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Urban Development in Hilly Terrain with Ecological

Management Practices(EMPs)

Prof. Arup Kumar Sarma

Civil Engineering Department

Indian Institute of Technology Guwahati

ECO-SYSTEM

Water

Soil

Vegetation

AirDwellers

All sorts of living being

Result of Imbalance in Nature

• Resulting from Natural Imbalance– Flood, Landslide, Avalanches, Tsunami …….

• Resulting from Man Made Imbalance– Flood due to failure of Dam and Dike,

– Human induced Landslide and Flood,

– Environmental pollution ……..

• Man-Made Imbalance is Highest in Urban Area

• In Hilly Urban Area Such Imbalances lead to Landslide

Ecological Disturbance of Guwahati

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Back

Landslide becomes more devastating when failure

occurs in a slope having soil and rock mass Landslide in Northeast

• Apart from geological causes, landslide Occurs in many cases due to land abuse

• In Guwahati, where landslide should not have occurred from the consideration of geological structure, devastating slide has taken place (Deka, 1991)

• High correlation (0.91) between number of

landslide and Population growth has been observed in the the Guwahati City (Sarma 1991)

• Landslide in the urban areas of NE India are generally rain triggered (Sarma 1994)

Year 1972 2000

Built up area in plains (Sq km) 38.7 126

Built up area in hills (Sq km) 4.8 40

Built up area in hills and plains

7 8

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9

Monthly Income

(% of Household)

Less than Rs 2000 12%

Rs 3000-Rs10000 68%

Rs10000-Rs 20000 18 %

Above Rs 20000 6%

% of Kutcha house 34%

% of Household without sanitary toilet 27%

% of Household without pipe water supply 79%

% of Household without access road 5%

Landslide prone zones Total : 93 nos

Very steep slope : 14 nos

Steep slope : 14 nos

Gentle slope : 29 nos

Socio-Economic survey in hilly areas of Guwahati

The socio economic condition of the people implies that

attention should be given for selecting efficient management

practices at least possible cost

Influence of Rainfall on Landslide

• Direct effect

– Saturation

– Weathering and saturation

– Seepage from a perched water table

– Erosion of surface soil

• Indirect Effect

– Washing out of finer fraction

– Unfavorable orientation of soil structure

– Weathering action of water

Vegetative Cover and Landslide• Removal of vegetative cover leads to

•Splash erosion

•Rill erosion

•Gully formation leading to instability

•Expansion of natural drainage line due to higher water yield

•Erosion of top soil leads to exposition of rock resulting in their

faster weathering.

•Thus the shear strength of soil and rock mass reduces

•Erosion of supporting soil may make a purse boulder unstable

• Failure of rock may lead to devastating slide

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Multiple slides of Kacharibasti, Guwahati, Assam, India

Failure of Oct’91

Failure in Jul’89

Rock

Rock

160 m

Soil

81 m

For analysis of such slope it is essential to consider

the effect of rock mass on the stability of soil phase

as well as effect of supporting soil mass on the

stability of rock phase.

Watershed Based LanduseManagement Practices Through Ecological Management Practices

Watershed is a Hydrological Unit such that precipitation falling

within the boundary of that unit moves to a single outlet.

What is an Watershed ?

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Watershed management Aims at:

Optimal utilization and development of Water

Soil

Vegetation and

Human being

Of the Watershed

Watershed Management can be regarded as any

form of environmentally sustainable and socially

acceptable management practice that facilitates

optimal utilization of land, water and vegetation

of the watershed for the benefit of the people

residing in the watershed.

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Effects of Vegetative Cover on Water Yield (Rational method)

Present

Maximum

outflow at

pilot watershed

(cumec)

Outflow if

bareland

and open

mix forest

area are

covered

by

vegetation(cumec)

Outflow if

all the

vegetation

cover is

removed

from the watershed

(cumec)

6.031 5.27 7.25

Effect of Deforestation (RUSLE)

Present

annual

sediment

yield in tons/yr

Annual

sediment

yield in

tons/yr if

bare land

and open

mix forest

area are

completely

covered by vegetation

Annual

sediment

yield in

tons/yr if

vegetation

cover is

removed

completely

from the watershed

20943.88 7903.27 289412.6

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Experimental Watershed at IITG CampusExperimental Watershed at IITG Campus

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Undisturbed

Disturbed

Sediments in runoffWater yield increase by 54%

Sediment yield increase by 20%

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Ecological Management Practices

Eco friendly sustainable management practices that are used for maintaining and enhancing land uses in a natural way

Some EMPs that can be used in a hilly urban area :

• Grass land

• Forest land

• Covering rain impacted areas with pebble, vegetation or wood chips

• Detention drain and Retention pond

• Sediment trap

• Vegetated waterways

• Rainwater harvesting system

Measures for runoff and

sediment control

Measures for Controlling Water and Sediment Yield

GRASS LAND

Perforated Concrete BlockSLOPE STABILIZATION STRUCTURE

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PAVED

GROUND

WITH SPACE

FOR

RAINWATER

PERCOLATION

HADGE FOR ROAD SIDE PROTECTION

ROFTOP RAINWATER HARVESTING

FOREST LAND

31

Perforated paved bocks for

the approach road

Hedge for roadside

protection

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Vegetative EMPs

Golden Glory

Grass

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Grass

Golden glory

As compared to Bare land

Grass was found 80% efficient and

Creepers and Herbs 60% efficient in

controlling surface erosion

An optimization model has been developed for determining Optimal EMP

DESIGN OF RAIN WATER HARVESTING

(RWH) SYSTEMS

�Two options for RWH are proposed and their Layout

and Designs are discussed

�Roof Top RWH(RTRWH)

• Rain water harvesting from roof top

�Flood Well RWH (FWRWH)

• Rain water infiltration through flood wells.

�may be used individually or in combination

depending on the hydrological needs for Flood

Peak Reduction

Summary of RWH Analysis (Contd.)

After solution

Parameters

Before

Solution Only

RTRWH

RTRWH +10

FW/ha

RTRWH +20

FW/ha

Water level in drains

(m)

1.78 1.62 1.44 1.29

Sediment in

drain (m)

0.5 0.5 0.18 0.18

Depth of outlet drain (m) 1.5 1.5 1.5 1.5

Flood with sediment

control(m)

0.78 0.62 0.11 0.00

% Reduction in

Maximum Runoff

Volume

- 12.2 21.54 30.87

% Peak Discharge

Reduction

- 12.20 12.70 22.9

% Flood Reduction in

Drains (without

Sediment Control)

- 20.5 43.6 62.8

% Flood Reduction in

drains (With Sediment

Control, Studyed by

Bracht and Sarma)

- 20.5 85 100

� Landslide /soil erosion and urban flood need to be considered as

two sides of a coin

�Identification of critical issues and bottlenecks

�Awareness programme to ensure public participation

�Development of a sustainable and comprehensive plan for

mitigating landslide and water related hazard

�Survey and base map preparation for the Pilot Project in

association with Govt. Departments/Organizations

�IIT and other educational organization can provide technical

backup to the Govt. departments/organizations for preparing

necessary DPR for the Pilot Project

�development of Ecological Management

Practices for controlling sediment and water yield

�hydrological analysis and design of structural components for

landslide prevention

� innovative design concepts for drainage system

General Solution Approach

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Expected Departmental Involvement for Finding Solutions

GDD

GMC GMDARevenue

ASTEC

Soil Conservation

Environment and Forests Water resources

UDD

PWDNational Highway

Authority

• Implementation of Master Plan proposals through detail planning schemes

• Enforcement of Building Byelaws

• Coordinate Development activities as per GMDA Act

GDD: GMC and GMDA

• Verification of land-status

• Identification of Govt. land

• Resettlement programmeRevenue

• Soil conservation by structural and non structural measures

Soil Conservation

• Afforestation programmes

• Identification of Reserve Forest areas/Forest Village

Environment and Forest

• Regional planning inputUDD

• Restoring natural streams and springsWater Resources

• Construction of retaining wall, roadside drain, catchwater drain etc based on hydrological study

Public Works Department

• Urban Mapping

Assam Science Technology and

Environment Council

• To revisit for designing drainage way along the National Highway

National Highway Authority

• Awareness programme

Local NGO/ Ward Committee (special

invitee) 40