Storage Units are drainage system nodes that provide storage volume. Physically they could represent storage facilities as small as a catchbasin or as large as a lake. The volumetric properties of a storage unit are described by a function or table of surface area versus height. In addition to receiving inflows and discharging outflows to other nodes in the drainage network, storage nodes can also lose water from surface evaporation and from seepage into native soil.
The input parameters for a Storage Unit are listed in the table below:
| Field | Description |
| Name | User-assigned storage unit name. |
| X-Coordinate | Horizontal location of the storage unit on the Study Area Map. If left blank then the storage unit will not appear on the map. |
| Y-Coordinate | Vertical location of the storage unit on the Study Area Map. If left blank then the storage unit will not appear on the map. |
| Inflows | Click the ellipsis button (or press Enter) to assign external direct, dry weather, or RDII inflows to the storage unit. |
| Treatment | Click the ellipsis button (or press Enter) to edit a set of treatment functions for pollutants within the storage unit. |
| Invert El. | Elevation of the bottom of the storage unit (feet or meters). |
| Max. Depth | Maximum depth of the storage unit (feet or meters). |
| Initial Depth | Initial depth of water in the storage unit at the start of the simulation (feet or meters). |
| Surcharge Depth | Additional depth above the maximum depth that allows the unit to pressurize before it overflows (feet or meters). Only used for covered units. |
| Evap. Factor | The fraction of the potential evaporation from the storage unit's water surface that is actually realized. |
| Seepage Loss | Click the ellipsis button (or press Enter) to specify optional soil properties that determine seepage loss through the bottom and sloped sides of the storage unit. |
| Storage Curve |
Method of describing how the surface area of the storage unit varies with water depth:
FUNCTIONAL uses the function: Area = A×(Depth)B + Cto describe how surface area varies with depth; TABULAR uses a tabulated area versus depth curve. In either case, depth is measured in feet (or meters) above the bottom and surface area in sq. feet (or sq. meters). |
| FUNCTIONAL | |
| Coeff. | A-value in the functional relationship between surface area and storage depth. |
| Exponent | B-value in the functional relationship between surface area and storage depth. |
| Constant | C-value in the functional relationship between surface area and storage depth. |
| TABULAR | |
| Curve Name | Name of the Storage Curve containing the relationship between surface area and storage depth (double-click to edit the curve). The curve will be extrapolated outwards to meet the unit's Max. Depth if need be. |