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The most complicated problem that threatens the spillway's overall stability is local scour downstream of the spillways due to hydraulic jumps and flow disturbance. A series of experiments were conducted in the laboratory of the Water and Soil Research Center to investigate the scour downstream of the hydraulic jump formed on the stepped spillway. Experiments were conducted under different approaching flow discharges, tail-water depths and sediment sizes. The optimal design of parameters including; type, crest and slope of chute, step height and type of flow stepped spillway has been done considering the economic reasons and criteria that lead to more energy dissipation. Generally, the scour dimensions decreased as sediment sizes and tail-water depth increased or particle's Froude number (Frd) and critical depth reduced. With the reduction of Frd, the relative scour depth, the relative distance of maximum scour depth and the relative scour length decreased by 68.6%, 75.6% and 73.4%, respectively. The empirical equations of regression analysis were developed to estimate the scour parameters.

The bed surface of alluvial rivers is rarely plane and takes different geometric configurations called bed forms. Bed forms are created by the movement of riverbed sediments, especially during floods. The interaction between the flow and bed form is very complex. The flow intensity controls bed forms, and the bed form significantly affects the properties of the flow (such as depth, velocity, and flow resistance). The Manning roughness coefficient is one of the most important flow resistance coefficients, which significantly affects the bed form shape and geometry. This study aimed to estimate the Manning roughness coefficient in rivers with bed forms, using soft computing models, including multilayer perceptron artificial neural network (MLPNN), group method of data handling (GMDH), support vector machine (SVM) model, and genetic programming model (GP). To this end, the energy grade line (Sf), flow Froude number (Fr), y/d50, ∆/d50, ∆\λ, and ∆/y were used as the input variables, and the Manning roughness coefficient was used as the output variable. The results showed that all the test models have acceptable accuracy, while the SVM model showed the highest level of accuracy with the coefficient of determination R2=0.99 in the verification stage. The sensitivity analysis of SVM and MLPNN models and the structural analysis of GMDH and GP models indicated that the most important parameters affecting the Manning roughness coefficient are Fr, Sf, ∆\λ.

Leakage in transmission pipelines and water distribution networks causes water and energy loss and reduces water quality. The accuracy of leakage detection using transient-based methods depends on several factors. This study investigated the sensitivity of location and size of leaks in simple polyethylene transmission pipelines to dynamic parameters, flow regime, sample size, spatial-step increment, and leak size and location. For this purpose, a hydraulic transient solver was first developed to take into account the dynamic effects of unsteady friction, viscoelasticity of the pipe wall, and the leak. The leakage was assumed to function with a quasi-normal distribution around its real location to reduce problem dimensionality and unnecessary computations. This approach was evaluated based on experimental transient data in which leaks were simulated in different sizes and locations. Results revealed that the hydraulic transient model that includes only viscoelasticity effects could pinpoint leakage characteristics. The sample size evaluation indicated that half and a single period of the pressure signal are sufficient to determine the leakage location and size in simple viscoelastic transmission pipelines, respectively. The optimal ratio of the spatial step to pipe length (Δx/L) was 0.025. HIGHLIGHTS Sensitivity analysis of leak detection and sizing in the viscoelastic pipeline.; Leakage simulation using a new approach with a quasi-normal distribution function.; Development of an experimental transient model to evaluate the proposed approach.

In this paper, the sequent depth ratio of a sill-controlled B-jump on sloping beds was investigated. Experiments were carried out to characterize the effect of the different design parameters such as the sill height, sill position relative to the jump toe, and chute slope on the sequent depth ratio under various up - and downstream hydraulic conditions. By applying the momentum conservation principle, a generalized relationship to estimate the sequent depth ratio was deduced. This analysis demonstrated that the sequent depth ratio depends on the upstream Froude number, the chute slope, the jump toe location on the chute, the sill height and its position, and the tail-water depth. Furthermore, the energy dissipation efficiency of a sill-controlled B-jump resulted greater than that for a free B-jump. Based on results of this investigation, the sill-controlled B-jump can be used as a novel alternative to the classical hydraulic jump to reduce cost where the length of the stilling basin must be shortened due to site restrictions and arrangement.

The effect of suspended sediment concentration on the characteristics of a hydraulic jump in a symmetrical trapezoidal channel was studied experimentally and compared with a classic jump. The first test series of the classical jump was performed in a rectangular flume, while the second series was conducted with two different trapezoidal side slopes. In both cases, the tests were conducted under clear water and with different concentrations (4, 8 and 12%) of fine sand of 0.22 mm as suspended sediment. The results of the tests showed that, with an increase in sediment concentration, the jump length ratio and the sequent depth ratio decreased and the energy dissipation increased. The present study considered three different sections (two sections of trapezoidal shape with side slopes of 60° and 75° and one rectangular section). A comparison of the results in flow with Fr1 = 10 for all three sections for a sediment concentration of 12% with clear water showed that the jump length ratio decreased by 14%, 22% and 18%, the sequent depth ratio decreased by 12%, 21% and 31% and the energy dissipation ratio increased by 9%, 12% and 11%, respectively. Some dimensionless relations for the prediction of jump characteristics were also developed.

Hydraulic jump is a phenomenon observed in open channel flow, and studying it has been a challenge for scientific communities. Most of the previous studies on this topic have been devoted to the cases of clear water in rectangular geometry. However, in nature river flows carry sediment loads; meanwhile, trapezoidal stilling basins are proved to be more economical as well. In this paper, the RNG turbulence model has been used to simulate jump characteristics in a symmetrical trapezoidal channel of 45° side slope for clear water flow and three different sediment concentrations of 4%, 8% and 12% and a range of initial Froude number between 1.5 and 12. The results indicate that by increasing the sediment concentration the bed shear stress amounts and energy loss ratio increase while the length of jump ratio decreases. In comparison with the clear water flow, for the case of Fr1 = 7 and sediment concentration of 12%, the length of jump ratio decreases by 18.1%, the sequent depth ratio increases by 17.2% and the energy loss ratio increases by 3.2%. Furthermore, the bed shear stress at the beginning and at the end of the jump is innovatively investigated. The results show that the shear stress at the initial depth section is not dependent on the sediment content, but at the secondary depth of flow, it is highly dependent on the suspended sediment loads content.

Controlling the bends migration in the large meandering rivers using common groins is too costly, time consuming and needs some types of river by passing. Developing deep scour around nose of groins can lead to failure of the structure. However, it is necessary to investigate the new measures and materials to have less scour and to easily be installed, respectively. The six-pillar concrete (SPC) element is one of the materials which have been used successfully in bridge scour control. By constructing rectangular vane with SPC elements (RV-SPC) can take advantage of both economy and scour mitigation. In the present experimental study, the application of new technique has been studied. Tests were carried out at 180° flume bend for high flow condition (Froude number = 0.263). Two series of tests were carried out: (1) the base line tests without installing RV-SPC and (2) with RV-SPC at various intervals (5L, 6L, 7L, 8L) with the effective length equal to 20% of flume width (L = 12 cm). By comparing the results of two series of tests, it was determined that by installing RV-SPC at interval of 6L from each other, the maximum scour depth around the structure is reduced up to 70.0%.

Previous research studies have shown that abutment scour makes a major contribution to bridge failures. Protecting bridges against scour is, therefore, a priority need. For existing bridges, armour...

River confluences have a complex flow and sedimentation pattern that have vital influences on the hydraulic and bed morphology of river reach and the surrounding area. Confluences can be observed in waterways with various situations such as live bed conditions. This condition is a hydro-morphological situation with a high densimetric Froude number, i.e., bed load transport is supplied from upstream. According to the literature review, most of the experimental studies investigate the flow pattern on the flatbed and not on the developed riverbed, or/and in the low densimetric Froude number, or/and without supplying the sediment from upstream. Therefore, in the present study for the quantification of the flow pattern under these conditions, each developed bed was fixed with the cement blanket method in the laboratory. Then, the 3D velocity was measured at specific points at the confluence. The current study was designed to understand the flow pattern corresponding to the river bed behavior in the case of large floods. It is expected that the morphological features downstream of the confluence have a different pattern than the ones in the condition described in other literature. Thus, this paper describes briefly what are the different bed features and investigates the corresponding flow pattern. The results of the flow pattern on the developed bed show that all zones at the river confluence can be observed except the point bar due to the approximate equality of the mean longitudinal velocity of the separation zone and the main channel upstream of the confluence. Moreover, results show that by increasing the bedload ratio (sediment discharge to water discharge of the main channel of upstream of the confluence) from 0 to 3 × 10−4, flow deflection to the outer bank of the channel decreased down to 45%, the stagnation equivalent area decreased down to 2.5 times, and bed shear stress decreased down to 40%. Hence, the momentum of lateral flow decreased with increasing bedload. Besides, the recovery zone occurred at a longer distance after the confluence compared to the case without bedload. Hence, the location of the maximum velocity zone, vortices, and secondary flows changed downstream of the confluence, by changing the bed load value.

River restoration aims to apply environmentally-friendly structures for bank protection in meandering rivers to restore their natural habitat. Enhanced Permeable Groin (EPG) is a novel river restoration technique that can improve the fish habitat environment in a river system by creating a series of eco-friendly scour pools. This study reports the results of two groups of 3D velocity measurements in a 180-degree channel bend in cases with and without an EPG for clear water conditions to characterize the mechanisms leading to the primary stages of the scouring phenomenon. The analysis revealed that the presence of an EPG amplified the velocity magnitude in the regions near the tip of the vane and increased its value in the middle of the channel 1.13 times the bend without the structure. In addition, the comparison showed that the EPG reduced the velocity magnitude in the recircu-lation zone by an average of 38%. Secondary currents including main and outer bank cells were observed in the case without the structure. The presence of the EPG in the flow field effectively increased the outer-bank cell strength by 11 times compared to that without the structure. The low-value contours of the bed shear stresses were observed in the zone downstream of the structure for a distance of 6 times the effective length of the structure. Based on the results of this study, the generation of a recirculation zone with low-velocity and shear stress values can provide suitable conditions for aquatic habitats, deep-bodied fish assemblages, aquatic vege-tation, shrub roots, and tree roots along the outer bank.

This experimental study investigated the physical model of a 180-degree river bend to introduce a new measure called as winged bandal-like (WBL) structure for river bed sediment management. The new structure is a combination of bandal-like (BL) and triangular vane structures. Nine different alternatives of the WBL structure, including three dimensionless vane effective lengths and three different vane angles, were tested in non-submerged and clear water conditions. A total of 18 attributes were then defined in accordance with the resulting river bed scouring and deposition. The multiple-attribute decision-making, simple additive weighting, and TOPSIS methods were employed to rank the alternatives. Baseline tests were also carried out for the BL and the impermeable spur dike (ISD) structures under similar flow conditions. Results revealed that the maximum scour depth, as the main cause of failure around the considered WBL structure, decreased by 31% compared to the scour around the ISD. The maximum deposition height behind the considered WBL structure showed an increase of 47% and 96% in comparison with ISD and BL structures, respectively. In the WBL structure, a longer, better-shaped sedimentary stack was developed along and close to the outer bank.

The bridge abutment is one of the main parts of a bridge and significantly contributes to bridge stability. This study experimentally investigated the effect of the unsteadiness characteristics of hydrographs on the scouring phenomenon around the bridge abutment under clear water conditions. The ability of the permeable and impermeable spur dikes and their distances from the abutment at its upstream on the control of scouring around the bridge abutment was also investigated. The experimental observations imply that the effect of unsteady flow on the scouring process is relatively similar to the steady flow conditions. The results showed that the base time of hydrographs, the type of spur dikes, and the distance of spur dikes from the bridge abutment were the dominant parameters among the considered parameters in this study on the scouring process around the abutment. The results also revealed that the impermeable spur dike was able to completely eliminate scouring around the bridge abutment for two distances of 2L and 3L (where L is the abutment length) for both steady and unsteady flow conditions.

Meandering river bend migration is a common phenomenon which destroys agricultural lands and civil infrastructures around the river. The main cause of such migration is due to developing a secondary flow within the bend in which a helicoidally circulation is developed and as a results the scour hole at the outer bank toe is created which causes collapse of the outer bank and its migration. Over the last decade many countermeasures against such scour have been developed. These measures modify the flow within the bend redistribute the local bed shear stress for the purpose of reducing the toe bank scour. Triangular vanes are one of such structures that help stabilize the outer bank by modifying the flow pattern in the river bend to prevent the scouring of the outer bank. Triangular vanes have been studied successfully by Bhuiyan et al. (2010) in a sinuosity river path and in a 90 degree flume bend by Bahrami-Yarahmadi and Shafai Bejestan (2016). Based on these studies this measure, if designed properly, not only can shift the scour from the outer bank toe to the middle of the river, it transport sediment to the downstream of the vane and deposited in between the vanes which create a new bank. The structure has been defined environment friendly since it create an environment suitable for aquatic animals. The aim of the present study is to investigate the application of triangular vanes in a 180 degrees of Jangiyeh bend in Karoon River south of Ahvaz and to determine the bets distance for installing the vanes.

Extending the dimensions of the scour hole in the riverbank near the outer bank of meandering river which usually developed in the flat area can cause river bank failure and thus extensive damage to the surrounding area. In this study, the permeable triangular vanes (PTVs) made by six-pillar elements were implemented to evaluate the scour and sediment deposition in a 180° flume bend. Vanes with three different effective lengths were attached to the outer bank with space equal to five times the effective length and angle of 60° to the upstream. Three different effective lengths were tested under two different hydraulic conditions with the Froude numbers = 0.227 and 0.261. At the end of each experiment, the flume bed topography with laser meter was measured. To better compare the effect of vanes on the pattern of sediment distribution, two control experiments without the presence of vanes were also performed under the defined hydraulic conditions. The results showed that the permeable triangular vanes with the ratio of the effective length of vane (L) to the flume width (B) equal to 0.20 reduced the maximum scour hole and shift the scour from the outer bank to the nose of the vanes. For this case, the maximum depths of the scour were measured to be 19% and 45% of the flow depth and occurred at the nose of the fifth vane (at 66.75° location) at Froude numbers of 0.227 and 0.261, respectively. Moreover, the maximum height of the point bar above the bed on the outer bank was found to be equal to 30% and 31% of the flow depth at Froude numbers = 0.227 and 0.261, respectively. The results of this study improved previous studies conducted in the 90° bend and can be used as a guide for design purposes as an environmentally friendly countermeasure against bank scour in the bend of meandering rivers with gentle slope.

The enhanced permeable groin is a novel eco-friendly and cost-effective technique for bank protection and restoration of meander bends. The behavior of bed deformations due to the distance between the structures has to be studied to design enhanced permeable groins in series properly. In this study, scour morphologies around enhanced permeable groins in series, characterized by four different distances and located in a 180&deg, mild flume bend, for clear water conditions were investigated. The analysis indicated that scour geometrical patterns such as the maximum scour depth nearby the structures and the maximum deposition height between them are strongly affected by the distance between the groins. The results revealed that the maximum scour depth around the structures increases with the distance between structures, the scour holes develop towards the outer bank and create a series of pools that can lead to the bank collapse. All experiments, carried out with different structure distances, demonstrated that the location of thalweg effectively shifted towards the middle of the channel and near the inner bank for high and low particle Froude numbers, respectively. As a general result, a distance between enhanced permeable groins equal to four times the effective length of the structure is recommended for a 180&deg, mild flume bend for the investigated particle Froude numbers. Finally, a general design guideline is presented to a proper design of enhanced permeable groins in series.

The Nowshahr port in the southern coastlines of the Caspian Sea is among the oldest northern ports of Iran, first commissioned in the year 1939. In recent years, this port has been faced with severe sedimentation issues in and around its entrance that has had negative impacts on the operability of the port. The present study aims at identifying major reasons for severe sedimentation in the port entrance. First, field measurements were evaluated to gain an in-depth view of the hydrodynamics of the study area. Numerical models then were calibrated and validated against existing field measurements. Results of numerical modeling indicated that wind-induced current is dominant in the Caspian Sea. The numerical results also indicated that in the case of an eastward current direction, the interaction between current and the western breakwater arm would lead to the formation of a separation zone and a recirculation zone to the east of the port entrance region. This eddying circulation could transport suspend settled sediments from eastern shoreline towards the port entrance and its access channel. The results of this paper are mostly based on the study of current patterns around the port in the storm conditions incorporate with the identification of sediment sources.

A block ramp is an environmentally friendly stream restoration structure consisting of a base material of stone with minimal negative environmental impact. This not only decreases riverbed ...

River outer bank erosion and associated inner bank sedimentation cause river morphological and environmental changes. Triangular vanes are eco-friendly structures used for protection of river bank from erosion and morphological changes, fish passage improvement, and also fish habitat enhancement. In the present study, the 3D velocity components at a mild 90-degree channel bend were measured via an electromagnetic velocity meter with and without installed triangular vane. These tests were conducted at a Froude number of Fr = 0.214. The analysis of data showed that the triangular vane decreased the bed shear stress near the outer bank at the upstream and downstream sections of the vane for a distance of about 11 times the effective length of the vane. The maximum reduction at the upstream and downstream of the structure was calculated to be 67% and 80%, respectively. The strength of the vane-induced secondary flow was greater than that of the bend-induced secondary flow. At the position of 0.8L in the structure's downstream, the strength of the vane-induced secondary flow was maximum, after which started reducing and reached the strength of the bend-induced secondary flow at the position of 7L in the structure's downstream.

Rock chutes are widely used to control erosion of river beds because of their high energy loss, low environmental impact, simple construction and low cost. They typically include a negatively sloped stilling basin, which leads to formation of a little-understood ‘B-F’ hydraulic jump. This has its toe located on the upstream positive slope of the chute and its roller length ending on the downstream negative slope of the stilling basin. In this study, a general equation for computing the sequent depth ratio of a B-F jump was developed using Buckingham dimensional analysis and the incomplete self-similarity theorem. A new non-dimensional parameter, E0, including the effects of the jump toe and the location of the end of the roller length, was introduced. Laboratory experiments of B-F hydraulic jumps were conducted for a wide range of upstream Froude numbers, relative bed roughness, three different upstream channel slopes and three different negative downstream channel slopes. The sequent depth ratio on rough rocky beds was found to be considerably smaller than those on a smooth concrete bed. Two new prediction equations, for smooth and rough bed slopes, are presented and the results show that the predictions agree reasonably well with the experimental data.

River confluences (RCs) are important features within river systems where the three dimensional (3D) flow structures and the downstream mixing of flows can cause deep scour holes. Despite this, few methods have been proposed to control scouring at RCs. In this study, application of a collar was experimentally examined for local scour control at the point where two rivers flow together. In particular, experimental tests were done with and without collar application at three different locations. The results reveal that the scour depth is directly proportional to the discharge ratio, i.e. the ratio of lateral discharge to that in the channel downstream of the confluence, and the densimetric Froude number (Frg). In addition, installation of a collar at RCs can decrease the scour depth up to 100%, thus completely avoiding the scour process. The results also show that by increasing the Frg the optimal installation location for a collar changes and moves towards the river bed level. Using a collar can also reduce the height of the point bar formed downstream of the confluence. The outcomes of the study allow derivation of an equation for predicting scour depth when a collar is applied as a countermeasure. The analysis of this equation shows that the estimates are mostly affected by the Frg.

River restoration refers to the environmental and ecological aspect of river engineering and aims to improve the natural habitat of a river system using eco-friendly methods. This paper introduces a new river restoration technique for bank protection and restoration of meander bends by combining a permeable groin with a triangular vane. Nine different combinations of permeable groins with triangular vane including three different effective lengths and three angles of vane were investigated in a 180 degrees mild laboratory flume bend in clear water conditions. Based on experimental tests, scour geometrical patterns were analyzed, classified, and compared with each other. This analysis showed that a triangular vane dramatically enhances the performance of the permeable groin to protect the outer bank from erosion. Then, using Buckingham's theorem of the dimensional analysis and the incomplete self-similarity (ISS) condition, generalized functional relationships for estimating scour main characteristics around an enhanced permeable groin (EPG) were deduced. This analysis showed that scour patterns depend on the upstream densimetric particle Froude number (A50) and the ratio between the effective lengths of the triangular vane and the permeable groin (Lt/Lp). The results showed that scour geometric characteristics estimated by the proposed equations agree reasonably well with the experimental values.

Triangular vanes are hydraulic structures used for bank protection and habitat restoration for fish and other aquatic organisms. There are limitations on the design criteria for this newly-introduced structure; therefore, the main goal of this paper is to present test results carried out on different alternatives of multiple vanes with different spaces between the vanes under different hydraulic conditions in a 90-degree mild flume bend. In addition, 3D components of flow velocity were measured in tests with and without an installed single vane. The triangular vanes create a counterclockwise secondary flow cell near the outer bank, which counteracts the clockwise main secondary flow cell in the bend for a distance of about 5le (le is the vane's effective length) downstream of the vane's position. With multiple vanes in place, the thalweg was found to be shifted toward the flume midway from the outer bank. Moreover, by increasing the space between the triangular vanes, the scour around the vane's tip and its development to the outer bank increased. Therefore, it is concluded that triangular vanes perform best when they are spaced at 5le or less.

Triangular weirs (Triangular vanes) and footing are measures which causes to control the scour in outer bend and keep out scouring hole from the outer bend. In this study, the main purpose is to experimentally study the effect of using both footing and triangular weirs on sedimentation and erosion of a bed of flume bend under different flow conditions (Froude numbers 0.243, 0.262, 0.292 and 0.321). Tests were conducted using triangular weirs with distance of 8 times of the effective length installed at an angle of 30 degree from the upstream bank. Footing width and effective length of triangular weirs were selected one-fifth the width of the canal. The results showed that using footing combined with the triangular weirs caused to reduce maximum scour depth at the toe of weirs and prevent from its extension to outer bend. Using footing reduced 70 percent maximum scour depth at the toe of weirs. Moreover using footing combined with triangular weirs had a little effect on flow diversion from outer bank towards the center of flume. The results show that using footing along with triangular weirs increased 9 percent maximum scour depth of thalweg and did not change the thalweg distance from the outer bank.

Over the past few decades, the cause of many bridge failures has been reported to be abutment scour. A large number of studies have been conducted to develop countermeasures to ensure the safety of existing bridges. A submerged vane is a measure that has recently been studied and found to be a promising scour mitigation technique for river bank erosion. Therefore, the main purpose of this study was to evaluate the performance of a submerged vane in the case of abutments. Several tests were conducted with and without vanes. Different vane positions and angles were examined. A single vane attached to the upstream nose of an abutment was found to be the most effective at decreasing, shifting, and warding off a scour hole. The results showed that the most appropriate vane angle was 40°. The efficiency of the new measure could reach 95% under some flow conditions.

A common and practical type of hydraulic jump at sloping bed (e.g., concrete, gabion or rock cover bed chutes) is B-jump which its toe located on the sloping bed and ended at the downstream horizontal channel. Determination of hydraulic jump characteristics such as the sequent depth ratio can help to design a safe and economic stilling basin. Many studies have been carried out for B-jump on smooth sloping bed; however on the effect of roughness on jump characteristics no relation is available. In this paper first a general non-dimensional relation was developed using Buckingham theorem. Then by applying the incomplete self similarity theory and using a new dimensionless parameter, N, a new non dimensional relation was developed. The significant of such relation is that it is independent of bed slope. To verified such relation two series of tests were conducted at the hydraulic lab using three different slope angles, five different roughness heights and five different flow conditions both on smooth and roughened bed. The collected data were analyzed by SPSS15.0 software and the required coefficients were obtained. The proposed expression was tested using wide range of data and the average absolute error was found to be 6.4%.

In gravel bed rivers, the flow resistance is mostly due to grain roughness. Strickler was the first who determined the grain roughness coefficient in terms of sediment particle size. In the so called Strickler’s formula, the Manning’s coefficient has been related to only the median particle size ( 6 / 1 S cD n = ). Therefore it is the purpose of this study to conduct experimental test to find out if the same sediment size but in different shapes, can produce different flow resistance and if so by how much. To reach such goals four different sizes of round sediment particles taken from natural river bed and four crushed sediment particles with the same sizes as river bed sediment were tested under constant flow conditions. The experimental tests were conducted in a 12 meter long flume of 25 centimeter wide. The energy gradient between the upstream and downstream stations was calculated by Bernoulli’s equation. Then the roughness coefficient was computed using the Manning’s formula. Comparison of the data shows that the particle shape can affect the particle roughness. The results also have been compared with the Strickler’s type of equation and the best relations have been developed. Introduction In many river engineering activity determination of river flow characteristics is the first step which usually is done by solving the governing equations of the flow which is known as Saint ve Nant equations. In solving these set of two equations, the energy gradient should be known which is calculated from one the flow resistance equations such as Manning’ formula (Eq.1): 2 1 3 2 1 f S R n V = (1) Where V is the flow velocity, R is hydraulic radius of river, Sf is the energy grade line and n is the Manning’s coefficient. During past decades many researchers have been trying to present criteria for predicting the n values. Any parameter which causes 1585 World Environmental and Water Resources Congress 2012: Crossing Boundaries © ASCE 2012