project report impact of mining on · pdf filegoswami, om (mining) and all other members of...
TRANSCRIPT
i
PROJECT REPORT
IMPACT OF MINING ON GROUNDWATER REGIME
IN GHOGHA-SURKA, KHADSALIYA-I AND
KHADSALIYA-II, LIGNITE MINE, BHAVNAGAR
DISTRICT, GUJARAT
Submitted to
GUJRAT POWER CORPORATION LTD., GHANDHINAGAR,
GUJARAT
By
NATIONAL INSTITUTE OF HYDROLOGY
ROORKEE-247667 (Uttaranchal)
April, 2012
ii
IMPACT OF MINING ON GROUNDWATER REGIME
IN GHOGHA SURKA, KHADSALIYA-I AND
KHADSALIYA-II, LIGNITE MINE, BHAVNAGAR
DISTRICT, GUJARAT
Submitted to
GUJRAT POWER CORPORATION LTD., GHANDHINAGAR,
GUJARAT
By
NATIONAL INSTITUTE OF HYDROLOGY
ROORKEE-247667 (Uttarakhand)
April 2012
iii
STUDY TEAM
Project Director
Er. R.D. Singh, Director, NIH
Project Coordinator
Dr. Bhishm Kumar, Scientist F
Principal Investigator
Dr. Sudhir Kumar, Scientist F
Dr. SP Rai, Scientist E1
Supporting Staff
Ms Kumkum Mishra, SRF
Ms. Manali Singh, JRF
iv
ACKNOWLEDGEMENT
The Principal Investigator is thankful to M/s Gujarat Power Corporation Limited,
Gandhinagar for sponsoring the consultancy on “Impact of Mining on Groundwater Regime
in Khadsaliya-1 Lignite Mine, Bhavnagar District, Gujarat” to National Institute of
Hydrology, Roorkee. Thanks are due to Sh. Nayan Chokshi, Company Secretary, Sh. S.K.
Goswami, OM (Mining) and all other members of GPCL, Gandhinagar for extending all the
help and support in completion of this report.
We are thankful to Er. RD Singh, Director, National Institute of Hydrology, Roorkee for
providing all administrative and financial support for the successful completion of the
project.
v
CONTENTS
1 INTRODUCTION ............................................................................................................ 8 1.1 Preamble ...................................................................................................................... 8
1.2 Objectives .................................................................................................................... 8
1.3 Scope of the Study....................................................................................................... 9
1.4 Data Used .................................................................................................................... 9
2 GENERAL DESCRIPTION OF THE STUDY AREA ............................................... 11 2.1 Location and Extent .................................................................................................. 11
2.2 Physiography and Drainage ...................................................................................... 12
2.3 Climate ...................................................................................................................... 15
2.4 Rainfall ...................................................................................................................... 15
2.5 Geology ..................................................................................................................... 15
3 HYDROGEOLOGY OF THE AREA .......................................................................... 17 3.1 Deccan Trap Formations ........................................................................................... 17
3.2 Alluvial and Tertiary Formations .............................................................................. 18
3.3 Ground Water Recharge: ........................................................................................... 19
4 ESTIMATION OF WATER BUDGET ........................................................................ 20
5 GROUNDWATER MODELLING ............................................................................... 22 5.1 Groundwater Flow Modeling .................................................................................... 22
5.2 Solute Transport Modeling (MT3D) ......................................................................... 23
5.3 Groundwater Modelling of Coastal Aquifers using SEAWAT ................................ 24
6 CONCEPTUAL MODEL .............................................................................................. 26 6.1 Model Framework ..................................................................................................... 26
6.2 Input Data .................................................................................................................. 29
6.3 Stress Periods ............................................................................................................ 31
6.4 Model Calibration ..................................................................................................... 31
6.5 Mass Balance............................................................................................................. 34
6.6 Sensitivity Analysis ................................................................................................... 35
7 IMPACT OF MINING ON GROUNDWATER REGIME ........................................ 36
8 RAINWATER HARVESTING ..................................................................................... 40 8.1 Advantages of Rainwater Harvesting ........................................................................ 40
8.2 Conditions for Artificial Recharge to Groundwater .................................................. 41
8.3 Rainwater Harvesting Systems.................................................................................. 41
8.4 Components of Rainwater Harvesting ...................................................................... 42
8.5 Artificial Recharge Structures ................................................................................... 43
8.6 Rainwater Harvesting Scheme .................................................................................. 45
9 CONCLUSIONS AND RECOMMENDATIONS ....................................................... 47
vi
LIST OF FIGURES
Figure 1: Location Map of the Study Area .............................................................................. 12
Figure 2: DEM of the Study Area. ........................................................................................... 13
Figure 3: Drainage Map of the Study Area .............................................................................. 14
Figure 5: Model Domain .......................................................................................................... 26
Figure 6: Discretisation of model domain (A) Plan, and sections across (B) Ghogha-
Surkha Block, (B) Khadsaliya-I Block (B) Khadsaliya-II Block. .......................... 28
Figure 7: Steady State calibration. ........................................................................................... 32
Figure 8: Calibrated hydraulic conductivity (K) of different layers along a row .................... 33
Figure 9: Simulated and observed heads for calibrated values of specific yield. .................... 34
Figure 10: Mass balance of mining lease area (all three). ....................................................... 34
Figure 11: Water table contours after (A) 0 yr, (B) 1yr, (C) 3 yrs, and (D) 5yrs. ................... 38
Figure 12: Water level along EW and NS cross sections. ....................................................... 39
Figure 13: Schematic diagram of a recharge pit ...................................................................... 43
Figure 14: Schematic diagram of a recharge shaft................................................................... 44
vii
LIST OF TABLES
Table 1: Monthly Rainfall for the period 2006 to 2010 at Bhavnagar. .................................... 15
Table 2: Local Geology of the area.......................................................................................... 16
Table 3: Layers of the Model ................................................................................................... 29
Table 4: Model input parameters ............................................................................................. 29
Table 5: Stress periods considered for each year ..................................................................... 31
Table 6: Calibrated specific yield and specific storage. .......................................................... 33
Table 7: Mining Schedule for 5 years period........................................................................... 36
Table 8: Illustrative Water Harvesting Potential for different land uses ................................. 45
Table 9: RWH Potential v/s Water Requirement in Mining Blocks (MCM/yr) ...................... 45
8
1 INTRODUCTION
1.1 Preamble
The natural and man-made influences are known to change the groundwater resource potential in
an area. To meet the energy demand and infrastructure development, mining is an unavoidable
activity in exploitation of hidden natural resources for the development of society.
Gujarat Power Corporation Limited is a progressive company in the state of Gujarat. The
company was established by the Government of Gujarat in June 1990 in association with Gujarat
Electricity Board for the purpose of raising investment in power sector by the private
entrepreneurs. The main objects of the GPCL includes power generation based on various fuels
and establishing power stations in various areas of the State by attracting more and more
investments from the private / public entrepreneurs.
GPCL has successfully commissioned many power projects in the state of Gujarat, which include
lignite based power station, gas based power project, solar and wing based power projects.
GPCL is in the process of commissioning 500 MW pit head lignite based power project in
Bhavnagar district, for this purpose, three lignite mines namely Ghogha - Surka, Khadsaliya-I
and Khadsaliya-II are to be opened in the Ghogha and Bhavnagar Taluks of Bhavnagar district of
Gujarat.
For the environmental clearance of these mines by MOEF, Govt. of India, GPCL has assigned
the work for preparation of EIA/EMP report to NEERI, Hyderabad. The task of groundwater
modeling to ascertain the impact of mining on the groundwater regime was assigned to National
Institute of Hydrology, Roorkee.
1.2 Objectives
The objectives of the task entrusted to National Institute of Hydrology, Roorkee, are:
1. To study the impact of mining and water abstraction on the hydrogeological and
groundwater regime of within core zone and 10 km buffer zone including long-term
modeling studies,
2. To study the impact of sea water ingress and cutting into groundwater aquifer, and
3. To suggest the rain water harvesting scheme and measures for recharge of groundwater.
9
1.3 Scope of the Study
The scope of the study is:
i. Site visit and discussion with client.
ii. Collection and review of the available data, relevant project reports and other
information about the study area.
iii. Processing of the available data.
iv. Estimation of water budgeting and evaluating surface water, groundwater component.
v. Ascertaining the groundwater flow direction.
vi. Figuring out the disposition of aquifer system,
vii. Determining the impact of long term pumping of groundwater regime in and around
the mining area through groundwater modeling.
viii. Assessment of the impact of pumping on the sea water ingress through groundwater
modeling.
ix. Impact of excavation of aquifer on groundwater regime
x. Impact of excavation of aquifer on groundwater regime.
xi. Rain water harvesting potential of the area.
xii. Rain water harvesting scheme and measures for groundwater recharge.
1.4 Data Used
Following data is required to decipher the groundwater regime and to study the impact of
dewatering (of the proposed mine) on the groundwater regime near the mine:
Physiographic Data / Maps
i. Topographical map of the study area (1:50,000 scale)
ii. Location map showing mining area, river, canals, and locations of rain gauges, G & D
sites, and climatologically station,
iii. Maps showing location of villages and indicating land-use pattern,
iv. Drainage map showing river, river basin, with all branches or tributaries,
Geological Data
i. Geological map of the area (1:10,000 Scale)
ii. Structural map of the area along with details of fractures, joints etc.
10
Surface Water Data
i. Monthly rainfall data (for past 5 years),
Groundwater data
i. Water level fluctuation in different piezometers for deeper aquifers,
ii. Lithological and geological information in the mining area and the surrounding area,
iii. Existing groundwater practices such as; withdrawal and uses,
iv. Pumping data
v. Aquifer parameters such as; hydraulic conductivity and storage coefficient of each
layer and thickness of each layer,
11
2 GENERAL DESCRIPTION OF THE STUDY AREA
2.1 Location and Extent
The study area is comprised of three mining blocks, Ghohga-Surka, Khadsaliya-I and
Khadsaliya-II, located in the Ghogha and Bhavnagar Taluks of Bhavnagar District of Gujarat.
Ghogha-Surka Block: The lease area is located between latitude 21˚36’00” to 21˚38’45” N
and longitude 72˚11’55” to 72˚15’00”E and is covered under Survey of India’s Toposheet Nos.
46 C/2 and 46 C/6 (Figure 1). Total lease area is 1355 ha which includes private land and Govt. /
Goucher land and other land (covering Nallah, Road and Ponds etc). There is no forest land
within the lease area. Bhavnagar, the District Headquarters is about 27 km in the north west of
the Ghogha Surka block. The mining site is well connected by state highways and district roads
with the major city (Bhavnagar) and towns of Gujarat. The villages covered under the Ghogha -
Surka mining area are Badi, Alapar, Malekvadar, Surka, Padva, Rampar, Thordi and Hoidad.
Khadsaliya-I Block: Mining lease area of Khadsaliya-I Block falls within the jurisdiction of
Ghogha and Bhavnagar Talukas of Bhavnagar district. The lease area is located between latitude
21˚31’25” to 21˚33’15” N and longitude 72˚13’30” to 72˚14’55”E and is covered under Survey
of India’s Toposheet Nos. 46 C/2 and 46 C/6 (Figure 1). Total lease area is 711.4247 ha which
includes private land and Govt. / Goucher land and other land (covering Nallah, Road and Ponds
etc). There is no forest land within the lease area. Bhavnagar, the District Headquarters is about
35 km due north of the Khadsaliya-I block. The site is well connected by an all weather road
which runs from Lakhanka to Bhavnagar via. Thalsar, Koliyak and Ratanpur villages. The
villages covered under the Khadsaliya-I mining lease area are Thalsar, Lakhanka, Khadsaliya
and Morchand villages.
Khadsaliya-II Block: Mining lease area of Khadsaliya-II block falls within the jurisdiction
of Ghogha and Bhavnagar Talukas of Bhavnagar district. The lease area is located between
latitude 21˚33’15” to 21˚36’30” N and longitude 72˚13’40” to 72˚15’25”E and is covered under
Survey of India’s Toposheet Nos. 46 C/2 and 46 C/6 (Figure 1). Total lease area is 914.1492 ha
which includes private land and Govt. / Goucher land and other land (covering Nallah, Road and
Ponds etc). There is no forest land within the lease area. Bhavnagar, the District Headquarters is
about 29 km in the north west of the Khadsaliya-II block. The site is well connected by State
highways and district roads with the major cities and towns of Gujarat. The villages covered
under the Khadsaliya-II mining lease area are Thalsar, Khadsaliya, Bhadbhadiya and Alapar
villages.
12
Figure 1: Location Map of the Study Area
2.2 Physiography and Drainage
Ghogha Surkha: The project area, in general, has plain topography in northern part while the
southern part exhibits undulated topography with low mounds. The maximum elevation in the
lease area is 45 m and the minimum elevation is 16 m above MSL (Figure 2). The general slope
of the ground is towards Malesari River, which flows from west to east direction, bisecting the
lease area, and finally debouching into Gulf of Khambhat (Figure 3). The river is seasonal and
flows only during the rainy season. The sea coast is about 4.5 km in eastern direction of the area.
13
One canal, Shatrunji Left Bank Canal running north to south also traverses through the area. The
canal only runs during the summer season.
Figure 2: DEM of the Study Area.
Khadsaliya-I: The area, in general, is undulating in most of the parts except the northern part
where there are cultivated fields due to plain topography. A number of rock outcrops stand out as
small mounds in the area. The maximum elevation in the lease area is 48.11 m and the minimum
14
elevation is 19.20 m above MSL. The general slope of the ground is towards east direction, i.e.,
Gulf of Khambhat (Figure 2). The river Ramdasia flows through the lease area and also some
small seasonal nallahs traverse the block and discharge in to Bay of Khambhat. The river is
seasonal and flows only during the rainy season. The Shatrunji Left Bank Canal, flowing in
south to north direction also passing through the block (Figure 3). The canal only runs during
the summer season. The sea coast is about 3 km in eastern direction of the area.
Khadsaliya-II: The project area presents generally plain topography in the eastern part while
the western part exhibits undulating topography with low mounds. The general elevation is in
the range of 10 to 60 m amsl, although variations as high as 63.30 m RL and as low as 12.04 m
in RL have been observed (Figure 2). The general slope of the area is towards east. Seasonal
nallah and a canal pass through the lease area. The rivulet namely Ramdasiya is also crossing
the lease area in south (Figure 3). The rivulet Ramdasiya is a seasonal river, which becomes
active during monsoon period only. The canal is bisecting the lease in north-south direction.
The seasonal river Maleshwari flows from southwest to eastern direction into the bay of
Khambat outside the lease area in north-eastern part.
Figure 3: Drainage Map of the Study Area
15
2.3 Climate
The climate of the area is mostly tropical. The summer temperature goes up to maximum of
46.7°C while the winter temperature as low as 7.4°C have been recorded. The summer season
spans from April to June and the monsoon season from June to September. The maximum and
minimum relative humidity ranges from 45 to 77% during July to September period and from 44
to 50% during November to February. February to April period is comfortable with low ranges
of humidity values. The wind blows mainly from south-west direction in the morning and south-
east direction in the evening.
2.4 Rainfall
Annual rainfall data shows wide variation during this period and ranged between 851 mm to 141
mm and do not fit in any cyclic pattern during this period. It is observed that average annual
rainfall during 1981-1992 was 660.8 mm. During the last five years (2006-2010) the rainfall has
shown an increasing trend and has an average of 722.6 mm. The rainfall data for 2006-2010 is
given in Table-1. The highest precipitation occurs normally from middle of June to September.
Table 1: Monthly Rainfall for the period 2006 to 2010 at Bhavnagar.
Monthly Rainfall (mm)
Year 2006 2007 2008 2009 2010
Jan 0.0 0.0 0.0 0.0 0.2
Feb 0.0 0.1 0.0 0.0 0.0
Mar 0.8 0.0 0.0 0.0 0.0
Apr 0.0 4.0 1.9 0.0 0.0
May 0.0 0.0 0.0 0.0 0.0
June 126.0 109.1 39.8 26.2 72.5
July 456.1 254.3 221.1 256.2 244.4
Aug 92.4 285.7 186.6 46.3 214.2
Sep 55.6 313.5 279.6 35.4 200
Oct 1.0 0.0 11.7 16.8 6.3
Nov 0.2 0.5 0.0 2.2 52.4
Dec 0.0 0.0 0.0 0.0 0.0
Total 732.1 967.2 740.7 383.1 790.0
2.5 Geology
Geologically the region is a part of the Saurashtra Peninsula, which is bounded by Arabian Sea
on all side expect on the north-east where it is flanked by alluvial plains. About 65% of the
16
peninsula is covered by basaltic lava flows (Deccan trap). In the northern part of the peninsula,
the traps are overlain by upper Mesozoic sediments. At the costal fringe, the traps underlie the
Tertiary-Quaternary sediments.
Locally, the geology of the area is obscured by thick cover of Red Soil/ lateritic soil except
isolated exposures of weathered sandstone in the south part of the block. The information about
the litho units, gathered during the course of drilling and from the surface geological mapping in
the area is given in Table 2.
Table 2: Local Geology of the area.
FORMATION AGE LITHO UNITS GENERAL THICKNESS (m)
Ghogha
Surkha
Khadsaliya-
I
Khadsaliya-
II
Recent Recent &
sub recent
Black cotton soil,
kankar, coarse
sandy zones etc.
0.50 – 3.00
0.00 – 2.00
0.00 – 2.00
Gaj formation Lower
Miocene
Pale Yellow non
plastic clay,
variegated clays
and argillaceous
gritty sandstones.
6.00 -
24.00
10.00 -
26.50
10.00 - 61.00
Khadsaliya
clays
Middle to
Upper
Eocene
Greenish grey to
grey clays with
lignite and
argillaceous
sandstone.
32.0-78.00 21.00 –
48.80
14.00– 46.00
Supra -
trappean
Upper
Cretaceous
to Lower
Eocene
Lithomargic clays 1.00 – 7.00 0.50 – 5.00 1.00 – 7.00
Deccan trap Cretaceous Greenish black
basalt with the
veins of siliceous
material.
Basement Basement Basement
The geological cross sections constructed based on the available borehole logs are given in
Figure 4. The figure indicates that the thickness of Khadsaliya clays more in the northern side
where as it is less in the southern and eastern side.
17
3 HYDROGEOLOGY OF THE AREA
In general, the area is covered with a thin layer of alluvial soil/black cotton soil, which has been
derived as a result of weathering of trap rock. This soil mantle is underlain by a column of
medium to coarse grained sandstone which also outcrops in the area. This litho-unit is one of the
important aquifer existing in the area and contains water throughout the year. Apart from this
weathered and fractured basalts also constitute an aquifer in the surrounding areas. This fact has
been duly supported by geophysical logs of boreholes besides existence of number of shallow
dug wells in the area. The water table during summer months remains at 3.1 m to 14 m depth
whereas during monsoon it is as shallow as about 5m from surface. The lithounit occurring
below this aquifer are mostly argillaceous in nature and do not contain much water.
3.1 Deccan Trap Formations
Nature of formations – Deccan formations in the west of the mining blocks are the oldest found
in the study area. The traps mostly consist of basaltic lava flows of volcanic igneous origin and
belong to Cretaceous to Eocene age (Chaulya, 2003). As these are basically hard formations,
they have low porosity and permeability and hence no well-defined aquifer system exists in the
area. The storage space is provided by the development of secondary porosity due to weathering,
development of fractures, joints and inner flow space. All these features vary in their intensity in
lateral and vertical direction, resulting in the development of storage space in the form of small
irregular pockets. These pockets may be weakly interconnected or may be separated from each
other by the impermeable barriers. By gravity and following weak planes, rain enters and slowly
moves down. This feature was often observed in exposed weathered rocks in excavation sites
and road cuttings. Groundwater flow continues down below to fractured rocks, controlled by
strike and dip of joints and other weak planes.
Groundwater conditions – Groundwater in the Deccan Traps occurs in the upper weathered
portion as well as in cracks, fissures, joints and fractures. Top 5 to 20 m of ballistic rocks are
weathered and fractured at varying degrees and the intensity of groundwater infiltration is
dependent on these fractures. Many wells are dug in this weathered zone with depths varying
from 5 to 15 m from ground level. Diameter of the wells vary from 2 to 6 m. Depth of water
from the ground surface depends on seasonal rainfall, the elevation of ground and also on local
startigraphy. It normally varies from 2 to 5 m west of the mining blocks and 2 to 10 m in the
buffer zone. The gradient of water table follows the surface elevation, which is west to east with
moderate slopes ranging from 1 in 300 to 1 in 150. But locally, this gradient varies erratically
and at some places is very high. This is due to the irregularities in the occurrences of water in the
trap areas. As rainfall is the major source of recharge, the dug wells show maximum fluctuation
between pre-monsoon and post-monsoon periods. Fluctuation of 3 to 4 m can be taken as typical
for the area. Yield of the individual wells also vary from place to place depending on the
18
localized geo-hydrological conditions. A properly constructed dug well of about 5 m diameter
and 10 to 15 m depth in a fairly well weathered and fractured strata could yield about 300 lpm.
Specific yield is also an important parameter for determining as to how much water will be
released from the storage of aquifer. Field studies/pumping tests have indicated a value of 3% as
specific yield for the formation up to a depth of 20m from ground level in the Deccan Trap area.
Hydraulic conductivity and transmissivity of the aquifer in the trap area showed area-wise
variation, depending upon the local stratigraphical conditions. Similarly, depth-wise variation
also occurs due to nature of the aquifer material, thickness, magnitude of weathering, etc. Based
on the pumping test results in the Deccan Trap area, hydraulic conductivity and Transmissivity
values varied from 3 to 8 m/d and 30 to 100 m2 day
−1, respectively.
3.2 Alluvial and Tertiary Formations
Nature of formations – Alluvial and tertiary formations are exposed within the mining block.
Alluvial formation comprises of silt, sand dune and beach sand. Geologically, these are of recent
origin. Tertiary formations of Lower Miocene consist of conglomerates, sandstones and clays.
Stretches of Supratrappean formations of Lower Eocene age, consisting of laterite and bentonite,
are exposed at the western and southern fringe. The storage is directly proportional to the
porosity of the formation in this type of soil.
(ii) Groundwater conditions – The thickness of alluvial formation together with upper
sandstone, clays and conglomerates varies from 10 to 30 m. Dug well constructed in these
formations vary in depth from 3.10 to 22.5 m and diameter of the wells varies from 2 to 5 m. The
depth of water in the dug wells depends on the elevation of ground surface, rainfall, season of the
year and stratigraphical conditions. Normal range is between 2 to 8 m from ground level. The
average water level fluctuations between pre-monsoon and monsoon seasons can be taken as
1.50 m for calculation purposes. Gradient of the water table normally follows the surface slope
and is from west to east with slope of 1 in 1000 to 1 in 500. Yield of the dug wells and dug-cum-
tube wells vary from place to place within the mining block and other areas of occurrence of
sedimentary formations. Normal range can be taken as 100 to 600 lpm. Specific capacity of the
wells in these formations is high, but shows wide variations from 50 to 300 lpm/m of draw
down. Based on the pumping test results, the hydraulic conductivity of the top 30 m of the
formation in Khadsaliya mining block showed appreciable vertical variation depending on the
type of strata i.e. alluvium or sandstone or conglomerate or clay. The normal range is 5 to 15
md−1
. The transmissivity values also correspondingly show variations depending on the
hydraulic conductivity of the formations and the thickness. The normal range is 100 m2d
−1 for
the formations encountered within the depth of about 30 m in the mining block and other
sedimentary zones.
19
3.3 Ground Water Recharge:
The main source of groundwater recharge in the area is by precipitation. The infiltration in the
rate varies with type of soil. Rainfall recharge in the area is reported to be 18 % of the normal
rainfall (Chaulya, 2003).
20
4 ESTIMATION OF WATER BUDGET
The mining lease area of Ghogha – Surka, Khadsaliya-I and Khadsaliya-II mining lease area are
mostly barren with patches of agriculture. The source of water to the area is precipitation.
Though a canal (Shatrunji Left Bank Canal) passes through the block on the eastern side, it
carries little water and that too far a shot period (3-4 months). Average annual rainfall of the area
is 722 mm, out of which 40% is lost as surface runoff. This quantity is quite high because around
38% of surface runoff water is used as consumptive use. As the area is very near to sea, surface
storage structures in the region are very less. The drainage in the area is a small river and does
not have much storage capacity. Further, out of total rainfall, 24% is partly lost through
evaporation and transpiration. This quantity is very low since the area has only few bushy plants
and large portion of the area is barren or animal grazing land with only one river having water
during rainy season only. The remaining 36% of rainfall water enter into the subsoil as
infiltration due to existence of porous soil cover in the area. About 50% of gravitational water,
entering into the soil, is lost through slow downward movement of groundwater towards the sea.
Therefore, only remaining 50% of gravitational water becomes utilisable as groundwater
resources based on the prevailing conditions of groundwater abstraction in the area (CMRI,
2001).
The surface water and groundwater budget of has been computed using rainfall infiltration
method and specific yield method.
Based on the above data, water resource availability for the Ghogha-Surka, Khadsaliya-I and
Khadsaliya-II blocks have been calculated by Rainfall Infiltration Factor and Specific Yield
methods. The details of the breakup of the two methods are given below in Table 3:
Table 3: Rainfall recharge in study area
Unit Ghohga Surka Khadsaliya-I Khadsaliya-II
Block area m2 13550000 7114247 9141898
Average annual rainfall m 0.722 0.722 0.722
Total precipitation within
the block
MCM 9.78 5.14 6.60
Rainfall Infiltration Factor Method (1)
Surface runoff MCM 3.91 2.05 2.64
Evapotranspiration loss MCM 2.35 1.23 1.58
Sub-surface loss MCM 1.76 0.92 1.19
Utilisable groundwater MCM 1.76 0.92 1.19
Specific Yield Method (2)
Specific yield % 7 7 7
Water level fluctuation m 1.5 1.5 1.5
Annual recharge MCM 1.42 0.75 0.96
21
Average Recharge
=[(1)+(2)] / 2
MCM 1.59 0.84 1.08
Water Demand MCM 0.157
(0.43 mld)
0.102 MCM
(0.27 mld)
0.092 MCM
(0.25 mld)
10% 12% 9%
The Table-3 indicates that the groundwater requirement for the mining activity is only 9-12% of
the average recharge within the mining lease areas. Therefore, it may be stated that the water
requirement of the proposed lignite mines will not affect the groundwater resource of the region.
22
5 GROUNDWATER MODELLING
Groundwater flow modeling is an important tool frequently used to study the dynamic behavior
of groundwater system. Groundwater flow models attempt to reproduce or simulate the operation
of a real groundwater system using mathematical equations solved by a computer programme.
Recent trend in groundwater modeling is to use the user-friendly and robust software packages to
develop groundwater management plans. A number of commercial groundwater software with
GIS capabilities like Visual MODFLOW, GMS, GW Vista, etc are being widely used for this
purpose.
5.1 Groundwater Flow Modeling
Groundwater flow modeling is an important tool frequently used for three general purposes
(Kresic, 1997):
To predict expected changes in the system (aquifer) studied.
To describe the system in order to analyze various assumptions about its nature and
dynamics.
To generate a hypothetical system that will be used to study principles of groundwater
flow associated with various general or more specific problems.
The applicability of a groundwater model to a real situation depends on the accuracy of the input
data and the parameters. Determination of these requires considerable study, like collection of
hydrological data (rainfall, evapotranspiration, irrigation, drainage) and determination of the
parameters mentioned before including pumping tests. As many parameters are quite variable in
space, expert judgment is needed to arrive at representative values.
“A Modular Three Dimensional Finite-Difference Groundwater Flow Model” i.e. MODFLOW
computer code, developed by McDonald and Harbaugh 1988, is the most common groundwater
model being used world over. It simulates steady and non-steady flow in three dimensions for an
irregularly shaped flow system in which aquifer layer can be confined, unconfined, or a
combination of confined and unconfined. Flow from external sources, such as flow to wells, areal
recharge, evapotranspiration, flow to drains, and flow through river, can be simulated
Mathematical Background
The three dimensional unsteady movement of groundwater of constant density through porous earth
material in a heterogenous anisotropic medium can be described by the following partial differential
equation:
23
t
hS = W -
z
hK
z +
y
hK
y +
x
hK
xszzyyxx
(1)
Where,
x,y,z = Cartesian coordinates aligned along the major axes of conductivity Kxx, Kyy,
Kzz
h = potentiometric head [L],
W = volumetric flux per unit volume (sources and/or sinks of water) [T-1
],
Ss = specific storage of the porous material [L-1
] and,
t = time [T].
In general, Ss, Kxx, Kyy and Kzz are function of space, for example; Ss = Ss(x,y,z), Kxx = Kxx(x,y,z),
etc. whereas W and h are functions of space and time i.e W = W(x,y,z) and h = h(x,y,z). Equation
(1) together with specification of flow conditions at the boundaries of an aquifer system and
specification of initial head conditions constitutes a mathematical model of ground water flow.
Except for very simple systems, analytical solutions of equation (1) are rarely possible. So, various
numerical methods are employed to obtain an approximate solution of the above equation. One such
approach is the finite-difference method. The continuous system described by equation (1) is
replaced by a finite set of discrete elements in space and time, and the set of finite difference
equations are solved numerically which yields values of head at specific points and times. These
values constitute an approximation to the time-varying head distribution that would be given by an
analytical solution of the flow equation.
5.2 Solute Transport Modeling (MT3D)
MT3D code retains the same modular structure as of the U.S. Geological Survey modular three-
dimensional finite-difference groundwater flow model, MODFLOW, (McDonald and Harbaugh,
1988; Harbaugh and McDonald, 1996). The modular structure of the transport model makes it
possible to simulate advection, dispersion/diffusion, source/sink mixing, and chemical reactions
separately.
MT3D code uses with block-centered finite-difference flow model such as MODFLOW and is
based on the assumption that changes in the concentration field will not affect the flow field
significantly. After a flow model is developed and calibrated, the information needed by the
transport model is used by the transport model.
The partial differential equation describing the fate and transport of contaminants of species k in
three-dimensional, transient groundwater flow systems can be written as follows:
24
(2)
where
Ck is the dissolved concentration of species k, ML
-3;
Θ is the porosity of the subsurface medium, dimensionless;
T is time, T;
xi is the distance along the respective Cartesian coordinate axis, L;
Dij is the hydrodynamic dispersion coefficient tensor, L2T
-1;
vi is the seepage or linear pore water velocity; LT-1
; it is related to the specific discharge or
Darcy flux through the relationship, vi = qi/θ.
qs is the volumetric flow rate per unit volume of aquifer representing fluid sources (positive)
and sinks (negative), T-1
;
Csk is the concentration of the source or sink flux for species k, ML
-3;
ΣRn is the chemical reaction term, ML-3
T-1
.
5.3 Groundwater Modelling of Coastal Aquifers using SEAWAT
Ground water in the coastal areas contains dissolved constituents, such as the salts commonly
found in seawater. At relatively low concentrations, dissolved constituents do not substantially
affect fluid density. As solute concentrations increase, however, the mass of the dissolved
constituents can substantially affect the fluid density. If the spatial variations in fluid density are
minimal, regardless of the actual density value, field and mathematical methods for quantifying
rates and patterns of ground-water flow are relatively straightforward. In many of these
hydrogeologic settings, an accurate representation of variable density ground-water flow is
necessary to characterize and predict ground-water flow rates, travel paths, and residence times.
In coastal aquifers, an interface exists between fresh ground water flowing toward the ocean and
saline ground water. Across the interface, the fluid density may increase from that of freshwater
(about 1,000 kg/m3) to that of seawater (about 1,025 kg/m
3), an increase of about 2.5 percent.
Field observations and mathematical analyses have shown that this relatively minor variation in
ground-water density has a substantial effect on ground-water flow rates and patterns. An
understanding of variable-density ground-water flow, therefore, can be important in many types
of studies of coastal aquifers, such as studies of saltwater intrusion, contaminated site
remediation, and fresh ground-water discharge into oceanic water bodies.
The source code for SEAWAT combines MODFLOW and MT3DMS (a solute transport model)
into a single program that solves the coupled flow and solute-transport equations. The SEAWAT
code also follows a modular structure, so new capabilities can be added with only minor
modifications to the source code. MODFLOW was modified to conserve fluid mass rather than
25
fluid volume and uses equivalent freshwater head as the principal dependent variable. In the
revised form of MODFLOW, the cell-by-cell flow is calculated from freshwater head gradients
and relative density-difference terms. The resulting flow field is passed to MT3DMS for
transport of solute; an updated density field is then calculated from the new solute concentrations
and incorporated back into MODFLOW as relative density-difference terms.
26
6 CONCEPTUAL MODEL
Groundwater modeling begins with a conceptual understanding of the physical problem. It
determines the dimensions of the numerical model and the design of the grid. The conceptual
model integrates the data and includes (a) the hydrogeological framework, (b) the physical
framework, (c) a detailed description of the water budget, (d) the physical and hydraulic
boundary conditions, (e) estimates of groundwater sources and sinks, and (f) information about
regional flow paths (Anderson & Woessner, 1992).
6.1 Model Framework
A conceptual model has been developed for the Ghogha-Surka and Khadsalia area, based on the
available data. The study area is bound by Arabian Sea in the east and two small seasonal rivers,
Malesari Nadi in the north and Ramdesia Nadi in the south (Figure 5). The model domain has
been considered large enough to nullify the effect of any boundary on the aquifer system, except
for the Arabia Sea in the east. Arabian Sea has been considered as constant head boundary. No
flow boundary has been considered on northern, western and southern boundaries.
Figure 4: Model Domain
27
In the finite difference method, the continuous system described by the governing equation is
replaced by a finite set of discrete points in space and time and the partial derivatives are
replaced by differences between functional values at these points. This requires discretisation of
the aquifer system into grids forming rows, columns and layers.
Grid: The study area is first discritised into 1,05,000 square cells (350 rows x 300 columns),
with each cell having the dimensions of 50 x 50 m. All the cells on the land area (79253 cells)
have been considered as active and the cells in the Arabian Sea (25747 cells) have been
considered as inactive. The active and inactive cells are separated by constant head boundary. All
the hydraulic and hydrogeologic properties are considered uniform over the extent of each cell.
The discretised model domain is shown in Figure 6 (A). The West to East sections across the
three proposed mines, i,e., Ghogha-Surka, Khadsaliya-I and Khadsaliya-II bare shown in Figure
6 (B), (C) and (D).
(A)
28
(B)
(C)
(D)
Figure 5: Discretisation of model domain (A) Plan, and sections across (B) Ghogha-Surkha
Block, (B) Khadsaliya-I Block (B) Khadsaliya-II Block.
Active cells are represented by White colour and inactive cells by Cyan colour.
Layers: The study area is composed of Deccan Trap, Gaj formations and Lakhankha formations.
Deccan Trap is overlain by bentonite and other clays (Lithomargic clays). For the modeling
purposes, Lakhanka formations and Gaj formations have been considered as same unit as both of
these formations have similar lithological characteristics, i.e., sandstones and conglomerates.
Therefore three layer model has been considered to assess the impact of mining on seawater
intrusion (Table 3).
29
Table 3: Layers of the Model
Layer No. Thickness
(m)
Litho units
Layer 1 28-110 Greasy/ Variegated Clay, weathered Basalt
Ferruginous sandstone, weathered Basalt
Layer 2 6 Lithomargic clay
Layer3 >8 Massive Basalt
6.2 Input Data
Input data requirement for the model includes hydraulic properties, initial conditions, boundary
conditions, stresses, groundwater draft and groundwater recharge has been taken from the
various reports of the Gujarat Power Corporation Limited, Gandhinagar. Wherever data was not
available, the values of parameters were assumed as per published literature. These data have
been prepared based on the available information from the study area.
The model parameters considered in the present study are summarized in Table 4.
Table 4: Model input parameters
Sl.
No.
Parameters Inputs Remarks
1 Cells 105,000 (50x50 m) (350 rows x 300 columns)
Active 79,253
Inactive 25,747
2 Layers Three
Layer-1 28 – 110m -
Unconfined
Top aquifer
Layer-2 6 m confined Aquitard
Layer-3 8-100 m confined Aquitard
3 Model Boundaries
Constant Head Eastern Side Arabian Sea
No Flow Boundary Northern, Southern
and western Side
Flow lines almost parallel to flow
direction
Recharge (RCH) Top layer
18% of rainfall in Gaj and Khadsaliya
formations (100 mm)
8% in weathered and fractured Basalts
(65 mm)
Evapotranspiration Top layer 300 mm from top of the aquifer with
extinction depth of 2 m
30
Sl.
No.
Parameters Inputs Remarks
4 Aquifer Parameters
Hydraulic
Conductivity (K)
0.001m/d to 5m/d
Varying with nature
of formations
3.5m/d in the Gaj and Khadsaliya
formations
1.8m/d in the weathered and fractured
Basalt
0.001 m/d in massive basalt and
lithomargic clays
Specific Yield (Sy) 1 to 6%
Varying with nature
of formations
6% for Gaj and Khadsaliya formations
2% for weathered Basalts
1% for massive basalt
5 Draft 70% of recharge Uniformly distributed during non
monsoon season
6 Simulation Period 5 years The period in which mine will be fully
developed
Hydraulic Properties
For groundwater modeling, hydraulic conductivity and specific storage are the most important
hydraulic properties. These parameters are usually estimated from the pump test data. In the
study area, hydraulic conductivity of the aquifers are reported to be 3-8 m/d in basalts and 3-15
m/d in alluvium and other formations (Chaulya, 2003). The data indicates low transmissive
characteristics of the formations present in the area. Vertical hydraulic conductivity is taken as
10% of horizontal hydraulic conductivity. The specific yield of the formations is as indicated by
the pump test results. A specific yield of 3% has been estimated in the Basalts by pump tests in
the area. The specific yield of Gaj and Khadsaliya formations has been estimated by steady state
and transient groundwater modeling (Chaulya, 2003).
Initial Conditions
Initial conditions are defined by the spatially distributed groundwater levels / peizometeric heads
of the aquifer at the start of the model period. In the present case, initial heads are taken to vary
as per the topography and the depth to water table has been considered to vary from 1m (near the
coast) m to 20 m in the western side of the area.
Boundary Conditions
No flow Boundary: All the boundaries of the model area are considered as a flow boundary
except the eastern boundary (Arabian Sea), which has been considered as constant head
boundary. The domain of the study area is taken large enough to nullify the impact of no flow
boundary in the area of interest.
31
Recharge boundary: Recharge is assigned on the top surface of the model as the recharge to the
groundwater system, through infiltration of rainfall and irrigation return flows, takes place from
top of the layer. Recharge equivalent to 18% of the normal rainfall has been considered.
Evapotranspiration Boundary: The study area is mainly agricultural area and the main crops
grown are wheat, pulses, and oilseeds. All these crops have shallow roots (<0.5m). For the
purpose of modeling, the maximum depth of evapotranspiration has been considered as 2 m
below ground surface. Below this no evapotranspiration has been consider.
Groundwater Draft
The top aquifer in the study area is stressed by pumping of groundwater through a number of
shallow wells. The draft from the dugwell and shallow tubewells is distributed almost uniformly
over the study area. Limited agricultural development was observed during the field visit to the
area. As per available information groundwater draft in the Bhavnagar district is about 70% of
the annual recharge. Therefore, draft has been considered 70%, evenly distributed in the model
domain. The draft is assumed during the nonmonsoon period.
No deep tube wells exist in the area, therefore, draft point draft has not been considered.
6.3 Stress Periods
Every year the simulation period has been divided into three stress periods depending upon the
monsoon season and non-monsoon months. First stress period ranged from January to May,
second June to September, and third October to December. The recharge and draft values
considered during the various stress periods are given in Table-5.
Table 5: Stress periods considered for each year
Stress Period Rainfall Recharge Groundwater Draft
From To Basalt
Area
Gaj and Khadsaliya
formations
Basalt
Area
Gaj and Khadsaliya
formations
0 150
29 41
150 270 82 115
270 365
18 18
6.4 Model Calibration
For a groundwater model with reliable input parameters and stresses, the response is generally
close to the observed field data. The disagreement in the model results may be either due to
32
unreliable input data or wrong conceptualization or uncertainty in the stress periods. For
example, hydraulic conductivity and specific yield are determined by pumping tests and are the
point values. These may vary in space depending on the heterogeneity of the aquifer media.
Therefore, calibration of the model parameters is thus necessary.
In order to calibrate the model parameters, a steady state simulation of the model was carried out
using the general information about the distribution of heads. The water table slopes from west to
east and the depth to water table decreases gradually from 20 in the west towards gulf of
Khambat.
Steady State Calibration
Figure 6: Steady State calibration.
(Black lines (thick) indicate specified groundwater heads and blue lines (thin) indicated
simulated heads)
33
The steady state model was calibrated to estimate the hydraulic conductivity (K) of the various
layers. Initially the hydraulic conductivity values as obtained by pumping test data (Chaulya,
2003) were specified in the model. The K values were adjusted to obtain the general water table
conditions in the field. The calibrated hydraulic conductivity values ranged from 0.001 m/d to
0.1.52 m/d in different layers of the model. The hydraulic conductivity of the Gaj and Khadsaliya
formations was estimated to be 0.86 m/d and that of weathered basalt to be 1.52 m/d. There is
good correspondence between specified and simulated heads within the lease area (Figure 7).
The calibrated hydraulic conductivities are shown in Figure 8.
Figure 7: Calibrated hydraulic conductivity (K) of different layers along a row
Transient Calibration
After the calibration of hydraulic conductivities, transient calibration was carried out to
determine the specific yield and recharge rates in the study area. It has been reported that the
normal pre and post monsoon water level fluctuations in the Gaj and Khadsaliya area is of the
order of 1.5 meters and 3-4 meters in Basaltic areas. Using this information, the specific yield of
different layers in the area has been calibrated. The calibrated specific yield values are given in
Table 6 and the calibration curves are shown in Figure 9. The specific yield values correspond
to the values published in the literature and the values given by CGWB for semi-consolidated
rocks and weathered basalt (GEC, 1997).
Table 6: Calibrated specific yield and specific storage.
Formation Specific yield Specific storage
Gaj and Khadsaliya 0.06 (6%) 0.001
Weathered Basalt 0.02 (2%) 0001
Massive Basalt 0.002 (0.2%) 1e-5
34
(a) Gaj and Khadsaliya Formations (b) Basalt
Figure 8: Simulated and observed heads for calibrated values of specific yield.
6.5 Mass Balance
As per the calibrated values of hydraulic conductivity, specific yield and groundwater recharge
in the area, the mass balance for the three proposed mining, i.e., Ghogha-Surka, Khadsalitya-I
and Khadsaliya-II, blocks has been simulated and is given in Figure 10. The graph shows that
most of the water to the lease area is coming as inflow from the adjacent areas. The component
of rainfall recharge is small.
Figure 9: Mass balance of mining lease area (all three).
35
6.6 Sensitivity Analysis
Sensitivity analysis was performed with changing the values of calibrated parameters (e.g., K
and Sy). The results indicated that hydraulic conductivity (K) is more sensitive than Sy in the
present case. However, the model has been run using the calibrated parameters as it produced
good results.
36
7 IMPACT OF MINING ON GROUNDWATER REGIME
Once the model was calibrated, the mining schedule was used to simulate the impact of mining
on groundwater regime of the area. As the mine is expected to develop fully in five years from
the date of opening, simulations were carried out for five year period.
The mining schedule of the three mines is given in Table 8 below:
Table 7: Mining Schedule for 5 years period.
BLOCK Ghogha-Surka Khadsaliya-I Khadsaliya-II
Year
Total
Pit
Area
Max
Top
RL
Floor
RL
Total
Pit
Area
Max
Top
RL
Floor
RL
Total
Pit
Area
Max
Top RL
Floor
RL
ha m m ha m m ha m m
IMC and
1st year 58.69 34 -45 35.76 40 -17 29.88 34 -22
2nd
year 98.70 34 -56 51.10 38 -25 42.18 34 -37
3rd
year 131.20 34 -81 68.36 38 -27 63.26 34 -41
4th year 161.20 34 -81 84.05 38 -29 83.68 34 -50
5th year 167.70 34 -87 96.04 38 -30 94.98 34 -52
It has been assumed that for mining operations to continue unobstructed, the groundwater table is
to be lowered below the bottom of the mining pit. For normal mining operations to continue, it is
proposed to lower the water table below 3 meters of the operation level. Therefore the water
table is to be depressed to -48 m, -59 m, -84 m, -84 m, and -90 m in Ghogha-Surka mine; -20 m,
-28 m, -30 m, -32 m, and -33 m in Khadsaliya - I mine, and -25 m, -40 m, -44 m, -53 m, and -55
m in Khadsaliya-II mine in phased manner in the 1st, 2
nd, 3
rd, 4
th, and 5
th year respectively.
It has been assumed that all the water seeping into the mine will have to be removed, so
the water table is to be depressed in this area at a time.
For simulation purposes, the net recharge (recharge – draft) has been considered uniform
throughout the year. The water table generated at the end of 1st, 3
rd and 5
th year is shown in
Figure 11.
37
(A) At the start of Mine
(B) At the end of one Year
38
(C) At the end of 3
rd year
(D) At the end of fifth year
Figure 10: Water table contours after (A) 0 yr, (B) 1yr, (C) 3 yrs, and (D) 5yrs.
39
The Figure 11 indicates that by dewatering the mine, the water levels in the nearby areas will
decline. The effect will be much more towards the Gulf of Khambat and less on the western side.
The cross-section of the area along EW and NS direction are shown in Figure 12.
(A) Cross section of the mine along EW direction (Ghogha-Surka Mine).
(B) Cross section of all the mines along NS direction.
Figure 11: Water level along EW and NS cross sections.
The model indicates that though there will be decline in the groundwater levels in the nearby
areas, but still there are no chances of ingress of sea water into the aquifers between the mine and
the sea coast due to mining. If the pumped water is discharged into the canal which runs to the
east of the area, the chances of sea water ingress are further reduced due to seepage of water
from the canal, which may form a constant head boundary on the eastern side (between sea and
mining area).
40
8 RAINWATER HARVESTING
Rainwater harvesting, in its broadest sense, is a technology used for collecting and storing
rainwater for human use from rooftops, land surfaces or rock catchments using simple techniques
such as jars and pots as well as engineered techniques. In India, rainwater harvesting has been
practiced for more than 4,000 years, owing to the temporal and spatial variability of rainfall. It is
an important water source in many areas with significant rainfall but lacking any kind of
conventional, centralized supply system. It is also a good option in areas where good quality
fresh surface water or groundwater is lacking. The application of appropriate rainwater
harvesting technology is important for the utilization of rainwater as a water resource.
Among the various alternative technologies to augment freshwater resources, rainwater
harvesting and utilization is a decentralized, environmentally sound solution, which can avoid
many environmental problems often caused in conventional large-scale projects using centralized
approaches.
Typically, once an open cast mine is opened, it will increases the porosity as well as the
permeability of the area. The infiltration within the mining area and the overburden dumps may
increase. The construction of power plant may reduce the infiltration in the plant area thereby
increasing the surface runoff. It has been reported that surface runoff can increase from 10% to
55% and infiltration volume can decrease from 50% to 15% in the industrial area. This causes
two types of problems, e.g., (i) lowering of the groundwater table due to less recharge, and (ii)
increase in localized flooding in power plant area. If designed properly good rainwater
harvesting system can address both the issues.
In the present case rainwater harvesting can be implemented only in the Power Plant area.
8.1 Advantages of Rainwater Harvesting
In the coastal areas, rainwater harvesting has many advantages, such as:
a. Improvement in the quality of ground water
b. Rise in the water levels in wells and bore wells that are drying up
c. An ideal solution to water problems in areas having inadequate water resources
d. Saving of energy, to lift ground water. (One-meter rise in water level saves 0.40-kilowatt
hour of electricity).
Apart from these, there are other advantages of rainwater harvesting, which includes:
a. Rainwater harvesting can co‐exist with and provide a good supplement to other water
sources and utility systems, thus relieving pressure on other water sources.
41
b. Rainwater harvesting provides a water supply buffer for use in times of emergency or
breakdown of the public water supply systems, particularly during natural disasters.
c. Rainwater harvesting can reduce storm drainage load and flooding in city streets.
d. Users of rainwater are usually the owners who operate and manage the catchment system,
hence, they are more likely to exercise water conservation because they know how much
water is in storage and they will try to prevent the storage tank from drying up.
e. Rainwater harvesting technologies are flexible and can be built to meet almost any
requirements. Construction, operation and maintenance are not labour intensive.
8.2 Conditions for Artificial Recharge to Groundwater
Artificial recharge techniques are adopted where:
a. Adequate space for surface storage is not available.
b. Water level is deep enough (> 8 m) and adequate sub-surface storage is available.
c. Permeable strata are available at shallow/moderate depth.
d. Ground water quality is bad and the aim is to improve it.
e. There is possibility of intrusion of saline water especially in coastal areas.
In other areas, rainwater-harvesting techniques may be adopted.
8.3 Rainwater Harvesting Systems
Typically, a rainwater harvesting system consists of three basic elements: the collection system,
the conveyance system and the storage system. Collection systems can vary from simple types
within a household to bigger systems where a large catchment area contributes to an impounding
reservoir. The categorization of rainwater harvesting systems depends on factors like the size and
nature of the catchment areas and whether the systems are in urban or rural settings. Some of the
systems are described below.
Simple roof water collection systems: While the collection of rainwater by a single household
may not be significant, the impact of thousands or even millions of household rainwater storage
tanks can potentially be enormous. The main components in a simple roof water collection
system are the cistern itself, the piping that leads to the cistern and the appurtenances within the
cistern.
Larger systems for Industrial areas: When the systems are larger, the overall system can
become a bit more complicated, for example rainwater collection from the roofs and grounds of
industrial area, storage in underground reservoirs, treatment and then use for non-potable
applications.
42
Land surface catchments: Rainwater harvesting using ground or land surface catchment areas
can be a simple way of collecting rainwater. Compared to rooftop catchment techniques, ground
catchment techniques provide more opportunity for collecting water from a larger surface area.
By retaining the flows (including flood flows) of small creeks and streams in small storage
reservoirs (on surface or underground) created by low cost (e.g., earthen) dams, this technology
can meet water demands during dry periods. There is a possibility of high rates of water loss due
to infiltration into the ground, and because of the often marginal quality of the water collected,
this technique is mainly suitable for storing water for agricultural purposes.
8.4 Components of Rainwater Harvesting
Catchment Surface: The effective catchment area and the material used in constructing the
catchment surface influence the collection efficiency and water quality. Materials commonly
used for roof catchment in industrial area are corrugated aluminum and galvanized iron,
concrete, fiberglass, etc. The materials of catchment surfaces must be non-toxic and should not
contain substances which impair water quality. Catchment surfaces and collection devices should
be cleaned regularly to remove dust, leaves and bird droppings so as to minimize bacterial
contamination and maintain the quality of collected water.
On the land surfaces, various factors increase runoff capacity, including: i) clearing or altering
vegetation cover, ii) increasing the land slope with artificial ground cover, and iii) reducing soil
permeability by soil compaction. Specially constructed ground surfaces (concrete, paving stones,
or some kind of liner) or paved runways can also be used to collect and convey rainwater to
storage tanks or reservoirs.
Conveyance Systems: Conveyance systems are required to transfer the rainwater collected on
catchment surfaces (e.g. rooftops) to the storage tanks. This is usually accomplished by making
connections to one or more down-pipes connected to collection devices (e.g. rooftop gutters).
The pipes used for conveying rainwater, wherever possible, should be made of plastic, PVC or
other inert substance, as the pH of rainwater can be low (acidic) and may cause corrosion and
mobilization of metals in metal pipes.
There are several possible options for selectively collecting clean water for the storage tanks.
The common method is a sediment trap, which uses a tipping bucket to prevent the entry of
debris from the catchment surface into the tank. Installing a first flushes (or foul flush) device is
also useful to divert the initial batch of rainwater away from the tank.
Gutters and down-pipes need to be periodically inspected and carefully cleaned. Regular
cleaning is necessary to avoid contamination.
Storage Tanks: Storage tanks for collected rainwater may be located either above or below the
ground. They may be constructed as a part of the building, or may be built as a separate unit
43
located some distance away from the building. The design considerations vary according to the
type of tank and other factors. Various types of rainwater storage facilities can be found in
practice. Storage tanks should be constructed of inert material. Reinforced concrete, fiberglass,
polyethylene, and stainless steel are suitable materials.
8.5 Artificial Recharge Structures
The selection of a suitable technique for artificial recharge of ground water depends on various
factors. They include:
a) Quantum of non-committed surface run-off available.
b) Rainfall pattern
c) Land use and vegetation
c) Topography and terrain profile
d) Soil type and soil depth
e) Thickness of weathered / granular zones
f) Hydrological and Hydrogeological characteristics
g) Socio-economic conditions and infrastructural facilities available
h) Environmental and ecological impacts of artificial recharge scheme proposed.
For the study area following structures may be constructed for artificial recharge.
Recharge Pit: Recharge pits are normally excavated pits, which are sufficiently deep to
penetrate the low-permeability layers overlying the unconfined aquifers (Figure 13).
Figure 12: Schematic diagram of a recharge pit
44
Recharge Pit/Shaft: Recharge pits and shafts are artificial recharge structures commonly used
for recharging shallow phreatic aquifers, which are not in hydraulic connection with surface
water due to the presence of impermeable layers. They do not necessarily penetrate or reach the
unconfined aquifers like gravity head recharge wells and the recharging water has to infiltrate
through the vadose zone.
Recharge Shaft: Recharge Shafts are similar to recharge pits but are constructed to augment
recharge into phreatic aquifers where water levels are much deeper and the aquifer zones are
overlain by strata having low permeability (Figure 14).
Figure 13: Schematic diagram of a recharge shaft
While recharging the groundwater through pit/shaft a bypass arrangement to divert first rain
water is to be installed, so that the chemical contaminants (which wash out from the roof after a
long dry spell) are not recharged into the groundwater and only subsequent clean water is
charged directly in to recharge pit having bore well through a filter unit. The recharge of good
quality rain water will not only result in increase in yield but also the quality of ground water.
Recharge / Infiltration Gallery/ Filtration Gallery: Infiltration Gallery is to store rainwater
temporarily and allow the stored water to infiltrate into underground aquifers. To support better
infiltration and for convenience of excavation, the infiltration gallery can be of minimum 5 ft.
and maximum 10 ft. depth and of similar width. Length of the Infiltration Gallery can vary to
accommodate runoff water from the roof during heavy intensity rains. The excavated pit has to
be filled layer by layer with material like pebbles, gravel, sand etc. These layers of different
45
material will allow the rainwater to flow gently without much of turbulence and accommodate
storing of rainwater temporarily. The sand layer will arrest silt coming in along with rainwater.
8.6 Rainwater Harvesting Scheme
The water harvesting potential of storm water is the amount of water that can be efficiently
harvested from the total amount of water that is received in the form of precipitation over an
area. This is influenced by climatic conditions such as rainfall, and its pattern. The land use wise
water harvesting potential for the proposed plant area is worked out as per estimates shown in
given in Table 8.
Table 8: Illustrative Water Harvesting Potential for different land uses
(Source: hpscste.nic.in/rwh/Blue_Drop_Series_01_-_Policy_Makers.pdf)
Sl.
No.
Description Water Harvesting potential
1 Average Annual rainfall 1131mm (1.31m)
2 Rainwater endowment of one acre
area (4047 m2) per year
4047 X 1.31= 5301.57 m3
per year
3 Water harvesting potential of
Roofed area
80% of sl. no. 2 i.e., 4241.26 m3
per year
Paved areas and road side drains 70% of sl. no. 2 i.e., 3711.10 m3
per year
Open Land (Barren Land) 20% of sl. no. 2 i.e., 1060.31 m3
per year
Green belt 10% of sl. no. 2 i.e., 530.16 m3
per year
As given in Table 8 the rainwater harvesting potential (RWH) from the mining lease area, which is in
general open land (Barren land), will 20% of the rainfall. Thus the total water harvesting potential from
the three mines will be as given in Table 9. The water collected from the rainwater harvesting may be
stored temporarily in a sump, and can be used subsequently. The Water requirement in the mining blocks
is also given in Table 9:
Table 9: RWH Potential v/s Water Requirement in Mining Blocks (MCM/yr)
BLOCK RWH
Potential
Water Requirement Requirement
v/s Potential
Potable
water
Other mining
activities
Total %
Ghogha Surka 1.96 0.0146 0.1424 0.1570 8.01
Khadsaliya-I 1.03 0.0073 0.0839 0.0912 8.85
Khadsaliya - II 1.32 0.018 0.084 0.102 7.73
46
The Table 9 shows that the quantity of water harvested is much more than the actual requirement
of the mining operations. The surplus water may be used in the Thermal power plant (in case
required) or can be recharged on the eastern boundary of the mining lease area to avoid depletion
of water table outside the mining pit.
47
9 CONCLUSIONS AND RECOMMENDATIONS
The Ghogha – Surka, KhadsaliyaI and Khadsaliya-II lignite mining lease areas, located in the
Bhavnagar District of Gujarat, forms a part of the Saurashtra Peninsula. Lignite is to be extracted
for a captive thermal power plant from these blocks by commissioning three opencast mines. The
mines will be excavated 30, 52, 87 m below sea level. For smooth functioning of the mines, the
groundwater from the mine is to be pumped out, so that at any time, water table should be atleast
3 m below the working level. This activity will cause a cutting of aquifer upto a depth of 110 m
from the existing surface.
To study the impact of dewateing of the mine on the sea water ingress into the aquifers, the
SEAWAT model (A 3-dimensional groundwater model) has been used. The model was
calibrated as per the available information from the area.
Conclusions
1. Geologically, the lignite deposit is present in the Khadsaliya formations, which have low
permeability.
2. The groundwater modeling study indicates that due to dewatering, the water table will
decline in whole of the mining lease area. The area outside the mining lease will also be
affected, but to a lesser extent. The impact will be more towards the Gulf of Khambat and
less in other directions.
3. There are little chances of sea water ingress due to mining in the area. As a groundwater
mound is expected to develop between the mine and the sea shore.
4. Water balance study indicates that the groundwater recharge in the three blocks is
substantially higher than the water requirement for the mining operations. Thus the
requirement of the mining activities can be met from the available groundwater
resources.
Recommendations
1. To reduce the impact of declined water table it is recommended to supply water in the
Shatrunji Canal throughout the year, which runs in almost NS direction. The recharge
from the canal will further reduce the decline in the area east of the mining lease area.
2. The surplus water from the water harvesting scheme may also by recharged through
infiltration galleries constructed outside the mining pit on the eastern side.
48
REFERENCES
Anderson MP, Woessner WW (1992) Applied Groundwater Modeling Simulation of Flow and
Advective Transport. Academic Press, Inc., California.
Beer J, Verruijit A (1987) Modeling Groundwater Flow & Pollution. D. Reidel Publishing Co.,
The Netherlands.
Chaulya, S.K., 2003, Water Resource Development Study for a Mining Region. Water Resources
Management. 17: 297–316, 2003.
Elango L, Senthil Kumar M (2006) Modeling the effect of sub-surface barrier on groundwater
flow regime. In: MODFLOW and More 2006 Managing Groundwater systems: Eds.
Poeter Hill, Zheng, pp.806-810.
Faust, C.R., Lyle R. Silka and James W. Mercer (1981). Computer Modelling and Groundwater
protection. Ground Water, Vol. 19(4), pp 362-365.
Kresic N (1997) Quantitative Solutions in Hydrogeology and Groundwater Modeling. Lewis
Publishers, USA.
McDonald MG, Harbaugh AW (1988) A modular three dimensional finite difference
groundwater flow model. US Geological Survey Technical Manual of Water Resources
Investigation, US Geological Survey, Reston.
Owais S, Atal S, Sreedevi PD (2007) Governing Equations of Groundwater Flow and Aquifer
Modeling using Finite Difference Method. In: Groundwater Dynamics in Hard Rock
Aquifer- Sustainable Management and Optimal Monitoring Network Design: Eds.
Ahmed, S and Jayakumar, R and Salih, A. Capital Publishing Co, India. pp. 210-218.
Rejani R, Jha MK, Panda SN, Mull R (2008) Simulation Modeling for Efficient Groundwater
Management in Balasore Coastal basin, India. Water Resources management Journal 22:
23-50.
Sakthivadivel R (2001) Artificial Recharging of groundwater Aquifers and Groundwater
Modelling in the Context of Basin Water Management. In: Modelling in Hydrology: Eds.
Elango L and Jayakumar R pp. 36-37. Allied Publishers Ltd, India.
Stephen WK, Nicolas RH, Baker C, Horn JD (2003) A Model for Groundwater Flow in alluvial
aquifer of the Arkansas River at Dardanelle, Arkansas.
Thangarajan M (2004) Regional Groundwater Modeling. Capital Publishing Co. India.
Thomas ER (2001) System and Boundary Conceptualization in Groundwater Flow Simulation,
Techniques of Water-Resources Investigations of U.S. Geological Survey Book 3,
Application of Hydraulics, Chapter B8. U.S. Geological Survey, Virginia.
Waterloo Hydrologic Inc (WHI) (2003), Schlumberger Water Services (2003) Visual
MODFLOW Ver. 4.0 –User’s Manual.