Land Uplift and Subsidence Study Land Uplift and Subsidence Study in Gujarat Region Using Global in Gujarat Region Using Global

Positioning SystemPositioning System

ICORGICORG

HyderabadHyderabad

5-8 June 20065-8 June 2006

PARUL R. PATEL *, M. N. KULKARNI PARUL R. PATEL *, M. N. KULKARNI Indian Institute of Technology Bombay,Indian Institute of Technology Bombay,

Powai, Mumbai 400 076, IndiaPowai, Mumbai 400 076, IndiaDepartment of Civil Engineering,Department of Civil Engineering,

* p5parul@iitb.ac.in* p5parul@iitb.ac.in

Land SubsidenceLand Subsidence

Land subsidence is a gradual settling Land subsidence is a gradual settling or sudden sinking of the earth's or sudden sinking of the earth's surface surface

Anthropogenic Land Subsidence Anthropogenic Land Subsidence mainly occurs due to extraction of mainly occurs due to extraction of natural resources like water, gas and natural resources like water, gas and oil, underground mining activities oil, underground mining activities and under ground construction and under ground construction

Mechanism of Land SubsidenceMechanism of Land Subsidence

Effect of Land SubsidenceEffect of Land Subsidence

Changes in elevation and slope of streams Changes in elevation and slope of streams canal and drainscanal and drains

Damage to bridges, roads, railway lines, Damage to bridges, roads, railway lines, storm drains, sanitary sewers, canals and storm drains, sanitary sewers, canals and leveeslevees

Damage to buildingsDamage to buildings Failure of well casings Failure of well casings Water intrusion in Coastal areas Water intrusion in Coastal areas Development of fissures Development of fissures Development of SinkholesDevelopment of Sinkholes

Failure of Well Casings Failure of Well Casings

FissuresFissures

Failure of BuildingFailure of Building

SinkholeSinkhole

SinkholeSinkhole

Homes at Greens Bayou near Homes at Greens Bayou near Houston, TexasHouston, Texas

Land Subsidence in San Joaquin Land Subsidence in San Joaquin Valley, CaliforniaValley, California

Monitoring TechniquesMonitoring Techniques

Conventional LevellingConventional Levelling Global Positioning SystemGlobal Positioning System Synthetic Aperture Radar Synthetic Aperture Radar

InterferrometryInterferrometry Radio Active MarkerRadio Active Marker Borehole ExtensometerBorehole Extensometer

Land Subsidence Monitoring Land Subsidence Monitoring with GPS in South Gujaratwith GPS in South Gujarat

Study areaStudy area Area near Surat in GujaratArea near Surat in Gujarat

Aim of StudyAim of Study To Measure and Monitor Land To Measure and Monitor Land

SubsidenceSubsidence To Study various parameters To Study various parameters

responsible for subsidenceresponsible for subsidence

Possibilities of Land Possibilities of Land SubsidenceSubsidence

Due to tectonic movementsDue to tectonic movements Ground water extraction Ground water extraction Extraction of other natural Extraction of other natural

resources like gas, oil etcresources like gas, oil etc

Data Collection Data Collection

A precise network of 31 GPS stations has A precise network of 31 GPS stations has been established in the study area, with been established in the study area, with four reference stations: R1, R2, R3, R4, four reference stations: R1, R2, R3, R4, and 27 deformation stations.and 27 deformation stations.

The reference stations were continuously The reference stations were continuously

running during the data collection. running during the data collection.

The approximate time for data collection The approximate time for data collection at each of the 27 deformation stations was at each of the 27 deformation stations was five hours. five hours.

Geodetic GPS receivers, Trimble Geodetic GPS receivers, Trimble 5700 receivers with Zephyr Geodetic 5700 receivers with Zephyr Geodetic type antenna type antenna

Trimble 4000 SSi receivers with Trimble 4000 SSi receivers with choke ring antenna were used choke ring antenna were used

Total Eight-field campaigns were Total Eight-field campaigns were carried out during February 04 to carried out during February 04 to March-06 at an interval of 3 to 4 March-06 at an interval of 3 to 4 months months

three-field

Reference NetworkReference Network

Local Network for Deformation Local Network for Deformation StationsStations

Control Parameters For Data Control Parameters For Data CollectionCollection

PDOP CutoffPDOP Cutoff : 4: 4

Logging Interval Logging Interval : 15 sec: 15 sec

Elevation maskElevation mask : 15 deg: 15 deg

Min. No. of satellitesMin. No. of satellites : 4: 4

Min. common observation timeMin. common observation time : 5 hours: 5 hours

Methodology Adopted for Methodology Adopted for Data ProcessingData Processing

The collected data were processed with scientific The collected data were processed with scientific data processing software Bernese v4.2 data processing software Bernese v4.2

The collected data and base lines were in the The collected data and base lines were in the World Geodetic System 84 (WGS 84) reference World Geodetic System 84 (WGS 84) reference systemsystem

Three International GPS Service (IGS) stations Three International GPS Service (IGS) stations were selected for constraining the solutions in the were selected for constraining the solutions in the International Terrestrial Reference Frame International Terrestrial Reference Frame 2000(ITRF 2000) reference system 2000(ITRF 2000) reference system

IGS data files as well as precise ephemeredes IGS data files as well as precise ephemeredes were downloaded from IGS data bank, which were were downloaded from IGS data bank, which were used for post processing the data used for post processing the data

Step 1Step 1

Precise coordinates were obtained Precise coordinates were obtained from IGS website for three nearby IGS from IGS website for three nearby IGS stations, namely LHAS, BAHR and IISC. stations, namely LHAS, BAHR and IISC. By tightly constraining these three By tightly constraining these three stations, the precise coordinates of all stations, the precise coordinates of all the four reference stations along with the four reference stations along with IIT Bombay permanent reference IIT Bombay permanent reference station were calculatedstation were calculated

Step 2Step 2

After computing the reference After computing the reference stations coordinates, all 27-stations coordinates, all 27-deformation stations were processed deformation stations were processed with two reference stations and IITB with two reference stations and IITB permanent reference station. Here permanent reference station. Here the coordinates of IITB and two the coordinates of IITB and two reference stations were tightly reference stations were tightly constrained to their calculated values constrained to their calculated values in step 1in step 1

Height Comparison for IGS reference Height Comparison for IGS reference stations and IITB stationstations and IITB station

Station Ellipsoidal Height in m Ellipsoidal Height Difference in mm

Feb 04 Feb 05 Jan 06 Feb 05- Feb 04 Jan 06 - Feb 04

LHAS 3624.638 3624.634 3624.635 -4 -3

BAHR -17.077 -17.076 -17.075 1 2

IISC 843.723 843.725 843.726 2 3

IITB -4.004 -4.013 -4.012 -9 -8

Precision Estimated for the Precision Estimated for the co-ordinatesco-ordinates

Estimated rms (mm)Estimated rms (mm)

Maximum Maximum rmsrms

Minimum Minimum rmsrms

Mean rmsMean rms

HeightHeight 3.73.7 0.60.6 2.32.3

LatitudeLatitude 0.20.2 0.10.1 0.30.3

longitudelongitude 0.60.6 0.10.1 0.30.3

Average Change in HeightsAverage Change in Heights

Stations Feb 05-Feb 04 in mm

Jan 06-Feb 04 in mm

Deformation Stations Within Reservoir Boundary

-4.9 -38.3

Deformation Stations Outside Reservoir Boundary

7.8 -26.9

Reference Station -2.8 -9.5

Actual Subsidence Over AreaActual Subsidence Over Area

Stations Feb 05-Feb 04 in mm

Jan 06-Feb 04 in mm

Deformation Stations Within Reservoir Boundary

-2.1 -28.9

Deformation Stations Outside Reservoir Boundary

5.0 -17.4

Average Change in HeightAverage Change in Height

Comparision of Height Changes

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

Campaigns

Ell

ipso

idal

Ht.

Dif

fere

nce i

n

m.

Average Ht.changes for points on reservoir

Average Ht.changes for allother points

Contours Showing Height Difference between Feb 04-Jan06

Water Level and Height ChangesWater Level and Height Changes

All points showing subsidence during All points showing subsidence during pre monsoon periodpre monsoon period

All points are showing upliftment All points are showing upliftment during post monsoon periodduring post monsoon period

These level changes observed are These level changes observed are mainly due to the local seasonal mainly due to the local seasonal variations in the area. variations in the area.

ConclusionConclusion The rate of subsidence over area has not been The rate of subsidence over area has not been

established established Long duration study is required to find rate of Long duration study is required to find rate of

SubsidenceSubsidence Correlation Coefficient between changes in ground Correlation Coefficient between changes in ground

water level and height changes of deformation water level and height changes of deformation stations is very poorstations is very poor

Extraction of water is very less over this area, hence Extraction of water is very less over this area, hence reasons for subsidence over area is other than reasons for subsidence over area is other than water extraction , like gas extraction etc.water extraction , like gas extraction etc.

Extensive study required to monitor subsidenceExtensive study required to monitor subsidence In future rigorous monitoring will be done to find In future rigorous monitoring will be done to find

the rate of subsidence and find out the factors the rate of subsidence and find out the factors affecting the land subsidenceaffecting the land subsidence

InSAR technique will be implemented to study the InSAR technique will be implemented to study the subsidence over the area in futuresubsidence over the area in future