جستجوی مقالات مرتبط با کلیدواژه « instantaneous unit hydrograph » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

In Nash's cascade model that is simple and efficient model for simulating hydrological response in watersheds, catchment behavior is considered same as n linear reservoirs with k storage coefficient. In this context, the accuracy of different methods of estimating the Nash model parameters (n and k) including moment, experimental Nash formula, Han’s graphical, time to peak-time to inflection point and Bhunya et al methods have been investigated in Manshad watershed in Yazd province. The n and k parameters were calculated using three storm events and physiographic parameters were used for experimental Nash formula. The mean value of calibrated parameters, were used for simulation of second subset of storm events as model validation. The results show that using Bhunya and Han’s graphical methods for n and k parameters estimation, lead to better agreement between observed and simulated hydrographs. Percentage of relative error in simulating peak discharge, time to peak and flood volume, in Bhunya method, were estimated equal to 28.24, 29.48 & 8.20% and in Han’s graphical method were estimated equal to 28.29, 29.48 and 8.52% , respectively. Also, the results indicate that time to peak-time to inflection point method and experimental Nash formula give weak results for simulating some flood characteristics. Thus, using these methods in similar catchments is not advised without more researches.

The hydrograph at watershed outlet can be expressed as hydrological response of watershed to geomorphological behavior. In present study with the aid of the GIS and the concept of instantaneous unit hydrograph, the watershed response was simulated. In present physical method, the IUH is derived from three parameters of time of concentration, storage coefficient and time-area curve of the basin. In the present study, the accuracy of various methods of determining time-area curve in providing Clark instantaneous unit hydrograph viz. channel profile, average velocity and Laurenson methods were therefore evaluated. The comparison of estimated and observed hydrographs by using qualitative and quantitative criteria showed that the average velocity method has had the highest accuracy in estimation of time-area method. The results of the quantitative statistics of root mean square of error, bias in peak discharge, coefficient of efficiency, and relative errors in peak discharge, time to peak and base time were respectively found to be 1.39, 0.93, 0.83, and 7.13, 33.33 and 15.38%. The results of this research also showed that the Clark model had a good efficiency in simulation of unit hydrograph in Kasilian watershed, Mazandaran Province, Iran.

Applications of rainfall-runoff models, are to determine the hydrologic behavior of watershed and to simulate the flow, for designing hydraulic structures and specially evaluating the impacts of operations on the flow regime. According to deficiency of hydrometer data in most of Iran’s watersheds, using simple and convenient hydrologic models and developing them for watersheds without stations is essential. In this context, several methods have been proposed. This study has been compared the consistency, accuracy and reliability of geomorphologic, geomorphoclimatic and nash instantaneous unit hydrographs, in estimating outlet runoff hydrograph characteristics, in Manshad watershed. For this purpose, six storm events were chosen, by using the area’s hydro-meteorological data. Then, the methods’ needing parameters, including the area’s morphometric characteristics and the events properties, were calculated. Thus, outlet runoff hydrographs, for each method were determined. Evaluations that have been carried out by using the mean relative error, the root mean square error and the Nash-Sutcliffe indices, confirmed the higher efficiency of Nash model, in estimating peak discharge, with an error of 23.75, time to peak with an error of 28.21 and the complete shape of hydrograph, with efficiency criterion of 0.4, than the other methods. In addition, this method has a high potential in simulating the actual amount of flood volume, with an error of 9.90. Thus, nash model, compared to other models (based on this study), is the most efficient model for estimating flood discharge.

Instantaneous unit hydrograph (IUH) is a hydrograph that has used for calculation of direct runoff hydrograph in watersheds and recent addition to formal methods, Shannon entropy theory consider for calculation of direct runoff hydrograph. If the system disorderly is measured in terms of entropy then the probability distribution of the events, provides in terms of entropy. In this theory, defined travel time as a random variable, the maximizing the entropy on based this parameter and also specifies constraints, the least-biased probability density function, determining parameters of the IUH and finally obtaining applicable IUH equation. In this study, six events of Lighvan watershed has been studied that located in Northwest Iran. After calculating travel time and determining parameters on based entropy, derivation applicable IUH equation and calculated direct runoff hydrograph. For estimated and more evaluated IUH and direct runoff hydrograph has used Gamma distribution that result showed good accuracy of the entropy theory. The results indicate acceptable performance of the entropy model shows the average correlation coefficient (0.828), mean error of peak (17.35%), entropy index (2.47 knot) and nash-sutcliff value (NS=0.742) in verification events.