Impact of climate and landuse changes on inflows, sediment yield and hydropower production a case of the Mangla Reservoir, Pakistan | |
| Author | Babur, Muhammad |
| Call Number | AIT Diss. no.WM-16-03 |
| Subject(s) | Climatic changes--Pakistan Water power--Pakistan |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Water Engineering and Management, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WM-16-03 |
| Abstract | In recent years , the assessment of the impact of climate change on water resources has advanced significantly. However, a comprehensive, integrated method to estimate the combined imp a ct of climate and land use changes on discharge, sediment yield, and h ydropower is still lacking. This kind of comprehensive method should maximize benefits from a reservoir through its optimal management. The economy of Pakistan mainly depends on agriculture , which primarily relies on direct rainfall and reservoir storage. R eservoir storage is crucial a s most of t he regions in Pakistan are semi - ari d . Two major reservoirs, Mangla & Tarbela, have lost their substantial capacities because of sedimentation. The capacity of the Mangla Dam is already reduced by 20%. Moreover, the capacity of the Mangla Dam is likely to r educe at a higher pace due to climate and land use transformations. Therefore, a quantitative assessment of sediment yield and its management under climate and land use variations is essential to maximize the benefit s from the reservoir . The focus of this research was to quantify the impacts of climate and land use changes on discharge, sediment yield, and HPP after projecting climate and land use changes. T his study also includes the analysis of various sediment management alternatives and recommends the most appropriate sediment management alternative to acquire the maximum benefit from the reservoir. This dissertation consists of a comprehensive method to optimize the reservoir thr ough sediment management. The historical climatic and gauging data were collected from various observatories that are operated by PMD, IMD, C FS R, and WAPDA within the watershed. GCM data was downloaded from Climate Model Intercomparison Project Phase 5 (CM IP5) . B ias correction was performed by l inear scaling of the temperature and precipitation data. Subsequently, the projected temperature and precipitation data were analyzed spatially and temporally on annual and seasonal bas es to comprehend the changes in future climate. In addition , the projected climate conditions under different RCPs , such as RCP 2.6, 4.5, 6.0 , and 8.5 were analyzed using SimClim for Pakistan . L and use change analysis was executed using IDRISI Selva. Afterward , land use was projected using 1 5 historical data laye r s for 2012 . Kappa Index of Agreement (KIA) and Cramer’s V were checked. After achieving an acceptable Cramer’s V and KIA , future land use maps were projected using IDRISI Selva. H istorical climatic and land use data were util ized for the calibration & validation of SWAT and HEC - ResSim models to simulate streamflow, sediment yield, and hydropower potential (HPP) . T he individual and combined impact s of forthcoming climate and land use variations were analyzed for discharge, sediment yield, and HPP. Most importantly, various sediment management alternatives , such as reservoir sediment management using a RESCON model and both structural and non - structural watershed sediment management strategies , were investigated by the SWAT m odel to attain maximum benefit from the reservoir. Finally, this study makes recommendations regarding the best suitable alternative which will be technically and economically feasible to maximize benefits from the reservoir. The results , obtained by usin g seven GCMs under representative concentration pathways (RCPs) 4.5 and 8.5, show that change s in projected average annual (2011 - 2100) maximum temperature (Tmax), minimum temperature (Tmin) , and precipitation (PPT) may vary from 0.4 to 8.3 °C, 0.6 to 7.3 ° C , and - 21.3 to 51.4 % , respectively . Using forty GCMs under RCPs 2.6, 4.5, 6.0 and 8.5, the changes in projected average annual (2020 - 2100) Tmax, Tmin, and PPT using SimClim may vary from 1.5 to 9.5 ºC, 2.0 to 7.5 ºC , and - 20 to 70 % respectively . Over t he historical period, forest cover in the area has reduced , and it reached its minimum level of 16 % in 2005. However, after the implementation of a forest conservation policy by the government, the forest cover grew back to 27 % in 2012. Projected land use map s using IDRISI - Selva show a projected increase in forest cover : 2025 (33 %), 2050 (39.2 %) , and 2100 (53.7 %). The grassy area is projected to decrease due to the increase in forest area. For the estimation of the impact of climate change on stream flow and sediment yield, bias corrected temperature and PPT data were taken as input s for the SWAT model. The SWAT model was calibrated and validated using observed daily streamflow from 1985 to 1995 and 1995 to 2005, respectively, at various measuring sta tions. The coefficient of determination (R 2 ), Nash - Sutcliffe efficiency (NSE), percent bias (P BIAS ) , and graphical visualization between observed & simulated streamflow show that the observed data were captured well by the simulated data . The changes in 2011 - 2040 the (2020s), 2041 - 2070 ( the 2050s), and 2071 - 2099 ( the 2080s) were analyzed against the baseline period (1981 - 2010). Then, the streamflow generated by the SWAT model for the period of 2011 - 2100 was taken as input for the HEC - ResS im model to examine the impact of future climate change s on hydropower. The reservoir simulations for the different time periods were not compared with the observed data ; instead, these simulations were compared with the simulated data of the baseline peri od. This strategy allow ed us to perform change analysis for a long - term average. Nevertheless, it should be stated that the simulated model overestimated the observed mean monthly power production by 0.05 %. Owing to only climate change , seven GCMs under RCPs 4.5 and 8.5 project that change s in average annual (2011 - 2100) discharge, sediment yield , and HPP may vary from - 27.2 to 97.7 %, - 42.9 to 39.4 % , and - 30.0 to 8.9 % respectively. Additionally, due to only climate change , forty GCMs under RCPs 2.6, 4.5 , 6.0 , and 8.5 project that change s in average annual (2011 - 2100) discharge, sediment yield , and HPP may vary from - 69.2 to 83.2 %, - 31.0 to 76.6 %, and - 76.6 to 12.3 % respectively. D ue to only land use change (forest cover) from 26 to 53 % , the impact o n average annual (2011 - 2100) discharge, sediment yield, and HPP may vary from 0 to - 1.1 %, 0 to - 27.3 % , and 0 to - 0.37 %. Due to the combined impact of climate and land use changes , average annual (2011 - 2100) discharge, sediment yield, and HPP may vary f rom - 71.8 to 77.3 %, - 73 to 86.5 % , and - 78.05 to 12.22 % , respectively. The se results indicate that climate change is may not be a threat ; rather, it may provide an opportunity to generate a substantial amount of extra power due to additional flows. The RESCON model of the Mangla reservoir demonstrated that sediment flushing is an economically preferable sediment management alternative , as compared to other sediment management strategies, such as hydro - suction, trucking, flushing, dredging , and do ing noth ing. A Sediment Balance Ratio (SBR) of greater than unity can be achieved by maintaining the reservoir level at 317 m above mean sea level (MSL) for 84 days with a discharge of 1,274 m 3 /sec. R esults also indicate that the maximum achievable long - term capac ity ratio (LTCR) is only 10 %. Owing to this low value of LTRC (less than 35 %), even flushing is not technically suitable. In that case, the best (economically and technically) available solution for sediment mana gement is watershed management. Watershed management includes structural and non - structural measures; t hese measures have been analyzed in this dissertation . Structural measures such as check dam, filter strip, grade stabilization structure, sediment basin, silt fence, terraces, tile drain, grassed waterway and channel protection can remove sediment by 55 %, 62 %, 5 %, 61 %, 67 %, 76 %, 25 %, 55 % and 30 %, respectively . Nonstructural measures such as riparian forest buffer, forest intensive and crop intensive scenarios can remove 40 %, 25 % and 6 %, respectively . The result s of this research provide trustworthy reference s and a scientific base for the assessment of climate and land use change s, and the impacts of these on discharge, sediment yield, and HPP in the Mangla watershed . The primar y o utcome of this research is that the reservoir ’s life span can be substantially increased from 200 years to 800 years by merely applying optimal watershed management strategies |
| Year | 2016 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-16-02 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Babel, Mukand S.; |
| Examination Committee(s) | Shrestha, Sangam ;Kawasaki, Akiyuki ;Tripathi, Nitin Kumar; |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship ;Higher Education Commission (HEC), Pakistan; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2016 |