Explanation:

The Ghaggar-Hakra River is an intermittent, endorheic river in India and Pakistan that flows only during the monsoon season. The river is known as Ghaggar before the Ottu barrage and as the Hakra downstream of the barrage.
The basin is classified in two parts, Khadir and Bangar, the higher area that is not flooded in rainy season is called Bangar and the lower flood-prone area is called Khadar.
Nineteenth and early 20th century scholars, but also more recent authors, have suggested that the Ghaggar-Hakra might be the defunct remains of the mythological Sarasvati of the Rig Veda. Recent geophysical research does not support this idea. It shows that the Ghaggar-Hakra system was not sourced by the glaciers and snows of the Himalayas, but rather by a system of perennial monsoon-fed rivers. Late Holocene aridification subsequently reduced the Ghaggar-Hakra to the seasonal river it is today.
Association with the Harappan civilization
Some estimate that the period at which the river dried up range, very roughly, from 2500 to 2000 BC, with a further margin of error at either end of the date-range. This may be precise in geological terms, but for the mature Indus Valley Civilization (2600 to 1900 BC) it makes all the difference whether the river dried up in 2500 (its early phase) or 2000 (its late phase). By contact with remnants of the IVC like the Cemetery H culture, legendary knowledge of the event may have been acquired.
In a survey conducted by M.R. Mughal between 1974 and 1977, over 400 sites were mapped along 300 miles of the Hakra river.[34] The majority of these sites were dated to the fourth or third millennium BCE.
S. P. Gupta however counts over 600 sites of the Indus civilization on the Ghaggar-Hakra river and its tributaries. For ereason stated above, only 90 to 96 Indus Valley sites have been discovered on the Indus and its tributaries (about 36 sites on the Indus river itself.) V.N. Misra states that over 530 Harappan sites (of the more than 800 known sites, not including Late Harappan or OCP) are located on the Ghaggar-Hakra. The other sites are mainly in Kutch-Saurashtra (nearly 200 sites), Yamuna Valley (nearly 70 Late Harappan sites) and in the Indus Valley, in Baluchistan, and in the NW Frontier Province (less than 100 sites).
Most of the Mature Harappan sites are located in the middle Ghaggar-Hakra river valley, and some on the Indus and in Kutch-Saurashtra. However, just as in other contemporary cultures, such as the BMAC, settlements move up-river due to climate changes around 2000 BCE. In the late Harappan period the number of late Harappan sites in the middle Ghaggar-Hakra channel and in the Indus valley diminishes, while it expands in the upper Ghaggar-Sutlej channels and in Saurashtra. The abandonment of many sites on the Ghaggar-Hakra between the Harappan and the Late Harappan phase was probably due to the drying up of the Ghaggar-Hakra river.
Painted Grey Ware sites (ca. 1000 BCE) have been found in the bed and not on the banks of the Ghaggar-Hakra river.
Because most of the Indus Valley sites known so far are actually located on the Ghaggar-Hakra river and its tributaries and not on the Indus river, some Indian archaeologists, such as S.P. Gupta, have proposed to use the term "Indus Sarasvati Civilization" to refer to the Harappan culture which is named, as is common in archaeology, after the first place where the culture was discovered.