Papers by Nilantha Gamage
Research Report. International Water Management Institute, 2004
Research Reports IWMI's mission is to improve water and land resources management for food, l... more Research Reports IWMI's mission is to improve water and land resources management for food, livelihoods and nature. In serving this mission, IWMI concentrates on the integration of policies, technologies and management systems to achieve workable solutions to real problems practical, relevant results in the field of irrigation and water and land resources. The publications in this series cover a wide range of subjectsfrom computer modeling to experience with water user associationsand vary in content from directly applicable research to more basic studies, on which applied work ultimately depends. Some research reports are narrowly focused, analytical and detailed empirical studies; others are wide-ranging and synthetic overviews of generic problems. Although most of the reports are published by IWMI staff and their collaborators, we welcome contributions from others. Each report is reviewed internally by IWMI's own staff and Fellows, and by external reviewers. The report...
Research Report International Water Management Institute, 2009
... Such characteristics should reflect multiple aspects of drought, ranging from quantification ... more ... Such characteristics should reflect multiple aspects of drought, ranging from quantification of drought ... Database: www.emdat.be/) and revised estimates of global drought-related deaths. ... The UNDP's Bureau for Crisis Prevention and Recovery (BCPR) developed an individual ...
Hydro Nepal: Journal of Water, Energy and Environment, 2011
Predicting river fows in basins where limited data is available is a challenge facing many hydrol... more Predicting river fows in basins where limited data is available is a challenge facing many hydrologists es-pecially in developing countries. In this study, the Pitman monthly model was applied to generate fows for the Lhasa basin in China (Tibet). As fow data was unavailable for the Lhasa basin, the model was frst calibrated for the upper Koshi Basin in Nepal and China. The Pitman model successfully predicted fows for the upper Koshi basin (R2 =0.88). Therefore, the estimated model parameters from the Koshi basin as well as climate data from the Lhasa basin were used to generate fows for the Lhasa basin outlet. The main modeling assumption is that the basin characteristics of the upper Koshi are similar to that of the Lhasa basin. Under present circumstances, where measured data is unavail-able, the model estimated monthly fows for the Lhasa basin can be used in further studies in basin water accounting and management.Key words: Un-gauged basins; Pitman monthly model; Stream fow gen...
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Hydro Nepal: Journal of Water, Energy and Environment, 2011
Predicting river fows in basins where limited data is available is a challenge facing many hydrol... more Predicting river fows in basins where limited data is available is a challenge facing many hydrologists es-pecially in developing countries. In this study, the Pitman monthly model was applied to generate fows for the Lhasa basin in China (Tibet). As fow data was unavailable for the Lhasa basin, the model was frst calibrated for the upper Koshi Basin in Nepal and China. The Pitman model successfully predicted fows for the upper Koshi basin (R2 =0.88). Therefore, the estimated model parameters from the Koshi basin as well as climate data from the Lhasa basin were used to generate fows for the Lhasa basin outlet. The main modeling assumption is that the basin characteristics of the upper Koshi are similar to that of the Lhasa basin. Under present circumstances, where measured data is unavail-able, the model estimated monthly fows for the Lhasa basin can be used in further studies in basin water accounting and management.Key words: Un-gauged basins; Pitman monthly model; Stream fow gen...
Geomorphology, 2009
The construction of multiple dams and barrages in many Indian River basins over the last few deca... more The construction of multiple dams and barrages in many Indian River basins over the last few decades significantly reduced river flow to the sea and affected the sediment regime. More reservoir construction is planned through the proposed National River Linking Project (NRLP), which will transfer massive amounts of water from the North to the South of India. The impacts of these developments on fertile and ecologically sensitive deltaic environments are poorly understood and quantified at present. In this paper an attempt is made to identify, locate and quantify coastal erosion and deposition processes in one of the major river basins in India-the Krishna-using a time series of Landsat images for 1977, 1990 and 2001 with a spatial resolution ranging from 57.0 m to 28.5 m. The dynamics of these processes are analyzed together with the time series of river flow, sediment discharge and sediment storage in the basin. Comparisons are made with similar processes identified and quantified earlier in the delta of a neighboring similarly large river basin-the Godavari. The results suggest that coastal erosion in the Krishna Delta progressed over the last 25 years at the average rate of 77.6 ha yr − 1 , dominating the entire delta coastline and exceeding the deposition rate threefold. The retreat of the Krishna Delta may be explained primarily by the reduced river inflow to the delta (which is three times less at present than 50 years ago) and the associated reduction of sediment load. Both are invariably related to upstream reservoir storage development.
... Such characteristics should reflect multiple aspects of drought, ranging from quantification ... more ... Such characteristics should reflect multiple aspects of drought, ranging from quantification of drought ... Database: www.emdat.be/) and revised estimates of global drought-related deaths. ... The UNDP's Bureau for Crisis Prevention and Recovery (BCPR) developed an individual ...
IWMI's mission is to improve water and land resources management for food, livelihoods and nature... more IWMI's mission is to improve water and land resources management for food, livelihoods and nature. In serving this mission, IWMI concentrates on the integration of policies, technologies and management systems to achieve workable solutions to real problems-practical, relevant results in the field of irrigation and water and land resources.
Precise information on irrigation performance and water consumption at field or canal command lev... more Precise information on irrigation performance and water consumption at field or canal command level is important to irrigation managers and policymakers to make appropriate decisions on water management. Use of irrigation performance indices cum water consumption are the tools make such decisions. Calculate those figures are a challenging task for the past cropping years, that essential to make correct decisions especially in data-scarce regions of Asia and Africa. Similarly, calculation of these above at field or canal command level over large irrigation schemes are laborious, costly, timely inefficient and less accurate. The necessity for these figures is rapidly increasing due to the need to make the correct decisions with the continually rising population and food demand cum declining water availability parallel to climatic change issues. Accordingly, well established surface energy balance algorithm (SEBAL) technique has been employed in large irrigated areas in Punjab, Pakistan, as a tool to estimate actual evapotranspiration (ET a ), i.e., water consumption for the cropping years of 2004/05 and 2006/07. Freely available medium resolute daily MODIS images and hydrometeorological data were used as inputs for the ET a calculation. Under this study irrigation performance indices of equity and adequacy were calculated using actual evapotranspiration and evaporative fraction. Results show that annual ET a varies from less than 100 mm/year in desert/barren areas to 1,650 mm/year over large water bodies. For cropped areas, the variation ranges from 400 to 1,200 mm per year for both cropping years. In rice-wheat area of Punjab, average ET a of the cropping year 2004/05 is 896 mm, and 971 mm for cropping year 2006/07. In lower and southern Punjab, ET a is low and varies from 805 to 870 mm during 2004/05 and 2006/07, respectively. ET a was further analyzed in depth on a seasonal and canal command basis for a better understanding and shows that an average of 9% more water has been consumed by crops during the Kharif 2007 season while 10% higher consumption was observed for the Rabi 2006/07 season than in the previous 2004/05 cropping year. ET a of the Thal Canal has increased by 44% in the Kharif 2007 season followed by Lower Jhelum Canal with 28%. ET a of Upper Jhelum Canal has also increased by about 20% while that of Panjnad Canal has increased by 22% in the Rabi 2006/07 season. Equity of water consumption in 2006/07 has improved considerably compared to 2004/05 in many canals, especially Central Bari Doab, Bahawal, Thal, Chashma Right Bank, Muzaffargarh and Panjnad, which figured as 2, 12, 11, 7, 8 and 8%, respectively. Similarly, adequacy has also improved in many canal commands in the 2006/07 cropping year when compared to 2004/05. This study demonstrates how a remote sensing based estimation of water consumption and water stress can be combined to provide a better estimation of system and irrigation performance at a variety of spatial and temporal scales that would assist water managers and policymakers.
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Papers by Nilantha Gamage