Estimation Of Time Of Concentration Using Triangulated Irregular Network Method

In Malaysia, Manual Saliran Mesra Alam (MSMA) has proposed two calculation methods to obtain areas between the isochrones that have been widely practiced at the moment. They are Grid method and Conventional method. However, these methods pose certain problems of their own. Although the Grid method is more detail and accurate when compared to the Conventional method, but that is extremely tedious and time consuming. Conventional method on the other hand is simpler to use. But, the results are not consistent. The results are very subjective because it depends on each user’s experience and judgement. Therefore, a new calculation method named Triangulated Irregular Network (TIN) method has been designed and developed in this research to improve the Time-Area method calculation. This method is computer based and thus the algorithm of TIN method was developed. The algorithm of the TIN method is explained in this research. A study site was constructed and eight sets of rainfall data were collected. All the results from each calculation method were verified with the collected site data to compare their accuracy. Investigation upon their efficiency and reliability were also presented in this research. The comparison showed that TIN method has higher accuracy. In the correlation coefficient comparison among the methods, TIN method has average accuracy of 0.988, Grid method has average accuracy of 0.936 and Conventional method has average accuracy of 0.948. When calculating their difference against the observed data in percentage, TIN method has average difference of 14.29%, Grid method has average difference of 25.67% and Conventional method has average difference of 24.52%. When using the peak flow comparison for the difference against the observed data, the results shows that TIN method has average difference of 3.48%, Grid method has average difference of 5.88% and Conventional method has average difference of 7.72%. Lastly, the methods were compared using the total flow volume. It was demonstrated that the TIN method has different of 0.19%, Grid method has different of 0.43% and Conventional method has different of 4.80% when compared to the observed data. The TIN method has the highest accuracy and reliability among the three methods. Besides, this research also showed that the newly developed TIN method algorithm is easier to use, less time consuming and more reliable

Sensitivity of Empirical Equation Parameters for the Calculation of Time of Concentration in Urbanized Watersheds

settingsOrder Article Reprints Open AccessArticle Sensitivity of Empirical Equation Parameters for the Calculation of Time of Concentration in Urbanized Watersheds by Jamilton Echeverri-Díaz 1,Óscar E. Coronado-Hernández 2,*ORCID,Gustavo Gatica 3ORCID,Rodrigo Linfati 4ORCID,Rafael D. Méndez-Anillo 2 andJairo R. Coronado-Hernández 5ORCID 1 Departamento de Recursos Hídricos, Sertet SAS, Montería 230002, Colombia 2 Facultad de Ingeniería, Universidad Tecnológica de Bolívar, Cartagena 131001, Colombia 3 Faculty of Engineering—CIS, Universidad Andres Bello, Santiago de Chile 7500971, Chile 4 Department of Industrial Engineering, Universidad del Bío-Bío, Concepción 4030000, Chile 5 Departamento de Productividad e Innovación, Universidad de la Costa, Barranquilla 080001, Colombia * Author to whom correspondence should be addressed. Water 2022, 14(18), 2847; https://doi.org/10.3390/w14182847 Received: 17 August 2022 / Revised: 5 September 2022 / Accepted: 9 September 2022 / Published: 13 September 2022 (This article belongs to the Section Urban Water Management) Download Browse Figures Review Reports Versions Notes Abstract The time of concentration is the time it takes a drop of water in a basin to travel from the most distant point to the outlet, and is one of the most important parameters, along with the morphometric characteristics, for determining the design flow rate in rainfall-runoff models. This study aims to determine the sensitivity of the parameters included in different equations for the calculation of the time of concentration. A case study was conducted on small, urbanized watersheds in the city of Montería, Colombia. The study uses information obtained through field work using GPS equipment and electronic total station, supplemented by geographic information contained in the city drawings of the local sewage company, which includes data on elevations above sea level with sub-metric precision. The time of concentration determined by the 12 empirical equations was compared to the results obtained from the equation proposed by the Natural Resources Conservation Service (NRCS), which was considered as a baseline formulation for the intricacy of calculation. Based on this comparison, it was found that the Carter equation is the one that best fits the results obtained from the NRCS equation because it displayed highly significant goodness of fit values. Even though the equations by Kirpich, Ventura, California Culvert Practice, Simas-Hawkins and TxDOT provide a relatively good fit compared to other empirical equations, they tend to over-estimate time of concentration values, which could lead to the under-estimation of the design flow rates. For this reason, sensitivity analysis of the parameters of these equations represents an alternative for improving the calculation of the time of concentration. The current research analyses deepen the influence of some parameters in the estimation of time of concentration. The research can also be used by designers and engineers in the city of Montería, Colombia, as an important reference to compute time of concentrations in urbanized watersheds

Time of concentration in an experimental basin: methods for analysis, backwater effects and vegetation removal

There are several empirical and theoretical formulas used for the estimation of the time of concentration (Tc). However, it has been shown that the Tc estimation may vary in several orders of magnitude depending on the method. In this study we compare 10 different methods for the estimation of the Tc using sub-basins and backwater effects to analyze those results. We also analyzed if the vegetation removal changes the Tc in the basin. The study area is the basin of the Federal University of Santa Catarina (UFSC) campus in Joinville with a significant part in a wetland and there is backwater effect caused by the Piraí river. Applying the empirical and theoretical equations found a significant variation of Tc estimates, the standard deviation in relation to the general average was around 65%. The influence of vegetation removal and drainage of a canal had an effect of reducing the Tc by 50%

A New Methodology For Deriving Regional Time Of Concentration Equations Using GIS And Genetic Programming

Time of concentration (ToC) is the most frequently utilized time-scale parameter in hydrology which must be estimated accurately to ensure correct simulation of many different hydrological processes. Hydrologists have developed many empirical and semi-empirical methods for estimating ToC which are regional, watershed, and site-specific. Modellers are often confused by the number of ToC estimation methods and formulas and often select an equation without evaluating its correctness which leads to inaccurate simulation results. The importance of deriving and using regional ToC equations has been highlighted in many studies. In this paper, a methodology is proposed for deriving ToC equation(s) for watersheds located in a specific geographic region using GIS and Genetic Programming (GP). The use of GIS data allows for easy extraction of multiple characteristics of a large number of watersheds and sub-watersheds. Also, integration of GIS maps into the TR-55 model enables the determination of “true” TOC values for the watersheds under study. The obtained physical and hydrological characteristics of the watersheds are combined with rainfall characteristics and computed ToC values to form a large database. GP is then used as a data mining tool for conducting symbolic regression and deriving the most accurate set of equations for the watersheds of the region. In a case study, the proposed methodology is applied to 72 watersheds and sub-watersheds in Khorasan Razavi province, Iran. The method provides a set of different ToC equations to be used for watersheds with different sizes in the region. The equations proposed by GP are evaluated and compared to other conventional ToC estimation methods. The set of equations found by GP provides insight on the relationship between ToC and other watershed and rainfall characteristics and highlights the potential role of GP as an attractive and effective Knowledge Discovery tool

A Simple Method to Develop a Formula for Estimating Concentration Time of Drainage Design

Concentration time of rainfall is an important aspect to determine drainage design. A general rational formula is used to determine design flood or peak flow in urban drainage planning, especially for storm sewer design. The use of this balanced formula requires rainfall intensity, whose duration of rain is equal or more than the time of concentration. This time of concentration is determined using an estimation formula whose formation requires measurement data of the time of concentration. This study introduces how to measure the time of concentration using the concept of-rational-hydrograph, in which peak flow occurs at the time of concentration. To fulfill the aim of this research, an experimental of catchment area planted with Zoysia Japonica grass and showered with a rainfall simulator was conducted. The length of the flow path on the land, L, given in 5 variations, namely 50 cm, 100 cm, 150 cm, 200 cm, and 250 cm, was used. The slope of the land, S, is given in 3 variations, namely 2.8 %, 5,6%, and 8.8%. For each variation of L and S, the experimental catchment area was poured with a fixed rainfall intensity, which is 60 mm/hour. The flow was measured every 5 minutes intervals. Then, from the relationship of flow and time, a rational hydrograph was formed, from which the time of concentration, Tc, was deduced. This Tc value was treated as the measured Tc to form the Tc estimation formula using the regression formula. The formula is Tc = 3.543 + 1.211 L – 17.119 S, with the coefficient of determination R2 = 0.98. These results show that the determination of Tc using the concept of the rational- hydrograph is acceptable. This formula applies to L and S values greater than zero and applies to land covered by Zoysia Japonica grass. Further research is needed for other types of land cover to validate the formula obtained in this research

Overland flow time of concentration on flat terrains

Time of concentration parameter is defined very loosely in literature and it is calculated rather subjectively in practice (Akan 1986). The situation becomes adverse as the terrain slope approaches zero; because the slope generally appears in the denominator of any formula for time of concentration, this time goes to infinity as the slope goes to zero. The variables affecting this time parameter on flat terrains have been studied through plot scale field experiments. It has been found that the antecedent moisture and rainfall rate control this parameter. Some of the existing time of concentration methods have been compared, and it is found that all the empirical models compared under predict this time parameter. This under prediction can be attributed first to the differing concepts of time of concentration previous researchers have modeled, secondly to the absence of any accounting for the initial moisture content in their respective equations and thirdly to the watersheds where these models have been calibrated. At lower time of concentrations, Izzard-based model predictions show some results close to the observed values. A methodology to determine the plot scale surface undulations has been developed to estimate the depression storage. Regression equations have been derived based upon the experiments to determine the overland flow times on a flat plot of 30 feet length with uniform rainfall intensity. The application of these equations on other lengths cannot be ascertained. Equations for the hydrograph slope on flat terrains have been determined for bare clay and grass plots

Revisiting Kirpich's Formula for calculating time of concentration

O presente trabalho apresenta a história sobre a origem e desenvolvimento da fórmula de Kirpich para calcular o tempo de concentração (tc) e a partir disso demonstra um equívoco que existe nesta fórmula. Por fim avaliou-se o erro relativo causado a este equívoco considerando duas situações: (i) valores de comprimento da bacia (L) medido ao longo do curso d’água, e de declividade do curso d’água (S) dentro do intervalo correspondente ao das bacias componentes do banco de dados utilizado na elaboração da fórmula; e (ii) valores de L e S em um intervalo mais amplo, porém possível em bacias reais. Na situação (i) o erro relativo nos valores de tc, estimados com a fórmula de Kirpich varia de 2 a 9%, e na situação (ii) o erro relativo pode chegar a 30%. A fórmula de Kirpich, na verdade não foi publicada por ele, e nem se originou somente do banco de dados que ele utilizou. Demonstrou-se a importância de ainda hoje se buscar a fonte original de publicação antes de citar, e/ou aplicar teorias, técnicas, métodos e inclusive fórmulas.The present work describes the history of Kirpich’s Formula which can be used to calculate the time of concentration (tc) and the misconception that exists regarding its well-known version. Finally, the relative error due to this misconception was evaluated considering two situations: (i) the interval of values of watershed length (L) measured along the water course, and the water course slope (S) corresponding to that of the data base used to elaborate the formula; (ii) more extensive interval of values of L and S, which could occur in real basins. The relative error of the tc values in the situation (i) varies between 2 and 9%, and in situation (ii) it can be 30%. Kirpich’s Formula was actually not published by him, and was not even elaborated only from the data base he used. The importance of looking for the original publication before citing and/or applying theories, techniques, methods, and formulas was demonstrated

Modelling and simulation of magnetic induction in magnetic particle imaging system

In the last century, tomographic imaging has become an essential tool for disease diagnosis. There are several dominant tomographic imaging methods used for medical application such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and single photon emission computed tomography (SPECT)