Steady State Gate Operation Model for Mun Bon Irrigation System

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1 Kasetsart J. (Nat. Sci.) 35 : 85-9 (00) Stead State Gate Operation Model for Mun Bon Irrigation Sstem Varawoot Vudhivanich and Supachai Roongsri ABSTRACT The stead state gate operation model was formulated in this stud to help irrigation engineers operating the complicated irrigation canal regulators. The computer program called GATEOP was developed for calculating the water surface profile of the canal reach and the gate opening. The model was applied to Mun Bon irrigation project. Six main regulators which are the entrance to 6 zones in water master were selected for the model testing. The field data of the regulators and the canal sections such as gate length, gate sill elevation, canal bed elevation downstream of the regulator, full suppl level, maximum design discharge, canal bed slope, bed width and side slope were investigated. The 6 regulators were calibrated intensivel. The field test during June-November 998 shown that the discharge control of the 6 regulators were less than ± 0% error. Ke words: gate operation, canal operation, canal control, water control, Mun Bon INTRODUCTION The objective of irrigation water management is to deliver the right amount of water to the right place at the right time. To achieve this objective, one has to understand the importance of 3 main activities related to water distribution. These are () planning () controlling (3) monitoring and evaluation of water distribution performance. Oftenl, man researchers have been emphasized their researches on improvement of planning, monitoring and evaluation such as the water allocation scheduling and monitoring sstem or WASAM (Ilaco/Empire M&T (986a, 986b); Vudhivanich et al.,000 ; RID, 996), the geographic information sstem for dail monitoring (Molle and Pongput, 997 ; Tienchai, 997). But onl a few works focus on the control of water distribution, particularl in Thailand. Most of the times, the control of water distribution in manuall operated canal networks is entirel left to the field staffs. Man canal sstems ma have more than 00 water level and discharge regulators. Operating one regulator (gate) will effect both upstream and downstream regulators, particularl when the gates are operated under submerged conditions. One important problem in the actual operation of canal sstem is the determination of the gate opening in order to control the desired discharge to the desired area. Proper gate opening depends on the gate tpe, desired discharge, water level uptream and downstream of the gate, etc. Moreover, the water level at the gate ma var according to the back water effect from the adjustment of downstream gate. Thus, the determination of gate opening is a complicated work. An irrigation projects that do not give enough attention to this issue, ma have problems on water deliver and distribution. It will Department of Irrigation Engineering, Facult of Engineering, Kasetsart Universit, Kamphaengsaen, Nakhon Pathom 7340, Thailand. Regional Office 6, Roal Irrigation Department, Nakhon Ratchasima 30000, Thailand.

2 86 Kasetsart J. (Nat. Sci.) 35 () directl effect the irrigation and water deliver performance of the project and also the irrigation efficienc. The objectives of this research are () to develop the stead state gate operation model and the computer program for determination of gate opening () to test the accurac and reliabilit of the method. Mun Bon irrigation project is selected as a case stud. MATERIALS AND METHODS Theoretical backgrounds of stead state gate operation model The calculation of gate opening depends on the flow conditions in the canal and the tpe of regulators. The flow conditions are classified into free flow and submerged flow. Free flow gate operation As shown in Figure, the free flow discharge can be calculated b the following orifice flow formula : Q = C d LGo gy... () when Q = Gate discharge, m 3 /s. C d = Discharge coefficient which is a function of Go L = Gate length, m. Go = Gate opening, m. Y = Upstream depth, m. g = 9.8 m/sec. From the principle of upstream control, the upstream water level is maintained at full suppl level (FSL). The upstream depth can be measured. If C d is a linear function of and can be expressed Go as Go = a C d+b, the gate opening (Go) for a given Q can be determined b the following equation. Go = Ê Á Ë Y b Q a ˆ - b L gy... () Submerged flow gate operation As shown in Figure, the calculation of Go under the submerged flow condition is more complicated than the previous case. The discharge through the upstream regulator ma be influenced b the back water effect from the operation of the downstream regulator as shown in Fig. 3. Therefore, the back water effect has to be examined before calculating Go. () No back water effect In case of no back water effect, the water depth downstream of the regulator ( in Figure 3) is the normal depth when the flow reaches the stead state. The downstream normal depth can be calculated b Manning s formula, Eq.3. Since the normal depth calculation is in implicit form, the upstream water level Y downstream water level sill elevation Go Q Figure A regulator with free flow discharge.

3 Kasetsart J. (Nat. Sci.) 35 () 87 Newton-Raphson technique is emploed to solve for iterativel, as shown in Eq. 4. With the calculated, the Go for the given Q can be calculated from the submerged flow formula and the C s function as shown in Eq.5 and Eq.6 b assuming that the upstream depth is at FSL (RID.997). Q = n AR 3 / S / 0... (3) j+ = j - Q Q j Ê dr Á + Ë 3R d A... (4) da ˆ d when j+, j = Calculated at j+ and j iteration Q = Given discharge, m 3 /s. Q j = Q evaluated at = j = n AR j 3 / j S / o Ê dr da ˆ Á + = Geometric function of Ë 3Rd A d trapezoidal canal section A = Cross sectional area of flow, m. R = Hdraulic radius, m. S 0 = Bed slope Q = Cs Lhs gh... (5) Go = hs b ac S... (6) () Back water effect In case of back water effect from the downstream regulator (regulator ) as shown in Figure 3, the water surface profile between the downstream regulator and the operating regulator (regulator ) has to be calculated in order to upstream water level Y h downstream water level Go sill elevation Q hs Figure A regulator with submerged flow discharge. FSL Back Water Effect FSL Q (Normal Depth) ELEVS Go Q ELEVB ELEVS S o Go Figure 3 The back water effect from regulator on the discharge through regulator.

4 88 Kasetsart J. (Nat. Sci.) 35 () determine the downstream depth of regulator ( ). It is assumed that the water level upstream of regulator is maintained at FSL. The step method called Depth Calculated from Distance is emploed in the water surface profile calculation as shown in Figure 4. From the energ balance equation, E + S O.Dx = E + S f. Dx E - S f D x = E - S f D x+ ( S f SO)D x... (7) V when E = Specific Energ = + m. g S f = Friction slope which can be Ê Qn ˆ calculated from Manning s formula = Á Ë AR /3 Dx = Canal reach distance, m. B Newton-Raphson technique, can be calculated iterativel b Eq.8. If the reach between regulator and regulator has laterals or farm turn out (FTO), this will reduce the discharge. The calculation of back water effect will have to take this effect into considerations. Once is calculated, the Go can be determined similar to the case of no back water effect. lj+ = - U j -U j Ê df ˆ Á Ë d j... (8) when U = Ê E - S f Ë ˆ + ( S f S O U j = E - S f D x Ê df ˆ Qb ( +z j) DxQn Á = ( ) 3 + Ë d j gaj AR / ( 3 ) j Ê dr da ˆ Á + Ë 3R d A d j If the downstream structure is a drop structure or inclined drop, that structure will act as a flow control. The flow at the control is the critical flow condition. The critical depth ( c ) for trapezoidal canal section can be calculated b Eq.9. Also the Newton-Raphson technique can be used to solve for c. Once the depth at the downstream control structure is calculated, can be determined b the step method. Thus, Go is calculated as previous described. Q B 3 g A =... (9) when B = Top width, m A = Cross sectional area, m. f( c = o ) o / f ( o ) when f( o ) = Ê Q (b+z ) Á Á Ë g ( b+zo) o 3 { o}... (0) ˆ S f FSL Q S o ELEVS Figure 4 Step method - depth calculated from distance. x

5 Kasetsart J. (Nat. Sci.) 35 () 89 f ( o ) = Q Ê z 3B ˆ g Á 3 4 Ë A A The computer program called GATEOP was developed to assist the irrigation project engineer in analzing the stead state gate operation problem. Model calibration and verification Six main regulators which are the entrance to six zones of water master, Mun Bon irrigation project, are selected for the stead state gate operation modeling. Those regulators are (see Figure 5.) : - Irrigation Outlet - Head Regulator of Right Main Canal (RMC (HR)) - Head Regulator of 9R-LMC (9R-LMC (HR)) - Check Regulator at Km..000 of LMC (LMC (CH-)) - Head Regulator of 38R-LMC (38R-LMC (HR)) - and Check Regulator at Km of 38R-LMC (38R-LMC (CH-3)). The discharges and the water level upstream and downstream of each regulator were measured on dail basis. The field data of the regulators and the canal sections including gate length (L), gate sill elevation (ELEVS), canal bed elevation downstream of the regulator (ELEVB), full suppl level (FSL), maximum design discharge (Qmax), canal bed slope (s), bed width (b) and side slope (z) were investigated. The discharge coefficients of each regulator were obtained from field calibration (RID, 997 ; Roongsri, 999). The design manning s roughness coefficients (n) of the canal were initiall used in the model, but the values were adjusted in order to obtain the satisfactoril water level calculation. The calculated gate opening (Go) and other parameters such as and h s were statisticall compared with the actual values using t-test. Finall, the accurac to control the discharge of the 6 main regulators was determined. RESULTS AND DISCUSSION Field calibration The discharge through the irrigation outlet was measured at different openings for 30 times during Jul 996- Februar 998. The average discharge coefficient (C d ) of the Irrigation outlet is Similarl the other 5 main regulators were calibrated under field conditions. The parameters of the calibration curve of the 5 regulators are shown in Table. It can be seen that the submerged flow discharge coefficient (C s ) is highl related to hs Go and the free flow discharge coefficient (C d) is also highl related to Go. Model test The statistic analsis (t-test) was performed to compare the mean values of the GATEOP calculated gate operation parameters (, hs and Go) with the actual values. It is found that the calculated values are not significantl different from the actual values at 0.0 significant level. Finall, the GATEOP was actuall tested for the gate operation of Mun Bon irrigation sstem during June-November 998. The operation test covered the normal operating range of most regulators as shown in Table. The result shown that the GATEOP calculated discharge of the 6 main regulators has the error of ± 0%, which is acceptable for field operation. Although the program GATEOP was specificall developed for Mun Bon irrigation sstem, it can be applied to an free flow and submerged flow gate operations which have similar configurations. Some modification in the computer code is needed if the gate configurations are different.

6 90 Kasetsart J. (Nat. Sci.) 35 () CS0 LMC(CH.DROP-37) CS9 CS6 38R-LMC(HR) 38R-LMC(DROP) CS3 38R-LMC(CH-3) CS4 38R-LMC(CH.PIPE-4) LMC(CH.PIPE-36) Zone 4 Zone 5 CS7 LMC(CH.DROP-3) CS7 Zone LMC(CH-) CS5 LMC(CH-9.0) CS4 LMC(CH-6.88) 9R-LMC CS 9R-LMC(HR) Zone 3 Smbol: CS Canal Section Main Regulator U/S or D/S Regulator Discharge Monitoring Point LMC CS3 LMC(HR) CS RMC(HR) Zone 6 RMC CS3 CS3 RMC(CH.PIPE-) Wastewa Zone CS Irrigation Outlet Mun Bon Dam Figure 5 Location of the 6 main regulators and other regulators in gate operation of Mun Bon irrigation sstem.

7 Kasetsart J. (Nat. Sci.) 35 () 9 Table The calibration curve parameters of the 5 regulators. Regulator a b R () Submerged Flow [ hs Go = ac S b ] LMC (CH-) R-LMC (HR) R-LMC (CH-3) RMC (HR) () Free Flow [ Go = ac d+b] 9R-LMC (HR) Table The percentage error in discharge control at the 6 main regulators. Regulator Range of Range of target Actual % Error of Observation gate opening discharge discharge discharge period (m.) (m 3 /s.) (m 3 /s.) control Irrigation Outlet Jun.5,98 - Nov. 8, 98 LMC (CH-) Sep.4, 98 - Nov. 9, 98 9R-LMC (HR) Aug.4, 98 - Nov. 6, 98 38R-LMC (HR) Sep.5, 98 - Nov. 0, 98 38R-LMC (CH-3) Sep.5, 98 - Nov. 0, 98 RMC (HR) Aug.4, 98 - Nov., 98 CONCLUSION The stead state gate operation model and the program GATEOP were developed under the assumption that the gate was operated under the stead state conditions. The check regulator has to control the water level upstream at the full suppl level. The field calibration must be done comprehensivel in order to get the accurate and reliable flow parameters. The gate operation test shown that the error in controlling the discharges of the 6 main regulators of Mun Bon project during June-November 998 is less than ± 0%. LITERATURE CITED Ilaco/Empire M&T. 986(a). Water management and O&M report no.5 : water allocation scheduling and monitoring at project level, supporting document 5.5-general program description (revised). Mae Klong Irrigation Project, Roal Irrigation Department, Bangkok. 60 p. Ilaco/Empire M&T. 986(b). Water management and O&M report no.5 : water allocation scheduling and monitoring at project level, supporting document 5.6-computer operator s manual (revised). Mae Klong Irrigation Project, Roal Irrigation Department, Bangkok. 09 p.

8 9 Kasetsart J. (Nat. Sci.) 35 () Molle, F. and K. Pongput NAGA version.0 : Documentation. DORAS Project, Kasetsart Universit, Bangkok. 40 p. Roongsri, S Development of GATEOP program for operation control structure of Mun Bon Dam, M.Eng. Thesis. Kasetsart Universit, (In Thai). Roal Irrigation Department Water Allocation Scheduling and Monitoring Program : WASAM for Windows, Version.. Ministr of Agriculture and Agricultural Cooperatives, Bangkok. 88 p. Roal Irrigation Department Technical Report No.3 : Operation and maintenance, Mun Bon Rehabilitation Project. Facult of Engineering, Kasetsart Universit, Bangkok. 33 p. Tienchai, S Monitoring and evaluation of water allocation in the upper greater Chao Phara Irrigation Project b using geographic information sstem. M.Eng. Thesis. Kasetsart Universit, Bangkok. (in Thai). Vudhivanich, V., J. Kaewkulaa, P. Sopaphun, W. Suidee, and P. Sopsathien Development of water allocation strateg to increase water use efficienc of irrigation project. Kasetsart J. (Nat. Sci.) 34 : Received date : /03/0 Accepted date : 30/03/0