Converting Large SSA model from Rational to SCS TR 55 Hydrological Method

Here is a workflow to change a large model from one Hydrological method to another. You may want to do this for a number of reasons. But SSA has very limited tools for bulk updating of data, given below are some work arounds to speed up the updating of data.

1. In SSA Change the Hydrological Method

a. Go to Input-> Project options. Change the hydrological method from Rational to SCS to Tr 55.

b. This will change the settings available under each subbasin, allowing a Curve Number (CN) to be entered.

2. Update the Subbasin Curve Numbers (CN)

Now you have to update the CN numbers for each Subbasin Unfortunately SSA does not provide a method to do this in bulk that I know of. To enter the curve number quickly to a large amount of sub basins you change use the SSA export to GIS tool and then edit the subbasin shp file data in Map 3D and reimport the subbasins.

To do this.

In SSA

a. Go to file export GIS export.

b. Choose file locations.

c. Select the sub basins only.

d. Select all properties.

e. Click export.

In Civil3d

a. In Civil 3D / Map3D type “mapwspace”.

b. Choose data connect. Show grounds to the shape files in connect.

c. Select everything in the drawing an Checkout all the information for editing.

d. Turn on the table of object data.

e. All the sub basin objects again.

f. Select to check all the updated objects into the shape on again.

g. Close the updated file.

Returning to SSA

a. Delete the existing sub basins by using the Polygon Selection tool. Draw a polyline around all the subbasins right click, and select done. To close the polygon.

b. Now do a group delete go to the edit menu with selection Polygon still showing and select “group delete” second from the bottom on the menu.

c. Choose to delete subbasins only.

Import Updated Subbasins from Shp file.

a. Go to file import GIS import.

b. Browns to the updated shp files of the sub basins and choose import.

c. The sub basins will import with the new CN values you assigned. To the right object data fields.

3. Update the Time of Concentration

a. You may have noticed that the time of concentration has been updated or set to zero for all your Sub-basins to fix this do a group edit.

b. Use the Polygon selection tool again to select all Sub-basins.

c. Go to edit group edit third from the bottom.

d. Choose sub basins time of concentration replace with say 10 minutes.

4. Assign Rain Gauges to Subbasins

Now to get SCS TR-55 method to run you have to assign Rain Gauges to each Sub-Basin. Again there is no command to do this in bulk in SSA. You can use the following work round if you like:-

a. Create a Rain Gauge.

b. Copy the Rain Gauges name

c. Export your SSA file to a swmm file.

d. Open the swmm file in notepad.

e. Search for the Sub Basin Section in the text file.

f. Do a find and replace on the * with the sub basin name copied above.

g. Save the updated file swmm .inp file.

Return to SSA

a. Go file import browse to the updated swmm file in and import.

You should now have a file with subbasins assigned rain gauges and should be able to run an analysis.