Presentation by Pavan Kumar Yeditha (IHE, Netherlands), at the Delft3D User Days, during Delft Software Days - Edition 2022. Tuesday, 15 November 2022.

1. Modelling the impact of dam operation on flood management
using D-Flow FM 1D coupled with D-Real Time Control: A case
study of Mettur Dam in Cauvery River (India)
Yeditha Pavan Kumar
IHE-Delft and Deltares, The Netherlands
Sanjay Giri
Deltares, The Netherlands
Biswa Bhattacharya
IHE-Delft, The Netherlands
Acknowledgements
Amgad Omer and Victor Chavarrias
Deltares, The Netherlands

2. Presentation outline
❑ Background
❑ Research objectives
❑ Computational modelling
❑ Results and analysis
❑ Conclusions and recommendations

3. Rivers are major source of surface water!
Source: https://openrivers.eu/online/
http://www.bankersexpress.in/list-important-indian-cities-river-banks-download-pdf/
They support the communities on their banks
and are considered as a boon.
Background

4. Rivers also cause hazards and disasters due to extreme (natural) hydrometeorological
conditions as well as due to human interventions and mismanagement that increase
vulnerability and risks!
https://www.theatlantic.com/photo/2013/06/early-monsoon-rains-flood-northern-india/100537/
Background

5. www.tasnimnews.com
✓ Dams are not always used in an optimal way considering their multifunctional aspects.
✓ For example, most of the dams in the region of India with water stress situation during low-flow
period are mainly used for irrigation and drinking water supply (and to a lesser degree for
hydropower energy).
✓ They do not always consider the flood management and river ecological aspects properly.
https://www.brisbanetimes.com.
Background
Dams in rivers are important measures for water security, green energy as well as for
flood management

6. ✓The main river of Cauvery basin
✓3rd largest river of India – “Ganges of
South”
✓It flows through Karnataka, Tamil Nadu,
Kerala and Puducherry.
✓Average annual rainfall about 1080 mm
(rainfall from South-West and North-East
monsoon)
✓Average annual discharge ≈ 700 m3/s
✓21 tributaries - the major ones are Kabini,
Hemavathi, Bhavani, Harangi
✓Major dams in the Cauvery River are
Krishna Raj Sagar (KRS) and Mettur dams
(there are several barrages).
✓There are more than 100 dams in the
basin that affects the flow in Cauvery.
1
Cauvery (Kaveri) River
Background
Courtesy: Central Water Commission
About 85% of annual rainfall occurs during the monsoon period!
Major floods in 2005, 2007, 2018, 2022
Mettur Dam

7. ❑ Studying the flood event of 2018 with a focus on the effect of dam operation
in the Cauvery River
❑ Investigating the scenarios to assess the flood management capability of
Mettur Dam
Research objectives
The study has been carried out using one-dimensional computational model
D-Flow FM 1D coupled with D-Real Time Control (RTC - to simulate reservoir
operation)

8. Details of Cauvery river basin observation stations& dams
Longitudinal profile of the modelled river reach
Data preparation and the model reach
Computational modelling

9. Computational modelling
Full river model for model calibration and verification Reservoir models for scenario simulations
Model development

10. Computational modelling
Reservoir operation using D-RTC
Model development
✓ D-RTC allows to simulate complex real-time
control of all hydraulic structures in
reservoirs, rivers and canals systems. This
module allows the system to react optimally
to actual water levels and discharges by
controlling gates, weirs, sluices and pumps.
An example of setting up gate operation rule
✓ In this work a simple PID controller and
Condition based PID controller are used.
✓ The Parameters which govern the accuracy of
PID controller are Kp, Ki and Kd. These are
gain factors which govern the optimal
operation of variable of interest varying
based on deviation of error from optimal
value.

11. Computational modelling
Modelling cases, scenarios and boundary conditions
✓ 2018 flood event is used for the model calibration and
verification including reservoir operation.
✓ Reservoir operation is based on the data from the same
period.
✓ Lateral inflows from tributaries are imposed based on
the data (the tributaries inflowing to the reservoir were
modelled)
Discharge condition at upstream boundary (@Kudige)
Q-h relation at Mettur dam

12. Computational modelling
Modelling cases, scenarios and boundary conditions
✓ Simulating various reservoir operation
scenarios to assess whether it could be
possible to manage 2018 flood in a
better way
✓ Simulating scenarios with two structural
measures to improve the flood
management capability of the dam, viz.
(i) lowering the spillway level to
increase the flow release from the
reservoir, and (ii) increasing the dam
height
Modelling scenarios and conditions

13. Result and analysis
Model calibration and verification
Water level rises faster
than the observed level
Early gate opening
Higher peak
outflow
Urachikottai, Kodumudi and Musuri indicate the same pattern of early peak and higher peak floods.

14. Verifying volume-elevation curve of Mettur reservoir
Result and analysis
Model calibration and verification

15. Mettur reservoir model (with branches in the model)
High peak outflow
High low flows
Faster rise in water level
at elevation 220-225
Slight lower
discharge
Result and analysis
Model calibration and verification

16. Result and analysis
Scenario simulations
Mettur reservoir volume and flood volume calculation
Date Flood
(m3/s)
Volume
(million
m3)
Cumulative volume
(million m3)
Water level in
reservoir(m)
09-08-2018 580,84 - 196,9
10-08-2018 1443,3 87.408288 87.40829 209,88
11-08-2018 3568,8 216.52272 303.931 215,85
12-08-2018 3624 310.72896 614.66 221,9
13-08-2018 3183,3 294.07536 908.7353 225,99
14-08-2018 3648,3 251.92512 1160.66 228,88
15-08-2018 3524,4 266.66064 1427.321 231,46
16-08-2018 4502,4 346.75776 1774.079 234,58
17-08-2018 4861,1 404.5032 2178.582 237,83
18-08-2018 5189,4 434.1816 2612.764 240,74
19-08-2018 5485,4 461.15136 3073.915 240,74
20-08-2018 4567,2 434.27232 3508.187 240,64
21-08-2018 3101,4 331.28352 3839.471 240,92
22-08-2018 1175,2 184.74912 4024.22 240,71
23-08-2018 345,48 65.693376 4089.913 240,73
Capacity of Reservoir is 2.6 billion m3
Volume of peak flood: 4.08 billion m3
In dry condition, the reservoir reaches FRL before
the arrival of flood peak
Flood management capability of the Mettur reservoir

17. Result and analysis
Scenario simulations
Scenario 1: Low water release level (234.69 m)
Water level condition: Original water level (215.45 m)
Case 1.1: Whole period of analysis
▪ Reservoir fills from 01-06-2018 to 15-07-2018
▪ Although the reservoir remains open, the water
level starts increasing after 1st week of August.
▪ The incoming flow is greater than the capacity of
the reservoir, hence the dam couldn’t capture the
incoming flood peak

18. Result and analysis
Scenario simulations
Case 1.2(a) Peak flood analysis Case 1.2 (b) Whole period of analysis
Outflow is not zero
Flood is not captured
Outflow is not zero
Flood is not captured
Scenario 1: Low water release level (234.69 m)

19. Result and analysis
Scenario simulations
Case 1.3(b): Whole period of analysis
Outflow is smaller
Flood is not captured
Case 1.3(a): Peak flood analysis
Scenario 1: Low water release level (234.69 m)

20. Result and analysis
Scenario simulations
Scenario 2: Low crest level of the spillway (215 m)
Water level condition: Original water level (215.45 m)
Case 2.1: Whole period of analysis
▪ Outflow is zero during flood peak
▪ Flood is captured in the reservoir
▪ Water level rises and the dam maintains it at FRL
▪ Water level is maintained at 215 until the period of
flood peak

21. Result and analysis
Scenario simulations
Case 2.2(b): Whole period of analysis
Case 2.2(a): Peak flood analysis
Outflow is ZERO
Flood is captured
Scenario 2: Low crest level of the spillway (215 m)

22. Result and analysis
Scenario simulations
Case 2.3(b): Whole period of analysis
Case 2.3(a): Peak flood analysis
Outflow is ZERO
Flood is captured
▪ The dam gate closes
from 16 August
▪ to 22 August
▪ Flood peak arrives
in the reservoir in
the same period
▪ The volume of flood
captured during
this period is 2.59
billion m3.
Scenario 2: Low crest level of the spillway (215 m)

23. Result and analysis
Scenario simulations
Water level condition: Original water level (215.45 m)
Case 3.1: Whole period of analysis
▪ Outflow of dam during smaller flood peak is
reduced.
▪ The dam gate closes from 16 August
▪ to 21 August.
▪ Flood peak arrives in the reservoir in the
same period.
▪ The volume of flood captured during this
period is 2.4 billion m3.
Scenario 3: Increase dam height

24. Conclusions and recommendations
Conclusions
• The main purpose of Mettur dam in the basin is supply of water for irrigation, drinking water and
power generation and does not seem to consider flood management as per the results of data
analysis and reservoir operation simulations.
• Current reservoir volume and spillway capacity does not seem to be enough for the purpose of flood
management. It might be possible only if there is proper monitoring and forecasting system with
enough lead time (however, our study showed that the forecasting lead time should be long that is
not feasible due to high uncertainties in forecasting).
• The results of scenario development showed that by decreasing the release level (scenario 2) and
increasing dam height (scenario 3), the reservoir can be used for flood management. However, these
options mean large structural interventions that will have social and environmental impacts. This
requires further detailed study.

25. Conclusions and recommendations
❑ Recommendations for model development
▪ Representation of gates at varying level along the dam structure which govern the outflow of the
dam cannot be done in 1D model, hence a 2D model can be used for a better representation of the
dam and its operation.
❑ Recommendation for flood management
▪ The proposed structural measures, i.e. lowering the spillway crest level and/or increasing the height
of the dam should be properly investigated considering impacts and risks.
▪ Application of nature based solutions like retention basin or other approaches can be explored for
flood management.
▪ Basin-scale dam analysis can be carried out to improve integrated flow management of the whole
basin.
Recommendations

26. Conclusions and recommendations
❑ The developed models cannot be applied to another flood year due to changes in channel bathymetry.
❑ Representation of dam and its gates at different elevations cannot be considered in 1D model.
❑ Effects of the proposed scenarios on other reservoir functions like water supply and irrigation are not
considered in this work.
Limitations

27. Thank you for your attention!