Interface Files

The file formats for the different types of interface files used by GeoSWMM are described below.

Rainfall and Runoff Files

The rainfall and runoff interface files are binary files created internally by GeoSWMM that can be saved and reused from one analysis to the next. The rainfall interface file collates a series of separate rain gage files into a single rainfall data file. Normally a temporary file of this type is created for every GeoSWMM analysis that uses external rainfall data files and is then deleted after the analysis is completed. However, if the same rainfall data are being used with many different analyses, requesting GeoSWMM to save the rainfall interface file after the first run and then reusing this file in subsequent runs can save computation time.

The rainfall interface file should not be confused with a rainfall data file. The latter is an external text file that provides rainfall time series data for a single rain gage. The former is a binary file created internally by GeoSWMM that processes all of the rainfall data files used by a project.

The runoff interface file can be used to save the runoff results generated from a simulation run. If runoff is not affected in future runs, the user can request that GeoSWMM use this interface file to supply runoff results without having to repeat the runoff calculations again.

Hot Start Files

Hot start files are binary files created by GeoSWMM that save the current state of the study area’s groundwater and conveyance system at the end of a run. The following information is saved to the file:

• The unsaturated zone moisture content and water table elevation for each subcatchment that has a groundwater zone defined for it.
• The water depth and concentration of each pollutant at each node of the system.
• The flow rate and concentration of each pollutant in each link of the system.

The hot start file saved after a run can be used to define the initial conditions for a subsequent run.

Hot start files can be used to avoid the initial numerical instabilities that sometimes occur under Dynamic Wave routing. For this purpose, they are typically generated by imposing a constant set of base flows (for a natural channel network) or set of dry weather sanitary flows (for a sewer network) over some startup period of time. The resulting hot start file from this run is then used to initialize a subsequent run where the inflows of real interest are imposed.

It is also possible to both use and save a hot start file in a single run, starting off the run with one file and saving the ending results to another. The resulting file can then serve as the initial conditions for a subsequent run if need be. This technique can be used to divide up extremely long continuous simulations into more manageable pieces.

RDII Files

The RDII interface file is a text file that contains a time series of rainfall-dependent infiltration/inflow flows for a specified set of drainage system nodes. This file can be generated from a previous GeoSWMM run when Unit Hydrographs and nodal RDII inflow data have been defined for the project, or it can be created outside of GeoSWMM using some other source of RDII data (e.g., through measurements or output from a different computer program). The format of the file is the same as that of the routing interface file discussed below, where Flow is the only variable contained in the file.

Routing Files

A routing interface file stores a time series of flows and pollutant concentrations that are discharged from the outfall nodes of drainage system model. This file can serve as the source of inflow to another drainage system model that is connected at the outfalls of the first system. A Combine utility is available on the File menu in EPA-SWMM 5.1 that will combine pairs of routing interface files into a single interface file. However, this option is currently unavailable in GeoSWMM but the users can generate these files after exporting the model input file for EPA-SWMM 5.1 and then by performing model simulation in EPA-SWMM 5.1. This combining utility allows very large systems to be broken into smaller sub-systems that can be analyzed separately and linked together through the routing interface files.

A single GeoSWMM run can utilize an outflows routing file to save results generated at a system's outfalls, an inflows routing file to supply hydrograph and pollutograph inflows at selected nodes or both.

RDII/Routing File Format

RDII interface files and routing interface files have the same text format:

1. The first line contains the keyword "SWMM5" (without the quotes)
2. A line of text that describes the file (can be blank)
3. The time step used for all inflow records (integer seconds)
4. The number of variables stored in the file, where the first variable must always be flow rate
5. The name and units of each variable (one per line), where flow rate is the first variable listed and is always named FLOW
6. The number of nodes with recorded inflow data
7. The name of each node (one per line)
8. A line of text that provides column headings for the data to follow (can be blank)
9. For each node at each time step, a line with:
10. • The name of the node
    • The date (year, month, and day separated by spaces)
    • The time of day (hours, minutes, and seconds separated by spaces)
    • The flow rate followed by the concentration of each quality constituent

Time periods with no values at any node can be skipped. An excerpt from an RDII / routing interface file is shown below.