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.

Stepped spillways are an accessory of reservoirs and water conveyance system, which dissipate flow energy and reduce the size and costs of stilling basins (SBs). As the reverse inclination of each step helps form a small SB, therefore, energy dissipation becomes more efficient. In this study, using a Plexiglas spillway (height: 72 em), which was installed in an experimental flume (width: 50 em), various arrangements of numbers and inclination steps of spillway were investigated installing 12 set-ups. The first experiment was conducted on the weir itself without any steps; another set-up was with one step without inclination and one step with reverse inclination. This procedure was continued asymmetrically with the array of 8 steps. As expected to efficiently dissipate the energy, more steps are required as the flow increases. It was observed that one inclined plus two horizontal steps provide the best energy dissipater array. Furthermore, it was revealed that there was a limit to increase the number of steps and their inclination in energy dissipation, i.e., efficiency may not be enhanced by increasing the number of inclined steps.

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.

Stepped spillways are used to discharge the floods flow entering the reservoirs. Along these spillways, the energy is highly dissipated. It consists of a series of arranged steps along the spillway to ensure a uniform flow depth and velocity. Stepped spillways improve the rate of longitudinal energy dissipation on the spillway. The energy dissipation affects the flow characteristics and the energy dissipaters at downstream. The flow over stepped spillways is divided into three regimes of nappe, transition and skimming flows. So far, limited numbers of studies have been performed on the basis of analytical and empirical information to check the features and complicated nature of nappe flows. Limitations on physical model studies are also important to mention. As a result, few relationships have been suggested to describe nappe flow characteristics over stepped spillways. In this study, a set of experiments were performed on three large-scales hydraulic spillway models of Siahbisheh upper and lower dams and Zhaveh spillway dam. The data cover six spillway slopes and 24 flow rates. Measurements of depth, velocity, and static pressure were made at 40 different cross sections along the chutes. Major effective geometrical and hydraulic parameters on energy dissipation in nappe flow regime over stepped spillways were analyzed, based on present measurements. A relationship was then suggested to calculate the rate of energy dissipation in nappe flow regime. This study showed that the ratio of critical depth to height of spillway is the most important dimensionless parameter in predicting energy dissipation, the increase of which reduces the relative energy dissipation in the nappe flow regime.

The present paper deals with a numerical method for prediction of cavitation damage level and location on dam spillways. A method was applied to predict the intensity of cavitation damage to spillways, using the fuzzy k-nearest neighbor algorithm. Five levels of damage intensity were considered to predict cavitation damage in the spillway of Karun-1 Dam in Iran. According to the results, the proposed model could properly predict the location and intensity of damage in comparison with the actual damage reports of past floods. According to the Pearson's correlation coefficient, mean absolute error, coefficient of residual mass, and normalized root mean square error, the fuzzy k-nearest neighbor model is efficient and suitable.

Hydraulics of stepped spillway is a very complicated phenomenon, as it consists of a two phase flow passing through a set of designed steps. The steps increase the rate of energy dissipation taking place on the spillway face. Turbulence, flow aeration and energy dissipation are the main tasks in the design of such structures. This study consists of the experimental investigation to determine the energy dissipation over stepped spillways. Experiments conducted at Water Research Institute on two physical models of the Siyah Bisheh stepped spillways in Iran. To develop a more generalized expression, the results of previous investigations were also considered in our study. Therefore, a wide range of variables were taken into account to estimate the energy dissipation along the non-uniform flow regime. Assuming the energy dissipation along the uniform flow regime to be equal to the vertical displacement of the jet, the total energy lost was calculated. A comparison of the results with those of measurements showed a regression of 0.92 for the total energy dissipation, which is one of the features of the present method for estimating of the energy dissipation, compared with the previous investigation.

In this study, the effect of different hydraulic parameters on the energy loss of flow over gabion stepped spillways are examined using physical models and comparisons are made with the other studies. Two end sills including rectangular and inclined shapes are used on each spillway step. The results showed that the influence of end sills in gabion stepped spillways with lower slopes is greater than that of spillways with higher slopes. The influence of end sills on energy loss in spillways with d50=40 mm and S = 1:2 is about 10% more than the spillways with d50=10 mm and S = 1:1 (d50 is the mean diameter of gravel in the gabion and S is the downstream slope of the gabion stepped spillways, vertical: horizontal). Energy dissipation in spillways with d50=10 mm and S = 1:2 is about 30 to 35 percent more than spillways with d50=10 mm and S = 1:1. Hence, end sills in spillways with gravel size of d50 = 10 mm have the most significant impact on the energy loss. Instead, the influence of the rectangular end sill on the energy loss is about 3-4% more than the effect of a triangular (inclined) end sill.

One of the objectives of utilizing stepped spillways is to increase energy dissipation along spillways and consequently decreasing dimensions of stilling basins. This influences the economical evaluation of the design by reducing costs. The hydraulics of flow over stepped spillways has been investigated by many researchers for the last decade. These investigations have resulted in many hydraulic relationships. Several equations regarding head-loss and friction factor have been developed. Most of these equations are based on an average depth or consider a constant friction factor. In this study, the most effective hydraulic variables have been considered to obtain a general relationship for the friction factor and used in the calculation of water surface profiles along stepped spillways. This relationship has been calibrated by using experimental data and a nonlinear optimization technique. Accuracy of the obtained relations have been evaluated by comparing their results with real ones.

In this study, the effect of sedimentation behind Ogee Spillway on the characteristics of flow including upstream head and velocity, discharge coefficient, water surface profile, critical depth position and flow conditions downstream of a spillway, are investigated experimentally. The experiments were carried out by using an Ogee spillway with height of 25 cm and different upstream side slopes as 1H: 3V, 2H: 3V and 3H: 3V. The used sediment had a diameter of 0.4 mm and sedimentation heights in the range of 0-24 cm were considered. The results showed that the upstream flow depth and upstream flow velocity are increased by increase of sediment level upstream of spillway. As a result, the design head (He) will be increased. A change in He decreases the discharge coefficient of spillway. It was also found that the discharge coefficient changes from 2.25 for no sediment deposition (first stage of operation) to 1.69 for full sediment deposition in upstream reservoir. Thus, these results showed that the design of diversion weirs based on initial conditions is not accurate and causes major problems during operation of diversion weir.

Vertical shaft spillways have been widely used in a number of dam projects since the late 19th century around the world. Although a number of studies oriented to the shape of the inlet of shaft spillways including bell mouth inlet, there are lack of research studies regarding to the improved inlet shape of these hydraulic structures. A brief review of the former studies shows that most of those have focused on the bell mouth inlet to enhance the flow field thereby increasing the discharge capacity using complementary structural elements such as; anti-vortex plates, trash racks etc. Improving the hydraulic performance of different types of spillways was a major objective of several studies, resulting in different forms of spillway crests such as; piano key weirs and Daisy (Marguerite) shape inlets. Daisy (Marguerite) shape inlets which are the subject of the present study have been applied in some dam projects. Applying certain shape of inlets e.g. installing a Daisy (Marguerite) shape inlet over the shaft entrance is an alternation to avoid the swirling flow effects thereby to increase the shaft spillway discharge coefficient. Marguerite shape inlet has been used in different existing dam projects. Marguerite inlet is a unique inlet to increase the discharge coefficient compared to the other shapes of spillway crests. This is in part due to generation of spatially varied flow inside the Marguerite inlet blades, which makes it capable to pass greater flow discharges. Although different types of dam spillways have been the subject of different investigations, there is a lack of study on Marguerite-shape spillways.In this study, the effects of a Daisy (Marguerite) shape inlet on radial or crest control flow regime through shaft spillways have been investigated based on model experimentation. For the case of symmetry location of a vertical shaft spillway in the dam reservoirs, radial flow around the spillway should be considered to analyze the hydraulic performance of these spillways. Dimensional analysis has been used to determine the effective dimensionless parameters. Experimental study was conducted in a hydraulic model of vertical shaft spillway equipped with the Marguerite-shape inlets. Tests were performed in a circular cylinder of 2 meter diameter and 1 m high. The flow discharges through models of Marguerite spillways with different geometries (including; the length, the height and the number of blades) were ranged until a crest control flow was established. Tests were performed based on a wide range of geometric and hydraulic parameters to study as well as to evaluate the effects of each dimensionless parameter on flow hydraulic characteristics. To create a crest control flow condition, the flow was entered the main reservoir throughout a pipe inlet installed under the floor of the reservoir. Three-dimensional flow velocities were measured by an ADV installed over the reservoir with Frequency of 200 Hz. The water free-surface profile was measured using piezometers installed under the reservoir floor.Applying nonlinear regression analyses, empirical correlations were obtained for estimating the discharge coefficient and the threshold depth of orifice flow over Daisy (Marguerite) shape inlets.