Hydraulics for Civil Engineering

Assignment Brief

Unit Number and Title: Unit 43 Hydraulics

Assignment Title: Hydraulics for Civil Engineering

Unit Learning Outcomes

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

LO2 Calculate forces related to fluids at rest and in motion.

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

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

Assignment Brief and Guidance

Scenario:

The company you work for has recently taken on work involved with hydraulic structures as someone who has recently graduated from a programme which includes significant civil engineering hydraulics you are asked to join the management team with respect to these projects.

Task 1.

1. Water flowing in a pipe, is taking water from a reservoir some 100m above a city what is the pressure in the pipe as its enters the city? If a open channel was to bring the water into the city from the same reservoir, what would the pressure be in the opne channel. Explain briefly why.

2. What are the two main forces of resistance to water flow in pipes?

3. How does water temperature affect these forces?

4. Explain the difference between laminar and turbulent flow.

5. What is Reynolds Number and how is it related to turbulent flow?

6. What is the boundary layer and how is it affected by the roughness of the surface over which water is flowing?

7. How is the resistance to water flow reduced either in a pipe or in an open channel?

8. The water supply to a rapidly expanding town was laid out many years ago when the town was small and appeared to have a stable population. Outline how additional supplies can be piped in without disrupting the current supplies

Task 2

1. Water is needed to supply a canal system, which may require up to 30m3 s -1 the channel is 2 metres wide calculate the depth of flow at maximum given that the Manning n value of this stretch of the channel is 0.02.

2. A proposal has been suggested that the excess water above a flow rate of 25m3 s -1 could be diverted through a pipe to a reservoir some 2km distant . An automatic system would be installed which opened a valve into this pipeline as soon as the flow exceeded this level. The pipe would need to be able to take water at the rate of 10m3 s -1 . Using the Darcey Weisbach equation for laminar flow calculate the head loss through a pipe with a friction factor of 0.006 and a pipe diameter of 1.5m.

3. The reservoir (in part b) is 50m below the surface of the river. Comment on whether it will be possible to achieve the 10m3 s -1 flow and what steps could be taken.

4. Comment on the differences between pipe flow and open channel flow and estimate the dimensions of an open channel 2m deep that would be needed to conduct 10m3 s -1 to reservoir.

Task 3

1. Estimate the head loss in a pipe line of 10km length and 1.4 m in diameter carrying water at the rate of 30m3 s -1 to supply a town. The Darcey Weisbach friction factor is 0.004 and the minor losses are 10 times the velocity head.

2. The difference in height between the start and end of the pipe line is 20m. What additional pressure would need to be supplied by a pump to achieve the required delivery?

3. As an alternative design the feasibility of using a bigger diameter of pipe needs to be considered. Find the smalledst diameter of pipe that would achieve this.

4. Discuss the real life factors that would go into deciding whether to use a pump based system or one based on gravity alone.

Task 4

1. Ground water is found at a depth of 1.5m and a below ground car park is being built in this area. The depth of the car park is 9m to allow for two levels of parking. Calculate the force on the boundary walls and the upwelling force on the floor. The dsimensions of the car park are 20m x 60m. Assume that this is fresh water with a density of 1000kgm-3

2. What materials and structures would be needed for the outer walls of the car park bearing in mind that they also act as the main structural support for the building.

3. What structure and materials would be suitable for the flooring?

Sample Answer

Hydraulics for Civil Engineering

Introduction

Hydraulics is central to civil engineering because it explains how fluids behave under pressure and motion. Every water distribution system, dam, or drainage network relies on understanding the physics of fluids. This report applies hydraulic principles to practical civil engineering problems, focusing on fluid pressure, open-channel flow, pipe friction, and hydrostatic forces acting on structures.

Task 1: Hydraulics Fundamentals

When water flows from a reservoir located 100 metres above a city, the pressure at the pipe entry point can be estimated using the basic hydrostatic pressure relationship: pressure equals fluid density multiplied by gravity and height. For water (density 1000 kg/m³ and gravity 9.81 m/s²) at a height of 100 metres, the pressure is roughly 981,000 Pascals, or 981 kPa.

If the same water were delivered through an open channel, the pressure at the surface would be zero (atmospheric), because open-channel flow is exposed to air. In that case, the driving force is the slope or elevation difference, not pressure.

The two main forces that resist water flow in pipes are wall friction and turbulence. Wall friction occurs as water rubs against the pipe surface, while turbulence adds energy losses through chaotic movement, especially in rough or irregular pipes.

Water temperature also plays a role: warmer water has lower viscosity, which reduces friction and increases flow rate.

The difference between laminar and turbulent flow lies in how fluid particles move. In laminar flow, the motion is smooth and orderly, with layers sliding past each other. In turbulent flow, eddies and swirls dominate, creating more resistance. The Reynolds Number (Re) is used to describe this behaviour: values below around 2000 indicate laminar flow, while values above 4000 suggest turbulence.

The boundary layer is the thin region near the pipe wall where the velocity changes from zero (at the wall) to the full stream velocity. Rougher surfaces increase the boundary layer thickness and friction losses.

To reduce resistance in both pipes and open channels, engineers often use smooth materials such as PVC or steel, streamline fittings, and gentle curves rather than sharp bends.

Finally, if a town’s population grows and requires more water, new pipelines can be added in parallel or looped into the existing network. This allows additional supply without interrupting current service and helps maintain adequate pressure across the system.

Continued...