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Defining HEC-HMS Storage Areas

Storage areas define the elements (i.e., reservoirs, lakes, detention ponds, storage nodes, etc.) where there are one or more inflows and only one computed outflow. Inflow comes from other elements in the model, such as drainage basins, routing reaches, or diversions. If there is more than one inflow, all inflow is added together before computing the outflow. It is assumed that the water surface in the storage area pool is level.

HEC-HMS storage areas can be defined by either drawing or assigning the boundary using the following commands:

  • Draw Storage Areas
  • Assign Storage Areas

Existing storage areas can also be georeferenced to a more accurate outline representation of the water body assigned. Additionally, the user can also revise the boundaries of the existing storage areas and extract the storage area volume from the terrain model.

Drawing HEC-HMS Storage Areas

The Draw Storage Areas command can be used to manually draw polygons, one-by-one, as storage areas on the Map View. Refer to this article in our knowledge base to learn how to use the Draw Storage Areas command.

Assigning HEC-HMS Storage Areas

The Assign Storage Areas command can be used to manually associate previously drawn polylines or polygons as storage areas. Refer to this article in our knowledge base to learn how to use the Draw Storage Areas command.

Georeferencing HEC-HMS Storage Areas

The Georeference Storage Areas command is used to manually georeference each of the storage areas to the background base map displayed in the Map View. Refer to this article in our knowledge base to learn how to use the Georeference Storage Areas command.

Revising HEC-HMS Storage Area Boundary

Existing storage area boundaries can be revised using the Reshape Polygon command. Refer to this article in our knowledge base to learn how to use the Reshape Polygon command.

Extracting Storage Area Volume Curve

GeoHECHMS software can be used to calculate how much storage area a site has and what volume it holds. After defining the storage area boundary, the software automatically computes the fixed area “footprint” that the storage area occupies to define the storage volume. This method works well in situations in which the storage area does not change with depth. However, defining the storage volume in this manner results in an inaccurate representation of the storage volume for regions where the storage area varies considerably with elevation change. For regions where a more accurate representation of the storage volume is required, the user can use the Extract Storage Area Volume Curve command to extract the storage volume from the terrain model if the bathymetry of the storage area is contained in the terrain model.

Refer to this article in our knowledge base to learn how to extract storage area volume from the terrain model.

About the Author Chris Maeder

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