Sustainable Management of Malwathu Oya Cascade-I: Present Status and Future Needs

Village tank cascade System is an old age art of irrigation technology presence, especially in North Central dry zone of Sri Lanka. Some of these cascades were already evaluated but most of them are not yet. In Malwathu Oya Cascade-I, no any comprehensive study was carried out yet, therefore this study aimed conduct a comprehensive study of Malwathu Oya cascade-I including demarcation of meso and micro catchments of this cascade, understanding of characteristics and hydrological endowment of the cascade, estimating tank water storage, runoff and irrigation water demand etc. Catchment, water spread and commanding areas of the individual tanks were measured and tank storage, effective runoff to tanks, irrigation water demand and cascade outflow were estimated. With the results, cascade was evaluated for hydrological endowment of the cascade, cascade water surplus and potential water availability. Malwathu Oya cascade-I is a branched type large cascade with the form index of 3.6. The total area of the cascade is 25.88 square kilometers with overall length of 7.1 kilometers. Total water spread area of the tanks and total commanding area of the tanks are 2.57 and 2.81 square kilometers respectively. Tank water supply adequacy showed that, cascade has adequate source of water to cater the irrigation requirement of the command area. All the individual tanks in the cascade except Kudawewa, Palugaswewa and Sattambikulama showed adequate storage capacity. According to the ratio of cascade area to the total tank water surface area of the cascade and ratio of cascade command area to the total tank water surface area, the cascade can be identified as a cascade with good hydrological endowment and stability. According to the cropping intensity of the cascade, cascade can be categorized as a well performing cascade

AGRICULTURAL RISKS OF RAINFALL IN MAPALANA AREA

The irregularity of rainfall in Mapalana area generates risks on agriculturecreating dry spells as well as heavy rainfall periods through out the year. Inorder to understand the behavior of rainfall in Mapalana area daily rainfalldata over 55 years (1950 - 2004) were assessed, considering the time units;days, weeks and months.Mean daily, weekly and monthly rainfall by arithmetic mean method anddependable rainfall at 75 % probability level were calculated. AgriculturalRainfall Index values were calculated using rainfall values at 75 %probability level and pan evaporation data at Mapalana area.Mean annual rainfall and annual dependable rainfall in the Mapalana area are2248.6 mm and 2026.5 mm respectively. The daily arithmetic mean rainfallat Mapalana area is stated as 6.2 mm (Range 0.7 - 24.3) whereas dailydependable rainfall at 75 % probability level is recorded as zero. The dailydependable rainfall at 50 % probability level is also zero for 212 days in theyear. The results reveals that even though the area receives 6.2 mm dailymean rainfall, there is not even 50 % probability of receiving rain in each dayper year.The weekly rainfall analysis shows that weekly arithmetic mean rainfall inthe Mapalana area is 43.2 mm (Range 17.0 - 82.6). However, whenconsidering the rainfall at 75 % probability level, 12 weeks per year showedzero dependable rainfall.The mean monthly rainfall and mean dependable rainfall at 75 % probabilitylevel are 187.4 mm (Range 88.0 - 313.1) and 104.9 mm (Range 16.2 - 205.5)respectively. According to the Agricultural Rainfall Index, seven months areunder water deficit condition.The results revealed that yearly variation and irregularity of rainfall withinthe month is high in the Mapalana area. Although the mean rainfallcalculated for daily, weekly and monthly records high values, water deficitperiods occur in the Mapalana area through out the year except in May, June,September, October and November

AGRO CLIMATIC RISK ASSESSMENT IN HAMBANTOTA REGION

In order to eliminate the risk on crop production in Hambantota region, spatial andtemporal variation of rainfall were analyzed based on rainfall magnitude, duration, riskand onset. The rainfall data over 42 years (1960-2002) in six rain gauge stations inHarnbantota region was assessed10 mm weekly rainfall at 75% probability level method was used to find the wet weeks ineach station throughout the year. 10 mm weekly rainfall at 50% probability level wasused for rainfall onset identification. Farmer survey was conducted to find the existingcropping calendar. The amount of rainfall, which accumulated on the date of cropcommencement, was identified using Forward accumulation methodThe results revealed that mean annual rainfall is decreasing in Harnbantota region. Allstations were recorded less than 20% wet weeks. It reveals that the high risk involveswith rain fed crop cultivation in Harnbantota region. Based on the 10 mm weekly rainfallat 50% probability level, rainfall onset for yolo and moho seasons varies from 11th to 16thweek and from 37th to 42nd week respectively.The farmers could be able to minimize theirrigation need using these rainfall onset weeks as their crop commencement weeks.Based on the farmer survey, crop commencement week in moho season varies between39th and 41"t week and farmers rarely cultivate during yolo season. According to theforward accumulation method at 75% probability level the amount of water accumulatedat crop commencement time was 75mm. The results indicate that the cropcommencement week based on farmer survey coincided with calculated rainfall onsetduring moho season.

A Functional Analysis of Pedotransfer Functions Developed for Sri Lankan soils: Applicability for Process-Based Crop Models

As measurements are expensive and laborious, the estimation of soil hydraulic properties using pedotransfer functions (PTFs) has become popular worldwide. However, the estimation of soil hydraulic properties is not the final aim but an essential input value for other calculations and simulations, mostly in environmental and crop models. This modeling approach is a popular way to assess agricultural and environmental processes. However, it is rarely used in Sri Lanka because soil hydraulic data are rare. We evaluated the functionality of PTFs (developed to estimate field capacity (FC) and the permanent wilting point (PWP) of Sri Lankan soils) for process-based crop models. We used the Agricultural Production Systems sIMulator (APSIM) as the test model. Initially, we confirmed the importance of PWP (LL15) and FC (DUL) by assessing the sensitivity of the soil input parameters on the growth and yield of rice under rainfed conditions. We simulated the growth and yield of rice and the four selected outputs related to the APSIM soil module using the measured and estimated values of FC and PWP. These simulations were conducted for ten years in 16 locations of Sri Lanka, representing wet, intermediate, and dry zones. The simulated total aboveground dry matter and weight of the rough rice, using both input conditions (the measured and PTF-estimated soil hydraulic properties), showed good agreement, with no significant differences between each other. Outputs related to the soil module also showed good agreement, as no significant differences were found between the two input conditions (measured and PTF-estimated soil hydraulic properties). Although the DUL and LL15 are the most influential parameters for the selected outputs of APSIM–Oryza, the estimated FC and PWP values did not change the predictive ability of APSIM. In this way, the functionality of PTFs for APSIM crop modeling is confirmed

Towards Coupling of 1D and 2D Models for Flood Simulation—A Case Study of <i>Nilwala</i> River Basin, Sri Lanka

The Nilwala river basin is prone to frequent flooding during the southwest monsoon and second intermonsoon periods. Several studies have recommended coupling 1D and 2D models for flood modelling as they provide sufficient descriptive information of floodplains with greater computational efficiency. This study aims to couple a 1D hydrological model (HEC-HMS) with a 2D hydraulic model (iRIC) to simulate flooding in the Nilwala river basin. Hourly rainfall and streamflow data of three flood events were used for calibration and validation of HEC-HMS. The model performed exceptionally well considering the Nash–Sutcliffe coefficient, percent bias, and root mean square error. The flood event of May 2017 was simulated on iRIC using the streamflow hydrographs modelled by HEC-HMS. An overall accuracy of 81.5% was attained when the simulated extent was compared with the surveyed flood extent. The accuracy of the simulated flood depth was assessed using the observed water level at Tudawa gauging station, which yielded an NSE of 0.94, PBIAS of −4.28, RMSE of 0.18 and R2 of 0.95. Thus, the coupled model provided an accurate estimate of the flood extent and depth and can be further developed for hydrological flood forecasting on a regional scale

Spatial Forecasting of the Landscape in Rapidly Urbanizing Hill Stations of South Asia: A Case Study of Nuwara Eliya, Sri Lanka (1996–2037)

Forecasting landscape changes is vital for developing and implementing sustainable urban planning. Presently, apart from lowland coastal cities, mountain cities (i.e., hill stations) are also facing the negative impacts of rapid urbanization due to their economic and social importance. However, few studies are addressing urban landscape changes in hill stations in Asia. This study aims to examine and forecast landscape changes in the rapidly urbanizing hill station of Nuwara Eliya, Sri Lanka. Landsat data and geospatial techniques including support vector machines, urban&ndash;rural gradient, and statistical analysis were used to map and examine the land use/land cover (LULC) change in Nuwara Eliya during the 1996&ndash;2006 and 2006&ndash;2017 periods. The multilayer perceptron neural network-Markov model was applied to simulate future LULC changes for 2027 and 2037. The results show that Nuwara Eliya has been directly affected by rapid urban development. During the past 21 years (1996&ndash;2017), built-up areas increased by 1791 ha while agricultural land declined by 1919 ha due to augmented urban development pressure. The pressure of urban development on forest land has been relatively low, mainly due to strict conservation government policies. The results further show that the observed landscape changes will continue in a similar pattern in the future, confirming a significant increase and decrease of built-up and agricultural land, respectively, from 2017 to 2037. The changes in agricultural land exhibit a strong negative relationship with the changes in built-up land along the urban&ndash;rural gradient (R2 were 0.86 in 1996&ndash;2006, and 0.93 in 2006&ndash;2017, respectively). The observed LULC changes could negatively affect the production of unique upcountry agricultural products such as exotic vegetables, fruits, cut flowers, and world-famous Ceylon tea. Further, unplanned development could cause several environmental issues. The study is important for understanding future LULC changes and suggesting necessary remedial measures to minimize possible undesirable environmental and socioeconomic impacts

Optimized Subsurface Irrigation System: The Future of Sugarcane Irrigation

Climate change may harm the growth and yield of sugarcane (Saccharum officinarum L.) without the introduction of appropriate irrigation facilities. Therefore, new irrigation methods should be developed to maximize water use efficiency and reduce operational costs. OPSIS (optimized subsurface irrigation system) is a new solar-powered automatic subsurface irrigation system that creates a phreatic zone below crop roots and relies on capillarity to supply water to the root zone. It is designed for upland crops such as sugarcane. We investigated the performance of OPSIS for irrigating sugarcane and evaluated its performance against sprinkler irrigation under subtropical conditions. We conducted field experiments in Okinawa, Japan, over the period from 2013 to 2016 and took measurements during spring- and summer-planted main crops and two ratoon crops of the spring-planted crop. Compared with sprinkler irrigation, OPSIS produced a significantly higher fresh cane yield, consumed less irrigation water and provided a higher irrigation water use efficiency. We conclude that OPSIS could be adopted as a sustainable solution to sugarcane irrigation in Okinawa and similar environments

Optimized Subsurface Irrigation System (OPSIS): Beyond Traditional Subsurface Irrigation

Technologies that ensure the availability of water for crops need to be developed in order for agriculture to be sustainable in the face of climate change. Irrigation is costly, so technologies need to be improved or newly developed, not only with the aim of the sustainable use of precious water resources, but also with the aim of reducing associated labor and energy costs, which lead to higher production costs. OPSIS (optimized subsurface irrigation system) is a super water-saving subsurface irrigation system developed to irrigate upland crops by soil capillarity. It is an environmentally-friendly, solar-powered automatic irrigation method with minimum energy consumption and operational costs. In soils vulnerable to drought damage, OPSIS can outperform other irrigation methods. This technical note introduces OPSIS

Application of Geospatial Techniques for Groundwater Quality and Availability Assessment: A Case Study in Jaffna Peninsula, Sri Lanka

Groundwater is one of the most important natural resources in the northern coastal belt of Sri Lanka, as there are no major water supply schemes or perennial rivers. Overexploitation, seawater intrusion and persistent pollution of this vital resource are threatening human health as well as ecosystems in the Jaffna Peninsula. Therefore, the main intent of the present paper is to apply geospatial techniques to assess the spatial variation of groundwater quality and availability for the sustainable management of groundwater in the coastal areas. The electrical conductivity (EC) and depth to water (DTW) of 41 wells were measured during the period from March to June 2014, which represents the dry period of the study area. Surface interpolation, gradient analysis, a local indicators of spatial autocorrelations (LISA) and statistical analysis were used to assess the quality and availability of groundwater. The results revealed that the drinking and irrigation water quality in the study area were poor and further deteriorated with the progression of the dry season. Good quality and availability of groundwater were observed in the western zone compared to other zones of the study area. A negative correlation was identified between depth to water and electrical conductivity in the western zone. Hence, relatively deep wells in the western zone of the study area can be used to utilize the groundwater for drinking, domestic and agricultural purposes. The outcomes of this study can be used to formulate policy decisions for sustainable management of groundwater resources in Jaffna Peninsula