# Hydraulic structures (Water Overlay)

The water system can be enhanced with a number of hydraulic structures. These are Buildings which transport water to, from, and between specified cells, according to their flow model and given parameters. The behavior of these Buildings can be adjusted by adjusting the related attributes.

In general, for ease of use, hydraulic structures are by default imported as underground Buildings.

In order to get more familiar with the different hydraulic structures in the Water Overlay check out Quadrant 3 of the Water Module Testbed. This Testbed is available to you as a project in the Tygron Platform.

## Types

Hydraulic structures can be either line-based or point-based:

Line-based buildings
Line-based buildings form a direct connection between two exact cells, allowing water to flow from one point to another. The flow is dictated by the Building's formula. The endpoints of a line-based Building, the exact cells which are connected by the Building, are computed based on the orientation and size of their polygon. Essentially, the furthest ends of the polygon are used as end-points. Because the cells of either endpoint are considered adjacent, any calculated flow through line-based hydraulic structures is instantaneous.
Point-based buildings
Point-based buildings add or remove water in one or more computational layers, based on their formula's. The center-point of a point-based building, the exact cell where the effect takes place, is the geometric center of the construction's polygon.
Area-based buildings
Area-based buildings add or remove water in one or more computation layers, based on their formula. In principle, all cells which the Building intersects are affected, though the exact effects may differ based on the presence of other features in those cells.

Note that the more complex the polygon is, the more difficult it is for the Tygron Platform to resolve it to a simple line or center point.

## Identification

Buildings can be identified as a hydraulic structure when this Building has the identification attribute. This is the first attribute in the described table of attributes for each hydraulic structure. They are also listed in the table above.

The identification attribute (and all other attributes used by hydraulic structures) can be configured as a key of the Water Overlay. Keys indicate which attribute of Buildings or features is used to represent specific geographical input parameters for the calculation. This can be of use when setting up a project or template which makes use of user-provided geodata.

## Total flow

When the calculation of the water overlay is completed, the total amount of water that has flowed through a specific Building is stored in an attribute in that Building. By default, this attribute is OBJECT_FLOW_OUTPUT, and the flow is expressed in m3. Since multiple water overlays can exist in the project simultaneously, the attribute name is appended with an underscore and the overlay ID such that each overlay (as they are added to the project) can write to a unique attribute.

## Water level

When the calculation of the water overlay is completed, the water levels at either side of a specific Building is stored in an attribute in that Building. By default, this attribute is OBJECT_DATUM_OUTPUT. Since multiple water overlays can exist in a project simultaneously, the attribute name is appended with an underscore and the overlay ID such that each overlay (as they are added to the project) can write to a unique attribute.

## Notes

• Only one hydraulic structure can be assigned to a particular grid cell. When the model attribute OBJECT_CORRECTION is active, hydraulic structures can be automatically moved to adjacent grid cells.
• The Base type result overlay visualizes which type of hydraulic structures are placed where.
• If a single Building has attributes related to multiple hydraulic structures, only one is selected. The selection order is: Weir, Sewer overflow, Inlet, Pump, Culvert.