Introduction: Labyrinth weirs compare with straight weirs had required less freeboard in upstream so they are more appropriate for the irrigation networks. So they could maked more space to sotrage water and restrained foold with higher discharge. Labyrinths weirs have three generally form triangles, trapezoidal and rectangular that Tullis et al. (15) presented formula (3) for discharge coefficient of labyrinth weirs (triangles and rectangular) and a few studiescarried out on rectangular shape and its hydraulic characteristics are not specified.Therefore main aim of this paper study and characterized hydraulic characteristics of rectangular labyrinth weirs by using laboratory data.Materials and Methods: In this study rectangular labyrinth weir discharge and coefficient discharge relationships used dimensional analysis and experiment on hydraulic modeling, constant coefficient was defined.Laboratory flume is shown in Figure 2 (0.5 m wide x 12 m long x 0.8 m deep). Models was made from clear plexiglass plate with 10 cm thickness thatcuted using leaser device and the crest manualy shaped quadrant with radius 10 cm, all models using silicon glue install in the flume. The upstream depth readership by point gauge that installed in upstream of models. Discharge calcutaed byupsterm depth of triangular weir that installed in down stream of flume. Data were analyzed by SPSS software and to compare relationships with each other used two parameter root mean square error and correlation coefficient and charts darw in Excel Results and Discussion: discharge coefficient formula (11) carried out by using SPSS software that compared with formula (3). Results showed (Tables 2 and 3) that the correlation coefficient of formula (11) was more than a formula (3) and formula (11) RSME was less than formula (3) RSME except in first and fifth hydraulic model (rectengular1 and 5) that they were almost equal. So the formula (11) was more accurate than a formula (3) to peredict discharge of flow in flume. In previous step we used all data, we saw flourmloa (11) had more accurate then we diceded data divided in to three groups: high change, length change and all that calculated correlation coefficient and RSME for formula (11) to figure out which group have more accurate, results was brought in table 4. The result showed that constant coefficient of formula (11) yields from all data was useful for the design proposed. Plotted discharge changes against H/P for rectangular labyrinth and straight weirs in Figs.3 and 4. In constant discharge and high with raising length weir, decreased depth of flow over the weir because the effective weir length was raised and the ratio of distributed length to apex length (b) was decreased. As well as in constant H/P and high weir with raising apex length, discharge was increased that similarity of the results of Tullis et al. (15) and Khode et al. (8). In length, and the ratio H / P constant with increasing height in the discharge coefficient due to submergence reduce local side Jt Hay reduce interference, but increases with increasing height from 0.20 to 0.25m m discharge coefficient decreases as flow rate and Weber number decreased as a result of the effect of surface tension and increased resistance to flow. In length, and the ratio H / P fixed amount of overflow discharge increases with increasing height as the ratio H / P value of the denominator increases and therefore increases the total height of the water upstream. For design overflow rectangular labyrinth weirs recommends0.20£H/P£0.40that maximum aeration and discharge coefficient in this range is the result of Hay and Taylor (7) and Darvas (4) is consistent. In discharge and fixed weir height and maximum height of the water upstream directly at least equal to 1.8 of the overflow stright weirs. So for the areas where there is a height restriction of water upstream, the water level upstream of rectangular labyrinth weirs less direct overflow weirs requires the use of this is recommended.Conclusion: The results showed the relationship (11) that uses most of effective parameters has more accurate results and proposed for design aim. In constant water head upstream discharge of labyrinth weir maximum 2.6 times more than straight weir discharge and in constant discharge water head upstream of straight weir 1.8 times more than upstream labyrinth weir water head so use a labyrinth weir appropriate for areas that have head and discharge restrictions. Best range of ratio H/P for of design was 0.20 to 0.40 and maxim coefficient discharge happened in this range.

Discharge coefficient of a semicircular labyrinth weir is a function of total head, effective length of crest and discharge coefficent. Discharge coefficient of such a weir is influenced by total head over the weir, height of weir, radius of weir, thickness of weir and shape of crest. In this paper the effect of imporant parameters affecting discharge coefficient are investigated. It was found that by increasing the radio us of weir, discharge coefficient increases. The rate of variations of discharge coefficient decreases by increasing depth of flow and finally maintain a constant value.Appropriate equations for discharge coefficient are introduced. New method of design is introduced.

A labyrinth spillway is an overflow spillway to regulate and control flow in canals, rivers and reservoirs. The main hypothesis for the development of such a spillway is to increase the discharge per unit width of structure for a given headwater. This type of structure is often an efficient alternative to a gated-spillway type where either the increase of the flood-passage capacity or the control of the water surface upstream is concerned. This study was aimed to investigate the hydraulic performance of labyrinth spillways of general trapezoidal plan form with simple curved apexes.In the experimental work, twelve spillway models with double cycles were considered using three different curved apexes (R/w=0.15, 0.2, 0.25), each with four different crest heights (w/P=1.5, 2, 3, 4). Based on the cited recommendations, the length magnification was set to a constant ratio of (l/w=3); the crest shape was to be of a semicircular form with simple radius (r=15 mm); and the spillway walls were vertical with the thickness of T=2r. An intensive experiment was carried out over a wide range of flows, providing 720 flow data ranging from free flow to submerged flow conditions. 1D flow equation was presented using combined mathematical and dimensional analysis. A coefficient of discharge, Cd, was introduced to represent the influence of the effective geometric and hydraulic parameters on the flow capacity over the spillway. Modular limit was also controlled to see whether the flow over the spillway would be submerged. The results of the study indicate that the modified curved plan form of the spillway apexes with consistent divergence in the downstream channel introduces a significant improvement in the flow efficiency over the labyrinth spillways. Spillways with narrower curved apexes (i.e. R/w4 0.2), and with the vertical aspect ratio of (24w/P<3) provide more stable and higher hydraulic performance than any other labyrinth plan forms over a wide range of flows (i.e. 0.1<H0/P<0.6). In terms of the flow capacity, the proposed spillway model is shown to be more efficient than other zigzag plan forms (i.e. triangular and trapezoidal shapes) with an identical crest length.

Labyrinth weirs are one of the kind of nonlinear crest weirs causing the increase of discharge capacity for specified height of water level in canals and dams. In this study, the effects of dentate and orifice labyrinth weirs on increasing the discharge capacity were investigated. Experiments were conducted in a laboratory flume with length of 12 m and width of 0.8 m. The nine experimental models with 15 cm height were used. The results showed that for L/W=2 and H/P=0.2, the discharge coefficient of the orifice-dentate labyrinth weir and the dentate labyrinth weir are 75.6% and 17.5%, more than the simple labyrinth weir, respectively. However, dent and orifice may decrease their efficiency in high heads and the discharge coefficient will be close to simple labyrinth weir. The reason for these changes was increasing the flow interference in downstream of labyrinth weir between dents, orifices and weir with increasing discharge. Also, the result showed the efficiency of orifice and dentate on labyrinth weirs will decrease with increasing the weir magnification (L/W) and they lose their effect.

Weirs are used in different ways to control water levels and flow measurement. One of the most effective and economical way to increase the effective length of weir is using labyrinth spillways. The direction of flow of the labyrinth spillways is not perpendicular to the edge of the weir and it is oblique. On the upstream and downstream of the weir, the flow direction of the symmetry axis of labyrinth weirs is parallel. This phenomenon is more common in the downstream overflow because of flow stacking and, thus efficiency of weir is reduced (Hay the Taylor, 1970). Since, study about the using of upstream guide vanes in the direct channel has not been yet published, in this paper, flow guide vanes were used in the upstream of the triangular labyrinth spillway with vertex angles of 45o or 90o. The main purpose is guiding flow on weir wall perpendicularly and study of discharge coefficient.The experiments were conducted in a canal with a length of 7 m, width of 0.32 m and height of 0.36m. The two triangular labyrinth spillways with vertex angle of 45o and 90o were used. The models were made of galvanized sheet with 1 mm thickness and smooth overflow threshold edge. According to previous researchers (w/P³2.5, in this case P is weir height and w is canal width), the height of the weir was considered equal to 12 cm. A direct spillway with the same width was used to calculate the equivalent discharge. Guide vanes were made from galvanized steel plates. The height of guide vanes was 12 cm and their widths were 2, 3, 4 and 5 cm. The width of guide vanes was a coefficient of the length of one side spillway. Spillways were installed at a distance of 4.5 meters from the beginning of the canal. The reason of choosing this distance is that the flow completely developed from 3.5 to 4.5 meters from the beginning of the canal. Height and velocity of upstream water flow were taken at 5 discharges. The upstream depth of water, above the weir and longitudinal profile of the water surface was measured by a depth meter. Acoustic Doppler Velocimeter was used to measure the flow velocity. The tests were conducted in 3 groups: Group I at vertex angle of 45 or 90o, the width of guide vanes were 2, 3, 4 or 5 cm at a direct distance of 8 cm from the weir with 45o wall angle. Group II at vertex angle of 45 or 90o, wall angle guide vanes with weir of 35, 45, 65 or 90 degrees at direct distance of 8 cm from the weir. Group III at vertex angle of 90o, direct distance of 8, 22 or 33 cm from the center.In this study, Group I on the weir at vertex angle of 90 degrees and direct distance of 8 cm from the upstream weir does not positive effect on overflow efficiency, because efficiency in all tests were less than simple triangular labyrinth spillway with vertex angle of 90 degrees. The comparison shows that the highest efficiency occurred on weir with vertex angle of 45 degrees with guide vane width of 2 cm and on weir with vertex angle of 90 degrees without guide vane. In group II at the weir with vertex angle of 90 degrees, existence of guide vanes at direct distance of 8 cm from the weir with all angles of 35, 45, 65 and 90 degrees is reduced efficiency of flow. It is determined by comparing the curve of models, the maximum of efficiency occurred with vertex angle of 45 degrees and wall angle of 35 degrees, and on weir with vertex angle of 90 degrees and wall angle of 35 degrees. In group III, efficiency in all tests were less than simple triangular labyrinth spillway with vertex angle of 90 degrees and adistance of 8, 22 and 33 cm. In triangular labyrinth spillway with small vertex angle, using guide vanes could affect on vertical velocity component and this component could be increased. So at the same time, the flow is passed more quickly from weir crest, discharge is increased then for the same height water, the discharge coefficient increased. It was found that the triangular labyrinth weir with less vertex angle had very disturbance flow with increasing of discharge. These vanes could be guided flow perpendicularly on wall weir and then efficiency was improved.

A ‘ spillway’ is a structure used to provide the controlled release of flood water from upstream into downstream area of a dam. As an important component of every dam, a spillway should be constructed strongly, reliably and efficiently to be used at any moment. Labyrinth and stepped spillways are presented as appropriate modifications to those spillways hardly capable of managing the maximum potential discharge. Owing to their nonlinear crests for a given width, labyrinth and stepped spillways have a larger discharge rate than linear-crest spillways at an identical height. Compared to other energy dissipaters, the combination of stepped and labyrinth spillways is known as a very strong energy dissipater. In the following part, the combination of these two structures and their dimensional change for increasing the water-energy dissipation are addressed. To conduct this study, an experimental flume with a 90-degree bend in the Islamic Azad University of Ahwaz was used. In total, 90 experiments were conducted on three different labyrinth-shape stepped spillway models with two different lengths, three different widths, and five different discharges. Analysis of the results showed a greater energy loss reduction in triangular rather than rectangular or trapezoidal labyrinth-shape stepped spillways. In addition, energy loss was greater in labyrinth spillways with two cycles than those with one cycle. Energy loss was increased by raising the Froude number from 0. 05 to 0. 1; in contrast, energy loss was decreased with increasing the Froude number from 0. 1 to 1. 0, which was due to the submergence of steps, a decrease in the roughness of steps and an increase in the intensity of aeration.

Nonlinear weirs are among the hydraulic structures that, despite their great importance and application, so far, no general method for estimating their discharge capacity has been accomplished. Laboratory or numerical modelling is commonly used to achieve nonlinear weir discharge capacity. It should be noted that employing the design equation from one geometric family of nonlinear weirs to another is impractical. The utilization of numerical or laboratory models in the preliminary stages of the design of these structures is a time and cost-consuming process, which is highlighted by the variety of nonlinear weir geometry. In this research, a general method for estimating the nonlinear weirs discharge capacity is presented. The proposed method analyzes nonlinear weir discharge capacity using energy and discharge equations for discretized solution fields. Furthermore, the local submergence in nonlinear weirs, which has a tangible effect on their discharge capacity, has been corrected. Results of laboratory models performed on the oblique weir, arced labyrinth weir, and Isabella dam weir have been used to evaluate the efficiency of the proposed method. The proposed method with high correlation and accuracy has estimated the discharge capacity of these weirs. The maximum error observed was 12 percent for the oblique weir,15 percent for the arced labyrinth weir, and 15 percent for the Isabella Dam weir.