SWAT-Based Hydrological Modeling and Water Balance Dynamics of West Rapti River Basin, Nepal
DOI:
https://doi.org/10.64862/ajeg.2025.202.04.301Keywords:
Hydrology, SWAT, Water balance, Model performance, Model calibration, Model validationAbstract
This study simulates the hydrological and sediment dynamics of Nepal’s West Rapti River basin (WRB) using the Soil and Water Assessment Tool (SWAT) to quantify water balance components and sediment yield. The model integrates a 30-m resolution DEM, soil maps, and land-use data, delineating the basin into 21 sub-basins and 180 hydrological response units (HRUs). Sensitivity analysis identified the curve number (CN2), base flow recession coefficient (ALFA_BF), and surface runoff lag time (SURLAG) as dominant parameters influencing hydrology. Calibration (2003–2011) and validation (2012–2020) using observed discharge at Jalkundi station yielded robust performance metrics (R² = 0.95–0.91, NSE = 0.76–0.75), with a slight overestimation of base flow (PBIAS = −7.7 to −13.5). Model performance indices values (R² and NSE) for sediment were determined at around 0.60, indicating fair model behavior for sediment. Long-term simulations (2000–2022) revealed an average annual precipitation of 1,676 mm, with 55% contributing to streamflow (mean water yield: 951mm/yr) and 42% lost to evapotranspiration. Surface runoff averaged 573 mm/yr, peaking in monsoon months (July–September). Sediment yield averaged 166 t ha-1yr-1, with significant spatial variability (15.68–468.05 t ha-1yr-1. Sub-basin 8 exhibited the highest sediment flux, attributed to steep slopes (>40%) and erosive land use. Water balance analysis highlighted seasonal dynamics: 68% of annual streamflow and 85% of sediment yield occurred during the monsoon (June–September), driven by intense rainfall (mean: 1,289 mm). The SWAT model effectively captured the basin’s hydrology-sediment nexus, emphasizing the role of topography and land use in governing erosion. These findings provide critical baseline data for optimizing sediment management and water resource strategies in the basin.
References
Abdullah, M., and Al-Ansari, N. (2022). Missing rainfall data estimation: An approach to investigate different methods: Case study of Baghdad. Arabian Journal of Geosciences, 15(23), 1740. https://doi.org/10.1007/s12517-022-10995-6
Arnold, J. G., Moriasi, D. N., Gassman, P. W., Abbaspour, K. C., White, M. J., Srinivasan, R., Santhi, C., Harmel, R. D., Van Griensven, A., Van Liew, M. W., Kannan, N., and Jha, M. K. (2012). SWAT: Model use, calibration, and validation. Transactions of the ASABE, 55(4), 1491–1508. https://doi.org/10.13031/2013.42256
Arnold, J. G., Srinivasan, R., Muttiah, R. S., and Williams, J. R. (1998). Large-area hydrologic modeling and assessment: Part I. Model development. Journal of the American Water Resources Association, 34(1), 73–89. https://doi.org/10.1111/j.1752-1688.1998.tb05961.x
Ayele, G. T., Kuriqi, A., Jemberrie, M. A., Saia, S. M., Seka, A. M., Teshale, E. Z., Daba, M. H., Bhat, S. A., Demissie, S. S., Jeong, J., and Melesse, A. M. (2021). Sediment yield and reservoir sedimentation in highly dynamic watersheds: The case of Koga Reservoir, Ethiopia. Water, 13(23), 3374. https://doi.org/10.3390/w13233374
Basnet, N., Sitaula, S., Bohara, R., Bhattarai, S., Rawal, S., Uprety, M. P., Awasthi, M. P., Varol, M., Kayastha, S. P., and Pant, R. R. (2024). Hydro-chemical characteristics of Biring and Tangting rivers (Nepal) and evaluation of water quality for drinking and irrigation purposes. Environmental Research, 261, 119697. https://doi.org/10.1016/j.envres.2024.119697
Becker, A., and Braun, P. (1999). Disaggregation, aggregation and spatial scaling in hydrological modeling. Journal of Hydrology, 217(3), 239–252. https://doi.org/10.1016/S0022-1694(98)00291-1
Bekele, S., and Abate, B. (2020). Estimation of sediment yield using SWAT model: A case of Soke River Watershed, Ethiopia. International Journal of Engineering Research and Technology, 9(12), 685–695.
Bhatta, B., Shrestha, S., Shrestha, P. K., Talchabhadel, R., 2019. Evaluation and application of a SWAT model to assess the climate change impact on the hydrology of the Himalayan River Basin. Catena, 181, 104082. https://doi.org/10.1016/j.catena.2019.104082
Bishwakarma, K., Wang, G., Zhang, F., Pant, R. R., Yuxuan, X., and Adhikari, S. (2024). Chemical weathering and CO2 consumption rates of the Koshi River Basin: Modeling and quantifying. Journal of Hydrology, 641, 131760. https://doi.org/10.1016/j.jhydrol.2024.131760
Bohara, R., Sitaula, S., Basnet, N., Awasthi, M. P., Rawal, S., Joshi, T. R., Byanju, R. M., and Pant, R. R. (2024). Hydrochemical characterization and water quality of perennial rivulets (Darchula), Sudurpashchim Province, Nepal. Tribhuvan University Journal, 39(2), 1–26. https://doi.org/10.3126/tuj.v39i2.72872
Chilagane, N. A., Kashaigili, J. J., Mutayoba, E., Lyimo, P., Munishi, P., Tam, C., and Burgess, N. (2021). Impact of land use and land cover changes on surface runoff and sediment yield in the Little Ruaha River Catchment. Open Journal of Modern Hydrology, 11(3), 54–74. https://doi.org/10.4236/ojmh.2021.113004
Chinnasamy, P., and Sood, A. (2020). Estimation of sediment load for Himalayan rivers: A case study of Kaligandaki in Nepal. Journal of Earth System Science, 129(1), 181. https://doi.org/10.1007/s12040-020-01437-6
de Oliveira Serrão, E. A., Silva, M. T., Ferreira, T. R., de Ataide, L. C. P., dos Santos, C. A., de Lima, A. M. M., da Silva, V. P. R., de Sousa, F. A. S., and Gomes, D. J. C. (2022). Impacts of land use and land cover changes on hydrological processes and sediment yield determined using the SWAT model. International Journal of Sediment Research, 37(1), 54–69. https://doi.org/10.1016/j.ijsrc.2021.04.002
Douglas-Mankin, K. R., Srinivasan, R., and Arnold, J. G. (2010). Soil and Water Assessment Tool (SWAT) model: Current developments and applications. Transactions of the ASABE, 53(5), 1423–1431. https://doi.org/10.13031/2013.34915
FAO (2002). FAO/UNESCO digital soil map of the world and derived soil properties (Land and Water Digital Media Series No. 1, Rev. 1). Food and Agriculture Organization of the United Nations, Rome.
FRTC (2022). Land cover of Nepal [Data set]. FRTC. https://doi.org/10.26066/RDS.1972729
KC, M., Aryal, I., Dhakal, N. R., and Marahatta, S. (2023). Application of SWAT hydrological model to simulate flow of the Seti-Gandaki Basin. Jalawaayu, 3(1). https://doi.org/10.3126/jalawaayu.v3i1.52060
Kumari, S., Singh, V., Suryavanshi, S., and Kumar, M. (2024). Application of the SWAT model for hydrological simulation of the Rapti River Basin. Journal of Experimental Agriculture International, 46 (6), 140-153. https://doi.org/10.9734/jeai/2024/v46i62466
Li, H., Yu, C., Qin, B., Li, Y., Jin, J., Luo, L., Wu, Z., Shi, K., and Zhu, G. (2022). Modeling the effects of climate change and land use/land cover change on sediment yield in a large reservoir basin in the East Asian monsoonal region. Water, 14(15), 1–19. https://doi.org/10.3390/w14152346
Liu, Y., and Jiang, H. (2019). Sediment yield modeling using the SWAT model: Case of the Changjiang River Basin. IOP Conference Series: Earth and Environmental Science, 234(1), 012031. https://doi.org/10.1088/1755-1315/234/1/012031
Michael, K. H., and Jain, M. (2013). Runoff and sediment modeling using SWAT in Gumera Catchment, Ethiopia. Open Journal of Modern Hydrology, 3(4), 196–205. https://doi.org/10.4236/ojmh.2013.34024
Moges, D., Moges, D. M., and Bhat, H. G. (2020). Watershed degradation and management practices in north-western highland Ethiopia. Environmental Monitoring and Assessment, 192(10), 664. https://doi.org/10.1007/s10661-020-08628-0
Moriasi, D. N., Arnold, J. G., Van Liew, M. W., Binger, R. L., Harmel, R. D., and Veith, T. (2007). Model evaluation guidelines for systematic quantification of accuracy in watershed simulations. Transactions of the ASABE, 50(3), 885–900. https://doi.org/10.13031/2013.23153
Nash, J. E., and Sutcliffe, J. V. (1970). River flow forecasting through conceptual models: Part I—A discussion of principles. Journal of Hydrology, 10(3), 282–290. https://doi.org/10.1016/0022-1694(70)90255-6
Nepal, J., Pant, R. R., Shrestha, S., Paudel, S., Bishwakarma, K., Awasthi, M. P., and Dhital, Y. P. (2024). Water balance estimation and runoff simulation of Chameliya Watershed, Nepal. Environmental Earth Sciences, 83(3), 117. https://doi.org/10.1007/s12665-024-11430-7
Nepal, S., Flügel, W.-A., and Shrestha, A. B. (2014). Upstream-downstream linkages of hydrological processes in the Himalayan region. Ecological Processes, 3(1), 19. https://doi.org/10.1186/s13717-014-0019-4
Neupane, S. N., and Pandey, A. (2021). Hydrological modeling of the West Rapti River Basin of Nepal using the SWAT model. In A. Pandey, S. Mishra, M. Kansal, R. Singh, and V. Singh (Eds.), Water management and water governance (Vol. 96, pp. XX–XX). Springer, Cham. https://doi.org/10.1007/978-3-030-58051-3_19
Owens, P.N.(2020).Soil erosion and sediment dynamics in the Anthropocene: A review of human impacts during a period of rapid global environmental change. Journal of Soils and Sediments, 20(12), 4115-4143. https://doi.org/10.1007/s11368-020-02815-9
Pandey, V. P., Dhaubanjar, S., Bharati, L., and Thapa, B. R. (2019). Hydrological response of Chamelia Watershed in Mahakali Basin to climate change. Science of the Total Environment, 650, 365–383. https://doi.org/10.1016/j.scitotenv.2018.09.053
Pant, R. R., Varol, M., Phuyal, S., Bhattarai, S., Awasthi, M. P., Thakur, T. K., Bohara, R., and Afandi, G. E. (2025). How sand mining is shaping the Trishuli River in the Himalayas of South Asia. Earth Systems and Environment, 1–17. https://doi.org/10.1007/s41748-025-00569-3
Rahman, M. M., Harada, D., and Egashira, S. (2024). Sediment transport processes in the Sangu River Basin using a rainfall-sediment runoff model for sustainable river management. Proceedings of IAHS, 386, 109–114. https://doi.org/10.5194/piahs-386-109-2024
Ren,S., Zhang,B.,Wang, W.J.Yuan,Y.& Guo, C (2021). Sedimentation and its response to management strategies of the Three Georges River, Yangste River, China.Catena, https://doi.org/10.1016/j. catena.2020.105096
Schweizer, M., Dieterich, A., Corral Morillas, N., Dewald, C., Miksch, L., Nelson, S., Wick, A., Triebskorn, R., and Köhler, H. R. (2018). The importance of sediments in ecological quality assessment of stream headwaters: Embryotoxicity along the Nidda River and its tributaries in Central Hesse, Germany. Environmental Sciences, 30(1), 22 https://doi.org/10.1186/s12302-018-0150-4
Shi, X., Zhang, F., Lu, X., Wang, Z., Gong, T., Wang, G., and Zhang, H. (2018). Spatiotemporal variations of suspended sediment transport in the upstream and midstream of the Yarlung Tsangpo River (the upper Brahmaputra), China. Earth Surface Processes and Landforms, 43(2), 432–443. https://doi.org/10.1002/esp.4258
Shinde, V. M., Deshpande, P. K., and Kumthekar, M. B. (2013). Application of ASTER DEM in watershed management as flood zonation mapping in Koyana River of the Western Ghats. International Journal of Scientific and Engineering Research, 4(5), 297–301.
Sinha, R., Gupta, A., Mishra, K., Tripathi, S., Nepal, S., Wahid, S. M., and Swarnkar, S. (2019). Basin-scale hydrology and sediment dynamics of the Koshi River in the Himalayan foreland. Journal of Hydrology, 570, 156–166. https://doi.org/10.1016/j.jhydrol.2018.12.051
Srivastava, A., Deb, P., and Kumari, N. (2020). Multi-model approach to assess the dynamics of hydrologic components in a tropical ecosystem. Water Resources Management, 34, 327–341. https://doi.org/10.1007/s11269-019-02452-z
Subedi, S. R., Lamichhane, M., Dhungana, S., Chalise, B., Bhattarai, S., Chaulagain, U., and Khatiwada, R. (2024). Assessing the impact of climate change on streamflow in the Tamor River Basin, Nepal: An analysis using SWAT and CMIP6 scenarios. Discover Civil Engineering, 1, 135. https://doi.org/10.1007/s44290-024-00143-2
Thapa, B., Shrestha, R., Dhakal, P., and Thapa, B. S. (2005). Problems of Nepalese hydropower projects due to suspended sediments. Aquatic Ecosystem Health and Management, 8(3), 251–257. https://doi.org/10.1080/14634980500218241
Thomas, J., Joseph, S., Thrivikramji, K. P., and Arunkumar, K. S. (2014). Sensitivity of digital elevation models: The scenario from two tropical mountain river basins of the Western Ghats, India. Geoscience Frontiers, 5(6), 893–909. https://doi.org/10.1016/j.gsf.2013.12.008
Toma, M. B., Belete, M. D., and Ulsido, M. D. (2023). Hydrological components and sediment yield response to land use and land cover change in the Ajora-Woybo Watershed of Omo-Gibe Basin, Ethiopia. Air, Soil and Water Research, 16, 1–17. https://doi.org/10.1177/11786221221150186
Van Oost, K., Van Rompaey,A. Poesen, J.Grovers,G& Verstraeten,G.(2002).Evaluating an integrated approach to catchment management to reduce soil loss and sediment pollution through modeling. Soil Use and Manangement , 18(4)386-394. https://doi.org/10.1079/sum.2001.150
Vercruysse, K., Grabowski, R.C., & Rickson, R.J(2017). Suspended sediment transport dynamics in rivers: multi-scale drivers of temporal variation. Earth _ science Reviews, 166, 38-52. https://doi.org/10.1016/j.earscirev.2016.12.016
Downloads
Published
Data Availability Statement
The research data would be available on request.
Issue
Section
License
Copyright (c) 2025 Nepal Society of Engineering Geology (NSEG)
This work is licensed under a Creative Commons Attribution 4.0 International License.
