Applied Hydrology
Flood Routing & Detention Basin
Design
Professor Ke-Sheng Cheng
Dept. of Bioenvironmental Systems Engineering
National Taiwan University
RSLAB-NTU
Lab for Remote Sensing Hydrology
and Spatial Modeling
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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 routing
Channel routing
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Lab for Remote Sensing Hydrology
and Spatial Modeling
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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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Lab for Remote Sensing Hydrology
and Spatial Modeling
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Comparison of flow routing under invariable and
variable stage-discharge (S~Q) relationships
Invariable S~Q relationship
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Lab for Remote Sensing Hydrology
and Spatial Modeling
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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+
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and Spatial Modeling
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An example
 Given the following storage-outflow relationship and inflow
hydrograph, calculate the outflow hydrograph. (Use 10minute routing interval).
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Lab for Remote Sensing Hydrology
and Spatial Modeling
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Stage~storage~outflow relationship
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and Spatial Modeling
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and Spatial Modeling
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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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Lab for Remote Sensing Hydrology
and Spatial Modeling
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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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Example of reservoir routing
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and Spatial Modeling
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Channel routing
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and Spatial Modeling
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