I Morphometric Survey :
Depth profile of the lake was collected using calibrated handheld Global
Positioning System (GPS). Surface area (area), shoreline, maximum length, maximum width, mean
width and volume were estimated using a geo-referenced vector layer.
- Verification of the Shoreline : Shoreline was digitised from the cadastral map of 1:6000 using
MapInfo Professional 5.0, verified with the topographic map of scale 1:50,000, the Survey of
Int. J. Ecol. Dev.; Vol. 9, No. W08, Winter 2008 41
India (SOI). Surface area (area), shoreline, maximum length, maximum width, and mean
width of the lake were estimated. The shoreline layer was overlaid on remote sensing data
of (MSS data of Indian Remote Sensing Satellite) December 1998 and 2002 using Idrisi 32
software (Ronald, 1999).
- Bathymetric Analysis : The depth of the lake was measured at randomly distributed points
around the lake. The location of these points was recorded using a handheld GPS (Global
Positioning System). The depth of the lake was sampled during November 2005 and
February 2006, corresponding to the post-monsoon and dry seasons, respectively. The
position of the GPS points taken in the field were rectified to fit the map of the lake by
comparing the GPS coordinates for two landmarks (the bridge over the northeast outlet and
the main irrigation canal) to previously established coordinates published by the Survey of
India, 1980. The November depth samples were measured with a weighted line and
measuring tape. A total of 31 sample points were recorded using this method. February
samples were taken from a coracle boat using a graduated aluminum pole with a flat disc
attached to the bottom. A total of 46 sample points were recorded with this method.
- Contour Mapping : The depth data collected in February were converted into data points on
the geo-referenced map of Varthur lake using MapInfo Professional 5.0 software. These
points were converted to isohyets - contours of 0.25 meter interval using the polyline tool
incorporated in the software.
Volumetric Analysis: Estimations of the February volume of Varthur lake were made using
two methods, (A and B), based on the data used in the calculations. Method A was a simple
manual calculation based on surface area slices at the 0.25 meter intervals used on the
initial digitised map. Method B was a more accurate computer-assisted analysis that used a
grid file of the lake extrapolated from the original data points and the contour map.
- Method A : This method subjected data from the contour map. The maximum
depth of the lake is represented by the 2.0 m contour. This procedure involved
finding the volume between the contours and subtracting the volume of each
layer that is lost due to the slope of the bottom of the lake.
- Method B : Depth profile was converted to grids at 5 meter intervals through
Kriging and volume was computed based on on the Trapezoidal Rule, Simpson's
Rule, and Simpson's 3/8 Rule.
II Characterisation of Lake and Ground water :
Water samples from Varthur lake were collected
during October - November 2005 and January 2006. October samples were collected from the
shoreline nearest to the following locations: Bellandur Canal, the south-southwest portion of the lake,
and the northeast and southeast outlets. Water samples were collected from 10 to 30 cm below the
surface of the water during the morning hours. These samples were collected and stored in 500 ml
polyethylene containers, with the exception of those collected in borosilicate glass bottles for
dissolved oxygen analysis. No preservatives were added as the samples were transported to the
laboratory within six hours and either refrigerated or analysed immediately. Bore well water samples
were collected in January, from four locations closest to the southern shore of the lake. These
samples were collected and stored in clean, white, 500 ml polyethylene containers. On-site analysis of
lake water included air and water temperature, transparency and, in the case of October and
November sampling, dissolved oxygen. Laboratory analysis included: acidity, alkalinity, biochemical
oxygen demand (BOD), chemical oxygen demand (COD), chloride, chlorine residual, coliform
bacteria, dissolve oxygen (DO), electrical conductivity (EC), fluoride, hardness, iron, nitrate, pH,
phosphate, potassium, sodium, sulphate, solids (total, total dissolved, and total suspended) and
turbidity. The water analyses followed standard procedures published by the Indian National
Environmental Engineering Research Institute (NEERI, 1988) and the American Public Health
Association (APHA, 1985) and Development Alternatives (Development Alternatives 2000).
Groundwater samples were tested for ammonia, chloride, coliform bacteria (DWIIH,1995), EC,
fluoride, nitrate, and pH using standard methods.
III Socioeconomic Survey :
Randomly chosen households from Varthur town, and Baligeri and
Ramagondanhalli villages were surveyed using a standard questionnaire (Ramachandra et al.,
2005b). 22 households took part in the survey, representing a total of 217 people. The questions
posed during the interviews were classified under the following headings: demographic information,
family history, domestic water usage, groundwater usage, irrigation, other commercial uses, water
usage for livestock, livestock fodder, aesthetic value and recreation, fishing and aquaculture,
waterfowl, spiritual value, health effects, community involvement in restoration, etc.
Questions regarding domestic water usage, irrigation, other commercial uses, water usage for
livestock, livestock fodder, and fishing and aquaculture attempted to quantify residents’ direct
economic reliance on lake and groundwater resources. Other direct uses, such as recreation and, in
some cases, spiritual value, were investigated using qualitative questions regarding use of the lake
(Edward, et al., 1997). Any changes in lifestyle, such as a change in occupation, that may have been
caused by deterioration in the quality of the lake were investigated in the family history section of the
questionnaire. The use of groundwater resources was included in the survey to identify trends in the
overall reliance on lake resources compared to groundwater. Usage of groundwater may be indirectly
associated with lake water resources as the Varthur lake could be responsible for recharging local
aquifers. Questions regarding groundwater recharge were intended to detect changes in the local
water table that could be the result of reliance on bore wells.
Questions regarding waterfowl and fish populations pertained to qualitative information about changes
in the ecology of the lake, especially the biodiversity and abundance of wildlife. These topics, along
with questions regarding aesthetic value, sought information on less tangible benefits provided by the
lake that may be affected by a decline in its overall condition. Potential harm to the local population as
a result of this deterioration was also investigated through questions regarding mosquito populations
and incidents of insect and water-borne diseases. The heritage value of the lake as well as family
commitment to remain in the area were investigated through questions regarding both family history
and their desire to see future generations remain near Varthur. Determining residents’ overall concern
for the future of the lake was the motivation behind the question regarding support for future
reclamations efforts.
