Rational Method Time of Concentration Can Underestimate Peak Discharge for Hillslopes

The geometry of hillslopes (plan and profile) affects soil erosion under rainfall-runoff processes. This issue comprises of several factors, which must be identified and assessed if efficient control measures are to be designed. The main aim of the current research was to investigate the impact of surface Roughness Coefficients (RCs) and Complex Hillslopes (CHs) on runoff variables viz. time of generation, time of concentration, and peak discharge value. A total of 81 experiments were conducted with a rainfall intensity of 7 L min−1 on three types of soils with different RCs (i.e., low = 0.015, medium = 0.016, and high = 0.018) and CHs (i.e., profile curvature and plan shape). An inclination of 20% was used for three replications. The results indicate a significant difference (p-value ≤ 0.001) in the above-mentioned runoff variables under different RCs and CHs. Our investigation of the combined effects of RCs and CHs on the runoff variables shows that the plan and profile impacts are consistent with a variation in RC. This can implicate that at low RC, the effect of the plan shape (i.e., convergent) on runoff variables increases but at high RC, the impact of the profile curvature overcomes the plan shapes and the profile curvature’s changes become the criteria for changing the behavior of the runoff variables. The lowest mean values of runoff generation and time of concentration were obtained in the convex-convergent and the convex-divergent at 1.15 min and 2.68 min, respectively, for the soil with an RC of 0.015. The highest mean of peak discharge was obtained in the concave-divergent CH in the soil with an RC of 0.018. We conclude that these results can be useful in order to design planned soil erosion control measures where the soil roughness and slope morphology play a key role in activating runoff generation.

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The floods in Greece: the case of Mandra in Attica

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.16419 ◽

2018 ◽

Vol 52 (1) ◽

pp. 131 ◽

Cited By ~ 1

Author(s):

Georgios Soulios ◽

Georgios Stournaras ◽

Konstantinos Nikas ◽

Christos Mattas

Keyword(s):

Climate Change ◽

Natural Disasters ◽

Rational Method ◽

Peak Discharge ◽

Human Intervention ◽

Return Periods ◽

Flooding Event ◽

Stream Characteristics ◽

Extensive Damage

Floods are one of the most common natural disasters and are extremely dangerous in a global range since they can cause extensive damage to properties or losses in human lives. According to the opinion of many expert scientists, climate change has led to the increase of flooding phenomena over the last years worldwide, as well as in Greece. The aim of this paper is to examine the flooding event that occurred in Mandra area, Attica (Greece) on 14-15 November of 2017. The peak discharge of the Agia Ekaterini and Soures streams was calculated using the rational method (Giandotti) for return periods equal to 10, 100 and 1000 years. The stream characteristics were studied and their behavior during the flood was investigated. Many of the impacts were attributed to the human intervention in the streambeds.

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Parameter Adjustment to Prevent the Overestimation of Peak Discharge in a Small Watershed

Korean Society of Hazard Mitigation ◽

10.9798/kosham.2021.21.6.285 ◽

2021 ◽

Vol 21 (6) ◽

pp. 285-291

Author(s):

JongChun Kim ◽

Jongho Jeong

Keyword(s):

Response Time ◽

Peak Discharge ◽

Small Watershed ◽

Unit Hydrograph ◽

Area Method ◽

Time Of Concentration ◽

Rainfall Duration ◽

Reasonable Range ◽

Specific Discharge ◽

Basin Response

We revisit empirical methods to prevent the overestimation of peak discharge in a small watershed, in particular investigating the time-area method, which has not been considered in the overestimation problem of peak discharge. To avoid misapplying the same inlet time between the unit hydrograph and rational formula, distinct parameter adjustments for each method are proposed. We adopt the secondary basin response time for the unit hydrograph, rainfall duration for the rational formula, and time of concentration for the time-area method, as suitable parameters to adjust the estimation of peak discharge. In conclusion, adding 10 minutes to secondary basin response time, 20 minutes to rainfall duration, and 30 minutes to time of concentration, respectively, yields estimates within a reasonable range of specific discharge in a small watershed.

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A Combination between Synthetic Unit Hydrograph (SCS) and Rational Method in a similar Conditions Water Shed

Asian Journal of Engineering and Technology ◽

10.24203/ajet.v9i3.6622 ◽

2021 ◽

Vol 9 (3) ◽

Author(s):

Mona Fathi ◽

Neveen B. Abelmageed ◽

M. Hassan

Keyword(s):

Rational Method ◽

Rainfall Data ◽

Return Periods ◽

Unit Hydrograph ◽

Engineering Applications ◽

Watershed Characteristics ◽

Time Of Concentration ◽

Excess Water ◽

The Difference ◽

Peak Runoff

Studying watershed characteristics and choosing the most applicable methods to determine the amount of access rainfall that ran off is very important in many engineering applications, especially hydrology applications. That is to know the more suitable methods for protection against floods and to maximize benefits from the excess water. This study aims to establish a relation between the rational method and the SCS method. A subbasin in Wadi Dahab in Sinai, Egypt is investigated as a study area. To achieve the study aims, HEC-WMS software is chosen, which can analyze a watershed by using DEM and delineating basin. It calculates also important watershed parameters like area, runoff distances, and slope. The rainfall data is compiled and arranged. A statical analysis is executed to obtain the IDF curves. Hyfran-plus software is employed to locate the maximum depths for different return periods. Various values for the time of concentration are studied. It is concluded that the difference between the rational and SCS methods is great for the time of concentration till 2 hours, then it decreases obviously from 2 till 6 hours. Also, it is concluded that the difference between the two methods is bigger for the small return periods of 2 and 5 years for all values of the time of concentration. Employing the obtained equations, the peak runoff for one of the two methods (the rational and SCS methods) can be calculated knowing the time of concentration and the peak runoff for the second method.

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A history of the concept of time of concentration

Hydrology and Earth System Sciences ◽

10.5194/hess-24-2655-2020 ◽

2020 ◽

Vol 24 (5) ◽

pp. 2655-2670 ◽

Cited By ~ 3

Author(s):

Keith J. Beven

Keyword(s):

Response Times ◽

Rational Method ◽

Unit Hydrograph ◽

Surface Flows ◽

Time Of Concentration ◽

Water Particle ◽

Subsurface Flows ◽

History Of ◽

The 1960S ◽

Catchment Responses

Abstract. The concept of time of concentration in the analysis of catchment responses dates back over 150 years to the introduction of the rational method. Since then it has been used in a variety of ways in the formulation of both unit hydrograph and distributed catchment models. It is normally discussed in terms of the velocity of flow of a water particle from the furthest part of a catchment to the outlet. This is also the basis for the definition in the International Glossary of Hydrology. While conceptually simple, this definition is, however, wrong when applied to catchment responses where, in terms of how surface and subsurface flows produce hydrographs, it is more correct to discuss and teach the concept based on celerities and time to equilibrium. While this has been recognized since the 1960s, some recent papers and texts remain confused over the definition and use of the time of concentration concept. The paper sets out the history of its use and clarifies its relationship with time to equilibrium but suggests that both terms are not really useful in explaining hydrological responses. An Appendix is included that quantifies the differences between the definitions of response times for subsurface and surface flows under simple assumptions that might be useful in teaching.

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Using the Rational Method for Design in Complex Urban Basins

Hydrology Research ◽

10.2166/nh.1998.0005 ◽

1998 ◽

Vol 29 (2) ◽

pp. 73-90

Author(s):

Lars Bengtsson ◽

Janusz Niemczynowicz

Keyword(s):

Peak Flow ◽

Drainage System ◽

Rational Method ◽

Design Flow ◽

Time Of Concentration ◽

Planning And Design ◽

Urban Planning And Design ◽

Derived Design ◽

Reduced Time ◽

Different Parts

Because of its simplicity the rational method is still frequently used in urban planning and design. In this paper using the time-area method and statistically derived design storms, the design peak flow is computed for urban basins of different complexity and compared with the design flow determined from the rational method. It is shown that the design flow is underestimated using the rational method unless a reduced time of concentration is used. The relation between travel times in different parts of a drainage system is used to correct the design flow computed by the traditional rational method.

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MEMBANGUN “SISTEM DINAMIS UNTUK MENGHITUNG DEBIT PUNCAK” (SDDP) DENGAN MENGGUNAKAN STELLA VERSI 9.0.2 (Uji Aplikasi Untuk Wilayah Banjir di Kecamatan Makasar Jakarta Timur)

Jurnal Air Indonesia ◽

10.29122/jai.v5i1.2434 ◽

2018 ◽

Vol 5 (1) ◽

Author(s):

Robertus Haryoto Indriatmoko

Keyword(s):

Key Words ◽

Catchment Area ◽

Rational Method ◽

Peak Discharge ◽

C Value ◽

Rain Fall ◽

Manual Calculation

Peak Discharge Dinamyc System (SDDP) is a program which apply to calculate peak of discharge a catchment area with area and rain fall intensity as parameters, with limited to maximal 50 km2 area and 100 mm/hour rain fall intensity. This program is develop by using System Dinamyc Stella version 9.0.2. Steps taken are, first by calculate runoff cooeficient use Bridge-Branch method and then calculate peak discharge with rational method. This program is tested on sub-catcment Makassar, East Jakarta and compare the result of the program with manual calculation, and concluded that no deviation between those 2 methods, and even more the SDDP program provide prediction of peak discharge with variable C value and data of calculation peak discharge with SDDP program presented in graphic and tabulation as well. Key words : Model, Sistem Dinamis, Stella, Banjir, Debit Puncak, Koefisien Aliran, Prediksi, Jakarta Timur

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Model Hidrograf Akibat Perubahan Tataguna Lahan DAS Batang Kuranji (Studi Kasus Sub DAS Danau Limau Manis)

Jurnal Ilmiah Poli Rekayasa ◽

10.30630/jipr.13.1.46 ◽

2017 ◽

Vol 13 (1) ◽

pp. 1

Author(s):

Elvi Roza Syofyan ◽

Amrizal Saidi ◽

Bambang Istijono ◽

Revalin Herdianto

Keyword(s):

Land Use ◽

Rational Method ◽

Peak Discharge ◽

Runoff Coefficient ◽

Number Increase ◽

Significant Change ◽

Using Data

The purpose of the study is to look at changes in land use and hydrograph models of Danau Limau Manis Sub-watershed using data 2011 until 2015.The results shows the change of land use of Batang Kuranji Watershed, Sub DAS Danau Limau Manis can decreased 3.03% from 2011 to 2015. It due to the opening of new land. While shrub rose rose 0360%, because was due of changes of forests that have not done processing. For an others using of the land the number increase 3.40%. It due to changes of forests and shrubs into failure land.. As the runoff coefficient (C) does not occur any significant change that is from 0.405 into 0.408. Peak discharge calculated by the Nakayasu method 128.02 m3 / dt, was greater by Rational method of 127,52 m3 / dt is caused no difference in the approach used.

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