Reservoir

Overview

Reservoirs are open bodies of water that store flow and are connected to nodes by means of an energy-based equation. Reservoirs are considered instantly well-mixed.

The Reservoirs Table specifies the identity and physical properties of the reservoir.
Connections to nodes are specified in the Reservoir Connections table.
Reservoir area as a function of elevation is specified in Reservoir volume table, while volume is calculated in code (since 8.2)

RESERVOIR Table

A sample is given below

Example

# Description:
# Setting of Clifton Court Forebay
RESERVOIR
NAME  AREA  BOT_ELEV   
clifton_court       91.868000   -7.748      
END

The RESERVOIR table defines the name and physical properties of the reservoir. In the case of a "tank" like reservoir the area and volume are simply defined by the constant area and bottom elevation times the constant area, respectively.

Field Descriptions

NAME

Name of the reservoir. This is the identifier of the reservoir used in other tables.

AREA

Surface area (in units of million sq ft) of the reservoir at typical depth. This area is used to calculate volume changes.

BOT_ELEV

Elevation (ft) of the bottom of the reservoir.

Table Info

Identifier:

NAME

Include Block:

GRID

RESERVOIR_CONNECTION Table

See sample below

Example

# Description:
# Setting of Frank Tract Connections
RESERVOIR_CONNECTION

RES_NAME  NODE  COEF_IN  COEF_OUT   
franks_tract        103   2250.000  2250.000     
franks_tract        216   1500.000  1500.000    
END

The RESERVOIR_CONNECTION table lists reservoir connections to neighboring nodes. Flow through reservoir connections is calculated using the following formula

Q = C_to sqrt[ 2g(z_node - z_res) ] ... z_res \< z_node

Q = C_from sqrt[ 2g(z_res - z_node) ] ... z_res > z_node

Where:

C_to and C_from are coefficients representing the hydraulic efficiency of the reservoir connection and the nominal Area perpendicular to flow.
g is gravity and
z_res and z_node are the water surface elevations at the reservoir and node (node surface is assessed by means of a reference channel that has no reservoirs attached to it).

Field Descriptions

RES_NAME

Name of reservoir at which connection is specified.

NODE

Number identifying the node at which connection is specified.

COEF_IN

Coefficient from node to reservoir, greater than zero. If you compare the reservoir equation to the gate or other orifice equation you will find that the reservoir coefficient actually folds several quantities into one parameter: a flow efficiency (between zero and one) and a area of flow. If you have an observation of the area normal to flow, the coefficient should be some fraction of this aperture.

COEF_OUT

Flow direction out of the reservoir.

Table Info

Identifier:

RES_NAME, NODE

Parent Table:

RESERVOIR

Parent Identifier:

RES_NAME

Include Block:

GRID

A node may not have more than three reservoir connections and must have at least one ungated channel connection.

RESERVOIR_VOL Table

See sample below

RESERVOIR_VOL
RES_NAME                 ELEV          AREA
liberty                -61.975          0.000
liberty                -32.808          2.478
liberty                -16.404         16.220
liberty                 -3.281        272.328
liberty                 -1.640       1017.270
liberty                  0.000       1999.522
liberty                  1.640       3031.999
liberty                  3.281       4209.851
liberty                  4.921       4584.028
liberty                  6.562       5190.456
liberty                  8.202       6359.679
liberty                  9.843       6636.050
liberty                 13.123       6731.118
liberty                 16.404       6830.894
liberty                 19.685       6876.916
liberty                 22.966       6890.138
END

Since version 8.2, reservoirs can also have variable area and volume defined as a function of elevation. This table still requires the reservoir to be defined in the RESERVOIR table even though the elevation area specified in the RESERVOIR table will be ignored if it is specified here.

Field Descriptions

RES_NAME

Name of the reservoir. This is the identifier of the reservoir should have been specified in the RESERVOIR table (Elevation and area from that table are ignored)

ELEV

Elevation (ft) of the reservoir at which the area and volume are specified. This elevation is to the datum of the rest of model (currently NAVD88)

AREA

Surface area (in acres) of the reservoir at specified elevation. The area is interpolated between elevations based on the current elevation of the water level

(Reference: Annual Report 2015, Chapter 2). See Figure below for a snippet

VOLUME

Volume (in units of acre-ft) of the reservoir at specified elevation. The volume is calculated as explained here.