Leakage is a major safety issue that, if left unchecked, may result in dam failure by various mechanisms. There is enormous pressure on dam operators to repair leaks without significant delays. Frequently, the need to reduce the risk of failure or control water loss has led to costly remedial repairs that are planned and executed without a complete understanding of the problem. A lack of appropriate leakage investigation and monitoring can result in repairs that are unsuccessful in controlling or reducing leakage. In the last few decades, a series of new hydrological techniques have been developed to help in the assessment of leakage and seepage in dams. It is important to make these techniques available to the engineers responsible for dam construction and management so that they become aware of these tools. The available literature on dam leak studies is relatively limited with regard to the use of these techniques when assessing dam leakage. It is difficult to find case studies that discuss integrating the use of several of these techniques in comprehensive evaluations that lead to successful leakage mitigation. These techniques allow identification of recharge zones, preferential paths, and transit times, which aid in monitoring and mitigating the dam leakage. The paper includes description of the techniques and projects in India involving prevention and detection of dam and reservoir leakage, including leakage evaluation, analysis, design, construction, and post-construction verification of repairs.

1. IDTENTIFICATION OF
SEEPAGE PATH BY
TRACER METHOD
By
Prashant Kumar Ojha
(1EW11CV049)
Under the Guidance of
Mr. Nagaraja Gupta MS
Associate Professor
Dept. of Civil Engineering
East West Institute of Technology
Bangalore-560091

2. CONTENTS
1. ABSTRACT
2. INTRODUCTION
3. ESTIMATION OF PERMISSIBLE SEEPAGE IN MASONRY DAM
4. TRACER TECHNIQUES
5. METHODOLOGY
6. CASE STUDIES
7. CONCLUSIONS
8. REFERENCES
CONTENTS

3. ABSTRACT
Leakage is a major safety issue that, if left
unchecked, may result in dam failure by
various mechanisms.
In the last few decades, a series of new
hydrological techniques have been
developed to help in the assessment of
leakage and seepage in dams.
These techniques allow detection of dam
leakage, including leakage evaluation,
analysis, design, construction, and post-
construction verification of repairs.
ABSTRACT

4. INTRODUCTION
 Dams have been a part of the economic development
model of almost all nations of the world. At some stage of their
development, most countries with water resources that can
be economically exploited have built dams for energy,
irrigation, and drinking water.
 The hydraulic structures viz. dam, reservoir, canal etc. are
although designed not to seep or leak, still minimum seepage
or leakage occurs through these hydraulic structures when
founded on pervious foundations.
 Generally, large quantity of seepage in dam occurs through
(i) the abutments i.e. through geological inhomogeneities
occurring in the vicinity of the structure,
(ii) the structure - foundation interface and
(iii) the body of the dam itself.
INTRODUCTION

5. ESTIMATION OF PERMISSIBLE SEEPAGE IN MASONRY DAM
Central Water Commission, New Delhi has
evolved a method for estimating permissible
seepage in masonry dam where drains are
provided. The methods assume:
1. No water escapes to downstream portion past the
drainage pipes.
2. Masonry is permeable having high coefficient of
permeability in horizontal direction.
Seepage in body of dam is a measure of
hydraulic head. When reservoir is at its full
level, the seepage is maximum.
ESTIMATIONOF SEEPAGE

6. Cross section and upstream elevation of the dam.
Cross section and upstream elevation of the dam.

7. By Darcy’s law Q = k*i*A
The notations used are:-
k= permeability of masonry and
h/d = i = hydraulic gradient of flow (linear pressure variation is
assumed).
Taking an elemental rectangle dl X dh at height ‘h’
below reservoir level and distance ‘l’ away from left
abutment
dQ=k*i*dh*dl
dQ=k*(h/d)*dl*dh
Darcy’s law

8. Darcy’s law

9. TRACER TECHNIQUES
 The tracer is a certain substance added to a
material in a chemical, biological or physical system
to mark that material for study, to observe its
progress through the system or to determine its final
distribution.
 Tracer technique is adopted by injecting a
predetermined quantity of tracer into borehole
located near to the suspected seepage zone of the
hydraulic structure and observing either the dilution
of the tracer in the injection bore holes itself or by
detecting its arrival in the observation bore holes
located near the injection boreholes in the
probable direction of seepage.
TRACERTECHNIQUES

10.  The major objectives of using tracer’s techniques in
geotechnical studies are to determine :-
(1) seepage in dams, reservoirs and canals,
(2) location of seepage entry zones, delineating
seepage path, assessing the efficiency of remedial
measures, examination of soundness of bedrock
etc.
(3) hydraulic parameters of subsurface flow or
seepage through hydraulic structures
(4) interconnection between solution cavities,
(5) seepage losses through irrigation canals etc.
TRACERTECHNIQUES

11. TYPES OF TRACERS
TYPES OF
TRACERS
ISOTOPES
TRACERS
STABLE
ISOTOPES
UNSTABLE
ISOTOPES
CONVENTIONAL
TRACERS

12. CONVENTIONAL TRACERS
 Conventional tracers are strong electrolytes like
Sodium Chloride (NaCl) and organic dyes like
Sodium Fluoroscene, Rhodamine-B, etc.
 Chemical and dye tracers are generally affected
by absorption and adsorption processes.
CONVENTIONAL TRACERS

13. ISOTOPES TRACERS
ISOTOPES TRACERS
 Isotope tracers can be subdivided into stable and
unstable isotopes.
 E.g. 3H, 51Cr, 60Co, 82Br, and 131I
 Stable isotopes include environmental isotopes
while unstable isotopes are radioactive

14. ISOTOPES TRACERS
Environment Isotopes
Tracers
 They are ideal
geochemical tracers of
water because their
concentrations are
usually not subjected
to change by
interaction with the
aquifer material.
 e.g.- Iodine, Cobalt
Radioactive (Unstable)
Isotope Tracers
 Radioactive tracers
have an optimum half-
life period.
 Ease and speed of
measurement are the
most significant
advantages of the
radioactive tracer
technique
 e.g.- Radon Gas, Tritium
ISOTOPES TRACERS

15. METHODOLOGY
TRACER
TECHNIQ
UE
SINGLEWELL OR
POINTDILUTION
TECHNIQUE
MULTIWELL
TECHNIQUE
METHODOLOGY

16. Single Well Technique
 The aim of the method is to obtain a
direct measurement of filtration velocity.
Multiwell Technique
 The method involves injecting a
predetermined quantity of tracer in the
form of a solution in one of the boreholes
and monitoring its appearance in a
number of boreholes located at the
downstream, in the anticipated
direction of flow.
METHODOLOGY

17. Conceptual model showing the field setup of tracer injection at dam site

18. CASE STUDIES
 Delineating path of seepage in the masonry at
Pawana Dam, Maharashtra
 Ascertaining seepage path in the foundation at
Nagarjunasagar Dam, Andhra Pradesh
 Delineation of Seepage path through galleries in
Koyna Dam, Maharsahtra
 Detecting path of seepage using tracer method in
Bhama-Askhed Irrigation Project, Maharashtra
 Delineation of path of seepage in the downstream
toe region of Salauli Irrigation Project, Goa
CASE STUDIES

19. Pawana Dam

20. Delineating path of seepage in the masonry at
Pawana Dam, Maharashtra
 Excessive seepage observed at drainage gallery
and downstream of the dam. Seepage was
observed like water jets on the downstream slope of
Left Hand Side (LHS) of masonry.
 The appearance of Potassium Permanganate dye
tracer was monitored at downstream observation
points at every 10 minutes interval for about two
hours after injection.
CASE STUDIES

21. Nagarjunasagar Dam

22. Ascertaining seepage path in the foundation at
Nagarjunasagar Dam, Andhra Pradesh
 Three Nx size boreholes viz. Nx-1, Nx-2 and Nx-3 were
drilled on the upstream side of the cavity area to
facilitate injection of tracer.
 Tracers used were sodium fluoresceine, Rhodamine-
B and common salt.
 The tracer studies revealed that there was a
hydraulic interconnection between the foundation
rock and the toe.
 High seepage velocity ranging between 3m/day to
7.8 m/day has also been observed.
CASE STUDIES

23. SALAULI DAM

24. Delineation of path of seepage in the downstream toe region of
Salauli Irrigation Project, Goa
 An excessive seepage was noticed in the
downstream toe of the earthen dam through the
foundation and dam abutment.
 For tracer studies, Rhoda mine-B, sodium chloride
and sodium flouroscein were selected as tracer.
 Point dilution tracer method was conducted to
measure the filtration velocity in the water bearing
formations.
 Seepage velocity was determined by knowing the
arrival of the peak in the concentration versus time
curve and the distance between the injection and
observation holes.
 The studies helped in finalizing design and
construction of diaphragm wall to stop excessive
seepage.
CASE STUDIES

25. CONCLUSIONS
 Tracer techniques play a prominent role in the
investigations required for different stages of hydraulic
structures such
 site selection,
 site investigations,
 watershed studies,
 dam design
 construction,
 leakage investigations,
 sediment control
 improving the longitivity of hydraulic structures
 Tracer technique is a definite, reliable and economic
tool for finalizing the design and construction of
diaphragm walls, cut-off-walls, grouting and guiniting of
the dams.
CONCLUSIONS

26. REFERENCES
 Tree Plantation for Intercepting Canal Seepage and Controlling Watertable, Pakistan Journal of Water Resources,
Vol.11 (2).
 Radio-tracer Techniques for the estimation of seepage losses from unline irrigation channels. Workshop on Nuclear
Technology in Hyderabad.
 “The future of applied tracers in hydrogeology”, Hydrogeology Journal, 13:255-258.
 “Radioactive Tracers in Hydrology”, Elsevier Sci., New York.
 “Borehole Dilution Technique, A critical Review”, IAEA.
 Guidebook on Nuclear Techniques in Hydrology.
 “Tracing Technique in Geohydrology”, A. A. Balkema, Brookfield, Vt.
 “Application of Tritium Tracer to canal seepage measurements” Proc. IAEA Symp.
 Isotope Tracers in Catchment Hydrology. Elsevier Science, Amsterdam.
 Applications of Uranium- and Thorium-Series Radionuclides in Catchment Hydrology Studies.
 Isotope Tracers in Catchment Hydrology, Elsevier, Amsterdam.
 “Radioactive tracer techniques used in solute transport studies in a field soil”, Int. Agrophysics.
 “Injected radiotracer technique in hydrology” Proceedings India Academy Science (Earth Planet Science), Vol
93.
 Ground Water Hydrology, John, Wiley & sons, New York
REFERENCES

27. THANK YOU