Hydraulics for Civil Engineering

Hydraulics for Civil Engineering

There is an error in task 2b)  of the Assignment.    

The last few words should read channel 1m deep and 4m wide it currently reads 4m deep and 1m wide 

Please change your copies otherwise this question does not make sense.

b) Using the Manning Equation, explain how the hydraulic radius affects the rate at which water can flow through a rectangular channel by comparing the amount of water that would flow through a channel with a slope of 0.002, n value 0.008 if the channel were 1m wide and 4m deep to a channel 1m deep and 4 m wide.

Higher National Certificate/Diploma in Construction and the Built Environment

You have recently joined a civil engineering company that is just starting a new contract with one of the leading water supply companies. As you have recently completed some hydraulics studies they need you to join a team who are developing irrigation and process water supply in an area of the East of the UK where, partly as a result of climate change water supply can be problematical during the summer months. 

Task 1 LO1 Apply concepts of physics to develop solutions for hydrostatic and hydrodynamic problems

a) What affect will temperature have on the following properties of water? Density, viscosity and surface tension. Explain how can this affect the flow of water through a pipe and in an open channel such as a river. 

b) Explain what the boundary layer is in fluid flow and show how the properties mentioned in part 

a) above influence this boundary layer and the distribution of velocity in a pipe or in a stream 

c) Explain the difference between laminar and turbulent flow and show how the Reynolds Number can be used to predict the type of flow. 

d) The water in a pipe is travelling at an average speed of 0.5ms-1 in pipe of diameter 0.1m the absolute viscosity is 0.001pascal s-1 Is the flow turbulent or laminar? Show your working 

e) Repeat the above calculation but with glycerine which has a viscosity of 4.22 Pascal s-1 

f) An area of a city is prone to flash flooding which occurs during exceptionally heavy rainfall. The fear is that such a once in a century occurrence will become more common with global warming and some suggestions are made to improve the drainage in the flash flood areas. One particular area is used as an example the problem arises from the fact that the area is at the bottom of a  

short steep hill and in the path of a natural drainage channel to a tributary of the Thames. Currently the storm water/sewerage system is used. Briefly discuss i) the disadvantages to the local population that arise from using the sewerage system to dispose of storm water and ii) to discuss whether the storm water should be disposed of through pipes or an open channel .

TASK 2 LO2 Calculate forces related to fluids at rest and in motion 

a) i)A reservoir is situated at a height of 50m above a town. The reservoir is connected to the town through a 1m diameter pipe. If the friction factor in the pipe is 0.008 and the distance the length of the pipe is 1000m and the normal delivery is 15m3 s -1 calculate the pressure at the end of the pipe as it goes into the town. (Hint, think of the head loss )

ii) At that point in the pipe there is a valve. If the valve is turned off what is the pressure on the valve?

b) Using the Manning Equation, explain how the hydraulic radius affects the rate at which water can flow through a rectangular channel by comparing the amount of water that would flow through a channel with a slope of 0.002, n value 0.008 if the channel were 1m wide and 4m deep to a channel 4m deep and 1 m wide. 

c) A pipe is taking water to a remote property from a main pipe some 500m distant. The flow of water has to be no less than 0.01m3 s -1 What is the smallest pipe diameter that flow would definitely be laminar? 

d) i) What is the “energy principle” ?

ii) Use this to explain what happens to the depth of the water in a long horizontal channel of constant width lined with smooth concrete with an “n” value of 0.011 delivering water at 0.1m3 s -1 

e) What are the advantages and disadvantages of bringing a water supply into a town using pipes rather than using open channels. 

LO3 Develop practical solutions for the distribution of fluids within correctly sized pipes 

a) The maximum pressure that can be provided in a pipe line carrying process water to a food plant is 50m. The length of the pipe is 2000m and the water requirements can be as high as

5m3 s -1 the pipe has a Darcey Weisbach friction factor of 0.008, what is the minimum diameter of pipe that can supply the factory? 

b) Calculate the Reynolds number for the water in the above pipe line. Comment on whether the water is being delivered using the minimum of energy. (assume absolute viscosity of water is 0.008Pascal s-1 ) 

c) Both the Chezy equation for open channel flow and the Manning Equation are to estimate flow from observations on the bed slope, a roughness related constant and the hydraulic radius. Compare the flow estimates given by each method for a rectangular cross section channel with a slope of 0.01, Manning n value of 0.011 and a width of the channel = 2m and water depth 1m. There are different thoughts on the relationship between Chezy’s “C” and Manning’s “n” however use the commonly agreed relationship C = R1/6/n where R is the hydraulic radius. Comment on any difference between the two.  

LO4 Calculate the hydrostatic pressure exerted on substructures for a given context 

a) A dam 80m long is holding water to a depth of 45m. Calculate what the total load on the dam is. Suggest how the water is kept at a safe level and what information is needed to design such a structure 

b) A two storey underground carpark has been designed to go down to a depth of 15m. The water table in that area is 3m below ground. The dimensions of the car park are 50m by 20m. Calculate the mean pressure on the walls and thus the total load that the water will exert on the structure from the sides.

 c) Calculate the upward pressure and the total force on the floor of the car park exerted by the water. 

d) A caisson is needed to build piers for a new bridge across a wide river. Each caisson will have a footprint of 10 x 10m and will need to deal with a depth of water of 12m at maximum. Outline the main considerations that will allow piles to be sunk and the bridge pieces to be constructed safely