Gross command area (or GCA) is the total area which can be economically irrigated from irrigation system without considering the limitation on the quantity of available water. It includes the area which is, otherwise, uncultivable. For example, ponds and residential areas uncultivable area of gross command area. An irrigation canal system lies in a doab (i.e., area between two drainages), and can economically irrigate the doab. It is, obviously, economical to use the irrigation system to irrigate across the two drainages. Thus, the boundaries of the gross command of an irrigation canal system are fixed by the drainages on outer side of the irrigation canal system.
The area cultivated land in the gross command of an irrigation system is called curable command area (CCA) and includes all land of the gross command on which cultivation possible. At any given time, however, all the cultivable land may not be actually under cultivation. Therefore, sometimes the CCA is divided into two categories: cultivated CCA and cultivable but be cultivated CCA.
Intensity of irrigation is defined as the percentage of CCA which is proposed to be annually treated. Till recently, no irrigation system was designed to irrigate all of its culturable in and every year. This practice reduces the harmful effects of over-irrigation such as inter logging and malaria. Also due to the limitations on the quantity of available water, it is referred to provide intensive reaction of a smaller area. The intensity of irrigation varied between 40 percent to 60 percent will recently. This needs to be raised to the raised to the range of 100 percent to 180 percent by cultivating of CCA for more than one crop in a year and through improved management of the string system. Future projects should be planned for annual intensities of 100 percent to 180 percent to percent depending on the availability of total water resources and land characteristics.
The culturable command area multiplied by the intensity of irrigation (in fraction) gives actual area to be irrigated. The water requirements of the controlling crops of two crop as may be quite different. As such, the area to be irrigated should be calculated for each season separately to determine the water requirements.