Engineering Center-Hydrologic Modeling System Research Articles

Hydrologic and hydraulic assessment of scour problems at bridge sites in Tigray region, northern Ethiopia

This study was conducted to assess scour problems at three selected bridge sites in the Tigray region, northern Ethiopia, namely the Ilala, upper Geba, and Tankwa bridges. Smart-GIS, ArcGIS, Hydrologic Engineering Centre Hydrologic Modeling System (HEC-HMS), and Hydrologic Engineering Centre River Analysis System (HEC-RAS) were used for the river morphology, hydrologic, and hydraulic analysis. The riverbanks were subjected to higher degradation and instability problems. The estimated 100-year flows were 272.5, 940.4, and 249.9 m3/s for Ilala, upper Geba, and Tankwa bridges, respectively. Flow depth calibration were resulted in model performance with Nash Sutcliffe Efficiencies of 0.90, 0.88, and 0.87 for Ilala, upper Geba, and Tankwa bridge sites, respectively. Scour depths were 1.3, 1.6, and 0.8 m at contracted sections; 3.2, 3.0, and 2.2 m at the piers; 2.6, 3.6, and 2.2 m at the left abutment; and 1.6, 3.0, and 2.1 m at the right abutment of Ilala, upper Geba, and Tankwa bridges, respectively. The use of riprap at the bridges resulted in the reduction of scour depths by 60–100%. Overall, the hydrologic and hydraulic models performed well.

Study on the early warning and forecasting of flash floods in small watersheds based on the rainfall pattern of risk probability combination

Flash floods cause great harm to people’s lives and property safety. Rainfall is one of the main causes of flash floods in small watersheds. The uncertainty of rainfall events results in inconsistency between the traditional single rainfall pattern and the actual rainfall process, which poses a great challenge for the early warning and forecasting of flash floods. To carry out the effective flash flood early warning and forecasting, this paper proposes a novel rainfall pattern by coupling total rainfall and peak rainfall intensity based on copula functions, i.e., the rainfall pattern of risk probability combination (RPRPC). On this basis, the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) hydrological model is used to simulate the rainfall-runoff process, the trial algorithm is used to calculate the critical rainfall (CR), and the optimistic-general-pessimistic (O–G-P) early warning mode considering the decision maker's risk preference is proposed. The small watershed of Xinxian in Henan province, China, is taken as a case study for calculation. The results show that the RPRPC is feasible and closer to the actual rainfall process than the traditional rainfall pattern, Frank copula function is the best for determining the joint distribution function of total rainfall and peak rainfall intensity, and the HEC-HMS model can be applied to small watersheds in hilly areas. Additionally, both RPRPC and antecedent soil moisture condition (ASMC) have influence on CR, and the variation of RPRPC will change the influence of ASMC on CR. Finally, the effectiveness of O–G-P early warning mode is verified.

Modeling the Hydrological Impacts of Vegetation Cover Changes in the Upper Oum Er-Rbia Watershed (Morocco)

In Morocco, the mountainous areas are often exposed to bulky and vicious flows of water and sediment. This process is exacerbated by the decrease in vegetation cover and the disruption in rainfall-runoff conditions that frequently cause significant flooding. By exploring the main hydrologic elements of these processes, it is possible to understand the behavior and hydrological response of watersheds and thus plan accordingly. In this study, the authors focused on determining the morphometric characteristics of the upper Oum Er-Rbia River basin (UOERRB by assessing/ evaluating the land use and land cover changes for a period of 32 years (1984–2016). Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) was applied to simulate four daily hydrological events. The concentration time was 7.7 hours. The four storm events examined to calibrate and validate the simulated outflow at the outlet indicated a good agreement between the hydrographs of the measured and simulated flows, with an average Nash-Sutcliffe efficiency (NSE) value ranging from 0.63 to 0.76. Between 2002 and 2016, an average 6.21 percent increase in vegetation cover of with annual rainfall increasing from 690 to 714.1 mm/year was observed. These results can contribute to a better understanding of the hydrologic processes and better estimation of the return flows and thus guiding management decisions and developments in the UOERRB.

Flood Mapping from Dam Break Due to Peak Inflow: A Coupled Rainfall–Runoff and Hydraulic Models Approach

In this study, we conducted flood mapping of a hypothetical dam break by coupling the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS) models under different return periods of flood inflow. This study is presented as a case study on the Kesem embankment dam in Ethiopia. Hourly hydrological and meteorological data and high-resolution land surface datasets were used to simulate the design floods for piping dam failure with empirical dam breach methods. Based on the extreme inflows and the dam physical characteristics, the dam failure was simulated by a two-dimensional, unsteady flow hydrodynamic model. As a result, the dam will remain safe for up to 50-year return-period inflows, but it breaks for 100- and 200-year return periods and floods the downstream area. For the 100-year peak inflow, a 208 km2 area will be inundated by a maximum depth of 20 m and for a maximum duration of 46 h. The 200-year inflow will inundate a 240 km2 area with a maximum depth of 31 m for a maximum duration of 93 h. The 2D flood map provides satisfactory spatial and temporal resolution of the inundated area for evaluation of the affected facilities.

Hydrological Models and Artificial Neural Networks (ANNs) to Simulate Streamflow in a Tropical Catchment of Sri Lanka

Accurate streamflow estimations are essential for planning and decision-making of many development activities related to water resources. Hydrological modelling is a frequently adopted and a matured technique to simulate streamflow compared to the data driven models such as artificial neural networks (ANNs). In addition, usage of ANNs is minimum to simulate streamflow in the context of Sri Lanka. Therefore, this study presents an intercomparison between streamflow estimations from conventional hydrological modelling and ANN analysis for Seethawaka River Basin located in the upstream part of the Kelani River Basin, Sri Lanka. The hydrological model was developed using the Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS), while the data-driven ANN model was developed in MATLAB. The rainfall and streamflows’ data for 2003–2010 period have been used. The simulations by HEC-HMS were performed by four types of input rainfall data configurations, including observed rainfall data sets and three satellite-based precipitation products (SbPPs), namely, PERSIANN, PERSIANN-CCS, and PERSIANN-CDR. The ANN model was trained using three well-known training algorithms, namely, Levenberg–Marquadt (LM), Bayesian regularization (BR), and scaled conjugate gradient (SCG). Results revealed that the simulated hydrological model based on observed rainfall outperformed those of based on remotely sensed SbPPs. BR algorithm-based ANN algorithm was found to be superior among the data-driven models in the context of ANN model simulations. However, none of the above developed models were able to capture several peak discharges recorded in the Seethawaka River. The results of this study indicate that ANN models can be used to simulate streamflow to an acceptable level, despite presence of intensive spatial and temporal data sets, which are often required for hydrologic software. Hence, the results of the current study provide valuable feedback for water resources’ planners in the developing region which lack multiple data sets for hydrologic software.

Hydrological Analysis of Extreme Rain Events in a Medium-Sized Basin

The hydrological response of a medium-sized watershed with both rural and urban characteristics was investigated through event-based modeling. Different meteorological event conditions were examined, such as events of high precipitation intensity, double hydrological peak, and mainly normal to wet antecedent moisture conditions. Analysis of the hydrometric features of the precipitation events was conducted by comparing the different rainfall time intervals, the total volume of water, and the precedent soil moisture. Parameter model calibration and validation were performed for rainfall events under similar conditions, examined in pairs, in order to verify two hydrological models, the lumped HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modeling System model) and the semi-distributed HBV-light (a recent version of Hydrologiska Byråns Vattenbalansavdelning model), at the exit of six individual gauged sub-basins. Model verification was achieved by using the Nash–Sutcliffe efficiency and volume error index. Different time of concentration (Tc) formulas are better applied to the sub-watersheds with respect to the dominant land uses, classifying the Tc among the most sensitive parameters that influence the time of appearance and the magnitude of the peak modeled flow through the HEC-HMS model. The maximum water content of the soil box (FC) affects most the peak flow via the HBV-light model, whereas the MAXBAS parameter has the greatest effect on the displayed time of peak discharge. The modeling results show that the HBV-light performed better in the events that had less precipitation volume compared to their pairs. The event with the higher total precipitated water produced better results with the HEC-HMS model, whereas the rest of the two high precipitation events performed satisfactorily with both models. April to July is a flood hazard period that will be worsened with the effect of climate change. The suggested calibrated parameters for severe precipitation events can be used for the prediction of future events with similar features. The above results can be used in the water resources management of the basin.

Estimation and analysis of the Antecedent Temperature Index–Melt Rate (ATIMR) function using observed data from the Kırkgöze-Çipak Basin, Turkey

The ability to manipulate multiple variable temporal and spatial atmospheric and earth-born parameters with a single air temperature value affecting the melting and accumulation processes of the snowpack is a convenient approach for the design of water policies and the effective use of water resources. Some of the temperature index models require snowpack’s melt rate as a function of the accumulated number of heating degree-days determined using a model with the Antecedent Temperature Index–Melt Rate (ATIMR) function, in which the modeler can adjust the melt rates during the season. The use of ATIMR function provides a reasonable method; however, the literature on the nature of the default ATIMR function (developed in 1991 and currently in use) is largely unclear and not understandable or practicable. For that reason, in this study, the point-specific and domain-based ATIMR functions specific to the region were determined physically in a logical manner using error propagation analysis. Thus, it was found that R-square values up to 0.99 precision can be obtained. The Hydrologic Engineering Center’s hydrologic modeling system (HEC-HMS) was used and the results were found to be characteristically and statistically effective and valid for various Snow Water Equivalent (SWE) simulations. In addition, it was revealed that the unexpected behavior of a rapid decreasing-increasing trend observed in the tail part of the modeled ATIMR function resulted from the metamorphic processes in the wet snowpack. Therefore, it is crucial to analyze snow metamorphism without simplistic assumptions of dry snow due to the interception of water in the snowpack, particularly in case of having ice and crust layers for the subject region (i.e., Radar Station at 2891 m. asl). Within this study, three-year data sets were obtained from three different meteorology and snow observation stations that have been specially constructed and operated at different elevations and aspects in Kırkgöze-Çipak Basin. The snowmelt-dominated basin is considered to be the source of the headwaters of the Euphrates River.

City scale urban flood modelling and mapping

Inadequate drainage capacity often fails to offer the desired response in urban flooding. This aim of this study was to develop a flood hazard map through a field survey and numerical modelling. The field survey comprises cross-sectional data for tertiary drains; these are then transferred for setting up the numerical model. To feature flooding conditions, both hydrological and hydraulic model studies were carried out using the Hydrologic Engineering Center–hydrologic modelling system (HEC-HMS) developed by the US Army Corps of Engineers, and the personal computer storm water management model (PCSWMM). The use of HEC-HMS generated the runoff; the PCSWMM model simulation was carried out for 760 conduits and 693 junctions in the city that was studied. Three major outlets were considered for model calibration for 2014, the model simulated runoff showed a reasonable match with field records – that is, R2 = 0.782, R2 = 0.719 and R2 = 0.768 for the reaches Chaktai Khal, Rajakhali Khal and Mahesh Khal, respectively. Thus, the validated model was used for flood hazard mapping. It is envisaged that development authority and city planners would benefit from this coupled model.

Comparing the Hydrological Response of Forested Headwaters (Unregulated and Regulated with Check Dams) under Mediterranean Semi-Arid Conditions

This study has evaluated the runoff and erosion rates in torrents of Southern Italy, two forested headwaters with very similar climatic, hydrological and geomorphological characteristics; in one headwater, 15 check dams were installed in the mid-1950s, while the other is not regulated with engineering works. To this aim, the hydrological variables have been modeled over 15 years after check dam installation using the HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) model coupled to the MUSLE (Modified Universal Soil Loss Equation) equation. The model simulations have shown that check dams have not played a significant role in reducing the surface runoff compared to the unregulated torrent; in both catchments, the well-developed forest cover determined very low runoff coefficients (lower than 0.3%) with a scarce runoff generation capacity. Additionally, the reduction in peak flow due to the check dams was not significant, on average −7.4% compared to the unregulated headwater. Check dams have retained sediments for about 8–10 years after their installation, reducing erosion by about 35%, although soil loss was much lower than the tolerance limit in both catchments. After the sediment retention capacity of the dam sediment wedge was depleted, the sediment yield in the regulated torrent was even higher (by about 20%) compared to the unregulated catchment. Overall, the study has shown that the use of check dams as a catchment management strategy of forested headwaters under semi-arid Mediterranean conditions should be considered with caution, since the structures could be ineffective to reduce water and sediment flows during floods or, in some cases, check dams may increase erosion rates.

Multi-Spatial Resolution Rainfall-Runoff Modelling—A Case Study of Sabari River Basin, India

One of the challenges in rainfall-runoff modeling is the identification of an appropriate model spatial resolution that allows streamflow estimation at customized locations of the river basin. In lumped modeling, spatial resolution is not an issue as spatial variability is not accounted for, whereas in distributed modeling grid or cell resolution can be related to spatial resolution but its application is limited because of its large data requirements. Streamflow estimation at the data-poor customized locations is not possible in lumped modeling, whereas it is challenging in distributed modeling. In this context, semi-distributed modeling offers a solution including model resolution and estimation of streamflow at customized locations of a river basins with less data requirements. In this study, the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model is employed in semi-distribution mode on river basins of six different spatial resolutions. The model was calibrated and validated for fifteen and three selected flood events, respectively, of three types, i.e., single peak (SP), double peak (DP)- and multiple peaks (MP) at six different spatial resolution of the Sabari River Basin (SRB), a sub-basin of the Godavari basin, India. Calibrated parameters were analyzed to understand hydrologic parameter variability in the context of spatial resolution and flood event aspects. Streamflow hydrographs were developed, and various verification metrics and model scores were calculated for reference- and calibration- scenarios. During the calibration phase, the median of correlation coefficient and NSE for all 15 events of all six configurations was 0.90 and 0.69, respectively. The estimated streamflow hydrographs from six configurations suggest the model’s ability to simulate the processes efficiently. Parameters obtained from the calibration phase were used to generate an ensemble of streamflow at multiple locations including basin outlet as part of the validation. The estimated ensemble of streamflows appeared to be realistic, and both single-valued and ensemble verification metrics indicated the model’s good performance. The results suggested better performance of lumped modeling followed by the semi-distributed modeling with a finer spatial resolution. Thus, the study demonstrates a method that can be applied for real-time streamflow forecast at interior locations of a basin, which are not necessarily data rich.

APPLICATION OF COUPLED HEC-HMS AND US EPA WASP FOR TRANSPORT MODELLING OF MERCURY IN THE MINING-IMPACTED AMBALANGA RIVER

This study provides a simulation of mercury (Hg) transport in water and sediments in the mining-impacted Ambalanga River located in Upper Agno Subbasin in the Philippines. The Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS) and Water Quality Analysis Simulation Program (WASP) of the US Environmental Protection Agency (EPA) were coupled to handle both hydrologic modelling and total Hg transport processes, respectively, for 12 months in the year 2014. Watershed delineation from Digital Elevation Model, rainfall and streamflow data from the local weather bureau, and dam operational data were used to develop the hydrological model. The calibrated HEC-HMS model satisfactorily simulated the flow in the river and its tributaries, which is then used as an input to the Hg transport model. The Ambalanga subbasin was conceptually divided into 29 segments in WASP to represent the water column and the surface benthic sediment. Time-variable sediment and Hg load were applied to the upstream of Ambalanga River. Total Hg concentration in water and sediments at five sampling locations along the Ambalanga River and two sampling locations along the Upper Agno River were measured in 2014-2015, in addition to the Hg monitoring data from the local environmental bureau. The gathered data were used to validate the WASP model, and results show that it was able to reasonably simulate the Hg fate and transport. Simulation results showed a downward trend in Hg concentration in surface water and sediments from upstream to downstream, while Hg in sediments was observed to stabilize over time. The model was further utilized to come up with exceedance curves of Hg in water and sediments as a result of the river’s response to different Hg loading from the known point sources. The exceedance curves derived from the model were used to determine the maximum permissible Hg loading to the river and identify pollution load reduction measures for river rehabilitation.

Event-based and continous flood modeling in Zijinguan watershed, Northern China

Hydrological models are a conceptual representation of a simplified hydrological cycle. The hydrological cycle is the water cycle that circulates water from the land surface to the atmosphere and back again to the land. With the use of Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS), an event-based model and a continous hydrological model were established in Zijinguan watershed of Daqinghe River basin. To study the loss methods provided by HEC-HMS and its appropriateness for model fitting, is the main objective of this paper. The watershed was delineated with HEC-GeoHMS in ArcGIS, and its properties were extracted from a Digital Elevation Model (DEM) of 30 m × 30 m. The HEC-HMS includes a soil conservation service curve number (SCS-CN) method and a soil moisture calculation (SMA) loss method, simulating the event and continuous runoff, respectively. SCS Unit hydrograph and Muskingum were used for flow routing. Specifically, eight rainfall events were selected for calibrating (6 events) and verifying (2 events) the event-based model. Similarly, for the continuous model the wet seasons of eight different years were used for calibration and verification. The calibrated parameters of the events model were used in the continuous model. The soil moisture and evapotranspiration data were decoded from the satellite data to set in the continuous model. The performance of SCS-CN and SMA models was compared. During the calibration period, the values of NSE, PEV and PEPF range from 0.605 to 0.744, 3.1 to 13.58%, and 11.104 to 27.72%, and during validation they are 0.527 to 0.634, 4.35% to 5.01%, and 13.66% to 27.88%, for SCS-CN model. For the SMA model, the values of NSE, PEV and PEPF during calibration range from 0.434 to 0.604, 2.879 to 34.326%, −4.831 to 57.48%, and during validation they are 0.094 to 0.624, −19.52% to −12.55%, and 40.213% to 50.15%. Overall, the performance of SCS-CN model is found more satisfactory than that of SMA model.

Prophesying the stream flow and perpetrating the performance of Halele-Werabessa reservoirs of Ethiopia using HEC-HMS and HEC-ResSim

Purpose To assess the impacts of climate change on stream flow and evaluation of reservoir performances, reliability, resilience and vulnerability (RRV) indices are contemplated. Precipitation, temperature (Tmax, Tmin), relative humidity and solar radiation are the hydrological and meteorological data which have been used extensively. Climate data like RCP2.6, RCP4.5 and RCP8.5 were evaluated for the base period 1976–2005 and future climate scenario for 2021–2050 and 2051–2080 as per the convenience. Design/methodology/approach The hydrologic engineering center hydrologic modeling system (HEC-HMS) model was used to simulate the current and future inflow volume into the reservoir. The model performance resulted as 0.76 Nash-Sutcliffe efficiency (NSE), 0.78 R2 and −3.17 D and during calibration the results obtained were 0.8 NSE, 0.82 R2 and 2.1 D. The projected climate scenario illustrates an increasing trend for both maximum and minimum temperature though a decreasing trend was documented for precipitation. The average time base reliability of the reservoirs was less than 50% without reservoir condition and greater than 50% for other conditions but volumetric reliability and resilience varies between 50% and 100% for all conditions. The vulnerability result of reservoirs may face shortage of flow ranging from 5.7% to 33.8%. Findings Evaluating reservoir simulation and hydropower generation for different climate scenarios by HEC-ResSim model, the energy generated for upper dam ranges from 349.4 MWhr to 331.2 MWhr and 4045.82 MWhr and 3946.74 MWhr for short and long-term future scenario, respectively. RCP for Tmax and Tmin goes on increasing whereas precipitation and inflow to reservoir decreases owing to increase in evapotranspiration. Under diverse climatic conditions power production goes on varying simultaneously. Originality/value This paper is original and all the references are properly cited.

Hydrologic Model for Flooding in Manupali Watershed and Its Implications to Land-Use Policies

Flooding has become a recurring event in the Province of Bukidnon causing severe destruction to houses, buildings, infrastructure and livelihood. Since the province is not exempted to flooding events as an impact of the typhoon, understanding the watershed hydrologic behavior is essential for vulnerability and risk assessment as to disaster preparedness and risk reduction. The study aims to analyze the hydrologic response of Manupali watershed through flood hazard maps, hydrologic and hydraulic models. This paper presents the combination of geographic information system, high -resolution digital elevation model, land cover, observed hydro-meteorological data and the combined Hydrologic Engineering Center-Hydrologic Modeling System and River Analysis System models. The hydrologic model assesses the relationship between rainfall and discharge of the watershed and the hydraulic model computes the flood depth and flow pattern in the floodplain. Upon calibration, the over-all performance of the hydrologic model is “very good” performance rating based on the standards set by Moriasi et.al. (2015) with index values of 0.89, 0.75, 0.46 for Nash-Sutcliffe Coefficient of Model Efficiency, Percentage Bias, and Root Mean Square Error, respectively. The calibrated hydrographs were used to produce flood hazard maps in 2, 5, 10, 25, 50, and 100-year return periods as well as determined the number of flooded buildings in each flood hazard level per return period. The flood hazard maps may contribute to science-based land-use policy formulation, land-use zoning, planning and management to mitigate extreme rainfall-induced flood risks in the affected Barangays in the Manupali watershed.

Estimation of Flood Resilience Index Using Hydrological and Hydraulic Models in Rural Area

Since countermeasures of floods in Korea are focused only on facility restoration, recovery from flood damage cannot be repaired quickly. Then, it is necessary to reduce vulnerability to flooding and restore the state before the flood. Since there is no application of flood resilience to rural areas, it is necessary to introduce the FRI (Flood Resilience Index) and to apply flood resilience assessment to systematically and efficiently recover and manage flood damage in rural areas as well as in cities. In this study, the discharge was calculated by HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) and the hydraulic analysis was conducted by HEC-RAS (Hydrologic Engineering Center-River Analysis System) and MIKE 21 for Dal Stream flood damage upstream of Goesan Dam in 2017. A flood map was made using three models and GIS (Graphic Information System), and then the FRI of Dal Stream was calculated. The calculated FRI values suggest methods that can be applied to the resilience to flood damage in rural areas as well as cities.

Hydrologic Model for Flooding in Manupali Watershed and Its Implications to Land-Use Policies

Flooding has become a recurring event in the Province of Bukidnon, causing severe destruction to houses, buildings, infrastructure, and livelihood. Since the province is not exempted in flooding events as an impact of typhoons, understanding the watershed hydrologic behavior is essential for vulnerability and risk assessment as to disaster preparedness and risk reduction. The study aims to analyze the hydrologic response of Manupali watershed through flood hazard maps, hydrologic, and hydraulic models. This paper presents the combination of geographic information system, high -resolution digital elevation model (DEM), land cover, observed hydro-meteorological data, and the combined hydrologic engineering center-hydrologic modeling system and river analysis system models. The hydrologic model assesses the relationship between rainfall and discharge of the watershed and the hydraulic model computes the flood depth and flow pattern in the floodplain. Upon calibration, the over-all performance of the hydrologic model was rated very good in its performance based on the standards set by Moriasi et al. (2015) with index values of 0.89, 0.75, 0.46. The calibrated hydrographs were used to produce flood hazard maps in 2, 5, 10, 25, 50, and 100-year return periods, and assessed the number of flooded buildings in each flood hazard level per return period. The flood hazard maps may contribute to science-based land-use policy formulation, land-use zoning, planning, and management to mitigate extreme rainfall-induced flood risks in the affected barangays in the Manupali watershed.

Hydrological Modelling Studies of Paravar River Basin, a Tributary of River Godavari using HEC-HMS Model

The Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) is designed to simulate the complete hydrologic processes of dendritic watershed systems. The software includes many traditional hydrologic analysis procedures such as event infiltration, unit hydrographs, and hydrologic routing. The model is applied to the Pravara River Basin, which is a tributary of the Godavari River in the Ahmednagar district of Maharashtra (India). For the simulation of runoff, the daily precipitation data and daily observed streamflow data from 1999 to 2012 was collected and ten years of data from 1999 to 2008 was used for the calibration of the model and 4 years of data from 2009 to 2012 was used for the validation of the model. The calibration of the HEC-HMS 4.0 model for the study area is carried out by comparing the simulated daily streamflow with the observed flow at the outlet of the basin. For this particular study, the deficit and constant loss model is used to compute the losses from the watershed. Under prediction of high flows is an inherent problem seen in hydrological modeling of the basin in the present study. This is due to the lack of extreme event modeling capability of the hydrological model. The daily flows except extreme flows are better simulated. The ability of HEC–HMS to simulate the magnitude of the peaks in extreme floods in the river basin underscores the significance of the model application as a flood prediction tool. The HEC–HMS successfully reproduced low flows and thus the model is a useful tool to estimate low flows in advance based on drought forecasts.

Artificial neural network based PERSIANN data sets in evaluation of hydrologic utility of precipitation estimations in a tropical watershed of Sri Lanka

<abstract> <p>The developments of satellite technologies and remote sensing (RS) have provided a way forward with potential for tremendous progress in estimating precipitation in many regions of the world. These products are especially useful in developing countries and regions, where ground-based rain gauge (RG) networks are either sparse or do not exist. In the present study the hydrologic utility of three satellite-based precipitation products (SbPPs) namely, Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), PERSIANN-Cloud Classification System (PERSIANN-CCS) and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Dynamic Infrared Rain Rate near real-time (PDIR-NOW) were examined by using them to drive the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) hydrologic model for the Seethawaka watershed, a sub-basin of the Kelani River Basin of Sri Lanka. The hydrologic utility of SbPPs was examined by comparing the outputs of this modelling exercise against observed discharge records at the Deraniyagala streamflow gauging station during two extreme rainfall events from 2016 and 2017. The observed discharges were simulated considerably better by the model when RG data was used to drive it than when these SbPPs. The results demonstrated that PERSIANN family of precipitation products are not capable of producing peak discharges and timing of peaks essential for near-real time flood-forecasting applications in the Seethawaka watershed. The difference in performance is quantified using the Nash-Sutcliffe Efficiency, which was > 0.80 for the model when driven by RGs, and < 0.08 when driven by the SbPPs. Amongst the SbPPs, PERSIANN performed best. The outcomes of this study will provide useful insights and recommendations for future research expected to be carried out in the Seethawaka watershed using SbPPs. The results of this study calls for the refinement of retrieval algorithms in rainfall estimation techniques of PERSIANN family of rainfall products for the tropical region.</p> </abstract>

기후변화에 따른 미래 강우유출량 예측을 위한 HEC-HMS 모델 활용 가능성 검토 연구 : 금강 대청댐 유역을 대상으로

In Korea, where more than half of annual precipitation (55%, 653.9 mm) occurs during the rainy season (June ~ September), it is difficult to efficiently store and manage water resources. These challenges are likely to be exacerbated by climate change, the impact of which was demonstrated in the summer of 2020 in the form of an unprecedented long rainy season. The purpose of this study is to help establish efficient future water resource management and water-related disaster prevention measures in response to climate change. Application of the HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modeling System) model was evaluated for simulation of rainfall runoff for the Daecheong Dam basin. During model set-up, parameter values for loss, transform and routing methods were calculated based on land cover/land use status and soil type. The calibration results for rainfall runoff at Junction-22 for the year of 2008 showed an excellent Nash-Sutcliffe Efficiency (NSE) value of 0.732, proving the high accuracy of the model. Simulation results for runoff volume at the same junction in 2017 using calibrated parameter values showed an acceptable NSE value of 0.535. Thus, the overall model efficiency of HEC-HMS was validated. The results of a pilot simulation of the impact of climate change on runoff volume under RCP scenarios 4.5 and 8.5 for the year 2050 forecast potential exacerbation of the seasonality in precipitation, in addition to showing a dissimilar pattern from the present, suggesting potential water management issues. Since future management methods should take into account the intensity and frequency of precipitation during the dry and rainy seasons, which vary due to climate change, validation of the HEC-HMS as a tool for predicting runoff volume in the mid- to long-term future is important.

Impact of climate change on the stream-flow of Ala River, Akure, Nigeria

Climate change is one of the notable changes experienced around the world today and this is as a result of Global warming. The environmental impact of climate change, especially in densely populated developing countries such as Nigeria cannot be overlooked without seeking to provide useful information to help avert the consequences arising from it. Therefore, the aim of this research is to simulate the effect of climate change on the stream-flow of Ala River, Akure, Nigeria and this aim is achieved by projecting future rainfall due to climate change and simulating a hydrologic model of the river. Precipitation change experienced in the world climate system was considered and projection of precipitation for Ala, Akure was done by statistically downscaling General Circulation Model (GCM) under the Representative Concentration Pathways (RCP 4.5 and RCP 8.0) climate scenario. The projected climate change alongside other hydrologic parameters was input into Hydrologic Engineering Centre-Hydrologic Modeling System (HEC-HMS) version 4.2 to simulate a hydrologic model so as to achieve the peak discharges at a different cross-section of the river reach. The peak discharges obtained for the Ala River basin indicate a continuous increase of the runoff generated as a result of an increase in precipitation as the years progresses resulting from a change in the climate system.