Mapping Salinity Ingress Using GALDIT Model

Dr.S.M.Yadav A i t P fAssociate Professor

CED, SVNITSURAT INDIASURAT, INDIA

Co-Authors

Dr.B.K.SamtaniProfessor

CED, SVNITSURAT, INDIA

H.D.VasavaJunior EngineerJunior Engineer

VMCVADODARA, INDIA,

Introduction

•The development and management of coastal•The development and management of coastal

ground water aquifer is a serious issue.g q

• Monitoring of sea water intrusion involves

determination and prediction of ground waterdetermination and prediction of ground water

deterioration and assesses other managerial

activities in coastal aquifers.

d if f d• Ground water aquifers are often exposed to heavy pumping and consequently risks of sea water intrusion in case of coastal aquifers

• Vasava et al (2010) studied the vulnerability of( ) ysea water intrusion in ground water as carriedout by Chachadi (2001, 2002) in coastaly ( , )aquifer of Goa, India.

• Coastin (2001) assessed ground watervulnerability to pollution.y p

Mi (2004) i d i i• Mitra (2004) carried out sea water intrusionstudy using remote sensing and GIS for theGulf of Cambay, Gujarat

• Kumar (2007) modelled sea water intrusion in

th Gnorth Goa.

•Sharma (1976) assessed quality of ground water

i h l if Vi kh I diin the coastal aquifer near Visakhapatnam, India.

•Number of solute transport models suitable for

the simulation of sea water intrusion and up

coning of saline water beneath pumping sites isconing of saline water beneath pumping sites is

commercially available.

•These include SUTRA(Voss,1984) , FEFLOW(

Diersch,1998),HST3D( Kipp,1987) and SALTFLOW(

Molson and Frind 1994)Molson and Frind ,1994) .

• The system presented here allows the user to

determine a numeric value for any hydrodetermine a numeric value for any hydro‐

geophysical setting by using an additiveg p y g y g

model.

• This model is an open‐ended model allowing

the user for addition and deletion of one orthe user for addition and deletion of one or

more indicators.

•However, under normal circumstance, present

set of indicators should not be deleted and anyset of indicators should not be deleted and any

addition of the indicator would require re‐q

deriving of the weights and the classification

table.

Suggested System of Vulnerability 

gg y yEvaluation and Ranking

•The system of vulnerability evaluation and

ranking is developed by Chachadi (2001) is used

in the present study.

The most important mappable factors that controlp pp

the seawater intrusion are found to be (Chachadi,

2002):

1. Groundwater Occurrence (aquifer type;

unconfined, confined and leaky confined).

2 Aquifer hydraulic conductivity2.    Aquifer hydraulic conductivity.

3 Depth to ground water Level above sea

4 Di t f th i t i ti f th4 Distance of the point in question from the

shore (distance inland perpendicular fromshore (distance inland perpendicular from

Shore line))

5 I t it d f th i ti t5. Impact magnitude of the existing seawater

i t i i th ifintrusion in the area, if any.

6 Thickness of the aquifer (which is being6. Thickness of the aquifer (which is being

mapped)mapped).

Th GALDIT i f d f h•The acronym GALDIT is formed from the

highlighted and underlined letters of the factorshighlighted and underlined letters of the factors

for ease of reference.

•These factors, in combination, are determined

t i l d th b i i t d d tto include the basic requirements needed to

assess the general seawater intrusion potentialassess t e ge e a sea ate t us o pote t a

of each hydro geologic setting.

• GALDIT factors represent measurable

parameters for which data are generally

il bl f i t f ith tavailable from a variety of sources without

detailed reconnaissance.

• A numerical ranking system to assess seawater

intrusion potential in hydro geologic settings

has been devised using GALDIT factorshas been devised using GALDIT factors.

•The system contains three significant parts:•The system contains three significant parts:weights, ranges and importance ratings.

• Each GALDIT factor has been evaluated withEach GALDIT factor has been evaluated withrespect to the other to determine the relativei f h fimportance of each factor.

•The various parameters adopted in the

evolution of the present indicator tool include:evolution of the present indicator tool include:

(i)Identification of all the indicators influencing

the seawater intrusion –This task was through

extensive discussions and consultations with theextensive discussions and consultations with the

experts, academicians etc.

• The basic assumption made in the

development of the tool includes: the

bottom of the aquifer(s) lies below msl so

that the seawater can move inside thethat the seawater can move inside the

aquifer laterally.

• Any event of seawater moving inland and causingseawater mixing in the freshwater aquifers such asseawater mixing in the freshwater aquifers such asstorm surges and tsunamis, which normally move

i l d b i l lif i id d iseawater inland by vertical uplift, is not considered inthe present model.

• (ii)Derivation of indicator weights –Indicator weightsdepicts the relative importance of the indicator todepicts the relative importance of the indicator tothe process of seawater intrusion.

•After identifying the indicators, a group ofpeople consisting of Geologists hydro geologistspeople consisting of Geologists, hydro geologists,environmentalists, students, and in house expertswas asked to weigh these indicators in order ofimportance to the process of seawater intrusion.• The feedbacks from all such interactions wereanalyzed statistically and the final consensus list ofanalyzed statistically and the final consensus list ofindicators weights was prepared (Table 1).

Table 1  Indicator weights.

Factors Weights

d1. Groundwater occurrence  1

2. Aquifer hydraulic conductivity 3

3. Height of groundwater level above sea  level

4

4. Distance from the shore 4

5. Impact of existing status of seawater     1Intrusion

6.Thickness of aquifer being mapped 2

•The most significant indicators have weights ofg g

4 and the least a weight of 1 in a five‐point scale

indicating parameter of less significance in the

process of seawater intrusionprocess of seawater intrusion.

•As the indicator weights are derived afterg

elaborate discussions and deliberations among

the experts, academicians, researchers, etc., they

must be considered as constants and may not bemust be considered as constants and may not be

changed under normal circumstances.

(iii)Assigning importance rates to indicator(iii)Assigning importance rates to indicator

variables using a scale of 2.5 to 10 – Each of

the indicators are subdivided into variables

di h ifi d ibaccording to the specified attributes to

determine the relative significance of thedetermine the relative significance of the

variable in question on the process of

seawater intrusion.

• The important ratings range between 2.5, 5,

7 5 and 10 Higher value of importance rating7.5 and 10. Higher value of importance rating

indicates higher vulnerability to seawaterg y

intrusion.

(iv) Decision criterion – It is the total sum of

the individual indicator scores obtained by

multiplication of values of importance ratings

with the corresponding indicator weights.

Higher the values of importance ratings of the

variable, more vulnerable are the aquifers to, q

seawater intrusionseawater intrusion.

Indicator Descriptions

Indicator Descriptions

Indicator‐1: Groundwater occurrenceIndicator 1: Groundwater occurrence(Aquifer Type)

I t d t ll iIn nature, groundwater generally occurs in

the geological layers and these layers may beg g y y y

confined, unconfined, and leaky confined or limited

b b d i Th fby one or more boundaries. The extent of seawater

intrusion is dependent on this basic nature ofp

groundwater occurrence.

Therefore, in assigning the relative weights to

GALDIT t G h ld f ll t d thGALDIT parameter G one should carefully study the

disposition and type of the aquifers in the studydisposition and type of the aquifers in the study

area.

• The confined aquifer is more vulnerable due

to larger cone of depression andto larger cone of depression and

instantaneous release of water to wells duringg

pumping and hence scores the high rating

compared to other types of aquifers.

• In case of multiple aquifer system in an area,

the highest rating may be adoptedthe highest rating may be adopted.

Table 2 Ratings for Ground Water

Table 2 Ratings for Ground WaterOccurrence.

Indicator            Indicator variablesImportanceRatings

Confined aquifer 10

Un confined aquifer 7.5

Groundwater Occurence

Leacky confined aquifer5

Aquifer type Bounded aquifer(recharge and/or    im pervious 

b d li d ll l2.5

boundary alined parallel to the coast)

Indicator‐2: Aquifer hydraulic conductivity

•The parameter aquifer hydraulic conductivity is

used to measure the rate of flow of water in the

aquifer and hence to and fro from the sea in the

coastal area.

•By definition, the aquifer hydraulic conductivity is

the ability of the aquifer to transmit water.

•The hydraulic conductivity is the result of they y

interconnected pores (effective porosity) in the

sediments and fractures in the consolidated

krocks.

•The magnitude of seawater front movement isThe magnitude of seawater front movement is

influenced by the hydraulic conductivity of the

aquifer.

•For a given hydraulic head, a high value of

hydraulic conductivity of an aquifer leads to larger

inland movement of the seawater frontinland movement of the seawater front.

• The high hydraulic conductivity also results in

wider cone of depression during pumping and

may allow greater seawater intrusion if located

close to the coastclose to the coast.

Length of seawater intrusion in the coastal aquiferg q

•The ratings for the GALDIT parameter A, which

are modified from Aller et al. (1987), are given in

table 3.

Table 3 Ratings Aquifer Hydraulic Conductivity.

Indicator variables Importance

y

Indicator  (A)Indicator variables Importance

RatingsClass Range,m

Hi h < 40 10Aquifer hydraulic conductivity 

High < 40 10

Medium 10‐40 7.5y

(m/day) Low 5‐10 5

V low >5 2.5

•The aquifer hydraulic conductivity can be

estimated from pumping test data as well as from

litho logical logslitho logical logs.

•The well log data and porosity logs can also be

used to compute the aquifer hydraulic

conductivityconductivity.

Indicator‐3: Height of groundwater level above sea ele ation

sea elevation

•The level of groundwater with respect to mean•The level of groundwater with respect to mean

sea elevation is the most important factor in thesea elevation is the most important factor in the

evaluation of seawater intrusion in an area,evaluation of seawater intrusion in an area,

primarily because it determines the hydraulicp y y

pressure availability to push back the seawaterp y p

front.

•As seen from the famous Ghyben‐Herzberg

(1888 1901) relation for every meter rise of fresh(1888‐1901) relation, for every meter rise of fresh

water above mean sea elevation, a freshwater

column of 40 m is developed below it down to the

interface and vice‐versa.

•In assigning the ratings to the GALDIT parameter

L, the long‐term spatial variations of the

groundwater levels in the area need to be carefullygroundwater levels in the area need to be carefully

studied.

•Generally, the values pertaining to minimum

groundwater levels above sea (pre‐monsoon

d i M ) b id d thi ldduring May) may be considered, as this would

provide the highest possible vulnerability risk.provide the highest possible vulnerability risk.

• The ratings adopted for L are given in table 3

•Groundwater level data with respect to msl canGroundwater level data with respect to msl can

be obtained by establishing observation wells in

the area and measuring the pre‐ and post‐

monsoon water levels and reducing them with

respect to the mean sea levelrespect to the mean sea level.

Table 4 Ratings for height of ground water.

Indicator (L)Indicator variables Importance

Indicator  (L)RatingsClass Range,m

High <1.0 10

Height of ground waterlevel above msl (m)

g

Medium 1.0‐1.5 7.5

Low 1.5‐2.0 5( ) Low 1.5 2.0 5

Very low >2.0 2.5

Indicator‐4: Distance from the Shore

•The magnitude of the impact of seawater

i t i ll d i l dintrusion generally decreases as one move inland

at right angles to the shore and the creek. Theg g

maximum impact is witnessed close to the coast

and creeks under favorable hydro geological

di iconditions.

•Table 5 provides the general guidelines for rating of

the GALDIT parameter D assuming the aquifer isthe GALDIT parameter D assuming the aquifer is

under undisturbed conditions i.e. the groundwater

development in the area has not been significant to

offset the balanceoffset the balance.

• The value of importance ratings is assumed to

chan e linearl ith distance Dchange linearly with distance D.

• Data for parameter D can be computed using

the topographical/ cadastral or any surveyed

d t f th h i th hi h tiddata map of the area wherein the high tide

line for the coast has been demarcated.

Table 5. Ratings adopted for distance of thei t f h D

d ( ) d blImportance

point from shore D.

Indicator  (L) Indicator variablesImportanceRatings

Class Range (m)g ( )

Distance of the Very small <500 10

Small 500‐750 7 5point fromShore ( m)

Small 500 750 7.5

Medium 750‐1000 5

Far >1000 2 5Far >1000 2.5

Indicator‐5: Impact of existing status of SeawaterIndicator 5: Impact of existing status of Seawaterintrusion

•Some times the area under mapping is already

under water stress conditions and this stressunder water stress conditions and this stress

might have affected the natural hydraulic balanceg y

between seawater and fresh groundwater.

• This existing imbalance in the seawater‐

f h f h ld b d dfreshwater interface should be considered

while mapping the aquifer vulnerability towhile mapping the aquifer vulnerability to

seawater intrusion.

•Revelle (1941) recommended the ratio of Cl /[HCO+ CO3] as a criterion to identify the extent of[HCO+ CO3] as a criterion to identify the extent ofseawater intrusion into the coastal aquifers.•Chloride (Cl) is the dominant ion in the seawaterand it is only available in small quantities inand it is only available in small quantities ingroundwater while bicarbonate (HCO3), which is

il bl i l i i i davailable in large quantities in groundwater, occursonly in very small quantities in seawater.

• This ratio can be used while assigning theimportance rating for the GALDIT parameter I,importance rating for the GALDIT parameter I,provided the chemical analysis data is

il bl f th d i ti tiavailable for the area under investigation.

•In case such chemical data is not readily available,

then information gathered from the field surveythen information gathered from the field survey

and inquiries from the water users in the area canq

be used in assigning the importance rating for I.

•The information required for the above rating can

b th d f hi t i l t i i fbe gathered from historical reports, inquiry from

the local people, farmers, and chemical analysisthe local people, farmers, and chemical analysis

data.

Table 6 Ratings for impact status of

Table 6 Ratings for impact status of existing sea water intrusion.

Indicator variables Importance

Indicator  (I) RatingsClass Range of 

CI/(HCO3+CO3)Ratio in lpm in  groundwater

Impact t t f

High >2 10status of existing seawater

Medium 1.5 – 2.0 7.5

Low 1 – 1.5 5seawater intrusion Very low <1 2.5

Indicator‐6: Thickness of Aquifer being mappedIndicator 6: Thickness of Aquifer being mapped

•Aquifer thickness or saturated thickness of an

unconfined aquifer plays an important role in

determining the extent and magnitude of

seawater intrusion in the coastal areas.

•Keeping this as a guideline the ratings given in 

T bl 7 d d f i f ifTable 7 are adopted for various ranges of aquifer 

thickness T The aquifer thickness in a given areathickness T. The aquifer thickness in a given area 

can be obtained from litho logical logs and can also 

be deduced from carefully conducted vertical 

electrical sounding data.

Table 7 Ratings for Aquifer thickness 

Indicator variables ImportanceIndicator  (T )

Indicator variables Importance Ratings

]Class Range

Aquifer thickness

Large >10 10

Medium 7.5‐ 10 7.5Aquifer thickness(saturated ) in meters Small 5 – 7.5 5

Very small < 5 2.5Very small < 5 2.5

Computing of the GALDIT Index 

Each of the six GALDIT indicators has a pre‐

determined fixed weight that reflects its relative

importance to seawater intrusion Computing theimportance to seawater intrusion. Computing the

individual indicator scores and summing them and

dividing by the total weight as per the following

expression gives the GALDIT Index:

where, w = Weight of the indicator R = Importance rating of the ithR   Importance rating of the i

indicator

•Thus, compute the indicator score from hydro

geologic and geological information from the area

of interest and variables to reflect specificof interest and variables to reflect specific

conditions within that area.co d t o s t t at a ea

•This system allows the user to determine a

numerical value for any hydro‐geographical setting

by using this additive model.

• The “maximum GALDIT Index” is obtained by

b hsubstituting the maximum importance ratings

of the indicators as shown in next slideof the indicators as shown in next slide.

Max = {(W1)×R1+ (W2)×R2 + (W3)×R3 + (W4)×R4 + 

(W5) ×R5 + (W6)×R6}/ ∑w

= {(1)×10+(3)×10+(4)×10+(4)×10+(1)×10 

+(2) ×10}/ 15 

= 10

•Similarly, the “minimum GALDIT Index is

obtained by substituting the minimum importance

ratings of the indicators as shown below:ratings of the indicators as shown below:

• Min = {(W1)×R1+(W2)×R2+(W3)×R3+(W4)×R4+(W5){( ) ( ) ( ) ( ) ( )× R5+(W6)×R6}/ ∑w

= { (1)×2 5 + (3)×2 5 + (4)×2 5 + (4)×2 5+= { (1)×2.5 + (3)×2.5 + (4)×2.5 + (4)×2.5+ (1)×2.5 + (2)  ×2.5 }/15

=  2.5

•Therefore the minimum and maximum GALDIT•Therefore, the minimum and maximum GALDIT

Index varies between 2.5 to 10.

• The vulnerability of the area to seawater

intrusion is assessed based on the magnitude of

th GALDIT I dthe GALDIT Index.

•In a general way, lower the index less vulnerableg y,

is the area to the seawater intrusion.

Decision Criteria

•Once the GALDIT Index has been computed it is•Once the GALDIT Index has been computed, it is

therefore possible to classify the coastal areas

into various categories of seawater intrusion

vulnerability the range of minimum and

maximum GALDIT Index scoresmaximum GALDIT Index scores

(i.e. 2.5 to 10) is divided into 3 groups.( ) g p

•All the six indicates have four classes i.e. 2.5,5,7

and 10 as their importance ratings. Table 8 provides

the detailed classifications of vulnerability classes ofthe detailed classifications of vulnerability classes of

GALDIT Index.

Table 8  Vulnerability classes

Sr No GALDIT Index Range Vulnerability ClassesSr No. GALDIT Index Range Vulnerability Classes

1 ≥7.5 High Vulnerability

2 5 t 7 5 M d t V l bilit2 5 to 7.5 Moderate Vulnrability

3 < 5 Low Vulnerability

Application of

GALDIT Mapping

•The coastal tracts in India cover parts of Gujarat,

M h ht K t k K l T il N d A dhMaharashtra, Karnataka, Kerala, Tamil Nadu, Andhra

Pradesh, Orissa and West Bengal.Pradesh, Orissa and West Bengal.

• Besides the inherent ground water salinity in the

coastal tract, Sea water intrusion is also one of the

bl h lmajor problems in the coastal region.

•In certain areas problem of up coning of saline waterp p g

has also been reported due to overexploitation of

ground water.

• Problem of salinity ingress has been noticed in• Problem of salinity ingress has been noticed in

Minjur area of Tamil Nadu and Mangrol – Chorwad‐

Porbander belt along the Saurashtra coast.

• In Orissa, in an 8‐10 km. wide belt of

S b kh S l di B h i t f llSubarnrekha, Salandi, Brahamani out fall

regions in the proximity of the coast, theregions in the proximity of the coast, the

upper aquifers contain saline horizons

decreasing landwards.

I P di h i t f N li li it•In Pondicherry region east of Neyveli lignite

mines salinity ingress has also been observed.y g

• The inland ground water salinity in India occurs

mainly in the states of Maharashtra, Punjab,

Rajasthan Haryana Gujarat Karnataka UttarRajasthan, Haryana, Gujarat, Karnataka, Uttar

Pradesh, Delhi, Orissa and Bihar.

• The occurrence of inland salinity may be due to

over exploitation of ground water, use of

f d d lsurface water and ground water in complete

isolation characteristics of aquifer or someisolation, characteristics of aquifer or some

other reasons.

About 1.93 lakh sq.km area has been estimated

to be affected by saline water of Electrical

Conductivity 4000 μS/cm There are severalConductivity 4000 μS/cm. There are several

places in parts of Rajasthan and southernp p j

Haryana where EC values of ground water are

greater than 10000 μS/cm making water non‐

potablepotable.

• In some areas of Rajasthan and Gujarat

ground water salinity is so high that the wellground water salinity is so high that the well

water is directly used for salt manufacturingy g

by solar evaporation.

•The present study area forms part of the

coastal tract of Surat coast.

•The Tapi river estuary in the South and the•The Tapi river estuary in the South and the

Chapora River in the North form the hydrologicalChapora River in the North form the hydrological

boundaries of the study area.

• The map along with the location of watershed

l h his also shown in the Fig 1.

Fig.2 Map of study area

Fig.3 Singanpore weir, Surat, Indiag g p

Fig.4 Line Diagram

•The tidal waves intrude in the river up to

Singanpore weir The Singanpore weir wasSinganpore weir. The Singanpore weir was

constructed on River Tapi. The River Tapi meets

Arabian Sea downstream of a Singanpore weir at a

distance of 2 km, from Singanpore weir.

• The tidal effect of sea reaches up to

Singanpore weir The weir was constructed inSinganpore weir. The weir was constructed in

1995.

• The area is mainly covered by laterites and

river alluvium and at some places the met

sediments are exposed in the northsediments are exposed in the north.

•In the study area 10 groundwater monitoring

wells have been established and monthlywells have been established and monthly

groundwater levels have been recorded in allgroundwater levels have been recorded in all

these wells for last 15 years.

• The aquifer is mainly shallow unconfined in

b h ll llnature occurring both in river alluvium as well

as laterites exposed in the low lying areas Theas laterites exposed in the low lying areas. The

plateau laterites generally lack water table

and at some places the water table is very

deep.

•The river alluvium is highly drainable whereas

the laterites are not The GALDIT scores at eachthe laterites are not. The GALDIT scores at each

of the groundwater monitoring wells were

computed for the study area.

•The map derived for this study area is shown in

the fig 1the fig.1.

•The table 10 presents the details of wells andp

their distances from sea shore and weir.

F ll i d t ll t d f GWRDCFollowing data were collected from GWRDC:

Groundwater data from Gujarat Water Resource

D l t C ti (GWRDC)Development Corporation (GWRDC)

Water quality parameters: Cl,TDSq y p ,

• Depth of the Well (TD)

• Static Water Level (SWL)Static Water Level (SWL)

For pre‐monsoon and post monsoon period of  f hof      the years

The data ranges used for present study are asg p y

shown in table 9 and location details of wells areshown in table 9 and location details of wells are

presented in table 10presented in table 10.

Table.9 Data Range

Rise/Fall CI R.W.L S.W.L R.W.L Rise/Fall Rise/Fall Rain fall Name of

well Year

Pre-Monsoon (May) Post-Monsoon (Oct)

S.W.L T.D.S

Hazira Well 1990-99 4.35-2.85 4360-410 2136-120 4.99-3.49 4.15-1.1 6.74-3.69 0.73--0.51 1.9--1.1 2.48-0.55 2169-659Dumas Well 1970-99 7.1-0.93 1790-146 664-208 0.88--1.47 6.2-3.4 2.23--0.57 2.2--1.2 2.2--2.25 2.7-0.1 2299-565Piplod Well 1970-2000 7.7-4.6 4430-740 3320-168 2.49--0.81 6.48-3.23 3.49-0.61 0.8--1.54 2.23--1.52 3.2-0.3 2886-616Rander Well 1970-2002 8.7-3 1750-670 544-88 4.1--1.6 7.7-1.2 0-0 5.9--0.6 2.55--4.08 2.8--5.13Sachin Well 1985-2003 7.9-3.95 2570-1800 840-320 13.49-9.34 6.47-2.98 14.26-10.77 1.9--2.35 2.65--2.85 4.02-0.13 2298-528Jahangirabad Well 1990-2006 5.1-3.25 2700-570 1523-160 8.63-6.78 3.8-1.05 10.83-6.8 1.1--0.6 3.28--1.33 3.15-0.02 2169-528Olpad Well 1990-2007 2.55-1.15 4310-1540 1840-392 13.68-12.33 1.84-0.85 14.03-13.04 1.35--0.65 0.69--0.64 1.56-0.1 1421-422Amroli 1990 2004 15 1 10 2 2350 1090 872 256 1 7 6 6 13 05 8 9 0 03 4 55 2 35 2 35 2 7 2 07 0 0Amroli 1990-2004 15.1-10.2 2350-1090 872-256 .-1.7--6.6 13.05-8.9 .-0.03--4.55 2.35--2.35 2.7--2.07 0-0Kathor Well 1985-2007 13.35-11.49 850-90 152-64 12.52-3.87 11.52-4.7 0-0 11.22-5.9 8.45--8 3.32--3.77Vav Well 1990-2007 8.15-3.6 1940-890 980-64 31.82-26.92 4.35-1.9 33.52-27.07 2.55--3.13 4.95--5.8 5.1--1.18 2476-495

Table.10 Observation well details

Results and Discussion

The GALDIT index is computed using followingThe GALDIT index is computed using followingconsiderations and presented in table 11.

Unconfined aquifer is observed throughout thestudy area hence, the weight 7.5 for G is consideredfor all wells.

Depths above mean sea level were computedDepths above mean sea level were computedfrom the well data.

Distance from the coastline was calculated usingthe satellite images.

Impact of existing ground water intrusion has beenconsidered only in case of two observation wellsconsidered only in case of two observation wellswhich are close to sea shore.

Thickness of aquifer was taken equal to the depthof the well as the wells penetrate full length of theaquifer.aquifer.

The analysis of results suggest that the Dumas

well and Hazira well which are on the down streamwell and Hazira well which are on the down stream

side of weir and near to seashore have high

vulnerability to sea water intrusion.

Table 11.  GALDIT index for wells

Sr No Well NameDistance from    the shore

Computed GALDIT Index

1 Hazira well 1.2 km 6.6

2 Dumas Well 0.5 km 7.14

3 Piplod Well 7.6 km 7.11

4 R d W ll 5 7 k 6 64 Rander Well 5.7 km 6.6

5 Jahangirabad Well 8 km 6.6

6 Amroli Well 18 km 5.00

7 Olpad Well 20 km 7.077 Olpad Well 20 km 7.07

8 Sachin Well 10 km 6.59

9 V W ll 21 k 3 329 Vav Well 21 km 3.32

10 Kathor Well 25 km 4.38

Conclusion

•Once the GALDIT index has been computed, it isp ,

possible to identify areas that are more likely to be

susceptible to sea water intrusion than other areas.

•In the present study the area down stream of the•In the present study the area down stream of the

Singapore weir is more susceptible to sea waterg p p

intrusion potential.

• It has been confirmed by field observation that

the salinity in this area has been increasedthe salinity in this area has been increased.

•To control further sea water intrusion and protect•To control further sea water intrusion and protect

ground water being more saline Surat Municipal

Corporation has proposed to construct Balloon dam

(storage dam) on the down stream side of the weir

about 4 5 kms away from Singapore weirabout 4‐5 kms away from Singapore weir.

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Th k•Thank you