applied hydrology rslab-ntu lab for remote sensing hydrology and spatial modeling 1 flood routing...
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Applied Hydrology
RSLAB-NTU
Lab for Remote Sensing Hydrology and Spatial Modeling
Flood Routing & Detention Basin Design
Professor Ke-Sheng ChengDept. of Bioenvironmental Systems Engineering
National Taiwan University
2Lab for Remote Sensing Hydrology and Spatial ModelingRSLAB-NTU
The storage effect
The storage effect of a water-retention structure or a channel reach can change the shape of the inflow hydrograph. Therefore two types of routing procedures are needed to calculate the outflow hydrograph. Level-pool routingChannel routing
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Level-Pool Routing (Reservoir Routing)
For a reservoir the outflow is uniquely controlled by the water depth (or stage) of the reservoir pool. Also, the reservoir storage is a single-value function of the stage.
Flow velocity in the reservoir is usually very low.
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Comparison of flow routing under invariable and variable stage-discharge relationships
Invariable S~Q relationship Variable S~Q relationship
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Discharge under variable S~Q relationship
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Reservoir routing
Modified puls method (Storage indication method)
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An example
Given the following storage-outflow relationship and inflow hydrograph, calculate the outflow hydrograph. (Use 10-minute routing interval).
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Stage~storage~outflow relationship
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Reservoir routing as a computation of mass balance
For a reservoir the outflow is uniquely controlled by the water depth (or stage) of the reservoir pool. Also, the reservoir storage is a single-value function of the stage.
As a result, given a stage the reservoir storage and outflow can be uniquely determined, if the stage~storage and stage~outflow relationships are known.
An intuitive trial-and-error approach for reservoir routing can be implemented.
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Alternative solution
Stage~storage
Stage~discharge
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Spreadsheet calculation
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Inflow-outflow-(10*storage)
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Channel routing