Flood Hydrograph Research Articles

Analysis of UNNES embung floor capacity

The purpose of this study was to analyze the capacity of the reservoir to the change in land use around the Unnes campus. The research method used is the flood hydrograph routing method in the reservoir using the Storm Water Management Model (SWMM) program to obtain the maximum capacity of the reservoir flood discharge, after which a comparison of the planned flood discharge of the resevoir to the flood discharge in the existing conditions of the reservoir is carried out to assess the capacity of the Unnes reservoir against land use change. Based on the results of the study, it was found that there was a change in the bottom depth of the reservoir at the beginning of the planning was 4.00 meters and in the current condition it became 3.00 meters, which means that the capacity is reduced by 1.00 meters with the ability to pass the flood discharge inflow which is still adequate and there is no overflow of flood.

Flood modeling of a large transboundary river using WRF-Hydro and microwave remote sensing

The Brahmaputra River, a trans-boundary river between India and Bangladesh experiences large scale floods with frequent inundation events affecting millions of people annually. An integrated approach for quantitative understanding of flood wave characteristics and real time flood modeling framework can be helpful for effective decision making and planning of flood risk management strategies. In this study, we have characterized the flood wave propagation in the Brahmaputra River using gauge observations and model simulations. The spatio-temporal variation of flood lift is estimated using stage hydrograph of different gauge stations along the river. The temporal variation in flood hydrograph is characterized by different flood wave parameters for a gauge station which govern the flood condition in the Brahmaputra River. These flood wave characteristics are used in the categorization of different intensity of flood events. To estimate the river discharge, the WRF-Hydro model was set-up over the Brahmaputra river basin for hourly discharge estimation. The satellite observations form altimeter and Synthetic Aperture Radar (SAR) are used to estimate river flood-plain elevation and inundation. Altimetry data from Jason-3 satellite was used for water level retrieval and compared with gauge and simulated discharge time-series for further validation of model capabilities. Sentinel-1 satellite SAR images are used to assess the flood inundation extent and probability based on flood wave characteristics in the downstream flood-plain region of Guwahati. Finally, we have integrated these data-sets for a flood modeling and forecasting framework for a braided transboundary river system. This integrated system is studied in detail for an extreme event that occurred during July 2019 in the Brahmaputra River. An hourly estimate of each event for the flood period proved the capability of this system for operational deployment in near real-time flood assessment and forecasting purposes for the flood-prone region of South Asia.

Risk variation of reservoir regulation during flood season based on bivariate statistical approach under climate change: a case study in the Chengbihe reservoir, China

The risk analysis of reservoir regulation in the flood season is crucial and provides the valuable information for reservoir flood control, safety operation, and decision making, especially under climate change. The purpose of this study is to propose a framework for reasonably estimating the variation of reservoir regulation risk including the dam extreme risk and the overtopping risk during the flood season under climate change. The framework consists of an integrated diagnostic system for detecting the climate abrupt change time, a copula function-based bivariate statistical approach for modeling the dependence between the flood peak and flood volume, a Monte Carlo simulation for generating numerous random flood peak–volume pairs, and a risk calculation model for routing the design flood hydrographs to obtain the frequency curve of the maximum water level reached in front of dam and evaluating the reservoir regulation risk. The methodology was implemented in the Chengbihe reservoir in south China by using the 55-year (1963–2017) hydrometeorological data, including temperature, evaporation, precipitation, and streamflow, in the flood season. Results show that the hydrometeorological series during the flood season changed abruptly in 1992 and the entire data can be divided into two periods (1963–1992 and 1993–2017). The dam extreme risk and overtopping risk during the two periods are assessed, respectively, and a comparison analysis is made based on different flood limit water-level schemes (185.00–188.50 m). It demonstrates that both the dam extreme risk and the dam overtopping risk increase under the influence of climate change. The dam extreme risk increases by 22.91–95.03%, while the climate change-induced increase in the dam overtopping risk is between 38.62 and 123.59%, which indicates that the dam overtopping risk is more sensitive to climate change than the dam extreme risk. The risk evaluations in the study are of great significance in the safety operation and risk management of reservoirs under future climate change.

Investigating sea‐state effects on flash flood hydrograph and inundation forecasting

AbstractA common source of uncertainty in flood inundation forecasting is the hydrograph used. Given the role of sea‐air‐hydro‐land chain processes on the water cycle, flood hydrographs in coastal areas can be indirectly affected by sea state. This study investigates sea‐state effects on precipitation, discharge, and flood inundation forecasting implementing atmospheric, ocean wave, hydrological, and hydraulic‐hydrodynamic coupled models. The Chemical Hydrological Atmospheric Ocean wave System (CHAOS) was used for coupled hydro‐meteorological‐wave simulations ‘accounting’ or ‘not accounting’ the impact of sea state on precipitation and, subsequently, on flood hydrograph. CHAOS includes the WRF‐Hydro hydrological model and the WRF‐ARW meteorological model two‐way coupled with the WAM wave model through the OASIS3‐MCT coupler. Subsequently, the 2D HEC‐RAS hydraulic‐hydrodynamic model was forced by the flood hydrographs and map the inundated areas. A flash flood event occurred on 15 November 2017 in Mandra, Attica, Greece, causing 24 fatalities, and damages was selected as case study. The calibration of models was performed exploiting historical flood records and previous studies. Human interventions such as hydraulic works and the urban areas were included in the hydraulic modelling geometry domain. The representation of the resistance caused by buildings was based on Unmanned Aerial System (UAS) data while the local elevation rise method was used in the urban‐flood simulation. The flood extent results were assessed using the Critical Success Index (CSI), and CSI penalize. Integrating sea‐state affected the forecast of precipitation and discharge peaks, causing up to +24% and from −8% to +36% differences, respectively, improving inundation forecast by 4.5% and flooding additional approximately 70 building blocks. The precipitation forcing time step was also highlighted as significant factor in such a small‐scale flash flood. The integrated multidisciplinary methodological approach could be adopted in operational forecasting for civil protection applications facilitating the protection of socio‐economic activities and human lives during similar future events.

Flood hydrograph simulation to estimate peak discharge in Ciliwung river basin

Ciliwung River Basin is one of 13 watersheds located in the Special Capital Region of Jakarta (DKI Jakarta), one of the most vulnerable cities facing flood disaster. Modeling hydrographs in a flood computer model is a crucial process in understanding the hydraulic processes in floods; however, more often than have adequately not studied watersheds do not available observed data. Well-calibrated hydrographs serve as the basis for a basin-wide flood model. In this study, the Snyder, ITB, and SCS Unit Hydrograph are constructed in the study case of flooding in the Ciliwung River Basin, with West Java rainfall distribution method and Alternating Block Method as the adopted rainfall distributions, providing six combinations of approaches. Calibration and validation analysis show a combination of West Java rainfall distribution and SCS UH with a lag time of 5.5 gives the smallest deviation, with an accuracy of 83.3%, therefore it is recommended for use to estimate design future flood hydrograph.

The hydraulics analysis of the USBR stilling basin type of a dam under multiple flow discharge scenarios (A case study of Temef Dam, East Nusa Tenggara, Indonesia)

Temef Dam was built to meet the needs of water supply and irrigation. Climate change and dam construction exaggerate security issues related to water resources. One important part of dam construction is the stilling basin, which can dissipate the energy from the discharge of the spillway and preserve the dam from flooding and degradation. The purpose of this study was to determine the most appropriate USBR stilling basin type under multiple flow discharge scenarios. The analysis involved 1) determining the designed flood hydrograph and 2) hydraulic analysis to select the USBR stilling basin. The study results showed that 1) analysis of the designed flood hydrograph for a 100-year return period up to the PMF showed values from 890 m3/second to 4300 m3/second and 2) the appropriate stilling basin is a USBR Type II. The results also presented detailed hydraulic structure calculations (stilling basin length = 47 m, stilling basin wall height = 15 m, steep channel blocks = 14 pieces, and indentation blocks = 9 pieces). This study is very useful because the right design will be able to ensure the smooth operation of the dam and prevent the dam from damage.

Analysis of Sedimentation for The Optimization of Lempake Dam Operations for Flood Control for The City of Samarinda, Province of East Kalimantan

The Lempake Dam currently functions as a dam that provides raw water for irrigation and clean water, besides its indirect functioning as the only flood control dam in the Karangmumus sub-watershed. Current conditions indicate that the Lempake Reservoir has experienced decreased capacity from year to year. At the normal water level, the reservoir capacity of Lempake Reservoir in 2013 was 0.76 million m3 and in 2018 was 0.39 million m3. Therefore, efforts are needed to control reservoir sedimentation and reservoir operations to allow the Lempake Dam to continue to function as a flood control reservoir. This study was carried out by analyzing the volume of sedimentation in the reservoir using the ArcGIS program and analyzing the flood hydrograph at the site by flood routing at the Pasar Segiri River, optimizing reservoir operations, and mapping flood inundation using the RAS Mapping program (HEC-RAS). The results showed that the storage volume in 2020 is predicted to be 0.241 million m3 with an annual sediment rate of 0.074 million m3. From the flood routing analysis and optimization of reservoir operations, the cross-sectional capacity of the river in Pasar Segiri (safe limit elevation +3.30 m) is insufficient for a flood discharge of a return period of more than 2 years (more than 222.14 m3/sec) for Scenario 1, and of more than 5 years (more than 320.48 m3/sec) for Scenario 2

An approach for prediction of flood hydrograph at outlet of an ungauged basin using modified dynamic wave model

ABSTRACT Floods are the most disastrous natural hazards, but the prediction of flood hydrographs is hindered due to the lack of Hydro-meteorological data. This paper presents an approach for flood routing of the ungauged basin using rainfall-runoff and Dynamic wave models. Specifically, the SCS-CN rainfall-runoff model is employed to obtain the inflow and lateral inflow hydrographs of the ungauged sub-basins, and a Modified Dynamic Wave Model is employed to anticipate the flood hydrograph at the outlet of the ungauged basins. The Modified Dynamic Wave Model for the parabolic channel (MDWMP) has been numerically solved using an implicit finite difference scheme considering both continuity and momentum equations. The method is tested in hypothetically considered ungauged Kulsi River Basin, a mountainous basin in Northeastern India, and the results obtained are compared with the observed data at the outlet of the Kulsi Basin. The approach is validated by considering four parameters RMSE, Peak flow Error, Peak time Error, and Total Volume Error. A high degree of affinity (i.e. peak flow error below 6%) was observed between the predicted outflow hydrograph and the observed hydrograph, which verified the satisfactory applicability of the developed approach to anticipate the flood hydrograph of an ungauged basin.

Reverse Flood Routing in Rivers Using Linear and Nonlinear Muskingum Models

AbstractOne of the key factors for flood modeling and control is the flood hydrograph, which is not always available due to lack of flood discharge observations. In reverse flow routing, hydraulic ...

Flood‐duration‐integrated stream power and frequency magnitude of >50‐year‐long sediment discharge out of a hyperarid watershed

AbstractDetermining sediment discharge out of watersheds is a global, long‐term challenge. In the vast, usually data‐poor, hyperarid regions of the world, this is a greater challenge. Here, we present a unique, decades‐long dataset of individual floods and their respective sediment discharge out of Nahal Yael, an experimental, well‐instrumented, hyperarid (~25–30 mm year−1) watershed in southern Israel. The high correlation between directly measured sediment yield by discrete individual floods and their respective total energy, represented by flood‐integrated stream power (FISP), serves here as a rating curve. Using this rating curve, the 51‐year‐long series of FISP in Nahal Yael, calculated from the detailed individual flood hydrographs, was converted into a series of sediment yield by these floods. This, in turn, allows determining the long‐term frequency‐magnitude of sediment exported out of this hyperarid basin. This can assist in landscape evolution modeling, in testing impacts of flood frequency changes enforced by altered regional climatology, and hint at changes needed in forming the observed alluvial fans. We conclude that, at the decadal scale, moderate floods are the most effective in terms of total sediment transport. However, the recurrence intervals of these moderate hyperarid floods are longer than in temperate regions and reach 5–10 years.

Comparison of snyder synthetic unit hydrograph with measured unit hydrograph on Bionga Kayubulan

Generally, the synthetic unit hydrograph had to be developed just like a kind of Snyder that found accord empire scientific in the United States. Determination of their parameters has been presented by various criteria, but so far, the results are still relatively deviated for watershed-watersheds in Indonesia. The study was conducted to Bionga Kayubulan sub-watershed that has properties and characteristics that need to be conducted regarding irregularities by comparing models HSS Snyder with unit hydrograph observations on sub-watershed. Hydrograph water level readings AWLR derived from a flood hydrograph, using the are discharge. to separate the base flow with runoff straight-line method is used to produce direct runoff hydrograph. From the data obtained ARR hourly rainfall records were then analyzed, using the equation effective rainfall of index Φ. Direct runoff hydrograph and rainfall effectively revealed to be the observation unit hydrograph using collins method. Based on topographic maps obtained watershed physical factors were then used to analyze HSS Snyder. Further comparison of the HSS Snyder constant adjustments made using software Microsoft Excel-Solver. Observation unit hydrograph Bionga Kayubulan sub watershed has a peak time (Tp) of 4.5 hours with a peak discharge (Qp) of 2.81 m3/sec while Snyder HSS obtained from the analysis of Tp and Qp of 5.15 hours of 0.33 m3/sec. The test results showed that the predicted ratio Snyder HSS HSS calibration better than Snyder before calibration. CE adjusted value is 0.11 and as adjusted to 0.93. The value of EV adjusted is 65.20% before and after adjustment to 2.70%. EQP value addition, AETR values, and values after adjusting widened AETp 0 hours.

Upstream flood hydrograph prediction of Chalakkudy River

Flood routing is an important step in any flood modelling study. When the upstream river station data is available the flow of flood water can be routed to downstream and flood inundation studies can be carried out. Flood hydrograph forms the crucial part of any flood routing study. But in certain cases the upstream flow data may not be available where one can use reverse flood routing technique to determine the upstream flood hydrograph, from the available downstream flow data. Reverse flood routing studies involve errors due to its inversing nature and any such reversing techniques are seldom available. Artificial intelligent techniques like genetic algorithm is a better resort where there is data deficiency to perform normal routing or reverse routing techniques. In the present study reverse routing model solved using genetic algorithm, is applied to one of the most flood affected river in Kerala, India during the flood in 2018.

Experimental Investigation of Scour Hole Characteristics for Different Shapes of Piers Caused by Flood Hydrograph Succeeding Steady Flow

In this study, the scour depth and dimensions of the scour hole around different shaped piers for the cases of hydrographs succeeding steady flow were studied experimentally. The experiments were carried out by using circular, square, rectangular, lenticular and rectangular with trapezoidal nose to compare the various scour hole geometries at the same flow conditions. Numerous experiments were conducted in a rectangular flume (18.6 m long, 0.80 m wide and 0.75 m deep) with different triangular shaped hydrographs. The flume bed of 26 cm thickness consists of uniform graded material with D50 =1.68 mm. The experiments were carried out in clear water conditions. The temporal variations of the equilibrium scour depths in front of the pier and the scour hole dimensions were recorded by two different cameras. The equilibrium scour depths at lateral sides and downstream of the piers were also measured. Regression analysis was performed in order to derive empirical relations to predict temporal variations of the scour depth in the case of unsteady flow. The shape factor values were also investigated based on the experimental findings and the obtained values were compared to those available in literature. The performance of the obtained empirical relation for circular pier was tested by using limited experimental data available in the literature. The smallest scour hole was observed for the rectangular with trapezoidal noses pier. The increase in the scour hole dimensions for other cross-sections was in the following order: rectangular with circular noses, circular, square and rectangular piers.

Hydro-sediment-morphodynamic processes of the baige landslide-induced barrier Lake, Jinsha River, China

A large landslide impacting a river may cause a multi-phase chain of hazards, comprising landslide-generated waves, inundation as a barrier lake develops upstream of a landslide dam arising from rapid sediment deposition, and downstream flooding due to barrier lake outburst. Two major landslides (each of volume ~ 107 m3) occurred successively on 10th October and 3rd November 2018 at Baige village, Tibet, China. Both landslides led to a natural dam that completely blocked the Jinsha River, along with a barrier lake filled with upstream river inflow. Although the first barrier lake breached naturally, a significant quantity of residual material from the first landslide dam was left behind without being eroded. After the second landslide occurred, a flood channel was urgently constructed to facilitate an artificial breach of the barrier lake as it formed. The Baige landslide-induced barrier lake is unique having triggered by two successive landslides and outbursts a mere five weeks apart. Here a computational investigation is presented of the hydro-sediment-morphodynamic processes of the Baige barrier lake, using a recent 2D double layer-averaged two-phase flow model. This is the first modelling study of the whole field and whole processes for the formation and outburst of a landslide-induced barrier lake as well as the resultant floods, without evoking presumptions on dam breach (which have prevailed for decades and bear much uncertainty). The computed results agree well with field observations in terms of landslide-generated waves, landslide dam morphology, stage and discharge hydrographs at the dam site and downstream flood hydrographs. The artificial flood channel is shown to be effective for alleviating downstream inundation. Water and grain velocities are demonstrated to be distinct, characterizing the primary role of grains in landslide dam and barrier lake formation and the dominant role of water in barrier lake outburst and the resultant flood. Relatively low inflow discharge and large initial landslide volume favour landslide dam and barrier lake formation, but delay the outburst and downstream flood. The present 2D double layer-averaged two-phase model holds great promise for assessing future landslide-induced multi-hazard chains in rivers, and informing mitigation and adaptation strategies.

Increasing the Efficiency of the Sacramento Model on Event Basis in a Mountainous River Basin

An evaluation of the Sacramento Soil Moisture Accounting (SAC-SMA) model was conducted to be used in flood event simulations with datasets at a time step up to one hour. The SAC-SMA model is a complex conceptual model which integrates two soil zones, the upper and lower zone, in order to provide current soil moisture conditions and generated streamflow. However, in flood events, where time intervals are small, the generated flood hydrograph is usually the product of only the upper soil layer runoff generation mechanism while the lower zone and baseflow have little impact. In this context, a modified version of the original SAC-SMA model was introduced, where only the upper zone processes are kept in order to reduce the parameter count and the overall model uncertainty involved, and a comparison was made against the original model output. The two models were calibrated and validated for a series of flood events occurred at the Karitaina basin of the Alfeios river, located in southern Greece. The results show that both model versions were able to reproduce the observed runoff with success. The simplified model showed high consistency with the original model in all cases, which is an obvious improvement to the original model, since it provided results of equal quality, while lowering significantly the total parameter count and the computing time. This contributes against the overall model generated uncertainty which is crucial for real-time data processing applications and flood forecasting systems. • Presentation of the SAC-SMA model concept, variables, parameters and flowchart. • Introduction of a modified – simplified version of the original SAC-SMA model to be used for event-based rainfall runoff applications. • Calibration and validation of the SAC-SMA using fine temporal scale datasets in a mountainous basin in Greece.

Flood hydrograph modeling using artificial neural network and adaptive neuro-fuzzy inference system based on rainfall components

Different limitations such as the lack of enough hydrometric stations, difficulty in collecting hydrometric data with costly data collection are caused to create hydrologic models for estimating the flood hydrograph. Based on the easy and more access to rainfall statistics, preparing the hydrologic model based on rainfall characteristics and data seems to be the very applicable and logical method. Data-driven models have increasingly been used to describe the behavior of hydrological systems, which can be used to complement or even replace physical-based models. In this study, the efficiency of two data mining models including artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) was evaluated in order to model flood hydrograph characteristics based on rainfall components in Kasilian Watershed, northern Iran. For this purpose, fifteen characteristics of rainfall (hyetograph) and eight characteristics of flood hydrograph were respectively considered independent and dependent variables for 60 rainfall-runoff events from 1975 to 2009. ANN with two functions of hyperbolic tangent and sigmoid and ANFIS with grid partitioning and subtractive clustering were used to estimate flood hydrograph. Variance inflation factor (VIF) (for selecting variables that are minimal multicollinearity) were used to select the input variables. ANFIS model with the grid partitioning method performs better than the ANFIS model with the subtractive clustering method. ANFIS with Nash-Sutcliff efficiency (NSE) of 0.87, root mean squared error (RMSE) of 0.38 m3/s, and deviation of peak time of observed and estimated hydrographs (DPOT) of 4.33 h was found to be superior to ANN with NSE of 0.40, RMSE of 0.88 m3/s, and DPOT of 1.14 h accurately and efficiently for modeling flood hydrograph. Therefore, ANFIS model is proposed for modeling the flood hydrograph based on rainfall characteristics.

Modeling of Extreme Hydrological Events in the Baksan River Basin, the Central Caucasus, Russia

High mountain areas are prone to extreme hydrological events, and their study is especially important in the context of ongoing intensive deglaciation. In this research, a model “chain” consisting of a hydrodynamic model and a runoff formation model is adopted to simulate a glacier lake outburst flood (GLOF) from Bashkara Lake (the Central Caucasus, Russia) and its effect on downstream. In addition to an actual GLOF event that occurred on 1 September 2017 and led to casualties and significant destruction in the Adylsu and Baksan Rivers valleys, possible scenarios for the re-outburst of the lake are considered. The hydrographs of the outburst and the downstream movement of the flood wave along the Adylsu River valley are estimated using STREAM_2D two-dimensional hydrodynamic model. The water discharges in the entire river network of the Baksan River are assessed using the ECOMAG (ECOlogical Model for Applied Geophysics) runoff formation model. The output flood hydrograph from the hydrodynamic model is set as additional input into the Baksan River runoff formation model in the upper reaches of the Adylsu River. As a result of the simulations, estimates for the contribution of GLOFs and precipitation to an increase in peak discharge along the Baksan River were obtained. The actual outburst flood contributed 45% and precipitation 30% to the peak flow in the Baksan River at the mouth of the Adylsu River (10 km from the outburst site). In Tyrnyauz (40 km from the outburst site), the contributions of the outburst flood and precipitation were equal and, in Zayukovo (70 km from the outburst site), the outburst flood contributed only 20% to the peak flow, whereas precipitation contributed 44%. Similar calculations were made for future potential re-outburst flood, taking into account climatic changes with an increase in air temperatures of 2 °C, an increase in precipitation of 10% in winter and a decrease of 10% in summer. The maximum discharge of the re-outburst flood in the Adylsu River mouth, according to model estimations, will be approximately three times less than the discharge of the actual outburst on 1 September 2017 and can contribute up to 18% of the peak discharge in the Baksan River at the confluence.

Nitrate removal processes in the riverbed during a single‐peak flood event

AbstractThe effect of the interplay between unsteady flow and bedform in a flood event on nitrogen cycling in the hyporheic zone (HZ) remains poorly understood. In this study, a reactive transport groundwater model with different flood hydrographs was proposed to investigate the effect of modified hyporheic flow on nitrate dynamics in the HZ, including nitrate source‐sink function, response to the single‐peak flood event and removal efficiency. The results demonstrate that there exists an optimal range of river channel gradients that could enhance the biogeochemical reactions (respiration, nitrification and denitrification) in a flood event. The HZ acts as a nitrate sink especially after the flood event, and its source‐sink function is independent of the unsteady discharge/stage conditions. The nitrate in the HZ has a hysteretic response to peak stage/discharge, and its removal efficiency is decreased by up to 70% compared to steady flow conditions. These findings not only provide a better understanding of nitrogen dynamics under the effect of unsteady channel flow, but also can be applied for river restoration to efficiently remove nitrate in the HZ by modifying river channel gradients.

Graded bed load transport in sediment supply limited channels under unsteady flow hydrographs

Natural river channels that are sediment supply limited due to upstream water management practices and/or flow regulation are often subject to in-channel bed degradation and bed surface restructuring during natural flood hydrographs or controlled flow releases from upstream dams. The heterogeneity of sediment sizes present in these channels means that different size classes are transported more actively during different parts of the hydrograph. A series of laboratory experiments is conducted to investigate the in-channel response of a graded sediment bed to a range of design flow hydrographs when no sediment is supplied at the upstream boundary. The results show varying temporal lag and bed load transport hysteresis for different transported fractions, defined by fine, medium and coarse size classes in the graded sediment mixture. The coarse size class typically exhibits clockwise hysteresis, indicating more active transport during the rising hydrograph limb, whereas the fine size class demonstrates either no/mixed or counterclockwise hysteresis, as it becomes more active during the falling limb. On this separate limb basis, predictions of fractional bed load transport rates are improved by calculating unique reference threshold shear stresses for each size class at the initiation and cessation of fractional grain motions on the rising and falling limbs, respectively. Corresponding temporal variations in the bed load median grain size vary depending on the hydrograph total water work and unsteadiness, with peak values generally attained during the rising limb and overall bed load fining observed during the falling limb. Analysis of the three size classes also indicates that the medium-coarse and fine fractions are transported in larger relative proportions during smaller magnitude, more flashy hydrographs and larger magnitude, flatter hydrographs, respectively. The resulting armouring of the post-hydrograph bed surface layer is most significant at the upstream end of the channel and decreases exponentially in the downstream direction. Two empirical models, based on combined hydrograph and bed sediment descriptors, are also shown to predict reasonably well the overall bed load yields generated under different flow hydrographs from the satisfactory collapse of the current experimental data and previous datasets for both uniform and graded bed sediments. These bed load yields provide an empirical means to describe the extent of upstream bed armouring and the downstream fining of the bed surface layer after the passage of individual hydrographs.

Estimated Flood Discharge in Downstream Krueng Meureubo of Pasi Pinang Section West Aceh Regency

The phenomenon of floods in Indonesia has become a routine thing that happens every year, almost all areas that are lowlands often flood when the rainy season arrives. Flooding is caused by high rainfall where the ability of the soil to absorb water decreases along with the rapid development of land that was once a rainwater catchment area, consequently surface runoff becomes high. Pasi Pinang Village can be categorized as a very flood prone village in Meureubo Subdistrict, due to the low condition of this village and directly borders the Meureubo river. Many adverse effects caused by floods and cause losses to the local community. The phenomenon of floods in Indonesia has become a routine thing that happens every year, almost all areas that are lowlands often flood when the rainy season arrives. Flooding is caused by high rainfall where the ability of the soil to absorb water decreases along with the rapid development of land that was once an area. In this case a study on flood discharge analysis needs to be done in order to reduce the incidence of flooding in the village of Pasi Pinang. The method used in this study is the Nakayasu HSS method, aim of this study is to determine the amount of flood discharge that occurred in the Krueng Meureubo River Basin in Pasi Pinang Village. Total hydrograph discharge calculated using the Nakayasu HSS method is the watershed area (A) = 1961.53 km, length of main river (L) = 157.02 km, time delay (tg) = 9.507 hours, duration of rain (Tr) = 7 , 13 hours, the time from the beginning of the flood to the peak of the flood hydrograph (tp) = 15.21 hours, the time of discharge 0.3 times the peak flood discharge (t0.3) = 19.01 hours and the peak flood discharge (Qp) = 23.109 m3 / sec then the total hydrograph discharge obtained by the Nakayasu method is equal to = 2040.26 m3/sec.