Keshav deshmukh

ROLE OF STORAGE IN RIVER REJUVENATION AND E-FLOWS

By

Keshav Deshmukh, General Manager (D&E) NHPC Ltd., Faridabad, India

NHPC Ltd.-OVERVIEW  NHPC Limited, a Govt. of India Enterprise, was incorporated in the year 1975

with an objective to plan, promote and organise an integrated and efficient development of hydroelectric power in all aspects.

 NHPC has become the largest organization for hydropower development in

India with capabilities to undertake all the activities from conceptualization to commissioning in relation to setting up of hydro projects.

 NHPC Limited presently has an installation base of 6507 MW from 20

hydropower stations on ownership basis including projects taken up in Joint Venture.

 The Hydropower power stations of NHPC are located in following hilly states

of India.

Sno.

State

No. Of Operating Power Stations

1

Jammu & Kashmir

7

2

Himachal Pradesh

5

3

Uttarakhand

2

4

Sikkim

2

5

West Bengal

1

6

Manipur

1

7

Madhya Pradesh (JV)

2

ďƒ˜ NHPC Limited is presently engaged in the construction of 4 projects

aggregating to a total installed capacity of 3290 MW. Given the renewed thrust on development of hydro power in the country, NHPC Limited has drawn up a massive plan to add about 10,000 MW of hydropower capacity by the end of XIII plan (year 2022).

RIVER REJUVENATION  In geomorphology, a river is said to be rejuvenated when the base level that it is

flowing down to is lowered. Rivers are always attempting to reach a state of dynamic equilibrium where erosion, deposition and transportation are in perfect balance.

 Rivers that have this form of profile are at an equilibrium with the environment.

 In recent times, river health is being deteriorated significantly due to pollution from

industrial and domestic waste, fertilizers and pesticides.

 Restoring the rivers to their original state has become the need of the hour as changes

in water quality, discharge and sediment load are constantly having negative impacts on sustainable development.

ENVIRONMENTAL FLOWS ďƒ˜ Environmental flows are those flows that are needed to maintain aquatic ecosystems, renewable natural resources production systems and associated livelihoods. ďƒ˜ The different components of an environmental flow regime contribute to different ecological processes.

NEED FOR STORAGE IN RIVER REJUVENATION AND E- FLOWS  India is blessed with a rainfall pattern that is distributed over 4-5

months in the year and that too in only a few hours of these months.

 Because of the sporadic spatial and temporal distribution of

precipitation, the only way water supply can be controlled to match demand is through storage. Seasonal variations and climatic irregularities in flow impede the efficient use of river runoff, with flooding and drought causing problems of catastrophic proportions.

 Dams clearly make a significant contribution to the efficient

management of finite water resources that are unevenly distributed and subject to large seasonal fluctuations.

Map showing the spatial variability of Annual rainfall

Temporal variation of rainfall 23.76

25

19.89

20 15.42

t ercn P

15 10 6.03 5 1.24 1.33 0

2.12

3.46

14.19

7.69 3.45 1.42

Water Scenario in India 12

Reducing per capita water availability 10 Per capita water availability in m3 /year 8 6

Water stress 1700 m3/capita/year

4 2

2061

2051

2041

2031

2021

2011

2001

1991

1981

1971

1951

0

1961

Water scarcity 1000 m3/capita/year

Map showing Per Capita Storage created in different countries of the world

CASE STUDY OF DIBANG MULTIPURPOSE PROJECT, ARUNACHAL PRADESH IN VIEW OF RIVER REJUVENATION AND E- FLOWS

Rejuvenation of the river in respect of storage projects can be broadly classified under following objectives: (A)Flood moderation in the river thereby providing protection against disastrous floods in the downstream.

(B)Enhancing the lean season flow of the river which further rejuvenate the river with respect to sustainable development of flora, fauna and associated eco-system health.

In case of ROR projects, it is difficult to maintain a certain amount of discharge in the downstream during lean season, where as in case of storage project the lean season flows can be increased substantially.

The applicability of above aspects in case of Dibang Multipurpose project has been represented in subsequent slides.

PROJECT BRIEF

 Dibang Multipurpose project is proposed across Dibang river, a

major tributary of Brahmaputra River, near Munli village in Dibang valley district of Arunachal Pradesh.

 Dibang river originates in India from snow covered Himalayas close

to Tibet border (at El 5000 m).

 The project envisages construction of 278 m high concrete gravity

dam across Dibang River and having reservoir storage of 3248 Mcum and reservoir surface area of 35.64 sq.km at Full Reservoir Level.

 Dibang Multipurpose project has been conceived with a dual

objective of flood moderation and electricity generation.

A VIEW OF DIBANG RIVER UPSTREAM OF DAM

CATCHMENT PLAN OF DIBANG MULTIPURPOSE PROJECT

(A ) EFFECT OF PROJECT DEVELOPMENT ON FLOOD MODERATION  Flood moderation through the project is proposed in the event of occurrence of a

100 year return period flood wave preceded and succeeded by a 25 year flood wave at dam site.

 Release from the reservoir has been restricted to 3000 cumec, which was

considered by Brahmaputra Board as the safe carrying capacity of the downstream channel reach.

 It was found that the storage of the order of 563 Mcum and 340 Mcum is required

for passing 1 in 100 year return period flood and 1 in 25 year return period flood respectively.

 Accordingly, the rule curve was adopted for reservoir of Dibang M.P. Project to

achieve the desired benefits of flood moderation .

Contd..

 Flood routing study has been carried out downstream of dam for 1 in

100 year return period flood (12756 cumec), 1 in 25 year return period flood (9750 cumec) and 3000 cumec discharge to assess the impact of flood moderation d/s of dam.

 Hydrologic Engineering Centre software HEC-RAS 4.1.0 has been used

for hydro-dynamic modeling.

 It was found that 45% of reduction in top width/area is envisaged due to

flood moderation.

 The relief in water level is of the order of 1 to 2 m beyond 20 km d/s of

dam for 1 in 100 year flood, which is quite significant considering the fact that Dibang is quite a wide river in these reaches.

 The plots showing variation in depth, water level, velocity and topwidth

are shown in subsequent slides:

18 17 16 15

1 in 100 year Flood = 12756 cumec

14 13

Release = 3000 cumec

12

Depth (m)

11 10 9 8 7 6 5 4 3 2 1 0 0

10000

20000

30000

40000

Distance d/s of dam (m)

Variation in Depth for Different Discharges

50000

60000

310 290 Minimum Bed Level (m) Water Level (m) for 1 in 100 year Flood = 12756 cumec Water Level (m) for Release = 3000 cumec

270

Water Level (m)

250 230 210 190 170 150 130 110 0

10000

20000

30000 40000 Distance d/s of dam (m)

Water Level Variation for Different Discharges

50000

60000

12

10

1 in 100 year Flood = 12756 cumec Release = 3000 cumec

Velocity (m)/s)

8

6

4

2

0 0

10000

20000

30000

40000

Distance d/s of dam (m)

Variation in Velocity for Different Discharges

50000

60000

14000

12000

1 in 100 year Flood = 12756 cumec Release = 3000 cumec

Top Width (m)

10000

8000

6000

4000

2000

0 0

10000

20000

30000

40000

50000

Distance d/s of dam (m)

Variation in Top Width for Different Discharges

60000

(B) ENVIRONMENTAL FLOWS IN VIEW OF STORAGE PROJECTS  In case of Dibang multipurpose project, dam operations have been

proposed in such a way that natural lean season flow is enhanced for river rejuvenation.

 The effect of peaking operation of Dibang project on water level

fluctuation in the downstream especially on Dibru-Saikhowa National Park was studied. The location of Dibru-Saikhowa National Park w.r.t.

Dibang Multipurpose Project is shown in subsequent slide.

 During monsoon season due to availability of high discharge in the

rivers, Dibang Multipurpose project shall operate through most part of the day to produce the power and thus there will not be much flow variation downstream of the project due to regulation for power generation.

Contd.

Dibru-Saikhowa National park

Map showing location of Dibang Multipurpose project w.r.t. Dibru-Saikhowa National Park

 However, during the lean season months, i.e. from November to February,

when the river discharges are considerably reduced, it is proposed to operate at least one turbine out of 12 turbines at 80% load continuously.

 In addition to this, 15 cumec environmental flow shall be released from the

dam.

 This essentially means that in the worst possible scenario, the project will

release only 15 cumecs as environmental flows supplemented by release of water by the operation of one turbine at 80% load continuously.

 Thus, the lean season discharge gets enhanced by about 20% in comparison

to natural lean season flow.

 A study carried out to assess the fluctuation in water level, flow, velocity and

topwidth at different reaches d/s of TRT along the river shows that the fluctuations in these parameters due to Dibang MPP are almost negligible considering the size & morphology of the river.

290 280

TRT outlet

270

10 km d/s

260 250 240 230

20 km d/s

Water Level (m)

220 210 200

30 km d/s

190 180 170

40 km d/s

160 150

50 km d/s u/s of confluence with Lohit

140 130 120 110 24

30

36

42

48

54

60 66 Time (hours)

72

78

84

Effect of peaking on W.L. variation

90

96

102

108

124.00

123.00 Post Project Scenario 122.00

Pre Project Scenario

Water Level (m)

121.00

120.00

119.00

118.00

117.00

116.00

115.00 24

30

36

42

48

54

60

66

72

78

Time (hours)

Fluctuation in W.L. at u/s of Lohit confluence (Pre & Post project scenario)

2,500 Post Project Scenario

2,300

Pre Project Scenario

2,100

Top Width (m)

1,900 1,700 1,500 1,300 1,100 900 700 500 24

30

36

42

48

54

60

66

72

78

Time (hours)

Fluctuation in Topwidth at u/s of Lohit confluence (Pre & Post project scenario)

2.00 1.80 Post Project Scenario

1.60

Pre Project Scenario

1.40

velocity (m/s)

1.20 1.00 0.80 0.60 0.40 0.20 0.00 24

30

36

42

48

54

60

66

72

78

Time (hours)

Fluctuation in Velocity at u/s of Lohit confluence (Pre & Post project scenario)

It is noteworthy to mention here that the storage dams have been instrumental in minimizing the devastation in the downstream areas caused due to floods: (a) Tehri dam in Uttarakhand saved the city of Haridwar and Rishikesh in the downstream from the fury of flash flood during 16-17 June 2013. A report said the fury of nature in Uttarakhand was such that waters rose as high as a four-storey building at Devprayag, where Alaknanda and Bhagirathi meet, in a 24-hour period after the cloud burst.

The rise at Devprayag, Rishikesh and Haridwar could have been much higher if the flow of Bhagirathi was not contained by the Tehri reservoir. It was seen during studies that in the absence of tehri dam, the flood peak at Haridwar would have been about 21500 cumec in place of actual observed about 14500 cumec. Hence due to Tehri dam the flood at Haridwar was mitigated by about 7000 cumec. (b) The Wular lake in Kashmir also prevented flooding in the downstream areas during September 2014 floods.

CONCLUSION  Rapid growth of industrialization and urbanization and rising standards

of living has exposed water resources to various forms of degradation.

 Creating water storage would go a long way in leading to river

rejuvenation by augmentation of e-flows especially during lean season by considered dam operation strategies.

 It can be seen from the above case study of Dibang Multipurpose project

that velocity/flow fluctuation in the downstream of dam is insignificant due to peaking operation. This could be achieved by proper planning of dam operation strategies.



In a long-term perspective, green growth is growth without unsustainable deterioration of the environment or growth with ‘modest’ negative impact on the environment in the short term and hydropower growth comes under this green growth category.

CONCLUSION  Any development ,big or small, has some impact on the environment. A

crucial decision concerns the desired condition or level at which the eco-system of the region is to be maintained.

 Sustainability concept suggests that we need to maintain the eco-

systems so that they yield the greatest benefit to the present generations , while retaining the ability to meet the needs and aspirations of future generations.

 There is a need to accelerate the development of new water storage projects for multiple purposes. Reservoir regulation must be optimised to store more flood waters while considering the requirements of upstream and downstream areas.  Storage projects are also needed for creation of water security which can

be put to multiple use. Hydropower could be one of the incidental benefits for these storages.

THANK YOU !!!