Limit Criteria of Post-Tensioned Thin Web Beams

A total of 45 partially prestressed post-tensioned thin web T-be answered tested to investigate their ultimates hear and flexural strengths and the service ability limit so reflection and crack width. The varying para meters included in the study are the amount of prestress, amount of supplementary nonprestressed reinforcements, prestressing tendons being bonded or unbonded, absence or presence of shear reinforcements and width of the web. Astrain compatibility method with the associated bond factors is presented for the ultimate flexural strength analysis of the beams. For prediction of the oreticalloads, material characteristics are taken at their ultimate with no materials safety factor associated

Managing Surged Furrow Irrigation

The behaviour of the infiltration process in an irrigation system is the most important feature that must be determined. Knowledge of soil infiltration, as it is a dominant physical process in surface irrigation, is crucial to the successful implementation of the scheme. This cannot be over-emphasized in surface systems, especially in furrow systems. This paper describes the infiltration behaviour of a furrow irrigation system under the surge flow regime. Infiltration behaviour over the various runs was studied, Suggestions for the implementation of such a management-oriented irrigation practice are discussed. The infiltration characteristics over the various flows are given

Engineering agricultural water resources

Malaysia has a long history of experience in rice irrigation which spans from when the first scheme was built in 1892. The Kerian-Sungai Manik Irrigation Scheme which is located at Bagan Serai, Perak has a total acreage of 24000ha and the scheme is still in operation today. With the setting up of the Department of Irrigation and Drainage in 1932, there was more land for rice tilled under irrigation. In the 1960s the MADA Irrigation scheme in Kedah and Perlis, encompassing approximately 97000ha, was completed. With the inclusion of other later schemes such as the Besut Irrigation scheme in Terengganu, KETARA (5200ha,), KADA Scheme in Kelantan (26000ha), the Projek Barat Laut Scheme in Selangor (18000ha), the Seberang Perak Scheme (8500ha), PPPB Scheme in Pulau Pinang (9500ha) and the Kemasin-Semarak scheme (6500ha), make up the eight rice granaries existing today (194700ha, almost 390000ha under double cropping). Irrigation in Malaysia is almost entirely devoted to rice cultivation. Most of the irrigated rice areas in Peninsular Malaysia are located in the eight designed granaries. With recent rice supply being a bit chaotic with the sharp rise in price in the ASEAN region in early 2008, due in part to the calamities faced by some regions in the area, the Malaysian government has decided to increase its rice stockpile as well as place more lands under rice cultivation in Sabah and Sarawak. Of the available total surface water resources of Malaysia, around 75% (10 billion cubic meters per year) is for use in agriculture. Irrigation is not only the largest consumer of fresh water in terms of volume, it is also associated with comparatively low economic value, low efficiency of use (< 50%) as well as being a highly subsidized natural commodity. However, it is a must-have venture in order to give a guarantee of at least 70% of the staple food of Malaysia some figure of security. Thus, dams have to be built and maintained, water conveyance channels laid, control structures put in place for irrigation and drainage and pumps operated. All of this is just a part of the larger scheme of things, which incidentally includes the whole range of agricultural practices required in getting the grains to the markets. With the above mentioned scenario and the associated costs incurred, it is thus necessary to seek ways to better engineer and manage the water resources aspect of rice production so as to reduce the total cost of production of per unit tonne of rice grains produced in Malaysia. The total unit cost would invariably include a host of costs, but suffice to say that reducing the cost of water used in its production would help in a long way. Many have ventured to say that if the water is not used, then we still have to build dams to store it lest it just flows to the sea. These words are true in every aspect but then again, it is during times of water stresses that these dams would be a real blessing to have. So where possible dams will have to be built if not for irrigation then for the sake of domestic supplies when a real emergency crops up like the infamous 1998 El Nino phenomenon. The present climate change agenda around the globe has made all governments more aware of the need to be safe rather than to be sorry

Stochastic Rainfall Model for Irrigation Projects

Stochastic rainfall models are concerned with the time of occurrence and depth of rainfall. Various rainfall models have been using different time scales. Daily rainfall models have gained wide applicability as being appropriate for use in detailed water balance and agricultural and environmental models. In this study a stochastic daily rainfall generation model was adapted for the Besut Irrigation Scheme located in Terengganu, Malaysia. The model simulates the sequence of rainfall occurrence using the method of transitional probability matrices, while daily rainfall amount was generated using a skewed normal distribution. Rainfall data from six meteorological stations located at the Besut Irrigation Scheme were used for this model. The model parameters were estimated from historical rainfall records. The model validation was then performed with a separate set of data. Results obtained showed that the model could be used to generate rainfall data satisfactorily

Decision support tool for water management of double cropping rice system: water allocation

Besut Irrigation Scheme is one of the main rice growing areas in Malaysia. This scheme faces water scarcity especially during pre-saturation period with the traditional water supply. It is necessary to evolve an innovative approach for water distribution and management. A decision support tool was developed to improve decision-making with respect to water release policies and timely water distribution in the large double cropping rice irrigation project. The tool was designed to focus on water allocation and release decisions in rice growing area. The decision support tool includes database management, a model management, a knowledge base, and a user interface. The knowledge base of the decision support tool was developed from the knowledge derived from field experts and from the results of the model management system. This paper presents an integrated decision support tool for generating alternative water allocation based on water availability. Thus, the final output is given in the form of specific water management actions for the irrigated areas

Water Use Efficiency in a Furrow System

An existing volumetric balance approach in conjunction with the Kostiakov infiltration equation for determining soil infiltration parameters in a furrow is used to study furrow irrigation in the local environment. Other parameters required include furrow geometry, assumed subsurface profile and flow advance data. A set of adjacent furrows is used to indicate the performance of the field system. The procedure outlined here can be used to evaluate efficiency of continuous mode furrow irrigation. The spatial and temporal variation of infiltration characteristics of a soil are well known. As such, the performance of a furrow irrigation system which uses the soil as a medium of conveyance varies with the ever-changing infiltration behaviour. There is therefore a need for an evaluation procedure to determine water use efficiency which can be followed throughout the irrigation season so as to enable the irrigator to make any necessary changes to improve its performance. This determination of irrigation performance hinges very much on the correct evaluation of the infiltration process, in this case, in dynamic infiltration water flowing overland in small channels. An evaluation example is given

Evaluation of Infiltration in Furrow Irrigation Part 2 : Basic Infiltration Rate

Part 1 of this title was the simulation of the recession flow in a furrow. This part uses the recession simulation further to establish the basic infiltration rate in a furrow and, therefore, the infiltration characteristics in a furrow. Determining infiltration in a furrow is complicated by the dynamic flow nature of irrigation water, as well as the geometric shape of the channel, among other factors. The evaluation of this infiltration in furrows is important in order to evaluate the water use in such irrigation systems. The use of the Kostiakov equation in its extended form has been suggested for the determination of infiltration characteristics in a furrow. This equation, however, depends on the evaluation of the long-term basic infiltration rate, which can be determined practically by a long-term tedious inflow/outflow hydrograph of the irrigation event. An analytical method based on the kinematic wave theory and recession flow data is proposed here to evaluate the long-term basic infiltration rate pertinent to the correct evaluation of the infiltration flow characteristics in a furrow

Estimating earthen tertiary water channel seepage losses as a function of soil texture

Estimation of seepage losses is important in the management of an irrigation scheme because such losses significantly affect the efficiency of water usage. An attempt was made to determine seepage losses as a function of soil texture. Losses were measured three times, with the inflow-outflow method, for each of the 30 channels made of sandy loam, clay, clay loam, silt clay, and silt loam (six channels for each soil texture), and the soil-specific losses were determined. The soil-specific values were validated in terms of computing outflows. The maximum seepage of 294 mm day-1 was found for sandy loam, followed by 200, 185, 144, and 96 mm day-1 for silt loam, silty clay, clay loam, and clay material channels, respectively. Two empirical equations requiring soil type constants were also evaluated-namely, the Moritz formula and the Molesworth and Yennidunia formula. Investigation using these two equations for seepage estimation showed either underestimation or overestimation for the soil textures investigated. Therefore, these equations should be used after calibration, in accordance with channel conditions

Evaluation of Infiltration in Furrow Irrigation Part 1: Recession Flow

Recession flow in a large field can be significant from the point of view of water-use efficiency. This is particularly important in the case where the furrow field is long, thus the receding flow can contribute to the irrigation of crops. Indeed, recession flow is very significant in the surge method of furrow irrigation. In the continuous mode of operation in very long furrows the amount of recession flow can be significant. Herein is presented the mathematical modelling of the recession flow. The analytical procedure is based on the kinematic wave approach used for the simulation of the advance-flow trajectory for furrows. This resulting recession simulation was found to be very useful for the evaluation of the basic infiltration rate in a furrow

Review of artificial neural network model for suspended sediment estimation

Prediction of sediment load are required in a wide spectrum of problem such as design of the dead volume of a dam, sediment transport in the river, design of stable channels, estimation of aggradation and degradation at bridge piers, prediction of sand and gravel mining effects on river-bed equilibrium, determination of the environmental impact assessment, and dredging needs. Generally, the sediment concentration in the river is related to water discharge. Researchers have been used the regression between sediment concentration and water discharge. Such relationships are obtained through the application of regression analysis in many studies. Unfortunately, in the classical regression approach to determine sediment concentration–water discharge relationships, internal uncertainties are not taken explicitly into consideration. However, this approach alone does not provide much physical meaning of the parameters used in the equations and does not improve understanding of sediment transport processes. It is important that the application of an equation derived mainly from the regression analysis of data should be limited similar conditions to those where the data were obtained. Recently because of these problems researcher looking for simpler, cheaper and easier methods to estimate sediment load and they begin to use nonlinear models like artificial neural network (ANN) technique to solve nonlinear problems. The neural networks approach has been applied to many branches of science. This approach is becoming a strong tool for providing civil and environmental engineers with sufficient details for design purposes and management practices. M otivated by successful applications in modelling nonlinear system behaviour in a wide range of areas, ANNs have been applied in hydrology and hydraulics. The main purpose of this paper is literature review of Artificial Neural Network for suspended sediment estimation