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

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.