seepage investigation by using isotope and geophysical

BD0510005

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Seepage Investigation by Using Isotope andGeophysical Techniques in Gumti Flood

Embankment/Dyke, Comilla

!N. Ahmed, 2B. G. Wallin, lR. K. Majumder,1M. Mikail and 3M. S. Rahman

'ISOTOPE HYDROLOGY DIVISION (IHD)

AL ATOMIC ENERGY AGENCY (IAEA), VIE3NUCLEAR AND RADIATION CHEMISTRY DIVISION (NRCD)

INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA), VIENNA, AUSTRIA

INSTITUTE OF NUCLEAR SCIENCE & TECHNOLOGYATOMIC ENERGY RESEARCH ESTABLISHMENT

GANAKBARI, SAVAR, P.O. BOX NO. 3787, DHAKA-1000, BANGLADESH

June2004

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TABLE OF CONTENTS

Abstract

2

2

2

3345577

8

11

11

12

13

13

15

1717

19

14. Resistivity Imaging Survey 21

14.1 Principles of Electrical Tomography 21

14.2 Techniques Applied in the Field 22

14.3 Observations from the Surveyed Image Data 22

15. Impacts of the Study and its Management Implications 26

16. Conclusions 27

17. Recommendations 28

Acknowledgements 28

References 29

ANNEXURE: Data of Apparent Resistivity and Self Potential Measured by SARIS A-lSystem

(0

1.

2.

3.

4.

5.

5.1

5.2

5.3

5.4

5.5

5.6

6.

7.

8.

9.

10.

11.

12.

13.13.1

13.2

Introduction

Problems Encountered in Gumti Dyke

Objectives

Study Area

Site Description

Physiography

Hydrometeorology

Hydrology

Geological Setting

Stratigraphy

Lithology

Water Level of Gumti River

Sediment Discharge

Historical Trend in Groundwater Table

Rainfall, Surface Water and Groundwater Relationship

Methodologies

Field Reconnaissance Survey and Observations

Sampling and Analysis

Results and Discussion

Hydrochemical

Isotopic

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ABSTRACT

Gumti Flood Control Embankment/Dyke is vital for irrigation water supply and flood control. Waterseepage/leakage and slope failures are the major issues in Gumti earthen dyke. The distinct seepageand slope failure zone were observed at three places (Farizpur, Kathalia and Ebdarpur) along thecountryside of left dyke.

The isotopic technique has been integrated in the conventional hydrologic investigations. The isotopemethodology works essentially by developing a characteristics pattern of the isotopic composition toidentify the sources and flow dynamics of seeping/leaking in the dykes. Two sampling campaignswere conducted; one was on October, 2002 and the other was on July, 2003; near the seepage/leakagesite for chemical analysis and stable isotopic analysis (2H & I8O). Both samplings were done afterrecession of peak water level in the Gumti river. Interpretation of the hydrochemical data implies thatthe groundwater near the investigated seepage zones is Na-Ca-HCO3 type and the river water is Ca-Mg-HCO3 type. The chlorides content of both groundwater and river water are found mostly similar,indicating mixing between the two water system.

The stable isotopes (2H & I8O) of groundwater fall on the Meteoric Water Line, ranging the oxygen-18 values from -4.98 to -5.46 per mil and deuterium values from -30.0 to -33.6 per mil. It indicatesthe recharge from the river water during peak water level in the river Gumti. On the otherhand, thestable isotopes of the Gumti river show some evaporation effect, which might have occurred due tostagnation of flowing water in the river. The oxygen-18 and deuterium values for river water rangefrom -3.61 to -4.43 per mil and from -22.30 to -28.48 per mil respectively. These isotope resultsreflect the hydraulic connectivity between the river water and groundwater through the base of dyke.

The earth imaging resistivity survey was carried out in the dry period along the four above mentionedareas of the Gumti dyke for localisation of seepage, leakage, slope failure and week zones of earthendyke. The resistivity sounding has provided information on active pathways of seepage and claylayers along the seeping zone of the dyke. The images show the demarcation of loose zones havinghigh resistivity and underlying silty clay composition of base of the dyke having low resistivity. Justafter the piping and slope failure on the dyke, gunny bags containing compact silty and sandy claywere dumped and consequently these show the high resistivity value.

(ii)

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1. Introduction

During the year 1964-65, Gumti Flood Control and Irrigation Project was undertaken by thegovernment and construction work was completed by 1978. The main objective of the project is toprotect the north-west and south-west of Comilla basin from the flash flood in the Gumti river and tosupply water for irrigation. Under this project, 32 km of dyke on left bank from Katak bazar toJafarganj and on the right to Bishnapur were constructed. Because of no dyke on the downstream ofJafarganj and Bishnapur every year flood water submerged the vast areas on both banks of the river.To protect these areas from floods Gumti, phase-I sub-project under FCD-3 was started in 1984-85.Under this project, 44 km of dyke from Jafarganj to Elliotganj on left bank and 31 km of dyke fromBishnapur to Puniaton on right bank were completed in 1991-92 [I]. Now, the total length of the dykeis 70 km. The height of dyke varies from 10.0m to 5.0m in the direction upstream to downstream ofGumti river.

Due to the construction of dyke on both banks covering almost the whole length Gumti river, therecreated a severe confinement effect on flash flood. This became more critical due to construction ofseveral bridges by different agencies at different locations across the Gumti river. There are someancillary regulators and cross-drainage structures within the dyke. The bed and flood plains of theGumti river also gradually started rising because of heavy siltation. As a result serious confinement offloodwater within the dyke took place. For this reason, each and every year, the dykes are threatenedby the floods. Sometimes, it overtops and breaches at different locations, flooding vast areas. Toprevent this unfortunate flooding the whole dyke was reconstructed for rehabilitation. Due to flashynature, the peak water level of the Gumti river exists for short period, such as two or three days,following the high monsoon rainfall in the month June-July. During the flash flood time, the Gumtidyke experiences a serious leakage/seepage problem through the body and foundation of the dyke insome particular locations.

Under the framework of RCA regional activity, the research project RAS/8/093 entitled "Use ofIsotopes in Dam Safety and Dam Sustainability" was executed by Isotope Hydrology Division,Institute of Nuclear Science & Technology, Atomic Energy Research Establishment, Savar, Dhaka.The name of thematic area is "Seepage investigation by using isotope and geophysical techniques inGumti Flood Embankment/Dyke, Comilla".

The investigation of origin and dynamics of groundwater in the vicinity of dyke is a majorrequirement to identify the leakage/seepage problems. Seepage/leakage of water from dykes mayoccur through the foundation, body or through natural geologic formations in which theserivers/reservoirs lie. The losses may be in the form of general seepage usually covering a wide area orthey may be due to specific leakage flowpaths. In most cases, local groundwater and river waterrelated to the leakage/seepage emerge in the country side of dyke with a complex mixing pattern. Theproper characterization of flow rate and flow patterns of water derived from the river requires the useof several hydrological techniques, including environmental isotopes and artificial tracers.

Gumti Dyke is vital for flood control, leading to the protection of vital installations - cantonment,Comilla city, industries, Asian highway, national highway, growth centers, agricultural lands, humanlives and livelihood. Water seepage, leakage and slope failures are the major issues in the Gumtiearthen dyke, which requires close monitoring observation. In consultation with Bangladesh WaterDevelopment Board (BWDB), the Gumti Flood Control Embankment/Dyke of Comilla has beentaken up as a case study of the research activity to find out the leakage/seepage or slope failure zonesof the dyke by applying environmentally safe stable isotope techniques along with contemporaryconventional methods. (BWDB) worked in the project as end user group.

Integration of isotope techniques in the hydrogeological characterization work in the study areaprovides the required information rapidly and at a much lower cost than possible with the non-isotopictechniques alone. The isotope methodology works essentially by developing a characteristics pattern

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of the isotopic composition to identify the sources and flow dynamics of seeping/leaking in the dykes.The isotopic technique has been integrated in the conventional hydrologic investigations.

The following works were carried out in the three distinct locations of seepage and slope failure zonesof the dyke, namely, Farizpur, Kathalia and Ebdarpur; (i) chemical and stable isotopic analyses (2H &I8O) of groundwater and river water near the seepage/leakage site and (ii) resistivity imaging surveyfor investigation of leakage/seepage in the dyke.

2. Problems Encountered in Gumti Dyke

The following major problems are encountered in Gumti dyke.

- Piping through the dyke toe and body. This is thought to be associated with a rapid increase ofwater level of Gumti river, derived from a flash flood situation during the monsoon.

- Slope failures on the countryside of the dyke. This is thought to be associated with thedevelopment of excessive leakage through the embankment foundation.

- Blow out, which is thought to occur due to high uplift water pressures on the riverside faces of theembankment.

- Due to high siltation in the river bed, the conveyance capacity of Gumti river is reduced and itfails to meet the extreme flood requirement.

3. Objectives

The overall objective of the project is to promote the use of environmentally safe isotope techniquesin the management of dykes and to protect the land from the flash flood, inter alia, augment thesustainable development. The specific objectives are enumerated as below:

• To integrate the isotope hydrology techniques with contemporary conventional methods ininvestigating the leakage/seepage pathways through and around the dykes,

• To establish the isotopic techniques, using environmental isotopes and artificial tracer forproblem identification, and

• To identify the weak (clay layer) or slope failure zones within the dyke using resistivity imagingsurvey.

Moreover, the benefit as identified for the end user from this project is to enable the planners anddecision makers to properly manage and protect the dyke by isotope applications.

4. Study Area

The study area is located some 60 km east of the Dhaka city. It is roughly a square of 50 x 50 kmlying between longitude 90°45'E to 91°15'E, and latitude 23°28'N to 23°38'N. The area is bounded bythe Meghna river to the west; the Indian border and Tripura Hills to the east; and Dhaka-Chittagongnational highway road to the south. The Gumti embanked from upstream of Comilla, almost to itsconfluence with the Meghna. The location map of study area is shown in Fig. 1.

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; LEOENO

IB fl«(d»kr

! u ISM* ttaiil-]u*rt<r*i O I > W h«»rt

Location Map of Gumti Embankment

AMidi

Fig. 1. Location Map of the Study Area

5. Site Description

5.1 Physiography

The topography of the project area has irregular micro reliefs on the different physiographiccondition. The physiographic condition is broadly divided into flood plains, piedmont plains, hills andterrace. Flood plains cover most of the area and include ridges and inter-ridge depressions along theMeghna and smoothed-out plains of very low relief, with low broad ridges and extensive shallowbasins in the central part of the area. The remaining minor area is situated on the piedmont plains,hills and terraces along the eastern edge of the area to the Tripura Hills. The terrain of the project areais generally flat with gentle undulations in parts of the area. Elevations vary between 2.4 mPWD and5.5 mPWD, despite the fact that the area is nearly 140 km from the coast. The contours of the projectarea are shown in Fig. 2.

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Fig. 2. Contours of the Project Area

5.2 Hydrometeorology

The climate station of relevance to the study is at Comilla. The daily rainfall and temperature data arecollected by BWDB at station no. R-356, Comilla. The location of rain gauge (R-356) close to thestudy area is shown in Fig. 1. The study area experiences a typical monsoon climatic, with hot wetsummers from May to September and cooler dry winters. Rainfall in the early and late monsoonperiods is highly variable. The mean annual rainfall is about 2365 mm. Evapotranspiration exceedsrainfall for the months of November to March. The peak rainfall months are June, July and August.During these months, about 55 - 60% of the annual rainfall total can be expected |21. The rainfallpattern in scries for the consecutive three years 2001, 2002 and 2003 are described in Sec. 9.

Mean daily temperatures are fairly constant between the months of April and September, and showlittle variation across the region, being about 28°C. From October, temperatures begin to decline, andmean daily temperatures reach a minimum of about I9"C in January. In April, maximum dailytemperatures in the region can often exceed 35°C. Relative humidity is high throughout the year.Maximum values occur in July, when the mean is about 87.5% throughout the region.

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5.3 Hydrology

The project area is drained by the upper Meghna river. Other significant rivers are the Gumti river andthe Titas. Meghna-Titas-Gumti river system is shown in Fig. 3. The Gumti, a perennial river andflashy in nature, originates from the Tipperan hilly region of India and flows into territory ofBangladesh through Katak Bazar border. The river has its course on the northern side of Daudkandi-Comilla road. The Gumti carries the direct precipitation runoff to the Meghna from the catchments onboth sides of the border. In the western part, the rivers generally have flat slopes and come under tidalinfluence. In the eastern part, the channels draining the Tripura hills (e.g. Gumti and Salda) are steeperand more liable to flash flooding. The Gumti river is embanked on both banks from the Indian border(Chainage 0.0 km) to 70 km downstream at Gounpur near its outfall. The dykes were built in theperiod 1983-1992 under the Gumti Phase-I Flood Control and Drainage project. Flash flood in theGumti river draining the Tripura hills to the eastern part of the project area can cause serious damage.During times of flood, water levels in the Gumti are significantly higher than the surrounding land.The maximum discharge passing through the river is normally 500-600 mVsec [1]. During very highflash floods breaches of the dyke have occurred in 1988 and 1993.

Fig. 3. Meghna-Titas-Gumti River System

There is a heavy sediment load coming annually into the east of the area from the Tripura Hills inIndia. As a result, the conveyance capacity of the Gumti river is reduced. This makes annualmaintenance of khal excavation in the area expensive.

5.4 Geological Setting

The study area is located on an extensive alluvial plain of quaternary sediments laid down by theGanges-Brahmaputra-Meghna river system, and known as the Bengal Basin. It is probable that10,000-12,000m of mainly unconsolidated sediments of tertiary to recent age exist beneath the projectarea [2]. The basin is bordered to the north by the Himalayas and the Shillong Massif, to the west by

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the Indian Shield and by the Arkan Chin Massif to the east. A geological map of the study area isshown in Fig. 4.

The study area is an active alluvial flood plain of low elevation within which approximately 90% ofthe area is below 5m, and just over 60% is less than 4.25m. Within the area an extremely gentletopography can be identified with separate tracts of land sloping in different directions towards themain rivers. The area is dominated by lower elevation cultivated land, much of which is susceptible toflooding, particularly in the eastern part of the dyke. There are no faults and folds in the study area,which can be regarded as being hydrogeologically significant.

9:" 15'

* •—^ \ S .

Terrace and meander deposits

Tippero surface

Older alluvial deposils

Fig. 4. Geological Map of the Study Area

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5.5 Stratigraphy

The stratigraphy of the study area is summarised in Table-1. The sedimentary units exposed at thesurface become progressively older away from the Meghna river towards the Indian border. Theyoungest sediments are the terrace and meander deposits, which are recent in age. These sedimentscontinue to accumulate from detritus deposited by the main rivers, particularly on the flood plain ofthe Meghna itself.

Late pleistocene to early recent sediments, referred to as the Tippera surface, occupy slightly moreelevated land in the central and eastern parts of the project area. These sediments were laid down byan ancestral river system and have subsequently been uplifted. Little active deposition takes place onthe Tippera surface, as indicated by the slightly compacted nature of the sediments.

Older pleistocene, alluvial deposits fringe the extreme eastern part of the project area adjacent to theIndian Border. Like the Tippera surface, these sediments have been uplifted and are at a marginallyhigher elevation than the recent Meghna floodplain deposits. The Pleistocene units arecharacteristically oxidized to a red/tan colour and are further compacted.

Table 1. Stratigraphy of the Study Area |Source: MPO, 1984]

Age Member Description

Recent Flood Plain Deposits Loosely compacted clay, silt and sand, dark greyin colour, unconsolidated, with high water contentand containing organic matter.

Early Recent Tippera Surface Similar to the above, but slightly more compactand oxidized, and slightly elevated with respect tothe Recent flood plain deposits.

Younger Pleistocene Older Alluvium Similar to the above, but conspicuously red/tancolour due to oxidizing, and contain ferruginousor calcareous nodules. Elevated and consolidated.

Older Pleistocene Dihingh/Dupitila Sands, silts and clays with nodules and petrified(Calunai Hills) wood fragments.

The older sediments are more compact and oxidized. The compaction is due to increasedconsolidation with age, and the oxidation is due to exposure of the sediments to aerobic conditions ator near the ground surface. The younger deposits are noticeably less compact and grey in colour bycomparison.

5.6 Lithology

The Table-2 shows the lithological distribution near the seepage zones. The location of the lithologyis at Kharera, Union- Baksimail, Thana- Burichang. It consists of a range of sediments from clay tocoarse sand, with occasional gravel. As would be expected from a major deltaic river system, thegeometry of individual units is complex. Generally, there is a tendency for fining-up of the sequence,with clays or silly clays commonly occurring at the surface and medium to coarse sands in the 70-180m zone.

The source of information is from BWDB exploratory wells. The lithological interpretation is directedtowards records of the occurrence of particle size, on a percentage bases. Because the samples aretaken from reverse circulation, open-hole drilling, and may be washed prior to recording, theoccurrence of finer particles may be underestimated, particularly clays.

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Table 2. Lithology of a borehole (ID: GL1918001) near the seepage zone [Source: BWDBj

Depth(m)

0.00-14.64

14.64-44.83

44.83-53.38

53.38-61.31

61.31 -61.9261.92-83.57

83.57-85.40

85.40-97.60

97.60-98.5198.51 -154.94

154.94-184.52

Thickness(m)

14.64

30.19

8.55

7.93

LithologicalSymbol

^ ^ ^ ^ H '.. .: .: .. ' '•0.61 ^ ^ ^ ^ ^ H21.65

1.83

12.20i ,;;,,,;•;, ,

0.91 ^ ^ ^ ^ ^ H56.43

29.58

.:„ , j

Lithology

Light brown clay

Light grey to light brown fine sand, very finesand, medium sand with mica and clay lenses.

Yellowish brown very fine sand, find sand withmica and silt.

Grey fine sand, very fine sand mixed with siltand mica.

Grey clay and very fine sand with gravel.Grey to light brown fine sand, very fine sand,medium sand with minor amount of mica andsilt.

Grey coloured medium sand, fine sand andvery fine sand with mica.Light grey to grey coloured fine sand, very finesand mixed with silt and mica.

Grey clay, silt with very fine sand and mica.

Grey to light grey fine sand, medium sand, veryfine sand with silt and mica.

Grey coloured medium sand, fine sand, veryfine sand, course sand with minor amount of siltand mica.

6. Water Level of Gumti River

The location of river water level recording station (WL-110) close to the study area is shown in Fig.1. The water levels in Gumti river have been presented in two different ways as follows:

(a) Hydrograph of water levels(b) Long profile of water levels

A series of concurrent hydrographs plots (Fig. 5) for the year 2001, 2002 & 2003 have been preparedfor the water levels at Comilla station (WL-110). The highest water level in the consecutive years2001, 2002 & 2003 are recorded 11.34 mPWD (on 09-06-2001), 11.512 mPWD (23-07-2002) &12.684 mPWD (01-07-2003) respectively. So, the peak water level usually occurs in July or Augustand it remains for a very short time due to flashy nature of the Gumti river. During flash flood, bothdischarge and velocity of the flowing water are tremendous, and water level rises very rapidly.

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WL=12.684 mPWDon 01-07-2003

Data Source: BWDB

WL=11.512 mPWDon 23-07-2002

d CN O CDO * - * - 3 2

tfs v> in t/>tiO

5 S tTime (Day-Month)

Fig. 5. Hydrographs of River Water Level Monitoring Station near seepage investigation area

The NAM (Nedbor-Afsramnings-Model) rainfall-runoff simulation model and hydrodynamic model forthe Comilla station was performed by the Institute of Water Modelling (IWM) for the historical periodfrom 1965 to 2000. This simulation model was calibrated against the monsoon of 1982, 1983, 1988,1993 and 1999, since these years were considered as the design event years for the dyke. The frequencyinalysis on simulated annual maximum water levels were performed by using Generalised ExtremeValue (GEV) distribution to obtain the water levels for 50 year return periods. Considering the 50-yeariesign event of the dyke, it is found that the simulated highest water level is reflected for the year 1983.The water level profile for the simulated and recorded maximum water levels are shown in theongitudinal section of Gumti dyke in Fig. 6.

— i — Simulated Max WL on 06-08-1983

Left Embankment

- - - Right Embankment

-~B— Recorded Max WL on 09-06-2001

— e — Recorded Max WL on 23-07-2002

o- Recorded Max WL on 01-07-2003

Dab Source: BWDB & IWM

H00

5"Q.

12 00 £

>~i

10 00 «u

i8.00

80000 70000 60000 50000 40000 30000 20000 10000 0

Distance (m)

Fig. 6. Gumti Dyke and Water Level Profile

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The water level station (WL-110) is at Ch. 8000 m. It is a non-tidal river. The vulnerable sections areobserved between Ch. 10000 m and Ch. 25000 m. The river cross section alongwith dyke sectional dataas surveyed by IWM were collected for the three chainages namely, 16631 m, 19839 m and 21950 mvicinity to the detected seepage zones. The different water level conditions in these three cross sectionsare shown in Fig. 7(a), 7(b) and 7(c).

16

14

12

~ 10

3•aa>o•oa>DC

13.484 mPWD (1983)Left

EmbankmentRightEmbankment

Data Source: BWDB & IWM

—Simulated Max WL on 06-08-1983

— Recorded Max WL on 09-06-2001

• Recorded Max WL on 23-07-2002

—Recorded Max WL on 01-07-2003

50 100 150 200 250 300 350

Distance (m)

400 450 500 550

Fig. 7(a). Cross Section and Water Level at Ch. 16631 m

600

14

12

10a.E

I

13.034 mPWD (1983)

Embankment«


Simulated Max WL on 06-08-1983 [ j

Recorded Max WL on 09-06-2001 ,1

— - Recorded Max WL on 23-07-2002

Recorded Max WL on 01-07-2003

100 200 300 400 500 600 700

Distance (m)

800 900 1000 1100

Fig. 7(b). Cross Section and Water Level at Ch. 19839 m

10

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14

12

10

12.911 mPWD (1983)

11 203mPWD(2003)

9.859 mPWD (2001)

RightEmbankment I


-Simulated Max WL on 06-08-1983

-Recorded Max WL on 09-06-2001

— - Recorded Max WL on 23-07-2002

-Recorded Max WL on 01-07-2003

50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

Distance (m)

Fig. 7(c). Cross Section and Water Level at Ch. 21950 m

The highest recorded water levels for the year 2001 and 2002 were almost similar and well below thedyke top. The highest recorded water level for the year 2003 is greater compared to the year 2001 and2002. The difference in water level is almost 1.26 m. These three cases of water levels are equallysusceptible to dyke failure, as investigated during survey and sampling in different seasons. Duringreconnaissance survey in the post monsoon period of the year 2002, the piping through the dyke toe andbody and the slope failure at the country side were observed. On the otherhand, severe slope failurewas observed near the section at Ebdarpur just after receding of peak water level on July 2003.

7. Sediment Discharge

There is a heavy sediment load coming annually into the east of the area from the Tripura Hills inIndia. The availability of sediment discharge data for Gumti river is quite limited. Under the GumtiPhase-II Sub-project Feasibility Study, the annual sediment yield from the Gumti was estimated to be770 tonnes/km2/year. For smaller catchments draining from the Tripura Hills, sediment yields couldbe in excess of those estimated for the Gumti. The composition of Gumti sediment is 700tonnes/km2/year of silt, and 70 tonnes/km2/year of sand [1].

8. Historical Trend in Groundwater Table

As a part of regular monitoring work by BWDB, the depths to groundwater are measured in theobservation well (COM-008) situated in the village named Kala Kachua, Thana- Burichang. Thelocation of groundwater monitoring station (COM-008) close to the study area is shown in Fig. 1. Thedepth of the observation well is 26.83 meter.

Groundwater flow occurs dominanlly from east to west. Generally, the hydraulic gradients are lowand lateral groundwater flow must be quite slow. The historical groundwalcr hydrograph (Fig. 8)shows that the aquifers are fully recharged every year and the broad monsoonal peaks of thehydrograph indicates that there are usually several months of'rejected recharge'. Natural recession ofgroundwater continues upto March or April. There is no systematic long-term water table variations,but seasonal fluctuations are due to dry and wet seasons. The depth to water is found to be within 0.50to 6.0 m bgl (below ground level).

II

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Year. 1977-2003

Stn. ID-COM008EGL = 7 01 mPWDPH = 0 46 m

Vill Kala Kachua, Thana: BurichangWell Depth = 26.83 m

- r-- co co a> o c NMD(0000)0)OOrT-rN(>j*rf* «W* ^ n «^V ri^ A t «V« fYl ^V^ ^V> ^ W ^4X V̂Ki

5 Z -

Time (Date)

Fig. 8. Hydrograph of Groundwater Observation Well (Data source: BWDB)

9. Rainfall, Surface Water and Groundwater Relationship

The study area falls into the humid area where the groundwater maintains the base flow of streams byseepage into stream channels. The long term hydrographs of surface water and groundwater, andrainfall histogram are drawn (Fig. 9) using the water level of piezometric well (Well ID. COM-008),the corresponding river stages (Stn. No. WL-110) and rainfall (Stn. No. R-356) data for the year2001-2003.

150

13 5

120

105

90

^ • R a i n f a l l at ComiHa (R-356)

River WL al Comilla (WL-110)

- e — Groundwater Level al Kala Kachua (COM-008)

Data Source: BWDB

2000

1800

1600

1400

1200

Time (Month-Year)

Fig. 9. Relationship between rainfall, surface water and groundwater at Comilla

12

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The hydrograph of representative observation well illustrates the behaviour of aquifer. In the wetseason upper aquifer is recharged vertically by rainwater and water level rises in the piezometer. FromFig.5, it is seen that water level fluctuations in the piezometer follow that of the river and thegroundwater level of the upper aquifer is lower compared to that of river throughout the year.Maximum water table elevation is 6.00 mPWD and minimum is 1.0 mPWD, whereas river waterelevation is maximum 12.7 mPWD and minimum 7.0 mPWD. So the aquifer is gaining waterthroughout the year from the river. Hydraulic continuity exists between surface water andgroundwater system and a relatively small volumetric transfer occurs due to low hydraulic gradientand low permeability in the surface layers.

10. Methodologies

Within the study plan the following methodologies were followed for delineating the hydrogeologicalfeatures and assessing the seepage/leakage problems.

(a) Desk Study: It included collection of background geology, hydrogeology, rainfall data, dailyrecorded water level data of Gumti river, adjacent groundwater level data of observation well,georeference data of Gumti dyke, cross sectional data of dyke & river, base map of the study area, andevaluation of analytical results and resistivity imaging survey.

(b) Field Survey and Sampling: It included reconnaissance surveys, seepage point inventories, andcollection of water samples from the various sources for chemical and isotopic analyses. On sitemeasurement of the physio-chemical properties (such as pH, temp, EC and HCO3') of well and riverwater were performed. Resistivity imaging survey was conducted on the berm portions of dyke.

(c) Laboratory Analysis: The major cation concentrations (Na\ K+, Ca+2 and Mg+2) were analyzed byflame atomic absorption spectrophotometer (AA-6800, Shimadzu) using acetylene and air gasmixture, following the manufacturer's recommendations with only slight modification. Calibrationcurves were plotted by using the commercial standards (Wako Pure Chemical Ind., Japan). The majoranion concentrations (Cl", SO4'

2 and N(X) were determined by standard methods (APHA, 1995) usingan UV-VIS spectrophotometer (UV-2401 PC, Shimadzu). The stable isotope analyses were performedin the Isotope Hydrology lab of PINSTECH, Pakistan.

11. Field Reconnaissance Survey and Observations

On 28 - 29 Sept. 2002, BAEC and BWDB jointly performed the reconnaissance survey and surfaceinvestigation of leakage/seepage points in Gumti Flood Dyke. The reconnaissance survey was carriedout along the left bank dyke of Gumti river starting from Katak Bazar to Jafarganj having length about37 km. The height of the dyke varies from 10.0m to 5.0m in the direction upstream to downstream ofGumti river. Typical cross section of the Gumti dyke is given in Fig. 10. The distinct seepage andslope failure zone were observed at three places (Farizpur, Kathalia and Ebdarpur) along thecountryside of dyke. All the observed seepage zones are protected by providing gunny bags with sandfilling on the slope and bamboo piling on the toe of dyke

GL

Fig. 10. Typical Cross Section of the Gumti Dyke

At Farizpur area (23°29.565' N & 91° 07.028' E) the seepage zone is about 120 ft long and at theseepage zone, a portion of soil has been eroded and slightly soggy. The height of the dyke at the

13

1NST-98/IHD-1

seepage zone is about 30 ft with distinct berm. There are borrow pits adjacent to the toe of the dyke.Kathalia seepage zone (23°30.853' N & 91° 06.917' E) is about 100 ft long along the country-side ofthe dyke. At this seepage zone the height of the dyke is about 25 ft and this zone is about 200 ftsetback from the river. Ebdarpur (23°31.607' N & 91° 05.882' E) seepage zone is about 140 ft longalong the country-side of the dyke. A localized slope failure line is observed at this seepage. The slopefailure line is crescent shaped and more or less 25 ft long and 1 foot wide. There is a private pondclose to the dyke. At this point the dyke is about 300 ft setback distance from the river. The followingphotos (Photo-1, -2 & -3) depict the vulnerable conditions of the Gumti dyke, as described above.

Temporary ProtectionWorks by Sand FillGunny Bags

, • ; • * :

Photo-1:Seepage zone on the Slopeof Dyke at Farizpur at Ch.16.85 km

Photo-2:Piping through the toe andbody of dyke at Kathalia atCh. 19.70 km

Photo-3:Slope failure on thecountry-side of dyke atEbdarpur at Ch. 22.36 km

INST-98/IHD-1

12. Sampling and Analysis

The first field sampling was carried out jointly by BAEC and BWDB on 30 Sept - 01 Oct 2002(especially the post-monsoon period). The second field sampling program was conducted jointly byBAEC and BWDB on 22 July 2003 (especially the monsoon period). Groundwaler and surface watersampling were performed close to the seepage zones of the three detected areas, namely Farizpur,Kathalia and Ebdarpur. GPS readings (latitude and longitude) were recorded at each sampling point.Field meters were calibrated using appropriate pH standards. On-site measurement of physio-chemical properties (such as pH, EC, TDS, HCCV and Temp.) of water samples were performed.Alkalinity (HCCV) was determined on-site by end-point titration. Six samples were taken from eachsite, four for chemical analyses (major cation and anion) and two for stable isotopes (]*Q and 2II)analyses. So, in total 18 water samples were collected during both sampling campaigns. Thegroundwater samples were collected from the tubewells located near the seepage zone. For cationanalysis, samples were filtered using membrane filters (0.45um pore size and 47mm diameter). Thesamples were collected in 500 mL polyethylene bottles for both cation and anion analyses. Thesamples for cations were acidified (using HNO3) to p H ^ in the field in order to avoid anyprecipitation of trace elements. Unfiltered samples were collected for analysis of anions. For stableisotope (2H & I8O) analysis, water samples were collected in a pre-cleaned, leak tight doublestoppered high density polyethylene (HDPE) bottle (size: 50 mL). As the river water is not clean, itwas filtered in the field (without evaporation losses) prior to collection. The following photos (Photo-4, -5 & -6) illustrate the field sampling fpr groundwater and river water near the seepage zones of thedyke, as described above.

Photo-4: Groundwatersampling from shallowtubewell near the dyke atFarizpur

Photo-5: Surface watersampling from the riverGumti at Farizpur

15

INST-98/IHD-1

Photo-6: On-site measurement of physio-chemical properties ofwater samples by HACH Water Quality Instruments

Major cation concentrations for Na+, K+, Ca+ and Mg+ and anion concentrations for C\\ SO/ 2 and

NO3" were determined. Stable isotopes (I8O and 2II) analyses were done in the laboratory of the

Radiation and Isotope Application Division, PINSTECH, Pakistan. The description of sample

collection with physio-chemical parameters of groundwater and river water samples are presented in

Table-3.

Table 3. Description of Field Sampling and Physio-Chemical Properties of Water Samples

Sample ID

GUM-1G

GUM-1R

GUM-2G

GUM-2R

GUM-3G

GUM-3R

GUNMG

GUM-4R

GUM-5G

GUM-5R

GUM-6G

GUM-6R

SamplingLocation

Farizpur (Mirpur)

- d o -

Descriptlon of samples

Hand Tubewell nearguard shade

Gumti riverside andsample from shallowdepth of river

Vill-Kathalia Union Darul Para HandMainamati Tubewell at house of

Kamal Chowdhury

- d o -

Vill -EbdarpurUnion-Bherellah

- d o -

Vill-EbdarpurUnion-Bherellah

- d o -

Fanzpur (Mirpur)

- d o -

Vill -Kalhalia Union-Mainamati

- d o -

Gumli riverside andsample from shallowdepth of river

Tara pump at house ofAli Azam Bhuiyan

Gumli riverside andsample from shallowdepth of river

Hand tubewell at houseof Khokan Miah


Hand Tubewell nearguard shade

3umti riverside andsample from shallowdepth of river

Darul Para HandTubewell al house ofKamal Chowdhury


Date ofSampling

30/09/2002

01/10/2002

01/10/2002

01/10/2002

01/10/2002

01/10/2002

22/07/2003

22/07/2003

22/07/2003

22/07/2003

22/07/2003

22/07/2003

GPS Reading(Lat t Long)

23° 29 434'

91° 07.096'

23° 29 434'

91° 07.096'

23° 30.678'

91° 07.045'

23° 23.745'

91°07.112'

23° 31.60V

91° 05.836'

23° 31.66V

91° 05.898'

23° 31.705'

91° 05.832'

23° 31.661'

91° 05 898'

23° 29 434'

91° 07.096'

23° 29 434'

91° 07 096'

23° 30 678'91° 07 045'

23° 23 745'

91° 07.117

Depth(ft.)

160

5

150

5

130

5

120

5

160

5

150

5

Temp. °C

264

301

261

30 3

26 4

30.7

26 4

30.6

266

31 3

26 0

31 0

pH

6 44

742

7.43

747

720

7 44

685

7 32

6.43

7.25

715

739

EC(uS/cm)

1854

888

355

894

451

897

315

943

1856

96.4

356

946

TDS(mg/L)

858

38

167 7

38 1

212

38 1

148 1

40

85 7

41 3

1679

404

HCOj

(mg/L)85

20

150

60

202

44

139

63

85

37

146

65

Note: G=Groundwater, R=River Water

16

INST-98/IHD-1

13. Results and Discussion

13.1 Hydrochemical

The groundwater temperature ranges from 26.0°C - 26.6°C and river water temperature ranges from30.1°C - 31.3°C with an average temperature difference of about 4.40°C. The average pH value ofgroundwater samples is about 6.92 whereas the average pH value of river samples is about 7.38. TheEC value of ground water at different seepage locations varies from 185-451 ^S/cm with an averagevalue of about 308 u,S/cm. The river water EC value ranges from 88 8 - 96.4 fiS/cm with an averagevalue of about 92.2 (iS/cm. Both the groundwater and river water EC values gradually increases fromup stream to down stream part of the Gumti River. But the average groundwater EC value is nearly3.5 times higher than the river water average EC value. The high EC values of groundwater from thenearby private shallow wells clearly show that these groundwater flow were influenced by the riverwater. Apart from the EC values, other chemical and isotopic parameters support the statement thatthe hydraulic connection exists between the river and shallow aquifer.

The summary of chemical analyses of the collected samples are given in Table-4. The chemicalcharacteristics of water quality data have been illustrated in the Piper Tnlinear Diagram (Fig. 11).Interpretation of the hydrochemical data implies that the groundwater vicinity to the seepage zones isNa-Ca-HCd type and for the river water is Ca-Mg-HCO, type

Table 4. Summary of Chemical Analyses of Water Samples

SampleID

GUM-1G

GUM-1R

GUM-2G

GUM-2R

GUM-3G

GUM-3R

GUM-4G

GUM-4R

GUM-5G

GUM-5R

GUM-6G

GUM-6R

SamplingLocation

Fanzpur (Mirpur)

- d o -

Vill -KathahaUmon-Mainamati

- d o -


- d o -


- d o -

Fanzpur (Mirpur)

- d o -

Vill -KathahaUnion-Mainamati

- d o -

Major Cations (mg/L)

Na+

71232

8 432

63 214

7 754

88 089

7 076

58 850

5 860

71 120

6 920

63 110

7 270

1 915

1 182

2 389

1068

2 170

1068

2 280

2 730

1 740

2 010

2 130

2 830

Ca+2

32 406

10 125

17 784

32 486

33 576

35 112

28 460

33 440

28 030

18 530

11 250

27 560

Mg t 2

8 252

8 129

8 275

7 813

8 446

8 261

5 260

4 080

7 110

3110

4 660

4 150

Major Anions

cr4 534

3 089

4 808

2 137

19 233

26 045

1 720

2 009

6 573

4 763

2 735

2 333

SO42

<0 4

<0 4

<0 4

<0 4

<0 4

1 04

0

3 00

1 00

1 00

0

0

mg/L)

NO,'

6 147

5 826

9 369

8 178

8 561

9 944

2 210

3 597

3 503

3 300

6 905

6 135

Note G=Groundwater, R=River Water

17

INST-98/IHD-1

80Legend

GroundwaterRiver Water

SO4

20

Fig. 11. Piper Trilinear Diagram for Water Samples of Groundwater and River Water

The chemical constituents of the collected groundwater and river water samples are described asbelow. The sodium (Na+) content in groundwater collected adjacent to the seepage zones varies from58.85 - 88.09 mg/L, but in river it varies from 5.86 - 8.43 mg/L. The average Na+ (69.27 mg/L)concentration in groundwatcr is nearly 10 times higher than Na' (7.22 mg/L) concentration in riverwater. The average K' (2.10 mg/L), Ca'2 (25.25 mg/L) and Mgl2 (7.00 mg/L) concentration ingroundwater are more or less similar to that of the average K+ (1.82 mg/L), Ca+2 (26.21 mg/L) andMg+2 (5.92 mg/L) concentration in river water respectively. So, the Na+ concentration of river waterdecreases from upstream to downstream direction of Gumti River. The average SG\f2 and NGVcontent in both groundwater and river water are more or less same. But the average bi-carbonateconcentration (135 mg/L) in groundwater is higher than that of river water (48 mg/L).

The chloride (Cl") content in groundwater varies from 1.72 - 19.23 mg/L, but in river water it variesfrom 2.01 - 26.05 mg/L. The average CY (6.60 mg/L) concentration in groundwater is mostly similarto that of the average CI" (6.73 mg/L) concentration in river water. It is very important to point outthat among all major ions usually dissolved in water, chloride is the most conservative ion. Thisbehaviour indicates that it is a good tracer of water, i.e. the behaviour of water and of the chloride ionis very similar. In most of the cases for both groundwater and river water samples, the chlorideconcentration shows the similar pattern. The average CI" (6.60 mg/L) concentration in groundwater ismostly similar to that of the average CI" (6.73 mg/L) concentration in river water. It suggests thepossibility of a hydraulic connection/mixing between these two water bodies.

18

INST-98/IHD-1

13.2 Isotopic

An integrated interpretation of hydrogeologic and isotopic data have been performed. The results forthe two sampling campaign are given in Table-5. Measurements of environmental stable isotopecomposition of water have been carried out as a complementary tool for this kind of investigation.The stable isotope composition of water provides information which cannot be obtained by othermethods. The important information based on stable isotope analyses of Gumti river water as well asgroundwater at the vicinity of the seepage/leakage points of Gumti dyke show sufficient differences inthe 5D and 5I8O existence.

Table 5. Summary of Stable Isotope Analyses of Water Samples

Sample ID

GUM-1G

GUM-1R

GUM-2G

GUM-2R

GUM-3G

GUM-3R

GUM-4G

GUM-4R

GUM-5G

GUM-5R

GUM-6G

GUM-6R

SamplingLocation

Fanzpur (Mirpur)

- d o -

Notes

Hand Tubewell near guardshade

Gumti riverside and samplefrom shallow depth of river

Vill -Kathaha Union- Darul ParaMamamati Hand Tubewell at house of

Kamal Chowdhury- d o -

Vill.-EbdarpurUmon-Bherellah

- d o -

Vill.-EbdarpurUnion-Bherellah

- d o -

Fanzpur (Mirpur)

- d o -


Tara pump at house of AhAzam Bhuiyan


Hand tubewell at house ofKhokan Miah


Hand Tubewell near guardshade


Vill -Kathaha Union- Darul ParaMainamati Hand Tubewell at house of

Kamal Chowdhury- d o - Gumti riverside and sample

from shallow depth of river

Date ofSampling

30/09/2002

01/10/2002

01/10/2002

01/10/2002

01/10/2002

01/10/2002

22/07/2003

22/07/2003

22/07/2003

22/07/2003

22/07/2003

22/07/2003

Oxygen-18(per mil)

-5 04

-4 26

-4 98

-4 39

-5 23

-4 427

-5 46

-3 93

-5 43

-3 61

-5 13

-3 78

Deuterium(per mil)

-30.04

-28 09

-30 00

-28 43

-32 22

-28 48

-33 60

-22 39

-32 36

-22 39

-31 00

-22 30

Note G=Groundwater, R=River Water

The stable isotopes (2H & I8O) data of both groundwater and river water are plotted in the same X-Ygraph (as shown in Fig. 12). The groundwaters sampled near the seepage zone area have stableoxygen and hydrogen isotope ratios ranging from —4.98 to -5.46 %o and -30.0 to -33.6 %o,respectively. Mostly all groundwater samples fall on the meteoric water line, indicating an origin ofrecharge from river without evaporation before infiltration. It focuses that the recharge of groundwateris influenced by the river water during peak water level in the river Gumti

19

INST-98/IHD-1

On the otherhand, the stable isotopes for river water show some enriched and evaporative values,ranging from -3.61 to -4.43 per mil and values from -22.30 to -28.48 per mil respectively. Thesamples for both sampling campaign were collected after the recession of peak flow in the Gumtiriver. Due to flashy nature of the Gumli river, the peak flow having velocity exists only for two orthree days. As soon as the river water recedes, the river flow decreases with time. As a result, thestable isotopes of the Gumti river show some evaporation effect, which might have occurred due tostagnation of flowing water in the river.

(In

o

r10

o m

1AIS

AI

E!r. -20

1 Is

oto

pe

Rat

io (

p<

Co

toO

C

Jl

©

?-35•o

-40-i

Evaporationeffect on riverwater duringlow flowcondition

Meteoric Water Line

\_x Evaporation

Groundwater isinfluenced byriver water

DGumti-1G +Gumti-1R

OGumti-2G OGumti-2R :

AGumti-3G XGumti-3R ,

• Gumti-4G +Gumti-4R

• Gumti-5G •Gumti-5R

AGumti-6G XGumti-6R ,

5 - 5 - 4 - 3 -2 -1 C

Oxygen Isotope Ratio (per mil. VSMOW)

Fig. 12. Stable oxygen and hydrogen isotope compositions of groundwater and surface wateradjacent to seepage zones

Evaporation is frequently responsible for important differences in isotopic composition of river waterwith respect to local groundwater. Due to stagnation of flowing water, when evaporation takes placeto sufficient degree, the river water becomes enriched in stable isotopes. Usually the 8D and 5I8O ofthe river is more depleted compared to that of the local aquifer. But in this case, the groundwatershow depleted values of stable isotope. This can help in calculating the contribution of river water inthe groundwater when mixing takes place. These stable isotopes likely indicate the migration of riverwater to the groundwater of country side through the base of dyke during the peak flow time. The 5Dand 5I8O content is thus an ideal tool for the evaluation of groundwater flow along the dyke createdby the leakage coming from the river. These isotope results reflect the hydraulic connectivity betweenthe river water and groundwater through the base of dyke. Geologic relationships are consistent withthe observation that hydraulic interconnections with the groundwatcr arc induced by the peak flow ofthe Gumli liver.

20

INST-98/IHD-1

14. Resistivity Imaging Survey

Resistivity imaging survey for investigation of leakage/seepage in the dyke had been carried out as asupplementary tool on 19 - 20 Oct 2003. The resistivity sounding helps to provide information onactive pathways of seepage and clay layers along the seeping zone of the dyke. This method is basedon the measurement of propagation through the ground of an induced direct electrical current bymeans of an appropriate network of electrodes. It measures the resistance to the flow of electricitythrough the geological horizons. The resistivity survey was carried out along the selected seepagezones of the Gumti dyke for localisation of seepage, leakage, slope failure and week zones of earthendyke.

14.1 Principles of Electrical Tomography

Electrical tomography (also referred to as electrical imaging) is a survey technique, which aims tobuild up a picture of the electrical properties of the subsurface by passing an electrical current alongmany different paths and measuring the associated voltage. The most useful technique is one in whichall the ground contacts are situated on the surface of the earth so that measurements in boreholes arenot required. A series of earth connections is made by inserting metal stakes (electrodes) into theground at equal intervals along a line.

There are two survey modes which can be employed to build up the data for an electrical image (i.e. across section of the distribution of subsurface resistivity) using a 4-electrode Wenner array; thetraverse mode and the roll on mode. To make a measurement of ground resistivity, current, I, isinjected into the ground through two electrodes, C| and C2, and a voltage V measured across a secondpair of electrodes, P| and P2. From the knowledge of resistance, R (V/l) and the intcr-electrodedistance, an apparent ground resistivity can be calculated.

To build up the data for an electrical image (i.e. a vertical cross section of the distribution ofsubsurface resistivity) a profile of resistance measurements is first measured with the unit electrodespacing, a and C1P1P2C2 (Wenner) electrodes arrangements. The spacing is then increased to 2a and asecond profile of measurements is made. The process is repeated, increasing the electrode spacingeach time in multiple N of the unit electrode spacing. The selection of electrodes connected to theinstrument at each measurement is controlled by the computer software. In Fig. 13 la 4-electrodeWenner array is used although it is also possible to use a variety of 2-, 3- or 4-electrode arrangements.

Wenner ArrayC, P, Pt c, Electrode Number

1 2 1 4 I I 7 I I 10 11 12 13 It 15 16 17 11 19 20 21 22 23 24 25

I • I « I » I I I I I I I I I I I I I I I I I I I I I I

Sequence of measurements to build up a pseudosectlon

Fig. 13. Arrangements of electrodes for a 2-D Electrical Imaging Survey and the sequence ofmeasurements used to build up a pseudosection.

21

INST-98/IHD-1

14.2 Techniques Applied in the Field

The observed pseudosection can be considered to comprise two components of information. Clearlythe section reflects the subsurface geology in some way but in addition strong effects of the electrodegeometry can distort the section leading to wrong geological interpretation. A survey carried out witha different arrangement of electrodes has produced a different pseudosection even though thesubsurface geology is the same. From experience, the Wenner array appears as a very satisfactoryconfiguration for imaging purposes. In general, provided the subsurface structure is not too complex,the unprocessed images are relatively contrast, either negative or positive, a fair amount ofinformation can be gained from visual inspection of the unprocessed images.

Nevertheless, in order to improve the resolution of the image it is necessary to process the data insome way. A technique published by Barker (1989) proved to be quick and useful in simple situationsbut in disturbed and complex areas it proved quite inadequate in removing geometrical effects. Amore recent technique developed by Lock and Barker (1995, 1996) takes a completely differentapproach and has proved to be markedly successful in eliminating electrode geometry effects so thatthe final processed image provides a good representation of the subsurface. This technique is based onthe smoothness - constrained least-squares methods (de Groot-Hedlinand Constable, 1990 and Sasaki,1992) and it produces a two dimensional subsurface model directly from the apparent resistivitypseudosection. The inversion is completely automatic and it does not even require the user to supply astarting model. Though the algorithm considerably sharpens the image and corrects the depthvariation in resistivity, sharp boundaries still appear gradational and resistivity contrasts can be lessthan true. Even so the method quickly produces an image that geometrically and quantitativelyapproaches a true resistivity cross-section of the subsurface. The following photos illustrate the fieldsampling for groundwaler and river water near the seepage zones of the dyke, as described above.

14.3 Observations from the Surveyed Image Data

An investigation was made on mid October, 2003 with 25 electrode sting/swift system to determinethe location of leakage which might have drained the river water during flash flood time. As it was notimmediately be obvious which array type would return the best data, one array such as, Wenner wasrecorded on the electrode layout. The 2D profiles have been developed from the obtained resolutionsin order to compare the similarities and differences. The data recorded has been interpreted using 2Dinversion software RES2DINV. The geophysical instrument used in the resistivity imaging surveywas the SARIS system of SCINTREX model (Photo-7). The system employed consists of 25electrodes being deployed at a time (Fig. 13); the unit electrode spacing being 1.0 to 1.5m indicating amaximum depth of investigation of 4.0 to 6.0m respectively. The roll on mode has been employed tobuild up the data for the electrical image. All the electrodes were addressable as either C|, C2, P| or P2.The EC and temp of water in the borrow pit vicinity to the toe of dyke were also recoded. The photos-8, -9 & -10 illustrate the resistivity imaging survey on the benn of the dyke closest to seepage zones.

Photo-7: Earth resistivitymeter of SARIS system,SCINTREX model

22

INST-98/IHD-1

Photo-8: Making layout ofWenner array with 25electrode sting/swift system

Photo-9: Recording theapparent resistivity and SPvalue using the SARISmeter

Photo-10: Taking EC andtemp of water in the borrowpit close to seepage zoneof the dyke

23

INST-98/IHD-1

Figs, from 14(i) to 14(iv) show the apparent resistivities for lines 1 to 4 plotted as a conventionalpseudosection. With no further processing, these sections indicate that the dyke body has in average aresistivity different from that of underlying original ground. The nature of topography can also bepredicted from these crude images. An approximate depth scale may be given by assuming that depthis equal to half the electrode spacing (in the case of Wenner Array). However, this depth scale is onlyapproximate, and so the data must be subjected to the inversion process.

14.3.1 At Farizpur (Ch. 16.845 - 16.875 km)

The seepage zone is located within the chainage 16.845 - 16.875 km. The soil on the berm iscomprised of highly compacted sandy clay. It was difficult to place the electrodes. During theresistivity survey on 20-Oct-2003, the day was sunny. The height of the image position wasapproximately 2.2 m above the ground level. The spacing between electrodes was given 1.0 meter,considering the depth range of imaging required. The presumed fracture appears to contain lowmoisture. The underlying original ground is reflected by low resistivity implying some silty claycomposition.

PsZ00 40 8.0

SemiDemo version

120 160 20.0

05

15

2.6

36

Measured Apparent Resistivity PseudosectionPsZ

0.0 40 80 12.0 160 200

0.5

1.5

26

3.6

Calculated Apparent Resistivity Pseudosection

Depth Iteration 3 RMS error = 1 98 %0 0 4 0

038.0 12 0 160 200

1.3

25(C)

Inverse Model Resistivity Section

39.9 45.7 523 600 687 7B8Resistivity in ohm m

902 103Unit electrode spacing 10 m

Fig. 14(i) Electrical image of Farizpur seepage point, (a) is observed data plotted as a colouredpseudosection, (b) is the pseudosection computed from the model and (c) is the image ormodel showing true depth and true formation resistivity.

14.3.2 At Kathalia (Ch. 19.700 - 19.718 km)

The seepage zone is located within the chainage 19.700 - 19.718 km. The dyke condition was foundquite satisfactory. During the resistivity survey on 20-Oct-2003, the seepage zone was found stable.The height of the image position was approximately 2.0 in above the ground level. The spacingbetween electrodes was given 1.0 meter, considering the depth range of imaging required. The truemodel resistivity appears to correlate with the dumped gunny bags containing highly compacted sandyclay. This high resistivity zone is underlain by original ground probably consisting of silty clay oflower resistivity.

24

INST-98/IHD-1

PsZ0 0 4.0 80

SemiOemo version

120 160 200

0.5

1.5

26

3.6

PsZ r

05

15

2.6

3.6

(a)

Measured Apparent Resistivity Psaudoseclion

10 4 0 8 0 120 1R 0 XIO

(b)


80Deplh lieialion 3 RMS error = 4.9 %

0.0 400.3

(C)


490299 362• ••fflDB

62 7 80.2 103Resistivity in ohm. m

131 168Unit electrode spacing 10 rn

Fig. 14(ii) Electrical image of Kathalia seepage point, (a) is observed data plotted as a colouredpseudosection, (b) is the pseudosection computed from the model and (c) is the image ormodel showing true depth and true formation resistivity.

14.3.3 At Ebdnrpur (Up) |Ch. 22.135 - 22.201 km]

The seepage zone is located within the chainage 22.135 - 22.201 km. The decrease in true resistivitycan be related to fractured zone filled with water. There was a raining just before the resistivitysurveying on 19-Oct-2003. The surface material on the berm was moist and loose. High apparentresistivity can be correlated with a poor coupling of electrodes. This line is located on a previouslyeroded zone. The berm line is at approximately 2.7 m above the ground level. The spacing betweenelectrodes was given 1.5 meters, considering the depth range of imaging required.

PsZoo 60 120

SemiDerno version

18.0 240 300

08

2.3

33

54

PsZ

(a)Measured Apparent Resistivity Pseudoseclion

0 0

08

23

38

54

— « « •••• I I T T

(b)

60 120

9MHKBBMMHEnMar '»^rwrMflTM

160

•MH|

HMBBB

24 0 30 0 n


Oepth Iteration 3 RMS error = 3.0 %00

3 4

1 9

37

^ !

(c)

60 12 0

• • I•B180

HE24 0 30 0 n


30 0 37 9 47 B 603 760 958Resistivity in ohm m

121 152Unit electrode spacing 1 5 rn

Fig. 14(iii) Electrical image of Ebdarpur-Up seepage point, (a) is observed data plotted as a colouredpseudosection, (b) is the pseudosection computed from the model and (c) is the image ormodel showing true depth and true formation resistivity.

25

INST-98/1HD-1

14.3.4 At Ebdarpur (Down) [Ch. 22.344 - 22.387 km]

The seepage zone is located within the chainage 22.344 - 22.387 km. The resistivity survey in thislocation was carried out at noon on I9-Oct-2003 and the day was sunny. The previously eroded zoneis just at the middle of the image line. The berm line is at approximately 2.5 m above the ground level.The spacing between electrodes was given 1.0 meter, considering the depth range of imagingrequired. The left hand portion of the line is characterized by low resistivity, where as the middle oneby high resistivity because of dumped gunny bags containing compact silty and sandy clay. Adistinction can be made between the seeping zone and uneroded zone. The underlying material oflower resistivity represents the original ground.

SenuDemo version

05

1 5

26

36

0

(a)

40t

80i

120 16 0•

200 n• . . .

i0*'

PsZMeasured AppaieiM Resistwvty Pseudosection

00 8.0 120 16 0

05

1.5.

26

36 (b)Calculated Apparent Resistivity Pseudosechon

Depth Iteration 3 RMS error = 2 3 %00 4.0 8.0 16 0 20.0

0.3

13

25 (C)


40.3 47.5 55.9 65 8 77 4 91.2Resistivity in ohm m

107 126Unit electrode spacing I 0 m

Fig. 14(iv) Electrical image of Ebdarpur-Down seepage point, (a) is observed data plotted as acoloured pseudoseclion, (b) is the pseudoscction computed from the model and (c) is theimage or model showing true depth and true formation resistivity.

15. Impacts of the Study and Its Management Implications

The study has some productive and positive impact on setting up an early warning system to controlthe possible seepage in the body of the dyke and to protect the dyke from failure. The isotopemethodology essentially develops a characteristic pattern or "fingerprint" of isotopic compositions (ofwater) to identify sources and pathways of seepage in the dyke.

Environmental isotope techniques have significantly contributed to solve the questions of damleakage, mixing and origin of water in the area studied. More specifically, the stable environmentalisotopes contributes to quantify mixing ratios of waters from different origin and to recognize theorigin of leakages. On the otherhand, the radioactive environmental isotopes provides the informationof mean residence times, indication of recharge and transport mechanism. It is comprehended thattracer tools become more efficient when combined with traditional methods. The implications of thisstudy lead to better management in dyke failure inducted by seepage/leakage. The achievements ofthe project are enumerated as below.

26

INST-98/IIID-1

End-user has a positive recognition of results of the study, as evidenced by their participation andproviding technical input to the development of isotope hydrology technique in investigation ofseepage/leakage in the dyke.

The study has provided a scientific basis in developing preventive strategies by characterizing thewater quality between the two flow systems. It reflects the hydraulic connectivity between thetwo water systems, complying with the results of conventional hydrological method.

The end user has got familiarized with this new technique and has got benefit from the results ofthis study. Participation in the regional training (held in Colombo, Sri Lanka on October, 2002)has helped the end user to have preliminary idea on application of isotope hydrology technique indam safety and management.

Participation in the different IAEA events have helped to gain more knowledge and experience inthe application of isotope technique in dam safety management through sharing of experienceswith other advanced Member States in the group.

Good coordination among the end user group has been established.

16. Conclusions

Gumti Flood Control Dyke is identified as having the problem of piping through the foundation andbody of the dyke, sloughing at the toe of the dyke, slope failure, siltation in the canals etc. Each andevery year, the dykes are threatened by flash floods originated from the Tipperan hilly region of India.

Isotope techniques are among many available technical tools and considered unique and have thepotential to solve certain types of problems common in dam safety activities, which couldcomplement existing conventional problem solving techniques. Chemical and isotope are used in thisway to prove the degree of hydraulic interconnection and mixing between two water bodies, as hasbeen shown previously. Electrical conductivity (EC) of river water showed reasonably good contrastwith the EC of local groundwater, i.e. the average groundwater EC value is about 3.5 times higherthan the river water average EC value. These high EC values of groundwater suggest that thegroundwater flow is influenced by the river water. Apart from the EC value, similar concentration ofchloride ion found in river water and groundwater reflects the possibility of a hydraulicconnection/mixing between these two water bodies.

The stable isotope results reflect the hydraulic connectivity between the river water and groundwaterthrough the base of dyke. It indicates the recharge of groundwater from the river water during peakwater level in monsoon. On the otherhand, the stable isotopes of the Gumti river show someevaporation effect, which are thought to have occurred due to stagnation of flowing water in the river.The general conclusions drawn from this study are as follows:

• Soggy soil conditions found in some points at countryside of the dyke are due to presence ofseepage and capillary rise of local shallow groundwater when the river water level reach to thepeak.

• The source of seepage water is likely from the river but believed to have mixed with localshallow groundwater along its pathway towards lower elevation surrounding the dyke toe.

• Uplift pressure develops at the river bed during peak water level is likely to cause seepage flowpaths, followed by some evidence of piping through the dyke body and sloughing at toe of thedyke.

27

INST-98/IHD-1

The results of resistivity sounding have focused on active pathways of seepage and clay layers alongthe seeping zone of the dyke. The images show the demarcation of loose zones having high resistivityand underlying silty clay composition of base of the dyke having low resistivity. Just after the pipingand slope failure on the dyke, gunny bags containing compact silty and sandy clay were dumped andconsequently these show the high resistivity value.

17. Recommendations

More isotopic studies are required in the same areas and other vulnerable areas of Gumti dyke. Inorder to check the seasonal variation and mixing period between two water bodies, the isotopesampling needs to be carried out routinely for every month. Along the water chemistry, especially thetemp., EC and chloride ion, could also be tested to bring some relation with the isotopic results. As aconsequence, some realistic findings in the aspects of leakage/seepage could be achieved. Thefollowing isotopic studies are recommended for getting more detailed information on mixingcondition.

- The Tripura hill is close to the Gumti dyke. So, the precipitation samples near the Gumti dykeneed to be collected for determination of isotopic composition of precipitation. This is importantto determine the local meteoric water line (LMWL) for interpretation of environmental isotopedata pertaining to river and groundwater systems.

- The stable carbon isotope (nC/l2C) ratios in the Total Dissolved Inorganic Carbon (TDIC) can beused to investigate some aspects of leakage/seepage problems, leading to showing isotopiccontrast between the two water types.

- Moreover, the environmental radioactive isotope namely, natural tritium (3H) of water canprovide similar information to that described above using stable isotopes of water. If thedifference in the stable isotopic composition of the river water and groundwater is low, in thatsituation natural tritium could possibly be tried.

- Groundwater tracing experiment by using artificial radioactive isotope can be carried out toidentify flow paths in boreholes and to determine other groundwater parameters. To investigatethe exact location of seepage/leakage zones of dyke it is necessary to find out the groundwaterfiltration velocity, flow direction and the vertical velocity. For carrying out this groundwatertracing experiment, at least six numbers boreholes in shallow depth (ranging from approx. 50 ft.to 80 ft.) near the seeping zone (especially, at toe of dyke and on the flat ground near the seepagezone) need to be constructed.

The resistivity imaging survey should be carried out both on the top and berm of the dyke. It isimportant to take the resistivity at the time of peak flow and to compare this situation with theresistivity during dry season.

Acknowledgements

The study was carried out under the IAEA/RCA regional program RAS/8/093 "Use of Isotopes inDam Safety and Dam Sustainability". The authors are thankful to BAEC for providing the financialsupport for field sampling. The IAEA is acknowledged for doing the environmental stable isotopeanalysis for the water samples in PINSTECH, Pakistan. The help rendered by Mr. M. A. Mannaf,SEO, Nuclear & Radiation Chemistry Division, INST in chemical analyses is thankfullyacknowledged. We appreciate the assistance rendered by Bangladesh Water Development Board(BWDB) and Institute of Water Modelling (IWM) in providing us hydrological & hydro-geologicaldata and study area map. The cooperation of Comilla O & M Circle, BWDB during reconnaissancesurvey, field sampling and resistivity survey is highly appreciated. In particular, we are appreciativeof Mr. Hasan Zobair, CE, Md. Aminul Islam, SE, Mr. Mahbubur Rahman & Mr. Jahangir Alain,XEN, and Mr. Md. Moniruzzaman, SDE, BWDB for their assistance in giving the logistic support andguidance in field survey. We also would like to express our thanks to Dr. Delwar Hossain, Professor,

28

INST-98/1HD-1

Dept of Geological Science, Jahangirnagar University for giving the guidelines and layout design ofresistivity imaging survey.

References

1. MOTT MACDONALD LTD. AND ET. AL., 1993: Gumti Phase-II Sub-Project FeasibilityStudy, Final Report (World Bank).

2. MPO (Master Plan Organisation), 1984: National Water Plan Project - Second InterimReport, Vol. Ill, Groundwater Availability, (Ministry of Irrigation, Water Development andFlood Control, Consultant: HARZA Engineering Comp., Intl. USA)

3 BARKER, R.D., 1989: Depth of investigation of a generalized collinear 4- electrode array.Geophysics, 54, 1031-1037.

4. BEDMAR, A. PLATA AND ARAGUAS, LUIS, 2002: Detection and Prevention of Leaksfrom Dams, A. A. Balkema Publishers, Lisse.

5 BWDB AND IWM, 2002: Progress Report-I, Feasibility and Model Study for Rehabilitationof Flood Control Embankment on Both Banks of Gumti.

6. BWDB AND IWM, 2003: Progress Report-II, Feasibility and Model Study for Rehabilitationof Flood Control Embankment on Both Banks of Gumti.

7. BWDB AND IWM, 2003: Progress Report-Ill, Feasibility and Model Study forRehabilitation of Flood Control Embankment on Both Banks of Gumti.

8. LOKE, M.H. AND BARKER, R.D., 1995: Least-squares deconvolution of apparentresistivity pseudosections. Geophysics, 60, 1682-1690.

9. LOKE, M.H. AND BARKER, R.D., 1996: Rapid least squares inversion of apparentresistivity pseudosections by a quasi-Newton method. Geophysical Prospecting, 44, 131-152.

10. SWMC, RRI AND DH1, 1995: One Dimensional Morphological Modelling, Gumti RiverSubmodel, Case Study Report, Surface Water Simulation Modelling Programme Phase-Ill.

29

INST-98/IHD-]

ANNEXURE

Data of Apparent Resistivity and Self Potential Measured by SARIS System

(A) Surveyed Area: Farizpur (Ch. 16.845 - 16.875 km)

Date of survey. 20/10/20032-D Electrical Tomography Survey Layout using Wenner configuration

Parameter measured in the stagnant water of borrow pit close to dykeElectrical Conductivity (EC) = 188 pS/cmTemperature (T) = 31.9 °C

Sequence ofElectrode Setting

1-2-3-42-3-4-53-4-5-64-5-6-75-6-7-86-7-8-97-8-9-10

8-9-10-119-10-11-1210-11-12-1311-12-13-1412-13-14-1513-14-15-1614-15-16-1715-16-17-1816-17-18-1917-18-19-2018-19-20-2119-20-21-2220-21-22-2321-22-23-2422-23-24-25

1-3-5-72-4-6-83-5-7-9

4-6-8-105-7-9-11

6-8-10-127-9-11-138-10-12-149-11-13-1510-12-14-1611-13-15-1712-14-16-1813-15-17-1914-16-18-2015-17-19-2116-18-20-2117-19-21-23

Distance bet.Electrode-1 &

Center ofElectrodes'Position (m)

1.502 503.504.505 506.507.508.509.50

10.5011.5012.5013.5014.5015.5016 5017 5018.5019 5020.5021.5022 50

3.004.005.006.007 008 009 00

10.0011 0012 0013.0014 0015 0016 0017 0018 0019 00

ElectrodeSpacing

(m)

1 001 001 001 001 001 001 001 001.001.001 001 001 001 001 001 001 001 001 001 001.001 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 00

ApparentResistivity(Ohm-m)

86 86102 3092 9498 4183 9697.7078 9595 5681 1388 4598 8697 53100 9107 597 04

100 3082 6377 5070 9177 8969 9586 9281 0879 1780 3580.1878 77814577 5877 6478 7585 5280 9782 8782 1986 1479 8372 8981 24

SP(mv)

-12-63-2914g

260

1096378731065

-4695

-146-1911239

-51-1434

17312-939-41468

-217

291921

11212

-64-139

-9

A-1

1NST-98/IHD-I


18-20-22-2419-21-23-251-4-7-102-5-8-113-6-9-124-7-10-135-8-11-146-9-12-157-10-13-168-11-14-179-12-15-1810-13-16-1911-14-17-2012-15-18-2113-16-19-2214-17-20-2315-18-21-2416-19-22-241-5-9-132-6-10-143-7-11-154-8-12-165-9-13-176-10-14-187-11-15-198-12-16-209-13-17-2110-14-18-2211-15-19-2312-16-20-2413-17-21-251-6-11-162-7-12-173-8-13-184-9-14-195-10-15-206-11-16-217-12-17-228-13-18-239-14-19-2410-15-20-251-7-13-192-8-14-203-9-15-214-10-16-225-11-17-236-12-18-247-13-19-251-8-15-222-9-16-233-10-17-244-11-18-251-9-17-25

Distance bet.Electrode-1 &Center ofElectrodes'Position (m)

20 0021 004 505 506 507.508.509.5010 5011 5012 5013 5014.5015 5016 5017 5018 5019 506 007 008 009.0010.0011 0012 0013.0014 0015 0016 0017 0018 007 508 509 5010 5011 5012 5013 5014.5015 5016 509.0010.0011 0012.0013.0014 0015 0010 5011 5012.5013 5012 00

ElectrodeSpacing

(m)

2 002 003 003 003.003 003 003 003 003 003 003 003 003 003 003.003 003 004 004 004.004 004 004 004.004 004 004 004 004 004 005 005 005 005 005 005 005 005 005 005 006 006 006.006 006 006 006 007 007 007 007 008 00


83.4478 2766 5371 4769 6073 3468 5669 6367 9873 1573 2275 5675 1576 4073 3574 8671.7473 9460 9862 3860 8960 6163 1163 0864.4968 7069 5770 8867 8365 1764 7153 5153 8854 3758 3058 5361 2661 9364 5860 9159 0250 8051 9853 9854 0956 7457 3755 2548 2550 6549 7451 3846 58

SP(mv)

-39-31229125805116-41-48-4171074765

-195-163-11246347043-7-29-778342439-53-97-3478-23170

-56516834291586356-219

-26241719-63-53212

A-2

INST-98/IHD-1

(B) Surveyed Area: Kathalia (Ch. 19.700 - 19.718 km)

Date of survey: 20/10/20032-D Electrical Tomography Survey Layout using Wenner configuration

Parameter measured in the stagnant water of borrow pit close to dykeElectrical Conductivity (EC) = 92 6Temperature (T) = 34 2 °C


1-2-3-42-3-4-53-4-5-64-5-6-75-6-7-86-7-8-97-8-9-10

8-9-10-119-10-11-1210-11-12-1311-12-13-1412-13-14-1513-14-15-1614-15-16-1715-16-17-1816-17-18-1917-18-19-2018-19-20-2119-20-21-2220-21-22-2321-22-23-2422-23-24-25

1-3-5-72-4-6-83-5-7-9

4-6-8-105-7-9-11

6-8-10-127-9-11-13

8-10-12-149-11-13-1510-12-14-1611-13-15-1712-14-16-1813-15-17-1914-16-18-2015-17-19-2116-18-20-2117-19-21-2318-20-22-2419-21-23-25



1.502.503.504.505.506.507.508.509.50

10.5011.5012.5013 5014.5015.5016 5017.5018.5019.5020.5021.5022.50

3 004.005.006.007.008.009.00

10.0011.0012.0013 0014.0015.0016 0017.0018.0019 0020.0021 00

ElectrodeSpacing (m)

1 001.001.001.001001 001 001 001001 001.001 001 001.001 001.001 001 001.001001 001 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 002 00


122 40133 90129 20126 00137 50146 00143 50158 50145 80163 30151.00139 00150 00144 20146 00147 90144.60140 60142 10130 70134 10137 50102 70102 90100 70102 90104 60106 10101 9010120106 30105 50104 70106 30105 40105 70103 80105 70110 00106 20100 50

SP(mv)

129-31-21-9062

-10765412

-48-19-4

-104-12-21-902

-7-2139

-24-39-36-31-51-26-51

-919

-73-104

-48-26-14

27

-79

1434

B-l

INST-98/IHD-1


1-4-7-102-5-8-113-6-9-124-7-10-135-8-11-146-9-12-157-10-13-168-11-14-179-12-15-1810-13-16-1911-14-17-2012-15-18-2113-16-19-2214-17-20-2315-18-21-2416-19-22-241-5-9-132-6-10-143-7-11-154-8-12-165-9-13-176-10-14-187-11-15-198-12-16-209-13-17-2110-14-18-2211-15-19-2312-16-20-2413-17-21-251-6-11-162-7-12-173-8-13-184-9-14-195-10-15-206-11-16-217-12-17-228-13-18-239-14-19-2410-15-20-251-7-13-192-8-14-203-9-15-214-10-16-225-11-17-236-12-18-247-13-19-251-8-15-222-9-16-233-10-17-244-11-18-251-9-17-25

Distance bet.Electrode-1 &Center ofElectrodes'Position (m)

4 505 506 507 508.509 5010 5011 5012.5013 5014 5015 5016 5017 5018 5019.506 007.008 009 0010 0011 0012 0013 0014 0015 0016 0017.0018 007 508 509 5010.5011.5012 5013.5014 5015.5016.509.0010 0011 0012 0013 0014 0015 0010 5011 5012 5013 5012 00


3 003 003 003 003 003 003 003 003.003 003 003 003 003 003 003 004 004 004.004 004 004 004 004 004 004 004 004 004 005 005 005 005 005 005 005 005 005 005 006.006 006 006 006 006 006 007 007 007 007.008.00


69 7672 1972 1175 5272 42414368 5172 0174 5975 3373 1271 3873 0974 6376 0175 0754 4357 9755 1455 8855 7352 5253 0254 3953 9456 1255 8255 3856 3346 7848 3346 0445 1043 8643 7844 4945 0746 3646.5241 7741 9040 9140 1840 2640 1239 1739 8939 8638 2038 7038 87

SP(mv)

-1297

-53-51-24779-73-21-9746-14-43-7-951-24-3639-4146134121-104-73-5614-39-53-19451-52-2980145-85-17-68-34-57-41923473-313448-41-95-78

B-2

INST-98/IHD-1


1-4-7-102-5-8-113-6-9-12

4-7-10-135-8-11-146-9-12-157-10-13-168-11-14-179-12-15-1810-13-16-1911-14-17-2012-15-18-2113-16-19-2214-17-20-2315-18-21-2416-19-22-24

1-5-9-132-6-10-143-7-11-154-8-12-165-9-13-17

6-10-14-187-11-15-198-12-16-209-13-17-2110-14-18-2211-15-19-2312-16-20-2413-17-21-251-6-11-162-7-12-173-8-13-184-9-14-195-10-15-206-11-16-217-12-17-228-13-18-239-14-19-2410-15-20-251-7-13-192-8-14-203-9-15-21

4-10-16-225-11-17-236-12-18-247-13-19-251-8-15-222-9-16-23

3-10-17-244-11-18-251-9-17-25

Distance b«tElectrode-1 &

Center ofElectro**'Positioning

6.753.250.75

11.25*2.751^2515.7517.25t8.75202521.75m25$47526.2527.752925

9.0010.5012.0013.5015.0016.5018.0016.5021.0022.5024.0025.5027.0011.2512.7514.2515.7517.2518.7520.2521.7523.2524.7513.5015.0016.5018.0019.5021.0022.5015.7517 2518.7520 2518.00


4.54.545454.5454.54.54.54545454.54.54.545606.0606.0606.0606.0606.0606.0607.5757575757.575757.5759.0909.0909.0909.0

10510510 5105120


52 0653 0049 6347 0248 9849 7148 2045 9144 0943 9146 2648 6548 1545 0842 7444 3449 6451 5852 35514651 8050 7948 6749 1550 0651 1851 5149 0247 6552 4862 5854 1753 4053 1754 3155 0553 8052 9352 4553 7156 7657 7157 9157 8657 9956 5257 6859 9160 7259 8660 41

SP(mv)

0-4324

-1234

-263943

-43-90-9

-43-85-51-61-46398558

-29-1792

-21-43

-143-75

-107-109-4648

9-17112-19-191441

-70-56-70122-1294

-1426

112-124

70-34-3666

C-2

1NST-98/IHD

(C ) Surveyed Area: Ebdarpur (Up) (Ch. 22.135 - 22.201 km]

Date of survey 19/10/20032-D Electrical Tomography Survey Layout using Wenner configuration

Parameter measured in the stagnant water of borrow pit close to dykeElectrical Conductivity (EC) = 245 uS/cmTemperature (T) = 31 7 °C


1-2-3-42-3-4-53-4-5-64-5-6-75-6-7-86-7-8-97-8-9-10

8-9-10-119-10-11-1210-11-12-1311-12-13-1412-13-14-1513-14-15-1614-15-16-1715-16-17-1816-17-18-1917-18-19-2018-19-20-2119-20-21-2220-21-22-2321-22-23-2422-23-24-25

1-3-5-72-4-6-83-5-7-9

4-6-8-105-7-9-11

6-8-10-127-9-11-13

8-10-12-149-11-13-1510-12-14-1611-13-15-1712-14-16-1813-15-17-1914-16-18-2015-17-19-2116-18-20-2117-19-21-2318-20-22-2419-21-23-25



2 253 755 256 758 259 75

11.2512 7514 2515 7517 2518 7520 2521 7523 2524 7526 2527 7529 2530.7532 2533 754.506 007 509 00

10 5012 0013 5015 0016.5018 0019 5021 0022 5024 0025 5027.0028 5030 0031 50


1 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 530303030303030303030303030303030303030


133 1083 3066 4556 1048 4844 2939 1838 8939 9835 3840 8436 3534 6038 7936 0639 6337 3239 8644 2852 6563 0167 1957 5961 5854 5647 0844 3244 2843.9942.3442 1440 7639 8340.6342 6553 5841 4940 6842 4145 7050 96

SP(mv)

-39-51-12-6162

-109-736121

-1458

-19-2

-68-80-12127

87-19

-16873

35390

128-19-26

-9-2452

-7073-7

-14-56

-9107-80-9529

-126

C-l

INST-98/1HD-


1-4-7-102-5-8-113-6-9-12

4-7-10-135-8-11-146-9-12-157-10-13-168-11-14-179-12-15-1810-13-16-1911-14-17-2012-15-18-2113-16-19-2214-17-20-2315-18-21-2416-19-22-24

1-5-9-132-6-10-143-7-11-154-8-12-165-9-13-17

6-10-14-187-11-15-198-12-16-209-13-17-2110-14-18-2211-15-19-2312-16-20-2413-17-21-251-6-11-162-7-12-173-8-13-184-9-14-195-10-15-206-11-16-217-12-17-228-13-18-239-14-19-2410-15-20-25

1-7-13-192-8-14-203-9-15-21

4-10-16-225-11-17-236-12-18-247-13-19-251-8-15-222-9-16-233-10-17-244-11-18-251-9-17-25

Distance beLElectrode-1 &


4.505.606.5a7.508.509.50

10.5011.5012.5013.5014.5015.5016.5017.5018.9019.506.007.008.009.00

10.0011.0012.0013.0014.0015.0016.0017.0018.007.508.509.50

10.5011.5012.5013.5014.5015.5016.509.00

10.0011.0012.0013.0014.0015.0010.5011.5012.5013.5012.00


3.003.003.003.003 003.003.003.003.003.003.003.003.003.003.003.004.004.004.004.004.004.004.004.004.004.004.004.004.005.005.005.005.005.005.005.005.005.005 006.006.006 006 006.006.006.007.007 007.007.008 00


55 7757 1461.3362.59612258 8858 8261 2363.2266 4863 9160.9959.2657 1355 4551.2854 5654 5453 1653 0550 3953 2453 9554.3058.6257 5857.1254.4251 0750 6550 3250 0950 6351 7052 2255 2156 4256 4754 6249.9952.0251 9153 7254 8755 3256 6753 8953 8855 3055 5155 52

SP(mv)

-6590

-51-80513973

-36-29-5817

-39-14-26

7131

-4-43

-11461

-46-73

-102-80-24-36

414

16163

134-19

-7-109-134

-82-31-68

-104-65-17-19-80

-187-82-21-9712

-43-46-56

D-2

seepage investigation by using isotope and geophysical

Documents