Modelling the Present and Future Water Level and Discharge of the Tidal Betna River
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Hydrodynamic Model Set Up
2.3. Bathymetric Survey and Mesh Generation
2.4. Meteorological and Hydrodynamic Data
2.5. Calibration, Validation and Sensitivity Analysis
2.6. Future Scenario Development
3. Results
3.1. Model Calibration, Validation and Sensitivity Analysis
3.2. Future Projections
4. Discussion
5. Conclusions
- increased precipitation and SLR are expected in the Betna River basin in the near and far future under both RCP 4.5 and RCP 8.5;
- in RCP 8.5, water level and discharge in the Betna River are expected to increase up to 16 and 13% for the 2040s, and up to 23 and 21% for the 2090s, respectively;
- in RCP 4.5, although the expected increase in river discharge is relatively low (i.e., between 7 and 16%), the increased discharge combined with an increased water level is likely to cause major floods in the Betna River basin;
- the modelling results suggest that during the dry season, a small decrease in discharge (up to 2%) is expected for the 2090s;
- SLR explains a larger part of the future increase in water level than increasing upstream discharge; and
- in the future, the duration above the current flood danger level and of the extreme discharge events is expected to increase by half a month (per year) in the 2040s and by more than one month in the 2090s, causing prolonged inundation in the river basin, particularly during the monsoon.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Data Type | Resolution | Period | Location | Source |
---|---|---|---|---|
River bathymetry | Cross-section 400–500 m | 2012 | Modelled stretch | IWM a |
Water level for calibration period | 0.5 h | 2012 | Maskhola, Noapara and lower boundary | IWM a |
Water level for validation period | 3 h | 2014–2015 | Near Noapara and lower boundary | BWDB b |
Discharge for calibration period | 0.5 h | 2012 | Near Noapara and upper boundary | IWM a |
Discharge for validation period | 1 week | 2014–2015 | Near upper boundary | BWDB b |
Precipitation | 1 day | 2012–2015 | BMD Satkhira | BMD c |
Air temperature | 1 day | 2012–2015 | BMD Satkhira | BMD c |
Wind speed and direction | 3 h | 2012–2015 | BMD Satkhira | BMD c |
Relative humidity | 1 day | 2012–2015 | BMD Satkhira | BMD c |
Parameter Type | Formulation | Calibrated Value | Note |
---|---|---|---|
Horizontal eddy viscosity | Smagorinsky formulation | Selected after multiple simulations where different values were tested. | |
Constant value | 0.28 m2/s | ||
Range | 1.8 × 10−06–1.0 × 108 m2/s | ||
Vertical eddy viscosity | k-epsilon formulation | ||
Range | 1.0 × 10−07–2.0 × 10−04 m2/s | ||
Bed roughness | Roughness height | ||
Constant value | 60 m1/3/s | ||
Wind friction | Constant value | 0.001255 | |
Heat exchange | Constant in Dalton’s law | 0.5 | |
Wind coefficient in Dalton’s law | 0.9 | ||
Sun constant, ‘‘a’’ in Ångström’s law | 0.176 | ||
Sun constant, ‘‘b’’ in Ångström’s law | 0.37 | ||
Light intensity | Light extinction coefficient | 0.5 |
GCMs | Near Future (2040s) | Far Future (2090s) | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
RCP 4.5 | RCP 8.5 | RCP 4.5 | RCP 8.5 | |||||||||||||
Monsoon | Dry | Monsoon | Dry | Monsoon | Dry | Monsoon | Dry | |||||||||
Flood Tide | Ebb Tide | Flood Tide | Ebb Tide | Flood Tide | Ebb Tide | Flood Tide | Ebb Tide | Flood Tide | Ebb Tide | Flood Tide | Ebb Tide | Flood Tide | Ebb Tide | Flood Tide | Ebb Tide | |
Water level (% change) | ||||||||||||||||
IPSL-CM5A | 11.1 | 11.3 | 10.6 | 10.7 | 15.5 | 15.1 | 14.2 | 13.9 | 15.6 | 15.4 | 14.5 | 14.4 | 21.4 | 21.7 | 19.7 | 19.9 |
MPI-ESM | 11.4 | 11.7 | 11.1 | 11.3 | 15.8 | 15.4 | 14.5 | 14.1 | 16.1 | 15.9 | 14.8 | 14.9 | 22.1 | 22.7 | 20.3 | 20.5 |
Discharge (% change) | ||||||||||||||||
IPSL-CM5A | 7.6 | 7.2 | 1.2 | 1.3 | 11.6 | 11.4 | 0.8 | 0.6 | 14.7 | 14.9 | 0.4 | 0.5 | 20.2 | 20.5 | −1.8 | −1.6 |
MPI-ESM | 8.2 | 8.1 | 0.8 | 0.9 | 12.4 | 12.7 | 0.7 | 0.7 | 16.1 | 16.2 | −1.3 | −1.2 | 21.3 | 21.1 | −2.2 | −2.3 |
GCMs | Scenarios | Duration above Flood Danger Level | Duration above Discharge of 400 m3/s |
---|---|---|---|
Baseline (2014–2015) | 13 days | 11 days | |
IPSL-CM5A | RCP 4.5 (2040s) | 25 days | 21 days |
RCP 8.5 (2040s) | 27 days | 24 days | |
RCP 4.5 (2090s) | 41 days | 35 days | |
RCP 8.5 (2090s) | 45 days | 46 days | |
MPI-ESM | RCP 4.5 (2040s) | 25 days | 22 days |
RCP 8.5 (2040s) | 28 days | 25 days | |
RCP 4.5 (2090s) | 43 days | 36 days | |
RCP 8.5 (2090s) | 47 days | 46 days |
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Islam, M.M.M.; Hofstra, N.; Sokolova, E. Modelling the Present and Future Water Level and Discharge of the Tidal Betna River. Geosciences 2018, 8, 271. https://doi.org/10.3390/geosciences8080271
Islam MMM, Hofstra N, Sokolova E. Modelling the Present and Future Water Level and Discharge of the Tidal Betna River. Geosciences. 2018; 8(8):271. https://doi.org/10.3390/geosciences8080271
Chicago/Turabian StyleIslam, M. M. Majedul, Nynke Hofstra, and Ekaterina Sokolova. 2018. "Modelling the Present and Future Water Level and Discharge of the Tidal Betna River" Geosciences 8, no. 8: 271. https://doi.org/10.3390/geosciences8080271