The Great Indian Water Divide in Aravalli distributes the river water of this region into the Bay of Bengal and the Arabian Sea. The rivers flowing in the west and south of Aravalli ranges, including Mahi, Som, Jokham and Sabarmati drain the water into the Arabian Sea. On the other hand, rivers flowing to the east, including Chambal and its tributaries, join the Bay of Bengal. There are also inland rivers like Luni and Ghaggar which drain out in the Rann of Kutch and Thar Desert respectively.
Rivers in Rajasthan are mostly seasonal, but this fact explains little because a river is not just the surface flow, evident to a naked eye. All the rivers and their floodplains in this desert state are vast grazing grounds supporting millions of livestock. These unseen rivers also recharge the groundwater making well irrigation possible.
Modern-day development activities, however, are putting an enormous pressure on them. If deforestation has reduced the water flow, rampant sand mining has affected the water retention and seepage into subsurface channels. Aravallis also has large number of marble mines and processing units. While digging operations extensively damage the environment, discharge of a large amount of slurry by processing units also blocks water channels. Industrial and domestic wastewater has further affected the quality and biodiversity of rivers. Reduced water flow is in turn making it easier for the encroachers to infringe upon these riverbeds.
This has also put most dams in the state in critical state as they are not getting water as per their designed depend abilities. This disrupts the water resources planning of the state and execution of contingency plan every year1.
Only two river basins (Chambal and Mahi) are perennial. In the recent past, many perennial rivers in these two basins became seasonal due to over-abstraction of groundwater from the catchment area of the rivers rendering reduced water table leading to reduced or nil base flow.
Rajasthan connects strongly with water through its heritage of lakes, ponds, stepwalls, dug wells and Tankas (underground tanks). Rivers thus have a limited presence in cultural and mythological landscape and are mostly seen as means of irrigation along their stretches. The region around Aravalis comprising south east Rajasthan has a stronger connection with rivers than the drier north-western and central plains. In fact, many of the forts had rivers as their natural defence against enemy attacks.
As per the latest estimates, the total internal surface water resources of Rajasthan are estimated at 25.93 BCM1 (21.71 BCM at 50% dependability and 14.12 BCM at 75% dependability) of which about 16.05 BCM are considered ―economically exploitable at 50% dependability. The state is allocated in addition, some 17.88 BCM in trans-boundary or inter-state river waters. The renewable groundwater resource (fresh, dynamic component) is placed at 10.61 BCM per year (10.79 BCM as of March 2009). The static reserve of fresh and saline groundwater reserves have been reported to be 32.9 BCM and 29.7 BCM respectively.
There are six major river basins in the State. Banas basin which is the largest drains out 45,833 Sq km. Luni basin, which comes next, drains out 37,363 Sq km. Chambal Basin, drains out 31,360 Sq km; Mahi basin drains out 16,985 Sq km, Banganga basin drains out 8,878 Sq km and Sabarmati drains out 4,164 sq km. There are more rivers like Sahibi, Ruparel and Ghaggar which have smaller catchment areas besides several streams which feed the bigger rivers. (Source: Water Resources Department, Rajasthan)
Five of these rivers can be further divided into sub-basins as given below:
- Luni Basin –Luni, Sukri, Redeye, Mithari, Bandi, Khari, Jawai, Guhiya and Sagi, and Jojari.
- Banas Basin – Banas, Berach, Dain, Gudia, Kalisil, Khari, Kothari, Mashi, Morel, Sudra. Indravati, Sabari, Pranhita, Lower Godavari, and Wainganga sub basin;
- Chambal Basin – Banas, Chakan, Chambal Downstream, Chambal Upstream, Kalisindh, Kunnu, Mej and Parwati.
- Mahi Basin- Anas, Bhadar, Jakham, Moran, Som and Mahi.
- Sabarmati Basin- Sabarmati, Sei, Vatrak and Wakal
Source: Study On Planning Of Water Resources Of Rajasthan