Flood Estimation for Rivers of Saurashtra Region Contributing into Gulf of Khambhat

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Flood Estimation for Rivers of Saurashtra Region Contributing into Gulf of Khambhat

Priyanka Kumari and N. K. Goel

Department of Hydrology Indian Institute of Technology Roorkee

Roorkee-247667, India

Abstract Water, as the most valuable part of the earth, is the major requirement for survival of life. Utilization of water resource is abruptly rising due to urbanization and development of civilization. For the design and planning of water resources structures design flood estimates are required. In the present study design floods have been estimated the 20 dams located in 9 river basinsnamely Wadhavan-Bhogavo, Limbdi-bhogavo, Sukhbhadar, Utavali, Padalio, Khalkhalia, Ghelo, Keri and Kalubhar of Saurashtra region. These rivers of Saurashtra region are contributing into the Gulf of Khambhat. 90 m SRTM Digital Elevation Model (DEM) has been used to estimate physiographic catchment characteristics of each basin. 25, 50 and 100 years return period design floods have been estimated using synthetic unit hydrograph and regional flood frequency relationships developed by CWC. The results suggest that the design floods given by the Synthetic Unit Hydrograph (SUH) approach may be more appropriate as the complete shape of the hydrograph may be obtained. The limitation of the study is that same values of rainfall have been used for the entire region, which may vary from one basin to another basin. The flood estimates of the present study shall be helpful to verify the existing design floods of the dams.

Keywords Flood design, Synthetic unit hydrograph, Saurashtra, Digital elevation model

  1. INTRODUCTION (HEADING 1)

    Gujarat, one of the states of India, has inland boundaries as well as coastal boundaries. It is divided in to four parts namely

    (1) North Gujarat, (2) CentralGujarat, (3) South Gujarat, and

    1. Saurashtra and Kutch. It shares boundaries with states of Rajasthan, Madhya Pradesh and Maharashtra. The rivers of Gujarat join Arabian Sea which has got two Gulfs namely Gulf of Khambhat and Gulf ofKutch.

      The state of Gujarat has seen many damaging floods in the past. Almost all the major rivers in Gujarat pass through a wide stretch of very flat terrain before reaching the sea. These flat low lands of lower river basins are prone to flooding because of flat terrain and poor drainage.

      Occasional cyclones and depressions are responsible for heavy rainfall in the parts of Saurashtra, Kutch, central and northern Gujarat. Gujarat has seen many disasters like Muchchhu II dam failure in 1979, loss of life and damage of property in years like 1927, 1970, 1979, 2003, 2005, 2006,

      2007, 2009, 2012, 2013 and 2014. The Figure 1 shows the flood prone areas of Gujarat.

      FIGURE 1: FLOOD PRONE AREAS OF GUJARAT

      (Source: Gujarat State Disaster Management Authority)

      1. PROBLEMS OF SAURASHTRA REGION

        Though Saurashtra region is one of the most water scarce regions of India, yet it suffers from the flooding problem, in spite of having lesser rainy days. The rainfall intensity usually is very high in this region. The topography of this region is of inverse bowl type that makes the water collection further difficult. It has highest point of 200 feet above the mean sea level.Typical problems of Saurashtra region are insufficient and inequitable water availability, erratic rainfall, Salinity Ingress in coastal areas and ground water depletion.

      2. BROAD OBJECTIVE OF THE STUDY

    The broad objective of the present study is to estimate design floods for various structures in the 9 river basins namely Wadhavan-Bhogavo, Limbdi-bhogavo, Sukhbhadar, Utavali, Padalio, Khalkhalia, Keri, Ghelo and Kalubharof Saurashtra region which are joining Gulf of Khambhatusing deterministic and statistical approaches. These estimates shall help in dam rehabilitation and improvement.

  2. STUDY AREA

    The nine river basins, namely Wadhwan-Bhogavo, Limbdi-Bhogavo, Sukhbhadar, Utavali, Padalio, Khalkhalia, Keri, Ghelo, Kalubhar, related to the study area lie in Northern

    part of Saurashtra region (Fig. 2; Table 1). Out of the above nine river basins Wadhwan-Bhogavo and Limbdi-Bhogavo drain into low level muddy plains lying adjacent to Sabarmati river basin.The area covered by Saurashtra region is 59,360 Km2, out of which 9000 Km2 area is covered under study. Suarashtra basin lies between latitude 20N to 24N and longitude 69E to 73E. There are 20 dams in these river basins (Table 2).

    Figure 2: River map of Gujarat

    Table 1: Details of River Basins

    S.No.

    Basin Name

    Catchment area

    (km2)

    Length (km)

    Eq.Slope (m/km)

    1

    Wadhavan-Bhogavo

    1517

    128

    1.19

    2

    Limbdi-Bhogavo

    915

    118

    1.4

    3

    Sukhbhadar

    1774

    145

    0.997

    4

    Utavali

    1206

    98

    0.751

    5

    Padalio

    311

    50

    0.779

    6

    Khalkhalia

    436

    47

    0.779

    7

    Keri

    556

    110

    1.537

    8

    Ghelo

    626

    94

    1.565

    9

    Kalubhar

    2047

    90

    1.42

    Table 2: Details of dams in 9 River Basins

    td>

    142

    S.N.

    Name of River

    Name of the Dam

    Area (km2)

    River Length (km)

    Eq. Slope (m/km)

    1

    Wadhwan- Bhogavo

    WB I

    389

    50

    1.86

    WB II

    159

    14

    1.22

    WB III

    303

    24

    1.81

    2

    Limbdi- Bhogavo

    LB I

    329

    33

    1.727

    LB II

    201

    19

    2.142

    LB III

    192

    36

    1.504

    3

    Sukhbhadar

    Sukhbhadar

    591

    45

    3.211

    Goma

    165

    24

    1.937

    4

    Utavali

    Khambhada

    255

    40

    3.332

    Senthali

    62

    18

    2.431

    5

    Keri

    Bhimdad

    126

    24

    2.931

    Gala

    169

    26

    3.892

    6

    Ghelo

    GheloSomnath

    56

    12

    5.662

    GheloItaria

    111

    16

    3.681

    Limbali

    27

    3.427

    Navagam

    60

    15

    1.988

    7

    Kalubhar

    Kalubhar

    592

    46

    2.47

    Rangholi

    397

    31

    2.570

    Malpara

    114

    23

    3.139

    8

    Padalio

    Bhambhan

    66

    14

    3.66

  3. DATA AVAILABILITY

    There are 13 rain gauge stations and 9 Gauge and discharge( G&D) sites in these river basins (Fig. 3 and Table 3 and 4.). These data were collected from IMD and Kalpasar Department of Gujarat

    FIG-3: LOCATION OF G&D SITES AND RAINGAUGE IN RIVER BASIN MAP

    Table 3: Details of G&D stations of Saurashtra region

    S.No.

    Station Name

    Longitude

    Lattitude

    Type

    DataAbvailability (Years)

    River Basin

    1

    Limbdi

    7143'8.39"

    2233'28.79"

    Daily

    1991-2011

    Limbdi

    2

    Ranpur

    7143'29.99"

    22 21' 18"

    Daily

    1991-2010

    Sukhbhadar

    3

    Bhimnnath

    72 5' 59.99"

    22 13' 1.19"

    Daily

    1999-2010

    Utavali

    4

    Barwala

    71 46' 8.4"

    2212'10.79"

    Daily

    1991-2009

    Utavali

    5

    Keria

    71 52' 33.6"

    22 6' 7.2"

    Daily

    1991-2010

    Padalio

    6

    Muldharoi

    7155'51.59"

    223'14.39"

    Daily

    1997-2010

    Padalio

    7

    Goradka

    71 28' 26.4"

    22 5'20.39"

    Daily

    1991-2010

    Keri

    8

    Vallabhipur

    71 52' 22.8"

    21 53'9.59"

    Daily

    1991-2010

    Ghelo

    9

    Umrala

    71 47' 56.4"

    21 50'56.4"

    Daily

    1991-2008

    Kalubhar

    Table 4: Details of Rain gauge stations of Saurashtra region

    S. No.

    Station Name

    Longitude

    Lattitude

    Type of Data

    Data Availability (Years)

    River Basin

    1

    WB II

    7131' 58.8"

    2243' 55.19"

    Hourly

    1906-2003

    WB

    2

    Sayla

    7127' 21.6"

    2232' 42"

    Hourly

    1969-2003

    WB

    3

    Chotila

    7112' 46.79"

    2225' 15.59"

    Hourly

    1968-2003

    WB

    4

    Limbdi

    7143' 19.19"

    2234' 15.6"

    Hourly

    1991-2010

    Limbdi

    5

    Dhandhuka

    71 58'29.99"

    22 23'27.59"

    Hourly

    1901-2006

    Sukhbhadar

    6

    Chorvira

    71 45'28.79"

    22 20' 45.6"

    Hourly

    1991-2010

    Sukhbhadar

    7

    Lakhavad

    71 31'55.19"

    22 19' 12"

    Hourly

    1982-2010

    Sukhbhadar

    8

    Dholera

    7211'41.99''

    2215'7.19"

    Hourly

    1901-2006

    Sukhbhadar

    9

    Bhavnagar

    72 8' 13.2"

    21 46' 55.2"

    Hourly

    1901-2006

    Kalubhar

    10

    Vallavipur

    7152'44.4"

    2153'27.59"

    Hourly

    1960-2003

    Ghelo

    11

    Umrala

    7148' 21.59"

    21 50' 38.4"

    Hourly

    1961-2007

    Kalubhar

    12

    Dedava

    7121' 18"

    2153' 45.6"

    Hourly

    1982-2010

    Kalubhar

    13

    Pipardi

    7120' 9.59"

    2150' 9.59"

    Hourly

    1983-2007

    Kalubhar

  4. METHODOLOGY

    Central Water Commission (CWC) has published flood estimation reports for various zones and subzones of India. Basin related to Saurashtra region of Gujarat is covered in

    WR50 = 0.827 / (qp )1.023

    WR75= 0.561 / (qp )1.037

    subzone 3(a). In these reports the relationships for synthetic unit hydrograph (SUH) parameters like time to peak (tp), peak discharge per unit area (qp), width of hydrograph at 50% of peak discharge (W50) and width of hydrograph at 75% of peak discharge (W75) etc. have been developed based on the catchment characteristics. Apart from SUH relationships, CWC (2000) has also developed regional flood frequency formulae and enveloping values for the estimation of design flood.

    Where,

    TB = 8.3758 * (tp

    Tm= tp + 0.5

    Qp = qp * A(9)

    )0.512

    1. SUH Relationships

      The following relationships have been developed by CWC (1987) for subzone 3a.

      tp = 0.433 * (L / Sc)0.704(1)

      qp = 1.161 / (tp )0.635 (2)

      W50 = 2.284 / (qp)1

      W75 = 1.331 / (qp )0.991

      A = Total catchment area in km2

      L = Length of longest main stream along the river course in km

      Sc = Equivalent stream slope in m/km

      tp= Time from the centre of effective rainfall duration to the peak in hr.

      qp = Peak rate of discharge in cumecs per sq. km. Qp = Peak discharge o(f3U) .G. in m3/s

      TB = Base width of U.G. in hr.

      Tm = time from the sta(r4t )of rise to the peak of U.G. in hr.

      W50 = Width of U.G. measured at 50% of peak discharge ordinate in hr.

      W75 = Width of U.G. measured at 75% of peak discharge ordinate in hr.

      WR50 = Width of rising limb of U.G. measured at 50% of peak discharge ordinate in hr.

      WR75 = Width of rising limb of U.G. measured at 75% of peak discharge ordinate in hr.

      Various steps to estimate the design flood hydrograph are described as under:

      1. Preparation of catchment area plan of the un-gauged catchment.

      2. Determination of physiographic parameters i.e. the catchment area (A), the length of the longest stream

        (L) and equivalent Stream slope (Sc).

        Basin Name

        Dam

        SUH Method

        RFF method

        Q

        Q

        Q

        Q

        Q

        Q

        Wadava n- Bhogavo

        WB I

        1345.53

        1676.05

        1868.75

        1261.18

        1566.76

        1882.22

        WB II

        754.02

        929.89

        1105.27

        1039.06

        1290.82

        1550.72

        WB III

        1348.32

        1666.65

        2029.65

        1544.16

        1918.30

        2304.54

        Limbdi- Bhogavo

        LB I

        1303.96

        1503.09

        1929.6

        1384.68

        1720.19

        2066.53

        LB II

        1140.6

        1389.58

        1658.26

        1293.99

        1607.52

        1931.18

        LB III

        749.15

        926.93

        1103.8

        734.48

        912.44

        1096.15

        Sukhbh adar

        Goma

        1034.31

        1204.52

        1497.79

        983.51

        1221.82

        1467.82

        Sukhbh adar

        1789.9

        2550.71

        3050.28

        2046.92

        2542.89

        3054.88

        Utavali

        Senthal i

        437.17

        533.07

        630.93

        455.27

        565.58

        679.46

        Khamb hada

        1118.01

        1380.51

        1642.09

        906.15

        1125.71

        1352.36

        Padalio

        Bhamb han

        510.88

        623.08

        735.27

        578.64

        718.84

        863.58

        Keri

        Bhimd ad

        745.08

        914.13

        1082.44

        738.48

        917.41

        1102.12

        Gala

        1057.66

        1294.23

        1531.72

        1005.44

        1249.05

        1500.54

        Ghelo

        Somnat h

        562.15

        683.43

        804.03

        604.54

        751.02

        902.24

        Itaria

        830.22

        1013.49

        1197.47

        887.28

        1102.27

        1324.21

        Limbal i

        895.08

        1094.84

        1251.58

        802.56

        997.01

        1197.75

        Navaga m

        388.78

        475.89

        562.89

        433.71

        538.80

        647.29

        Kalubh ar

        Malpar a

        721.43

        882.32

        1044.39

        699.35

        868.80

        1043.73

        Rangh oli

        1871.56

        2307.04

        2744.37

        1874.26

        2328.39

        2797.20

        Kalubh ar

        1904.34

        2370.23

        2843.88

        2149.38

        2670.16

        3207.78

        Basin Name

        Dam

        SUH Method

        RFF method

        Q

        Q

        Q

        Q

        Q

        Q

        Wadava n- Bhogavo

        WB I

        1345.53

        1676.05

        1868.75

        1261.18

        1566.76

        1882.22

        WB II

        754.02

        929.89

        1105.27

        1039.06

        1290.82

        1550.72

        WB III

        1348.32

        1666.65

        2029.65

        1544.16

        1918.30

        2304.54

        Limbdi- Bhogavo

        LB I

        1303.96

        1503.09

        1929.6

        1384.68

        1720.19

        2066.53

        LB II

        1140.6

        1389.58

        1658.26

        1293.99

        1607.52

        1931.18

        LB III

        749.15

        926.93

        1103.8

        734.48

        912.44

        1096.15

        Sukhbh adar

        Goma

        1034.31

        1204.52

        1497.79

        983.51

        1221.82

        1467.82

        Sukhbh adar

        1789.9

        2550.71

        3050.28

        2046.92

        2542.89

        3054.88

        Utavali

        Senthal i

        437.17

        533.07

        630.93

        455.27

        565.58

        679.46

        Khamb hada

        1118.01

        1380.51

        1642.09

        906.15

        1125.71

        1352.36

        Padalio

        Bhamb han

        510.88

        623.08

        735.27

        578.64

        718.84

        863.58

        Keri

        Bhimd ad

        745.08

        914.13

        1082.44

        738.48

        917.41

        1102.12

        Gala

        1057.66

        1294.23

        1531.72

        1005.44

        1249.05

        1500.54

        Ghelo

        Somnat h

        562.15

        683.43

        804.03

        604.54

        751.02

        902.24

        Itaria

        830.22

        1013.49

        1197.47

        887.28

        1102.27

        1324.21

        Limbal i

        895.08

        1094.84

        1251.58

        802.56

        997.01

        1197.75

        Navaga m

        388.78

        475.89

        562.89

        433.71

        538.80

        647.29

        Kalubh ar

        Malpar a

        721.43

        882.32

        1044.39

        699.35

        868.80

        1043.73

        Rangh oli

        1871.56

        2307.04

        2744.37

        1874.26

        2328.39

        2797.20

        Kalubh ar

        1904.34

        2370.23

        2843.88

        2149.38

        2670.16

        3207.78

      3. Determination of 1-hour SUH parameters i.e. peak discharge per km2. (qp), the peak discharge (Qp), the basin lag (tp), thepeak time of U.G. (Tm), widths of the U.G. at 50% and 75% of Qp (i.e. W50 and W75), widths of the rising limb of U.G. at 50% and 75% of Qn (i.e. WR50 and WR 75) and time base of U.G.(TB).

      4. Drawing of a SUH.

      5. Estimation of design storm duration (TD or TB).

      6. Estimation of point rainfall and areal rainfall to obtain design storm duration (TD).

      7. Distribution of areal rainfall during design storm duration (TD) to obtain rainfall increments for unit duration intervals.

      8. Estimation of effective rainfall units after substraction of prescribed design loss rate for this zone from rainfall increments.

      9. Estimation of base flow (qb).

      10. Calculation of design flood peak.

      11. Calculation of design flood hydrograph.

    2. Regional Flood FrequencyFormulae (CWC, 2000)

    The regional flood frequency formulae developed by CWC for 25, 50 and 100 years return period are summarized as follows:

    A = Catchment Area in km2;

    S = Equivalent slope of main stream in m/km; RT= Storm depth of return period T in cm;

    L = Longest length of main stream in km.

    25, 50 and 100 years return period rainfall values for the region under study work out to be 20, 24 and 28cm respectively using the iso-pluvial maps prepared by IMD.

  5. RESULTS AND DISCUSSION

Using SUH and regional flood frequency formulae developed by CWC, the design floods for the 20 dams are tabulated in Table 5.

It may be seen from Table 5 that the design floods given by the two approaches are comparable. The design floods given by the SUH approach may be more appropriate as the complete shape of the hydrograph may be obtained. The limitation of the study is that same values of rainfall have been used for the entire region, which may vary from one basin to another basin. However the design floods computed in the present study may be used for cross verification of the adopted design flood values for these existing dams.

Table 5: Design Floods for 20 dams using 2 approaches

(0.978)

(0.25)

(1.19)

(0.618)

Q = 1.005 * A

* S * R /L

(10)

Q = 1.164* A(0.947) * S(0.242) * R (1.143)/L(0.566)(11)

Q = 1.161* A(0.96) * S(0.241) * R (1.126)/L(0.568)(12)

The above formulae can be represented by the following equation:

b c d e

QT = a * A * S *RT /L

Where,

(13)

a, b, c, d and e are return period dependent coefficients; QT = Design flood for a desired return period T in m3/s;

VI. CONCLUSIONS

The study has been undertaken with the objective to estimate design floods for 20 dams located in rivers of Saurashtra region which are contributing into Gulf of Khambhat. SUH and regional flood frequency formulae developed by CWC have been used. The design flood estimates by the two approaches have been summarized. The design floods computed in the present study may be used for cross verification of the adopted design flood values for the existing dams, which have been investigated in this study.

REFERENCES

  1. CWC(2001), Manual of estimation of Design Flood, Hydrology studies Organisation, Central water Commission, New Delhi

  2. CWC (1987), Flood estimation report for Mahi and Sabarmati (Subzone 3a), Hydrology Directorate, Central Water Commission, New Delhi.

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