Alpha Parameter Modeling of Nakayasu Synthetic Unit Hydrograph Based on the Watershed Shape Factor

Acep Hidayat, Lily Montarcih Limantara, Widandi Soetopo, Dian Sisinggih


The limitation of hydrograph data availability becomes an obstacle for the design of water resources. The obstacle makes the Synthetic Unit Hydrograph give the big enough benefit for the design of water resources. Ideally, every watershed has its unit hydrograph. The Nakayasu Synthetic Unit Hydrograph is one of the synthetic unit hydrographs frequently used in the analysis of design flood discharge in Indonesia. However, the Nakayasu Synthetic Unit Hydrograph concept has been widely used and evaluated in some areas in Indonesia, and there is bias in determining the watershed characteristic coefficient. This research intends to investigate the characteristic of the observed hydrograph in every watershed and the whole watershed in the South Sulawesi Province-Indonesia. The research aims to build the alpha formula using alpha modeling with the affected parameters of watershed area, river length, river bed slope, shape factor, and the time concentration. Based on the ArcGIS version 10.7, most of the watershed’s shapes are elongated. The methodology consists of analyzing observed unit hydrograph by using the Collins method and Nakayasu Synthetic Unit Hydrograph. Then the model is built by using the statistical analysis of SPSS version 23 software for obtaining the affected level of each parameter that is determined. However, the modeling analysis uses the non-linear regression after there is carried out the descriptive test. The alpha formula for the elongate watershed in the Jeneberang River is proposed.


Keywords: alpha parameter, watershed area, river length, slope, shape factor.


Full Text:



TUNG B.Z., YEH Y.K., CHIA K., and CHUANG J.Y. Storm resampling for uncertainty analysis of a multiple-storm unit hydrograph. Journal of Hydrology, 1987, 194: 366-384.

HOLKO L., and LEPSITO A. Modelling the hydrological behavior of mountain catchment using TOPMODEL. Journal of Hydrology, 1997, 196: 361-3773.

KAMILA D., LIMANTARA L.M., BISRI M., and SOETOPO W. Alpha modelling of Nakayasu Synthetic Unit Hydrograph for parts of watersheds in Indonesia. International Journal of Recent Technology and Engineering, 2019, 8(4): 5509-5514.

LIMANTARA L.M. Evaluation of roughness constant of river in the Synthetic Unit Hydrograph. World Applied Sciences Journal, 2009, 7(9): 1209-1211.

NANDAKUMAR M., and MEIN R.G. Uncertainty in rainfall-runoff model simulations and the implications for predicting the hydrologic effect of land-use change. Journal of Hydrology, 1987, 192: 211-232.

BLAZKOVA S., and BEVEN K. Flood frequency prediction for data-limited catchments in the Czech Republic using a Stochastic Rainfall Model and TOPMODEL. Journal of Hydrology, 1997, 195: 256-278.

LIMANTARA L.M. The limiting physical parameters of Synthetic Unit Hydrograph. World Applied Sciences Journal, 2009, 7(6): 802-804.

KAMILA D., LIMANTARA L.M., BISRI M., and SOETOPO W. The limiting physical parameters of Nakayasu Synthetic Unit Hydrograph. International Journal of Innovative Technology and Exploring Engineering, 2019, 8(6C2): 30-33.

SOEMARTO C.D. Hidrologi teknik. Penerbit Erlangga, Jakarta, 1987.

DEWI R., LIMANTARA L.M., and SOETOPO W. Analisis parameter alfa Hidrograf Satuan Sintetis Nakayasu di Sub DAS Lesti. Jurnal Teknik Pengairan, 2016, 7: 107-116.

RAMADANI M., FAUZI M., and HANDAYANI W. Pemodelan parameter α pada Hidrograf Satuan Sintetik Nakayasu (Studi banding dengan Hidrograf Satuan Sintetik GAMA I). Universitas Riau, 2016.

PRIYANTORO D., and LIMANTARA L.M. Conformity evaluation of synthetic unit hydrograph (case study at upstream Brantas sub-watershed, East Java Province of Indonesia). Journal of Water and Land Development, 2017, 35: 173-183. DOI: 10.1515/jwld-2017-002

WULANDARI E., LIMANTARA L.M., ANDAWAYANTI U., and SUHARTANTO E. Model of alpha parameter development at Nakayasu Synthetic Unit Hydrograph based on the watershed physical characteristic in some parts watersheds of Java Island. Technology Reports of Kansai University, 2020, 62(4): 1711-1720.


  • There are currently no refbacks.