Bandara Nawarathna

Integrated modeling framework to evaluate conjunctive use options in a canal irrigated area

AbstractIn canal irrigated areas, where interactions between surface water and groundwater are high, the conjunctive management of surface water and groundwater can play a significant role in improving water availability in time and space, thereby promoting more equitable distribution of water while maintaining long-term availability of groundwater resources. Achieving a harmonious balance between the use of surface water and groundwater requires careful consideration of the associated benefits, impacts, and trade-offs. In this study, a simple, integrated framework was developed and implemented to characterize and quantify interactions between surface water and groundwater in a canal irrigated area; this framework was used to evaluate the impacts of alternative levels of conjunctive use under varying climate and cropping conditions. Applying the model to a case study area of the Srisailam Right Branch Canal project in Andhra Pradesh, India, indicated that regulating canal supplies to optimum levels can pr...

Ensemble forecasting of short-term system scale irrigation demands using real-time flow data and numerical weather predictions

Irrigation demands fluctuate in response to weather variations and a range of irrigation management decisions, which creates challenges for water supply system operators. This paper develops a method for real-time ensemble forecasting of irrigation demand and applies it to irrigation command areas of various sizes for lead times of 1 to 5 days. The ensemble forecasts are based on a deterministic time series model coupled with ensemble representations of the various inputs to that model. Forecast inputs include past flow, precipitation, and potential evapotranspiration. These inputs are variously derived from flow observations from a modernized irrigation delivery system; short-term weather forecasts derived from numerical weather prediction models and observed weather data available from automatic weather stations. The predictive performance for the ensemble spread of irrigation demand was quantified using rank histograms, the mean continuous rank probability score (CRPS), the mean CRPS reliability and the temporal mean of the ensemble root mean squared error (MRMSE). The mean forecast was evaluated using root mean squared error (RMSE), Nash–Sutcliffe model efficiency (NSE) and bias. The NSE values for evaluation periods ranged between 0.96 (1 day lead time, whole study area) and 0.42 (5 days lead time, smallest command area). Rank histograms and comparison of MRMSE, mean CRPS, mean CRPS reliability and RMSE indicated that the ensemble spread is generally a reliable representation of the forecast uncertainty for short lead times but underestimates the uncertainty for long lead times.

Greenhouse Gas Emissions of Decentralised Water Supply Strategies in Peri-urban Areas of Sydney

Quantification of greenhouse gas emissions for decentralised water supply systems is essential for water policy development, decision making and implementation of these systems. Two potential water supply strategies ‘Effluent Reuse’ and ‘Stormwater Harvesting’ applicable for the planned growth centre development of Western Sydney were developed. The associated energy intensities and operational greenhouse gas emissions of these two strategies were quantified by using the factors and methods prescribed by the Department of Climate Change and Energy Efficiency National Greenhouse Accounts Factors, 2011. It was found that in terms of operational greenhouse gas emissions, stormwater harvesting performs marginally better than effluent reuse while the cost of stormwater harvesting is expected to be about four times cheaper than effluent reuse in Australia.

Valuing the Water Used in Peri-urban Regions of Hyderabad, India and in Western Sydney, Australia

Economic theory suggests that resources should be employed in different sectors to the point where their marginal values are equal. Yet what has been observed in many instances is that the marginal values of a resource tend to differ, depending on what they are used for. While this occurs for a variety of reasons, it is argued in this paper that the observable relative differences in the marginal values of a resource are a measure of the pressures forcing a reallocation of those resources within a region. This issue is most acute in peri-urban regions (those places where cities and the rural environment meet) as the competition between a declining agricultural sector and the growing domestic and industrial sectors is most intense. The argument arises as to what extent is the pressure to transfer resources between these declining and expanding sectors. To answer that question it is necessary to value the resource in question in a consistent and comprehensive manner across all sectors. Once done, the forces exerted on the resource can be gauged by observing the relative differences in the values placed on it in each use. The purpose of this paper is to present the results of a method that has been used to undertake this task with respect to the allocation of water resources. However, analyzing this question in the water sector has been stymied by the fact that the value of water deployed cannot be compared easily with that allocated to other sectors. The approach taken is an extension of the Residual Method that is used to calculate the marginal value product of water used in each crop and then aggregated to obtain the total value of water allocated to the agricultural sector as a whole. These results are then compared to the more conventionally obtained values of water used in other sectors. The results presented in this paper were drawn from research that has been published on two very different peri-urban sites, in Western Sydney, Australia and in Hyderabad, India. It can be concluded that despite the differences in the circumstances, conditions and concerns of stakeholders, the approach is robust enough to be used in a variety of situations where the competition for water between sectors exists. It was found that the value of water used for domestic purposes is significantly greater than that deployed to the agricultural sector in both peri-urban regions. In addition, it does not matter that the quantities used in the urban areas for domestic and industrial uses are relatively small when compared to those in the agricultural sector (as is the case in Hyderabad) or not (as in the case in Western Sydney). Just like other resources (principally land) it is inevitable that in peri-urban regions water will be and should be allocated to the use that it is most valued; towards urban expansion and away from agriculture.