Chapter 4: CALCULATE the WATER REQUIREMENT of the SYSTEM4.1 the purpose, meaning and content of the calculated4.1.1 purposeWater supply for agricultural irrigation is one of the important problems of agricultural production. Excess water crops decline, in contrast to lack of water the plant can not grow. Therefore the irrigation water supply problems is of paramount importance in the planning design of irrigation systems.In an irrigation system in the intra coastal Ha-Thanh Tri, Hanoi water supply objects mainly for shallow plants, so we need to determine:-Coefficient of irrigated crops. -Establish a process of sugar water supply coefficient with precipitation model selected, corresponding with a kind of known water supply and drought regime.4.1.2 the meaningThe calculation of irrigation mode for both systems in order to determine a reasonable size scale of the irrigation water supply, ensure the technical and economic requirements.4.1.3 calculation contentTo determine irrigation regime for the whole system we need to perform the following: -Coefficient of irrigated for crops: + Time watering (watering day); + Irrigation Levels each (m): is the amount of irrigation water per unit area of crops (unit: m3/ha); + Number of times watered during the growth of the tree; + The irrigation time every time (t): watering duration is as watered each time (day); + Total irrigation Level (M): by the total irrigation levels each; + Coefficient of irrigated (q): is the irrigation flow per unit area; (l/s-ha) Where: m: irrigation Levels each (m3/ha); t: watering duration (days) -Coefficient for each irrigation systems and irrigation schemes. 4.2 calculate evaporation surface of paddy field In the area of cultivation always occurs the process of evaluating the water due to evaporation. The water caught Hoi face rice include: -Evaporated Wage gaps; -Evaporation through the leaf stems help for metabolic processes, the amount of water is in the non-root from arable land. Evaporation surface of paddy fields for any plant would be determined according to the general formula:Etc = Kc. ET0Of which: ETC-evaporation calculated cells thựcc paddy field surface; ET0-reference evaporation (evaporation), calculated according to a formula based on the results of strictly defined conditions; KC-crop coefficient, depends on plants and growth stage of the crop is determined empirically.A number of methods to determine the ETo: -Marine target methods (Lysimeter). Penman-Monteith-method. -The Penman method. -The method of Blaney-CrriddleIn this thesis, I use evaporated under the formula of the modified Penman.Paddy field surface evaporation ET0 formula the modified Penman
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