Central Water Commission
Design Flood Study of Maithon Dam
Dam Rehabilitation and Improvement Project (DRIP)
March 2017 EGE_JH05HH0008_TDFA_001_A
Quality Control:
Version Date Writers/Contributors Checked by
1 09/03/2017 Ashoke Basistha (AB) VK Kapoor (VKK)
Issued/Copied to:
I/C Date Name Organisation Issued 09/03/2017 Sh. Pramod Narayan Central Water Commission EGE_JH05HH0008_TDFA_001_A
Design Flood Study of Maithon Dam March, 2017 Index
Executive Summary (vii)
Contents
1. Introduction ...... 1
1.1 General ...... 1 1.2 The Ganga Basin ...... 1 1.3 Maithon Reservoir Project...... 2 1.1 Upstream and Downstream Projects ...... 3 1.2 Geographical Features ...... 3 1.3 Earlier Design Flood Studies...... 4 2. Design Flood Estimation ...... 11
2.1 Hydro-Meteorological Approach ...... 11 2.2 Unit Hydrograph ...... 12 2.2.1 Physiographic Parameters for Derivation of Unit Hydrograph ...... 13
2.2.2 Unit Hydrograph for Sub-catchments ...... 17
2.3 Design Storm ...... 18 2.3.1 Design Storm Duration ...... 18
2.3.2 Time Distribution of Rainfall ...... 19
2.4 Design Loss Rate ...... 27 2.5 Critical Sequencing of Effective Rainfall ...... 28 2.6 Base Flow ...... 34 2.7 Flood Routing Through Channel Reaches ...... 34 2.8 Alternatives Considered for Arriving at Peak Inflow at Maithon ...... 36 2.9 Design Flood Hydrograph ...... 36 2.10 Discussions and Conclusions ...... 38
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List of Tables Page Table No. Description No. 2.1 Parameters of Unit Hydrograph 17 2.2 Physiographic parameters of the sub-catchments 17 2.3 Values of Unit Hydrograph Parameters for Sub-catchments 18 2.4 PMP Values for Maithon Sub-catchments 18 2.5 Rainfall Distribution for Barakar Catchment R1 for 24 and 48 hours 19 Rainfall Distribution for Barakar Catchment R2-R5 for 24 and 48 2.6 20 hours 2.7 Total Rainfall in 4 Bells 21 2.8 Normalized Rainfall Distribution for 12 hours for Sub-catchment R1 21 Normalized Rainfall Distribution for 12 hours for Sub-catchment 2.9 22 R2-R5 Hourly Rainfall Distribution for Sub-catchment Barakar R1 for 12 2.10 22 Hours Hourly Rainfall Distribution for Sub-catchments Barakar R2-R5 for 2.11 23 12 Hours Hourly Cumulative Rainfalls in Each Bell for Sub-catchment Barakar 2.12 24 R1 Hourly Cumulative Rainfalls in Each Bell for Sub-catchments 2.13 24 Barakar R2 & R3 Hourly Cumulative Rainfalls in Each Bell for Sub-catchments 2.14 25 Barakar R4 & R5 2.15 Hourly Rainfalls in Each Bell for Sub-catchment Barakar R1 26 2.16 Hourly Rainfalls in Each Bell for Sub-catchments Barakar R2 & R3 26 2.17 Hourly Rainfalls in Each Bell for Sub-catchments Barakar R4 & R5 26 2.18 Effective Rainfalls in Each Bell for Sub-catchment Barakar R1 27 2.19 Effective Rainfalls in Each Bell for Sub-catchments Barakar R2 & R3 28 2.20 Effective Rainfalls in Each Bell for Sub-catchments Barakar R4 & R5 28 Critical Sequence of Hourly Effective Rainfalls for Sub-catchment 2.21 Barakar R1 considering Unit Hydrograph of Sub-catchment Barakar 29 R4 Critical Sequence of Hourly Effective Rainfalls for Sub-catchments 2.22 Barakar R2 & R3 considering Unit Hydrograph of Sub-catchment 29 Barakar R4 Critical Sequence of Hourly Effective Rainfalls for Sub-catchments 2.23 Barakar R4 & R5 considering Unit Hydrograph of Sub-catchment 30 Barakar R4 2.24 Reverse Critical Sequence of Effective Rainfalls for Sub-catchment 30
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Page Table No. Description No. Barakar R1 considering Unit Hydrograph of Sub-catchment Barakar R4 Reverse Critical Sequence of Effective Rainfalls for Sub-catchments 2.25 Barakar R2 & R3 considering Unit Hydrograph of Sub-catchment 31 Barakar R4 Reverse Critical Sequence of Effective Rainfalls for Sub-catchments 2.26 Barakar R4 & R5 considering Unit Hydrograph of Sub-catchment 31 Barakar R4 2.27 Channel Parameters for Muskingum Routing 36 2.28 Design Flood Hydrograph at Maithon Dam 36
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List of Figures
Figure No. Description Page No.
1.1 Index Map of Maithon Dam 3 1.2 Ganga Basin Map 7 Landsat Natural Colour Composite Image of the Maithon 1.3 9 Dam Catchment acquired on 21st December 2016 1.4 Elevation Zone Map of the Maithon Dam Catchment 9 1.5 Slope Map of the Maithon Dam Catchment 10 2.1 Sub-catchments of Maithon Dam Catchment 12 2.2 Parameters for Estimation of Equivalent Stream Slope 14 Centroid, Longest Stream and Stream to Centroid for Sub- 2.3 15 catchments 2.4 Unit Hydrograph Parameters 16 Interpolated and Adjusted Cumulative Rainfall Distribution 2.5 22 for Sub-catchment Barakar R1 Interpolated and Adjusted Cumulative Rainfall Distribution 2.6 23 for Sub-catchments Barakar R2-R5 Hourly Distribution of Rainfall Excess Values for Sub- 2.7 32 catchment Barakar R1 Hourly Distribution of Rainfall Excess Values for Sub- 2.8 33 catchments Barakar R2 & R3 Hourly Distribution of Rainfall Excess Values for Sub- 2.9 33 catchments Barakar R4 & R5 2.10 Channel Reaches for Sub-catchments of Maithon Dam 34 2.11 Design Flood Hydrograph at Maithon Dam 38
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List of Annexure Annexure No. Description Page No.
Annexure I Salient Features of the Maithon Dam 39 Adjusted Unit Hydrographs for Sub Catchments of Annexure II 41 Maithon Dam
Annexure III Design Storm for Maithon Dam Project by IMD 57
Computations of Flood Hydrographs for Sub-catchments Annexure IV 63 of Maithon Dam Computations of Channel Routing for Maithon Dam Annexure V 81 Catchment using Muskingum method
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EXECUTIVE SUMMARY
The Maithon Dam is located at latitude 23°47ʹ13.06ʺ north and longitude 86°49ʹ01.44ʺ east on river Barakar at Maithon in District Dhanbad in the state of Jharkhand. It is in the Lower Ganga basin. The catchment area up to Maithon Dam has been estimated as 6388.69 km², using SRTM DEM. The height of the dam is 56.08 m. The dam has a total length of 4426.76 m comprising 4064.35 m long earthen embankment and 362.41 m long concrete overflow section. The reservoir has a live storage capacity of 441.64 Mm³ and a gross storage capacity of 1,093.54 Mm³. The project was constructed between 1951 and 1957. The spillway has been designed to pass a maximum discharge 13,592 m3/s. As per criteria specified in BIS 11223-1985, the dam qualifies for a large dam and should therefore be designed to safely pass Probable Maximum Flood (PMF). This report deals with the estimation of design flood for the dam following current practices.
The estimation of design flood for the project has been carried out by hydro- meteorological approach. For this purpose, the catchment area up to Maithon Dam has been divided 5 sub-catchments. In the absence of adequate observed data, synthetic unit hydrograph for each sub-catchment has been prepared following the methodology suggested in Flood Estimation Report for Lower Ganga Subzone – 1(g), November 1994, by the Central Water Commission (CWC). The estimated floods from the sub-catchments were routed through 4 channel reaches to arrive at the design flood at the Maithon Dam.
The design storm rainfall (Probable Maximum Precipitation, PMP) assessed by IMD for the Maithon catchment has been used. For sub-catchments R1, R2 & R3 and R4 & R5 of the Maithon Dam catchment, IMD has estimated one day Probable Maximum Precipitation (PMP) of 43.2 cm, 37.6 cm and 37.4 cm respectively and two day PMP values of 66.8 cm, 64.5 cm and 64.0 cm respectively. These were used as design storm rainfalls.
The design flood study was carried out using Microsoft Excel spreadsheets developed for the purpose. The loss rate and base flow have been adopted from FER 1(g).
The peak of PMF has been estimated as 19,049 m3/s.
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1. Introduction A brief sketch of the Ganga Basin and the Maithon Dam catchment has been presented in the following sub-sections, to provide a background for the current study.
1.1 General The Maithon Dam Project is located on the River Barakar, a tributary to the River Damodar in District Dhanbad of the state of Jharkhand. The River Damodar is a tributary to the River Ganga. Following BIS 11223-1985, the dam has been categorized as a large dam due to its storage and height. Accordingly, the design flood is Probable Maximum Flood (PMF). This report deals with the estimation of PMF for the dam.
1.2 The Ganga Basin The River Ganga originates in the Himalayas as Bhagirathi, in the District Uttarkashi of the State of Uttarakhand. The River Bhagirathi comes out of the Gaumukh Glacier at Gaumukh, an elevation of about 4255 m above the mean sea level. The River Bhagirathi is joined by the River Alaknanda at Devprayag. The combined stream flows through the mountains as Ganga, before entering the plains at Rishikesh. It is joined by a large number of tributaries on both the banks through its total course of 2,525 km, before it debouches into the Bay of Bengal. The important tributaries are the Yamuna, the Ramaganga, the the Betwa, the Chambal, the Gomti, the Ghagra, the Kali, the Sone, the Gandak, the Burhi Gandak, the Kosi, the Damodar and the Mahananda.
The Ganga Basin extends between longitude 73° 02ʹ east to 89° 05ʹ east and latitude 21° 06ʹ north to 31° 21ʹ north, spread over four countries, viz., India, Nepal, Tibet (China), and Bangladesh. It covers an area of 10, 86,000 km². The major part of the basin (8, 62,769 km²) is in India, comprising about 26.2% of the total geographical area of the country. It is spread over the states of Uttarakhand, Himachal Pradesh, Uttar Pradesh, Rajasthan, Haryana, Delhi, Chhattisgarh, Jharkhand, Bihar and West Bengal. The basin is bounded by the Himalayas on the north, the Aravalli on the west, the Vindhyas and Chottanagpur plateau on the south and the ridge separating Brahmaputra Basin on the east.
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The climate of the basin is “Tropical Monsoon type”, dominated by the southwest monsoon which brings in major fraction (about 84%) of the annual rainfall. Spells of heavy rainfall are also received during tropical cyclones, which originate in the Bay of Bengal in the months of June to October. Only a small amount of rainfall occurs in the winter months of December and January, usually caused by the western disturbances. The western part of the basin is hot and arid, whereas the eastern part is warm and hot. The average annual rainfall varies from about 760 mm at the western end of the basin to more than 2,290 mm at the eastern end. There is high seasonal variability in the total amount of rainfall as well as its spatial distribution. Accordingly, the river shows a marked seasonal variation in flow. From April to June, the low flows in the river is mostly supported by the melting of Himalayan snows. The heavy rains brought during the monsoon months of July to September leads to high flows, sometimes causing floods. The river flow declines during the winter months.
The mean maximum daily temperature even in the coldest month (January) does not drop below 21°C, except in the higher hills. Usually, May is the hottest month. The mean daily maximum temperature in May shoots up to 40°C near west of Gaya (Gangetic plains) and 42.3°C in Kota (Central Indian upland). The average annual mean temperature is 24.82°C. The average annual maximum temperature is 31.22°C and the average annual minimum temperature is 18.44°C.
1.3 Maithon Reservoir Project The Maithon Dam is located at latitude 23°47ʹ13.06ʺ north and longitude 86°49ʹ01.44ʺ east on the River Barakar. The Maithon town is situated just downstream of the dam. A few other nearby habitations include Anand Bihar, Hadla, Kamaliya, Netaji Nagar, Debipur and Beliyad. The catchment area spreads over the districts Dhanbad, Jamtara, Giridih, Kodarma, Hazaribag and Chatra of the state of Jharkhand. The catchment area has been estimated as 6391.74 km², using SRTM DEM. It extends between latitude 23°46ʹ34.12ʺ north and longitude 85°09ʹ16.26ʺ east, to latitude 24°32ʹ09.80ʺ north and longitude 86°53ʹ19.20ʺ east. The dam has a height of 56.08 m above the lowest river bed level and a total length of 4426.76 m comprising 4064.35 m long earthen embankment and 362.41 m long concrete overflow section. The reservoir has a gross
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storage capacity of 1,093.54 Mm³ and a live storage capacity of 441.64 Mm³. The project was constructed between 1951 and 1957. The spillway, comprising 12 bays with gates 12.19 m wide and 12.50 m high gates over Ogee profile, was originally designed to pass a maximum discharge 13,592 m³/sec. The index map of Maithon Dam is shown in Figure 1.1. Salient features of the dam are in Annexure I.
1.1 Upstream and Downstream Projects Tilayia Dam is the nearest project upstream of Maithon Reservoir, and Durgapur Barrage is the nearest project downstream.
For the purpose of estimation of design flood in this study, attenuation and translation of flood peak during their passage through the upstream reservoirs have been ignored, as during such extreme events the reservoirs may be expected to be full, with the spillways discharging the inflow at maximum capacity.
1.2 Geographical Features The Ganga Basin mostly has level plains or slopes which are very gentle in general. But some parts of Uttarakhand, in the Lesser Himalayas and the Shiwalik ranges, has steep slopes. Steep slopes are also found in some parts of Madhya Pradesh. The lower parts of the basin viz., Jharkhand, Chhattisgarh and West Bengal, as also parts of Rajasthan have a gentle slope. A map showing the location of project catchment within the Ganga Basin has been presented in Figure 1.2. It shows that the project catchment is in Lower Ganga catchment number 324. The figure also shows the location of rain gauges maintained by IMD and river gauging stations maintained by the CWC within the basin.
Landsat L8 natural colour composite image of the project catchment acquired on 21st December 2016 has been shown in Figure 1.3. This shows the presence of forest in limited patches near the southern edge of the catchment. Most part of the catchment presents a barren look, as the paddy crop cultivated in the plains appear to have been harvested.
A map showing the elevation zones within the project catchment up to the Maithon Dam, based on SRTM DEM has been portrayed in Figure 1.4. This brings out that the elevation in the project catchment varies between 123 to 1359 m. The Slope Map of the
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Maithon Dam Catchment has been presented in Figure 1.5. It shows that most part of the catchment is relatively flat, having a slope of 3% to 10%. High slopes are present only near the hills bordering the southern edge of the catchment
The Ganga basin is home to a wide variety of soils. Alluvial soil, endowed with rich soil nutrients, covers more than 52 percent of the basin. While most parts of the Ganga Basin is covered with soil of fine texture, there are some parts of Uttarakhand and Bihar, which have soils of very course texture, sometimes rocks. Soils with course texture is also noticed in parts of Haryana and Rajasthan.
The major part of the Ganga basin (65.57 %) is under agriculture. Other major land cover types are deciduous forest (16 %), wasteland (8.89 %), built up land (4.28 %), water bodies (3.47 %), snow / glaciers (0.94 %) and grassland (0.85 %).
The Ganga Basin supports nearly 600 million people, which includes some of the most densely populated regions of the world. It has 1949 cities and towns, with an estimated population of 125 million.
1.3 Earlier Design Flood Studies The original design flood had a magnitude of 14724 m³/s. Details of the estimation procedure could not be obtained.
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Figure 1.1: Index Map of Maithon Dam
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Figure 1.2: Ganga Basin Map
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Figure 1.3: Landsat Natural Colour Composite Image of the Maithon Dam st Catchment acquired on 21 December 2016
Figure 1.4: Elevation Zone Map of the Maithon Dam Catchment
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Figure 1.4: Slope Map of the Maithon Dam Catchment
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2. Design Flood Estimation The study for design flood estimation of Maithon Dam has been discussed in brief under the following sub-sections.
BIS 11223 -1985 stipulates that for the dams having gross storage more than 60 Mm³ or the hydraulic head more than 30 m, the inflow design flood for safety of the dam should be Probable Maximum Flood (PMF).
Because of its large gross storage of 1,093.54 Mm³ and dam height of 56.08 m, Maithon Dam is categorized as large dam. So the applicable design flood is Probable Maximum Flood (PMF).
2.1 Hydro-Meteorological Approach For the current study, the design flood estimation has been carried out using hydro- meteorological approach. In this approach the design flood estimation involves derivation of catchment response function (unit hydrograph), establishing critical design storm hyetograph and application of convolution to obtain the storm hydrograph. For a catchments larger than 5,000 km², the unit hydrograph approach cannot be applied directly. In such cases, the entire catchment has to be divided into several sub-catchments. Estimation of flood hydrograph has to be carried out for each of the individual sub-catchments, using unit hydrograph derived for the same. Finally, these hydrographs are needed to be routed through the connecting river reaches, to arrive at the design flood at the catchment outlet point. The steps involved can be summarized as: • Dividing the catchment into suitable sub-catchments • Derivation of unit hydrograph for each of the sub-catchment • Choosing a suitable loss rate for design storm rainfall • Establishing the critical sequence of effective rainfall for obtaining the largest flood peak magnitude • Estimation of base flow contribution • Computation of flood hydrograph using the critical combination of design storm parameters and catchment response function (unit hydrograph) for each sub- catchment
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• Routing the flood hydrographs through river reaches and reservoirs as applicable and adding up to arrive at the design flood hydrograph at the catchment outlet.
2.2 Unit Hydrograph The unit hydrograph (UH) is the hydrograph of direct runoff resulting from one unit (1 cm) of rainfall excess occurring uniformly over the catchment at a uniform rate during a specific period of time (unit duration). The Maithon catchment is very flat. The catchment up to Maithon Dam was divided into 5 sub-catchments ranging between 910.66 km² and 1768.83 km², following the delineation pattern adopted by the DVC and the IMD for estimation of the design storm rainfall. As concurrent rainfall and runoff data for flood events was not available, synthetic unit hydrographs were prepared for each sub-catchment following the methodology suggested in Flood Estimation Report for Lower Ganga Subzone 1(g) by the Central Water Commission (November, 1994), based on physiographic parameters derived from SRTM DEM. The sub-catchments are shown in Figure 2.1 below.
Figure 2.1: Sub-catchments of Maithon Dam Catchment
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2.2.1 Physiographic Parameters for Derivation of Unit Hydrograph The physiographic parameters considered are: • Catchment area (A in km²) • Length of the longest stream (L in km) • Length of longest stream from a point near the centre of gravity of the catchment
to the catchment outlet (Lc in km) • Equivalent slope (S) is computed using formula = {∑ × ( + )}⁄ Where, S = Equivalent stream slope in m/km
th = Length of the i stream segment in km