ENVS117/ENVS602: Hydrology of Urban Streams - Benefits of Restoration - Scientific Report Writing Assessment Answer

Scientific Report Assignment

Assignment Task

In Rivers Practicals 2 and 3 you undertook a surveying exercise across an urban stream on the Macquarie University campus. You then processed this data and used the discharge and velocity equations to analyse and quantify the flow velocity and discharge characteristics for this stream. You will be using the skills learnt in these practicals (and the lecture on Stormflow) in this assignment.

In this assignment you will:

1) use the information provided below to undertake calculations of flow velocity and discharge for the channel cross section provided and using three different roughness (Manning’s n) values.

2) research the scientific literature using your library database skills to investigate urban stream restoration approaches and their effects on stream flow and storm flow (hydrology). At least 10 scientific references should be used in your assignment including the compulsory reading, Chin et al. (2013).

3) write a scientific report. Only the scientific report is to be handed in to Turn It In. Do not hand in this assignment information and calculation sheet. The Data and Calculations section below should be written up (transferred) to the results section of your report (see section below on report structure).

DATA AND CALCULATIONS – URBAN STREAM CROSS SECTION AND HYDROLOGY

Figure 1 shows a cross section of an urban stream. You will use this cross section to calculate flow velocity and discharge for a range of different roughness (Manning’s n) scenarios.

Remember:

Flow velocity equation

V = [(D2/3) x (S1/2) / n], where

V = mean channel velocity (m/s)

D = flow depth (m)

S = water surface slope (m/m; often approximated by the slope of the bed)

n = Manning's roughness coefficient

Discharge equation

discharge = velocity x cross-sectional area

Q = V x A, where

Q = discharge (m3/s)

V = velocity (m/s)

A = cross-sectional area (m2)

floodplain

Using this channel cross-section, complete Table 1. Channel slope has been provided for you. This table will need to be reproduced as part of the results section of your scientific report.

Table 1 Hydrology of an urban stream at Macquarie University

Three different Manning’s n roughness parameters have been provided in Table 2. Use these to calculate the flow velocity and discharge for scenarios 1, 2, and 3. This table will need to be reproduced as part of the results section of your scientific report.

Table 2 Roughness scenarios, flow velocity and discharge characteristics of an urban stream at Macquarie University

THE ASSIGNMENT QUESTIONS

1) As part of the introduction - What are the characteristics of stream flow (hydrology) in urban environments?

2) As part of the results - Using the results of your calculations, explain how changing roughness impacts on stream flow hydrology in an urban stream?

3) As part of the discussion - Assume that the aim of urban stream restoration is to reduce flow velocity to improve public safety, minimise sediment erosion and improve physical structure (i.e. geomorphology). What types of restoration/rehabilitation can be undertaken to achieve these aims? [Hint: read Chin et al. (2013) and take a walk around campus for examples (Mars Creek behind Y3A, University Creek between Research Park Drive and Innovation Rd)].

4) As part of the discussion - What might be some additional benefits of undertaking urban stream restoration (e.g. on stream ecology and/or water quality)?

SCIENTIFIC REPORT PRESENTATION

You will present this assignment as a scientific report with appropriate referencing. Below is a rough guide of the proportion of the report that should comprise each section. Your scientific report will comprise the following:

Introduction

• Short literature review on the topic, using an appropriate referencing style.
• You will need to define terms such as urban hydrology. Answer assignment Question 1 as part of the introduction.
• State the aims of the assignment.

Methods

• Brief summary of how you went about calculating the data for your report and the methods you used in your research of the topic.

Results

• You will present the data and calculations you undertook in the section above on Data and calculations.
• You can present this in any way you wish, but good use of figures and tables is critical. Be imaginative! You should reproduce the cross section and tables provided above as a minimum.
• You need to describe, in the text, the values you have calculated and any trends you see in the data and support this with figures (i.e. put the text first!). You should never put a figure or table into a report and then provide no description of what they show. Answer assignment Question 2 in the results.
• Make sure you add titles to your figures and tables and you place these into the correct locations in the report.
• You can choose to include any other information you think is necessary to present the data.

Discussion

• • This is where you interpret the data and answer assignment Questions 3 and 4. This should be a coherent body of text with a well argued and researched case (i.e. no dot points).
  • You may chose to use subheadings to define each question/section – this is fine.

• To do this section well you will need to relate your answers to the literature and use an appropriate referencing style.

Conclusion

• One paragraph summary of findings.

Reference list

• • Set out in the style of the journal Geomorphology.
  • At least 10 scientific references should be used in your assignment including Chin et al. (2013).

IntroductionThe fluvial system gets affected drastically by the changes in the urbanization more than any other activities by the human. In the paper by Chin et al., 2013, it has been shown how urbanization affects the river channels and what the nature of it is. They also show how the changes in land coverage and hydraulic as well as sediment affect the channel morphological properties and also the aquatic life.

Urban channels can be produced up to fifteen times larger compared to its natural counterparts due to the morphological (Bernhardt et al, 2002,2005) adjustments. They give plans for the scope for the fluvial geomorphology which takes into a complete approach with the restoration wherever possible. These are in line with an urban future which can easily be sustained (Hobbs et al, 1996).

Earth’s surface is changed when the natural land cover is replaced with the impervious surfaces by the urbanization. Sewers and different flood prevention measures leads to the changes in the water course and also to the river networks. Hydrolofical and sedimentological process gets disrupted in the process and causes the alterations in the river channel geometry.

Restoration of urban streams is not only expensive but also very difficult compared to the case where resotoration is done in less densely inhabited catchments. The extent to which spatial urban restoration can be achieved is limited by the high value of the property as well as densely packed human infrastructure (like roads and sewer lines). The storm waters and the allied sediment and pollutant leads to the limitation in the scope for the restoration to adverse effects (Bernhardt, E.S. and Palmer, M.A. 2007).

Catchment urbanization usually causes the streams to change in the direction of three axes 1) simple geomorphic change in the heterogeneity of the area and also the reduction in the connectivity of the flood plan 2) social value gets diminished in the stream channels making it not worthy and it should be avoided for the recreation purpose 3) as there is simplification in the ecology, stream biodiversity gets reduced and thus the ecosystem of the stream does not function (Alberti et al, 2003). This leads to the reduction in the capacity of the streams and the declined downstream loss of the nutrients. So there are many constraints in the restoration of the urban stream channel and this makes it highly improbable that pre urbanization state of the stream channel will ever be achieved (Bernhardt et al, 2002). The main objective of the efficient restoration should instead be to make the movement (Coulson, H. 1959) of the stream far back in the direction of the three axes to the larger extent possible provided the constraints that exist. As of now, all the restoration efforts are mainly focussed on the channel form restoration and also the maintenance (Arnold C. & Gibbons C. ,1986) of the channel stability in artificial ways upon advancement in the direction of axes 1 and 2. The third axes of the improvising the biological systems/ecology is generally avoided (Brookes, A. ,1988).

The aim of the report is to use the information to calculate the flow velocity and discharge for the channel cross section provided for three different roughness (Manning’s n) values. Detailed research is carried out to examine urban stream restoration approaches and their effects on stream flow and storm flow (hydrology).

Methods

From the cross sectional view of the figure, we get the ban full depth as well as width.

Now ,

Flow velocity equation

We know that for flow velocity

V = [(D2/3) x (S1/2) / n], where

V = mean channel velocity (m/s)

D = flow depth (m)

S = water surface slope (m/m; often approximated by the slope of the bed)

n = Manning's roughness coefficient

Discharge equation

For the discharge

discharge = velocity x cross-sectional area

Q = V x A, where

Q = discharge (m3/s)

V = velocity (m/s)

A = cross-sectional area (m2)

These equations are used to flow velocity and discharge for different scenarios.

Results

From the cross sectional view of the figure, we get the bank full depth as well as width.

Now cross sectional area=depth*width

Table 1 Hydrology of an urban stream at Macquarie University

Sample calculation

For scenario 1; Manning’s roughness factor, n=0.007

Flow depth, D= 20 m

Slope, S=0.005 m/m

So, flow velocity,

V=[(D2/3) x (S1/2) / n]

=(202/3 0.0051/2)/0.007

=74.429 m/s

Discharge ,

Q = V x A

=74.429*200 m3/s

=14885.8 m3/s

Table 2 Roughness scenarios, flow velocity and discharge characteristics of an urban stream at Macquarie University

As can be seen from the data, with the increase in the manning roughness factor the flow velocity decreases and it also leads to the reduction in the discharge velocity. So the roughness has huge impact on the stream flow.

Discussions

There are five broad methods by the means of which one can manage urban fluvial networks. These comprise land use planning that takes into account the management of the urban area within the catchment, retention of precipitation, urban runoff delaying, and effects management in the urban area and finally plans for the consequences in the downstream.

If the aim of urban stream restoration is to reduce flow velocity to improve public safety, minimise sediment erosion and improve physical structure (i.e. geomorphology), we will use management of effects in the urbanized area and to alleviate probable effects of the urban drainage. The way to do the restoration is by reduction in the channel velocities by incorporating roughness. This will have room for the delayed pollutant loads. As can be seen from the data, with the increase in the manning roughness factor the flow velocity decreases and it also leads to the reduction in the discharge velocity. So the roughness has huge impact on the stream flow. Separation of foul water and storm water system is also required. Channel residence time can also be increased.

There are lot of probable benefits of urban stream restoration which are listed below.

• Improvement of the storm water quality by means of natural systems and riparian filtering
• Improvement in the drainage and in the control of flood
• It also improves the demand management and also leads to the reduction in pollution change.
• Improvement in the temperature control can also be achieved by means of shading of streams.
• It also leads to the improvement in the maintenance of base flows, reduction in flow and also it attenuates the flood.

Conclusions

If the aim of urban stream restoration is to reduce flow velocity to improve public safety, minimise sediment erosion and improve physical structure (i.e. geomorphology), we will use management of effects in the urbanized area and to alleviate probable effects of the urban drainage. The way to do the restoration is by reduction in the channel velocities by incorporating roughness. This will have room for the delayed pollutant loads. As can be seen from the data, with the increase in the manning roughness factor the flow velocity decreases and it also leads to the reduction in the discharge velocity. So the roughness has huge impact on the stream flow. Separation of foul water and storm water system is also required. Channel residence time can also be increased.