HEC-6 Model Research Articles

Possible options to slow down the advancement rate of Tarbela delta.

The pivot point of delta in Tarbela dam has reached at about 10.6km from the dam face which may result in blocking of tunnels. Tarbela delta was modeled from 1979 to 2060 using hec-6 model. Initially, the model was calibrated for year 1999 and validated for years 2000, 2001, 2002, and 2006 by involving the data of sediment concentration, reservoir cross sections (73 range lines), elevation-area capacity curves, and inflows and outflows from the reservoir. Then, the model was used to generate future scenarios, i.e., run-1, run-2, and run-3 with pool levels; 428, 442, and 457m, respectively, till 2060. Results of run-1 and run-2 showed advancement to choke the tunnels by 2010 and 2030, respectively. Finally, in run-3, the advancement was further delayed showing that tunnels 1 and 2 will be choked by year 2050 and pivot point will reach at 6.4km from the dam face.

Analysis of the Effect of Dredging and Weirs on Bed Change in the Nakdong River and its Tributary using HEC-6

It is necessary to evaluate the effect of dredging and weir operation on the flow and long-term bed change for river management. Especially, large scale river treatment project, with dredging or weir installation and operation, can increase the instability of riverbed in tributaries as well as mainstream. This study focuses on the effect of weir installation and dredging on the long-term bed change in Nakdong river (Gangjeong- Goryeong Weir~Dalseong Weir) and its tributary (Geumho river). HEC-6 model has been used to analyze the amount of long-term bed change and sediment transport resulted from the river treatment including dredging or weir installation. From the result, it was concluded that a large scale river treatment can accelerate and increase the long-term bed change both in mainstream and tributary.

FLUSHING TECHNIQUE FOR SEDIMENT DISPOSAL CASE STUDY- A RIVER IN HIMALAYA

ABSTRACT Sedimentation is a major problem in alluvial areas due to which reservoirs are losing their water storage capacity. The rivers in Himalaya especially have steep slope about 1:70 and carries heavy sediment during flood. The reservoir under such condition is likely to be silted up rapidly and sediment may enter into the intake of power development unit. Therefore removal of sediment from reservoir is of utmost importance. Different methods are available for removal of sediment, most of which are uneconomical except flushing techniques. Determination of optimum discharge for effective flushing and its duration are important aspects of flushing technique. Knowledge of bed profile at the end of one or two years should be known, so that it can be used in physical model for determination of optimum flushing discharge and duration. In this paper, the one year deposition profile at upstream of dam was obtained using HEC-6 model. Using this profile, the optimum discharge and duration of flushing were obtained using physical model for a particular case. This technique may be applicable to any river in alluvial area.

A two-step approach to investigate the effect of rating curve uncertainty in the Elbe decision support system

For river basin management, the reliability of the rating curves mainly depends on the accuracy and time period of the observed discharge and water level data. In the Elbe decision support system (DSS), the rating curves are combined with the HEC-6 model to investigate the effects of river engineering measures on the Elbe River system. In such situations, the uncertainty originating from the HEC-6 model is of significant importance for the reliability of the rating curves and the corresponding DSS results. This paper proposes a two-step approach to analyze the uncertainty in the rating curves and propagate it into the Elbe DSS: analytic method and Latin Hypercube simulation. Via this approach the uncertainty and sensitivity of model outputs to input parameters are successfully investigated. The results show that the proposed approach is very efficient in investigating the effect of uncertainty and can play an important role in improving decision-making under uncertainty

Field validation of two river morphological models on the Pasak River, Thailand

A comparison is made of the quasi-two-dimensional GSTARS2.1 mathematical model, which can analyse lateral erosion, and the well-known one-dimensional HEC-6 model. Also, both models are validated by means of comparison with observations. The study emphasizes the differences in principle, concept, results and efficiency of the two models. The morphological processes over the 56-km reach of the Pasak River, downstream of Pasakjolasid Dam in Thailand, are considered. The analysis was carried out on a 14-year continuous period (1990–2004). The computational results are compared with the observed data, collected from six river cross-sections in 1990 and 2004. Compared with the observed bed level data, the results computed by using HEC-6 and GSTARS2.1 are similar for one-dimensional simulation without the consideration of lateral change of bed elevation. However, when both bed change and lateral erosion were considered, the GSTARS2.1 model gave better agreement to the measured river cross-sections than the HEC-6 model, due to the advantage of the stream tube technique.

Case Study: Application of the HEC-6 Model for the Main Stem of the Kankakee River in Illinois

This case study paper presents results on the application of the HEC-6 model to the main stem of the Kankakee River in Illinois, a distance of about 39.3 km. Modeling was performed to develop comprehensive plans for enhancing the aquatic habitats and also to forecast future sedimentation problems if specific management practices are implemented. The paper concentrates on the modeling aspects of this research. The extent of the model was from the Stateline Bridge to Kankakee Dam in Kankakee. The HEC-6 model, originally developed by the Hydrologic Engineering Center (HEC) of the U.S. Army Corps of Engineers, was adapted for this application. The model was run, calibrated, and verified for both the hydraulic and sediment components. The hydraulic component was calibrated through comparison of measured yearly hydrographs with computed values for three gauging stations on the river. The hydrologic component was verified for the same three gauging stations for two yearly hydrographs for 2 additional water years. The sediment component was calibrated with river cross-sectional data collected by the Illinois State Water Survey in 1980 and 1999. The calibrated and verified hydraulic and calibrated sediment components then were used to predict future changes in water surface elevations and thalweg elevations for a 20-year period beginning in 1999, the last date for which river cross-sectional data are available.

유사량 산정공식에 따른 유사 및 하상변동 예측에 관한 연구

The purpose of this study is to analyze the characteristics of riverbed variation due to the sediment protection weir located on the estuary of the main stream of Taehwa river using I-D finite difference model, HEC-6 model, and the followings are the results of estimating sediment transport rate, amount of scour or deposition, and accumulated amount of deposit according to before and after of the sediment protection weir removal with various flow rates in the channel. Ackers-White transport function produced the greatest sediment transport rate while Meyer-Peter showed the smallest sediment transport rate at the most down stream area of the watershed through the sediment transport rate analyses for various flow rates according to the existence or nonexistence of the sediment protection weir. Toffaleti's and Colby transport function were closest to the average value, and the difference among the results of the sediment transport functions showed up to 8～9 times. Duboy's transport function produced the greatest riverbed variation while Toffaleti's showed the smallest variation through the riverbed variation analyses according to the existence or nonexistence of the sediment protection weir. Yang's was closest to the average value, and the difference among the results of the riverbed variation analyses ranged from 1.4 times to 11 times. It is thought that a sediment transport function must be selected very carefully with respect to the criteria of sediment yield estimation because the analysis results of the sediment transport rate and riverbed variation according to flow rates showed significant differences among the sediment transport functions, and the differences of sediment transport rate and riverbed variation according to the various sediment transport functions decreased as the flow rate increased.

STAND, a dynamic model for sediment transport and water quality

We introduce a new model–STAND (Sediment-Transport-Associated Nutrient Dynamics)–for simulating stream flow, sediment transport, and the interactions of sediment with other attributes of water quality. In contrast to other models, STAND employs a fully dynamic basis for quantifying sediment transport, thus distinguishing it from the well-known HEC-6 model. This latter, in particular, computes a steady-state form of sediment transport based on an approximation of transient flow regimes by a sequence of steady-state hydraulic conditions. STAND has a three-level structure. The first level accounts for the hydraulics of open-channel flow, using the conventional St Venant equations. The second level computes sediment transport potential and actual transport rates based on the information provided by the first level. In the third level (not discussed herein), changes of nutrient concentrations along the studied river can be computed as a function of nutrient transport, adsorption/desorption of nutrients to suspended sediment, and releases from bed-sediment pore water. Having introduced STAND and compared and contrasted its structure with HEC-6, STAND's performance is evaluated against a comprehensive data set obtained from a section of the Weihe River, a major tributary of the Yellow River, in China, and compared to results from HEC-6. From both visual evaluation and the statistics of the residual time series, it can be concluded that STAND provides the better simulation, notably under conditions of strongly transient stream behavior.

Flood risk mapping for Pari River incorporating sediment transport

Geographic Information Systems (GIS) are an efficient and interactive spatial decision support tool for flood risk analysis. This paper describes the development of ArcView GIS extension — namely AVHEC-6.avx — to integrate the HEC-6 hydraulic model within GIS environment. The extension was written in an Avenue Script language and Dialog Designer with a series of ‘ point and click’ options. It has the capability of analyzing the computed water surface profiles generated from HEC-6 model and producing a related flood map for the Pari River in the ArcView GIS. The user-friendly menu interface guides the user to understand, visualize, build query, conduct repetitious and multiple analytical tasks with HEC-6 outputs. The flood risk model was tested using the hydraulic and hydrological data from the Pari River catchment area. The required sediment input parameters were obtained from field sampling. The results of this study clearly show that GIS provides an effective environment for flood risk analysis and mapping. The present study only concentrates on the flood risk within the boundary of the bunds.

수치모형을 이용한 하상변동 예측

본 연구는 보청천 하도형태의 변화를 해석하기 위해 1차원 유사이동 모형인 HEC-6 모형과 준 2차원 유사이동 모형인 GSTARS 2.1 모형을 적용하였다. GSTARS 2.1 모형에 포함된 Ackers와 White공식, Engelund와 Hanson공식 그리고 Yang공식의 세 가지 유사이송공식이 1993년부터 2000년까지의 하상재료에 대해 모의되었으며, 그 결과 Ackers와 White공식이 실측치에 근사한 것으로 나타났다. 1차원 유사이동 모형인 HEC-6모형과 GSTARS 2.1 모형과의 장기 하상변동 분석에 있어서 두 모형 모두 하천변화에 대한 전반적인 경향이 실측치의 하상변동 경향의 결과와 유사했다. 실측치와의 횡단면 변화의 비교에서 GSTARS 2.1 모형이 HEC-6모형의 모의결과보다 양호한 결과를 나타내었다. In this study, one dimensional sediment movement numerical model(HEC-6) and semi-two dimensional sediment movement numerical model(GSTARS 2.1) were applied to solve the change of channel geometry in Bocheong stream. GSTARS 2.1 model was applied for the three selected sediment transport formulas(Ackers and White's, Engelund and Hanson, Yang formula) from 1993 to 2000 measured data on each section. The simulation results of Ackers and White formula for long -term bed changes are good when compared to the measured data. The HEC-6 model was applied for the simulation of one dimensional sediment movement for the same period. Comparison of the long-term simulations by GSTARS 2.1 and HEC-6 models with measured data shows that simulations by both models are in fair agreement with measured data in overall trend of the river bed changes. Comparisons of simulated cross sectional bed-elevations with measured data shows that GSTARS 2.1 model gives better agreement with than simulated results bed changes on the HEC-6 model.

Effect of Water Withdrawal on Hydraulics and Morphology of Pumduang River, Thailand

The HEC-6 river morphological mathematical model is applied to predict the effect of water withdrawal from the Pumduang River on its water surface and bed profiles. The river is situated in the Surat Thani province in the south of Thailand. The HEC-6 model is calibrated and verified based on field data. After the model calibration and verification, the HEC-6 is applied to predict the effect of water withdrawal on changes in water level and bed level of the river. The predicted changes are compared with the results of a physical movable bed hydraulic model of scale 1:60. The agreement is found to be satisfactory. The equilibrium river bed and water surface profiles are determined for the annual average flow and the 2-, 10-, 25- and 100-year return period floods for the cases with and without water withdrawal. The water withdrawal of 16 percent of the average annual discharge of the Pumduang river is found to have no endangering effect on the flow and morphological condition of the river

Effects on Dredging due to Diversions from the Lower Mississippi River

This paper presents the development, calibration, and use of a model to analyze the long-term effects on dredging due to freshwater diversions along the lower Mississippi River. The study area includes the Mississippi River from Tarbert Landing, Miss., located at mile 306 above Head of Passes, just downstream of the control structure at Old River, to the Gulf of Mexico by way of Southwest Pass. To determine the extent of the riverine effects, an HEC-6 model was developed. HEC-6 is a numerical model used to predict changes in river profiles due to deposition and scour over a period of time. Modification to the HEC-6 code was necessary to accurately reflect the actual processes occurring in the Mississippi River. An option allowing the reintroduction of dredged material back into the system was added. The calibration, choice of parameters, and results obtained from the model are presented and discussed.

EXPERIMENTAL INVESTIGATION AND ANALYSIS OF HEC-6 RIVER MORPHOLOGICAL MODEL

Only comparatively few experimental studies have been carried out to investigate the performance of the HEC-6 river morphological model. The model was developed by the Hydrologic Engineering Center of the US Army Corps of Engineers. In this study, experiments were carried out in a 20 m long concrete flume 0.6 m wide with varying rectangular cross-sections. The channel bed is paved with uniform sand of D50 = 0.9 mm and D90 = 1.2 mm within the test reach of 12 m. Two types of experiments were carried out with sediment transport, one under steady uniform flow and another under steady non-uniform flow conditions. Nine steady uniform flow experiments were carried out to compare the measured equilibrium relationship of flow and sediment transport rate with two bedload formulae, namely, Du Boys and Meyer–Peter and Muller, and with three total load formulae, namely, Toffaleti, Laursen and Yang. It was found that even though the sediment transport consists of a certain portion of bedload, the total load formulae give satisfactory results and better agreement than the two bedload formulae. Five steady non-uniform flow experiments were carried out under various conditions of varying bed profile and channel width and also with sediment addition and withdrawal. The measured transient water surface and bed profiles are compared with the computed results from the HEC-6 model. It was found that the Toffaleti and Yang total load formulae used in the HEC-6 model give the most satisfactory prediction of actual bed profiles under various conditions of non-uniform flow and sediment transport. The effects of Manning's n, variations of sediment inflow, various sediment transport formulae, sediment grain size and the model numerical parameters, i.e. distance interval Δx and numerical weighting factor, on the computed water surface and bed profiles were determined. It was found that the selection of the sediment transport formulae has the most significant effect on the computed results. It can be concluded that the HEC-6 model can predict satisfactorily a long-term average pattern of local scour and deposition along a channel with either a small abrupt change in geometry or gradually varying cross-sections. However, the accuracy of the model prediction is reduced in the regions where highly non-uniform flow occurs.

Hydrologic and sediment modelling studies in the environmental impact assessment of a major tropical dam project

AbstractA computer‐based study of the impact of the proposed Wabo hydroelectric scheme on the Purari River, Papua New Guinea was carried out. The HEC‐6 model, Scour and Deposition in Rivers and Reservoirs developed by the Hydrologic Engineering Centre was used to simulate the effect of the dam on sediment transport and erosion in the lower Purari. Two runs with the model were carried out. The first one was used to establish baseline conditions and the second modelled dam impact.Before the study was carried out, data had to be collected on channel geometry, sediment input, river bed material size composition and hydraulic conditions in the river. Supplementary models also had to be developed to fill in gaps in runoff records and to describe flow in the river during power generation.Results of the investigation indicate that limited erosion will occur because of bed‐armouring and the river will adjust towards a new equilibrium condition quite rapidly. The sediment output of the river into the Purari delta will change, load in the clay, silt and sand/gravel fractions decreasing by 22, 53 and 78 per cent respectively.