Physical modelling of energy losses at surcharged three-way junction manholes in drainage system

Motivated by the observation that vortex flow structure was evident in the energy loss at the surcharged junction manhole due to changes of hydraulic and geometrical parameters, a physical model was used to calculate energy loss coefficients and investigate the relationship between flow structure and energy loss at the surcharged three-way junction manhole. The effects of the flow discharge ratio, the connected angle between two inflow pipes, the manhole geometry, and the downstream water depth on the energy loss were analyzed based on the quantified energy loss coefficients and the identified flow structure. Moreover, two empirical formulae for head loss coefficients were validated by the experimental data. Results indicate that the effect of flow discharge ratio and connected angle are significant, while the effect of downstream water depth is not obvious. With the increase of the lateral inflow discharge, the flow velocity distribution and vortex structure are both enhanced. It is also found that a circular manhole can reduce local energy loss when compared to a square manhole. In addition, the tested empirical formulae can reproduce the trend of total head loss coefficient.

Experimental Investigation of 900 Intake Flow Patterns with and without Submerged Vanes under Sediment Feeding Conditions

In this study, two experiments were conducted in a 90⁰ water intake to study 3D flow patterns and sediment distribution using submerged vanes under sediment feeding and live-bed conditions. One column three vanes were installed at a 20⁰ angle maintaining for a water discharge ratio of q_r ~ 0.1. Three-dimensional mean and turbulent velocity components of flow in 90⁰ channel intake were measured by Acoustic Doppler Velocimetry (ADV). Flow characteristics of the intake structure area with no vanes are compared with those condition. Results showed that three vanes with single column reduced the amount of sediment by 20% in the intake diversion. In the downstream corner of the intake, high velocities were measured where scouring occurred. The vanes affected the intensity of secondary flow, turbulence energy, flow separation, and moved sediment deposition downstream of the main channel.

Effect of Coagulants Variations in the Coagulation Unit on the Efficiency of Raw Water Turbidity Removal Sedimentation Unit Continuous Discharges Flow (CDF) as a New Method

Variations in the type of coagulant resulted in different floc characteristics. The sedimentation unit with continuous discharges flow or (CDF) method is a sedimentation unit that applies the leaking tank phenomenon, so it is possible that it will affect the condition of the floc that has been formed and in the end can affect the efficiency of turbidity removal. This study was to determine the effect of the type of coagulant in the coagulation unit on the removal of raw water turbidity in the sedimentation unit using the CDF method with a 6% discharge ratio to the product discharge. The raw water used is Sungai Batang Kuranji water with a turbidity of 27.63 NTU. The experimental reactor consisted of a coagulation-flocculation unit and a sedimentation unit with various coagulants being Poly Aluminum Chloride (PAC), Ferric Chloride, and Alum. The results showed that the efficiency of removing turbidity from the Sungai Batang Kuranji by PAC coagulant was 90.12%, Ferric Chloride 86.99%, and Alum 81.72%. The Spearman correlation value of the coagulant variable on the efficiency of the removal of turbidity is 0.948, indicating a unidirectional effect between the two variables. The addition of 6% CDF flow in the settling zone did not break the floc because the flow formed was still laminar.

An Experimental Study on the Influence of Drastically Varying Discharge Ratios on Bed Topography and Flow Structure at Urban Channel Confluences

The confluences of rivers are important nodes for energy conversion and material transport in the river network. A slight morphological alteration of the confluences may trigger the “butterfly effect”, which will bring about changes in the ecology and environment of the entire river network. During the transition period of the wet and dry seasons, the variation of discharge ratio will make the originally balanced river bed change again, which will bring a series of follow-up effects. This research mainly studied the features of water flow itself and results showed that the variation of discharge ratio caused secondary erosion of the balanced bed surface and transported the sediment downstream. Thus, the zone of maximum velocity was enlarged and the maximum flow velocity at the equal discharge was reduced, and more intense vortex and turbulence were generated. The lateral velocity, vertical velocity, and turbulent structure were mainly controlled by the quantity and ratio of the discharge, and the varying topography only played a minor role in local areas. Nowadays, some scholars have been studying the combination of flow field features and various environmental substances and biological habitats, and the basic work done in this article has laid the foundation for these studies.

Assessment of Treated Wastewater Reuse in Drip Irrigation under Different Pressure Conditions

This study aims to investigate the influence of treated wastewater (TWW) on the hydraulic performance of drip irrigation emitters. A field experiment was conducted in order to test two types of online emitters, a low pressure (LP) and a standard pressure (SP), at different working pressures (0.25 bar, 0.50 bar, and 1.00 bar) using TWW. The emitters were initially evaluated in the laboratory and the field for the discharge exponent (X), discharge coefficient (Kd), average emitter discharge (Qavg), coefficient of variation (CV), distribution uniformity (DU), the mean discharge ratio (Dra), and the main degree of clogging (DC). The main effect of the emitters on the hydraulic parameters of irrigation performance was not significant, while the operational pressure and operational time of irrigation had a significant effect. For the LP emitter, the average emitter discharge was 7.6, 7.7, and 7.8 Lh−1 at 0.25, 0.50, and 1.00 bar, respectively. For the SP emitter, the average emitter discharge was 7.6, 7.8, and 7.8 Lh−1 at 0.25, 0.50, and 1.00 bar, respectively. The EU values for the LP and SP emitters varied from low to moderate at 0.25 bar, as the EU values at 0.50 and 1.00 bar were considered high for both emitter types.

Effect of a Submerged Vane-Field on the Flow Pattern of a Movable Bed Channel with a 90° Lateral Diversion

This laboratory study focused on the effect of a submerged vane-field on the flow pattern and bed morphology near and inside the entrance reach of a movable bed 90° lateral diversion. The system was modelled under live bed conditions for a water discharge ratio of ≈0.2. Two experiments were run until bed equilibrium was reached: with and without a vane-field installed close to the diversion entrance to control the transfer of sediments into the diversion channel. The equilibrium bed morphology and the associated 3D flow field were measured in great detail. The bed load diverted into the diversion was reduced by approximately one quarter due to the action of the vane-field. The vanes prevented the formation of the diversion vortex in the main channel, upstream of the diversion’s entrance, thus contributing to that decrease. They also created a main channel vortex that started at the most upstream vanes and further decreased the amount of bed load entering the diversion. The flow separation zone inside the diversion was larger with vanes, but conveyance was balanced through a slightly deeper scour trench therein. The flow structures described were confirmed through the measurements of the turbulent kinetic energy.

A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions

A rapid downstream weakening of the processes that drive the intensity of transverse mixing at the confluence of large rivers has been identified in the literature and attributed to the progressive reduction in channel scale secondary circulation and shear-driven mixing with distance downstream from the junction. These processes are investigated in this paper using a three-dimensional computation of the Reynolds averaged Navier Stokes equations combined with a Reynolds stress turbulence model for the confluence of the Kama and Vishera rivers in the Russian Urals. Simulations were carried out for three different configurations: an idealized planform with a rectangular cross-section (R), the natural planform with a rectangular cross-section (P), and the natural planform with the measured bathymetry (N), each one for three different discharge ratios. Results show that in the idealized configuration (R), the initial vortices that form due to channel-scale pressure gradients decline rapidly with distance downstream. Mixing is slow and incomplete at more than 10 multiples of channel width downstream from the junction corner. However, when the natural planform and bathymetry are introduced (N), rates of mixing increase dramatically at the junction corner and are maintained with distance downstream. Comparison with the P case suggests that it is the bathymetry that drives the most rapid mixing and notably when the discharge ratio is such that a single channel-scale vortex develops aided by curvature in the post junction channel. This effect is strongest when the discharge of the tributary that has the same direction of curvature as the post junction channel is greatest. A comprehensive set of field data are required to test this conclusion. If it holds, theoretical models of mixing processes in rivers will need to take into account the effects of bathymetry upon the interaction between river discharge ratio, secondary circulation development, and mixing rates.

Scour depth in confluences considering tributary flow, bank slope, and post-confluence conditions

In this paper, scouring in confluences was experimentally studied considering the effects of bank slope angle (θ) of the main channel, discharge ratio (Qr) of tributary channel and densimetric Froude number (Frg3) of the post-confluence channel. The experiments were conducted using a constant confluence angle (α) equal to 90° and various bank slope angles of 45°, 60°, 75° and 90°. Applying different Qr and Frg3, the maximum effect of θ on scour depth was observed when the minor Qr was used in the tributary channel. The mildest bank slope angle caused the minimum scour depth for any given Frg3. Generally, the experiment using θ = 45° and Qr = 0.194 showed the best performance and reduced the maximum scour depth by 46%. Considering two obtained empirical relationships, it was concluded that the effect of θ on the height of the point bar is more than its effect on the scour depth. Finally, Frg3 and θ demonstrated their greatest influences on dimensionless scour depth (dse/y3) and dimensionless height of point bar (Hse/B3), respectively.

Eccentricity forcing of Saharan climate drives fluvial strath terrace formation in the High Atlas

<p>River strath terraces reflect changes in lateral and vertical erosion rates within mountain valleys related to changes in the sediment to water discharge ratio. In contrast to the formation of terraces in high latitude glaciated catchments, little is known about the timing and mechanisms of river valley aggradation and incision in response to climate in low latitude, non-glaciated arid regions. To investigate the timing of river strath terrace formation in North-West Africa, we developed and applied a new approach to OSL dose rate correction of gravels. We sampled terraces in the M’Goun catchment crossing the thrust front and a thrust-sheet-top basin of the south-central High Atlas in Morocco, totalling 23 dated samples. Strath surfaces are elevated 10 to 40 m above the modern river plain, depending on local valley and bedrock configuration, and are overlain by 2 to 10 m of fluvial conglomerates. Burial ages of conglomerates in the first strath terrace level span from 180 to 60 ka, with widespread abandonment and incision post 60 ka throughout the catchment. This timing coincides with an eccentricity-driven decrease in African summer insolation and a decrease in the fluvial signature of Saharan dust recorded in an offshore Atlantic sediment core. We propose enhanced precipitation from the African summer monsoon during high insolation periods led to increased sediment yield and aggradation in the southern High Atlas, whilst low insolation and dry periods led to sediment-starved incision. To our knowledge, the M’Goun river terrace record is the most detailed record of long-term landscape evolution in response to climate fluctuations in northwest Africa to date.</p>