TIDE PREDICTION FOR THE DOWNSTREAM BOUNDARY CONDITION OF THE CHAO- PHRAYA RIVER MODEL USING HARMONIC ANALYSIS

Transcription

1 TIDE PREDICTION FOR THE DOWNSTREAM BOUNDARY CONDITION OF THE CHAO- PHRAYA RIVER MODEL USING HARMONIC ANALYSIS Supatchaya Chuanpongpanich Dr-Ing. Phatcharasak Arlai Prof. Manfred Koch PAssoc. Prof. Keni Tanaka Prof. Tawatchai Tingsanchali

2 Floods in Thailand 995 Total damage cost = 2.3 Billion USD 20 Total damage cost = 42.2 Billion USD We need a flood prediction for the Chao Phraya River!!!!

3 Study Area Chao-Phraya river basin 30% of Thailand's land area 40% of the country's population Over 90% of agriculture area Capital city, Bangkok located on the area

4 ANN Weather Prediction and Downscaling: CReSSand SiBUC Side Flow Side Flow HEC-RAS For Chao Phraya River HM Gulf of Thailand Conceptual Idea of Integrated Models for 7 days early flood prediction

5 Side flow Ra&Runoff Rainfall -Building height distribution -SST -NDVI

6 CReSSand SiBUCModel Boundary Condition : JCDAS (.25deg, 6hr interval) CReSiBUCresolution : dx= dy= 0km Center : E0, N6 0 days forecasting

7 HEC-RAS Model

8 Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth. Tide characteristics ) sinusoidal oscillation containing either two main cycles per day - semidiurnal tides 2) one cycle per day - diurnal tides 3) a combination of the two - mixed tides

9 day day GULF OF THAILAND one cycle per day -diurnal tides

10 Set up a harmonic analysis to predict the 7 days ahead tide at Fort Chula gaging station (C.54) for the downstream boundary condition of Chao Phraya River model

11 Harmonic Analysis The purpose of tide analysis is to determine the amplitude and phase (the socalled tidal harmonic constants) of the individual cosine waves, each of which represents a tidal constituent identified by its period in mean solar hours or, alternately, its speed in radians per mean solar hour (speed = 360 /T where T = period). Where η r a 0 N a i δ i T i a a N 2πt ηr ( t) = a0 + ai sin + δi i= Ti is the tidal water level recorded as a function of time t at any station is the mean sea level is the total number of constituents th is the amplitude of the i constituent th is the phase of the i constituent th is the period of the i constituent The values of 0, i, δ can be determined for each corresponding value of i i using the data information that are obtained from tidal records. T

12 Harmonic Analysis = = M r M a 0 ) ( η )cos ( 2 )sin ( 2 + = = = M i r M i r i T M T M a π η π η = = = M i r M i r i T T 2 sin 2 cos tan π η π η δ The values of a 0, a i, can be determined for each corresponding value of T i using the data information that are obtained from tidal records. δ i

13 Principal tidal constituents (Defant, 96) Name Symbol Period (hr) Luni-solar diurnal K Principal lunar diurnal O Principal lunar M Principal solar S Larger lunar elliptic N Luni-solar semidiurnal K Larger lunar evectional ν Variational µ Smaller solar elliptic L Larger solar elliptic T Lunar elliptic second order 2N Smaller lunar evectional ʎ Principal solar diurnal P Larger lunar elliptic Q Smaller lunar elliptic M Small lunar elliptic J Lunar fortnightly M f Lunar monthly M m Solar semiannual S sa

14 The optimum set of parameters for predicting 7 days ahead tide is M = 35 N = 4 Principal lunar M2 (T= hr, a = m) Principal solar S2 (T= hr, a 2 = 0.874m) Luni-solar declinational K (T= hr, a 3 = m) Large lunar declinational O (T = hr, a 4 = m)

15 The best set of parameters : RMSE 0.78 meters and Efficiency Index (EI) of 96%.

16 7 Days predicted vs observed Tides

17 The downstream boundary of the Chao-Phraya river flow model is located at Fort Chula gaging station at the river mouth ust at the sea in the Gulf of Thailand. The water level at Fort Chula is influenced by the upstream of river discharge and the tidal wave from the sea. Therefore, Harmonic Analysis method is applied at Fort Chula gauging station for prediction of water level at this gagingstation. The results of harmonic analysis show an accuracy performance of 87% Efficiency Index for water level forecasting at Fort Chula gauging station based on the four main tidal constituents (M2, S2, K and O) with the recorded tides of prior 35 days.

18 FOR YOUR ATTENTION