1. Under the guidance of
Dr. Arun Kumar
Alternate Hydro Energy
Centre
IIT Roorkee
1
Presented by
GURDEEP SINGH

2. OUTLINE
2
Problem of sediment in SHP
Desilting basins
Need of Performance Evaluation of Desilting basins
Objective of Study
Methodology Adopted
Analysis and Evaluation
Results
Conclusion
Literature Review
References

3. Problem of sediment in SHP Plants
 Sedimentation problem in Hydropower starts from headwork’s to power
house. Each and every Structure intact with water is susceptible and vulnerable
due to sediment laden water.
 This problem is more serious in Himalayan region where good potential of
SHP exist.
 In the case of run-of-river, a relatively small dam or a barrage is built across a
mountain stream to divert the river water into the intake which in turn feeds
the power house through a water conductor system. Due to the large quantities
of sediment likely to be transported by the rivers. This will leads to various
problems:-
1. The diversion dam/barrage may get silted up to the crest within short period of
construction.
2. Thus large quantity of sediment may enter the intake and decrease in the
discharge carrying capacity of the water conductor system.
3. Cause damage to the tunnel lining,
4. Erode the turbine blades and auxiliaries
3

4. Effects on civil structures
Sediment deposited in lined channel Sediment deposited in tailrace channel
of hydropower plant
Sediment deposited near
diversion weir
4

5. Sediment erosion at Pelton
turbine needle
Sediment erosion at Pelton
turbine
Eroded guide vanes
Erosion(At Runner) at pressure
side of blade
Effects of
Erosion on
various
components of
Turbine
5

6. DESILTING BASIN
Desilting basins are constructed close to the intake to trap incoming sediment
before leading to water conductor system/turbine.
Removal of sediment in desilting basins is done by reducing the velocity of
flow through them and remove settled sediment under gravity or mechanical
or manually.
There are two types of desilting basin mainly used for SHP sites in India are :-
i. Settling basin
ii. Vortex settling basin
6

7. Design parameters for settling basin
7
1. Size of sediment load to be removed
2. Settling basin dimensions
3. Velocity in chamber basin
4. Flushing discharge
5. Trap Efficiency
6. Sediment removal techniques

8. 8
1. Basin diameter d, and basin height H;
2. Flushing discharge, Qo or flushing pipe diameter, d0
3. Depth of flow in the basin;
4. Radial slope of basin floor, Sc (horizontal to one vertical)
5.Basin depth at periphery, h2
6. length of overflow weir, Li, and
7. Modelling criteria to ascertain the performance of the designed VSB with the aid
of a physical model
Design parameters for vortex settling basin

9. Need for performance evaluation
9
1. Settling basin are being designed oftenaly by Indian shp designer on basis of
limited data on sediment due to its poor availability on account of not using
skilled persons which are not available easily.
2. It has been observed that often desilting basins are inefficient for silt
removal. The silt removal arrangement are poor, resulting in frequent
choking. This result frequent forced outrage of plant.
Thus performance of these desilting basin are evaluated to make aware to plant
owner sediment impact and loss of generation

10. 10
Desilting tank in himanchal
pradesh 3MW SHP project
Desilting tank in Uttrakhand
5MW SHP project

11. Objective of study
11
The objective of this work :-
1.To evaluate the performance of existing desilting devices.
2.To study the impact of sediment on turbine runner
corresponding to desilting basin efficiency

12. Methodology Adopted
12
1. Reviewed various desilting devices deployed for small hydro
power plants.
2. Identified the projects for data collection covering high and
medium head in different location.
3. Prepared a questionnaire, approach the project owner for data and
visit the site. Data covering the type of desilting devices,
dimension ,number of chamber provided and flushing arrangement
and impact of sediment on turbine and other components.
4. Collected sediment(inflow and flushed out) from different SHP
sites by undertaking site visits.
5. Sieve analysis of sample collected.
6. Evaluation is done by :-
1. Comparing the relation/charts of efficiency of desilting
basin given by different author’s with observed efficiency.
2. Impact of sediment on turbine runner.

13. Site visit details
13
Location Visit duration
Sites located in Chamba and Kangra District visited
(Tarila shp station, Tarila-II shp station, Upper awa shp, Baner-III shp,
Sahu shp station, Iku-II shp, Upper khauli shp, Drinidhar shp station,
Bhuri singh power house, Khauli shp station, Gaj shp)
Nov 17-29,2012
Sites located in Kullu and Mandi District visited
(Jirah shp station, Aleo shp station, Baragan shp station, Sarbari shp ,
Brahmaganga shp station, Patkari shp station, Gurahan shp station
Jan 25- Feb 5,2013
HPPCL design office,Sunder nagar,HP May 22- 26,2013

14. 14
Sr.
no
Name of station Name of
stream
Installed
capacity(
MW)
Type of
Turbine
Head
(m)
Discha
rge
(cume
c)
Inlet
channel
width(m)
Desilting basin dimensions(m) no.
of
outl
et
Flushing
conduit(
mm)
U/S
Transi
tion
Leng
th
Wi
dth
Depth D/S
Transi
tion
1 TARILA
Tareila
nallah 2X2.5 Francis 184 6.00 2.0 10.4 54.7 7.5 4.5 7.8 1 600Ø
2 TARILA-II
Tareila
nallah 2X2.5 Francis 133 6.10 2.0 5.0 36.0 8.5 3.1 5.0 1 600Ø
3 BANER-III Baner khad 2X2.5 Pelton 302 2.70 1.8 7.5 30.0 5.0 2.5 1 500x500
4 IKU-II Iku khad 2X2.5 Pelton 362 3.96 1.8 7.7 52.0 5.0 2.5 4.0 1 500x500
5 UPPER KHAULI
Khauli
Khad 2X2.5 Pelton 430 2.34 1.8 8.0 51.5 4.5 4.1 4.0 1 500x500
6 DRINIDHAR
Brahl
Khad, 2X2.5 Pelton 249 3.10 1.8 10.5 45.0 5.0 2.5 5.0 1 500x500
7 ALEO MANALI
Allain
stream 2X1.5 Pelton 290 1.60 1Ø 25.0 5.0 2.0 5 300Ø
8 BARAGOAN
Sanjoin
nallah 1X1.9 Francis 170 4.25 2.3 18.0 62.0 6.0 3.0 1 1000Ø
9 SARBARI
Sarbari
khad 2X2.25 Pelton 202 4.50 43.9 9.4 4.1 4 300Ø
10 JIRAH
Jirah
Nallah, 2X2 Pelton 348 1.31 1.2Ø 9.5 30.0 5.0 6.0 3 800Ø
11 TOSS Toss nallah 2x5 Pelton 186 4.32 45.0 7.0 3.0
12
BRAHMAGANG
A
Bharamgan
a 2X2.5 Pelton 230 3.15 1.6Ø 20.6 40.0 7.0 3.0 6.0 1 500Ø
13 GURAHAN
Gurahan
Khud 1X1.5 Pelton 216 1.10 1.2 4.5 40.0 3.0 1.0 4.5 1 300Ø
14 PATKARI
Bakhli
khad 2X8 Pelton 375 5.83 3.5 10.0 54.0 7.0 3.5 3 500Ø

15. 15
Sr
.n
o
Name of
station
Name of
stream
Installe
d
capacity
(MW)
Type of
Turbin
e
Head
(m)
Disc
harg
e
(cum
ec)
Inlet
cha
nnel
widt
h(m
)
Desilting basin
dimensions(m)
slope(
1V:H)
no.
of
outl
et
Flushin
g
conduit
(mm)
Diameter Depth
15 GAJ Gaj & Leond 3x3.5 Pelton 213 6.93 3.4 17 2.05 01:10 1 600Ø
16 KHAULI Khauli Khad 2x6 Pelton 475 3.19 2.4 12 2.00 01:10 1 450Ø
17
BHURI
SINGH Sal nallah 0.45 Francis 13.72 5.14 3.4 17 2.15 01:10 1 600Ø
Vortex settling basin sites

16. 16
1 2
11
10
12
9
7
14
13
8
6
4
5
16
15
17

17. 17
D-tank Baragran shp station(1x1.9MW) D-tank Drinidhar shp station (2x2.5MW)
D-tank Sarbari shp station (2x2.25MW)D-tank Jirah shp station (2x2.0MW)

18. 18
D-tank Tarila-II shp station (2x2.5MW) D-tank Tosh mhp station (2x5 MW)
D-tank Upper khauli shp station (2x2.5 MW) D-tank Tarila shp station (2x2.5MW)

19. 19
Vortex Settling Basin
D-tank Khauli shp station(2x6 MW) D-tank Bhuri singh power house(450 kW)
D-tank Gaj shp station(3x3.5 MW)

20. Efficiency evaluation of desilting basin
20
I. Efficiency of settling basin and vortex settling basin first computed by
relation /charts given by various authors and then compared with observed
efficiency.
II. Observed efficiency of desilting basins calculated by comparing the GSD
curve at inlet and flushing oulet.
III.Relation and charts used for efficiency evaluation of settling and vortex
basin are:-
settling basin:-
a. Camp Dobbins curve
b. Garde method
c. GSD curves (At inlet and flushing outlet)
vortex settling basin:-
a. T.C Paul relation
b. M.Ather relation
c. GSD curves (At inlet and flushing outlet)

21. Efficiency evaluation of settling basin
1. The minimum size of particle to be removed is selected.
2. Then with help of Hunter Rouse curve fall velocity(Vs) of the selected square
quartz particle at particular temperature is obtained. The Hunter Rouse curve
of fall velocity(Vs) .
3. Parameters comprising of flow velocity, settling velocity, length and depth of
basin calculated. The following parameters are:-
(a) Settling velocity x depth of tank(1/6)
Flow velocity x regosity coefficient x √g
(b) Settling velocity x length
Flow velocity x Depth of tank
21
I. Camp-Dobbins curve

22. Hunter Rouse curve Fall velocity of quartz
sphere in water and air
22

23. Sediment removal Efficiency of settling basin
by Camp-Dobbins
23

24. 24
II.Garde method
Relationship developed by Grade to find the sediment removal efficiency of settling basin
give by:-
where ηo is the limiting efficiency obtained for a given w/u* at large values of
L/D and k is a coefficient.

25. 25
Efficiency evaluation of vortex settling basin
I. Paul’s relation
The Efficiency computation relation given by T.C Paul et al. is :-
Where P is Efficiency in (%),
Dt = Diameter of tank
Sc = slope adopted at all project sites (10H : 1V)
Vs is settling velocity of particle
W is vertically upward velocity(W=(4Qs/πDt2
).
Qs= overflow Discharge(Qi-Qo)
Qi= Inlet discharge
Qo= Flushing discharge

26. 26
II.Ather’s relation
The efficiency computed method given by M. Ather relation is as follows:-
Where Qi =Discharge in the inlet channel ;
Qu =Discharge flushed out through the under flow
ω = Fall velocity of sediment;
d = Sediment size;
hp =Depth of flow at periphery of the chamber;
Zh
=Elevation difference between inlet and outlet channel beds at their junctions
with the vortex chamber,
RT
=Radius of the vortex chamber,
g = Gravitational acceleration,
v = Kinematic viscosity and
K =Coefficient
Qw= Qu+k(Qi-Qu)

27. Grain size Distribution
27
With the help of this distribution ,percentages of various size of soil grain in a
given dry soil sample can be find out.
Sieve analysis
The soil sample is separated in to two fraction by sieving through 4.75mm sieve.
 The fraction retained on this sieve (+4.75 mm) is called gravel fraction which is
subjected to coarse sieve analysis.a set of sieve sizes 80mm, 20mm 10mm and 4.75mm
is used for further gravel fraction.
The material passing through 4.75mm (-4.75mm) is subjected to fine sieve
analysis.the set of I.S. sieves for fine sieve analysis consist of 2mm, 1mm, 600μ, 425μ,
212μ, 150μ,75 μ sieves.

28. Procedure
28
A suitable sieve size for the aggregate should be selected and placed in order of
decreasing size, from top to bottom, in a mechanical sieve shaker.
 A pan should be placed underneath the nest of sieves to collect the aggregate that
passes through the smallest. The entire nest is then agitated (10 -15 min), and the
material whose diameter is smaller than the mesh opening pass through the sieves.
 After the aggregate reaches the pan, the amount of material retained in each sieve
is then weighed.
Results
The results are presented in a graph of percent passing versus the sieve size. On
the graph the sieve size scale is logarithmic.
To find the percent of aggregate passing through each sieve, first find the percent
retained in each sieve.
To do so, the following equation is used,

29. 29
The cumulative percent passing of the aggregate is found by subtracting
the percent retained from 100%.
%Cumulative Passing = 100% - %Cumulative Retained.
Sieves used in grain size distribution
Experiment Set-up for Sieve analysis
Efficiency computed by comparing the GSD curves :-

30. 30

31. 31

32. 32
Vortex settling basin GSD curve

33. 33
ANALYSIS AND EVALUATION
Performance of desilting basin are evaluated by :-
1.Comparing the results computed from different methods
2.Effect of desilting basin efficiency on turbine runner

34. 34
size of particles in (mm) 0.15mm 0.2 mm 0.25 mm 0.5 mm 1 mm
Site location
Efficien
cy from
Camp
Dobbin
s curve
Efficie
ncy
from
Garde
metho
d
Oserv
ed site
efficie
ncy
Efficien
cy from
Camp
Dobbin
s curve
Efficien
cy from
Garde
metho
d
Oserv
ed
site
efficie
ncy
Efficien
cy from
Camp
Dobbin
s curve
Efficie
ncy
from
Garde
metho
d
Oserv
ed site
efficie
ncy
Efficien
cy from
Camp
Dobbin
s curve
Efficie
ncy
from
Garde
metho
d
Oserv
ed site
efficie
ncy
Efficien
cy from
Camp
Dobbin
s curve
Efficie
ncy
from
Garde
meth
od
Oserv
ed site
efficie
ncy
TARILA SHP
STATION,TARILA 100% 85% 30% 100% 95% 33% 100% 95% 41% 100% 95% 46% 100% 95% 75%
TARILA-II SHP
STATION,TARTILA 75% 37% 63% 97% 94% 60% 100% 94% 58% 100% 94% 58% 100% 94% 67%
BANER-III SHP,BANER 78% 37% 33% 98% 94% 41% 100% 94% 56% 100% 94% 78% 100% 94% 91%
IKU-II SHP 88% 23% 30% 99% 69% 29% 100% 99% 38% 100% 99% 58% 100% 99% 85%
UPPER KHAULI SHP,KHAULI 98% 95% 58% 100% 95% 69% 100% 95% 74% 100% 95% 89% 100% 95% 90%
DRINIDHAR SHP
STATION,DRNIDHAR 95% 31% 0% 100% 95% 0% 100% 99% 25% 100% 99% 44% 100% 99% 82%
ALEO SHP STATION,MANALI 95% 86% 14% 100% 95% 36% 100% 95% 67% 100% 95% 100% 100% 95% 100%
BARAGRAN shp
station,baragran 97% 48% 50% 100% 99% 56% 100% 99% 60% 100% 99% 53% 100% 99% 61%
SARBARI SHP ,SARBARI 98% 93% 71% 100% 93% 60% 100% 93% 38% 100% 93% 47% 100% 93% 74%
JIRAH SHP STATION,TOSH 100% 70% 50% 100% 70% 50% 100% 70% 57% 100% 70% 92% 100% 70% 97%
TOSH MHP STATION,TOSH 92% 60% 4% 100% 97% 5% 100% 97% 8% 100% 97% 34% 100% 97% 79%
BRAHMAGANGA SHP
STATION,MANIKARAN 98% 94% 90% 100% 96% 88% 100% 96% 89% 100% 96% 100% 100% 96% 100%
GURAHAN SHP STATION 97% 19% 38% 100% 43% 36% 100% 76% 36% 100% 100% 57% 100% 100% 80%
PATKARI SHP
STATION,PATIKARI 90% 43% 22% 100% 97% 21% 100% 98% 22% 100% 98% 51% 100% 98% 82%
Computation efficiency of settling basins

35. 35
Efficiency of settling basin evaluated by
different methods

37. 37

38. 38
Variation of efficiency of settling basin w.r.t paricle size(mm)

39. 39
Name of
site 0.15 0.2 0.25 0.3 0.5 1
Effici
ency
from
Paul
relati
on
Effici
ency
from
Ather
relati
on
Obse
rved
site
efficie
ncy
Effici
ency
from
Paul
relati
on
Effici
ency
from
Ather
relati
on
Obse
rved
site
efficie
ncy
Effici
ency
from
Paul
relati
on
Effici
ency
from
Ather
relati
on
Obse
rved
site
efficie
ncy
Effici
ency
from
Paul
relati
on
Effici
ency
from
Ather
relati
on
Obse
rved
site
efficie
ncy
Effici
ency
from
Paul
relati
on
Effici
ency
from
Ather
relati
on
Obse
rved
site
effici
ency
Effici
ency
from
Paul
relati
on
Effic
iency
from
Athe
r
relat
ion
Obse
rved
site
efficie
ncy
Bhuri
singh
SHP 75% 98% 91% 84% 98% 93% 91% 98% 92% 97% 98% 100%113% 98% 100%141%99% 100%
Gaj SHP 82% 98% 80% 92% 98% 81%100% 98% 75%106% 98% 82%123% 98% 97%155%99% 100%
Khauli
SHP 82% 98% 12% 92% 98% 100% 98% 50%106% 98% 67%124% 98% 86%155%99% 94%
Computation efficiency of vortex settling basins

40. 40
Efficiency of vortex settling basin evaluated
by different methods

41. 41
Variation of efficiency of settling basin w.r.t particle size(mm)

42. Impact of turbine runner
42
Factors influencing erosion -
Silt characteristics
I.Size and Shape of Particles
II.Hardness of Particles
III. Concentration
Resistance of turbine Material,
Net Head on turbines
Velocity of water carrying silt
HEAD (M) MAXIMUM SIZE OF PARTICLES
100 – 200 0.60 mm to 1.00 mm
200 – 300 0.50 mm to 0.60 mm
300 - 500 0.30 mm to 0.50 mm
> 500 0.10 mm to 0.30 mm

43. Erosive Wear on turbine
43
To calculate erosive wear on turbine following relation to be used:-
For Pelton Turbine:-
Where,
‘S’ silt particle size (m).
‘t’, operating hour (h)
‘V’ velocity of flow (m/s) =0.47x0.98x√(2gh)
‘W’ normalized wear (g/g) per unit discharge (m3
/s)
For Francis Turbine:-
Where
W = erosion rate in kg/h,
V = velocity of particle in m/s = 0.4x√(2gh)
d = particle size in meter,
C = silt concentration in g/liter, and
K, β, γ and ψ is equal to 0.98, 1.1, 0.8 and 0.85 respectively.
( M.K.Padhy & R.P. Saini, 2008)
(B.K.Gandhi et. al,1999)

44. Continue…
44
Erosive wear at different sites due to particle size(0.2mm-1mm) have
concentration 3000 ppm during the monsoon season in north region of India
( from July to September,t ime=24x90 =2160 hours) calculated.

45. 45
Wt loss in kg for particle size
Head
range(m)
Sr.no Name of site Capacity
(MW)
Type of
turbine
Design
dischar
ge(cum
ec)
Head(m) Velocit
y(m/sec
)
0.2mm 0.25mm 0.3mm 0.5mm 1mm
100-200
1 Tarila-ii shp station,tartila 2 x 2.5 Francis 2.26 133 20.43 0.065 0.078 0.090 0.135 0.236
2
Baragran shp
station,baragran 1x1.9 Francis 1.5 170 23.10 0.074 0.089 0.103 0.155 0.270
3 Tarila shp station,tarila 2 x 2.5 Francis 1.589 184 24.03 0.078 0.093 0.108 0.162 0.282
4 Tosh mhp station,tosh 2 x 5 Pelton 3.2 186 27.82 0.094 0.095 0.096 0.099 0.103
200-300
5 Sarbari shp ,sarbari 2 x 2.25 Pelton 1.373 202 29.00 0.047 0.048 0.048 0.050 0.052
6 Gaj shp,dharamshala 3 X3.5 Pelton 3.1 213 29.78 0.118 0.119 0.121 0.124 0.129
7
Brahmaganga shp
station,manikaran 2 x 2.5 Pelton 2.52 230 30.94 0.111 0.112 0.113 0.117 0.121
8 Gurahan shp station 1 x 1.5 Pelton 0.83 215.5 29.95 0.032 0.033 0.033 0.034 0.035
9
Drinidhar shp
station,drnidhar 2 x 2.5 Pelton 1.49 249 32.19 0.076 0.077 0.078 0.080 0.083
10 Aleo shp station,manali 2 x 1.5 Pelton 0.63 290 34.74 0.043 0.044 0.044 0.045 0.047
300-500
11 Baner-iii shp,baner 2 x 2.5 Pelton 1.19 302 35.45 0.088 0.089 0.090 0.092 0.096
12 Iku-ii shp 2 x 2.5 Pelton 1.69 362 38.82 0.176 0.178 0.180 0.185 0.192
13
Patkari shp
station,patikari 2 x 8 Pelton 5.83 374.5 39.48 0.646 0.654 0.661 0.681 0.708
14 Upper khauli shp,khauli 2 x 2.5 Pelton 0.834 430 42.31 0.120 0.122 0.123 0.127 0.132
15 Khauli shp station,khauli 2 x 6 Pelton 1.525 475 44.47 0.265 0.269 0.271 0.279 0.291

46. 46
location Site Type of turbine Head(m) Head range Efficiency(%) of settling basin
computed from G.S.D curves w.r.t size
of particles (mm)
Remarks
0.15 0.3 0.5 1 Regarding efficiency Effect on turbine
TARILA-II FRANCIS 133
100 to 200
63 57 58 67
Inefficient in removing
particle size upto 1mm Susceptible to erosion
BARAGOAN FRANCIS 170 50 56 53 61
Inefficient in removing
particle size upto 1mm Susceptible to erosion
TARILA FRANCIS 184 30 42 46 75
Inefficient in removing
particle size upto 1mm Susceptible to erosion
TOSH PELTON 186 4 6 34 79
Inefficient in removing
particle size upto 1mm Susceptible to erosion
SARBARI PELTON 202
200 to 300
71 33 47 74
Inefficient in removing
particle size upto 0.5mm Susceptible to erosion
GURAHAN PELTON 216 38 42 57 80
Inefficient in removing
particle size upto 0.5mm Susceptible to erosion
BRAHMAGANGA PELTON 230 90 92 100 100
efficient in removing
particle size upto 0.5mm
Not susceptible to
erosion
DRINIDHAR PELTON 249 0 20 44 82
Inefficient in removing
particle size upto 0.5mm Susceptible to erosion
ALEO PELTON 290 14 92 100 100
efficient in removing
particle size upto 0.5mm
Not susceptible to
erosion
BANER-III PELTON 302
300 to 500
33 76 78 91
Inefficient in removing
particle size upto 0.3mm Susceptible to erosion
JIRAH PELTON 348 50 83 92 97
efficient in removing
particle size upto 0.3mm
Not susceptible to
erosion
IKU-II PELTON 362 30 40 58 85
Inefficient in removing
particle size upto 0.3mm Susceptible to erosion
PATKARI SHP PELTON 375 22 29 51 82
Inefficient in removing
particle size upto 0.3mm Susceptible to erosion
UPPER KHAULI PELTON 430 58 81 89 90
efficient in removing
particle size upto 0.3mm
Not susceptible to
erosion

47. 47
Site
location
Type of
turbine
Head
(m)
Head
rang
e(m)
Efficiency(%) of
settling basin computed
from G.S.D curves w.r.t
size of particles (mm)
Remarks
0.15 0.3 0.5 1
Regarding
efficiency
Effect on
turbine
BHURI
SINGH FRANCIS 13.75 <100 91 100 100 100
efficient in
removing
particle size upto
1mm
Not susceptible
to erosion
GAJ PELTON 213
100-
200 80 82 97 100
efficient in
removing
particle size upto
0.5mm
Not susceptible
to erosion
KHAULI PELTON 475
300-
500 12 67 86 94
Inefficient in
removing
particle size
upto 0.3mm
Susceptible to
erosion

48. 48
Economic evaluation of desilting basin
The project taken for the economic study of desilting basin is Upper khauli SHP
situated in Kangra, Himanchal Pradesh. The features of project as follows:-
Design discharge = 2.3cumec(including flushing discharge)
Head = 430m
Capacity = 2x2.5 MW
Type of turbine = Horizontal pelton
Comparative features of Desilting basins
Inlet Discharge (cumec) 2.3 2.3
Basin Dimensions(m) 51.5(L) x 4.5(B) x 6(D) 9m(dia) x 2.55m(D)
Volume of Basin(m3
) 1390.5 162
Flushing Discharge(cumec) 0.58 0.23
Water Available for power
generation(cumec) 1.73 2.07
Cost of Basin(Millon of Rs.) 4.5 0.93
Power generation(kW) 5000 6025
Settling Efficiency(%) 95 98

49. 49
Economic analysis
Difference saving in construction cost = 4.5-0.92 = Rs3.58 Millon
Assuming life of project 35 years and internal rate of return (IRR) as 8%
Annual equivalent saving = Rs. 3.58x105
x(1.0835
x0.08 )/( 1.0835
– 1)
=Rs. 0.31 Millon/ year
Annual Power saving assuming 60% generation = (6024.99 -5000)x8760x0.60
= 5.2 million units
Net increase in saving due to increase in power assuming rate Rs. 3/kWh =5.2x3
= 15.6 Millon
Thus total saving per year if vortex settling basin is adopted instead of settling basin
= 0.31+15.6
= 15.91 Millon

50. 50
Settling basin
.
Designed settling basin at the selected sites are sufficient to tap the particles less than
0.5mm in spite of that, these settling basin showing less efficiency this may due to:-
Inadequate design flushing arrangement.
Turbulence in water, causes the sediment in suspension.
Transitions are not designed properly.
These settling basin mostly designed for intermittent flushing, but timely flushing are not
done due to this flushing arrangement get chocked frequently causes decrease in
efficiency of these basins.
.
Vortex settling basin
The observed efficiency of vortex settling basin is very close to designed efficiency for all
particle Further these basin required less volume of water to flush the sediment and proves
to be economical desilting device specially for removal of particle size 0.1mm- 0.2mm
cause sediment erosion on hydro mechanical components.
RESULTS

51. 51
Comparative study of settling basin and vortex settling basin shows that vortex
settling basin is efficient and economical desilting device as compared to settling
basin for small hydropower sites having advantages:-
Land area required for sedimentation is less.
Require lower flushing.
Cost of construction is about one fourth of settling basin cost.
Hydraulic efficiency as compared to settling basin is high.
In vortex settling basin water may diverted directly to power channel during
lean season when water is almost free of sediments. This is important in cold
region where settling basin freeze due to lower vicinity and causes the shutting
down of machines.
CONCLUSIONS

52. Author Title of Paper Objective Results
Develay
et al.
(1996)
Desilting basin of
Dul Hasti hydro
electric project
To trap a high percentage of the
coarser particles generally made of
quartz
The trapping efficiency increases with the sediment
concentration.
Raju, et
al. (1999)
Sediment Removal
Efficiency of
Settling Basins
To find a new relationship for
sediment settling basin for non-
cohesive sediments
It was also found that Continuous flushing of the
basin improves the sediment removal efficiency of
settling basins.
Weerakoo
n et al.
(2007)
Effect of the
Entrance Zone on
the Trapping
Efficiency of
Desilting Tanks in
Run-of-River
Hydropower Plants
To find effect of the entrance zone
on the sand trapping efficiency of
the desilting tanks
The sand trapping efficiency was found to vary
from 50% to 85% with the reduction of expansion
angle from 30o to 10o.The trapping efficiency of the
tank increases with the reduction of the expansion
angle of the entrance zone in the desilting tanks,
the optimum expansion angle was found to be
about 10 deg.
Shah et
al. (2008)
Transitions For
Desilting Basin
With Open Channel
Flow
To study the effect of Transitions
For Desilting Basin With Open
Channel Flow
The hydraulic model studies by providing a simple
hump and a central divide wall
Literature Review
Efficiency of Desilting Basin
Efficiency of Settling Basin
52

53. Author Title of Paper Objective Results
Alired D.
Mashauri
(1983)
Removal of sediment
particles
By vortex basin
discussed the hydraulic
performance of vortex-type
settling basins both, with
horizontal and sloping floor
settling efficiency η , and amount of water through
orifice arc given for both versions - horizontal
floor and sloping floor showed a respectable
performance
Paul et al
(1991)
Vortex Settling
Basin Design
Consideration
vortex settling basin design for
extraction of sediment smaller
than 0.5 when a diaphragm and a
deflector were incorporated in
the inlet canal and basin,
respectively
Diameter of the flushing pipe and flushing
discharge depend on the grade of sediment
transported by the inlet canal
Athar et al
(2002)
Sediment Removal
Efficiency of Vortex
Chamber Type
Sediment Extractor
Studied the sediment removal
efficiency of vortex chamber
type sediment extractors.
a new relationship was developed for
determination of the sediment removal efficiency
of the vortex chamber type sediment extractors.
Nguyen
Quang
Troung
(2010)
Effect of deflector
on removal
efficiency of a deep-
depth vortex
chamber sediment
extractor
To study effect of deflector in
circular basin
The experimental results also indicate that the
values of η was considerably stable and reach the
maximum value for the case of three deflectors.
Naser et al.
(2011)
Improvement the
Trap Efficiency of
Vortex Chamber for
Exclusion of
Suspended Sediment
in Diverted Water
To improve trap efficiency of
vortex sediment settling basin.
It was found that the best location for the deflector
is between the inlet channel and the outlet
overflow weir, when the inlet channel is located
under the overflow weir increases the trap
efficiency and the hydraulic efficiency
Efficiency of vortex type of settling basin
53

54. Author Title of Paper Objective Results
Thapa et al.
(2005)
Problems of Nepalese
hydropower projects
due to suspended
sediments.
To study effect of type mineral of
sediment on turbines.
It was found that higher amount of quartz content gives
higher erosion rate and the percentage of quartz, shape
of the particles also has influence in erosion rate.
Bajracharya
et al.(2008)
Sand erosion of
Pelton turbine
nozzles and buckets.
To find effect of sediments on pelton
turbine.
It was found that High quartz content and increase
sediment load during monsoon along with the small
particle size are the major cause for the severe erosion
of turbine parts.
Padhy et al.
(2009)
Effect of size and
concentration of silt
particles on erosion
of Pelton turbine
buckets
To study effect of concentration and
size of silt on erosion of pelton turbine.
The erosive wear rate increases with an increase in the
silt concentration irrespective of the silt size.
Prasad et al.
(2010)
Sediment Erosion in
Hydraulic Turbine
Using Rotating Disc
Apparatus
To find relation between erosion and
run time.
From this study, erosion (weight loss) was found
directly proportional with sediment size and also erosion
was found directly proportional with run time.
Hari Prasad
Neopane
(2010)
Sediment Erosion in
Hydro Turbines
To find sediment erosion effects on
hdro turbines
It was found that erosion is strongly depended on the
shape of the particle.
Poudel et al.
(2012)
Sediment impact on
turbine material case
study of Modi river
To find out the impact of sediment on
turbine material.
The sediments in course of rolling down from upstream
to downstream its shape and size changes and have less
eroding property than one found in upstream of the
river.
Padhy et al.
(2012)
Effect of shape of silt
particles on erosive
wear of pelton
turbine bucket
To investigate effect of shape of silt
particles on erosive wear of pelton
turbine bucket.
It has been concluded that the sharp particles have more
eroding capacity than the rounded shaped particles.
Characteristics of sediments
54
SILT EROSION ON TURBINE

55. B.S.
Mann
(2000)
High-energy particle
impact wear
resistance of hard
coatings and their
application in hydro
turbines
To study, hard coatings such as hard
chrome plating, plasma nitriding, D-
gun spraying and boronising were
studied for high-energy impact wear
resistance
It was found that Borided T410 steel appears to be an
excellent erosion resistance shield to combat high-
energy particle impact wear. It can provide an
appropriate solution to the hydropower stations
severely affected due to silt.
Padhy et
al. (2008)
A review on silt
erosion in hydro
turbines
Survey various aspects related to silt
erosion in hydro turbines, different
causes for the declined performance
and efficiency of the hydro turbines
It was found that Silt erosion in hydro turbines cannot
be avoided completely, but can be reduced to an
economically acceptable level
Peter
Joachim
Gogstad
(2012)
Hydraulic design of
Francis turbine
exposed to sediment
erosion
To carried out new hydraulic design
of runner and guide vanes of existing
francis turbine at La Higeura power
plant where velocity component were
reduced.
The best way of reduce erosion will therefore be
coating of all wet surfaces.
Thapa et
al. (2012)
Empirical modeling
of sediment erosion
in Francis turbine
To dentify an appropriate erosion
model for Francis turbine
It has been found that sediment data from the site can
be analyzed to predict the damage in Francis runner
due to erosion
Thapa et
al. (2012)
Current research in
hydraulic turbines
for handling
sediments
To create and optimize the design of
Francis runners.
It was also observed that optimization of hydraulic
design of blade profile alone can reduce sediment
erosion more than 30%
Design parameters of turbine
Author Title of Paper Objective Results
55

56. Research paper
56
Gurdeep singh, Arun kumar, “A Review of Desilting Basins Used in Small
Hydropower Plants”, International journal of emerging technology and
advanced engineering, ISSN 2250-2459, ISO 9001:2008 certified journal,
Volume 3, Issue 5, May 2013 pp 440-444. (published)
Gurdeep singh, Arun kumar “Performance evaluation of desilting basin used in
small hydropower projects” (in process)

57. 57
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