(c) Induced Recharge

Injection Well

Recharging Well

Induced Recharge

GOVERNMENT PROJECTSSr.No.

Various Works of Salinity Ingress Under Scientific System

1 Management SystemRegulation of lifting underground water and change in crop – System

    Change in crop System

2 Recharge System Check-Dam

    Recharge-Dam

    Recharge-Well

    Recharge Reservoir Spreading Channel

3 Salinity Ingress System Tidal Regulators, Weirs

    Fresh Water Barrier

    Extraction Water Barrier

    Static Barrier

4 Coastal Land ReclamationRejuvenation of salinity land of oceanic areas

GOVERNMENT PROJECTS

Sr. No.

  Estimated cost (Rs. in Lacs.)

(i) 500 No. of Checkdams 4000

(ii) 25 No. of Recharge Tank 1000

(iii) 150 No. of Recharge Well 1500

(iv) 20 No. of Coastal Bund 1000

  Total : 7500

Conclusion

Thus from the above study we can understand the effect of the salinity and how worse it can be for all. It should be taken seriously and the government has taken it seriously in many extend and done many projects for the betterment. The completion of the projects in the slower side and there are failures in some of the projects too. Still the government is doing a lot and some of its projects are successful in reducing the Salinity ingress.

Reference www.cspc.org.in/

en.wikipedia.org/wiki/Saltwater_intrusion

Images from https://www.google.co.in/search?q=seawater+intrusion&es_sm=93&biw=1242&bih=606&tbm=isch&tbo=u&source=univ&sa=X&ei=7d52VNrDNIme8QW5m4KACQ&sqi=2&ved=0CCcQsAQ

www.wrd.org/engineering/seawater-intrusion-los-angeles.php

http://water.epa.gov/type/groundwater/uic/class5/upload/2007_12_12_uic_class5_study_uic-class5_classvstudy_volume20-salineintrusionbarrier.pdf

http://guj-nwrws.gujarat.gov.in/showpage.aspx?contentid=1470&lang=english

http://iced.cag.gov.in/wp-content/uploads/2014/02/3.-PA-of-Salinity-Ingress-Prev.-Prog.-Gujarat.pdf

Thank You For Bearing

By,

Bhavik Shah – (130210106049)

Kartik Hingol – (130210106030)

Digvijay Solanki – (130210106055)

Nitin Charel – (130210106011)