EFFECT OF URBANIZATION ON THE MITHI RIVER BASIN IN MUMBAI: A CASE STUDY

P.E.Zope 1, T.I.Eldho 2 and V.Jothiprakash 3

2012 International SWAT Conference

INDIAN INSTITUTE OF TECHNOLOGY, DELHI

1 Research Scholar , Dept. of Civil Engineering , IITB, Mumbai 2 Professor, Dept. of Civil Engineering, IITB, Mumbai 3 Associate Professor, Dept. of Civil Engineering, IITB, Mumbai

URBANIZATION EFFECT

Increased surface runoff in

annual stream flow. Increase magnitude of peak

runoff. Decreased lag time between

rainfall and runoff response. Increased rate of hydrograph

rise and recession. Decreased mean residence

time of stream flow. Topographical changes Population growth. Densification of structures. Less Evapotranspiration. No detension Basins.

Source : Dellur , 2003

EFFECT OF URBANIZATION

Heavy Rainfall Intensities

Tidal Influence

Effect of Urbanization

Inadequacy of Drainage Channels

Change in LU/LC

Urban Flooding

3

OBJECTIVES OF URBAN STORM WATER MANAGEMENT SYSTEM

To safeguard health , safety and property of citizens/ residents. To reduce inconvience to citizens by having an integrated approach.

Better quality of life for the society.

To achieve greater sustainability .

To avoid floods .

To improve the storm water quality .

GEOGRAPHY OF MUMBAI

Lat 180N to 19.200N, Long. 720E to 730E

An area of 437.71 sq. km.

An ancient city comprising seven islands joined with land filling.

Divided into 24 Municipal administrative areas called wards.

Coastal length of 140 Km.

Average annual rainfall of 2129 mm in the monsoon months from June to September.

Limitations to cope up the infrastructure with population growth rate.

Source : MCGM

DELUGE ON 26TH JULY 2005 Hyetograph of 26th July 2005 rainfall :

Unprecedented downpour of 944.2 mm. within 24 hours ending at 8.30 hours on 27th July.

While the Colaba observatory recorded only 74 mm of rain.

14:30 to 18:30 – 481.2 mm exceeded the rainfall record of Cherapunji.

Maximum tide level – 4.48 meter .

Till 1989 – Average rainfall – 2129 mm.

2005-2006 – 3214 mm

419 people & 1600 cattle lost lives. 216 people lost lives due to flood related illness. 100,000 residential and commercial establishment. 30,000 vehicles. 22% of Mumbai’s land (excluding forest) inundated.

FLOODING AT MUMBAI- 26 JULY2005:

FLOODING AT MUMBAI- 26 JULY2005:

Source : MCGM

JULY 2005 FLOODS IN MUMBAI

Flooding at Mithi River on 26th July 2005

EXISTING STORM WATER DRAINAGE SYSTEM IN MUMBAI The drainage system of

Mumbai is a mix of simple drains and complicated network of rivers, creeks, drains and ponds.

Separate systems for disposal of sewage and storm water.

Underground S.W .drains in city and open in suburb.

Road side S.W. drainage is designed for rainfall intensity of 50mm/hr for 2 year return period.

Source : MCGM

Mithi River From Vihar Lake to CST Bridge

Mithi River From CST Bridge to Mahim creek.

Origin of Mithi River

Origin of Mithi River Origin of Mithi River Vihar Lake Overflow

DEM and Catchment Area

As the corrected DEM generated from CARTOSAT -2009 gives perfect results about stream network , it is considered for study area.

Elevation ranges from 4.0 m to 380 m

Sub Catchment wise statement of Mithi River

Catchment Number Catchment Area (Sq.Km.) Catchment Number Catchment Area (Sq.Km.)

1 1.24 13 1.24

2 2.233 14 0.525

3 0.728 15 8.234

4 0.446 16 2.719

5 0.938 17 4.741

6 0.347 18 10.342

7 0.774 19 5.938

8 0.695 20 0.642

9 0.573 21 4.072

10 6.357 22 1.082

11 6.481 23 0.508

12 5.227 24 2.757

Total 68.839

Total catchment area of Mithi River consists of 24 sub – catchments. Total catchment area is 68.839 Sq.Km.

Slope Map

Slope of the catchment varies from 0 to 62%. Very steep slope : 1:200 upto 4 Km from Origin. Slope : 1 :450 – from 4.00 to 7.50 Km : 1:850 – from 7.50 to 12.0 Km : 1:4000 – from 12.0 to 17.8 Km.

Change in River Course

Runway of airport extended on the river course of Mithi. Development of reclamation , buildings and slums along the mud flat area of Mithi river

near Mahim bay. Construction of infrastructure such as roads , Bandra Kurla complex on the mud flat area

of Mithi.

Change in River Course

During 1992-2009 , all the mud flat area which was acting as holding pond , fully developed .

River course of Mithi and Vakola river reduced and encroached drastically by infrastructural development , slums… etc.

Change in River Course

Runway of airport extended on the river course of Mithi. Development of reclamation , buildings and slums along the mud flat area of Mithi river

near Mahim bay. Construction of infrastructure such as roads , Bandra Kurla complex on the mud flat area

of Mithi.

Summary of Changes in Mithi River Course

Year Area Encumbered(Sq.Km)

Net River course area including mud

flats (Sq.Km) Type of Changes

1966 nil 6.513 nil 2001 2.464 4.049 Airport Runway

extended, Reclamation at Mahim bay and Bandra Kurla complex area

2009 3.002 3.511 Entire Bandra-Kurla complex area

reclaimed, some part of Vakola basin

Mithi River before July 2005 floods

Mithi Near Marol Industrial Estate, Andheri (E)

Way to Airport from Saki Naka

River course of Mithi encroached on the banks by unauthorized slums reducing the width of river drastically.

Mithi River before July 2005 floods

Moraraji Nagar Slum Encroachment Mithi on Kurla – Saki Naka Road

Siltation / garbage in river course due to unauthorized slums on the banks of river.

Mithi River before July 2005 floods

Moraraji Nagar Slum Encroachment Mithi on Kurla – Saki Naka Road

Extension of Runway within Mithi River Course.

Land Use- Land Cover ( LU-LC)

DD/MM/YY Satellite/ Sensor Resolution (m)

13th November 1972 Landsat/MSS 80

9th November 1992 Landsat/TM 30

27th November 2001 Landsat/ETM 30

6th March 2009 IRS P6/L-4 5

Built up land : in 1996 : 27% In 1972

:28.56% Water Body : in 1966 :

13.8% in 1972 :

9.96%

Land Use- Land Cover ( LU-LC)

For the year 1992 For the year 2001 For the year 2009

Built up land increase from 27 % to 34.49% . Water body reduced to 8.73% from 20.15%. Due to change in month ( March & November ) of images , there is misclassification in open

land and vegetation.

(In sq.km)

Land use 1966 1972 1992 2001 2009

Open land (%)

19.17 (27.85)

15.94 (23.16)

13.59 (19.74)

16.34 (23.74)

19.30 (28.18)

Vegetation (%)

17.21 (25)

26.38 (38.32)

25.88 (37.59)

22.71 (32.99)

19.69 (28.60)

Water body (%)

13.87 (20.15)

6.86 (9.96)

6.39 (9.28)

6.7 (9.73)

6.11 (8.73)

Built up land (%)

18.59 (27)

19.66 (28.56)

22.98 (33.39)

23.09 (33.54)

23.74 (34.49)

Total 68.84

Due to change in land use , the river course of Mithi reduced drastically .

Mud flats area which was earlier acting as a holding pond , vanished completely due to infrastructural development , urbanization and unauthorized slums.

Land Use- Land Cover ( LU-LC)

Improvement of Mithi River By Constructing Retaining Wall

SUMMARY AND CONCLUSION

In urban flood estimation, effect of urbanization, land use change and hydrological extremities is vital.

In coastal cities, problem of flooding is due to high rainfall coinciding with high tide.

In Mithi river catchment built up area i.e. urban area is increasing drastically as compared to in year 1966.

From the analysis it is found that there is a rise in built up area from 27 to 34.49% between 1966 and 2009, which is the main cause of increase in impervious surface, which in turn increased the runoff resulting in severe flooding.

In 1966 at downstream side of the river, there was huge open land, mud flat area and wide channel area of river for smooth flow.

In 2001, about 37.81 % of mud flat area has been encroached by unauthorized slum, construction of building and infrastructural work reducing width of river and smooth river flow.

In 2009, 45.09 % of mud flat area covered by buildings and slum at Bandra Kurla complex area, reducing the river width and flow drastically.