M. Rezaee; A. Emadi; Q. Aqajani Mazandarani

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**Abstract **

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, ...
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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 leaserdevice 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 designoverflow 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.