SEV322 Hydrology and Hydraulics Question 1, T1 2022 Page 1 of 13 Hydrology and Hydraulics(SEV322)…

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 1 of 13

Hydrology and Hydraulics(SEV322)

T1 2022

Assignment 1– Hydraulics

(Weight = 30%)

Due:

Week 6, 8:00 PM (AEST)

Sunday 17 April 2022,

Via CloudDeakin

This is an individual assessment task.

Plagiarism and collusion is unacceptable practice at Deakin University.

Where applicable, you must appropriately reference your work. Failure to

do so will result in disciplinary action. For more information on plagiarism

and collusion please see the CloudDeakin website.

All submissions must be typed, not handwritten, and must be recognisable

to Turnitin. Submissions that cannot be assessed by Turnitin will not be

awarded a mark.

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 2 of 13

LearningOutcomes

This assessment task has been devised to allow students to demonstrate progress towards

achieving the following Unit Learning Outcomes and Deakin Graduate Learning Outcomes:

At the completion of this Unit, you will be able to:

ULO 3 Describe the hydraulic behaviours observed in open channel flow.

ULO 4 Identify, define and use hydraulic properties of flow in open channels

when design canals, sluice gates, energy dissipating structures.

ULO 5

Apply hydrology and hydraulic principles to real world civil engineering

problems such as storm water management and design and analysis of

open channels.

GLO 1

Discipline

knowledge and

capabilities

Demonstrate discipline knowledge and capabilities appropriate to the

level of study.

This will be assessed through the student’s ability to show an

understanding of hydraulic principles in open channel flow and

structures.

GLO 4

Critical thinking

Evaluate information using critical and analytical thinking and

judgment.

This will be assessed through the student’s ability to investigate and

correctly evaluate practical problems in open channel flow.

GLO 5

Problem solving

Create solutions to authentic (real world and ill-defined) problems.

This will be assessed through the student’s ability to apply hydraulic

principles to solve commonly encountered problems in open channel

flow.

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 3 of 13

Background of the Problem

You are working in a water engineering consulting company as a graduate civil engineer.

Your company has just won a contract from Torrents River Irrigation Trust to design an

open channel to deliver water from Redfish Reservoir to Bigpond Dam, from where the

water will be distributed for irrigation purpose.

The conceptual design has been developed by senior engineers and illustrated in Table 1

and Figures 1 and 2. The first reach of the channel will be a rectangular concrete (gunite)

channel with a total length of 300 m, a width of 2.0 m and a depth of 2.5 m. The first 100 m

of the rectangular concrete channel will be horizontal, then the bed slope will change to 1-

in-500 (0.2%). At the upstream end of the first rectangular reach, a sluice gate will be built

for flow control.

The second reach will be a circular channel made from reinforced concrete pipes (RCP). The

diameter will be 2.0 m, the length will be 200 m and the slope will be 1-in-500 (0.2%). It will

be buried underground since there is a small hill to get across.

The third reach will be a trapezoidal earth channel (straight and uniform in each section)

with a total length of 2 km, a bottom width of 1.0 m, a side slope of 1.5-horizontal to 1-

vertical (1.5H:1V), and a depth of 2.0 m. The first 1 km of the second reach will have a

slope of 1-in-500 (0.2%), then it will change to 1-in-100 (1%) for 200 m, and finally will

change back to 1-in-500 (0.2%) for the rest 800 m.

The fourth and final reach will be a rectangular earth channel (straight and uniform) with a

total length of 500 m, a width of 2.0 m, a depth of 2.5 m, and a bed slope of 1-in-200

(0.5%).

You are tasked to solve a number of specific engineering problems for the design. Critical

steps of the calculations should be documented such that your results can be double

checked by your colleagues.

Table 1 Proposed design of the irrigation channel

Start

Chainage

(m)

End

Chainage

(m)

Channel

Material

Channel

Geometry

Bed

Slope

S0

Bottom

Width b

(m)

Depth D

(m) Side Slope

m (H:V)

Diameter

(m)

0 100 Gunite Rectangular 0 2.0 2.5 0 N/A

100 300 Gunite Rectangular 0.001 2.0 2.5 0 N/A

300 500 RCP Circular 0.002 N/A N/A N/A 2.0

500 1500 Earth Trapezoidal 0.002 1.0 2.0 1.5 N/A

1500 1700 Earth Trapezoidal 0.01 1.0 2.0 1.5 N/A

1700 2500 Earth Trapezoidal 0.002 1.0 2.0 1.5 N/A

2500 3000 Earth Rectangular 0.005 2.0 2.5 0 N/A

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 4 of 13

Figure 1. Schematic of the irrigation channel system (top view).

Torrents River

Redfish

Reservoir

Bigpond

Dam

Sluice gate

1st Reach: Rectangular

concrete (gunite)

channel

3rd Reach: Trapezoidal

earth channel 4th Reach: Rectangular

earth channel

Direct connection

(freefall)

2nd Reach: Circular

RCP channel

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 5 of 13

Figure 2. Schematic of the irrigation channel system (side view).

1st Reach:

Rectangular

concrete

(gunite)

channel

Redfish

Reservoir

Chainage

(m) 500 Bigpond

Dam 0 100 1500 1700 2500 3000

3

rd

Reach:

Trapezoidal earth

channel

4

th

Reach: Rectangular

earth channel

H1

H2

300

2nd Reach:

Circular

RCP

channel

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 6 of 13

Q1

You are tasked to provide information to the client on how the opening of the sluice gate

should be set to achieve the designed flow in the channel during normal conditions and

prevent flooding during storm events.

The sluice gate used in the rectangular concrete channel has a width same to that of the

channel, as shown in Figure Q1. The sluice gate is installed close to the reservoir outlet. The

maximum depth of the channel bank upstream of the sluice gate is 3.5 m and that

downstream of the gate is 2.5 m. Under the normal reservoir operation condition, water

surface level in the Redfish reservoir is 2.0 m higher than the bottom of the channel (i.e. y1 =

2.0 m). During storm events, the reservoir level can be up to 3.0 m above the bottom of the

channel (i.e. y1 = 3.0). It is known that the energy loss when water passing through the sluice

gate is 10% of the velocity head of the flow just underneath the gate (cross-section 3). A

designed flow rate of 3.0 m3/s is to be achieved in the channel under normal reservoir

operation conditions. Frictional loss due to wall sheer stress can be neglected due to the

short distance considered in this scenario.

To be able to achieve a well justified recommendation, you take the following steps:

(i) Establish an energy equation between a point at the surface of the reservoir and

the point just below the sluice gate. Determine the opening height of the sluice

gate y3 that would result in the designed flow rate under the normal reservoir

operation condition. If multiple solutions are obtained, determine which one

should be adopted. (6 marks)

(ii) Based on the results from part (i) and taken into consideration of practical

constrains, the tentative sluice gate opening y3 is determined as 0.25 m. Under

the normal operation condition, y1 is 2 m and less than the channel bank depth

downstream of the sluice gate, such that there is no flooding risk. Considering

that the reservoir level would be higher (y1 = 3 m) during storm events, you want

to estimate the flow condition downstream of the sluice gate for the maximum

depth scenario. Based on the information obtained so far, determine the flow

rate, velocity, Froude number and flow regime for the flow through the sluice

gate under the maximum reservoir depth scenario. (9 marks)

(iii) Based on the information obtained, for relative reservoir level y1 = 3.0 m and the

sluice gate opening y3 = 0.25 m, determine whether a hydraulic jump is likely to

occur downstream of the sluice gate. If so, estimate the depth of flow

downstream of the jump and the associated energy loss. (10 marks)

(6 + 9 + 10 = 25 marks)

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 7 of 13

Figure Q1 Side view of the sluice gate used for flow control

y1

1 y3 2

Possible

hydraulic jump

y4

4

Reservoir

Rectangular

channel y2

3

Top of channel

bank

Top of channel

bank

3.5 m

2.5 m

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 8 of 13

Q2

The client wants to know the maximum flow capacity and the corresponding flow condition

of the channel system (in particular, normal depth and critical depth). This would be useful

for developing flood mitigation plans. The ageing of the channel should be considered since

it delivers raw water and ageing can occur not long after the commission. For the circular

channel, as per the convention, the design maximum flow is the full pipe flow without

pressurisation. For other types of channels, a minimum freeboard of 0.3 m is required (i.e.

the distance between the surface of the water and the top of the channel bank needs to be

0.3 m or more). The velocity should not be greater than 3.0 m/s under the maximum

design flow.

To determine the maximum flow capacity of the channel system under aged condition, you

take the following steps:

(i) Find the suitable design values of the Manning’s coefficient n for each section of the

channel from credible references. Clearly specify how you find the information such

that your colleague or the client can check if needed. Justify the values selected. (5

marks)

(ii) Using the Manning’s equation, determine the maximum allowable normal flow rate

and corresponding velocity for each individual channel section (except for the first

horizontal section). Demonstrate the calculation and tabulate the results for all the

channel sections. If the velocity is higher than the allowable maximum of 3 m/s,

make adjustment to the maximum normal flow accordingly. Summarise results in

Table Q2-1. (8 marks)

(iii) Based on the maximum allowable normal flow for individual sections as determined

in part (ii), determine the maximum allowable flow for the whole channel system,

and explain it to the client. (2 marks)

(iv) Based on information obtained previously and other practical considerations, the

client would like to set the maximum allowable flow for the whole channel system

as 4.80 m3/s. Based on this value, determine the corresponding normal depths and

critical depths for all the relevant channel sections. Demonstrate the calculation

and tabulate the results for all the channel sections using Tabel Q2-2. (6 marks)

(v) Make a schematic of the side view of the channel (use Figure 2). Based on the

normal depth and critical depth results obtained in part (iv), draw the normal depth

line (NDL) and the critical depth line (CDL), respectively. Label the values of NDL and

CDL. (4 marks)

(5 + 8 + 2 + 6 + 4 = 25 marks)

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 9 of 13

Table A2-1 Maximum normal flow and velocity for each individual section along the channel

Start

Chainage

(m)

End

Chainage

(m)

Channel

Material

Channel

Geometry

Bed

Slope

S0

Bottom

Width

b (m)

Depth

D (m)

Side

Slope m

(H:V)

Diameter

(m)

Manning’s

n (s/m3)

Max

Normal

Flow depth

y0 (m)

Max

Normal

Flow

Q (m3

/s)

Max Normal

Flow Velocity

V (m/s)

0 100 Gunite Rectangular 0 2.0 2.5 0 N/A N/A N/A N/A

100 300 Gunite Rectangular 0.001 2.0 2.5 0 N/A 2.2

300 500 RCP Circular 0.002 N/A N/A N/A 2.0 2.0

500 1500 Earth Trapezoidal 0.002 1.0 2.0 1.5 N/A 1.7

1500 1700 Earth Trapezoidal 0.01 1.0 2.0 1.5 N/A 1.7

1700 2500 Earth Trapezoidal 0.002 1.0 2.0 1.5 N/A 1.7

2500 3000 Earth Rectangular 0.005 2.0 2.5 0 N/A 2.2

Table A2-2 Maximum allowable flow and corresponding normal depth and critical depth for the channel system

Start

Chainage

(m)

End

Chainage

(m)

Channel

Material

Channel

Geometry

Bed

Slope

S0

Bottom

Width

b (m)

Depth

D (m) Side

Slope m

(H:V)

Diameter

(m) Manning’s

n (s/m3)

Max

Allowable

Flow

Q (m3

/s)

Normal

Flow

depth y0

(m)

Critical

Depth

yc (m)

0 100 Gunite Rectangular 0 2.0 2.5 0 N/A 4.8 N/A

100 300 Gunite Rectangular 0.001 2.0 2.5 0 N/A 4.8

300 500 RCP Circular 0.002 N/A N/A N/A 2.0 4.8

500 1500 Earth Trapezoidal 0.002 1.0 2.0 1.5 N/A 4.8

1500 1700 Earth Trapezoidal 0.01 1.0 2.0 1.5 N/A 4.8

1700 2500 Earth Trapezoidal 0.002 1.0 2.0 1.5 N/A 4.8

2500 3000 Earth Rectangular 0.005 2.0 2.5 0 N/A 4.8

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 10 of 13

Q3

The flow surface profile is important since rapidly varied and gradually varied flows are

expected to co-exist with normal flow. You are asked to visualise the possible flow surface

profile for the whole channel. It is known that under typical operation condition, the water

surface in Bigpond Dam is about 0.5 m above the invert level of the channel end (i.e. H2 =

0.5 m, Figure 2).

(i) Based on the Normal Depth Line (NDL) and Critical Depth Line (CDL) for the channel

at the maximum allowable flow condition as you determined in Q2 (iv), create a

separate drawing for the whole channel and sketch the possible flow surface profile

when considering the surface level in Bigpond Dam is H2 = 0.5 m. Show the control

points. Label the type of gradually varied flow surface profiles involved (M1, M2, S1

etc.; no detailed calculation needed). (10 marks)

The rectangular earth channel that links to the Bigpond Dam requires some further

analysis. Since the dam only has a relatively small capacity, the water level in the dam can

increase significantly after a storm event. The maximum possible surface level of the

Bigpond Dam is H2 = 2.0 m, i.e. 2.0 m above the invert level of the channel end, as

illustrated in Figure Q3. It is important to understand how this high water level at the Dam

will impact the water level upstream.

Figure Q3 schematic of the channel section connecting to Smallpond Dam.

To obtain all the details for the scenario H2 = 2.0 m, you take the following steps

(ii) Determine, with appropriate calculations and justifications, the type of flow surface

profile for the rectangular earth channel upstream of the Bigpond Dam (chainage

2500 to 3000 m). (5 marks)

(iii) Determine the detailed flow surface profile from end of the channel (where water

depth is 2.0 m) to the upstream cross-section where the depth of water is the normal

depth, or to the interface between the trapezoidal and the rectangular channels (i.e.

chainage 2500 m) if the normal depth cannot be achieved. Use the step method with

a step interval ????? = 0.20 m. Demonstrate the key calculation steps, fill in Table Q3,

and sketch the flow surface profile. (10 marks)

(10 + 5 + 10 = 25 marks)

Bigpond

3000 Dam

H2

Chainage (m) 2500

S0 = 0.005

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 11 of 13

Hints:

1. Identify the control points (cross-sections) to help determine the surface profile.

Subcritical flow has control at the downstream; supercritical flow has the control at the

upstream.

2. When calculating the detailed surface profile using the step method, keep at least four

significant figures in your calculation to avoid significant rounding error.

3. In the step method calculation, the final step will finish at the normal depth or at the

upstream end of the rectangular earth cannel, so the step size of the final step doesn’t have

to be 0.2 m.

4. Depending on the normal depth you calculated previously, after calculating the gradually

varied flow surface profile, you will see whether the normal flow would present or not. One

approach is that you decrease y step by step until reaching the normal depth and calculate

the distance ?x. If the distance is more than the overall length of the channel section, it

means the calculated surface profile beyond the length of the section will not be able to

realise.

Table Q3 Results of step method calculations for the flow surface profile

y (m) A (m2

) R (m)

V

(m/s) E (m) Sf Sf_ave

?E

(m)

S0 –

Sf_ave

?x

(m)

?x

(m)

2.00

1.80

1.60

…

Normal depth

Or the depth at

the upstream

end of the

rectangular

channel

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 12 of 13

Q4

Although the upstream sluice gate can control how much water flowing into the channel

from the Redfish Reservoir, the flow can increase due to runoff from surrounding

catchment, or decrease due to evaporation, seepage or even water theft. The client

Torrents River Irrigation Trust asks to have a flow measurement structure designed in the

last reach of the channel (the rectangular earth channel). You propose that a smooth hump

can be built and used as a low-cost critical-depth flow meter, as shown in Figure Q4. The

client likes your idea and asks you for details of the design.

It is estimated that the energy loss at the transition (when flowing from the original

channel to the top of the hump) HL,hump is R% of the velocity head on top of the hump,

where R is calculated by the last two digits of your student ID and the following formula

R = (+50)/10where+50)/10where represents the last two digits of your student ID. For example, if your student ID

ends with 57, then R = (57+50)/10 = 10.7.

Due to the short length of the hump and the relatively mild channel slope, the elevation

difference caused by the slope of the channel can be neglected when analysing the hump

(i.e. assume the channel is effectively horizontal for the short section around the hump). To

obtain the details of the design, you take the following steps.

(i) Assuming that the designed critical-depth flow meter can measure flow up to 5.0

m3/s, determine the normal depth, critical depth and flow regime (subcritical or

supercritical) in the original rectangular channel for flow ranging from 1.0 m3/s to

5.0 m3/s with an interval of 0.5 m3

/s. Tabulate the results using Table Q4. (10

marks)

(ii) Determine the minimum height of the hump ???????? that would result in critical flow on

top of the hump for the designed maximum measurable flow (i.e. 5.0 m3/s). (10

marks)

(iii) Based on the information obtained from previous steps, and considering practical

constrains, the height of the critical-depth flow meter (hump) is decided to be 0.6

m. The channel may subject to flooding and therefore higher flow than the

designed maximum measurable flow. Calculate the new upstream depth y1, new

when the flow rate is 8.0 m3/s, and check if it is still in the safe range (i.e.

considering the requirement of at least 0.3 m freeboard). (5 marks)

(10 + 10 + 5 = 25 marks)

SEV322 Hydrology and Hydraulics Assignment 1, T1 2022

Page 13 of 13

Figure Q4 Schematic (side view) of the proposed critical-depth flow meter

Table Q4 Normal depths and critical depths for various flows

Flow Rate

(m3/s)

Normal Depth

(m)

Critical Depth

(m)

Flow Regime

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

End of Assignment 1

y1 or

y1, new

y2

z

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