|WATER HARVESTING IN POOLS AND CISTERNS
Definition characters description and diffusion
Water is the most precious underground resource: water dripping from walls, seeping out from the rocks, forming puddles. In some caves, vapour-laden air caused by the heat coming up from the magma under the earth’s crust are condensed along the walls to produce water.
General characters description and diffusion
In prehistory, seeping water, as well as water dripping from stalactites was collected into pools carved out under the stalactites inside specially made cavities. Caves kept a constant temperature throughout the year and were the ideal shelters for human beings and animals, for the storage of grain and mainly of water.
It is a very old traditional method to collect water in the arid and semi-arid areas. For instance, in most counties in central Gansu Province and some parts of Ningxia of China, annual rainfall varies from 150 mm to 250 mm and mostly concentrates in the rainy season from July to September. The sowing season and growing season from March to the end of June are the driest seasons of the year. Available water resource is limited and crop cultivation is mainly the rain-fed farming type and the yield is determined by the volume of runoff harvest and the storage of water kept in the artificial mud-made water pool underground or small sub-soil water reserving reservoir.
Even today, farmers and herdsmen households are used to practice these methods in central arid provinces in China. Normally, each family has to dig three or four small sub-soil water reserving reservoirs to keep sufficient water. The underground mud-made water pool and small sub-soil water reserving reservoirs are 10 metres in depth and 3-5 metres in diametre. The low part of the pool and reservoir, in a height of 3-5 metres, is cemented with Gaoling mud or the red earth to avoid infiltration
Advantages and sustainability
Water harvesting in pools and cisterns is beneficial because it is a source of water that is available all year round. It also takes place in a setting that is ideal for human activity in the cold of the winter or the heat of the summer.