Spatial Objects

Landscape Unit

A landscape unit is a collection of HRUs. A landscape units can be equivalent to a subbasin, a floodplain or upland unit, or a grid cell with multiple HRUs. Landscape units are only used for output. The landscape unit output files (water balance, nutrient balance, losses, and plant and weather) are output for HRUs, landscape units, and for the basin. Two input files are required: 1) landscape elements and, 2) landscape define. The elements file includes HRUs and their corresponding LSU fraction and basin fractions. The define file specifies which HRUs are contained in each LSU.

Routing Unit

The routing unit is the spatial unit in SWAT+ that allows us to lump outputs and route them to any other spatial object. The routing unit can be configured as a subbasin, then total flow (surface, lateral and tile flow) from the routing unit can be sent to a channel and all recharge from the routing unit sent to an aquifer. This is analogous to the current approach in SWAT. However, SWAT+ gives us much more flexibility in configuring a routing unit. For example, in CEAP, we are routing each HRU (field) through a small channel (gully or grass waterway) before it reaches the main channel. In this case, the routing unit is a collection of flow from the small channels. We also envision simulating multiple representative hillslopes to define a routing unit. Also, we are setting up scenarios that define a routing unit using tile flow from multiple fields and sending that flow to a wetland. Routing units will continue to be a convenient way of spatial lumping until we can simulate individual fields or cells in each basin.