(A) U.S. water conservation measures
In the United States of America's development and utilization of water resources in the main measures taken include: reduce water consumption and loss, rational water use, water conservation. Including: protection of water sources, prevent soil erosion; water reuse, focusing on urban sewage treatment, and then as an irrigation water source; regulation of river runoff; breeding of drought-resistant varieties; diversion of water to recharge the groundwater; reduce evaporation, the application of plant growth regulators; adjust the types of crops and market supply and so on. Currently, the United States to develop water-saving irrigation agriculture mainly using advanced water-saving irrigation technology and agricultural technology combined to replace the traditional single surface irrigation technology, farmland irrigation water use efficiency has reached 70-80%.
(1) Water Conservation Measures in the City of Tucson, USA
Tucson is located in the south-central part of Arizona, with hot summers and temperatures often exceeding 37.8 degrees Celsius. The City's peak water use is determined by the hot summer months. The city receives an average of 245 millimeters of precipitation per year, about half of which occurs during the summer months, while the average annual evaporation ranges from 1,524 to 1,778 millimeters.
Of the many categories of water users at the Tucson Water Works, some are seasonal in nature: winter water use is minimal and steady; summer water use is high and peaks with temperature and rainfall conditions.During the summer of 1974, Tucson experienced the hottest dry season in its history, and the city's wells were no longer able to meet the peak water use, and the system experienced localized section The water system was shut down in localized areas and water delivery pressure dropped. The City of Tucson cut back on peak water use in order to provide regular water deliveries and use water regardless of the season. As a result of this program, all types of water users have gradually adjusted their outdoor water use, and total daily water use per person has dropped from 776.5 liters in 1974 to about 549.2 liters today.
(2) Rainwater Harvesting Systems for Residents of California, USA
The 1975-1977 drought in California, USA, created an urgent need to explore appropriate water supply options. Generally, the most feasible way to provide water to rural residents was to collect rainwater from roofs, store it in containers, and make it available for use. The collection of rainwater is sufficient to meet the low domestic water needs.
(2) Israel's water-saving irrigation measures
Israel is located in the arid and semi-arid desert area, the rainfall in the north of 700-800 mm, the central 400-600 mm, and only 25 mm in the south. in order to overcome the problem of insufficient rainfall, Israel vigorously develop irrigated land. At present, of the 437,000 hm2 of cultivated land, 193,000 hm2 (about 44.2% of the total cultivated land) is irrigated, and the water used for agricultural irrigation amounts to 1.18 billion m3 per year, of which 900 million m3 is potable water. Agricultural irrigation methods are pressure irrigation, mainly drip irrigation and sprinkler irrigation, with water utilization rates of up to 95% and 80%, respectively, and all of them are computerized, utilizing water sensors to automatically regulate irrigation, including irrigation time, frequency, interval, and irrigation volume. According to Israel's water law, all water within the country is state-owned and managed by the Water Commission, including the formulation of policies, the determination of water use quotas and the formulation of water resources development plans. In order to encourage farmers to conserve water, on the one hand, farmers are required to pay a water fee, and on the other hand, it is stipulated that the price of water for the second half of the quota within the quota is higher than the first half. At present, the main direction of research in the irrigation industry is to develop non-potable water resources, such as wastewater, flood water, saline water, etc., to ensure the continuous increase of water for agriculture.
In the early 1990s, sprinkler and drip irrigation technologies were applied to 25% and 75% of the country's planted area, respectively. Sprinkler and drip irrigation are generally used for farmland and lawns and are highly automated, all computerized, with each central computer controlling dozens or even hundreds of hectares of land around it. Drip irrigation technology has been widely used throughout the country. The application of sprinkler and drip irrigation has greatly improved the utilization of water resources, so that the amount of water used for irrigation per hectare of land has been reduced by 1/3. Moreover, 70% of the country's wastewater is treated for agricultural irrigation.
( iii) Australia's water conservation measures
Australia has 70% of the area with rainfall below 500 millimeters, which is prone to drought. The country has few surface water sources, with an average annual runoff of only 345.4 billion cubic meters. Although groundwater is abundant, 60% is artesian well areas, with only 1.76 million square kilometers of water available. Australia is constantly adopting new water-saving irrigation methods. Burying 12-centimeter drip tubes into the ground to drip irrigate water and fertilizer solutions directly onto the roots of tomatoes and other crops not only saves a lot of water and fertilizer, but also harvests 90% of high-quality vegetables, whereas traditional irrigation methods can only harvest up to 60%-70%, and this method of irrigation prevents excess fertilizer from polluting the waterways. Another example is in the orchard, spring defoliation on fruit trees do not water or less watering, inhibit the growth of fruit trees, into the summer is more irrigation to promote fruit growth. This method makes fruit trees grow short, do not need too much watering and pruning, but the fruit yield has increased. Tests have shown that it can save 20% of water and increase fruit production by 20%. Most orchards have adopted this measure.
(D) the former Soviet Union water conservation measures
The former Soviet Union joining **** and countries per unit of land area of water and per capita water distribution is extremely uneven, the figures gap up to dozens of times. The former Soviet Union has 11 trillion cubic meters of atmospheric precipitation, of which about 40% is converted into river runoff. However, the regional distribution is extremely uneven, in some developed regions, which account for 90% of the cultivated area and 80% of the industrial output, there are only 24% of the water resources of the entire former Soviet Union, while some of the southern regions, which have a huge demand for water resources, have only about 16% of the available water resources. In addition to these deficiencies, an important feature of the rivers of the former Soviet Union is that they are also unevenly distributed in time. In order to solve these deficiencies, the only way to solve the problem of severe water shortages was to realize water transfers from other basins through large diversion and transfer channels and to build many seasonal regulation reservoirs.
In order to rationalize the use of water resources, the former Soviet Union developed a series of water conservation measures: (1) the city sewage for three-stage treatment and then use; (2) the surface runoff treatment and then use (3) research on the use of industrial and mining enterprises of drainage water; (4) pumping pit water and industrial and mining areas of stratum water; (5) the development of coastal areas to make use of seawater; (6) some of the equipment to use air-cooling, do not use water-cooled; (7) increase the capacity of power generation unit; (8) strengthen water management and treatment; (9) adopt progressive water tariff system and so on.
(V) Measures for Water Conservation and Rationalization of Water Use in India
In many parts of India, surface water is more abundant than groundwater, but the supply of surface water in many channels is often erratic, and sometimes grossly insufficient, so that groundwater replenishment of surface water is becoming increasingly necessary. Groundwater replenishment of canals increases the availability of canal water, which can be used directly for irrigation during periods of low canal water supply or during canal closures for annual maintenance. In many areas, potential groundwater can be effectively combined with surface water for intensive irrigation.
In order to control rainwater runoff due to over-concentration of precipitation, India has adopted the practice of utilizing ponds in agricultural catchments to capture surface runoff and conserve rainwater in arid lands for supplementary irrigation during the dry season. This practice saves irrigation water and supplements the shortage of irrigation water during the dry season to ensure normal growth and stable, high crop yields.
In terms of irrigation technology, in India, in order to improve the utilization of water resources and prevent soil salinization, the irrigation method is required to be determined according to the depth of the regional water table. Due to seasonal imbalance in water availability, the research department has proposed a scheme of pumping large quantities of groundwater near rivers for irrigation before the onset of the rainy season so as to lower the water table and allow more infiltration of flood water during the rainy season. This requires rationing of water supply and recycling of irrigation before the dry season in an effort to conserve water resources.