study on water quality and lime leaching in dams •the soil
TRANSCRIPT
Study on Water Quality and Lime Leaching in DamsEr. N. Pandian Er. A. Kalimuthu Sri. E. RajuExecutive Engineer, PWD, WRD Research Officer II, PWD, WRD Research Assistant, PWD, [email protected]
•The Soil Mechanics & Research Division have been monitoring the health status of the dams in TNWRD through Water Quality & Lime leaching studies.
•Till 1984, the studies were confined to (1) Periyar (2) Vaigai and (3) Manimuthar Dams
• and gradually extended to 14 dams till March 2014 and now 9 more dams are added.
Hard Waters
Low Hard Waters
Soft Waters
Mordhana
Krishnagiri
Sathanur
Mettur
Bhavani Sagar
Amaravathi
Vaigai
Periyar
Manimuthar
Pechiparai
Perunchanai
Parambikulam
Sholayar
Lower Nirar
Tamil Nadu Reservoirs
Legends
Tamil Nadu Reservoirs
pH 8.50TDS 200 ppmFluoride 0.9 ppm
pH 8.50TDS 540 ppmChloride 175 ppmNitrate 5.0 ppm
pH 8.18TDS 315 ppmFluoride 0.3 ppm
pH 7.50TDS 378 ppmChloride 120 ppmNitrate 1.0 ppm
pH 6.90TDS 39 ppmNitrate 1.2 ppm
pH 7.5TDS 149 ppmAlkalinity 125 ppm
pH 6.50TDS 77 ppm
pH 6.75 TDS 66 ppmNitrate 1.7 ppm
pH 6.90TDS 17 ppm
pH 7.50TDS 33 ppm
pH 5.5 TDS 37 ppm
pH 5.5 to 6.5TDS 20 to 30 ppm
‐ Originating from western Ghats ‐ Dam at 64 km‐ confluence with Amaravathy at 104 km
Case study 1: Water quality of River and Dam of Kodaganar‐ Impact on dam structures (Shutters)
• Failure of Kodaganar Dam shutters necessitated to take up the study as a special case
• Preliminary investigation reveals ‐ unnatural surface water‐ results indicated industrial contamination
Need of the Study
River Kodaganar sample locationsAuthur Anicut
Authur Reservoir
Sithalakundu - ThamaraikulamAnicut
Boothipuram Anicut
Kodaganar Anicut
Venkatrama Iyengar Anicut
Lakshmanampatti Anicut
Bhoothipuram AnicutVedachandur
Kodaganar Dam
Pollution Entry 1
Pollution Entry 2
Down stream of Dam
Ground Water
Kodaganar DamOBSERVATIONS: pH value at site is between 8.0 and 9.0
Water is polluted with chlorides and sulphates
Deposits found all over the Shutters and structures
Scaling formed throughout the structure
Shutters are completely corroded
Chloride attack on Shutters
‐ increase in volume
‐ Decrease instrength
Reason for the Non‐operation of shutters
Back side ‐Thick Corroded shutter which
was mobile
Scale formation in the front side
0
1000
2000
3000
4000
5000
6000
7000
1 2 3 4 5 6 7 8 9 10 11
Total Dissolved Salts in mg/l
PollutionEntry point 2
Pollution entry point 1
1 Authoor Reservoir2 Sithalakundu ‐
Thamaraikulam3 Boothipuram Anicut4 Kodaganar Anicut5 Near Bridge NH76 Venkatarama
Iyengar Anicut7 Lakshanapatti
Anicut8 Bhoothipuram
Anicut, Vedachandur9 Kodaganar Dam10 D/s Kodaganar Dam11 Ground Water
6
7
8
9
10
0 50 100 150 200 250 300 350
pH
Corrosive
Scale ‐ forming
Kodaganar Dam
Alkalinity (ppm) ‐‐‐‐‐
Safe Zone
Case Study 2 : Lime Leaching Study of Manimuthar Dam
• Comparison of water quality in reservoir and gallery reveals the loss of lime from the dam structure.
• Low pH & Low TDS main causes for Lime leaching
Reference• Methodology confirmed by the “Guidelines for Measurement,
Testing and Analysis of Seepage from Masonry and Concrete Dams” by CBIP, New Delhi.
&
LI is based pH, Ca hardness, TA, T i C & TDS ( 1000 )
Various stages of Lime Leaching process
Stage I
Stage II
13
No Deposit
pH 13.0
NaOH, KOH
White Colour
pH 13.0 – 12.5
CaO
Various stages of Lime Leaching process
Stage III
Stage IV
14
Creamy white
pH 12.5 – 12.0
Calcium Oxide + little Alumina & Iron Oxide
Yellowish brown
pH 12.0 – 10.0
More Alumina & less Iron Oxide
Various stages of Lime Leaching process
Stage V
Stage VI
15
Dark Brown
pH 12.0 – 10.0
Less Alumina & More Iron Oxide & at last Silica gel
Black
pH 10.0 – 8.0
Fungi
Between Block 10 and Block 8 In Block 6
Advanced stage of Lime leaching
• Seepage water from 15 Nos. of V notches of Manimuthar Dam is being tested for Lime content.
• Lime leached out from the Manimuthar Damfrom 1959 to August 1984
• Percentage of Lime leached out = 3.89 %
• Lime leached out from the Manimuthar Dam from september 1984 to March 2014
• Percentage of Lime leached out = 0.99 %
• Total Lime lost (from 1959 to 03/2014) = 3.89+0.99= 4.88 %