Non monsoon flows of Indian rivers are declining
Recent evidence shows that monsoon flows in Indian rivers are almost unaffected, but the non-monsoon flows show a declining trend. This has manifested in the form of:
- Medium and small rivers originating from mountains, ponds, pools, forests or springs turning into seasonal rivers. Impact is wide spread
- Drying of rivers in the non-monsoon season
- Watershed, river linking, catchment treatment programmes or MGNREGA interventions may not resolve the situation
Why has this happened
Ground water (GW) is regarded as a reliable water source in India and continues to be used on a large scale for agriculture, drinking water supply in rural areas and in the industrial sector. This preference has resulted in over exploitation of GW. While near normal GW replenishment is generally attained in the monsoon, lack of proportionate recharge mechanisms and excess exploitation of GW in the Rabi season has led to drying up of wells, tube wells and ponds. As a result, contribution by tributaries to major rivers has decreased leading to decreased flow of major rivers.
What needs to be done
It is important to understand the relation between water table and non-monsoon flow of rivers and initiate the flow revival movement through combined efforts by the government and the community that include:
- Balancing the water cycle for revival of non-monsoon flows in rivers
- Support works that help revive the natural functions and biodiversity revival of a river
- Facilitate activities for self purification of river waters
- Facilitate community managed systems at the local level for river water use
- Facilitate livelihood activities for people dependent on river water
What is the concept behind flow revival
The concept of flow revival can be easily understood by taking the example of a tree. A tree has three main parts – roots, stem and branches. Roots draw nutrients and water from sub-soil and transfer them to the stem and branches. When water around the roots is exhausted, the supply ends and tree dries up.
Same is the story of a river. It also has three main parts – tributaries, main stem and delta. In the non-monsoon season, tributaries collect GW from sub-soil and transfer the same to the Main River. The Main River, in turn, transfers the same to the delta. The role of tributaries, in the non-monsoon season is to hand over GW to the Main River. In the non-monsoon season, when GW supply stops, the tributaries dry. Reduced supply reduces the flow in the Main River.
The real challenge for river revival is maintaining the continuous discharge of GW into the river. We know that in non-monsoon season, the river flows only because GW is discharged in the river. Discharge takes place only because the lowest point of the regional water table is above the river’s bed (which is the lowest point of the area). The moment it drops below river bed level, the discharge stops and therefore flow in the river ceases. Therefore the challenge of a perennial river is to keep water table above the bed level till next monsoon.
In the past, GW exploitation was meagre and therefore the water table decline was also meagre. These days GW exploitation has increased manifold. It has resulted in the drop of the water table proportionately. Optimum GW recharge is required to slowdown the process of decline of water table. If water table decline is managed, the flow can be sustained.
River revival philosophy in rocky and alluvial terrain is the same, but sub-surface storage capacities are different. Therefore, a slight difference lies in their respective treatment. This refers to water requirement of aquifers in different formations. Thus the flow revival in Main River must initiate from its tributaries. There is thus a need for a map which shows the Main River and its tributaries clearly.
What kind of maps are ideal for this purpose
For flow revival, map of that hydrological unit whose geographical area is appropriate for planning, execution and management and that which possesses the ability to yield results in a logical time frame is ideal. These can include:
- Basin map of Central Water Commission - These maps are very useful for location of dams and flood forecasting. Can be used when need arises.
- Maps of Central Ground Water Board - These maps are very useful for Hydrological project. Not useful for revival of flow.
- Maps of National Watershed Atlas - Map of the fifth unit (Watershed- average area one lakh hectare) of National Watershed Atlas meets the requirement. It may therefore be accepted as an ideal unit. For better planning, execution and management, it should be further sub divided into smaller units.
- Milli-watersheds (sub-unit of WS) Average Area 5000 to 10,000 hectares.
- Micro-watersheds (sub-unit of MWS) Average Area 500 to 1,000 hectares.
Possibilities for flow revival
Sandy soil, low rainfall and harsh climate of the Thar Desert are not appropriate for revival of non-monsoon flows. However, in remaining areas of the country, due to adequate rainfall and favorable conditions, flow revival in non-monsoon season is possible. Chances in basins are better. Apart from this, original flow revival in the downstream of dams may need additional efforts.
At the same time, working plans of forest department need inclusion of suitable interventions for improvement of flow and its duration. Continuous monitoring is essential for assessing improvement in the quantity and duration of non-monsoon flows and also where rivers leave forest areas and enters into revenue areas.
Status of GW recharge and efforts
The CGWB issued Master Plan in 2013 for Artificial Recharge. According to this Master Plan, only 9, 41,541 sq. km area lacks normal recharge and needs artificial recharge. Current situation reveals that areas where replenishment is adequate, rivers are facing decline in non-monsoon flow. It indicates that additional efforts are needed everywhere.
Status of water availability in India
Water availability in India shows that:
- Total rainfall – 4000 lakh hect meter
- Total Run-off – 1963 lakh hect meter
- Water allocated for dams – 690 lakh hect meter.
- Unused run-off – 1273 (1963-690) lakh hect. meter
- GW reserves – 398 lakh hect meter
- Current use of GW – Slightly more than 245 lakh hect meter
Thus, if slightly more than 10% (127 lakh hect meters) of balance run-off (1273 lakh hect meters) is used for artificial recharge, the problem can be solved. It is not possible to recharge entire 127 lakh hectare metre run-off in one year. So it has to be done in steps such that situation improves every year. For this, we need a river manual and campaign. Planning and implementation should be done keeping in mind the properties of the river basin.
Strategies for flow enhancement
Flow enhancing interventions can be grouped in following two categories -
- Scientific interventions
- River Water Management with social consent
Interventions that influence flow enhancement should be undertaken keeping in mind the following natural characters and desired calculations-
- Geology and structural features
- Zoning of the unit
- Drainage pattern and drainage density
- Area of the unit
- Shape of the unit
- Slope of the unit
- Other, if any
Observations and calculations
For flow revival, it is necessary to determine following components:
- Natural indicators
- Average annual rainfall run-off
- Monsoon recharge
- Non-monsoon flow in the river and its relation with decline of water table
- Factors responsible for decline of water table and their quantification
- Quantity of water required, its duration and source of availability
- Proportionate recharge (During rain and after rainy season)
Few practical suggestions
It is important to ensure:
- Conjunctive use of Surface Water (SW) and Groundwater (GW) – balance in use
- Use designs that fulfill natural responsibilities of a river vis-à-vis meet requirements
- Focus on Organic/traditional/natural agriculture
- Develop properties that enhance moisture retention in the soil
- Develop and use indigenous seeds whose water requirement is low and yield is adequate
- Focus on water efficiency
- Sprinkler irrigation
- Focus on efforts to maintain good water quality
Water management with community consent
Under present conditions, it is very difficult to revive non-monsoon flows and ensure its sustainability only through technical interventions. It is therefore desirable to manage it with community support and maintain:
- Balance between demand and supply
- Sustain environmental flows
- Encourage wise use
- Reduction in stage of pollution
- Improvement in water availability. Jal Swaraj.
- Availability of environmental flow
- Revival of biodiversity
- Revival of naturally self cleaning capabilities of the river
- Reduction in water borne diseases and having healthy communities
- Employment generation for river dependent communities
- Development of balanced and safe model
- Improved water availability in ponds, wells and tubewells
- Reduction in water scarcity and migration
- Reduction in pressure on metros for meeting basic amenities and employment of rural population
- Many other direct and indirect benefits
About the author: K. G. Vyas is a geologist and a well-known writer on environmental issues. He has served as a consultant for the Rajiv Gandhi Drinking Water Mission in Madhya Pradesh.
Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the policy or position of India Water Portal.