Afflux is an increase in water level that can occur upstream of a structure, such as a bridge or culvert, that creates an obstruction in the flow. Afflux is shown as the maximum increase of water level above normal depth in the undisturbed stream.
What is afflux in bridge?
Afflux is defined as the increase in upstream water depth as a result of constriction of a flow channel. Prior to the. placement of a bridge across a watercourse, the water surface for a given flood discharge may be assumed a normal. profile.
What is afflux map?
“afflux refers to the predicted change, usually in flood levels, between two scenarios. It is frequently used as a measure of the change in flood levels between an existing scenario and a proposed scenario.” TUFLOW Manual, 2019. Afflux in motion developed in OpenFOAM a free CFD Modelling program, shown below.
How is afflux caused?
It is caused by energy losses at high flows through bridges and culverts, and it is made worse by blockage. Afflux can be physically significant in terms of flood levels and leads to a potential for increased losses due to blockage.
How do you find afflux?
Cd and Co values are given in the IRC code, h*1 = afflux = (Du-Dd). Du and Dd are the upstream and downstream depths measured from the lowest bed level under the bridge taken as datum.
What is back water curve?
Afflux : It is defined as maximum increase in water level due to obstruction in the path of flow of water. The profile of rising water on the upstream side of dame is called as back water curve.
How does afflux influence the design?
The area of submergence and the design of guide banks depend on the afflux. If afflux is large, from weir formula, the length of the weir will be small for a given design discharge and, in turn, the discharge intensity (q) over the crest will increase.
What is economical span?
When the total cost of the sub structure equals the total cost of super structure, that span is considered as economical span. The design has been performed for a number of spans, that is from 10m to 40 m with 5m interval.
What is a scour critical bridge?
A scour critical bridge is one with abutment or pier foundations which are rated as unstable due to (1) observed scour at the bridge site or (2) a scour potential as determined from a scour evaluation study. 9 – Bridge foundations (including piles) on dry land well above flood water elevations.
What is scour depth?
Abutment scour occurs near the abutment, because the water must accelerate around the abutment. Note that, at the pier, the total scour depth is the sum of the pier scour and the contraction scour, whereas at the abutment, the total scour depth is the abutment scour depth.
Why is hydraulic jump important?
Hydraulic jumps are an important natural phenomenon with many engineering applications. Hydraulic jumps are often engineered into hydraulic systems to dissipate fluid mechanical energy into heat. This reduces the potential for damage by high velocity liquid jetting from spillways.
Is used for single span of 3m or double span of 6m?
Box culvert is usually constructed of precast RCC slabs. Box culverts are mainly constructed where the soil is soft and the load has to be distributed over a wider foundation area. This type of culvert can be conventionally used for a single span of 3 m or for double span of 6 m.
What is retrogression in Weir?
Retrogression: It is a temporary phenomenon which occurs after the construction of barrage in the river flowing through alluvial soil. As a result of backwater effect and increase in the depth, the velocity of water decreases resulting in deposition of sedimentation load.
How is scour depth calculated?
Scour depth should be less than or equal to 2.4 times the pier width if Froude number is less than 0.8. Scour depth should be less than or equal to 3.0 times the pier width if Froude number is greater than 0.8. Note: If K4 is not 1.0, K4 = 0.4 (VR)0.15. From HEC-18 Equation 6.5.
What is freeboard in bridge?
Freeboard at a bridge is the minimum clearance between the bottom of the girders and the design highwater or ice elevation. Recent practice has accounted for potential to optimize a bridge opening by considering a range of freeboard amounts and selecting the optimal value.
What is waterway in bridge?
35) LINEAR WATERWAY : The linear waterway of a bridge shall be the length available in the bridge between extreme edge of a water surface at the highest flood level, measured at right angles to the abutment faces.
What is clearance in bridge?
Clearance of bridge span is generally measured from the water surface (or ground, if there is no water) to the undersurface of the bridge. Enough clearance should be considered in the bridge design to ensure the traffic safety under the bridge.
Which is the intermediate support of a bridge superstructure?
A pier is an ____ supporting structure of bridge. A pier is an Intermediate supporting structure of bridge.
What is back water curve and draw down curve?
obtained is called Backwater Curve or Rising Curve. 3. If < 0, then in the direction of flow, depth of flow will decrease. The profile of water so obtained is called Drawdown Curve or Dropdown Curve or Falling Curve.
What is length of back water curve?
c — the coefficient applicable to the particular channel in the formula (y = c A/RS ) for the discharge of the channel. 2 S = 32-2. the total length of the backwater curve, as given by this formula, is theoretically infinite.
What is the specific energy curve?
h = flow depth V = velocity q = unit discharge = Vh g = acceleration due to gravity The specific energy curve shown in Figure 2 illustrates that when the flow is near critical, the conditions associated with a minimum specific energy, a small loss in energy can cause large changes in flow depth.
What is weir proper?
The weir proper is constructed in the middle portion of the diversion headworks an at the ends under sluices are provided adjacent to the canal head regulators. If canal takes off only from one side, the under sluice section is provided near that end only.
What is the purpose of guide bank?
Guide banks mainly serve two purposes: They protect the approach embankment for the bridge from attack of the water. Approach embankments extend from the bank of the river to the guide banks generally in perpendicular direction to both.
What is abutment in bridge construction?
Abutments are used at the ends of bridges to retain the embankment and to carry the vertical and horizontal loads from the superstructure to the foundation, as illustrated in Figure 12.1-1.
What is suitable for long span and heavy loads?
Steel is the major material for long-span structures.
What is the economical span for collar beam roof?
The tie beam is usually known as collar beam. Collar beam roof is suitable for spans upto 5 meters.
Which causeways are suitable for long span and heavy loads?
Steel Bridge Steel bridges are constructed using steel bars, steel trusses or cables. It can withstand heavy loads and are suitable for longer spans. Steel bridges are commonly seen in Railways.
What is the difference between scour and erosion?
Soil scouring vs erosion Soil erosion is a natural process that happens when areas of the earth’s surface or substrate wear down because of wind, ice, and water flow. Scouring is a term used by engineers to describe the particular type of localized soil erosion that happens around elements of a foundation.
What is scouring effect?
1.0 INTRODUCTION. Scour is a natural phenomenon caused by erosive action of flowing water on the bed and. banks of alluvial channels. In other words, Scour is defined as the erosion of streambed. sediment around an obstruction in a flow field .
What is scouring protection?
The protection of soil or other submerged material against scour, by the use of steel sheet pilings, revetment, riprap, or brushwood, or by combining any such methods as most suited to the site.
Should be taken below the deepest scour level?
Explanation: According to IRC code, it is recommended that the minimum depth of embankment below the scour level should not be less than 2.0 m for piers and abutment with arches and 1.2 m for other types of structures.
What is maximum scour depth?
Maximum scour depth is relatively more at just upstream of the bridge pier as compared to the downstream side. It is observed by authors, scour hole spread up to a width (W) of 1–2.5 times of pier diameter from the center of pier.
What is Lacey scour depth?
When equation (15) is applied to rivers in flood the value of R gives the normal depth of scour. Hence this formula is very useful determining the levels of foundations, vertical cutoffs etc. This formula is popularly called Lacey’s scour depth formula.
What you mean by hydraulic jump?
Hydraulic jump, Sudden change in water level, analogous to a shock wave, commonly seen below weirs and sluice gates where a smooth stream of water suddenly rises at a foaming front. The fact that the speed of water waves varies with wavelength and with amplitude leads to a wide variety of effects.
What are the effects of hydraulic jump?
(i) Its main aim is to perform as an energy-dissipating device to reduce the excess energy of water flows. (ii) The jump generates significant disturbances in the form of eddies and reverse flow rollers to facilitate mixing of chemicals.
What is dynamic form of hydraulic jump?
Explanation: Open channel flow is a flow that deals with hydraulics in fluid mechanics. It is a type of liquid flow that flows through a free surface. Explanation: When the hydraulic jump is dynamic or in a moving form it is called as positive surge.