Tawatchai Tingsanchali

Application of tank, NAM, ARMA and neural network models to flood forecasting

Two lumped conceptual hydrological models, namely tank and NAM and a neural network model are applied to flood forecasting in two river basins in Thailand, the Wichianburi on the Pasak River and the Tha Wang Pha on the Nan River using the flood forecasting procedure developed in this study. The tank and NAM models were calibrated and verified and found to give similar results. The results were found to improve significantly by coupling stochastic and deterministic models (tank and NAM) for updating forecast output. The neural network (NN) model was compared with the tank and NAM models. The NN model does not require knowledge of catchment characteristics and internal hydrological processes. The training process or calibration is relatively simple and less time consuming compared with the extensive calibration effort required by the tank and NAM models. The NN model gives good forecasts based on available rainfall, evaporation and runoff data. The black-box nature of the NN model and the need for selecting parameters based on trial and error or rule-of-thumb, however, characterizes its inherent weakness. The performance of the three models was evaluated statistically. Copyright

Numerical modelling of dam failure due to flow overtopping

Abstract A one-dimensional numerical model for dam failure due to flow overtopping is developed. The MacCormack explicit finite difference scheme is used to solve the one-dimensional equations of continuity and momentum for unsteady varied flow over steep bed slopes. In the computation of erosion process, sediment transport equations are considered and the modified Smart formula developed for steep bed slope is selected. The sliding stability of the overtopped dam is checked by modified ordinary method of slices. The model has been successfully calibrated and verified using laboratory experimental data. By comparing with the experimental results, it was found that the model accuracy depends largely on the sediment transport formula and pore water pressure coefficient. The model was found to predict actual breach outflow of the Buffalo Creek Dam reasonably well and closer than other existing numerical models.

Non-deposition design criteria for sewers with part-full flow

In this study, the existing self-cleansing design criteria for sewers based on minimum velocity and minimum bed shear stress have been reviewed. Based on several laboratory experiments, the study then develops non-deposition criteria for non-cohesive sediment in uniform flow. The developed criteria take into account geometry of flow sections, hydraulic and sediment properties based upon three dimensionless parameters, namely, the densimetric Froude number, the volumetric sediment concentration and the relative grain size. The proposed criteria provide improved estimates of self-cleansing minimum velocities compared to the traditional one-parameter design criteria and agree well with the well-known existing design criteria, namely, Mackes formula for suspended load and Mays formula for bed load. The present study therefore contributes new non-deposition design criteria for sewers with part-full flow in the range of the experiment conducted and yet which are simple for practical applications. Further research work is required to substantiate the preliminary character of the results presented for wider application of the proposed self-cleansing design criteria.

Flood-hazard assessment and risk-based zoning of a tropical flood plain: case study of the Yom River, Thailand

Abstract This study contributes to the comprehensive assessment of flood hazard and risk for the Phrae flood plain of the Yom River basin in northern Thailand. The study was carried out using a hydrologic–hydrodynamic model in conjunction with a geographic information system (GIS). The model was calibrated and verified using the observed rainfall and river flood data during flood seasons in 1994 and 2001, respectively. Flooding scenarios were evaluated in terms of flooding depth for events of 25-, 50-, 100- and 200-year return periods. An impact-based hazard estimation technique was applied to assess the degree of hazard across the flood plain. The results showed that 78% of the Phrae flood-plain area of 476 km2 in the upper Yom River basin lies in the hazard zone of the 100-year return-period flood. Risk analyses were performed by incorporating flood hazard and the vulnerability of elements at risk. Based on relative magnitude of risk, flood-prone areas were divided into low-, moderate-, high- and severe-risk zones. For the 100-year return-period flood, the risk-free area was found to be 22% of the total flood plain, while areas under low, medium, high and severe risk were 33, 11, 28 and 6%, respectively. The outcomes are consistent with overall property damage recorded in the past. The study identifies risk areas for priority-based flood management, which is crucial when there is a limited budget to protect the entire risk zone simultaneously. Citation Tingsanchali, T. & Karim, F. (2010) Flood-hazard assessment and risk-based zoning of a tropical flood plain: case study of the Yom River, Thailand. Hydrol. Sci. J. 55(2), 145–161.

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 Mannings 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.

Flood risk assessment in the region surrounding the Bangkok Suvarnabhumi Airport

Flood hazard, vulnerability, and risk assessments were conducted in the area surrounding the new Bangkok International Airport. A hydrodynamic model was used to simulate the flood flow through the study area. Results show different levels of flood hazard for risk zones for 25-, 50- and 100-year return periods of rainfall.

Optimum Water Resources Allocation for Mekong-Chi-Mun Transbasin Irrigation Project, Northeast Thailand

ABSTRACT System analysis and a mixed integer linear programming technique are used to undertake comparative analysis to find an optimum development option of the Mekong-Chi-Mun transbasin irrigation (KCM) project in Northeast Thailand within a total potential area of 692,258 ha. The optimization model considers ten key integer variables, decisions, and constraints on improvement of existing irrigation and hydropower systems and development of new irrigation areas. The optimum solutions are determined for various cases based on maximizing net benefits for a maximum irrigation area within the given limit of potential area. Additionally, sixty irrigation development options with prespecijied irrigation components are also considered in the optimization to compare and verify the results with the optimum mixed integer solutions. In this study, the considered irrigation area development options include the possibility of having the proposed Huailuang Reservoir serve a maximum possible irrigation area in the Mek...

Flood Simulation in the Tidal Delta of the Mekong River by the SSARR Model

ABSTRACT The SSARR model is applied to simulate flood levels in the Mekong river delta. The Mekong and Bassac rivers which are two main rivers and the Vaico river are interlaced together with canals and floodplains with storage. The flow exchanges between these rivers, and the tidal influences in their estuarial reaches make it necessary to utilize the backwater mode of the SSARR model in the simulation. In addition to the backwater mode, the diversion algorithm of the SSARR model is also used to take into account the over bank flow conditions. Since the river storages during the flood periods are considerable, the rivers have been divided into several storage reaches or reservoirs. The flow between these storage reaches depends on the water level differences between each pair. Moreover, the various flood plain storages are also represented by a network of interconnected storage reaches or reservoirs. The upstream boundary condition is the discharge in the Mekong river at Phnom Penh, and the downstream bo...

Subsidence of flood waves in overbank flow areas

Those semi-empirical exponential equations which can describe subsidence of flood peak discharges in channels during overbank flow periods are developed by using dimensional analysis to analyze the numerical results computed from various flood routing techniques based on unsteady free surface flow equations. The subsidence is expressed as a function of eight dimensionless parameters related to the geometry and Manning roughness coefficients of main channel and overbank sections, bed slopes, duration of flood wave, rising time and recession time of overbank flow hydrograph. Two different shapes of inflow flood hydrographs are considered. The derived equations are tested by applying them to calculate the subsidence of flood peak discharges in the Nam Pong and Chao Phraya Rivers in Thailand. The results are found to be very good. Sensitivity analysis shows that the method is not sensitive to error of + 20% in input data. Backwater effects may be included with some modifications.

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

Abstract 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.