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20 Cards in this Set
- Front
- Back
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What is the function of a water supply reservoir? |
To stabilise the flow of water either by; -regulating a varying supply in a natural stream -satisfying a varying demand irrespective of natural flow |
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What are the 3 main types of reservoirs? |
-direct supply -regulating -pumped storage |
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Describe direct supply reservoirs |
-oldest type -formed by damming river -stored water is piped directly to treatment plant or demand centre -can be expensive -can merge 2 catchments supply by divert supplementary water there via canal/pipe -compensation flow |
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what are the advantages of allowing for a compensation flow? (such as in direct supply reservoirs)
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-the regular releases ensure a healthy downstream environment -ensures downstream user needs are met -usually fixed by legislation |
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Describe a regulating reservoir
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-releases stored water into the river -river acts as a pipe to the treatment plant/demand centre (cost effective) -cheaper than equivalently sized direct supply reservoirs -more beneficial to river environment as greater flow -generally satisfies bigger demand than direct |
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Describe a pumped storage reservoir
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-similar to direct supply except inflow is pumped -commonly associated with hydroelectric schemes (higher elevation to provide head for turbine) -for hydroelectric: water pumped to reservoir during off peak electricity demand periods & released during peak demand |
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what is the definition of yield in terms of reservoir water?
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The constant rate of supply which can be maintained from the reservoir through a historic drought
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What is active storage?
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It is the provision for the yield during drought
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What is dead storage?
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The provision for sediment (usually below active storage)
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What is flood storage?
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The extra provision for storing flood water
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What is compensation water?
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The release from a direct supply reservoir to meet in-steam requirements downstream of dam
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Difficulties with Primary evaporation?
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can be a major source of water loss in certain areas of the world -can therefore make it difficult to meet essential demands |
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What is seepage?
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-the continuous movement of water from upstream face to downstream face of dam ( Often impractical to accurately account for such losses with most reservoir sizing techniques) |
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What is a reservoir mass curve?
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a plot of the cumulative flow at a dam site against time (used in Rippl mass curve technique)
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What is the required storage size judged from?
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the difference between the total water available and total water demanded over the critical period
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What is the critical period?
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a phase of extreme low flow in the data record such that if the reservoir is full at the start of the period it will be empty at the end (after supplying yield)
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How is the active storage size determined from the mass curve technique?
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it is the largest vertical distance between the mass curve and cumulative demand line (storage required)
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Name 2 reasons why the storage size obtained by the mass curve technique may not be possible in reality?
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due to; topography environmental factors |
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Advantages of mass curve technique?
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-simple and easy to use -uses entire flow data record -can be used to determine yield given storage size and vice versa |
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Disadvantages of mass curve technique?
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-can only consider a constant yield per period -assumes that the reservoir is initially full -only designs for worst drought in historic record (future droughts may be worse & unable to sustain yield)-no account taken for losses-difficult to implement graphical approach on computer
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