Showing papers in "Journal of Irrigation and Drainage Engineering-asce in 1994"
TL;DR: In this paper, the Penman combination equation has been used to estimate the reference evapotranspiration (ET) measured by lysimeters of various grasses and/or alfalfas.
Abstract: Values of reference evapotranspiration (ET0) are used with crop coefficients (KC) for many aspects of irrigation and water resources planning and management More than a score of methods are used for estimating ET0 Estimated values vary widely due to the lack of standardization of the reference Evaporation (ET) measured by lysimeters of various grasses and/or alfalfas has been used as the standard for developing estimating equations Due to variation in the references used, some international organizations now wish to promote the use of a single equation or method to avoid the confusion caused by the current diversity Different versions of the Penman combination equation have been proposed The Research Center for the European Community and the ASCE Committee on Irrigation Requirements have evaluated various equations for estimating ET0 Due to its simplicity and the accuracy of estimates, the 1985 Hargreaves et al equation is recommended for general use ET0 is used in irrigation planning, design, an
450 citations
TL;DR: In this article, the characteristics of flow over side weirs are taken into account to determine the discharge coefficient for subcritical flow conditions under the assumption of constant-specific energy, and the relationship is of linear form and provides an easy means of estimating Cd.
Abstract: The characteristics of flow over side weirs are taken into account to determine the discharge coefficient for subcritical flow conditions under the assumption of constant‐specific energy. The main‐channel discharge, length of the weir crest, and sill height of the weir are treated as the controlled variables. The discharge coefficient Cd is found to depend on the upstream Froude number F1 and, contrary to earlier findings, also on the ratio of sill height to upstream flow depth s/y1. Multiple regression analysis is conducted to establish the relationship of Cd with both F1 and s/y1 taken together. The relationship is of linear form and provides an easy means of estimating Cd.
169 citations
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TL;DR: In this paper, the discharge-head relation for submerged flow is analyzed under a novel approach, and recommendations are specified under which a broad-crested weir may be used as a discharge measurement structure.
Abstract: The flow features over the broad-crested weir with vertical upstream wall and sharp-crested corner are analyzed experimentally. Only the long-crested weir is considered, for which the discharge coefficient remains practically constant. For a relative overflow depth between 10% and 40%, the surface profile, the bottom pressure profile, the boundary separation profile, and the velocity profiles close to the upper corner are self-similar, provided effects of scale may be dropped. For extremely long-crested weirs, undular flow occurs. The first wave profile is shown to be identical with the solitary wave profile. The main properties of the undular hydraulic jump are explored. The broad-crested weir is characterized by insensitivity to tailwater submergence. The modular limit is found practically constant at 75% of the tailwater level, independent of the relative head on the weir. The discharge-head relation for submerged flow is analyzed under a novel approach. Finally, recommendations are specified under which a broad-crested weir may be used as a discharge measurement structure.
143 citations
TL;DR: In this paper, a pilot-scale treatment system for developing drip-irrigation pretreatment criteria was designed, installed, and operated intermittently over 5,300 h using activated sludge secondary effluent.
Abstract: A pilot-scale treatment system, for developing drip-irrigation pretreatment criteria, was designed, installed, and operated intermittently over 5,300 h using activated sludge secondary effluent. Principal unit processes studied were granular-medium filtration and screen filters for removal of suspended solids, and chlorination treatment at various injection frequencies and concentrations to prevent biofilm formation in emitters and distribution lines. Two types of 4 L/h (1 gal./h) drip emitters were tested—automatic self-flushing and tortuous-path turbulent-flow emitters. Adequate filtration reduced both the required frequency of chlorination and lateral flushing. Intermittent chlorination with 2 mg/L free residual chlorine during the last hour of an irrigation cycle was found as effective as continuous chlorination with 0.4 mg/L free residual chlorine in preventing biofilm formation in emitters and distribution networks. Pretreatment recommendations for these types of emitter designs are presented.
86 citations
TL;DR: In this paper, a concept for an elementary discharge coefficient that is related to the discharge flowing through an elementary strip along the side-weir length is presented, and generalized equations for elementary discharge coefficients for rectangular and triangular side weirs are proposed.
Abstract: A side weir is a flow diversion device, which is widely used in irrigation as a head regulator of distributaries and escapes. This paper presents a concept for an elementary discharge coefficient that is related to the discharge flowing through an elementary strip along the side‐weir length. Generalized equations for an elementary discharge coefficient for rectangular and triangular side weirs have been proposed. Experimental results show the accuracy of the proposed equations.
78 citations
TL;DR: In this article, the use of mathematical programming theory is proposed to define optimization criteria for the deficit irrigation of an area, which is carried out on a sample farm in the Upper Tiber Valley (Central Italy).
Abstract: In the present paper the use of mathematical programming theory is proposed to define optimization criteria for the deficit irrigation of an area. A first application, which was carried out on a sample farm in the Upper Tiber Valley (Central Italy), gave significant results. By using a multiplicative Stewart’s formula, it was possible to determine, for various crops, the relationships between \Icrop yield and applied water\N, which depend on the deterministic component of the process of water exchange \Isoil-crop-atmosphere\N. The stochastic component of the same process is defined by the hypothesis that the functions are variable from year to year. These relationships were introduced as a constraint in a mathematical programming framework, with the aim of optimizing, in economic terms, the application of available irrigation water taking into account the possibility of varying the crop pattern. Finally, since the optimal solution can be found only on an annual basis, due to the stochastic component of the process, an attempt was made to define a method for determining a single, constant and optimal solution.
77 citations
TL;DR: In this article, the authors presented existing streamflow data for the Blue Nile River and its tributaries within the blue Nile River basin in Ethiopia and used that data to provide insight into the river's hydrology in Ethiopia.
Abstract: The Blue Nile River in Ethiopia has a drainage area of approximately 324,530 km2 and supplies nearly 84% of the water to the Nile River during high‐flow season, making it the main source of water for Ethiopia, Sudan, and Egypt. Relatively few analyses have been conducted on the Blue Nile River basin largely due to the lack of hydrologic data. The objective of this paper is to present existing stream‐flow data for the Blue Nile River and its tributaries within the Blue Nile River basin in Ethiopia and to use that data to provide insight into the river's hydrology in Ethiopia. A monthly water‐balance model was developed for this purpose. Comparisons of the predicted and observed monthly hydrographs are provided for selected subwatersheds within the Blue Nile basin. Spatial distribution of the calibrated coefficients is also discussed. Results will be useful in forecasting flows along the Blue Nile and Nile Rivers and in determining the effect of global climatic changes on continental hydrology.
76 citations
TL;DR: In this article, a leapfrog explicit finite-difference numerical scheme was applied to solve this system of equations for the initial and boundary conditions that characterize level-basin irrigation, and data from two field tests were used to validate the model in quasi-one-dimensional and two-dimensional conditions.
Abstract: Overland flow of water over a porous bed in two spatial dimensions is governed by three partial differential equations accounting for continuity of momentum in the \ix- and \iy-directions and continuity of mass. A leapfrog explicit finite-difference numerical scheme was applied to solve this system of equations for the initial and boundary conditions that characterize level-basin irrigation. The numerical procedure is stable and robust for different applications, and can accommodate three different inflow configurations: line, corner, and fan. These configurations simulate inflow from an overflowing canal on a field boundary and at point sources from a corner or in the middle of a straight boundary, respectively. A numerical test was performed to assess the effect of grid fineness on the results of the simulation and on central-processing-unit time requirement. Data from two field tests were used to validate the model in quasi-one-dimensional and two-dimensional conditions.
68 citations
TL;DR: In this article, the Lagrange multipliers were used to find the most efficient hydraulic cross-section for channels of trapezoidal shape where top width and depth are limited by site conditions.
Abstract: Dimensions of the most efficient hydraulic cross section are found for channels of trapezoidal shape where top width and depth are limited. The resulting nonlinear constrained optimization problem is solved using the method of Lagrange multipliers. Without top-width or depth constraints the optimal section dimensions can be calculated without iteration. For channels in which top-width or depth constraints are imposed an iterative solution is needed to solve the resulting system of nonlinear equations. However, the calculations can be greatly simplified using accurate approximations of the general solutions that yield direct estimates of the best trapezoidal-cross-section dimensions. The computational procedure will be useful for designing nonerodible open channels of trapezoidal shape where top width or depth is constrained by site conditions.
67 citations
TL;DR: In this paper, the authors present explicit equations for normal depth in various irrigation-canal sections based on Manning's equation, which is valid for a hydraulically rough boundary having a narrow range of relative roughness.
Abstract: Normal depth is an important parameter occurring in the design of irrigation canals. Direct analytic solution of normal‐depth problems is not possible, as the governing equations for the practical canal sections are implicit. The solution requires tedious methods of trial and error. Tabular and graphical methods also available for solution are subject to errors of double interpolation and errors of judgment in reading the graphs. Furthermore, the methods are based on Manning's equation, which is valid for a hydraulically rough boundary having a narrow range of relative roughness and involves a roughness coefficient having awkward dimensions. Reported herein are explicit equations for normal depth in various irrigation‐canal sections.
66 citations
TL;DR: One aspect of the riparian stream ecosystem, which is imperative for the restoration or reestablishment of a streambank and streambed that has been disrupted, is the ability of the stream system to...
Abstract: One aspect of the riparianstream ecosystem, which is imperative for the restoration or reestablishment of a streambank and streambed that has been disrupted, is the ability of the stream system to ...
TL;DR: In this article, the best hydraulic channel section is determined by using Lagrange's method of undetermined multipliers for a given flow, roughness coefficient, and longitudinal slope, this method optimizes the channel section by minimizing the wetted perimeter subject to a constraint.
Abstract: The best hydraulic channel section is determined by using Lagrange's method of undetermined multipliers. For a given flow, roughness coefficient, and longitudinal slope, this method optimizes the channel section by minimizing the wetted perimeter (or the cross‐sectional area) subject to a constraint. Any flow equation, e.g. Manning, can be used as the constraint. The channel section could contain any number of variables; e.g., two variables (rectangular and triangular sections), three variables (trapezoidal and round‐bottom triangular sections) and so forth. The approach presented is more general than the conventional methods given in the textbooks. It is shown that minimization of the wetted perimeter and minimization of the cross‐sectional area are mathematically equivalent. The method is applied to the standard sections as well as the round‐bottom triangular section. The best hydraulic round‐bottom triangular section, the determination of which is made possible by this approach, is slightly more effici...
TL;DR: In this paper, a concept of elementary discharge coefficient for the discharge of an elementary rectangular strip along the weir crest is presented, which is related to the head weir height ratio only.
Abstract: Side weirs are flow‐diversion devices widely used in irrigation, land drainage, urban sewage systems, and so forth. For computation of side‐weir discharge, the de Marchi equation is widely used. Using de Marchi's equation, various investigators have related the weir discharge coefficient with the main channel's upstream Froude number. Thus, the dominant variable ratio of head to weir height has not been considered in previous investigations. Presented herein is a concept of elementary discharge coefficient for the discharge of an elementary rectangular strip along the weir crest. Like that of a normal weir, this elementary discharge coefficient has been related to the head weir height ratio only. Using this relation, a methodology for determination of the weir discharge is described.
TL;DR: In this article, the de Marchi equation for the free surface profile of a side weir in a prismatic circular-shaped channel as used in sewage and irrigation systems is presented.
Abstract: The flow features of a side weir in a prismatic circular‐shaped channel as used in sewage and irrigation systems are considered The complex cross‐sectional channel geometry is simplified, and a generalized de Marchi equation is presented for the free‐surface profile The general solution is further modified to obtain a similarity plot of normalized flow depth as a function of normalized location for arbitrary weir height The solution for supercritical approach flow is compared to experimental data for one‐ and two‐sided lateral outflow Although the agreement between theory and experiment is only fair, the normalized parameters yield all data on a single curve Eq (15) may be regarded as the generalized free‐surface profile, provided no hydraulic jump occurs The hydraulic jump is studied with a modified momentum approach, and a simple relation comparable to that for rectangular channels is obtained No indications on the length or the velocity distribution in jumps with spatially decreasing discharge
TL;DR: In this paper, a mass-water-balance approach that accounts for the influence of tributary runoff contribution and evaporation loss in a typical arid catchment in Southwestern Saudi Arabia is proposed.
Abstract: Quantification of transmission loss was estimated through a mass-water-balance approach that accounts for the influence of tributary-runoff contribution and evaporation loss in a typical arid catchment in Southwestern Saudi Arabia. Regression equations were developed to relate the magnitude of transmission loss to the controlling parameters of upstream inflow, channel-flow width, and antecedent-soil conditions. Equations developed to relate inflow to outflow can be used to estimate flood volume or magnitude of transmission loss. The proposed techniques can be used by hydrologists and engineers to estimate channel-transmission loss from wadi beds having similar characteristics. The analysis also provides further clarification of transmission loss phenomena and additional field data from an extremely arid region of the world.
TL;DR: In this paper, a new design technique for sprinkler irrigation laterials with equally spaced sprinklers and constant longitudinal slope is presented, which accounts for the variation of the friction coefficient for a significant practical portion on a Moody diagram.
Abstract: This paper addresses a new design technique for sprinkler irrigation laterials with equally spaced sprinklers and constant longitudinal slope. The technique uses the Darcy-Weisbach friction formula and accounts for the variation of the friction coefficient for a significant practical portion on a Moody diagram. The head loss in sprinkler risers as well as losses in lateral pipe fittings are considered. A computer program employing this technique is designed so as to provide sprinkler outflows and pressure head distributions along the lateral pipe. The results from two numerical examples are compared with results obtained from a widely used classical method. In some cases it is found that designs are substantially different.
TL;DR: In this paper, the problem of seepage from an unlined earthen canal is considered and a closed-form analytical solution to the linearized Boussinesq equation was derived.
Abstract: The problem of seepage from an unlined earthen canal is considered. The phreatic surface generated on the two sides of the canal is characterized by the nonlinear Boussinesq equation incorporating the slope element. A closed‐form analytical solution to the linearized Boussinesq equation was derived. A finite‐difference solution to the nonlinear Boussinesq equation was also obtained using the unconditionally stable Du Fort‐Frankel explicit method for the seepage problem in the semiinfinite flow problem. The numerical solution in general predicted a higher phreatic surface than the analytical solution.
TL;DR: In this article, a new method, based on the routing of surface erosion through time-area segments, is proposed to produce the sediment yield more accurately than those it has been compared with.
Abstract: The prediction of sediment yield from catchments is necessary for studies of reservoir sedimentation, morphologic modeling, and soil‐conservation planning. Though records on sediment yield are generally not available, methods that can be used to predict sediment yield from other commonly available hydrologic data, are available in the literature. In this study some of these methods are verified for their accuracy, using carefully collected data from experimental catchments. It is found that existing methods do not adequately account for the process of sediment delivery; hence these produce a less accurate prediction of sediment yield. A new method, based on the routing of surface erosion through time‐area segments, is proposed. This method is found to produce the sediment yield more accurately than those it has been compared with. The method being proposed for the prediction of sediment yield has a more sound basis for further use in distributed models.
TL;DR: In this paper, the effects of seepage on flow over a sand bed in a straight rectangular flume under two conditions: (1) when the channel bed is plane, horizontal, and nontransporting; and (2) the bed is transporting at a constant sediment concentration.
Abstract: ExperimentS were conducted to find the effects of seepage on flow over a sand bed in a straight rectangular flume under two conditions: (1) When the channel bed is plane, horizontal, and nontransporting; and (2) when the bed is transporting at a constant sediment concentration. Effects of both injection and suction, caused by seepage flow into and out of the channel bed, are studied for condition 1; and only suction effects are studied for condition 2, Three sands, sizes 0.34 mm, 0.53 mm, and 0.80 mm, are used in the study. It is found that seepage can cause an increase or decrease in the bed shear stress relative to no seepage for the two conditions. The change in bed shear stress depends on the relative magnitudes of the bed shear stress and the critical shear stress of particles under the no-seepage condition, sediment concentration, and the seepage rate. Quantitative relationships giving the ratio of bed shear stresses with and without seepage are presented for both conditions of the bed. A procedure to estimate the changes in bed shear stress, friction factor, Manning's n, and stream power due to seepage for known initial conditions of the channel and the amount of applied seepage is presented
TL;DR: In this paper, the authors describe a simple set of infiltration equations to predict the infiltration rate and cumulative infiltration rate in bounded soil columns, and demonstrate that the reduction in cumulative infiltration in bounded soils is roughly proportional to the water-table depth.
Abstract: Infiltration into soils is affected by several factors, including the soil-air pressure. Soil air may become compressed between a confining layer (water table) and a nearly saturated surface soil. Compressed and counterflowing air substantially reduces soil infiltration rates resulting in potential practical problems of excess runoff and erosion. Using results from laboratory column studies, we describe a simple set of infiltration equations to predict infiltration rate and cumulative infiltration. Infiltration rates progressively declined in bounded soil columns until the soil-air pressure head exceeded the sum of the ponded water depth and the capillary driving head at the wetting front. After a brief transition period during which stable air channels formed in the porous media, the infiltration rate approached a constant value. We demonstrate a simple method to predict this stable infiltration rate based on the permeability-saturation relationship for the soil. Finally, we illustrate that the reduction in cumulative infiltration in bounded soils is roughly proportional to the water-table depth, and that this reduction is greater in sands as compared to loamy soils.
TL;DR: In this article, the authors developed a two-dimensional hydrodynamic simulation model of basin irrigation, and applied it to simulate a hypothetical case study involving the design of a square level-basin irrigation field with spatially varied infiltration irrigated from a corner.
Abstract: The development of a two‐dimensional hydrodynamic simulation model of basin irrigation is reported in a companion paper. This article presents four applications of the model. Two hypothetical case studies are used to illustrate the ability of the model to accommodate multiple inflows and irregular field shapes including internal high spots. The model is applied to study the effect of field shape on irrigation performance. The particular case of a rectangular basin irrigated from a corner is considered. Results show that one‐dimensional models can underestimate the time of advance by up to 20%. Finally, the model is applied to explore the effects of spatially varied infiltration on irrigation performance. A series of infiltration observation points is used to estimate the infiltration rate in unmeasured locations. The model is used to simulate a hypothetical case study involving the design of a square level‐basin irrigation field with spatially varied infiltration irrigated from a corner. Results show that...
TL;DR: In this article, a three-dimensional Green-Ampt analysis is developed, and the infiltration capacity curve for a threedimensional infiltration model is presented, which represents the time distribution of wetting pattern volume of a water source with unlimited inflow supply.
Abstract: A three‐dimensional Green‐Ampt analysis is developed, and the infiltration capacity curve for a three‐dimensional infiltration model is presented. The infiltration‐capacity curve represents the time distribution of wetting‐pattern volume of a water source with unlimited inflow supply. A significant feature of the infiltration‐capacity curve is that the infiltration‐capacity rate increases with time during extended infiltration periods. This feature is different from the one‐dimensional infiltration model where the infiltration‐capacity rate decreases with time. The infiltration‐capacity curve is applied to describe the wetting pattern of a surface emitter with a constant discharge by matching the emitter discharge with the average infiltration‐capacity rate. Algebraic solutions of the wetted radius and the maximum wetting‐pattern depth are derived. Graphical solutions of the infiltration‐capacity curve are presented. A numerical example is prepared to illustrate the procedure for estimating time of applic...
TL;DR: In this article, the experimental results of unsaturated water infiltration under two conditions: vertical columns of homogeneous soil and two columns of twolayered soil were presented, respectively.
Abstract: This study presents the experimental results of onedimensional unsaturated water infiltration under two conditions: vertical columns of homogeneous soil and vertical columns of twolayered soil. The...
TL;DR: In this article, the authors developed a methodology to simulate the transport of cadmium in soil water and its uptake by plant roots, where the transient unsaturated water flow equation with a root extraction term was coupled with mass transport equation and mass balance of solute concentration.
Abstract: Among various toxic substances that contaminate plants and enter the food chain, thereby posing health problems to human beings, heavy metals are particularly severe in their action. The behavior of heavy metals present in sewage sludge and industrial wastes that are used in agricultural practices has been the center of much attention during the last decade. Among these heavy metals, cadmium has been identified as the most critical metal due to its human toxicity. The presence of cadmium and its accumulation in the plant root zone also results in decreased crop yield. This study develops a methodology to simulate the transport of cadmium in soil water and its uptake by plant roots. The transient unsaturated water flow equation with a root extraction term is coupled with mass transport equation and mass balance of solute concentration. The model takes into account the root growth with time. The macroscopic root‐soil water flow and solute (cadmium) movement model yields a set of partial differential equatio...
TL;DR: In this article, the authors estimated evaporation E and transpiration T losses separately during various growth stages of a tomato crop (Lycopersicon escallen mill), in Davis, California.
Abstract: The present study estimated evaporation E and transpiration T losses separately during various growth stages of a tomato crop (Lycopersicon escallen mill. UC 82 variety), in Davis, California. Micr...
TL;DR: In this article, a downstream control algorithm for on-demand operation of irrigation canal systems is presented, which is based on an explicit finite-difference solution procedure of the St. Venant equations.
Abstract: A downstream control algorithm for on‐demand operation of irrigation canal systems is presented. A constant water level is maintained at the downstream end of the pool. The approach is based on an explicit finite‐difference solution procedure of the St. Venant equations. The upstream gate settings are corrected according to the water level and the flow rate at the information nodes along the canal. The method is illustrated for the control of a canal pool bounded by an upstream gate and a downstream gate or pump. The effectiveness of the control has been tested using an unsteady‐flow simulation model that is based on the complete St. Venant equations and the implicit Preissmann scheme. The simulation results show that the proposed control method can cope with rapid variations of water demand and unknown disturbances in the system. The influence of the number of information nodes and the assessment of the physical parameters of the system on the response of the system has been investigated. Unless the esti...
TL;DR: In this article, the authors used a 3.5-m diameter by 1.0-m deep polyethylene tanks to measure water balance parameters for citrus trees in the Florida Flatwoods.
Abstract: Twenty‐one drainage lysimeters were installed in 1988 to measure water balance parameters for citrus trees. The lysimeters were designed to simulate the high water‐table conditions that exist for the more than 150,000 ha of citrus grown in the Florida Flatwoods. The lysimeters were constructed from 3.5‐m diameter by 1.0‐m deep polyethylene tanks. Young trees were transplanted into the lysimeters in 1988. Four experimental treatments consisting of constant water tables at depths of 0.61 m, 0.76 m, and 0.91 m plus a fluctuating water‐table treatment were included in the study. Trees were watered with a microirrigation system and all irrigation and drainage water was metered. Water‐table levels were maintained by float‐controlled pumps. Annual evapotranspiration (ET) averaged 16,030 L tree−1 for March 1989 to March 1990 and 11,733 L tree−1 for March 1990 to March 1991. ET rates were not significantly different among water‐table treatments. Tree growth, yield, and juice quality were not affected (p=0.05) by t...
TL;DR: In this paper, the maximum surface storage provided by crop residue is derived assuming that residue elements were oriented end-to-end, at uniform intervals, in a direction perpendicular to flow.
Abstract: Small ponds created by crop residue serve to store water on upland areas. The present study is conducted to identify the maximum surface storage provided by crop residue. Equations for estimating surface storage are derived assuming that residue elements were oriented end to end, at uniform intervals, in a direction perpendicular to flow. Separate equations are developed for conditions where average slope was greater than or equal to residue cover, or less than residue cover. Both equations relate average surface‐storage depth to residue cover, residue diameter, and average slope. Data to test the reliability of the equations are obtained in a laboratory investigation. Artificial residue elements are glued onto a 1‐m2 test section positioned at slopes of 1%, 10%, or 20%. Four sizes of residue elements and three surface‐cover conditions are examined. Surface‐storage depth for each experimental condition is measured. Close agreement is found between predicted and measured surface‐storage values. Surface sto...
TL;DR: In this paper, statistical techniques were used to test for changes in water quality data from watersheds where best management practices (BMPs) were implemented using regression methods, and none of the techniques identified changes in suspended sediment, primarily because of the small degree of BMP implementation and because of potential errors introduced through the estimation of stormmass transport.
Abstract: Little has been published on the effectiveness of various management practices in small rural lakes and streams at the watershed scale. In this study, statistical techniques were used to test for changes in water‐quality data from watersheds where best management practices (BMPs) were implemented. Reductions in data variability due to climate and seasonality were accomplished through the use of regression methods. This study discusses the merits of using storm‐mass‐transport data as a means of improving the ability to detect BMP effects on stream‐water quality. Statistical techniques were applied to suspended‐sediment records from three rural watersheds in Illinois for the period 1981–84. None of the techniques identified changes in suspended sediment, primarily because of the small degree of BMP implementation and because of potential errors introduced through the estimation of storm‐mass transport. A Monte Carlo sensitivity analysis was used to determine the level of discrete change that could be detect...
TL;DR: In this article, the reliability of open drainage channels under three possible failure modes is examined, and the failure probability of each mode is estimated using the advanced first-order second-moment (AFOSM) method.
Abstract: Open drainage channel design involves variables that are uncertain. Because the performance of the channel system is also uncertain, reliability analysis is used to measure the reliability of the system performance. In this paper, the reliability of open drainage channels under three possible failure modes is examined. The first failure mode occurs when the runoff exceeds channel capacity. The runoff and channel capacity are random variables that are estimated using the rational method and the Manning equation, respectively. The second failure mode occurs when the actual flow velocity exceeds the maximum allowable velocity for erosion control. The third failure mode occurs when the actual flow velocity is less than the minimum allowable velocity for deposition control. The minimum and maximum allowable velocities are considered random variables. The failure probability of each mode is estimated using the advanced first‐order second‐moment (AFOSM) method. The overall failure probability of the system that ...