Canal Seepage
The Canal Seepage method category is used to model seepage from the canal. This category controls how to apply the seepage.
NoneThis is the default method. It performs no calculations.
There are no slots specific to this method.
Input SeepageThis method allows you to input values into the Seepage slot manually, or to set the slot with a rule.
Slots Specific to This Method
Canal Seepage
Type: SeriesSlot
Units: FLOW
Description: the calculated amount of flow lost as seepage
Information:
I/O: Input only
Links: May be linked to the Inflow slot on a Groundwater Storage object or to a series slot on the Data object.
Proportional SeepageThis method uses constant parameters to model seepage. Seepage is lost from the canal after any flow that exceeds the Maximum Capacity is spilled, but before the flow is routed.
Slots Specific to This Method
Canal Seepage
Type: SeriesSlot
Units: FLOW
Description: the calculated amount of flow lost as seepage
Information:
I/O: Output only
Links: May be linked to the Inflow slot on a Groundwater Storage object.
Maximum Seepage
Type: SeriesSlot
Units: FLOW
Description: represents the maximum amount of flow that can be lost as seepage
Information:
I/O: Optional; this slot is not used if it is not input.
Links: Not linkable
Seepage Flow Fraction
Type: ScalarSlot
Units: NO UNITS
Description: represents the fraction of Inflow that is lost as seepage
Information: Entered as a decimal value which is greater that or equal to zero but less than one.
I/O: Optional; set to zero if not input.
Links: Not linkable
Method Details
Canal Seepage is calculated as follows:
Canal Seepage is then subtracted from the Inflow before the flow is routed.
Canal Seepage is accounted for when routing requests upstream (it is added it to the request).
Variable SeepageThis method uses variable parameters to model seepage. Seepage is lost from the canal after any flow that exceeds the Maximum Capacity is spilled, but before the flow is routed.
Slots Specific to This Method
Canal Seepage
Type: SeriesSlot
Units: FLOW
Description: the calculated amount of flow lost as seepage
Information:
I/O: Output only
Links: May be linked to the Inflow slot on a Groundwater Storage object.
Maximum Seepage
Type: SeriesSlot
Units: FLOW
Description: represents the maximum amount of flow that can be lost as seepage
Information:
I/O: Optional; this slot is not used if its not input.
Links: Not linkable
Variable Seepage Flow Fraction
Type: SeriesSlot
Units: NO UNITS
Description: a time series of values representing the fraction of Inflow that is lost as seepage
Information: Entered as a decimal value which is greater than or equal to zero but less than one.
I/O: Optional; set to zero if not input.
Links: Usually not linked
Method Details
Canal Seepage is calculated as follows:
Canal Seepage is then subtracted from the Inflow before the flow is routed.
Canal Seepage is accounted for when routing requests upstream (it is added it to the request).
Head Based SeepageThe Head Based Seepage method, based on the method of the same name for the reach object, calculates seepage based on the elevation of the canal water relative to the groundwater elevation. If the groundwater head is below the canal bed elevation then the seepage will be based on the difference between the canal water surface elevation and the canal bed elevation.
Note: All elevations should share the same datum.
Slots Specific to This Method
Canal Water Surface Elevation
Type: TableSlot
Units: LENGTH
Description: Average elevation of the water in the canal
Information: Should have the same datum as stage and the previous water table elevation
I/O: Required input
Links: Not linkable
Seepage
Type: Series Slot
Units: flow
Description: The canal loss to groundwater
Information: A positive number represents a losing reach while a negative number represents a gaining reach
I/O: Output only
Links: Usually linked to the groundwater object
Previous Water Table Elevation
Type: Series Slot
Units: length
Description: The previous elevation value computed by the connected groundwater object
Information: Seepage is computed based on the difference between the current canal water surface elevation and the previous water table elevation
I/O: Output only
Links: Linked to the Previous Elevation slot on the connected groundwater object
Conductance
Type: Scalar slot
Units: area per time
Description: The riverbed conductance
Information: The conductance is defined as the hydraulic conductivity of the streambed material, multiplied by the width of the streambed bottom, multiplied by the length of the stream segment, divided by the streambed thickness (Conductance = KwL/m).
I/O: Input or computed; see Canal Conductance Specification.
Links: Not linkable
Canal Bed Elevation
Information: Scalar Slot
Units: length
Description: The elevation of the canal bed at the center of the canal segment; that is, average canal bed elevation.
Information: Should have the same datum as Canal Water Surface Elevation and the Previous Water Table Elevation
I/O: Required input
Links: Not linkable
Method Details
The method computes the seepage to groundwater as follows:
• If the Previous Water Table Elevation is greater than the Canal Bed Elevation:
• If the water table elevation at the previous timestep is below the Streambed Elevation:
Note: These equations use the water table elevation at the previous timestep. This simplification is done to avoid iteration problems that would result if the current groundwater elevation was used. A positive seepage is limited to be less than or equal to the Inflow to the canal.
Revised: 08/02/2021