Optimal water store control of ponds in irrigation district based on stochastic precipitation simulation

Abstract: Ponds are widely distributed throughout Southern China. However, ponds have not fully played their role because of the shortage of the feasible optimal operating schemes for ponds. The main purpose of this paper was to determine an optimal operating scheme of ponds through mathematical statistics method and simulation. Firstly, distribution of a ten-day rainfall in the past 30 years (1981-2012) was fully analyzed. Then the Monte Carlo method was used to simulate the ten-day rainfall in the next 500 years. After that, a model was constructed to calculate the water quantity balances in fields, ponds and reservoirs, with the goal of maximizing the yield per unit area. Based on their built-in flexibility for storing water and their timely and reliable water supply, ponds were firstly used. Then reservoirs and ponds were adopted to irrigate crops in irrigation peak periods. The model was to simulate the different operating rules of ponds in each year, and the optimal operating rule of ponds for each year was selected by using orthogonal experiment method. At last, the operating rule under different typical year was attained by analyzing the above results. The methodology was applied to the Yangshudang reservoir irrigation district, which is a sub-region of Zhanghe irrigation district, to demonstrate its applicability. It features a subtropical monsoon climate with an average annual rainfall of 862.8 mm. Although the Yangshudang reservoir with the active storage capacity of 13.5 million cubic meters is the main irrigation water source, there are more than 3480 ponds with the storage capacity of 3.7295 million cubic meters that can support supplementary irrigation. From the results, in normal year, ponds should reserve 10% in mid-June, reserve 20% in mid-July, reserve 30% in late May, early June, late June, early July, and could be used up in the other ten-day. In dry year, ponds should reserve 10% in late May, reserve 20% in early June and late June, reserve 30% in mid-June, early July and mid-July, and could be used up in the other ten-day. In special dry year, ponds should reserve 10% in late May and mid-July, reserve 20% in late June, early July and late July, reserve 30% in early June and mid-June, and could be used up in the other ten-day. Comparing the probability to ensure basic yield, the irrigation effect was obvious under the optimal operating rule. In normal year, the probability of relative yield greater than 0.6 was increased by 2.38%. In dry year, the probability of relative yield greater than 0.6 was increased by 8.80%. In special dry year, the probability of relative yield greater than 0.6 was increased by 11.29%. This study is of great significance for reservoir-pond co-regulation and improving the irrigation effect.