The Environmental Impact of Dams (Research Report)

| January 7, 2015

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Research Report: The environmental impact of dams
For this report you will examine the 1st, 2nd and 3rd order effects of a dam on a selected Australian river and describe any management actions that can be implemented to mitigate these effects. You will need to submit your assignment as a report, including references, figures and tables.
1. Select an Australian River which has been dammed for at least 30 years and for which hydrological data are available at a gauging site downstream of the dam for at least 30 years prior to damming and for the post-dam period.
2. Gather background information relevant to your assignment on the dam the river and its catchment. This is all important information and should include background information on catchment size, rainfall, stream order, reason for dam being built hydropower, irrigation, domestic water supply, flood control etc.
3. Determine the 1st order effects – that is changes in the flow regime, sediment
regime and temperature regimes downstream of the dam
• Characterise the hydrology of that river at gauging site downstream of the dam for the pre-dam and post-dam periods. Figures and table will be expected to be used. Important components to consider are; has there been a change in the annual volume of water, mean annual flows, size of individual flows, the main seasonal period of flows.
• Determine the sediment trap efficiency of the dam and the likely changes to the sediment regime of the river downstream of the dam
• Determine the nature of the dam off take (multi-level or single bottom-level) and the likely changes to the temperature regime of the river downstream of the dam
4. Determine/or assess 2nd order effects – that is changes to the river channel.
Determine what channel changes are likely to have occurred as a result of the changes to water and sediment regimes downstream of the dam. Use any empirical evidence that you can find about the river itself as well as your theoretical understanding. Empirical evidence may be in the form of specific studies that have been on your river or even raw data on channel morphology.
For example, channel cross-sections at gauging station sites may be surveyed at regular intervals to recalibrate the discharges for given river heights. These cross-sections may be available from your local water authority or council.
5. Determine the 3rd order effects – ecological changes
• Determine what ecological changes are likely to have occurred as a result of the changes to water, sediment and temperature regimes and channel changes downstream of the dam. As for second order effects, base your comments on your theoretical understanding as well as any empirical evidence you can find. You may be able to find specific studies that focus on ecological changes. You may also be able to access large scale regional surveys of ecological condition that include your river such as the Sustainable Rivers Audit, an on-going program run by the Murray-Darling Basin Authority or the National Land and Water Audit carried out by the Australian Government. Alternatively, state government Authorities such as DECCW in NSW or local Catchment Management Authorities may have conducted smaller-scale surveys that include your river.
6. Management options
• What specific management actions, if any, that have been instituted to mitigate the various 1st, 2nd and 3rd order effects of the dam?
• What effect, if any, do you think they have had?
• What, if any, other management actions could be implemented?
• What, if any, are the impediments to the implementation of these actions?
Report structure
Present your assignment in report-form using following sections and content guides:
1. Introduction
• Describe the context for your report (ie why be concerned with dams?)
• Describe the conceptual framework you will use to explore the effects of the dams (1st, 2nd, 3rd order effects)
2. Study area and methods
• What river have you chosen?
• Where is it located?
• What is the approximate size of the river?
• What land uses occur in the catchment?
• What dams have been built,
• Where are they and when were they built,
• What is the capacity of the dam and what purpose does it serve (hydro- electricity generation, domestic water supply, irrigation)
3. Results and discussion
Present your results and answers with regard to:
• 1st order effects o 2nd order effects o 3rd order effects
• Management actions
Suggested readings
There have been many studies of the impact of dams on rivers. A useful starting point is the international journal River Research and Applications formerly known as Regulated Rivers: research and management
Assessment criteria for Research Report
Assignments will be assessed on content of the report (all necessary information included, quality of arguments) (~30%) and on the format and presentation of your report (~10%). Format and presentation refers to the use and correct citation of appropriate literature, English expression, succinctness and the overall quality of the presentation of the report (consistent use of headings, correct labelling of figures and tables etc.).
Below are some questions from students and answers and comments from the professor that will help this this report:
Question from several students:
Student 1: In the assignment instructions it says in the 1st order effect of dams to determine the sediment trap efficiency (TE) of the dam. I found an article showing how this is calculated according to Brune, Churchill and Chen. I find this to be a little out of my depth mathematically. Do we have to determine this? or can we find a study on the subject river or similar river type (in my case with significant grazing and some forestry in the catchment and not much riparian veg.) and dam type?
Student 1: an update on my lack of mathematical ability. I have used the TE according to Brune which seems to be the simplest, but I calculate the TE as 136%. From reading it appears that the TE is different for different sediment types eg suspended or larger bed load etc. But the Brune method doesn’t consider this? Or am I not reading correctly? The dam capacity is 1,150,000 ML and the annual inflow is 820,702 ML. Some confirmation on whether a TE can be greater than 100% would be good.
Student 2: Are we expected to determine using mathematical equations? Or is it ok to provide a brief discussion?
Answer: The Sediment Trap Efficiency according to Brune is the easiest to use – it is not difficult at all. Basically it is saying that the ability of a dam to trap sediment is related to the size of the dam relative to the amount of water flowing into the dam. So – a large dam capacity that experiences a small inflow is likely to have a high trap efficiency – ie will likely trap all sediment flowing into it. Conversely, a small dam that experiences relatively high inflows will likely trap less sediment.
The trap efficiency of a dam is also related to the size of the incoming sediment – this is where the Churchill method is better but more involved. Larger sediments are more likely to be trapped by a dam than smaller sediments. So this preferential trapping is an important aspect to consider downstream of dams. Sediment transported downstream of dams changes in size.
Question: I was just wanting some clarification on whether we are to develop our own methods, or you just want us to simply to discuss the 1st, 2nd, and 3rd order of effects.
Answer: No you do not need to develop your own methods – you do need to tell us how you got the results you got.
Comment from professor: The most reliable place to go for long term river flow data is the MDBA site
and click on the region of the map that want data from. This will take you to a detailed map of that area showing the gauge locations. If you click on a gauge, you will be taken to a new page such as this one:
These pages show the latest recordings and graphs of the last month’s data. To get the older data you need to click on the link saying “download CSV”.
This will download a csv file with all the historical data which can be opened in excel (and saved as an excel file if you wish).
Below are the links that will help you in particular with this assignment:
Murray River at Hume dam is here
Murray River at Corowa gauge is here
I have obtained the mean discharge and mean water levels from 1909 at the Corowa Gauge. So considering the Hume Dam was completed in 1936, please uses the Corowa data.
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