Note: The total flow from a Subcatchment is the sum of the flow from the impervious area with and without depression storage and the pervious area with depression strorage. The same width, slope but different roughness applies to the impervious and pervious portions of the subcatchment.
Note: There are Three Types of Surfaces in each Subcatchment of SWMM 5. The overall depth in a subcatchment is the weighted average of the impervious without depression storage area, the impervious with depression storage area and the pervious area depth. The depths on each type of area are independent of each other.
Figure 1: The processes that occur on each type of Subcatchment Area.
Figure 2: The three independent Depths on a Subcatchment. The SWMM 5 reported Depth is the weighted average of the three depths.
Note: The surface runoff is a non linear function of the independent depth in both the pervious and impervious areas of the subcatchments. No surface runoff occurs until the depth over either the impervious or pervious area is greater than the respective depression storage (Figure’s 1, 2, 3 and 4).
Figure 1: Surface Runoff, Depth and Depression Storage Relationship.
Figure 2: Subcatchment Runoff and Depth over time with a Subcatchment Width of 500 feet.
Figure 3: Subcatchment Runoff and Depth in a Scatter Graph with a Subcatchment Width of 500 feet.
Figure 4: Subcatchment Runoff and Depth in a Scatter Graph with a Subcatchment Width of 2000 feet.
Note: How to Make a New Project INI file for InfoSewer
Step 1: Make a new InfoSewer Project as a New Empty Map and use the ArcGIS Default as the spatial reference.
Step 2: Save your new empty model.
Step 3: Copy your old model DB folder to the new MyEmptyModel DB folder
Step 4: Open up the mxd file MyEmptyModel and Initialize it – it should be a valid model now.
Note: The depth in a manhole or node in SWMM 5 can be higher than the depth in the connecting links if the link is surcharged. Typically the upstream link depth is equal to the upstream node depth (if there is not link offsets) and the downstream link depth is equal to the downstream node depth (if there is no offsets) until the link is surcharged and then the node surcharge depth algorithm is used in SWMM 5 and point iteration equation is used to calculate the surcharge depth in the node.
