Step 1: Draw the subcatchment boundaries and flow lines

Subcatchment boundaries and flow lines can be drawn by hand, or you can use the automatic watershed analysis tools in Carlson Hydrology to draw these layers based on the terrain model.

Although flow lines are not required, they are recommended for automatic calculation of the time-of-concentration using the Curve Number (Lag) method.

Each subcatchment is also labeled with a number that will associate it with the matching node in HydroCAD.

Step 2: Draw the soil group boundaries

Draw the soil group boundaries based on your own soil survey, or import NRCS soil maps directly into your drawing.

Step 3: Draw the ground covers

Using the standard HydroCAD ground-cover table, draw the pavement, rooftops, grass, and other elements of the site.  Or you can create a custom ground-cover table.

Ground covers are drawn as closed polylines, with a default ground cover that is automatically applied to any unmapped area.

HydroCAD also associates each ground cover with a specific land-use, allowing you to perform automatic pollutant loading calculations.  Just set the desired pollutant concentrations, pick the calculation method, and view the reports.

Step 4: Putting everything together

Now that we have the subcatchments, soil groups, and ground covers, we're ready to extract the individual sub-areas for each subcatchment.  When you click the "Update" button, Carlson Hydrology finds the intersections of all the layers and builds the table of sub-areas for each subcatchment.

Step 5: Subcatchment data is automatically transmitted to HydroCAD

When the layer analysis is complete, the results are automatically transmitted to HydroCAD for additional modeling and analysis.  Setup your flow routing, define ponds and other drainage elements, just as you normally would in HydroCAD.

Step 6: Working with HydroCAD and Carlson Hydrology

HydroCAD and Hydrology have been carefully designed to work together.  By having both programs open at the same time, changes to the site plan can be quickly analyzed by Hydrology, and the updated data is automatically merged into the HydroCAD model, causing the report windows to be immediately updated.

With Hydrology and HydroCAD, changes to your existing or proposed conditions are no longer a problem.  Just edit the necessary CAD layers and press Update, and your HydroCAD model is instantly updated.

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