Once the flood wave passes, and you are on the receding limb of the flood hydrograph, the water that had gone into storage now returns to the active discharge. Wider floodplains and shallower reaches have more available storage volume, which is why flow attenuation is pronounced under these situations. Water going into storage is taken away from the flow going downstream and that is why you see a decrease in discharge as you move in the downstream direction. The physical process is as follows: As the flood level rises, water moving downstream fills in available volume. In very steep streams, you may not notice flow attenuation at all. The shallower the reach, or the wider the floodplain, the more pronounced this effect will be. You see this to varying degrees in all unsteady flow models and it is a real phenomenon. The following dialog allows for selection of tables to be created.When running an unsteady flow model with a single inflow hydrograph, why does my discharge decrease in the downstream direction for a given output profile? Users create new tables using Database -> Create River Database Tables or tool. There are three tables always required for a model creation: river lines, cross-sections and flow paths. If a table needs a user specified attribute, it is given in the User defined attributes column. The table below lists river database tables created by RiverGIS. There is a table for river lines, cross-sections etc. Model geometry data are stored in a river database tables. When a schema is created from outside the RiverGIS use the Database > Refresh Connections List or the tool. If a connection or schema was created in a previous session, it can be chosen from the DB Connection or Schema dropdown lists. RiverGIS will automatically switch to the newly created schema, as shown below. Users can create a schema in a number of ways: using pgAdmin, QGIS’ own DB Manager or from within RiverGIS dialog by choosing Database > Create New Schema or clicking tool icon from Database toolbar.
Therefore, the first step is to create a new schema for a model. Each model goes to its own schema, a kind of database directory for data grouping. Until a database and schema are set in RiverGIS window, most of the tools are inactive.Ī single PostgreSQL database can be used to store many models geometries. A term river database refers to a database used by RiverGIS.
A fundamental difference from HEC-GeoRAS is that the RiverGIS uses a PostgreSQL database with PostGIS spatial extension for data storage (see Requirements for installation instructions).
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