2. The centralized surface water source protection zone for drinking water, habitats for rare aquatic organisms, spawning grounds for fish and shrimp, and feeding grounds for larvae and juveniles are Class II.
3. The centralized drinking water surface water source secondary protection areas, fish and shrimp wintering grounds, migration routes, aquaculture areas and other fishery waters and swimming areas are Class III?
4. General industrial water areas and recreational water areas that are not in direct contact with human body are classified as Class IV.
5. The waters required for agricultural water and general landscape are: Class V..
Surface water is accumulated by natural precipitation and accumulated snow over the years, and naturally loses to the ocean or disappears through evaporation and seeps into the ground.
Although the natural water source of any surface water system only comes from the precipitation in the catchment, there are still many factors that affect the total water volume of the system.
These factors include the water storage capacity of lakes, wetlands and reservoirs, soil leakage and the characteristics of surface runoff in this basin. Human activities have a great influence on these characteristics. In order to increase the water storage capacity, human beings build reservoirs and release water in wetlands in order to reduce the water storage capacity. Human reclamation activities and ditch construction have increased the quantity and intensity of runoff.
Extended data:
In order to promote the balance between supply and demand of water resources in a river basin, region or irrigation area, surface water and groundwater should be developed, utilized and managed reasonably and uniformly. In farmland irrigation, the main form of combined use is the combination of well and canal. Large-scale water diversion projects have been built in some areas, which are connected with the original well irrigation areas into a system; However, in some large gravity irrigation areas, due to the shortage of surface water resources, pump wells are built in the irrigation areas.
By combining surface water and groundwater, the following objectives can be achieved.
① Regulating and storing surface runoff. Using the water storage function of aquifer, excess surface water can be stored for use in dry season.
② Improve the quality of groundwater. Regulating and storing surface runoff water can dilute groundwater with high salt content. Some irrigation districts in Pakistan and Israel have used this method to reduce the salt content of groundwater. In the Heilonggang area of the Huang-Huai-Hai Plain in China, shallow mineralized groundwater has also been "ready for desalination". In the Netherlands, water with high temperature in summer is also reinjected into the ground, and greenhouse flowers and vegetables with high water temperature requirements are extracted for irrigation in winter.
③ Adjust the groundwater level. The construction of large reservoirs and irrigation areas has increased the supply of groundwater, led to the rise of groundwater level, and led to waterlogging and secondary salinization of irrigated land. In these areas, the development and utilization of groundwater can reduce the groundwater level, cooperate with surface drainage, and carry out comprehensive control of drought, flood and salinity; However, over-exploitation of groundwater will lead to the decline of groundwater level and increase the cost of well construction and pumping.
Long-term over-exploitation will form a large area of groundwater level decline funnel, leading to land subsidence and seawater intrusion in coastal areas. In this case, surface water can be introduced to reduce groundwater exploitation and replenish groundwater to adjust groundwater level.
The dynamic quantity of surface water is river runoff and glacier runoff, and the static quantity is expressed by the storage capacity of various water bodies. The world's surface water reserves are 24,254 trillion cubic meters, accounting for only1.75% of the global total water reserves; However, surface water bodies are constantly supplemented by atmospheric precipitation. After runoff generation and confluence, 43.5 trillion cubic meters of river runoff and 2.3 trillion cubic meters of glacier runoff flow into the ocean every year, accounting for 94.7% of the total 47 trillion cubic meters entering the sea, which plays a very important role in the global water cycle.
In addition, the inflow area produces 1.0 trillion cubic meters of river runoff every year, which flows into inland lakes and is consumed by evaporation. The form of surface water is closely related to climate. Of the global1490,000 square kilometers of land, about 62% are rivers, lakes and swamps, about 12% are covered by glaciers, and the remaining 26% are deserts and semi-deserts.