Introduction

Fresh water resources since historic times have shaped the physio-biological features on earth with constant interaction with biotic (flora and fauna) and abiotic (terrain, minerals, chemicals, rock types etc.) resulting in the eco system functioning. Flow is a master variable in any river / stream catchment since it has direct impact on the aquatic biodiversity, river morphology, river connectivity, biotic life and water quality. Rivers, Streams and Wetlands need certain amount of water to support the aquatic health, ecosystem and biodiversity. The fresh water flows in terms of quantity and timing are essential to maintain the process and functioning of fresh water resource. The ecological integrity of river ecosystems depends on their natural dynamic character. Over exploitation of these fresh water resources to cater irrigation, power, agriculture, industrial and other societal needs have led to degradation of perennial resource turn intermittent/seasonal in India  and across the globe  altering the flow regimes hampering the physical, biological, hydrological functions and sustainability of resource. Based in the idea that the health of the river (water bodies) deteriorates if the flow is below a threshold the concept of minimum flow in rivers came into practice in 1970s, since then various studies have been carried out to understand the various elements of the natural flow. The concept of environmental flow was developed to understand, check the negative impact of large scale withdrawals of water from a natural system. These natural flows/ minimum flows are referred to as Environmental Flows that are necessary to maintain the health and biodiversity of water bodies, including rivers, coastal waters, wetlands and estuaries. The current Issue of Shayadri E News (Issue LXXXV) presents the ecological status of Cauvery river basin.

River Cauvery one of the 7 major rivers in India, having its significance in the south since the Puranas. The river is also known as Dakshina Ganga due to its sanctity, ability to cure skin disorders, services to mankind (such as food, agriculture, water source etc.), supporting numerous flora and fauna, etc. The river can be said to have geological history past the Himalayas when linked to the birth of Western Ghats, whereas the mythological history is past Ramayana (Skanda Purana). Originating at Talakaveri, Bramhagiri hills of Western Ghats, near Bhagamandala of Kodagu district of Karnataka State, Cauvery (Kaveri) flows east for distance over 750 km joining the Bay of Bengal at the Paziyar of Nagipattanm District, Tamil Nadu State. Cauvery river catchment spatially is spread across an area over 85300 square kilometers along the states of Karnataka, Kerala, Tamil Nadu and Union territory – Puducherry, of which Tamil Nadu encompasses about ~55.3%, followed by Karnataka with ~41.1%, Kerala with ~3.3% and Puducherry with ~0.2% of the catchment area. Population in the catchment has increased from 112 persons per square kilometer in 1901 to 452 persons per square kilometer in 2011.

The river is lifeline to people along riparian states since it is used to cater various domestic and agricultural demands, but improper practices such as over exploitation of water through intense agricultural activities for water intensive crops have led to depletion of both surface and sub-surface resources resource. It can be observed that irrigation lands have increased from 11453 sq.km in 1928 to over 28730 sq.km as on current, whereas the vegetation cover has drastically declined from 33% in 1965 to 18% in 2016. The catchment is dominated by water intensive crops such as paddy (variety of paddy), sugarcane, etc. which is inappropriate for the quantum of rainfall received. Rainfall in the catchment varies between 500 mm at the Plains to over 1000 mm at the Coast and over 2000 mm at the Ghats. In order to store runoff water there are nearly 98 dams/reservoirs (such as Mettur, KRS, Kabini, Hemavathi Harangi, Nugu, Emerald, Avalanche, Siruvani, Bhavani etc.) having live storage capacity of 287 TMC and numerous lakes and tanks in the catchment which are used for irrigation, power generation, etc.

Table I gives details of the water availability and water demand in the catchment across each of the riparian states.

Table 1: Water availability and demand in the catchment

Sl.no.	Description		Units	Kerala	Karnataka	Tamil Nadu	Puducherry	Basin
1	Catchment Area		Sq.km	2880.83	34936.80	47391.17	154.20	85363
			%	3.39	41.07	55.37	0.18
2	Length of River		Km	41.00	320.00	456.00	Delta	776
3	Population	1901	Number	185845	2782853	6616239	38880	9623817
		1911	Number	201226	2908352	7051111	40796	10201486
		1921	Number	208649	3011543	7264981	39906	10525079
		1931	Number	234392	3294931	7741150	41139	11311613
		1941	Number	268438	3696012	8746583	44126	12755158
		1951	Number	356537	4581965	10168222	51176	15157899
		1961	Number	475461	5542202	11244716	56465	17318844
		1971	Number	639036	6972389	13504325	65703	21181454
		1981	Number	814478	8962232	15619448	75282	25471439
		1991	Number	967716	10842857	17769656	84747	29664976
		2001	Number	1102453	12593792	19971075	92161	33759480
		2011	Number	1179200	14642518	22732461	100929	38655107
		2021	Number	1265657	1955661	25957876	110605	44749799
4	Vegetation Cover	1965 Dense	sq.km	966	8668	7876		17510
			%	33.5%	24.8%	16.6%		20.5%
		1965 Degraded	sq.km	78	8405	2202		10684
			%	2.7%	24.1%	4.6%		12.5%
		2016 Dense	sq.km	707.74	5062.72	5616.71		11387
			%	24.6%	14.5%	11.9%		13.34%
		2016 Degraded	sq.km	56.41	2345.78	1555.72		3958
			%	2.0%	6.7%	3.3%		4.6%
5	Irrigation	1928	sq.km		1193.40	6556.14
		1956	sq.km		2104.44	9348.57
		1971	sq.km		2713.41	11398.90
		Current*	sq.km		8497.00	20233.00
6	Reservoirs	Storage Structures	Number	4	57	37		98
		Gross Storage	TMC	13	157	160		316
		Live Storage	TMC	10	133	154		287
		Major Reservoirs		Kuttiyadi, Kottagiri,  Siruvani	Krishnaraja Sagara, Hemavathi, Kabini, Harangi, Nugu, Ygachi, Taraka	Mettur, Lower Bhavani,  Amaravathi, Upper Bhavani, Avalanche, Emerald
7	Water Usage as per Cauvery Tribunal Report	1901	TMC	0.1	73	430		503
		1928	TMC	0.1	73	432		505
		1956	TMC	2	146	537		684
		1971	TMC	5	171	573		750
		Current	TMC	5	171	573		750
		Proposed	TMC	209	410	642		1260
8	Average Rainfall	Annual	mm	1100	793	679		957
		South West	mm	781	445	233		467
		North East	mm	176	193	312		307
9	Average Rainfall During Drought	Annual	mm	932	650	554		785
		South West	mm	656	368	188		385
		North East	mm	149	156	251		248
10	Average Yield	Annual	TMC	111	348	325	2	786
		South West	TMC	98.5	238.0	81.2	0.2	418
		North East	TMC	7.8	72.0	220.1	1.6	302
11	Average Yield during Drought	Annual	TMC	84.6	245.6	203.2	1.1	535
		South West	TMC	76.2	177.0	49.2	0.1	302
		North East	TMC	5.3	45.7	141.2	1.0	193
12	Ground Water Recharge	Average Year	TMC	41	109	118	1	269
		Drought Year	TMC	32	69	72	1	173
13	Livestock Demand		TMC	0	4	5	0	9
14	Domestic Demand		TMC	2	30	45	0	78
15	Agriculture Demand	Scenario as Usual	TMC	62	529	585	5	1180
		Scenario 1	TMC	37	417	461	3	918
		Scenario 2	TMC	32	382	366	3	783
		Scenario 3	TMC	31	317	338	2	689
		Scenario 4	TMC	26	227	207	2	462
16	Total Demand	Scenario as Usual	TMC	64	563	634	5	1267
		Scenario 1	TMC	39	451	511	3	1004
		Scenario 2	TMC	34	416	416	3	869
		Scenario 3	TMC	34	350	388	3	775
		Scenario 4	TMC	29	261	257	2	549
17	Water Usage as per Cauvery Tribunal Report	1901	TMC	0	73	430		503
		1928	TMC	0	73	432		505
		1956	TMC	2	146	537		684
		1971	TMC	5	171	573		750
		Current	TMC	5	171	573		750
		Proposed	TMC	209	410	642		1260

 

Current Problems in the Basin.

1. Reduction in water retention capacity of catchment (evident from reduction in flow duration, flash floods, etc)
2. Reduction in the natural green cover catchments.
3. Unsustainable sand mining.
4. Inappropriate cropping pattern and inefficient water usage.
5. Decline in forest cover with increase in monoculture (sugar cane, tree plantations, tea, etc.)
6. Erosion in indigenous management system of tanks and the practice of growing summer crops (legumes, millets, etc.)
7. Erroneous judgement in water allocation based on water demand, rather than water availability

Suggestions/Recommendations

1. Improve green cover of the catchment with native vegetation species
2. Incentive based tree planting programs to farmers located in the buffer zones of streams and river
3. Restriction on over exploitation of sand.
4. Need for national water policy to ensure sustainable resources.
5. Appropriate Cropping Pattern
6. Desilting of Lakes and Reservoirs
7. Regular maintenance of Reservoirs
8. Practice Desilting in the basin and use of traditions framing practices
9. Silt for Agricultural fields, brick manufacturing,
10. Growing Pulses after desilting during summer
11. Leaving plants in the field itself as it gives nitrogen which helps to reduce consumption of fertilizers
12. Growing less water intensive variety of crops rather to improve the water use efficiency.
13. Insisting on growing millets, Pulses followed by legumes during dry season
14. Watershed management programs in the catchments of lake, stream and river.
15. Allocation of water based on water availability rather than demand/usage considering rainfall pattern with the changes in the climate due to global warming and other factors.
16. Social forestry/village forest of native species (fruit yielding) that can meet the biotic requirement

 

REFERENCE

Ramachandra T V , Vinay S, Bharath S and Bharath H A, 2020., Cauvery River: Land use dynamics and Hydrological Status, , ENVIS Technical Report 161, Sahyadri Conservation Series 90,  Environmental Information System,  CES, Indian Institute of Science, Bangalore