4　Analysis of Calculation Results

By using the constructed water resources supply and demand balance mode,the water supply and demand balance of Jingnan river network was calculated,and the change rule of every irrigated area'water deficient ratio and probability of irrigation were analyzed.

4.1　The water shortage rate of different irrigation districts in different level years

The shortage ratio of Paifangkou irrigation district(PFKID),Babao irrigation district(BBID),Dongfengzha irrigation district(DFZID),Nanhaiyuan irrigation district(NHYID),Donggangyuan irrigation district(DGYID),Caozu irrigation district(CZID),Xingxueyuan irrigation district(XXYID),Guanjiapu irrigation district(GJPID)and the Lianxinyuan irrigation district(LXYID)is low,but that of other irrigation districts is all high.And the water shortage rate of all the irrigation districts(except the Paifangkou irrigation district(PFKID))show an increasing trend over time,which mainly due to the development of irrigation technique,the increase of utilization coefficient of irrigation water and the change of river water level and flow rate.Furthermore,the downstream of the Ouci River,the Songzi River and the Hudu River are the main water shortage area,and the water shortage in Ouci River is especially serious.

4.2　Irrigation guarantee rate of irrigation districts in different level years

(1)In general,the irrigation guarantee rate of Paifangkou irrigation district(PFKID),Lianxinyuan irrigation district(LXYID)and Nanhaiyuan irrigation district(NHYID)is relatively high.The irrigation guarantee rate of other irrigation district s,however,is too low to meet the demand of irrigation.

(2)The irrigation guarantee rate of Babao irrigation district(BBID),Dongfengzha irrigation district(DFZID),Donggangyuan irrigation district(DGYID),Mishi irrigation district(MSID),Jingjiang irrigation district(JJID),Nanwuzhou irrigation district(NWZID),Guanjiapu irrigation district(GJPID)and Diaodong irrigation district(DDID)in status quo year is high,whereas that in planning year is low.And the irrigation guarantee rate of other irrigation districts,both in the status quo and planning years,is low,which cannot meet the irrigation demand.

(3)The trend of irrigation guarantee rate's changing with time:because of the implement of water-saving reform of irrigation districts,the irrigation guarantee rate of Paifangkou irrigated district(PFKID),Lianxinyuan irrigation district(LXYID)and other irrigation districts that take the Yangtze River as the water source,increases with the passing of time;the irrigation guarantee rate of the irrigation areas with three rivers in Jingnan as the main water sources,on the contrary,deceases with the passing of time,which is influenced by the reduce of split flow to three outlets.

Fig.4　The water shortage rate of different irrigation districts in different level years

(4)The irrigation guarantee rate is generally calculated by the unit of irrigation district.But for the irrigation districts with multi-water sources,the irrigation guarantee rate of the whole irrigation area cannot reflect the problems of a certain water source or water source project.To handle this problem,the irrigation guarantee rate of irrigated subarea with different water sources in a irrigation district was determined(Table 1).Table 1 shows that the Paifangkou irrigation district(PFKID),Donggangyuan irrigation district(DGYID),and Diaodong irrigation district(DDID)mainly exist the problem of insufficient water supply of reservoir,and other irrigated areas mainly exist the problem of insufficient water supply and engineering shortage of the intake at three rivers in Jingnan.This method figures out the shortage link of every irrigation district,and it has important guiding significance to not only the construction of continue auxiliary projects and water-saving reform of the irrigation districts but also water resources allocation.

Table 1　The irrigated guarantee rate of irrigation districts in different years