Synthetic Unit Hydrograph Methods Research Articles

Estimation of Catchment Parameters of Snyder's Synthetic Method for Water Resources Planning and Flood Management in Sri Lanka

Snyder's synthetic unit hydrograph method is widely recognized for synthesizing unit hydrographs. This paper illustrates a study demonstrating how to estimate catchment parameters using Snyder's synthetic method for hydro-meteorological stations maintained by the Irrigation Department and its application to Sri Lanka. Updated Snyder's Unit Hydrograph parameters, including coefficient accounting for flood wave and storage condition (Cp) and coefficient representing variations of catchment slop and storage (Ct) for 15 river gauge stations spread across the island, have been presented in this paper. The Cp values vary from 0.22 to 0.7, and the Ct values vary from 0.48 to 5.76. Updating the Snyder parameters is a long-term requirement, and these values can be used to update the previous values estimated in 1980.

Hydrological Modelling with HEC-HMS in Krueng Peudada Sub-Watershed Bireuen Regency

The flood that occurred in Krueng Peudada was influenced by several factors, such as watershed conditions. Heavy rains caused Krueng Peudada to overflow so that a number of villages adjacent to the river were submerged. Based on these problems, to minimize the occurrence of flooding in Krueng Peudada building, namely by carrying out occurrence of flooding in Krueng Peudada to be used to obtain peak discharge as a reference in building planning in Krueng Peudada using HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modelling System). The benefit of the research is that the resulting model can be useful as a guide in calculating flood discharge considerations. The scope of this research includes the research location at Krueng Peudada using annual maximum daily rainfall data, calculating the return period of rainfall using of Gumbel probability distribution, Normal Log, Normal, and Pearson III Log as the basis for calculating the discharge and continuing the calculation of the hours with Manonobe and ABM. The results of calculations of the Nakayasu Synthetic Unit Hydrograph Method and running from HEC-HMS found that the flow that occurred in the Krueng Peudada two sub-watershed was 2903m3/second and 2723,0 m3/second, it can be concluded that in determining watershed management the flood discharge obtainded has error as much as 6,2%. The difference in the results obtained is due to the number of sub-watersheds in the watershed based on different flows and the value of the curve number for each area of the sub-watershed.

Hydrological Analysis of the Makassar-Pare Corridor Rail Elevated Bridge in Pangkep Regency South Sulawesi Province

Hydrological analysis is an important stage in the development of water resources. Determining hydrological quantities is actually not too difficult if the data for analysis purposes is available in sufficient quantity and quality. The method used for the analysis of the planned flood discharge depends on the amount of discharge data and rainfall data. Based on the analysis of discharge data and rain data. For planning the storage capacity of the river crossing the railway bridge, using the Nakayasu Synthetic Unit Hydrograph (HSS) Method, the river water level to the JEKA 2 structure is 13.38 m and the river water level to the tracks is 16.38 m so that the railroad tracks at Bridge 2 can be said to be safe against the river water level. Hydrological analysis is one part of a whole series in the planning of transportation structures such as roads, bridges and railway bridges including flood barrier embankments and so on.

Increasing surface impermeability influences peak discharge with the Snyder method in the Ngadipiro sub-watershed of the Bengawan Solo watershed

This research was conducted to determine the effect of increasing soil impermeability in the Ngadipiro Sub-watershed on Cp and Ct numbers in 2015 and 2021. The measured unit hydrograph is used as a reference in calculating the Synder synthetic unit hydrograph method. Test the validation of the two methods using the correlation coefficient. The results of this study showed an increase in tightness in the form of an increased runoff coefficient from 0.26 in 2015 to 0.34 in 2021. This increase in tightness is also in line with the increase in peak discharge using the Measured unit hydrograph in 2015 of 73.3757 m3/s and 2021 of 139.1005 m3/s. The results obtained using the Snyder method obtained peak discharges in 2015 and 2021 of 75.10 m3/s and 148.89 m3/s. The results of the correlation test between the two methods obtained very strong correlation results with a 2015 R-value of 0.96 and a 2021 R-value of 0.92. The non-physical parameters of the watershed, namely Ct and Cp, were optimal in the Ngadipiro Sub-watershed in 2015, the Ct value was 2.2 and the Cp value was 0.9, while in 2021 the Ct value obtained was 1.3 and the Cp value was 1.1.

ANALISIS BANJIR SUNGAI MENGGUNAKAN MODEL HEC-RAS DI WILAYAH DAS TABANIO KABUPATEN TANAH LAUT PROVINSI KALIMANTAN SELATAN

This study aims to determine the amount of water runoff and water depth in the Tabanio Watershed, Tanah Laut Regency. The study was conducted using the HEC-RAS software to generate a flood simulation model. Data analysis included Digital Elevation Model for National Scale (DEMNAS) data, flood discharge data, rainfall data, river bathymetry, and tidal data. DEMNAS data was obtained from the website of the National Geospatial Information Agency (BIG), rainfall data was obtained from the Center for Hydrometeorology and Remote Sensing (CHRS) website. Rainfall data analysis involves selecting the maximum daily rainfall value to determine the flood discharge. The hourly flood discharge is calculated using the Synthetic Unit Hydrograph method with the Nakayasu approach. River bathymetry data is processed as additional data for DEM, with interval recording done every 0.2 seconds. Tide data was obtained through prediction based on the location constant closest to the research area and analyzed using the Pasut.exe software for a period of 6 days. Based on the results of flood analysis research using the HEC-RAS model in the Tabanio Watershed, Tanah Laut Regency, South Kalimantan Province, it can be concluded that the model results show the water depth and area of water runoff at maximum discharge. as follows: less than 0.5 meters with a very low category covering an area of 4,168.86 hectares, 0.51 to 1.5 meters with a low category covering an area of 6,417.79 hectares, 1.51 to 2.5 meters with a medium category covering an area of 1,987, 25 hectares, 2.51 to 3.5 meters with a high category of 741.47 hectares, and above 3.51 meters with a very high category of 113.69 hectares. So that the total water runoff reaches 13,429.05 hectares.

Analisis Banjir Metode Hidrograf Satuan Sintetis SCS dan Nakayasu DAS Pesung, Batam

Design discharge is discharge with a certain return period which is used as a reference or parameter in a water building construction planning. Calculation of the design discharge can be done by using the synthetic unit hydrograph method. The calculation of the planned discharge using the Nakayasu and SCS-CN synthetic unit hydrographs aims to compare the calculation of the maximum discharge in the Pesung Watershed, Batam. The design discharge analysis was carried out without calibrating with AWLR data (observed flow) due to the unavailability of AWLR data at the study site. Thus, in this study using HDRO (high direct runoff) as a comparison. The purpose of this study is to estimate the magnitude of the design flood discharge in the Pesung Watershed, Batam City. The methods used in this calculation of the flood hydrograph is using an empirical formula, namely SCS Synthetic Unit Hydrograph and Nakayasu. The results of the HDRO calculation analysis show that the largest flood discharge occurs in the Nakayasu synthetic unit hydrograph method with details of the SCS synthetic unit hydrograph method, the peak time (Tp) is obtained at 4.46 hours, with a return period flood discharge of 5 – 50 reaching 215,488 – 584,308 m3/ s. Whereas in the Nakayasu synthetic unit hydrograph method, the peak time (Tp) is obtained at 1.47 hours, with a return period flood discharge of 5 – 50 years reaching 360.526 – 986.535 m³/s.

Runoff hydrographs using Snyder and SCS synthetic unit hydrograph methods: A case study of ungauged watersheds of Imam Turki Bin Abdullah Royal Nature Reserve (ITBA) - Saudi Arabia

Background: The estimation of surface runoff and discharge peak using the Snyder’s model and SCS Dimensionless UH (SCS-DUH) method are one of the best alternatives solutions appropriate for analyzing the hydrologic systems in the ungauged watersheds. These two methods were applied to estimate the discharge peak and design their hydrographs in the drainage basins of Royal Nature Reserve (Imam Turki Bin Abdullah) in Saudi Arabia. - Aims: To estimate the discharge peak by applying Snyder’s model and SCS-DUH method using the morphometric parameters deriving from the SRTM DEM30m and three rainstorms of 40, 50 and 60mm. - Methods: The estimation of discharge peak (Qp) using Snyder’s model was depended on the SRTM DEM30m outputs and the hydrology parameters of the duration (Td) of Unit Hydrograph (UH), time to peak (Tp), time base of the UH (Tb), UH width at 50% and 75% of the peak discharge. However, the estimation of the discharge peak by The SCS-DUH method was computed using the drainage area (A), the direct runoff (Qd) and the time to peak (Tp). The direct runoff was determined by the runoff ratio 0.20 of the unimproved areas, proposed by the Soil Conservation Service (SCS). But, the time to peak was computed using the average of the concentration time obtained from Johnstone-Cross and Dooge models. The hydrographs design was done by the time ratio method recommended by the SCS. - Results: The estimated discharge peak computed by Snyder’s model varies with a maximum of 93.4 to 2092.9 m3/s, an average of 61.1 to 1368.4 m3/s and a minimum of 28.7 to 644.0 m3/s in Al Shuwaiki and Khtal watersheds, respectively. The estimated discharge peak computed by SCS-DUH method was ranged from 21.5 to 482.3 m3/s for the rainstorm of 40mm in Al Suwayki and Khtal, respectively, from 28.5 to 602.9 m3/s for the rainstorm of 50mm and from 34.1 to 723.5 m3/s for the rainstorm of 60mm, in Um Nqy and Khtal, respectively. - Conclusion: The hydrology study of ungauged basins in Royal Nature Reserve (ITBA) shows the great potential of the integrated emplyement of GIS technics and the hydrology models to estimate the discharge peak and design their hydrographs.

Flood Water Level Simulation Bringin River, Semarang City By Using The HEC-RAS 6.3.1 Programming

The Bringin River is a river in West Semarang, Semarang City, with the Tugu Region drainage subsystem. The Bringin watershed covers parts of the area in Tugu District, Ngaliyan District, and Mijen District. The overflow of water caused by high rainfall resulted in river flooding. The cross-section of the Bringin River cannot accommodate the magnitude of the flood discharge. The purpose of this study was to determine the cross-section of the Bringin River which was experiencing an overflow by carrying out a Hydrological Analysis and using the HEC-RAS 6.3.1 Program as a 1-dimensional cross-sectional design. Calculation of the planned flood discharge with periods of 2, 5, 10, 25, and 50 years using the Nakayasu Synthetic Unit Hydrograph method with a peak discharge Q2years : 52.45 m3/second, Q5years : 62.43 m3/second, Q10years: 68.44 m3/second, Q25years : 75.09 m3/second, and Q50years : 79.95 m3/second. The results of the calculation of the design discharge will be used in the HEC-RAS 6.3.1 programming so that from these results it can be seen that several cross-sections of the river have flood overflows that exceed the capacity of the Bringin River under review.

ANALYSIS OF FLOOD HYDROGRAPH IN THE LANDAK SUB WATERSHED

This research is motivated by the natural flooding disaster in the Landak sub-watershed area, which can be caused by river overflow due to high rain intensity. Flood discharge can be calculated using the Synthetic Unit Hydrograph method if the available data is limited, such as only obtaining rainfall data and watershed characteristics.Several Synthetic Unit Hydrograph (SUH) methodologies, including SUH Snyder, Nakayasu, Soil Conservation Services (SCS), Gama I, ITB, and Limantara, were utilized in this study. The analyzed data included precipitation data and measured discharge data. Rainfall data are analyzed using the homogeneity test, statistical descriptors, and chi-squared to determine the planned flood discharge. Then, continue with the study of rainfall frequency and analysis of rainfall intensity so that the maximal discharge can be analyzed using three SUH methods: HSS Snyder, Nakayasu, and SCS. The analysis of measured release is conducted by statistically analyzing estimated discharge data.The analysis results are then compared to obtain the percentage error between the discharge plan and the minimum measured discharge. The results showed that the HSS Snyder method was selected for analyzing flood discharge in the Landak sub-watershed basin because it has the minimum percentage error from comparing planned release and measured discharge values. Therefore, for the calculation of flood discharge analysis of the Landak sub-watershed basin, the HSS Snyder method is used with the acquisition of flood discharge plans for the return period of 2, 5, 10, 20, 50, and 100 years of 648,880 m3/sec, 896,335 m3/sec, 1025,954 m3/sec, 1132,006 m3/sec, 1252,788 m3/sec, 1335,273 m3/sec.

Analisis Debit Banjir Rancangan Dan Kapasitas Tampang Sungai Di Sekitar Kawasan Sempadan Sungai Sokong Kabupaten Lombok Utara

In line with the North Lombok Regency (KLU) government program to prioritize handling and structuring residential areas and disaster-prone areas in the Pemenang-Tanjung sub-district in 2022, it is necessary to carry out several technical studies to support the program. One of the technical studies that can be carried out is an analysis of the design flood and river capacity around the Sokong River section in Tanjung Village, which is a location that is classified as densely populated, with slums and residential areas close to the river border. This study aimed to determine the magnitude of the design flood discharge and the cross-sectional capacity of the Sokong river section. The method used in this study is a hydrological analysis using the Nakayasu Synthetic Unit Hydrograph method to determine the amount of design flood discharge for the 25-year return period (Q25th) and analysis of river cross-sectional capacity using Hec-RAS 4.1.0 software. The results of the analysis show that the Q25th that occurs along the Sokong River section is 131.32 m3/s and the simulation results use Hec-RAS 4.1.0 software. shows that the capacity of the Sokong River segment cannot accommodate the Q25th. Therefore, it is necessary to plan the arrangement of residential buildings around the border area of ​​the Sokong River by raising the elevation of the building to be free from flood inundation.

Comparison of flood hydrograph prediction between synthetic unit hydrograph methods and rain-on-grid model for Katulampa watershed, Indonesia

Comparison of flood hydrograph prediction between synthetic unit hydrograph methods and rain-on-grid model for Katulampa watershed, Indonesia

Evaluation of Flood Control Performance in the Talangsari Watershed, Samarinda, East Kalimantan

The flood issues in the Talangsari River in Samarinda City were not only caused by high rainfall but also by the significant sediment accumulation and waste along the river, the encroachment of residential areas onto the river section, and the lack of public awareness regarding environmental cleanliness. As a result, flooding occurs throughout the Talangsari River, from upstream to downstream, indicating significant damage to the river. Considering these issues, proactive measures are necessary to address the flood problems. One such measure is the normalization of the Talangsari River to ensure smooth land transportation from and to Apt Pranoto Airport in the Sei Siring area, Bontang City, Sangatta, and Kutai Kartanegara. The flood discharge plan was estimated using Nakayasu and SCS synthetic unit hydrograph method. The analysis revealed a peak discharge of 6.39 m3/s for the existing conditions (2-year return period) and 13.38 m3/s for the normalization conditions (25-year return period). Subsequently, the simulations were performed using the HEC-RAS program by two scenarios: the existing river condition and the normalization scenarios. Following the simulation with the 2-year return period discharge for the existing conditions, the Talangsari River experienced upstream to downstream flooding, underscoring the need for flood mitigation measures. The river normalization simulation using the 25-year return period discharge considered dimensions such as a channel width of 7m and a depth of 3.5m. As a result of the normalization simulation, the Talangsari River successfully accommodated a flow of 13.38 m3/s without experiencing flooding, confirming that the decision to pursue normalization was the best choice.

Artificial viscosity technique for direct runoff calculation

In this study, an Artificial Viscosity (AV) technique was developed for direct runoff calculation, instead of using the conventional Synthetic Unit Hydrograph (SUH) methods. We solved the Shallow Water Equations (SWE) with second-order accurate Godunov finite volume model and fourth-order Runge-Kutta explicit scheme. The AV technique was devised with a Laplacian and a biharmonic operator, and employed to solve the convective terms of the SWE. This technique was applied to rainfall-runoff laboratory cases with the measured rainfall and observed direct runoff values. For comparison purpose, several SUH methods commonly used such as SCS, Snyder, GAMA-1, ITB-1, ITB-2, and Nakayasu, were also used to compute the direct runoff values. The results showed that the AV technique could predict three parameters (i.e., peak discharge, time-to-peak, and shape of the direct runoff hydrograph) accurately. Meanwhile, significant discrepancies were shown by the SUH methods in estimating such parameters, thus indicating that the SWE modeling with an AV technique is significantly more accurate than the SUH methods in predicting the direct runoff hydrograph. This study shows an interesting example of how modern numerical computations can improve the runoff prediction and may be included as a standard technique for runoff computation in the future.

PEMANFAATAN DEM-SRTM DAN DEM-NAS SEBAGAI DASAR SIMULASI HUJAN-DEBIT DI DAS KALIWADAS

The accuracy of flow prediction in a watershed for water resource development is highly dependent on various factors such as the transformation model used, the availability and accuracy of hydrological data and watershed characteristics such as topography, drainage networks, land cover and soil texture. Watershed characteristics are considered as the most dominant determinants in various hydrological analyzes, especially with regard to the data used to compile the watershed model, in this case the Digital Elevatian Model (DEM) data. This study aims to develop a watershed model based on National DEM (DEMNAS) data to estimate daily discharge using the HEC-HMS model and design discharge using the Nakayasu Synthetic Unit Hydrograph (SUH) method. The research was conducted in the Kaliwadas watershed, which is located in Kandang Serang District, Pekalongan Regency, Central Java Province. Kaliwadas River is one of the sub-watersheds with a drainage area of approximately 165.78 km2 which has a good enough potential to supply hydro-based electricity. The performance of the DAS model formed with DEMNAS data is compared with the performance of the watershed model formed with the DEM Shuttle Radar Topography Mission (SRTM) data, where these two DEM data have a resolution of 8 meters and 90 meters, respectively. Performance testing is based on the Root Mean Square Error (RMSE) number of the two predictive flow from the HEC-HMS Model to the observed discharge. The results showed that the estimated discharge of the HEC-HMS Model using the DEMNAS Watershed Model showed slightly better performance than using the SRTM DAS Model, with a RMSE difference of 0.27.

Flood Modelling due to Dam Failure Using HEC-RAS 2D with GIS Overlay: Case Study of Karalloe Dam in South Sulawesi Province Indonesia

A dam is one of the water structures that have many benefits for humans. However, flood disasters caused by dam break may have a very bad impact on human life. This study specifically analyzed the impact of flooding caused by the failure of the Karalloe dam in Bone Regency, South Sulawesi Province, Indonesia. For the first time, the selected flood discharge used in the dam break analysis was verified using the Creager graph by comparing the calculated discharge from several synthetic unit hydrograph methods (HSS) with the flood discharge measured on the automatic water level recorder (AWLR) at the monitoring point. The impact of flooding due to dam break was simulated using HEC-RAS 2D combined with ArcGIS for mapping. The calculation results of the design flood discharge based on rainfall data using the methods of HSS Nakayasu, HSS ITB I, HSS ITB II, and HSS SCS (HEC-HMS) as well as the calculation of the designed flood discharge based on the discharge data showed that the design flood discharge value which is closest to the measured discharge value and Q1000 Creager was the HSS SCS method. The flood discharge values obtained based on the HSS SCS method for Tr (return period) 2 years, Tr 5 years, Tr 10 years, Tr 20 years, Tr 25 years, Tr 50 years, Tr 100 years, and Tr 1000 years were 322.70 m³/s, 464.10 m³/s, 560.40 m³/s, 658.40 m³/s, 682.70 m³/s, 787.00 m³/s, 885.70 m³/s, and 1202.60 m³/s, respectively. The simulation results showed that 22 villages will be affected by flooding due to the failure of the Karalloe dam and the fastest standby time of the flood is 12 minutes, namely at Lookout Point 7 in Paitana Village. This result suggests that early warning system should be installed at the downstream of the dam and flood disaster mitigation should be adopted and applied to these threatened area.

Testing of The Method of Gama I Synthetic Unit Hydrograph in The Analysis of The Tojo Watershed Design Flood

Floods occur due to several factors including topographic conditions, high rainfall intensity, blockage of water flow, lack of water infiltration areas, deforestation, and so on. The Tojo watershed is included in the Parigi-Poso river area, with an area of 211,830 km2 and a river length of 25.52 km. In the Tojo watershed, it is necessary to study flooding, because the watershed always flows every year. This research aims to find out how much flood discharge was obtained from the analysis of the Tojo watershed design flood with the Gama I synthetic unit hydrograph method and to find out how much the Gama I synthetic unit hydrograph analysis compared to the design flood discharge based on river discharge data (AWLR). From the calculation results obtained a comparison between the design flood discharge value processed by rainfall data using the Gama I Synthetic Unit Hydrograph method to the design flood discharge value processed by the Tojo river discharge data using the log person III distribution method for a 2 year return period is 1957,45 %, for the 5-year return period is 1347,64 %, for the 10 year return period is 1224,65 %, for the 25 year return period is 1169,96 %, for the 50 year return period is 1165,67 % and for the 100 years is 1178,75 %.

Flash Flood Susceptibility Assessment Based on Morphometric Aspects and Hydrological Approaches in the Pai River Basin, Mae Hong Son, Thailand

Flash floods are water-related disasters that cause damage to properties, buildings, and infrastructures in the flow path. Flash floods often occur within a short period of time following intense rainfall in the high, mountainous area of northern Thailand. Therefore, the purpose of this study is to generate a flash flood susceptibility map using watershed morphometric parameters and hydrological approaches. In this study, the Pai River basin, located in Mae Hong Son in northern Thailand, is divided into 86 subwatersheds, and 23 morphometric parameters of the watershed are extracted from the digital elevation model (DEM). In addition, the soil conservation service curve number (SCS-CN) model is used to estimate the precipitation excess, and Snyder’s synthetic unit hydrograph method is used to estimate the time to peak and time of concentration. With respect to the rainfall dataset, in this study, we combined CHIRPS data (as satellite gridded precipitation data) with rainfall data measured within the study area for the runoff analysis. According to the analysis results, 25 out of 86 subwatersheds are classified as highly susceptible areas to flash floods. The similarities in the morphometric parameters representing watersheds in highly flash flood-susceptible areas indicate that this categorization included areas with high relief, high relief ratios, high ruggedness ratios, high stream frequencies, high texture ratios, high annual runoff, high peak discharge, low elongation ratios, and low lemniscates ratios.

ANALISIS DEBIT BANJIR RANCANGAN DENGAN METODE HIDROGRAF SATUAN SINTETIS NAKAYASU DI SUB DAS KEDUANG (Analysis of planned flood discharge using the Nakayasu synthetic unit hydrograph in Keduang Sub Watershed)

Keduang Sub Watershed was an area prone to flooding. This happens because of the varied land cover followed by low forest cover. This circumstance leads to an increase in runoff which has the potential to become flooded. This study aims to analyze the planned flood discharge in the Keduang Sub Watershed with several return periods. The study was conducted using secondary data analysis in 2007-2018. Rainfall analysis was performed by several methods, namely normal method, normal log, pearson III log, and gumbel and tested with chi square and kolmogorov smirnov tests. Planned flood discharge analysis was using the Nakayasu synthetic unit hydrograph method. Results showed that the rainfall analysis chosen is normal method. The planned flood discharge obtained that the maximum discharge of the 2-yearly return period was 1,375.20 m3/s, the 5-yearly return period was 1,724.92 m3/s, the 10-yearly return period was 1,908.10 m3/s, the 20-yearly return period was 2,057.97 m3/s, the 25-yearly return period was 2,087 m3/s, the 50-yearly return period of 2,228.67 m3/s, the 100-yearly return period of 2,345.24 m3/s, and the 1000-yearly return period of 2,661.64 m3/s. Flood discharges are increasing in the larger return period, and the largest flood discharge occurred in the 1000-yearly return period. The results of this study are expected to be used in watershed planning and management for flood disaster mitigation in Keduang Sub Watershed.

Time Lag Modeling in Modification of Nakayasu Synthetic Unit Hydrograph

In the development of the synthetic unit hydrograph method, the empirical formula expresses the relation between the watershed morphometry characteristic and the constituent elements of hydrographs that are peak discharge (Qp), time to peak (tp), time lag (TL), and time base (Tb). This research intends to build a model of time lag in order to modify the Nakayasu SUH modeling. The Nakayasu synthetic unit hydrograph (SUH) model, seen as very popular and widely used by practitioners, needs to be adjusted for the main parameters that form the hydrograph to be able to be directly used based on the watershed morphometry characteristic. Based on the specific characteristic of the Nakayasu SUH formulation, this research will focus on developing the Nakayasu SUH model by the modification with adding the watershed characteristic parameter to the time lag parameter (tL). This research was conducted in 23 watersheds in Indonesia. The previous research in the same watersheds indicates five morphometry parameters with a positive effect on the time lag with the ranking due to the strongest effect as follows: watershed area (A), the river length from outlet to the weight point of the watershed (Lc), H = L.Lc, and the main river length (L). However, the two other parameters negatively affect the time lag with the ranking due to the strongest effect as follows: river network density (D) and river slope (K). Then, the modeling of time lag is carried out based on the research result, and the result of the time lag model is as follows: tL=Lc0.1809H-0.00159A0.003459

Perbandingan Debit Limpasan Langsung antara Pendekatan Model Numerik dan Konvolusi Hidrograf Satuan Sintetis

This paper compares the results of direct runoff obtained by a numerical model of the shallow water equations (SWE) with the synthetic unit hydrograph (SUH) methods generally used in Indonesia. It is known that such SUH methods are still empirical, thus making it difficult for users to determine a representative method. Meanwhile, the hydrodynamic approach such as the SWE numerical model can achieve more accurate results in predicting the direct runoff compared to the SUH methods, because the model itself is derived mathematically based on the physical processes. The findings indicate that the direct runoff predicted using the SWE numerical model (HEC-RAS 5.0.7) produced more accurate results for the peak discharge with an average error of -0.07%, the peak time with an average error of 19.77%, and the shape of the hydrograph with the smallest Root Mean Square Error (RMSE) from all the cases tested. Therefore, it can be concluded that in the future the use of a hydrodynamic approach is highly recommended for the direct runoff prediction. This paper was also aimed to be used as a reference in the development of new, more accurate SUH method in the future.