Creating a runoff model is very much like creating a model in the simulator window. From the file menu, choose “New Runoff Model”. This will get the palette and a workspace as shown.

As with the simulator, choose the basin icon (the one on the left) and drop it onto the workspace by double clicking. All mouse gestures for the runoff model are the same as for the simulator. Open the basin either by clicking on it with the right mouse button and choosing “Open” from the pop up menu or by double clicking on the icon in the workspace.

The slot display is the same as for the simulator, as are the Basin Name and Display Name fields.

The edit boxes on the right side of the dialog have the following meanings:

Snow Parameters

• Dt is the density threshold above which the snow pack collapses and begins to melt.

• Dns is the density of newly falling snow.

• Melt is the rate (in inches of snow water equivalent) at which the snow back begins to melt once it has collapsed.

Unit Hydrograph

• Delta is the duration of excess precipitation.

• Lag is the time from the centriod of excess precipitation to the peak of the hydrograph.

• Tb is the base time of the basin hydrograph.

• Troute is the routing time for water coming in to the top of the basin to reach the basin outlet.

Parameters Group

There are two buttons in this group which activate secondary displays. The Area / Elevation button brings up:

This dialog must be filled out first, it is what establishes the elevation bands for the basin. The elevation column may have any increment, or it may have a single elevation with no bands if snow melt is not going to be a factor.

Perhaps the only column that needs explanation is the Precip Wgt. This allows for orographic effects in the distribution of precipitation. Thus, a uniform depth of precipitation is applied to the entire basin at the beginning of each time step. That precipitation is then multiplied by the band weighting factor and adjusting the depth for that band.

Notice also that the SCS curve numbers need not be uniform

The other button in the Parameters group is Initial Conditions which brings up the following dialog:

The elevations are taken from the Area / Elevation dialog which must be filled out first. Notice that antecedent moisture may have fractional values between one and three. The software will interpolate a curve number based on the AMC for the elevation band.

Snow water equivalent and snow depth are denominated in inches at present.

The Unit Hydrograph group has a button that will pop up the following display:

The first column in the graph is the ratio of time to time to peak of the unit graph. The second column is the ratio of flow to max flow. The hydrograph shown in the figure is a triangle, but RiverSim is not limited to such.