International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Harikrishna Karanam ,Venkateswara Rao Velaga, Ramprasad Naik Desavathu, Jaisankar Gummapu, Amminedu
Edara
Department of Geo-Engineering, A.U.College of engineering, Andhra University, Visakhapatnam, Andhrapradesh,
India – 530003
Abstract
Fresh ground water is widely distributed in subsurface sediments below the beach ridges of
Kolleru Lake. Beach ridges were formed at down stretch of Kolleru Lake with width of 2 to3 km but going towards to coast the width of beach ridge is going to limit up to 1km only. This study investigated the shallow subsurface of the beach ridges in down stretch of Kolleru Lake. The depth of sand deposition was calculated through geophysical resistivity survey.
The agricultural lands in the catchment area use high amount of fertilizers as well pesticides and the runoff from this area also become one of the pollution source. Number of aqua culture farm ponds is created since last 10 to 15 years with in the lake area and lot of aqua feed and pesticides are used for the culture.
All the above mentioned pollution sources might have induced pollution into the groundwater which is to be studied. Hydrogeomorphological study indicates that the potential aquifers around the
Kolleru Lake are paleo beach ridges, buried river courses. All other geomorphic features either aquiclude or aquitards and may not be considered as prospective zones for groundwater. Though there are number of open wells present in the villages used for potable water, people are depending on imported water as their drinking water source, which signifies the contamination of groundwater resources. Present land use activities like aqua-culture, agriculture, large-scale industries and allied industries in and around the Kolleru Lake Region has large contribution for the change of water quality. The paleo beach ridge areas, where the permeability of the sandy soil is very high are also converted into aqua ponds.
Integrated study using remote sensing, hydrogeology, hydrochemistry and geophysical investigations along the beach ridges. The electrical resistivity of aquifers is less than 1.0 (ohm-m) having salinity of more than
1.2 ppt and the resistivity is around 20 (ohm-m) where the salinity is less than 0.5 ppt, has also served as an excellent criteria for delineating the fresh-water and salt-water interface. Lenses of fresh water/ brackish water are noticed only in the beach ridges limiting to 2-8m depth below the natural ground level.
I. INTRODUCTION
Kolleru, the largest freshwater lake along the east coast of India in Andhra Pradesh (AP) had been encroached, mainly for aquaculture, to such an extent that most of the lake area was highly compartmentalized by 3–4 m high embankments of hundreds of fish tanks that had sprung up
In the lake bed. Groundwater conditions in the multiaquifer system in the Kolleru region were studied through an integrated approach using Geophysical, hydrochemical, hydrogeological, Remote sensing and
GIS techniques. This study was taken up because of the reported seawater intrusion into the groundwater system of this agriculturally rich region. The results, of hydrochemistry and Geophysical soundings indicate that the origin of salinity in the aquifer systems is due to palaeo-geographical conditions.
The modern irrigation practices using intensive canal network has led to refreshening of the aquifer systems. The recharge of groundwater by the canal system can be expedited by developing the canal network in the area having high potential for groundwater recharge. This will result in further reduction of salinity in the kolleru region.
Aquaculture is one of the fastest growing food industries and the rapid growth of aquaculture worldwide has resulted in growing concerns about its impact on important ecosystems. To assess the impact of aquaculture on Kolleru and surrounding areas, Geophyysical resistivity soundings, water quality assessment and satellite data were found appropriate because of the synoptic-detailed overview and accuracy. Satellite data of IRS 1D,
LISS IV from 2009 and Survey of India topographic maps from 1967 were processed using image
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International Journal of Engineering Trends and Technology- Volume4Issue3- 2013 processing techniques in ERDAS IMAGINE and analysed in Geographical Information System (GIS) such as ARC GIS 9.2. The effect of the rapid growth of aquaculture on ground water was assessed by resistivity survey and water quality. Lake Kolleru is a sprawling shallow coastal wetland with a maximum depth of about 2.0 m. It was initially formed as a coastal lagoon about 6000 years ago, as is evident from the presence of a series of relict sandy beach deposits of mid-Holocene origin right up to the seaward margin of the lake which is about 35 km inland from the present coast (Nageswara Rao;2010).
Aquaculture has developed rapidly over the last two decades and has become an important economic activity worldwide. This rapid expansion of aquaculture in India has led to a growing concern about its impact on the environment. Major environmental issues such as the conversion of important coastal ecosystems like lakes, groves and agricultural lands to aquaculture farms and pollution of drinking water resources adjacent to aquaculture farms have been raised over the development of aquaculture ( Perez et al. 2003). It was estimated from the topographic maps of 1967 that the total lake boundary area was 180.38 km2, in which 70.70km2 had water throughout the year and 100.97 km2 had water during the rainy season (Marappan 2006).
Now, the Government of Andhra Pradesh, India, has initiated schemes and laws to restore the lake to its pre-development state. Lessons learnt from the
Kolleru Lake cautioned that there is a need for regular monitoring of important water resources throughout the world to protect the biodiversity of the earth. Owing to the lack of awareness among people about the importance of ecosystems, degradation of lakes and coastal wetlands is still continuing and has reached an alarming state (Clark1998).
Geological formation of the area consists of alluvial deposition with Khondalite, the Gondwana and
Deccan trap rocks on all sides. Topographically the
Lake is located over a deep-seated tectonic depression, which is geo-physically known as
Gudivada sub-basin between the Bapatla and Tanuku subsurface ridges or highs (Raju et al., 2003). The unique topography of the area is an important reason for the lake’s existence. The lake is believed to have been formed during the Holocene epoch (around
6000 years BC). The progradation of the coast line and evolution of the delta and transformation of the lake from an open marine bay to tidal lagoon delta and mangrove swamp to fresh water lake is discussed by several geologists (Babu, 1978; Mahendra Reddy and Shah, 1991; Biswas, 1993) .
Geologists consider the presence of a series of relict sandy beach-dune ridges right up to the southern margin of the lake near
Kaikalur and Akiveedu towns as evidences for the narrowed shore line to the far inland during the geological past that eventually broadened up in the later years (Sadakata and Rao, 1997) .
The only out let of the lake to Bay of Bengal, the Upputeru channel, an intricately meandering tidal channel playing crucial role in the maintenance of wetland’s hydrological regime, is also distinctive evidence of it as a one-time coastal lagoon. It is assumed that as the
Krishna and Godavari deltas became wider, the lagoon receded and got restricted to inlands (Rao et al., 2004). The landforms in the Kolleru basin are of different origin; fluvial, marine, fluviomarine, and denudational (Ramana Murty and Reddy, 2010).
Major geomorphic features identified in the basin are palaeo-lagoons, palaeo-channels, beach ridges and swales, deltaic plains, and the palaeo-channels, a fluvial landform of significance, which are concentrated towards the east and south of the lake.
Palaeo-channel (low) is within the frequently flooded region. Other landforms of fluvial origin seen in the basin include palaeo-channel bars, palaeo-islands, present-islands and swamps. Landforms of marine origin include the present extent of palaeo-lagoon, beach-ridge and swale.
Kolleru is one such wetland in a low-lying deltaic setting acting as an important flood-balancing reservoir, a haven for migratory and resident birds, and a source of livelihood for traditional fishermen.
However, largescale encroachments for aquaculture during recent decades, even into the core area of the lake, have disturbed the ecosystem to such an extent as to almost completely efface the lake’s identity. As expected, the image enhanced through ALR technique distinctly shows the fishponds with depth effect, while the lake areas with 2–3 m tall elephant grass are clearly separated from the paddy-crop zones. Furthermore, the lake areas with dense and sparse weed could also be separated. Similarly, the dry fishponds and the lake areas under reclamation could be identified separately. Thus the output image of the ALR enhancement technique was used to classify the various land-use/land-cover categories in the lake through on-screen digitization. The resultant polygon coverage map was used to extract area statistics. The lake is about 35 km inland from the present coast, it was a coastal lagoon in the geological past, believed to have been formed around
6000 years BP, when the shoreline was far inland along the southern (seaward) margin of the lake, as evident from the presence of a series of relict sandy beach-dune ridges right up to the southern margin of the lake near Kaikalur and Akividu towns .
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International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
II. STUDY AREA
The study area is located in between 16°29'00'' and
16°37'00'' N latitudes and 81°12'00'' and 81°28'00''
E longitudes, covering down part of Kolleru lake region Present study area is 543.78 km
2
(Fig. 1).
Excess water from the applied irrigation around the lake area also joins the lake through number of drains. The outlet of the lake is a t lead channel joins with Bay of Bengal and is about 11 km, which also allow salt-water during high tide and summer because of back-waters.
Fig.1: Location Map of the study area
III. HYDROGEOMORPHOLOGY
Geomorphology provides knowledge of the geological environment and tectonic structure is the key element in groundwater resources investigation and development (W.D. Thornbury, 1986).
Hydrogeomorphological maps depicting the occurrence of aquifers containing potable water and groundwater vulnerability maps are both important means by which to present the outcomes of such complex investigations of groundwater resources (A.
Thomas, 1999). Landforms are delineated using the image characteristics (IRS-P6, LISS IV) along with the available geological and geomorphology details
(Fig. 2). Ground truth verification was done in needy and problematic areas. The geomorphic units thus delineated are paleo beach ridges, paleo lagoon plain, paleo tidal channel.
Fig.2: Geomorphology map with VES
Traverses and wells locations
Beach Ridge: Linear ridge of unconsolidated sand / silt parallel to shore line. The beach ridges are present in three curvilinear rows parallel to coast between the southern boundary of the lake and the coast line. The ridge near the lake is continuous on which settlements and roads are developed. It is relatively elevated ground than the surroundings, offer protection from frequent floods in this lowlying coastal region. A group of beach ridges and swales occurring together are present in the downstream of Kolleru Lake. Beach ridges consist of fine to medium sand and allow more rainwater to percolate and forms high yielding aquifer.
Paleo Lagoon plain: It is an elongated body of water lying almost parallel to the coastline and separated from the sea by a paleo beach ridge. It is observed in the coastal region of central Godavari delta. The paleo-lagoon is no more connected with the sea.
Paleo tidal channel: An earlier river course filled with channel-lag or channel-fill sediments due to tidal action, which is cutoff from the main river.
Several paleo tidal channels are observed throughout the Godavari delta.
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International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
V. GEOPHYSICAL STUDY
Resistivity survey has been carried to delineate sea water-fresh water interface and
Fig.3: Apparent resistivity contours Map of the Traverses in the Study Area the extent of aquifer zones. In the present study
Vertical Electrical Soundings (VES) have been carried out at 1.0 km interval along 4 traverses in north-south orientation, perpendicular to the coastline namely E,F,G and H respectively, a total of 61 VES data are collected using Schlumberger electrode configuration with an electrode spacing varying between 60m. All the VES apparent resistivity data are plotted traverse wise. Resistivity contours are drawn for 1 ohm-m, 2 ohm-m, 5 ohm-m and 10 ohm-m for all the traverses. All the VES locations are referred with respect to geographic coordinates with
GPS and the locations are shown on the satellite image (Fig.3 and Fig.4).
Fig.4: Lithology Map of the Traverses in the Study
Area
Analysis of Vertical Electrical Soundings data:
Each VES data is interpreted with the standard techniques and the subsurface layers are arrived. The cross sections shown in Fig. 4 shows the apparent resistivity contours drawn for i) less than 1.0 ohm-m, ii) 1-2 ohm-m, iii) 2-5 ohm-m, iv) 5-10 ohm-m and v) >10 ohm-m.
Resistivity is variable with the aquifer material, percentage of fluids filled in it and the quality of fluid. It is comparable with the quality of groundwater in which the parameters - salinity, TDS, electrical conductivity are closely related. Resistivity is low with increase of these parameters in the groundwater which is filled in the pore spaces of the subsurface lithological layers(K.Hari krishna, 2012).
Resistivity variations along the geophysical traverses are shown below.
Results of Resistivity Surveys
Traverse-E : This traverse runs in the northern portion of the beach ridges for a length of 20km starting at the kaikaluru and ending at kalidindi village. Apparent resistivity more than 10 ohm-m area is matching with the geomorphology unit ‘beach ridge’ and groundwater in the wells present in this zone are used for domestic needs other than drinking.
Less than 1.0 and 1-2 ohm-m zones are present for the entire traverse length starting at E18 (near to the kalidindi village) and their extent increased vertically towards the coast area and this zone is treated as salt water intrusion zone. Dark red colour indicates the salt water intrusion zone and its thickness increased towards coast between VES E10 and E13.
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International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Lithology along this traverse is from E3 to
E10 and E14 to E17 sand was existed as a topmost layer and depth vary from 2m to 5m. From E17 to
E20 soft clay was existed as a topmost layer and depth vary from 2m to 6m. From E1 to E12 clay sand was existed primarily as a first layer than as a second layer and depth vary from 2m to 12m. Between E1 to
E12 soft clay as third layer and depth vary from 4m to 27m. Sand clay was formed as a next layer depth vary from 4m to 44m. Than hard clay was formed as a next layer.
Traverse-F: This traverse is across the beach ridges and runs for a length of 16km starting near bujabala patnam and ending at potumarru. Most of the region comes under 5-10 ohm.m zone is noticed on the main beach ridge along the traverse and the fresh-water zone is extended up to 5 to 8m depth. Salt water zone is indicated between F1 to F3 which is near by bujabala patnam. Between F7 to F16 also salt water zone indicating 9m depth from surface.
Lithology along this traverse is from F1 to
F3 soft clay was existed as a topmost layer. From F3 to F16 soft clay was existed as a third and second layer depth varies from 2m to 27m. As a next layer
From F1 to F16 sandy clay was existed from 22m to
46m. Hard clay was existed as a last layer up to 60m depth from surface.
Traverse -G: This runs for length of 13 km along the middle part of beach ridges. More than 10 ohm-m zone is limited between G2 to G9 and G10 to G13 and is limited to 3 to 4m electrode separation.
Resistivity of less than 1.0 ohm-m indicates saltwater intrusion i.e. between G1 to G2 and G9 to G10.
Sand was existed as a first layer between G1 to G4, G5 to G8 and G10 to G13 and electrode separation is up to 9m. Soft clay was formed as a second layer depth vary from 0 to 25m. Between G5 to G13 sandy clay was formed with depth vary from
20 to 45m. Hard clay was existed as a next layer from
G1 to G13.
Traverse -H: This traverse runs for a length of 12 km between undi and kopalle villages. Salt-water zone (<1 ohm.m and 1 ohm.m to 2 ohm.m) exists beyond 2 to 4m electrode separation and extend up to coast line. Between H9 to H12 fresh water was existed 4m depth from surface of the earth.
Sand was existed as a first layer between H1 to H3 and H8 to H12 and electrode separation is up to
4m. Soft clay was formed as a first and second layer depth vary from 0 to 30m. Between H1 to H12 sandy clay was formed with depth vary from 23 to 38m.
Hard clay was existed as a next layer from H1 to
H12.
V.COMPARISON OF RESISTIVITY -
CHEMICAL QUALITY-
HYDROGEOMORPHOLOGY
Resistivity of subsurface layers obtained from the interpretation of the field resistivity data contains i) thickness of layers and ii) resistivity of the formations. Each sounding is interpreted in which 3 to 4 layers are identified within the depth of investigation. VES data near to the existing open wells are considered and Resistivity of aquifer zone is compared with the groundwater quality parameters
– Total Dissolved Salts (TDS), Electrical conductivity (EC) and salinity data which are more related. Table-1 shows the nearest VES location, observation well coordinates and dimensions, aquifer level and true resistivity of the aquifer. Resistivity data and the chemical parameters along the traverses
E, F, G and H are compared and in total 14 observation wells data compared with the nearby
VES data. The distance between the compared VES and the observation well may vary between 10m to
200m.
All the observation wells are located predominantly in the hydrogeomorphic unit- paleo-beach ridges and regularly used for domestic needs. With the introduction of aqua farms even in the beach ridges, quality of water deteriorated to non potable at some places. However, thickness of sand in the paleo beach ridges may vary from the centre of the ridge to the fringes across the longitudinal direction of the ridge alignment. All these wells shallow and mostly less than 5m depth. Resistivity of the aquifer zone is less than 1.0 ohm-m where salinity is >1.2 ppt, EC is >2
µmhos and TDS is >1.5ppt. Resistivity varies between 10 and 30 ohm-m when the salinity is <0.5 ppt. EC is <1 µmhos and TDS is <0.5ppt. There may not be exactly a multiple or divide factor to demarcate the resistivity and compared water quality parameters may be due to the aquifer material and the influence of other quality parameters. Broadly, the resistivity and groundwater quality are comparable.
Out of the 14 observation well locations, only 3 are within the potable quality standard which is an indicative of ground water quality deterioration.
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International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Table:1- Comparison of certain chemical parameters with field Resistivity of the aquifer
VES Traverse-E,G E2,E3 E6 E9 E11 G1 G3
Latitude
Longitude
E.C(µmhos)
TDS (ppt)
16.53912
81.22095
4.82
2.63
16.53618
81.2371
1.41
0.76
16.5327
81.24788
0.806
0.46
16.52642
81.2535
2.1
1.1
16.56297
81.37193
3.27
1.71
16.54348
81.36948
0.747
0.47
G7,G8
16.51693
81.35765
3.23
1.75
Salinity (ppt)
Depth to watertable(m)
Total Depth(m)
Resistivity(ohm-m)
VES-Traverse-F,H
Latitude
Longitude
E.C(µmhos)
TDS (ppt)
Salinity (ppt)
Depth to watertable(m)
5.2
3.04
5.8
3.86
F2
16.56397
81.26205
5.81
3.1
3.59
0.88
11.6
3.9
1.2
F7
16.54487
81.29373
0.76
0.48
1.1
0.9
0.52
3.12
2.09
2.42
1.28
1.49
26
1.27
4.06
2.4
F10 F13
16.53912 16.52962
81.22095 81.31235
5.48
2.98
3.44
1.98
0.4
3.56
2.31
F14
16.47958
81.21118
2.32
1.28
1.48
0.47
1.0
3.56
2.18
H6
16.52962
81.31235
33.3
17.8
20.6
30.0
2.02
3.36
2.1
H10
16.56067
81.46748
5.22
2.79
3.23
3.3 2.75 4.25 2.9 4.65 4.16 5.89
Total Depth(m)
Resistivity(ohm-m) 0.5
2.53
5.0
1.71
CONCLUSION
Remote sensing study indicates the various Land use/land cover patterns. Most of the sattelments are existed along the beach ridges. Cultivation and aquaculture are the major activities in this region.
2.48
0.82
1.15 2.27 2.59
0.25 0.56 0.62 0.86 changes in terms of increased or decreased risk status.
2.93
ACKNOLEDGEMENTS
The authors acknowledge DST, Ministry of Science
Because of high density aquaculture ground water is polluting. Remote sensing study indicates the various hydrogeomorphic units that contain fresh-water and saline aquifers. Paleo beach ridges are the potable groundwater potential zones in and around the kolleru lake. Geophysical data are compared qualitatively to delineate the saltwater intrusion zones vertically as well as lateral direction. Chemical analysis of groundwater samples collected from the open wells clearly indicates the level of salinity.
Comparison of resistivity and chemical quality is helpful in demarcating the seawater intrusion vertically as well in the lateral direction. and Technology, New Delhi, for sanctioning the research project “Hydrogeological and Groundwater resource evaluation studies in and around Kolleru
Lake”.
REFERENCES
[1] K. Nageswara Rao, K. Ch. V. Naga Kumar, P.
Subraelu, B. Visweswara Reddy, B. Hema Malini
“Kolleru lake revisited: the post ‘Operation Kolleru’ scenario”. CURRENT SCIENCE, VOL. 98, NO. 10,
25 MAY 2010
[2] Perez O.M., Tefler T.C. & Ross L.G. (2003) Use of GIS based models for integrating and developing
Extensive field verification of sample wells and integration with geomorphological and socioeconomic factors will aid GIS based demarcation of seawater intrusion which is to be carried further.
Through extensive ground surveys, examination points will be established as part of the study and results will superimposed on remote sensing data sets. Measured parameters will be integrated in a GIS platform. Points of intense exploitation for aqua ponds farming using groundwater and associated seawater intrusion status will be exhaustively studied to serve as Bench mark points for monitoring future marine fish cages within the tourism industry in
Tenerife (Canary Islands). Coastal Management
31,355-366.
[3] Marappan Jayanthi, Peter Nila Rekha, Natarajan
Kavitha
679-684. and Pitchaiyappan Ravichandran
“Assessment of impact of aquaculture on Kolleru
Lake (India) using remote sensing and Geographical
Information System”. Journal Compilationr 2006
Blackwell Publishing Ltd.
[4] Clark J.R. (1998) “The ecosystems approach from a practical point of view”. Conservation Biology13,
ISSN: 2231-5381 http://www.internationaljournalssrg.org
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International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
[5] Raju D.C.V., Rajesh R.S. & Mishra D.C. (2003)
“Bouguer anomaly of the Godavari basin, India and magnetic characteristics of rocks along its coastal margin and continental shelf”. Journal of Asian Earth
Science 21,535-541.
[6] Babu PVLP (1978) Geomorphology of the
Krishna Godavari delta region interpreted from
Landsat imagery. The National Geographical Journal of India 24: 55-61
[7] Magendra Reddy K and BM Shah (1991)
Evolution of Krishna delta, Andhra Pradesh.
Memoirs of Geological Society of India 22: 57-64-
285
[8] Biswas SK (1993) Major neotectonic events during the quaternary in Krishna-Godavari basin.
Current Science 64 (11-12): 779-803
[9] Sadakata N. & Rao K.N. (1997) “Radiocarbon ages of the subsurface sediments in the Krishna delta and their geomorphological implications”. Quarterly
Journal of Geography 49,163-170.
[10] Rao K.N., Krishna G.M. & Malini B.H. (2004)
Kolleru lake is varnishing-a revelation through digitalprocessing ofIRS-1D LISS III sensor data.
Current Science 86, 1312-1316.
[11] Ramana Murty MV and K Mruthyunjaya Reddy
(2010) Flood hazard zonation around the Kolleru lake, Andhra Pradesh, India – A remote sensing and
GIS based approach. In proceedings of the 3rd
International Conference on Hydrology and watershed management with a focal theme on climate changes – water, food and environmental security, 3-
6 February 2010, Centre for Water resources,Jawaharlal Technological University,
Hyderabad. Pp1010-1021
[12] W.D. Thornbury, “Principles of
Geomorphology” Wiley Easter , pp.165-194. 1986.
[13] A. Thomas, MK. Sharma and Anil Sood“
Hydrogeomorphological mapping in assessing groundwater by using remote sensing data- A case study in Lehra Gage Block, Sangrur district, Punjab”.
Journal of Indian Society of Remote Sensing, vol.
27(1), pp 31-42. 1999.
[14] K.Hari krishna, D.Ramprasad Naik,
T.Venkateswara Rao, G. Jaisankar, V.Venkateswara
Rao. “A Study on Saltwater Intrusion Around
Kolleru Lake, Andhra Pradesh, India”. International
Journal of Engineering and Technology (IJET), Vol 4
No 3, pp 133-139, Jun-Jul 2012
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