Irrigation systems in arid lands divert the discharge of a large river, such as the Nile, Indus, or Colorado, into a distributary system that allows the water to infiltrate the soil of areas under crop cultivation. Ultimately, such irrigation projects suffer from two undesirable side effects-salinization and waterlogging of the soil.
The irrigated area is subject to very heavy water losses through evapotranspiration. Salts contained in the irrigation water remain in the soil and increase in concentration-the process of salinization. Ultimately, when salinity of the soil reaches the limit of tolerance of the plants, the land must be abandoned. Prevention or cure of salinization may be possible by flushing down soil salts to lower levels by use of more water. This remedy requires more water use than for crop growth alone. Furthermore, when salts are flushed down to lower levels, they may enter the ground water body and contaminate it with toxic ions, such as nitrates.
Infiltration of large volumes of water causes a rise in the water table, any may ultimately bring the zone of saturation close to the surface-a phenomenon known as waterlogging. Crops cannot grow in perpetually saturated soils. Furthermore, when the water table rises to the point that upward movement under capillary action can bring water to the surface, evaporation is increased and salinization is intensified.
One of the largest of the modem irrigation project affected adversely by salinization and waterlogging lies within the basin of the lower Indus River in, West Pakistan. Here the annual rate of rise of the water table has averaged about one foot (0.3m), while the annual increased in land areas adversely affected is on the order of 50,000 to 100,000 acres (20,000 to 40,000 hectares).
Locals hypothesize that the legacy of Italian blood and culture in Cologne, colonized by the Romans more than 1500 years ago, makes the people more jovial and lighthearted. Cologne is the largest city on the Rhine.
Kolsch is not only the dialect spoken here but, also the name of their own top-fermented beer. There are more than 4,000 pubs, restaurant's and brewery taverns in Cologne.
Unlike many of the world's large cities, Cologne, with a population of over a million, gets better every day, there are more things to do and see, more new and innovative buildings... more
Travel is an opportunity to learn, whether geography, languages, history or other subjects.
Cologne is situated on the beautiful Rhine River.