Hydraulic Jumps

CIVE 401 Project

Nicolette Lind - Jessica McCallum - Maiwand M-Yaqoob

What is a hydraulic jump?● A hydraulic jump is defined as a rise in the level of water in an open channel

● Can be calculated, designed and controlled by engineers

● Often designed to occur over dam spillways

When/why do they occur?● A hydraulic jump occurs when a liquid at a high velocity discharges into a zone

that has a lower velocity

● The slowing of the liquid leads to an increase in height that changes the kinetic

energy of the liquid into potential energy

● Some of the energy is dissipated in the form of heat due to turbulence

Theory● Raleigh (1914) calculated the change in fluid depth associated with the shock

wave from a hydraulic jump and introduced the principles of continuity and

conservation of momentum

● The continuity states that the flow rate (Q) must be equal before and after the

hydraulic jump

● The conservation of momentum helps determine the energy dissipated within the

hydraulic jump

DiagramsExample diagrams of hydraulic jumps are shown below.

Applicable Equations Froude Number: Fr = V/√(gL)

Where: Fr = Froude number

V = Velocity

g = gravity

L = depth of flow

Critical Flow Depth: yc = (y₁/2)(√(1+8Fr₁²)-1)

Where: yc = critical flow depth

y₁ = upstream measured depth

Fr = Froude number

Upstream Energy Level: E₁ = y₁ + (V₁²/2g)

Where: E₁ = upstream energy level

V₁ = Velocity upstream

y₁ = upstream measured depth

g = gravity

Head Loss: hL = (y₂-y₁)⁸/(4y₁y₂)

Where: hL = head loss in the hydraulic jump

y₁ = upstream measured depth

y₂ = downstream measured depth

Importance of Froude Number● Defines subcritical flow or supercritical flow

● A froude number greater than 1 is a supercritical flow whereas a froude number

less than 1 is a subcritical flow

● In order to have a hydraulic jump the froude number needs to be greater than or

equal to 1

● A hydraulic jump occurs when the flow goes from supercritical flow (Fr > 1) to

subcritical flow (Fr < 1) or from an unstable flow to a stable flow

● A hydraulic jump will not occur when a flow goes from subcritical flow (Fr < 1) to

a supercritical flow (Fr > 1)

Types of Jumps● Weak (Undular) Jump

○ Low energy dissipation rate

○ Smooth downstream water surface

● Oscillating Jump

○ Irregular fluctuations of flow

○ Causes turbulence downstream

● Steady Jump

○ Jump forms steadily at same location and is well balanced

○ Turbulence is confined within the jump

● Strong Jump

○ Large change in depth of the water surface

○ High energy dissipation rate

Hydraulic Jump Classification

Advantages ✔● Dissipates the energy of water over a spillway

● Prevents scouring on the downstream side of the dam structure

● Traps air in the water

○ Useful for removing wastes and pollution in the water

● Reverses the flow of water

○ Can be used to mix chemicals for water purification

● Maintains a high water level on the downstream side

○ Useful for irrigation purposes

Disadvantages ✖● Downstream turbulence can cause damage and degradation of

channel banks

● May cause erosion on hydraulic surfaces

● Undesirable condition for fish passage

Energy Dissipation● Hydraulic jumps are one of the most effective options in dissipating energy over

water structures

● Energy is dissipated in the form of heat

● Turbulent flow and secondary waves cause most of the energy dissipation

● Applying the conservation of momentum equation, the energy loss can be

calculated by:

ΔE = (y₂ - y₁)³ / (4y₁y₂)

Where:

y₁ = Flow depth at supercritical flow

y₂ = Flow depth at subcritical flow

The diagram above illustrates a hydraulic jump and the energy loss from E1 to E2. The supercritical depth (y1) jumps to a larger depth, subcritical depth (y2), as the velocity decreases from V1 to V2.

Energy Loss Diagram

Applications● Industrial

○ Hydraulic jumps are commonly designed by engineers to dissipate energy below dam spillways,

weirs and outlets.

● Recreational

○ Hydraulic jumps in rivers are often used for fun/sport by kayakers, canoers, and rafters.

Well-Known Hydraulic Jumps● Hoover Dam

● Crystal Rapid in Grand Canyon

● Cache la Poudre River Spillways

● Your sink!

Crystal RapidCrystal Rapid is one of the most feared rapids in the Colorado River. It has several

large holes with a garden of rocks beneath. The rapids were formed in 1966 when a

flash flood washed debris into the river. The large holes are great examples of

hydraulic jumps and make Crystal Rapid one of the most complex environments for

water sports enthusiasts.

Important People● Leonardo Da Vinci first described hydraulic jumps in the 16th Century

● Giorgio Bidone published the first experimental investigations

● Henry Darcy calculated flow measurements in open channels

● Henry Bazin, a colleague of Henry Darcy, continued Darcy’s work of flow

measurements and flow over weirs

● Adhemar Barre de Saint Venant developed shallow water equations which still

hold even during hydraulic jumps

Interesting Facts● BYU conducted research relating the number of fatalities due to submerged

hydraulic jumps in the United States

● The number of deaths recorded was 458 and the number of fatal sites was 244

● The majority of these deaths occurred in dams

Conclusion● A hydraulic jump is defined as a rise in the level of water

● Hydraulic jumps occur when a supercritical flow (Fr > 1) encounters a submerged

object such as a dam or weir throwing the water upward and changing the flow

from a supercritical flow to a subcritical flow (Fr < 1), which causes a “jump”

● An advantage of hydraulic jumps is the ability to dissipate energy in dams,

channels, and similar structures

● A disadvantage of hydraulic jumps is the downstream turbulence which can cause

erosion and degradation of channels

Questions?

Referenceshttp://udel.edu/~inamdar/EGTE215/Jump_weirs.pdf

http://89.31.100.18/~iahrpapers/82799.pdf

https://www.rdb.ethz.ch/projects/project.php?proj_id=9798&z_detailed=1&z_popular=1&z_keywords=1

http://www.aboutcivil.org/hydraulic-jump-calculations-effects-applications.html

http://optimist4u.blogspot.com/2011/04/hydraulic-jump-and-its-practical.html (photo)

http://www.engineeringexceltemplates.com/blog.aspx?categoryid=5 (photo)

http://onlinecalc.sdsu.edu/onlinechannel12.php

http://www.fsl.orst.edu/geowater/FX3/help/4_Calculations/_Hydraulic_Jumps.htm

http://krcproject.groups.et.byu.net/

http://www.aboutcivil.org/hydraulic-jump-calculations-effects-applications.html

https://barr.com/projects/2331107900 (photo)

http://krcproject.groups.et.byu.net/ (photo)

http://large.stanford.edu/courses/2007/ph210/bechtol1/

http://www.usbr.gov/lc/hooverdam/history/articlesmain.html

http://grandcanyonhistory.clas.asu.edu/sites_coloradorivercorridor_crystalrapids.html