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Advances in Environmental Biology Neural Network
Advances in Environmental Biology, 8(22) November 2014, Pages: 783-790 AENSI Journals Advances in Environmental Biology ISSN-1995-0756 EISSN-1998-1066 Journal home page: http://www.aensiweb.com/AEB/ Water Level Elevation Variations Modeling Using Support Vector Machine and Neural Network 1MojtabaNoury, 2Maryam Khalilzadeh Poshtegal, 3Seyedahmad mirbagheri, 4Mansoor Pakmanesh, 5MahsaMemarianfard 1 Department of civil Engineering, College of Engineering, Islamic Azad University, Malard Branch, Malard, Iran. Phdcandidate in Department of Civil Engineering, K.N.Toosi University of Technology, Tehran, Iran Department of Civil Engineering, K.N.Toosi University of Technology, Tehran, IRAN 4 Phd student in Department of water Science and Engineering, College of Agriculture, Tehran Science and Research Branch, Islamic Azad University, Tehran, Iran. 5 Environmental Faculty, Civil Engineering College, K.N.Toosi University of Technology, Tehran, Iran 2 3 ARTICLE INFO Article history: Received 25 September 2014 Received in revised form 26 October 2014 Accepted 25 November 2014 Available online 31 December 2014 Keywords: Water level fluctuation, Urmia Lake, Support Vector Machine (SVM), Artificial Neural Network (ANN), Neural Wavelet Network (NWN) ABSTRACT This study aimed at analyzing the hydrological changes in the Lake Urmiabasin with focus on the response of the lake water level to meteorological factorsby means of two models was applied. For this, Support Vector Machines (SVM) and MLP- Artificial Neural Network (ANN) models developed for simulating the Urmia Lake water level variations. The yearly historical data of rainfall, temperature and discharge of the Urmia Lake basin and lake water level fluctuation were used. The outcome of the SVM based models are compared with the ANN.The root mean squareerrors (RMSE), sum square errors (SSE) and determination coefficient statistics (R2) are used as comparison criteria. Analysis results showed that the (RMSEs) of 0.23and 0.5 m obtained by SVM and ANN respectively and SSEs of 0.43 , 2.01 and R 2 of 0.97, 0.93 obtained by SVM and ANN respectively. The results of SVM model show better accuracy in comparison with the ANN models. © 2014 AENSI Publisher All rights reserved. To Cite This Article: MojtabaNoury, Maryam Khalilzadeh Poshtegal, Seyedahmad mirbagheri, Mansoor Pakmanesh, Mahsa Memarianfard., Water Level Elevation Variations Modeling Using Support Vector Machine and Neural Network. Adv. Environ. Biol., 8(22), 783-790, 2014 INTRODUCTION An artificial neural network (ANN) has gained significant attention in past two decades and has been widely used for hydrological forecasting. Dawson and Wilby give state-of-the-art reviews on ANN modeling in hydrology [1]. Good state-of-the-art reviews on ANN modeling in hydrology. Wua, attempt to seek a relatively optimal data-driven model for rainfall forecasting from three aspects: model inputs, modeling methods, and data preprocessing techniques [2]. Chen et al proposes a two-step statistical downscaling method for projection of daily precipitation [5]. The proposed statistical downscaling method is developed according support vector machine (SVM) and support vector regression (SVR), and the other is multivariate analysis, including discriminate analysis (for classification) and multiple regression. Results shown that projection of local daily precipitation are performed, and future work to advance the downscaling method is proposed. Asefa et al, present the SVMs have three advantages over back-propagation networks (BPNs), which are the most frequently used convectional NNs. Firstly, SVMs have better generalization ability. Secondly, the architectures and the weights of the SVMs are guaranteed to be unique and globally optimal. Finally, SVMs are trained much more rapidly [4]. Wang et al. autoregressive moving-average (ARMA) models, artificial neural networks (ANNs) approaches, adaptive neural-based fuzzy inference system (ANFIS) techniques, genetic programming (GP) models and support vector machine (SVM) method are examined using the long-term observations of monthly river flow discharges. Two case study river sites are also provided to illustrate their respective performances. The results indicate that the best performance can be obtained by ANFIS, GP and SVM, in terms of different evaluation criteria during the training and validation phases [5]. Lin et al. effective reservoir inflow forecasting models based on the support vector machine (SVM), which is a novel kind of neural networks (NNs), are Corresponding Author: MojtabaNoury, Department of civil Engineering, College of Engineering, Islamic Azad University, Malard Branch, Malard Iran. Tel: +989149382757; E-mail: [email protected]. 784 MojtabaNoury et al, 2014 Advances in Environmental Biology, 8(22) November 2014, Pages: 783-790 proposed. The results indicate that the proposed SVM-based models are more well-performed, robust and efficient than the existing back propagation neural network (BPN-based) models. In addition to using SVMs instead of BPNs, typhoon characteristics, which are seldom regarded as key input for inflow forecasting, are added to the proposed models to further improve the long lead-time forecasting during typhoon-warning periods [6]. A comparison between models with and without typhoon characteristics is also presented to confirm that the addition of typhoon characteristics significantly improves the forecasting performance for long lead-time forecasting. Finally, the proposed modeling technique is expected to be useful to improve the reservoir inflow forecasting. Paulin investigates the potential of reservoir computing for long-term prediction of lake water levels [7]. Great Lakes water levels from 1918 to 2005 are used to develop and evaluate the ESN models. Three datapreprocessing techniques, moving average (MA), singular spectrum analysis (SSA), and wavelet multiresolution analysis (WMRA), were coupled with artificial neural network (ANN) to improve the estimate of daily flows [8]. Çimen and Kisi compares the potential of support vector machines (SVM) and artificial neural network (ANN) in modeling lake level fluctuations. The SVM method is applied to the monthly level data of Lake Van which is the biggest lake in Turkey and Lake Egirdir. The estimated lake levels are found to be in good agreement with the corresponding observed values. The results of the SVM based models are compared with those of the ANN. Based on the comparison, it is found that the SVM based model performs better than the ANN [9]. Wu et al. a novel distributed support vector regression (SVR); (D-SVR) model is proposed [10]. It implements a local approximation to training data because partitioned original training data are independently fitted by each local SVR model. ANN-GA and LR models are also used to help determine input variables. A two-step GA algorithm is employed to find the optimal triplets for D-SVR model. Results reveal that the proposed D-SVR model can carry out the river flow prediction better in comparison with others, and dramatically reduce the training time compared with the conventional SVR model.Yu and Lionga ridge linear regression is applied in a feature space [11]. A support vector machine (SVM) approach is proposed for statistical downscaling of precipitation at monthly time scale [12]. Wei used wavelet support vector machines (wavelet SVMs), for forecasting the hourly channel downstream water levels at gauging stations. An ANN is a massively parallel distributed information processing system with highly flexible configuration and so has an excellent nonlinearity capturing ability. The feed-forward multilayer perceptron (MLP) among many ANNs is by far the most popular, which usually uses the technique of error back propagation to train the network configuration. The architecture of the ANN consists of the number of hidden layers and the number of neurons in input layer, hidden layers and output layer. ANNs with on hidden layer are commonly used in Hydrologic modeling [1, 13, 8] The combination of wavelets theory and neural networks has lead to the development of neural wavelet networks [14, 15]. Moreover, there are other models regarding water level fluctuation modeling, such as Hsu and Wei developed ANN model for simulation the water levels of gauging points that are affected by tidal effects [16, 17,18] Pointed out that the neural networks are simpler and more reliable than the conventional time-series methods such as the autoregressive model (AR). Chang and Chen employed radial basis function (RBF) neural networks for estuary water-stage forecasting in order to solve the more complicated problem of water level fluctuation simulation, Moreover, This study developed SVMs, MLP-ANN and Neural wavelet Network (NWN) models that conjugated both the wavelet function and the ANN for simulating the Urmia Lake water level fluctuation [19]. In this research, two intelligent models were applied; ANN and SVM model for the simulation of the water level variations of Urmia Lake that is one of the important and strategic lakes which is faces with the threat of drought were used and the results of models were compared with each other. MATERIALS AND METHODS Case study, Urmia Lake: Lake Urmia resembles the Great Salt Lake, U.S.A. in many respects of morphology, water chemistry, and sediments. The present lake area is about 5000 km2, shallow (8–12 m), and a perennial sodium chloridesulfate system (22% salts). Urmia Lake in the northwest of Iran is the second largest hyper-saline lake worldwide. During the past two decades, a significant water level decline has occurred in the lake. The existing estimations for the lake water balance are widely variable because the lake bathymetry is unknown. The Urmia Lake surface water levels were 1275.67 meters and 1277.71 meters above open sea surface level on January 1966 and December 2006, respectively. Rainfall, temperature, river flow and fluctuation of water level data: For simulation, at first all the historical data were evaluated and considering the common data, 41 years were selected for investigation from 1996 to 2006. In this research the data of precipitation, temperature and yearly discharge are considered as input of model which in the other hand the data of Lake water level are considered as output of the model. The variation (fluctuation) of Urmia lake water level is shown as table 1 and fig.1. It is clear that the minimum water level of the lake is 2.5m less than average that indicates the climate 785 MojtabaNoury et al, 2014 Advances in Environmental Biology, 8(22) November 2014, Pages: 783-790 change and negative balance. According to the common statistic year, 18 rain gage station table 2, 24 rivers and (table3 and fig. 3) 19 temperature survey station (table 4), were selected for simulation. Fig. 1: map of study area. Table 1: Related Information for Yearly Urmia Lake Water Level. µx(m) Sx(m) TOTAL 1275.672 1.220 TR 1,275.942 0.857 CV 1276.562 0.927 TE 1274.363 1.315 TR: Training Data CV: Cross Validation Data TE: Testing Data Xmax(m) 1277.951 1,277.951 1277.951 1276.967 Xmin(m) 1273.057 1,273.857 1275.337 1273.057 Fig. 2: Urmia lake Water Level fluctuation (1996-2006). Table 2: Related Information for Yearly Rainfall. µx(mm) station TR CV TE SaeedAbad 428.88 438.52 314.01 Zinjenab 305.89 303.43 303.21 Tabriz 234.40 231.18 227.79 Maragheh 347.48 305.95 299.47 Gheblalo 391.32 436.38 493.14 Chobloche 338.94 328.79 269.91 Dashband 441.46 404.43 362.66 GizilGabir 341.72 348.33 328.82 P.Mahabad 379.93 392.63 344.16 G. Jacob 296.85 256.83 279.95 Pey Gala 532.43 496.25 474.55 Oshnaviye 484.52 508.32 440.97 Mirabad 659.88 649.32 526.15 M.Serow 379.75 413.96 373.82 Band 433.90 430.53 380.50 Mosh abad 278.91 254.33 226.63 Ghasemlo 333.15 387.58 342.45 Germzigol 320.91 310.04 278.50 TR: Training Data CV: Cross Validation Data Sx(mm) TR CV 133.45 110.43 94.53 79.65 59.60 49.18 119.74 102.34 97.22 105.33 91.48 119.90 174.78 141.51 111.79 81.90 103.78 116.07 91.60 102.38 127.61 126.73 136.03 158.94 157.99 164.17 96.77 104.64 92.83 109.92 79.38 82.47 120.80 124.48 95.63 79.03 TE: Testing Data TE 110.43 79.65 49.18 102.34 105.33 119.90 141.51 81.90 116.07 102.38 126.73 158.94 164.17 104.64 109.92 82.47 124.48 79.03 TR 813.7 549.5 345.0 774.5 602.5 544.0 920.4 742.5 622.5 485.0 778.0 810.6 941.8 564.0 624.0 510.0 581.0 593.0 Xmax(mm) CV TE 658.9 451.5 420.0 379.8 343.1 298.0 527.3 424.3 602.5 1049.0 544.0 441.0 675.7 657.8 476.5 696.0 598.4 747.8 455.0 630.0 765.0 834.0 746.2 776.0 926.1 1008.6 564.0 735.0 624.0 718.0 388.0 465.0 581.0 692.0 430.0 379.5 TR 247.0 151.0 49.4 180.5 209.0 172.5 197.8 200.5 232.9 21.5 317.0 257.0 325.0 179.0 288.5 151.0 110.5 159.0 Xmin(mm) CV 250.9 151.0 151.0 180.5 315.0 163.0 197.8 230.0 232.9 21.5 335.0 257.0 436.8 249.0 291.8 154.5 223.0 159.0 TE 155.5 218.5 168.4 188.7 186.0 142.5 152.3 124.5 144.6 135.0 295.0 270.0 319.3 238.0 224.0 102.0 200.0 199.0 786 MojtabaNoury et al, 2014 Advances in Environmental Biology, 8(22) November 2014, Pages: 783-790 Fig. 3: Urmia lake watershed rivers yearly discharges (1996-2006). Table 3: Related Information for Yearly River Flow. 3 Station Vanyar Anakhaton Pole sinikh Zinjenab Germizigul Ajabshir Khormazard TazeKand G. Amir ShirinKand QizKorpi Chobloche Dashband Chalkhamaz Kotar Jan Agha PoleBahramlo Baba rud Urban Daryan Tapik Band Bitas Lighvan TR: Training Data 3 µx( M / s ) Sx( M / s ) TR CV TE TR CV TE 15.01 12.09 5.94 6.94 5.68 3.43 1.86 1.59 1.06 1.09 0.95 0.83 0.93 0.86 0.53 0.46 0.33 0.22 0.30 0.32 0.27 0.11 0.17 0.16 1.20 1.03 0.89 1.42 0.31 0.33 1.75 1.29 1.21 1.22 0.03 0.03 0.34 0.36 0.29 0.13 0.17 0.22 4.40 4.18 3.27 1.31 1.06 0.84 3.00 2.88 2.03 0.90 1.05 0.79 2.18 1.97 1.50 0.67 0.73 0.88 54.35 39.15 26.99 23.91 4.61 4.24 4.98 4.69 3.40 1.81 1.47 2.35 18.82 18.08 9.79 8.72 9.47 5.25 2.27 2.09 1.90 0.81 0.71 0.71 7.73 7.93 7.33 2.52 2.94 3.96 3.85 4.10 4.09 1.34 1.42 2.80 14.55 14.35 7.01 5.93 6.46 4.94 10.52 11.17 5.38 4.33 5.00 3.08 0.57 0.44 0.27 0.25 0.19 0.15 0.46 0.52 0.37 0.27 0.33 0.21 13.96 16.05 8.44 6.65 7.18 3.72 5.71 6.40 3.93 2.03 2.45 1.95 1.70 1.87 1.29 0.85 0.89 0.76 0.83 0.86 0.74 0.28 0.25 0.21 CV: Cross Validation Data TE: Testing Data 3 Xmax( M TR CV 42.84 5.68 5.52 0.95 2.33 0.33 0.53 0.17 8.65 0.31 7.83 0.03 0.71 0.17 8.50 1.06 5.10 1.05 3.42 0.73 157.86 4.61 10.04 1.47 39.43 9.47 4.42 0.71 14.50 2.94 7.05 1.42 31.28 6.46 19.27 5.00 1.21 0.19 1.13 0.33 28.70 7.18 10.81 2.45 3.98 0.89 1.52 0.25 /s) TE 23.46 3.44 1.53 0.64 1.47 1.34 0.71 5.86 4.74 3.28 46.18 7.17 39.43 3.35 14.50 6.74 27.98 18.91 0.96 1.13 27.87 10.81 3.98 1.30 3 Xmin( M TR CV 11.28 6.08 2.45 0.32 0.88 0.30 0.64 0.10 1.47 0.54 1.25 0.96 0.88 0.12 4.06 2.47 3.24 1.37 3.49 1.08 33.39 24.50 8.33 2.73 18.46 7.73 3.39 1.17 16.30 3.84 10.64 1.99 15.87 6.86 9.69 4.98 0.60 0.30 0.89 0.04 13.27 3.56 6.55 3.03 2.34 0.81 1.01 0.32 /s) TE 6.08 0.36 0.45 0.10 0.54 1.24 0.12 2.47 1.37 1.08 32.11 2.73 7.73 1.17 3.84 1.99 6.86 5.27 0.20 0.13 7.07 3.57 0.90 0.58 Table 4: Related Information for Yearly Temperature. o µx( c ) TR CV TE Maragheh 11.30 11.96 11.83 Gheblalo 12.05 11.61 12.63 Dashband 11.79 10.99 11.46 P. Mahabad 13.03 13.12 13.39 Pey Gala 12.30 12.38 11.87 Oshnaviye 12.79 12.98 13.27 Ghasemlo 10.75 10.70 11.64 Mirabad 9.83 9.63 10.57 M.Serow 8.15 8.33 9.51 TR: Training Data CV: Cross Validation Data station o Sx( c ) TR CV 1.09 0.67 0.60 0.44 0.86 0.36 0.81 0.98 1.45 1.83 0.77 0.71 0.89 0.74 1.11 0.82 1.69 1.18 TE: Testing Data o TE 0.59 0.51 0.78 0.72 0.58 0.57 0.59 0.52 1.41 TR 7.20 11.16 9.80 10.90 9.40 11.00 8.40 7.20 4.50 Xmax( c ) CV 10.94 11.16 10.43 11.50 9.40 11.10 9.30 7.80 5.60 o TE 10.80 11.80 10.33 12.50 11.10 12.80 10.70 9.89 6.70 TR 12.92 13.50 13.80 15.30 14.64 14.90 12.60 12.70 10.80 Xmin( c ) CV 12.92 12.63 11.54 15.30 14.64 14.20 12.00 10.40 9.80 TE 12.90 13.50 12.40 15.00 13.10 14.60 12.60 11.30 11.00 Implementation of models: This study investigate two different data-driven models, support vector machines (SVM) and artificial neural network (ANN) in order to modeling lake level variations. SVM method which are a new procedure in water resources are applied to the yearly level data of Urmia Lake that is the biggest and the hyper saline lake in Iran. Support vector machine (SVM): In 1995, Cortes and Vapnik suggested a modified maximum margin idea that allows for mislabeled examples If there exists no hyper plane that can split the "yes" and "no" examples, the Soft Margin method will choose a hyper plane that splits the examples as cleanly as possible, while still maximizing the distance to the 787 MojtabaNoury et al, 2014 Advances in Environmental Biology, 8(22) November 2014, Pages: 783-790 nearest cleanly split examples[20]. The method introduces slack variables, ξi, which measure the degree of misclassification of the datum xi. The objective function is then increased by a function which penalizes nonzero ξi, and the optimization becomes a tradeoff between a large margin, and a small error penalty. If the penalty function is linear, the optimization problem becomes: subject to (for any).This constraint along with the objective of minimizing can be solved using Lagrange multipliers as done above. One has then to solve the following problem with [20]. Support vector machine (SVM), which is analytically solved to reach its optimal structural formula, can be represented as a network architecture resembling artificial neural networks (multilayer perceptrons) that have been pruned to obtain model parsimony or improve generalization. New examples are then mapped into that same space and predicted to belong to a category based on which side of the gap they fall on. More formally, a support vector machine constructs a hyper plane or set of hyper planes in a high or infinite dimensional space, which can be used for classification, regression or other tasks. Intuitively, a good separation is achieved by the hyper plane that has the largest distance to the nearest training data points of any class (socalled functional margin), since in general the larger the margin the lower the generalization error of the classifier. Artificial neural networks (ANN): Artificial neural networks (ANN) can be an efficient way of modeling the water level fluctuations process in situations where explicit knowledge of the internal hydrologic processes is not available. An ANN is a flexible mathematical structure that is capable of identifying complex nonlinear relationships between input and output data sets[21]. The structure of neural network is shown in the fig5. Fig. 4: The structure of ANN. RESULTS AND DISCUSSION The mean square errors (RMSE), sum square errors (SSE) and determination coefficient statistics are used as comparison criteria. N RMSE ( N 2 1 Ym Yo ) 2 N i 1 R2 1 (Y i 1 N m (Y i 1 m Yo ) N Y ) SSE (Ym Yo ) 2 In which N is the number of data set, i 1 Yo is the yearly observed values lake level, Ym is the measured values lake level and Y is the average observed Urmia lake water level. If too many neurons are used, the network has too many parameters and may over fit the data. In constant, if too few neurons are included in the network, it might not be possible to fully detect the signal and variance of a complex data set[9]. In this paper the number of hidden neuron and delay and translation factor determined using the trial and error method. The optimum hidden neuron numbers of NWN models and are found to vary between 1 and 20 and delay and translation factor are found 1-10.A difficult task with SVM involves choosing the capacity (Cc), epsilon ( ) and gamma ( ) parameters values. For the Urmia lake, the capacity (Cc), epsilon ( ) and gamma ( ) parameters of optimum SVM model for each input combination are given in table 6. In this research the value of the capacity (Cc), epsilon ( ) and gamma ( ) parameters determined using the trial and error method. The optimum capacity (Cc), epsilon ( ) and gamma ( ) parameters SVM models are found to vary between 1-50, (0.01-0.9) and (0.0001-0.9) respectively. Here the SVM (25, 0.002, and 0.078) denotes a SVM model having the capacity, epsilon and gamma parameter value as 25, 0.002 and 0.078 respectively. Table 6 indicates that the SVM (25, 0.002, and 0.078) model whose inputs are the lake level of one previous year and rainfall, temperature and runoff of each year has the lowest RMSE and SSE and best R 2. 788 MojtabaNoury et al, 2014 Advances in Environmental Biology, 8(22) November 2014, Pages: 783-790 Table 5 indicates that the ANN(18,24,1) model whose inputs are the lake level of one previous year and rainfall, temperature and runoff of each year has the lowest RMSE and SSE and best R 2 . Table 5: The SSE, RMSE and R2 statistics of ANN in test period. Model inputs Ann structures SSE RMSE R2 ANN(18,28,1) 10.25 4.83 0.43 ANN(24,29,1) 8.68 4.15 0.61 ANN(42,32,1) 4.16 3.84 0.74 L F [( P1 ,..., P18 ), (Q1 ,..., Q24 ), (T1 ,..., T9 )] ANN(51,33,1) 4.12 3.56 0.76 L F [( P1 ,..., P18 ), (Q1 ,..., Q24 ), (T1 ,..., T9 )], Lt 1 ANN(52,44,1) 2.01 0.50 0.93 L F ( P1 ,..., P18 ) L F (Q1 ,..., Q24 ) L F [( P1 ,..., P18 ), (Q1 ,..., Q24 )] Table 6: The SSE, RMSE and R2 statistics of SVM in test period. Model inputs L F ( P1 ,..., P18 ) L F (Q1 ,..., Q24 ) L F [( P1 ,..., P18 ), (Q1 ,..., Q24 )] L F [( P1 ,..., P18 ), (Q1 ,..., Q24 ), (T1 ,..., T9 )] L F [( P1 ,..., P18 ), (Q1 ,..., Q24 ), (T1 ,..., T9 )], Lt 1 1277.500 1277.000 1276.500 SSE 5.58 RMSE 4.27 R2 0.54 SVM(10,0.61,0.25) 5.07 4.16 0.68 SVM(20,0.52,0.81) 4.34 3.26 0.73 SVM(15,0.5,0.61) 1.92 1.32 0.81 SVM(25,0.002,0.078) 0.43 0.23 0.97 SVM Predict SVM 1278.000 SVM structures SVM(20,0.02,0.63) Linear (SVM) y = 0.8766x + 157.27 R2 = 0.9786 1276.000 1275.500 1275.000 1274.500 1274.000 Observed 1273.500 1273.000 1273.000 1274.000 1275.000 1276.000 1277.000 1278.000 1279 1278 predict ANN Fig. 5: Comparison of SVM lake level estimates with the observation for the test period. ANN Linear (ANN) y = 1.0721x - 92.051 R2 = 0.9371 1277 1276 1275 1274 1273 Observed 1272 1273.000 1274.000 1275.000 1276.000 1277.000 1278.000 Fig. 6: Comparison of ANN lake level estimates with the observation for the test period. Conclusion: In this research two models were applied for simulation of the water level variations of Urmia Lake. This study investigates the potential of SVM model to simulation the yearly Urmia lake water level variations. The lake level variations estimates of SVM and ANN are compared and the results shown that the SVM results are better than ANN model. Finally it is recommended that the SVM model is suitable alternative for the which can be applied in different fields of hydrology and water resource modeling. 789 MojtabaNoury et al, 2014 Water Level Advances in Environmental Biology, 8(22) November 2014, Pages: 783-790 1279.000 1278.000 Observed SVM 1277.000 1276.000 1275.000 1274.000 1273.000 1272.000 Year 1271.000 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 1279.000 1278.000 Water Level Fig. 7: Yearly lake level estimates of SVM model in test period. Observed ANN 1277.000 1276.000 1275.000 1274.000 1273.000 1272.000 1271.000 Year 1270.000 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Fig. 8: Yearly lake level estimates of ANN model in test period. REFERENCES [1] Dawson, C.W., R.L. Wilby, 2001. Hydrological modelling using artificial neural networks. Prog. Phys. Georgr, 25(1): 80-108. [2] Wua, C.L.B., K.W. Chaua and C. Fanc, 2010. Prediction of rainfall time series using modular artificial neural networks coupled with data-pre-processing techniques ,Journal of Hydrology, 389(1-2): 146-167. [3] Chen S.T. and P. Shan, 2007. Pruning of support vector networks on flood forecasting, Journal of Hydrology, 347(1-2): 67-78. [4] Asefa, T., M. Kemblowski, M. McKee and A. Khalil, 2005. Multi-time scale stream flow predictions: The support vector machines approach, Journal of Hydrology, 318(1-4): 7-16. [5] Wang, W.C., K.W. Chau, C.T.C. Lin Qiu, 2009. 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