Trapezoidal Canals Research Articles

Evaluation of Irrigation Canal Maintenance according to Roughness and Active Canal Capacity Values

This work assesses the state of maintenance of the concrete-lined trapezoidal canals of the Menemen irrigation system at the end of the Lower Gediz Basin according to the values of roughness (n) and active canal capacity (ACC). The study was carried out on two main canals, five secondary canals, and 12 tertiary canals at 45 measurement points. Average values of n and ACC were found to be 0.023 and 69%, respectively, for the main canals, 0.018 and 93%, respectively, for the secondary canals, and 0.023 and 81%, respectively, for the tertiary canals. The fact that values of n for the selected canals were higher than projected values and higher than the limit values, which would indicate adequate maintenance, and that the related ACC values were low, indicates that maintenance is insufficient in these canals. In order for maintenance work to be carried out more effectively, it may be suggested that new techniques should be applied for canal linings, which are economical and longer lasting, that farmers who be...

Mechanics models of frost-heaving damage of concrete lining trapezoidal canal with arc-bottom

Mechanics models of frost-heaving damage of concrete lining trapezoidal canal with arc-bottom

Influence of roughness changes on offtaking discharge in irrigation canals

The paper shows how a change in irrigation canal roughness can influence the flow passing through offtakes. HEC-RAS steady state model was calibrated with changing Manning's “n” and used for flow simulation in a modern irrigation system in Iran. Results showed that the Manning's “n” obtained from the model calibration procedure (0.025) was different significantly from its primary value (0.015) along the canal. The increase was due to poor canal maintenance. The changes in roughness of about − 20%, − 40%, 40%, and 100% of the primary value can significantly influence the upstream water level and the discharge passing through some offtakes. In order to better evaluation and comparison of offtakes, sensitivity indicator “offtake sensitivity to roughness” was introduced. An analytical approach helped us to define an equation for direct estimation of the sensitivity indicator under steady state uniform conditions for trapezoidal canals. Evaluation of water level fluctuations and the sensitivity indicator shows that only two of the offtakes are sensitive to roughness changes because of being located at the upstream of submerged cross-regulators. It can be concluded that the effects of roughness changes could be more important for offtakes located far from the downstream cross-regulators or near the submerged cross-regulators.

Optimal Design of Transmission Canal

This paper presents design equations for the least-cost canal sections considering earthwork cost which may vary with depth of excavation, cost of lining, and cost of water lost as seepage and evaporation from irrigation canals of triangular, rectangular, and trapezoidal shapes passing through a stratum underlain by a drainage layer at shallow depth. The optimal design equations are in explicit form and result into optimal dimensions of a canal in single-step computations. Using these least-cost section equations and applying the Fibonacci search method, equations for computation of the optimal subsection length and corresponding cost of a transmission canal have been presented. The optimal design equations along with the tabulated section shape coefficients provide a convenient method for the optimal design of a transmission canal. A step-by-step design procedure for rectangular and trapezoidal canal sections has been presented to demonstrate the simplicity of the method.

Design of minimum water-loss canal sections

The canal water losses constitute of seepage and evaporation losses. Whereas seepage loss depends on the channel geometry, evaporation loss is proportional to the area of free surface. On account of complexities of analysis, the design of minimum water loss section has not been attempted as yet. In this investigation explicit equations for the design variables of minimum water loss sections for triangular, rectangular, and trapezoidal canals have been obtained using non-linear optimization technique. The proposed equations along with tabulated section shape parameters facilitate easy design of the minimum water loss section and computation of water loss from the section without going through the conventional and cumbersome trial and error method. A design example has been included to demonstrate the simplicity of the method.

Design of Minimum Seepage Loss Canal Sections with Drainage Layer at Shallow Depth

This paper presents an analytical solution for the quantity of seepage from a rectangular canal underlain by a drainage layer at shallow depth. The solution has been obtained using inverse hodograph and conformal mapping. Using the solution for the rectangular canal and the existing analytical solutions for triangular and trapezoidal canals, simplified algebraic equations for computation of seepage loss from these canals, when the drainage layer lies at finite depth, have been presented, which replace the cumbersome evaluation of complex integrals. Using these seepage loss equations and a general uniform flow equation, simplified equations for the design variables of minimum seepage loss sections have been obtained for each of the three canal shapes by applying a nonlinear optimization technique. The optimal design equations along with the tabulated section shape coefficients provide a convenient method for design of the minimum seepage loss section. A step-by-step design procedure for rectangular and trapezoidal canal sections has been presented.

Extension of Vedernikov's graph for seepage from canals.

In this investigation, using previously derived equations by Vedernikov and Morel-Seytoux, closed-form solutions have been obtained to compute the seepage from a slit and a strip. Also, a graphical solution as an extension of Vedernikov's graph has been presented for computing quantity of seepage from triangular, rectangular, and trapezoidal canals. The solution replaces approximately the cumbersome evaluation of improper integrals with unknown implicit transformation variables.

Determining Irrigation Canal Seepage with Electrical Resistivity

Procedures were developed and tested for quantifying seepage losses in unlined irrigation canals for reaches on the order of 100 ft (30 m). The procedure is appropriate for trapezoidal canal sections underlain by clay with a layer of more permeable material at depth. These conditions prevail throughout much of the Central Nebraska Public Power and Irrigation District (Central) canal system. The procedure uses electrical resistivity (ER) measurements while canals are in service to determine the resistivity of the underlying clay layer. ER data were correlated to canal depth and then to seepage rate. Seepage rates were determined using seepage meters. Field test sites showed seepage rates from 0.07 to 0.62 (ft3⋅s) (ft width⋅mi) [0.0041 to 0.036 (m3⋅s) (m width⋅km)]. Accuracy is approximately ±20%, comparable to that achieved using stream-gauge methods, which can achieve a ±5% error of total canal discharge. The ER approach, however, can easily pinpoint seepage zones more precisely than accomplished using stream gauging and will allow Central to reduce the length of canal lining projects. The methods outlined in this paper are simple, relatively quick, and can provide seepage estimates for short reaches in extensive conveyance systems. Such information will be valuable to managers as they make decisions regarding water conservation and ground-water management and where to invest limited resources.

Design of Minimum Seepage Loss Canal Sections

The minimum area section is a thoroughly investigated problem in the hydraulics literature. However, because of the complexities of the analysis, the design of a minimum seepage loss section has not been attempted as yet. In this investigation, using previously derived results, simplified algebraic equations for computation of seepage loss from triangular, rectangular, and trapezoidal canals have been presented, which replace accurately the cumbersome evaluation of complex integrals. Using these seepage loss equations and the general uniform flow equation, explicit equations for the design variables of minimum seepage loss canal sections have been obtained for each of the three canal shapes by applying nonlinear optimization technique. The optimal trapezoidal section has the least seepage loss and cross-sectional area among the three optimal sections. A step-by-step design procedure for rectangular and trapezoidal canal sections has been presented. The analysis also includes the sensitivity of the seepage loss to design variables around the optimum value.

Closure to “Measuring Water in Trapezoidal Canals” by Zohrab Samani and Henry Magallanez (January/February, 1993, Vol. 119, No. 1)

Closure to “Measuring Water in Trapezoidal Canals” by Zohrab Samani and Henry Magallanez (January/February, 1993, Vol. 119, No. 1)

Discussion of “Measuring Water in Trapezoidal Canals” by Zohrab Samani and Henry Magallanez (January/February, 1993, Vol. 119, No. 1)

Discussion of “Measuring Water in Trapezoidal Canals” by Zohrab Samani and Henry Magallanez (January/February, 1993, Vol. 119, No. 1)

Measuring Water in Trapezoidal Canals

Laboratory experiments were conducted to evaluate the hydraulic characteristics of a simple portable flume. The flume consists of a pipe installed axially inside a trapezoidal channel with side slopes of 1/1. The ratio of the diameter of the pipe to channel bottom width was approximately 90% or more. The presence of the column reduces the cross section of the flow, creating a critical‐flow condition. A gage is installed at the upstream side of the column to measure the depth of the water upstream of the critical‐flow section. The reading on the gage is directly related to the flow rate. Based on the parameters measured in the laboratory, a computer model is developed for calibration of this type of flume. The computer model is tested using data collected from flumes installed in the field. The computer model predicted the measured flow rates with a maximum error of 5.1%. The maximum submergence limit was measured at 81%.

Flow in Trapezoidal Channels

Four charts are presented for the selection of standard concrete trapezoidal canals. The charts cover Systeome International (SI)– and English-dimensioned canals. If the channel invert slope and flow are known, a standard section can be chosen (bottom width and side slope) and the flow depth determined. Alternately, the invert slope and average cross-sectional velocity can be used as a basis of selection. Procedures are given for using the charts for channels of Manning roughnesses not included in the standards.

Turbulence intensity in transition sections of pools in trapezoidal canals

Turbulence intensity in transition sections of pools in trapezoidal canals

Kinematic structure of flow in a trapezoidal channel

1. Under conditions of designing earth canals for a maximum permissible noneroding velocity a trapezoidal channel shape is potentially unstable. 2. In trapezoidal channels the distribution of the velocity over the width does not correspond to the calculation by the Chezy formula with the use of local (on verticals) hydraulic radii. 3. To provide slope stability of trapezoidal canals it is necessary when estimating the design velocity to take into account the actual distribution of the velocity over the channel width, which practically leads to a decrease of the design velocity. 4. From the viewpoint of cost effectiveness of designing large canals in a deformable earth channel it is necessary to reject trapezoidal shapes. It is necessary to adopt a parabolic configuration corresponding in shape to the diagram of the velocity distribution over the channel width; in this case the design flow velocity can be taken with respect to a depth close to the maximum.

Head-Loss Measurements on Hydroelectric Conduits

Prototype head-loss measurements on tunnels and other water conduits are reported. The measurements were done on water-power conduits of the Hydro-Electric Commission of Tasmania, Australia. Friction factors are given for an unlined tunnel, a mechanically bored partly lined tunnel, and a fully lined tunnel. Steel and woodstave friction factors are included together with factors for a concrete-lined trapezoidal canal. The effect of slime growth on head losses is discussed.

Effect of Slope on Submergency Ratios for Standing Wave Weirs.(Dept.C)

It has been always the main objective of many of the Egyptian investigators to find the best ways to restore enough irrigation water to be well regulated and distributed with the right amount and the best HOW and WHEN to be applied all over the agricultural lands. Standing wave we are became, since long time ago, one of the very widely traditional irrigation work used to regulate, control and measure flow rates through irrigation distribution system. The main objective of this research study was to find out the effect of changing the top slope of the standing wave weirs on the ratio of submersion for the sake of practicing higher flow rates Influenced by higher values of submergency ratios, experiencing minimum heading up, resulting the least head lose through the system. A well proportional scaled dynamically similar standing wave weir model was constructed across an artificially made controllable trapezoidal canal. Under different flow condition and with the variation of seven top slopes, (3: 1, 4 : 1, 5:1, 10 : 1, 15 : 1, 20 : 1 and Zero : 1), relationship between upstream and down-stream water heads were drawn to reach the modular ranges applying different flow rates. Also, distinct Correlations between submergency ratio and the upstream water heads versus the seven top slopes individually, 88 a third variable, were achieved where an inverse relationship was found Moreover, illustrations regarding the effect of the top slope on both the stabil1ty of flow over the weir and on the submergency ratios and thus on the weir flow rates were demonstrated. Definite conclusions were drawn, anong them the suitability of the top slope 5:1 for relatively smaller discharges while the top slope 20.1 were found to be sutiable for the higher ones. Also, several recommendations were emphasised concerning the limitations for using some of these top slopes for practical purposes. That in addition to other recommendations for future studies relevant to the same course of study.

Seepage from Trapezoidal Canal in Anisotropic Soil

An analytical solution is found for the problem of seepage flow from an unlined trapezoidal canal, taking into account the general anisotropic behavior of the porous medium. Since a canal in an anisotropic medium transforms into one with unequal slopes in an equivalent isotropic porous medium, the solution here is concerned with the problem of seepage flow from an unsymmetrical trapezoidal canal. The method of inversion of hodograph is made use of and expressions for the seepage loss and the locations of the phreatic lines are obtained. Numerical results are presented for the equivalent isotropic flow domain. Using the transformation formulas given, the actual discharge and the locations of phreatic lines in anisotropic medium can be easily obtained for given physical parameters of the actual flow domain. The nonsymmetry of trapezoidal canals of side slopes less than one has considerable influence on the quantity of seepage.

Studies on Seepage from Canals with Partial Lining

A study of seepage from partially lined trapezoidal canals in a homogeneous isotropic porous medium of large depth is done using inversion of hodograph and Schwarz-Christoffel transformation. The two cases studied are: (1) seepage from canals whose sides are lined but bottom unlined; and (2) seepage from canals whose bottom is lined but sides unlined. It is found that for every side slope of the canal there is a particular aspect ratio at which the sides lining or bottom lining results in the same reduction of seepage. For canals having an aspect ratio more than this, bottom lining is more effective and for a lesser aspect ratio, sides lining will be more effective. For a canal having an aspect ratio of 9 and a side slope of 2.5:1, a 50% reduction in seepage is ensured by sealing the bottom. The loci of the phreatic lines, resulting in the aforementioned two cases, are also studied.

Variation of α and β Values in a Lined Open Channel

A study of the variation in magnitude of the energy coefficient, α, and the momentum coefficient, β, was conducted for subcritical open-channel flow in concrete-lined trapezoidal canals containing horizontal curves. The Manning’s \In\N was 0.013 for reaches without bends; values of α and β were found to be smaller than values proposed in current literature, and there was only small variation of α and β values with stage, channel geometry, position, and radius of curvature. For all cross sections analyzed, the energy and momentum coefficients may be considered constant with values of 1.04 and 1.02, respectively.