Homework answers / question archive / Assessment Tasks   This assignment is comprised of two tasks: Task 1 — Vegetated Channel   Task 2 — Flow measurement Device Task 3 — Dam Spillway   Task 1 Vegetated Channel   Your local council is building a retention basin as part of a new subdivision

Assessment Tasks   This assignment is comprised of two tasks: Task 1 — Vegetated Channel   Task 2 — Flow measurement Device Task 3 — Dam Spillway   Task 1 Vegetated Channel   Your local council is building a retention basin as part of a new subdivision

Electrical Engineering

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Assessment Tasks

 

This assignment is comprised of two tasks:

Task 1 — Vegetated Channel

 

Task 2 — Flow measurement Device

Task 3 — Dam Spillway

 

Task 1 Vegetated Channel

 

Your local council is building a retention basin as part of a new subdivision. Once leaving the basin this water must traverse down an existing green space with a width of 40m. The size of the detention basin and the control structure releasing water from that basin must be designed such that the discharging water can be accommodated within this 40m space. You must design a vegetated channel which can fit within this allowable width. The local soil is similar to that found in Toowoomba, i.e. is a Red Ferrosol, a type of erosion resistant soil.

Figure 1 — Subdivision for task 1

The slope of this green space is equal to Sp = 0.01 + N/300 where N is the last digit of your student number.

if your student number is equal to 0061261309 then your slope will be equal to 0.01 + 9/300 = 0.04.

The channel is of trapezoidal cross section as shown below and is vegetated with a grass of your choice. The side slopes on the channel are open to your choosing but the entire channel must fit within the 40m width.

‘40m

Figure 2 — suggested channel shape for vegetated channel Your Task:

Your task here is to design a vegetated channel that will take the discharge from the detention basin and deliver it safely through the 40m wide green space. This will require you to select a channel cross section (base width and side slope) and vegetation cover. Once a channel is chosen, you must determine the discharge that can be accommodated in this channel considering both stability and capacity.

Clearly discuss and justify any assumptions that you make in regards to the vegetation in the channel.

The required Outcomes from your work:

 

1) The channel design (shape and vegetation)

 

2) The maximum flow possible through your channel (considering capacity and stability)

 

3) The water depth in your channel at this design velocity

 

4) The likely depths at 50% of this design flow under the two extremes of the likely

 

retardance in this channel

5) Present your working in a brief project format with introduction and conclusion.

Marking Scheme:

Desian process Design for stability and capacity. Documented the design

gnP methodology. Full working provided

. Clearly document your design using a sketch of the cross section

 

Channel design ye y g gaand specify slopes, grass type & condition

Depths at 50% Working and results for calculating the water depth at 50% of the

Task 2 Flow measurement Structure

 

In Task 1 you determined the potential flow that would occur in the vegetated drainage channel from a new subdivision. Now you have been asked to design a measuring structure which can be used to determine the flow discharging from this channel before it enters a wetland downstream (Figure 3). At your disposal you have access to devices which can measure water depth to mm precision (i.e. +/- mm accuracy) and you wish to use this device(s) to monitor the hydrograph that occurs during flow events. In order to do this you will need to (a) build a hydraulic structure and (b) produce a rating curve which can convert the measured depth(s) into a flowrate in m?/s.

Figure 3 — Location for flow measuring device

 

You have been given two options for flow measuring devices for this task:

 

 V notch Weir and Venturi Flume

Your activity is to conduct preliminary designs for both structures and to produce a rating curve (depth vs flow) for each.

There is no limitation to the channel shape or depth once the water enters the wetland but themost successful design should be practical.

You will make a recommendation on the most appropriate design based on your findings.Your Task:

Your task is to design a flow measuring structure which can function over the range from 0 m/s up to the maximum flow determined in Task 1.

 

The required outcomes from this work are:

 

Design for a V-Notch weir highlighting important dimensions and or required changes to the width of the channel. Include both a top and side view of the structure andsurrounding channel. Include the incoming velocity in your calculations.

 

e Rating curve (y vs Q) for the V-notch weir over the range identified in Task 1. Include the incoming velocity in your calculations

 

Design for a Venturi flume highlighting important dimensions and or required changes to the width of the channel. Include both a top and side view of the structure and surrounding channel.

 

 Rating curve (y vs Q) for the flume over the range identified in Task 1

 

Your recommendation for the most suitable flow measuring device for this situation.

Marking Scheme:

Design for V-notch Design the V notch structure including the channel with and impact on water depth.

V-notch Rating Produce the rating curve H/y vs flow for your design | 10 |

. Design the flume structure including the channel with and

Design for Flume.impact on water depth

Flume Rating Produce the rating curve H/y vs flow for your design | 10 |

Introduction, recommendation for the measurement device,conclusion

Task 3 - Dam Spillway

A dam is being constructed on a river and you have been tasked with the preliminary design calculations to determine the size of the spillway required. You have decided that a standard spillway design similar to Figure 4.1 (Studybook) will be sufficient. The main dam wall is 200m long and has a height of 36 m above the existing stream. The full supply level of this dam, when water reaches the crest of the spillway is a total of 200 GL. However, this dam also serves to reduce the severity of flood events in this river and has an extra 5.0 m of flood capacity above the full supply level.

Your focus is to design an Ogee spillway which limits the maximum spillway flow to 150 m°/s while maintaining a head over the spillway of less than 3 m for the 120 hour design flood event provided to you on studydesk.

The basic equation for an Ogee spillway is given by equation 4.1:

2

C, =0.585+0.04H ford0<H<4.0m

The basic continuity equation can be used to model the storage capacity and head level in the dam.

AS

Qin, ~ Qou =—_

"At

Where Qin (m°/s) is the flow entering the dam from the river upstream, Qour (m?/s) is the flow leaving the storage through the spillway and S is the volume within the dam storage at that point in time. This equation can be rearranged to calculate the new Storage capacity (S) at the end of each time step.

Q = Cyb\2gH™

Where Cd is the discharge coefficient, b is the width of the spillway and H is the water head in the storage measured relative to the crest of the spillway. It will be assumed that due to the storage size, the impact of upstream velocity can be ignored but you must explain why we can make this assumption in your report.

A water balance model of the dam storage requires a dam capacity curve, based on a survey of the land are that will be inundated as the dam fills beyond 200 GL. This relationship between water level and storage capacity is given below in Table 1. In order for this data to be useful you may need to develop a mathematical expression which calculates spillway head from a known flood storage volume.

Table 1 - Dam Storage Rating Data

(1046 m’) (m)

P|

The design flood event for the modelling exercise will be provided as a download on

studydesk. This data may be individualised, so it is important that you use the data that is given to you. The data will be presented in a discharge hydrograph with two columns in a similar format as shown in the sample in Table 2 below. Please note that the time step on the design flood may differ from this table.

Table 2 - Sample Flood Hydrograph Data (please download your file from studydesk)

(hours) (m3/s)

 

Pol OT lt

 

ee ee ee ee

 

Po Tc

 

ee ee ee

It is strongly encouraged that you use a computer program (e.g. Excel, Matlab) to perform these simple but repetitive calculations. You must include the Excel or Matlab files as an appendix to your submission as we will assess this model.

 

Your Tasks

1) Develop a simple model using the continuity equation to model the spillway flow for the 120 hour duration of the supplied design flood event. This model should include:

 

- Ability to calculate dam storage (S) and water level (H) for each time step

 

- Variable Co based on head level over spillway

 

- Ability to change spillway width

 

- Include sufficient detail so that others can understand how to use the model

 

- Documented in the report

2) Use this model to determine the correct spillway width that satisfies the design criteria

(150m*%/s & 2.5m). Clearly explain how you arrived at this width including evidence of testing other widths.

3) Plot the incoming (Qin) and outgoing (Qo) discharges and the storage volume over time for the dam when subjected to the provided design flood.

4) Create your own design flood hydrograph and plot Q,, and Qou on the same set of axes.

Comment on the ability of the dam and your spillway to alter the shape and or magnitude of the flood hydrograph.

 

- You may use the same timestep and flood length as the provided hydrograph.

 

- You are encouraged to use a different hydrograph shape but do not exceed the existing

 

peak.

 

5) Produce a report for this question which introduces the design tasks, outlines assumptions, explains your logic and discusses the results and outcomes.