Document Type : Research Paper
Authors
1 PhD Student, Department of Range and Watershed Management Engineering, Faculty of Natural Resources, Lorestan University, Khorramabad, Iran
2 Associate Professor, Department of Range and Watershed Management Engineering, Faculty of Natural Resources, Lorestan University. Khorramabad, Iran
Abstract
Introduction
Due to the heterogeneity in watersheds and the non-linearity of hydrological behaviors, it is very complicated and difficult to fully understand the relationships within watersheds. Therefore, in evaluating these systems, a modeling process is necessary. Over the last few decades, hydrological/hydraulic models have become essential in hydrology studies due to the development of programming languages and the provision of optimal and efficient algorithms for solving differential problems. The application of rainfall-runoff simulation models for flood events has been extensively studied by researchers in the field of water and soil protection, leading to the development of various models to simulate rainfall-runoff processes. One of the successful models in this field is the TOPKAPI-X model. This model was created in the 1990s at the University of Bologna by Professor Todini as a distributed rainfall-runoff model in watersheds. An important feature of distributed models is their ability to simulate components at any point of the watershed, allowing results to be extracted at any required point. Unlike lumped models that consider the entire watershed as a single unit, distributed models allow spatial distribution at any point in the watershed. Therefore, in this research, after calibrating and validating the TOPKAPI-X physical-distributed model in the studied basin, the model was optimized for flood estimation.
Materials and methods
The Gamasiab basin is located in the west of Iran, in the northern region of the Zagros mountain ranges, to the north of the Karkheh dam basin, and primarily within the territories of Hamadan and Kermanshah provinces. The mountainous regions of this basin are mainly concentrated in the northern and southern parts, while its lowlands and plains are mostly located in the middle and southeastern parts of the basin (Ministry of Energy, 2014). In this research, the TOPKAPI-X model was used to simulate floods in the Gamasiab watershed. First, the watershed boundary was delineated using a digital elevation model (DEM) with a resolution of 30 meters. Land use maps, soil texture, watershed network, and climatic components were entered into the TOPKAPI-X model. The outlet location of the basin (hydrometric station) was used to simulate the flow using the TOPKAPI-X distributed hydrological model. Continuous time series data on a daily time step were used in this rainfall-runoff model. Specifically, daily rainfall data from 13 rain gauge stations and temperature data from 4 synoptic stations during the statistical period (1999 to 2020) were used to simulate the flow. After running the model several times, the general parameters were manually adjusted each time until the optimal values of the general parameters were obtained by considering the appropriate values of the evaluation criteria (NS and Bias) for the basin.
Results and discussion
This research was conducted to analyze the flood discharge of one of the main sub-basins of the Karkheh dam basin using the TOPKAPI-X model on a daily time scale. In the TOPKAPI-X software environment, simulations were performed during the calibration period using input maps and observational rainfall, temperature, and discharge data. A visual comparison of the observed and simulated hydrographs allows for a general and quick evaluation of the model's accuracy. The graphical results of the comparison between the discharge generated by the TOPKAPI-X model with the calibrated parameters and the measured discharge in the Gamasiab basin were presented. The TOPKAPI-X model has the ability to estimate the maximum daily flow rates of the Gamasiab basin; however, some of the simulated flow rates are higher than the observed flow rates. Four criteria—NSE, R, BIAS, and RMSE—were used to evaluate the model. The evaluation results of the TOPKAPI-X model indicate the accuracy of flow simulation, with a Nash-Sutcliffe criterion of 0.697 during the calibration period (1999-2014) and 0.660 during the validation period (2015-2020) for the Gamasiab basin. Therefore, it can be concluded that this model has good performance for flow simulation.
Conclusions
The importance and usefulness of hydrological models for water resources management, understanding hydrological processes, and conducting impact assessment studies is clear. Hydrological models are crucial tools that enable scientists and policymakers to make informed decisions based on simulations of watershed behavior. Considering the increasing demand for water and the impact of climate change, hydrological simulation will be one of the essential methods for future water management. The results of this study showed that the TOPKAPI-X model has potential in simulating runoff in the selected basin. Due to the capabilities of the TOPKAPI-X distributed hydrological model, this software is recommended as a modeling tool for other basins.
Keywords
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