1,721,425 research outputs found
Flow resistance law under equilibrium bed-load transport conditions
No full textThe uniform flow resistance equation, in the form due to Manning or Darcy-Weisbach, is often applied to determine the stage-discharge relationship of a river cross-section. The application of this equation, namely the slope-area method, allows to indirectly measure by water level readings the corresponding river discharge. In this paper, a recently deduced flow resistance equation for open channel flow was tested during conditions of equilibrium bed-load transport. First the flow resistance equation was determined by dimensional analysis and applying the condition of incomplete self-similarity for the flow velocity profile. Then the analysis was developed by the following steps: (i) the flow resistance equation was calibrated by available laboratory measurements of flow velocity, water depth and bed slope carried out in 143 flume experimental runs during conditions of equilibrium bed-load transport; (ii) a relationship (Eq. (33)) between the Γ function of the velocity profile, the channel slope, the Shields number and the Froude number was established by the available measurements; (iii) the relationship for estimating the Γ function (Eq. (33)) and the theoretical flow resistance equation were tested by 127 independent flume measurements carried out for flows with bedload transport (iv) Eq. (33) and the flow resistance law were tested by field measurements carried out in 104 reaches of some Calabrian gravel bed rivers; and (v), finally, the relationship for estimating the Γ function was recalibrated (Eq. (34)) using all laboratory measurements (270 experimental runs). The proposed theoretical resistance law, calibrated by the measurements of Recking et al. (2008), allowed an estimate of the Darcy-Weisbach friction factor which is more accurate than that obtained by the original approach of Recking et al. The theoretical flow resistance law (Eq. (28)) coupled with the relationship for estimating the Γ function (Eq. (34)), which is characterized by the applicability of a wide range of flow conditions, allowed to estimate the Darcy-Weisbach friction factor for flows with and without bed-load
Testing the stage-discharge relationship of a sharp crested sluice gate deduced by the momentum equation for a free-flow condition
No full textIn this paper the stage-discharge relationship of a sharp crested sluice gate is deduced by applying the momentum equation for a free flow condition. The theoretically deduced stage-discharge formula was then calibrated using experimental flume data obtained in previous investigations carried out for a free-flow condition. The deduced stage–discharge relationship is characterized by a momentum coefficient which is empirically estimated by the ratio between the height of the orifice and the water depth in the section upstream the gate. The relative errors are always less than or equal to - 10% to +10% and 71.4% of the errors are less than or equal to ± 2%
New stage-discharge relationship for inclined non-rectangular weirs
No full textIn this paper, the outflow process of inclined non-rectangular weirs is studied applying the dimensional analysis and the incomplete self-similarity theory. At first, a new stage-discharge equation, applicable for the non-rectangular weirs having a different geometrical shape (parabolic, semicircular, inverted semicircular), is theoretically deduced using a characteristic width. Then, this power stage-discharge relationship (Eq. (17)) is calibrated and tested using measurements carried out by Raiknar for parabolic, semicircular and inverted semicircular weirs having different inclination respect to the vertical (10° 20° 30° 40° and 45°). For each geometrical shape, the analysis showed that the exponent of the power stage-discharge relationship is quasi constant while its coefficient is related to the weir inclination. Finally, the accuracy of the stage-discharge relationship was improved taking into account the effect of the weir inclination angle. The proposed stage-discharge equations (Eqs. (20)–(22)) allow to calculate discharge values which are characterized by an estimate accuracy always greater than that of the corresponding values calculated by relationships proposed by Raiknar
Comments on “Measurement of dimensionless Chezy coefficient in step-pool reach (Case study of Dizin River in Iran)” by Torabizadeh A., Tahershamsi A., Tabatabai M.R.M
No full textThis paper is a comment on a previous published paper
Assessing flow resistance in gravel bed channels by dimensional analysis and self-similarity
No full textIn this paper a new flow resistance equation for open channel flow, based on the integration of a power velocity profile, was tested for gravel bed channels. First this flow resistance equation, theoretically deduced by dimensional analysis and incomplete self-similarity condition, was reported. Then a relationship between the Γ function of the velocity profile, the channel slope and the Froude number was calibrated by the available laboratory measurements of flow velocity, water depth and bed slope carried out in 416 flume experimental runs with a gravel bed. Then the relationship for estimating Γ function and the theoretical resistance equation was tested by 83 independent flume measurements. The analysis also showed that the proposed flow resistance equation allows an estimate of the Darcy-Weisbach friction factor which is more reliable and accurate than that obtained by a semi-logarithmic flow resistance law or a variable-power resistance equation, calibrated with the same gravel bed measurements. For testing the applicability of the proposed Γ function (Eq. (17)), whose coefficients were estimated by flume measurements, available fields measurements were used. The analysis demonstrated that a scale factor (equal to 0.7611) is necessary to convert Γ values obtained by flume measurements into those corresponding to gravel bed rivers. The similitude between flow resistance in a gravel bed flume and in a gravel bed river is governed by the Γ function and a scale factor, equal to 1.6, is required to upscale the Darcy-Weisbach friction factor values obtained by flume measurements to the river case. In conclusion, the analysis showed that the Darcy-Weisbach friction factor for gravel bed channels can be accurately estimated by the proposed theoretical approach based on a power-velocity profile
Discussion of “Three Simple Flumes for Flow Measurement in Open Channels” by Zohrab Samani
No full textIn this paper the results on three simple flumes for flow measurements are discussed
Modelling sediment delivery using connectivity components at the experimental SPA2 basin, Sicily (Italy)
No full textSediment delivery ratio can be used as a measure of sediment connectivity and it can be linked to the structural connectivity (morphological unit, slope length, slope steepness, travel time) of a basin and to the functional connectivity (rainfall-runoff processes at morphological unit scale). In this paper the sediment connectivity approach was applied at basin scale both using Sediment Delivery Distributed (SEDD) model, which takes into account the hillslope sediment transport, and sediment yield measurements carried out at SPA2 experimental basin (Sicily, Italy). The expression of the sediment delivery ratio SDRi of a morphological unit was modified for highlighting two components corresponding to the structural (SDRF,i) and functional (SDRF,i) sediment connectivity, respectively. For SPA2 basin the frequency distribution of the travel time of each morphological unit was used to estimate the coefficient βL of the structural component of the sediment delivery ratio of each morphological unit. Then, using the sediment yield measurements carried out at the outlet of the experimental SPA2 basin in the period April 2000-March 2015, the SEDD model was calibrated at event scale for estimating the coefficient βF of the functional component of the sediment delivery ratio. At event scale the developed analysis stated that the functional connectivity is dependent on the magnitude of erosion events. Intermediate and high events, which were characterized by the lowest values of the functional coefficient, determine a more high functional connectivity and are characterized by a more efficient sediment transport along the hillslopes. Finally, at annual scale, the model was calibrated for the period 2000–2015 and relationships for estimating the coefficient βF,a of the functional component of the sediment delivery ratio taking into account the intensity of erosion events occurring in each year were determined. At annual scale, the analysis demonstrated that the functional coefficient was always greater than the landscape coefficient and the sediment connectivity was always controlled by the low values of the functional component
Measuring the USLE soil erodibility factor in the unit plots of Sparacia (southern Italy) experimental area
No full textThe Universal Soil Loss Equation (USLE) is still widely used to predict soil loss by water erosion and to establish soil conservation measures. In this model, the soil erodibility factor K accounts for the susceptibility of the soil to be eroded due to the detachment and transport processes operated by the erosive agents. According to the USLE scheme, the K factor should be measured on unit plots, i.e., bare plots of given length (22 m) and steepness (9%) tilled along the maximum slope direction, but there is little evidence that there ever existed an actual unit plot between the plots used to develop the USLE. Given the difficulty in collecting sufficient
data to adequately measure K, the nomograph method was early developed to allow estimation of K based on standard soil properties. First, in this investigation the soil erodibility factor was experimentally determined for the clay soil of the Sparacia
(Sicily) experimental station, based on the available measurements collected in two unit plots. Although a limited database was available for this analysis, a very low value (0.0038 t ha h ha-1 MJ-1 mm-1) was determined, which was an order of magnitude lower than the nomograph value. Then, the values of the plot steepness factor S were determined using soil loss measurements collected on plots varying in steepness from 9 to 26% and resulted higher than the estimated values by a well-known literature expression. Finally, the plot length factor L resulted independent of the plot length and equal to one. The former result was explained by the different flow transport capacity in the unit plot and plot with increased steepness, while the result of a constant length factor was supported by other experimental investigations
Rainfall Erosivity Estimators for Application in Burundi
Full text linkIn this paper, following the results of previous studies and using the monthly rainfall data of 13 sites in Burundi, a comparison between two different estimators (modified Fournier index MFI and FF index) of the rainfall erosivity factor of the Universal Soil Loss Equation (USLE) was firstly developed. The theoretical relationships between MFI and the mean annual rainfall P and between FF and P were tested by the available rainfall data. The constants Km and K, linking MFI and FF with P, were used to assess hydrological similitude with other geographical regions. Then, in order to predict the erosion risk corresponding to a climatic condition of given return period, the applicability of the Extreme Value Type 1 (EV1) probability distribution to the annual values of the Fa,j index was tested by an at-site analysis. Finally, the descriptive ability of the EV1 distribution was investigated by a regional procedure
Experimental study and numerical simulation of inclined rectangular weirs
No full textInclined rectangular weirs, also named pivot weirs, are used both to adjust the upstream water level and to increase the flow capacity compared with that of normal rectangular weirs. However, the experimental studies available in the literature present contradictory conclusions for the inclined weir discharge capacity. In this paper, new experimental runs and numerical simulations were performed to investigate the effect of the rectangular weir inclination angle on the stage-discharge formula. The experiments were carried out using inclination angles ranging from 30° to 90°. Buckingham's theorem of dimensional analysis was used to obtain an equation for the flow magnification ratio (the discharge through the pivot weir divided by the corresponding discharge over the vertical weir) as a function of theweir inclination angle. The experimental observations revealed that the flow magnification ratio increases with the inclination angle to a maximum of 1.082 for 30° of inclination. Bidimensional (2D) numerical analysis using theOpenFOAMcomputational fluid dynamic toolbox was also used. The flow magnification ratios obtained numerically confirmed those obtained experimentally
- …
