 |
Eco-Hydrological Footprint of a River Basin in Western Ghats |
 |
|
Materials and Methods
Study Area
Eco-hydrological footprint assessment is carried out in the Kali river basin of central Western Ghats, consid-ering hydrologic regime with the ecological and anthro-pogenic (domestic, agriculture, livestock, etc.) footprints. The Western Ghats sustains perennial rivers, while en-suring the peninsular India’s water and food security and hence aptly branded as the water tower of peninsular In-dia. These series of hills are located in the western part of peninsular India with undulating terrains running in the
North-South direction for about 1,600 km parallel to the Arabian Sea along the west coast from south of Gujarat to the end of the peninsula (8°- 21° N and 73°- 78° E) with the spatial extent of about 1,64,280 km2 (< 5 percent of India’s geographical area). This region with exceptional biodiversity of endemic flora and fauna is one among 35 global biodiversity hotspots.
River Kali originates at Diggi village of Supa Taluk in Uttara Kannada District, Karnataka, India (Figure 2). This magnificent west flowing river flows for a distance of 184 kilometers and joins the Arabian Sea at Karwar [47-49]. River Kali has a catchment area of 5086 sq.km
extending across three districts and nine taluks name-ly Uttara Kannada (Ankola, Karwar, Supa, Yellapur, Haliyal), Dharwad (Kalgatgi, Dharwad), and Belgaum (Khanapura, Bialhongal). Due to the topography and poor vegetation cover, stream network towards Belgaum and Dharwad, are sparse and the region is endowed with the interconnected lake systems. Denser stream networks are present in Sahyadrian Ghats, Transition zones and Coast. Some of the major tributaries of Kali include Pan-drali, Kali, Tattihalla, Vaki, Kaneri, Thananala, Kariholé, etc. Geologically, Kali River is as old as the Western Ghats, major rock types in the region include granites
such as schist, shale, quartzite, phyllites, and soils such as red soil, lateritic soils, black soil, etc., are found in abundance. Ore found in the catchment are iron, baux-ite, quartz, limestone, sand, clay, lime shell, manganese, asbestos, and mica [47]. River Kali has about six major dams namely Supa, Kodasalli, Tattihalla, Bommanalli balancing reservoir, Kaneri and Karda dams. Kali catch-ment has a rich terrestrial flora consisting of about 325 species in the evergreen, semi evergreen, moist decidu-ous, scrub, thorny, un-wooded forest type. The region is endowed with rich fauna with 190 species of avifauna, mammals, reptiles, amphibians, etc. Kali basin, due to its ecologically sensitive regions with large forest expanses have major wild life sanctuaries such as Kali Tiger Re-serve, Hornbill reserve, and habitat for wild elephants [50-52]. Alteration in the physical integrity through the construction of a series of dams have altered the estuary productivity and diversity. Kali estuary has 37 fish species [53], bivalves, etc., which is relatively lower compared to the neighboring unaltered Aghanashini river catchment
[54]. Human population in the catchment increased from 3,67,604 (in 1991) to 4,97,892 (in 2001) and 5,42,036 (in 2011) [55] and is expected to reach 5,91,488 by 2021 at the same growth rate. Population density between 1991 and 2021 is as depicted in Figure 2. Population density has increased from 72.1 persons per hectare from 1991 to 106 persons per hectare in 2011 and is expected to reach 116.1 persons per hectare by 2021. Kali has a diverse population with over 30 communities [47,56]. Figure 2 depicts the rainfall variability ranging from 1000 mm in the Eastern plain to 4500 mm in the Ghats, with a tropical climate in the undulating topography of the catchment. Kali River catchment has been witnessing large scale land use changes leading to deforestation with the unplanned developmental activities altering hydrological regime leading to the decline of the supporting capacity and in-creases in water demand (domestic, agriculture, etc.).
Data
Optical remote sensing data acquired through Land-sat MSS™ and OLI sensors between 1973 and 2016 were used to assess the landscape dynamics [57]. Long-term rainfall data for the period 1901 to 2010 were collected from the Directorate of Economics and Statistics [58] across rain gauging stations spread across the regions - Uttara Kannada, Belgaum, and Dharwad districts. Pop-ulation data were obtained between 1991 and 2011 from Census of India [55], Livestock population and Crop data across all the three districts were obtained from re-spective districts at a glance [59]. Temperature data were downloaded from WorldClim [60], extra-terrestrial solar radiation from FAO [61]. Crop water requirements as per the crop calendar and growth stages were acquired from the Agriculture Department of Karnataka and National Food Security Mission [62,63]. Digital Elevation Model from SRTM [57,64]. In addition to these data, Virtual data such as Google Earth [65], NRSC-Bhuvan [66], Survey of India Topographic sheets [48,49], and French Institute maps [67] were used for the spatial analysis.
Method
The method depicted in Figure 3 involved in assess-ing the overall water footprint of the sustenance of water resource. Assessment of eco-hydrological footprint in the catchment involved the following:
Land Use Analysis: Land use in the catchment plays a decisive role in the hydrological processes such as infiltration, surface and subsurface flows, and storages, etc. Assessment of constituents in the landscape under different vegetation types such as agriculture, forest, and plantation helps in assessing the water demand in these sectors. Land use analysis using remote sensing data in-volved (i) generation of False Color Composite (FCC) of
remote sensing data (bands–green, red, and NIR). This composite image helped in locating heterogeneous patch-es in the landscape, (ii) selection of training polygons covering 15 percent of the study area (polygons are uni-formly distributed over the entire study area) (iii) loading these training polygons co-ordinates into pre-calibrated GPS (Global Positioning System), (iv) collection of the corresponding attribute data (land use types) for these polygons from the fiield. GPS helped in locating respec-tive training polygons in the fiield, (v) supplementing this information with Google Earth and (vi) 60 percent of the training data has been used for classifiication, while the balance is used for accuracy assessment by error matrix and Kappa statistics. The land use analysis was done using a supervised classification technique based on the Gaussian maximum likelihood (GML) algorithm with training data (collected from field using GPS). GML is a widely used statistical classification method assigning a given pixel to a specific class based on the conditional probability [68-70]. SRTM DEM, SOI Topographic maps [48,49] were used to delineate sub basins in the Kali river catchment.
Assessment of Hydrological Footprint: Hydrologic footprint is a function of land use, climatic factors (such as rainfall, temperature, solar radiation, etc.), surface and subsurface flows, ground water, vadose water, etc. Spatial and temporal (monthly variability) patterns of rainfall were assessed using data of 110 years from rain gauge stations distributed in the catchment. Net rainfall in each sub-basin were quantified based on deducting interception storage in each land use. Runoff in the ba-sin was quantified using Rational equation [71], runoff coefficients were based on the earlier field estimations
carried out in Sharavati basin and Aghanashini basin [72]. Infiltration is quantified as difference between net rainfall and runoff (overland flow). Ground water recharge was estimated using Krishna Rao equation [73]. Water in the hypomorphic zone (vadose zone) was estimated as the difference between net rainfall, runoff, and ground water recharge. Subsurface flows were derived [72] based on soil and lithological characteristics of the catchment.
Assessment of Ecological Footprint: Ecological footprint depends on the ecological, agriculture, domes-tic, and livestock water demands. Based on the cropping pattern, growth phase and water requirement for each crop, agriculture water demand was quantified. Based on livestock census and water requirement for each animal per day was used to estimate water demand for livestock. Similarly, water demand for the domestic sector is as-sessed based on the population and per capita water de-mand. Evapotranspiration from forests was used as a part of terrestrial natural water demand and quantified using maximum, minimum temperatures and extra-terrestrial solar radiation [73-75] based on the modified Hargreaves
[76] method. Environmental flow was estimated as 30 percent mean annual runoff based on Tennant method
[77-79].
Quantification of Eco-hydrological Footprint: Eco-Hydrological footprint is evaluated using eco-hydro-logical indices developed in the model to understand the role of forests in maintaining the hydrological cycle and catering the biotic demands. Eco-hydrological index is quantified as the ratio of infiltration to evapotranspiration in the catchment. Lower the values of infiltration i.e., less than 1 indicates poor water availability and values greater than 1 indicates better water availability sustaining the domestic and ecological demands.
Assessment of Eco-hydrological status: Hydrological supply and ecological demand were analyzed monthly to understand the eco-hydrological status. The region in-dicates deficit (supply < demand) and surplus (supply > demand) situation.
|
|
Citation :T.V. Ramachandra, S. Vinay, S. Bharath, A. Shashishankar, 2018. Eco-Hydrological Footprint of a River Basin in Western Ghats. Yale Journal of Biology and MEDICINE 91 (2018), pp.431-444.
|