A B S T R A C T
Different river basins use hydrological models to simulate available rainfall-runoff, land use and soil characteristics data. The main objective of this study is to use the HEC-HMS model to simulate the rainfall-runoff of the Chalosroud watershed as a useful tool to prevent and reduce flood risks. By preparing the Digital Elevation Map (DEM) in GIS and adding the GIS menu in the developed version of the model, the spatial information of the study area and hydrological parameters were calculated directly in the HEC-HMS software. The model was calibrated and validated after preparing soil maps, slope, daily rainfall, and discharge data (model inputs) during 1981-2017 for rainfall-runoff modeling. Curve number (CN), Muskingum routing and unit hydrograph methods were set for the model The coefficients of explanation (R2) and Nash-Sutcliffe (NSE) statistics were used to evaluate the model. The R2 (0.71 and 0.64) and NSE (0.67 and 0.72) values of the calibration and validation periods indicated good agreement between the observed and simulated flows. The correlation between simulated and observed values was good, but the total discharge volume was slightly overestimated for these years. Therefore, the model well simulated the daily discharge flow. The results obtained by the HEC-HMS model are satisfactory and acceptable as an alternative model to other models in runoff prediction. So, the output hydrograph of this model, combined with other hydrological models (HEC-RAS and SWAT) methods, can be used in various fields of study and management for extreme events.
Extended Abstract
Introduction
Rainfall-runoff modeling is one of the most important hydrological processes, especially large-scale processes. Also, nonlinearity and multidimensionality make the modeling of rainfall-to-runoff conversion very complicated. Rainfall-runoff models are classified based on model input, parameters, and the number of physical principles applied to the model. These models can be classified based on the model's parameters as a function of space and time under the integrated and distributed model title and based on other criteria into deterministic and random models. Also, the runoff model can be defined as a set of equations that help to estimate the runoff and a function of the various parameters used to describe the characteristics of the basin. The main reasons for a hydrologist to use process simulation modeling tools are to learn system behavior, support decision-making, and predict future behavior. Many researchers have reported that hydrological models depend mainly on input data, hydrological parameters, and model structure. In particular, river modeling studies in an ungauged catchment using climate and physiographic features are only possible if detailed information on topography, land use, soil, vegetation, and climate is available based on the data. Today, several studies have been done to simulate the rainfall-runoff process by comparing experimental, data-driven, hydrological, and statistical models. All these studies have considered the appropriate simulation of the HEC-HMS model. Thus, the HEC-HMS model can be used to conduct studies such as water availability, urban drainage, flow forecasting, flood event simulation, future urbanisation impact, flood damage reduction, wetland hydrology, reservoir overflow design, flood plain regulation and system performance. In general, the HEC-HMS model seems to be the most useful for predicting discharge in watersheds. Therefore, river discharge models are designed to better understand a basin's hydrological characteristics and generate synthetic hydrological data for river flow programs such as flood protection, water resources planning, pollution reduction or early flood prediction and warning. Specifically, this study aims to simulate rainfall-runoff through the HEC-HMS hydrological model in the Chalosroud watershed.
 
Methodology
This study was used to simulate rainfall-runoff in Chalous River watershed of the HEC-HMS model. The model was implemented through recorded daily rainfall data. The study area is defined by creating 7 sub-basins based on the physical characteristics of the study area, i.e. LULC and soil distribution, using the GIS interface in the HEC-HMS model. The stages of producing the soil map for the study area were carried out using the Harmonized World Soil Database viewer (HWSD). After running this software under Windows, the data was entered into an Arc map to prepare a map of the hydrological soil groups in the study area. A series of necessary parameters, including primary losses, conversion of excess rainfall to surface flow, determination of base flow, calibration, and validation of the model, are needed to implement the rainfall-runoff model. In other words, this model routing considers flow loss and conversion in calculating runoff. As mentioned earlier, after data analysis, the HEC-HMS model created several parameters and a meteorological model (precipitation and evapotranspiration information), control profiles (rainfall start and end date and time, as well as time steps for simulation calculations) and the watershed model (methods of rainfall loss rate, conversion of precipitation to runoff and flow routing) was implemented through the input parameters to obtain the results. Historical data from different periods were used to validate and calibrate the HEC-HMS model. Daily rainfall and runoff data from 2011-1981 were used for calibration and from 2012-2017 for validation. LULC and sub-basin soil characteristics were considered unchanged during these two periods. R2 and Nash-Sutcliffe determination coefficients were also used to evaluate the model's performance.
 
 
Results and Discussion
The curve number of each sub-basin was calculated based on the prepared LULC and soil maps and the provided relationships. The results showed that, in the main part, due to the low runoff potential of the river basin, the amount of CN is not very high. Statistical analysis (determination and Nash-Sutcliffe coefficient equal to 0.71 and 0.64) of the time series of simulated and observed discharge and the scatter diagram in the calibration period showed that the hydrological model for Polzoghal station, the daily observed discharge hydrograph, well simulated. The peak discharge value simulated in the model compared to the observed discharge of the outlet station had an acceptable match in most years. Also, based on the calibrated parameters and values, the model was validated, and the performance slightly improved. The daily hydrograph was simulated with the observed discharge. Statistical analysis (determination and Nash-Sutcliffe coefficient equal to 0.64 and 0.72) in the validation period also showed that the developed hydrological model for Polzhoghal station performed well. However, like the calibration period, the validation period matches the predicted peak flow well. The estimated NSE values, show a good match between the observed and simulated hydrographs, which have been presented in the studies of other researchers. On the other hand, a significant point in the rainfall-runoff simulation process is access to good-quality rainfall-runoff observational data. During the calibration period, the simulated flow was slightly higher than the observed values during 1992-2012 but slightly lower than before. In the validation period, the simulated and observed flow in all years (except 2012) showed excellent agreement. The slight difference in simulated and observed data may be due to the land use map prepared by Landsat data in 2024 and used for the entire study period. In this regard, if there is suitable rainfall-runoff data, the performance of the model can be evaluated more accurately, and better results can be presented. Therefore, it is necessary to analyze the uncertainties caused by the data, model, and user when modeling the rainfall-runoff process.
Conclusions
This study, conducted in the Chalosroud watershed of Mazandaran province, considered rainfall-runoff modeling using the latest version of the HEC-HMS model and without using the HEC-GeoHMS extension. In the hydrometric station of Polzoghal, the output flow was observed, calibrated and validated. The results show a good agreement between the observed and simulated currents, and R2 for calibration and validation was 0.71 and 0.64, respectively. The correlation between the simulated and observed values was good, but the total discharge storage volume was slightly overestimated for these years. Therefore, the model simulated the daily discharge flow well. However, there is an under- and over-prediction of flows. This is a common feature of hydrological models. The obtained results are satisfactory and acceptable. Therefore, the HEC-HMS model is recommended as an alternative to other runoff forecasting models. So, the output hydrograph of this model, combined with other hydrological models such as HEC-RAS and SWAT, can be used in various fields of study and management for extreme events. Thus, considering the coastal location of Chalous city in Mazandaran province, flood planners and managers can use the results of this research to prevent and control floods and, as a result, reduce their social and economic damages.
 
Funding
There is no funding support.
 
Authors’ Contribution
Authors contributed equally to the conceptualization and writing of the article. All of the authors approved thecontent of the manuscript and agreed on all aspects of the work declaration of competing interest none.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
We are grateful to all the scientific consultants of this paper.