6.1 Surface water Scenario
On an average, India receives about 4000 Cubic Kilometers (1 Cubic Km is same as one billion cubic meters, abbreviated as bcm) of precipitation every year. Precipitation means rainfall and snowfall together. As explained above, this precipitation is not uniformly distributed over the entire land area and varies from less 100 mm in Rajasthan to more than 12000 in Meghalaya. Of all the rain that falls on the land and mountains and forests, some evaporates back into the atmosphere, some percolates in the ground and some is used by the forests. The remaining that flows into the rivers is less than 50% on the total precipitation. The total annual water resources availability is estimated as 1869 bcm. The basin wise figures are as follows.
Basin-wise Surface Water Potential (All figures in BCM) | ||
Name of the River Basin | Average flow | Estimate Utilizable Flow |
Indus (up to Border) | 73.31 | 46.00 |
a) Ganga | 525.02 | 250.00 |
b) Brahmaputra Barak and others | 585.6 | 24.00 |
Godavari | 110.54 | 76.30 |
Krishna | 78.12 | 58.00 |
Cauvery | 21.36 | 19.00 |
Pennar | 6.32 | 6.86 |
East Flowing Rivers Between Mahanadi and Pennar | 22.52 | 13.11 |
East Flowing Rivers Between Pennar and Kanyakumari | 16.46 | 16.73 |
Mahanadi | 66.88 | 49.99 |
Brahmani and Baitarni | 28.48 | 18.30 |
Subernarekha | 12.37 | 6.81 |
Sabarmati | 3.81 | 1.93 |
Mahi | 11.02 | 3.10 |
West Flowing Rivers of Kutch, Sabarmati including Luni | 15.10 | 14.98 |
Narmada | 45.64 | 34.50 |
Tapi | 14.88 | 14.50 |
West Flowing Rivers from Tapi to Tadri | 87.41 | 11.94 |
West Flowing Rivers from Tadri to Kanyakumari | 113.53 | 24.27 |
Area of Inland drainage in Rajasthan desert | Negligible | Negligible |
Minor River Basins Draining into Bangladesh and Myanmar | 31.00 | Negligible |
Total | 1869.00 | 690.00 |
1. Hard-rock aquifers of peninsular India:
These aquifers represent around 65% of India’s overall aquifer surface area. Most of them are found in central peninsular India, where land is typically underlain by hard-rock formations. These rocks give rise to a complex and extensive low-storage aquifer system, where in the water level tends to drop very rapidly once the water table falls by more than 2-6 meters. Additionally, these aquifers have poor permeability* which limits their recharge through rainfall. This implies that water in these aquifers is non- replenishable and will eventually dry out due to continuous usage.
2. Alluvial aquifers of the Indo-Gangetic plains:
These aquifers, found in the Gangetic and Indus plains in Northern India have significant storage spaces, and hence are a valuable source of fresh water supply. However, due to excessive groundwater extraction and low recharge rates, these aquifers are at the risk of irreversible overexploitation.
Total groundwater Resources | ||
1. | Total Replenishable Ground Water Resource | 433 km3 |
2. | Net Annual Ground Water Availability | 398 Km3 |
3. | Annual Ground Water Draft for Irrigation, Domestic & Industrial uses | 245 km |
4. | Stage of Ground Water Development | 62 % |
System | Coverage | Ground Water Potential |
Unconsolidated formations - alluvial | Indo-Gangetic, Brahmaputra plains | Enormous reserves down to 600 m depth. High rain fall and hence recharge is ensured. Can support large-scale development through deep tube wells |
Coastal Areas | Reasonably extensive aquifers but risk of saline water intrusion | |
Part of Desert area– Rajasthan and Gujarat | Scanty rainfall. Negligible recharge. Salinity hazards. Availability at great depths | |
Consolidated/semi-consolidated formations - sedimentary, basalts and crystalline rocks | Peninsular Areas | Availability depends on secondary porosity developed due to weathering, fracturing etc. Scope for GW availability at shallow depths (20-40 m) in some areas and deeper depths (100-200 m) in other areas. Varying yields. |
Hilly | Hilly states | Low storage capacity due to quick runoff |
The groundwater behaviour in the Indian sub-continent is highly complicated due to the occurrence of diversified geological formations with considerable lithological and chronological variations, complex tectonic framework, climatological dissimilarities and various hydro-chemical conditions.
A perusal of past records reveal that there is a general decline in the water level as observed mostly in northern, north western and eastern parts of the country covering Uttar Pradesh, Rajasthan, Bihar, Jharkhand, West Bengal, Punjab and Haryana and in parts of Tamil Nadu and Andhra Pradesh. It also observed some rise in water level at isolated areas and is attributed to local causes or due to higher rainfall experienced in the area during the period of observation.
The assessment of the resources indicate that the replenishable Groundwater resource is estimated significantly high in the Indus–Ganga–Bramhputra alluvial belt in the North, East and North East India covering the states of Punjab, Haryana, Uttar Pradesh, Bihar, West Bengal and valley areas of North Eastern States, where rainfall is plenty and the aquifers found have high storage capacity and favor the recharge. The coastal alluvial belt particularly Eastern Coast also has relatively high replenishable groundwater resources while in western India, particularly Rajasthan and parts of northern Gujarat the annual replenishable groundwater resources are scanty as the region experiencing the arid climate. Similarly, in major parts of the southern peninsular India covered with hard rock aquifers, the replenishable groundwater recharge is less which is attributed to comparatively low infiltration and storage capacity of the rock aquifers. The Central Indian region is mostly accounted for moderate recharge.
Level of ground water development | Explanation | % of districts in 1995 | % of districts in 2004 | % of districts in 2009 | % of districts in 2011 |
0-70% (Safe) | Areas which have ground water potential for development | 92 | 73 | 72 | 71 |
70-90% (Semi-critical) | Areas where cautious ground water development is recommended | 4 | 9 | 10 | 10 |
90-100% (Critical) | Areas which need intensive monitoring and evaluation for ground water development | 1 | 4 | 4 | 4 |
>100% (Overexploited) | Areas where future ground water development is linked with water conservation measures | 3 | 14 | 14 | 15 |
7.1 Creation of Surface Storage
Large parts of the country are endowed with only 45 to 50 rainy days a year. Out of this also the major share of rainfall is concentrated in only a couple of days. Water resources development which received high priority in the successive five year plans initiated after independence has resulted in many achievements that are discernible. Many major, medium and minor water resources projects have been constructed during the past five-six decades. India ranks third in the World after China and USA in terms of number of dams. There are about 4850 completed large dams and another 250 are under various stages of constructions. All these projects have resulted in increasing the live storage capacity from 15.6 BCM at the time of independence to 253 BCM now. Projects under construction are likely to add another 51 BCM. Further 108 BCM is expected to be contributed by the projects under consideration. Storages held in these dams are an insurance against the vagaries of nature.
Major, Medium & ERM projects in India | ||||
| Major | Medium | ERM | Total |
Completed | 295 | 1018 | 140 | 1453 |
Ongoing | 176 | 170 | 66 | 412 |
Sub-Total | 471 | 1188 | 206 | 1865 |
Total | 1659 |
| ||
Irrigation through groundwater has been achieved, mainly through construction of 9.2 million dug wells and 9.1 million shallow tube wells.
Water Demand for Various Sectors | |||
Sector | Future Water Demand (BCM) | ||
| 2010 | 2025 | 2050 |
Irrigation | 688 | 910 | 1072 |
Drinking Water | 56 | 73 | 102 |
Industry | 12 | 23 | 63 |
Energy | 5 | 15 | 130 |
Others | 52 | 72 | 80 |
Total | 813 | 1093 | 1447 |
(Ref: Assessment of Availability and Requirement of Water for Diverse Uses in the Country - 2000) | |||