Swmm users manual

It supersedes the material in the older SWMM 4 manual. There were some unfortunate formatting glitches introduced into the hydrology reference manual when converting the original MS Word manuscript to a compliant PDF file such as misaligned equation numbers, some blank pages, and awkward page breaks. Also, Wayne Huber's name was inadvertently omitted as a co-author on the title page. It is open source public software and is free for use worldwide.

SWMM is used for single event or long-term simulations of water runoff quantity and quality in primarily urban areas—although there are also many applications that can be used for drainage systems in non-urban areas. SWMM provides an integrated environment for editing study area input data, running hydrologic, hydraulic and water quality simulations, and viewing the results in a variety of formats.

These include color-coded drainage area and conveyance system maps, time series graphs and tables, profile plots, and statistical frequency analyses. These include the ability to do the following:. SWMM accounts for various hydrologic processes that produce runoff from urban areas, which include the following:.

Spatial variability in all of these processes is achieved by dividing a study area into a collection of smaller, homogeneous sub-catchment areas.

Each of the areas contains its own fraction of pervious and impervious sub-areas. Overland flow can be routed between sub-areas, between sub-catchments, or between entry points of a drainage system. SWMM can estimate the production of pollutant loads associated with stormwater runoff. This version is the official release of the older SWMM4 program, but it's somewhat out of date. The zipped file contains the self-installing program, support files, example files, and release notes.

Beginner or seasoned user, our flexible training options help you understand and master the full capabilities of PCSWMM. Please note that trial license requests are typically processed Monday to Friday from 8 a. Please also note that if you are affiliated with an educational institution, you must apply for a CHI educational grant instead of a trial license.

Thank you for contacting us. Please note our office hours are Monday to Friday from 8 a. Version: 5. SWMM 5. Released: July 20, Engine updates A mix of infiltration methods can now be used within a project. Monthly adjustments to depression storage are now applied only to the pervious area of subcatchments instead of to both pervious and impervious areas. The Status Report now includes a grouped frequency table of the variable routing time steps used during a simulation.

An error in the average summary statistics reported for projects with a reporting start date later than the simulation start date was fixed. A fatal error is now issued if a storage node's area curve produces a negative volume when extrapolated to the node's full depth. A pollutant mass balance error occurring when very shallow storage units lost all inflow to flooding was fixed. Conduit evaporation and seepage losses are now applied directly to the conduit's flow rate instead of just to the downstream node's inflow to reduce water quality mass balance errors.

Released: March 16, Engine updates Fixed a refactoring bug that produced incorrect rainfall when the same time series was used by one rain gage assigned to a RDII Unit Hydrograph and also by another gage assigned to a subcatchment.

Fixed skipping the first rain gage in a project when checking if two gages have the same station ID but use different data files. Fixed a program crash when running projects with LID units but no subcatchments.

Fixed having LID underdrain pollutant loads incorrectly added to the mass balance totals. Fixed the program from hanging when an LID unit sent its outflow back onto the pervious area of its own subcatchment. Fixed a failure to re-initialize layer volumes as each LID unit is evaluated which could cause incorrect results for certain combinations of LID units. Fixed street sweeping being ignored when the sweeping period began with a higher day of the year than the end of the period.

Fixed incorrect adjustments being made for conduit evaporation and seepage losses under dynamic wave flow routing. Fixed having soil moisture deficit recovery be ignored for Green-Ampt exfiltration from storage units.

Fixed a possible program crash when using the option to report average values within each reporting time interval instead of point values. Released: July 31, Engine updates A subcatchment's depression storage depth, its pervious surface roughness Mannings n and its hydraulic conductivity can now be adjusted on a monthly basis by assigning monthly time patterns to these properties.

For conductivity, a subcatchment-specific adjustment pattern will override any project-wide set of climate adjustment factors. Permeable pavement LID units subjected to clogging over time can now have their permeability only partly restored at periodic time intervals The following options were added to control flow out of LID units through their underdrains: A storage layer water depth above which a closed drain automatically opens. A storage layer water depth below which an open drain automatically closes.

A control curve that specifies how the nominal drain flow rate is adjusted as a function of the head seen by the drain. Pollutant removal percentages can now be assigned to LID processes that have underdrains. The removals apply to flow leaving the unit through the drain and not to any surface overflow from the unit. The Subcatchment Runoff Summary Report now includes both pervious and impervious total runoff volumes prior to any LID treatment for each subcatchment. A choice of method used to handle surcharging has been added to the list of Dynamic Wave options.

A closed vessel can now be modeled as a storage unit node that is allowed to pressurize up to a designated Surcharge Depth value. If this depth is 0 then the unit is modeled as before as an open vessel. A weir's discharge coefficient can now be allowed to vary with head across the weir by assigning it a Weir Curve see Weir Properties.

Weir curves tabulate coefficient values at specific head levels. When the upstream offset of a regulator link is below the invert of its downstream node it is now automatically raised only for Dynamic Wave flow routing with a warning message issued. For other flow routing choices only the warning message is issued and no automatic offset adjustment is made. Users can now choose to set a periodic time step for control rule evaluation.

If this step is 0 then rules are tested as before at every routing time step. The option was added to have time series results for a project's nodes and links be reported as average values computed over a reporting time step instead of being interpolated point values at the end of the reporting time step. The following bugs were fixed: Unused rain gages are no longer examined when adjusting the wet runoff time step.

The Minimum Nodal Surface Area dynamic wave routing option was being used as surface area always available at a node instead of an amount available only when the surface area of the node's connecting links fell below it. The top width of a full closed rectangular cross section shape is now set to 0 since it can no longer supply any surface area.

An incorrect reporting of flow continuity error for systems with backflow through outfall nodes was fixed. Released: March 14, New features The direct. Released: August 22, New features Detailed flow routing can now be restricted to a set of pre-defined event periods.

This fixes the problem of having no inflitration out of a Rain Garden. Monthly adjustments for hydraulic conductivity are now also applied to the internal Green-Ampt "Lu" parameter which varies with the square root of conductivity. A check was added to insure that subcatchment imperviousness does not exceed percent.

Runoff time steps are now adjusted to stay aligned with the Report time step making model validation easier. A time step correction was made when computing the outflow volume produced by an outfall that sends its outflow back onto a designated subcatchment.

The LID routines were modified so that native soil infiltration is satisfied first when it occurs along with underdrain flow, instead of the other way around. The allowable offset height for an LID underdrain is no longer limited to the top of the storage layer thus allowing upturned drains to be modelled.

If the offset of the opening of a regulator link is below its downstream node invert it is now raised to the invert level and a warning message is still issued. A weir with an open rectangular shape and non-zero slope parameter will no longer generate an input error message - the slope value is now ignored.

Node surcharging is now only reported for dynamic wave flow routing and storage nodes are never classified as surcharged. The Status Report no longer lists control actions taken by modulated controls since they occur continuously over time and can produce an enormous number of actions. An illegal array index bug that could occur when checking the pump curve type for an Ideal Pump in dynamic wave flow routing was fixed. A redundant unit conversion of max.

A failure to convert a storage unit's surface area curve from metric to internal units when computing bottom exfiltration was fixed. A bug that caused a link's TIMEOPEN variable used in control rule conditions to be re-set to 0 when its setting changed from one partly opened state to another was fixed.

A failure to convert a Roadway Weir's road width that was in metric units was fixed. A bug that caused the saved link settings read from a hot start file to be incorrect in a model containing pollutants was fixed. A refactoring bug that affected water quality mass balance results for Steady Flow routing was fixed. Microsoft exception handling statements are now only enabled when the engine is compiled with the Microsoft C compiler.

When events are used, maximum routing time step can be more than specified routing time step. Released: August 05, It will produce more infiltration for storm events that begin with low rainfall intensities, such as the SCS design storm distributions.

Rule premises can now test whether a link has been open or closed for a specific period of time. See the Help file for more details. Unsaturated hydraulic conductivity "K" was added to the list of variables that can be used in a user-supplied groundwater flow equation.

Other improvements The Hargreaves evaporation forumla was modified to use a 7-day running average of daily temperatures, instead of just single day values, as recommended by the formula's authors.

Daily potential evapotranspiration PET was added as a system output variable. The qualrout. Storage seepage and evaporation losses are now based on the storage volume at the end, not the start, of the prior time step.

Bug fixes A bug introduced in update 2 of release 5. A bug that failed to properly initialize the flag indicating that one or more LID controls was initially wet was fixed. Duplicate printing of the first line of an LID detailed report file was corrected. Documented bugs Maximum reported depth incorrect for SI units Rain garden has no infiltration Issue with hotstart files LID evaporation occurs only during dry weather Side slope for transverse weir issue.

Released: April 30, Improvements A new warning message was added for when a control rule premise compares two different types of variables. Bug fixes A re-factoring bug that prevented running simulations longer than 68 years was fixed.

An input parsing error that prevented the program from recognizing a comparison between two variables in a control rule premise was fixed. When implementing 5. A bug was fixed that allowed LID units to return outflow to a subcatchment's pervious area even though LIDs occupied the entire subcatchment. Documented bugs Missing groundwater recharge from LID infiltration. Released: April 02, New features Monthly adjustments for hydraulic conductivity used for rainfall infiltration and for exfiltration from storage nodes and conduits was added.

LID drains can now send their outflow to a different node or subcatchment than the parent subcatchment in which they were placed.

Conveyance system Outfall nodes now have the option to send their outflow onto a subcatchment, to simulate irrigation or complex LID treatment options.

It allows one to explicitly model roof runoff with an optional limit on the flow capacity of their downspouts. An optional soil layer has been added to Permeable Pavement LIDs so that a sand filter or bedding layer beneath the pavement can be modeled. Several new built-in variable names can now be used in custom groundwater flow equations for porosity, unsaturated hydraulic conductivity, infiltration rate, and percolation rate.

A Groundwater Summary table has been added that reports several groundwater statistics for each subcatchment. A new option, the Minimum Variable Time Step, was added that limits the smallest time step that can be computed under variable time stepping for dynamic wave flow routing.

In previous releases it was fixed at 0. The smallest value it can now have is 0. The dynamic wave routing procedure was parallelized to take advantage of multiple processors, making it run several times faster. A new column was added to the Node Depth Summary report table that shows the maximum depth recorded at the Reporting Time Step so it can be compared to the maximum depth attained over all routing time steps also shown in the table. Control rule premises can now contain conditions that compare the values of a node or link variable at two different locations e.

The threshold value for reporting a non-zero runoff result was changed from 0. The calculation of overall flow routing mass balance was modified to account for cases where some flow streams, like total external inflow, are negative.

The pollutant washoff routines were moved to a new code module surfqual. Initial flows for Steady Flow routing are now ignored since they are not used in the routing calculation and the initial volume associated with them contributed to system mass balance error. The final runoff and routing time steps are adjusted to insure that the simulation's total duration is not exceeded.

When evaluating user-supplied math expressions, any NaN Not a Number result caused by an underflow, overflow or divide by zero is set to 0 so that the NaN doesn't propagate through subsequent calculations. Bug fixes The evaporation rates read from a time series would only change when a new day was reached even though values at more frequent intervals were present and could cause a run to stop pre- maturely in some rare cases. The runoff read from a Hot Start file should have been assigned to a subcatchment's newRunoff property, not to oldRunoff.

An indexing bug that caused Hot Start files with snowmelt parameters to be read incorrectly was fixed. The setting for a non-conduit link read from a Hot Start file was not being used to initialize the link. A bug in adjusting snowmelt for snow covered area derived from an areal depletion curve was fixed.

Snowmelt should not have been included in the total precipitation reported for a subcatchment since the snowfall which produced it was already accounted for. These include the ability to do the following:. SWMM accounts for various hydrologic processes that produce runoff from urban areas, which include the following:. Spatial variability in all of these processes is achieved by dividing a study area into a collection of smaller, homogeneous sub-catchment areas.

Each of the areas contains its own fraction of pervious and impervious sub-areas. Overland flow can be routed between sub-areas, between sub-catchments, or between entry points of a drainage system. SWMM can estimate the production of pollutant loads associated with stormwater runoff. The following processes can be modeled for any number of user-defined water quality constituents:.

SWMM includes a software utility that allows future climate change projections to be incorporated into modeling. SWMM-CAT accepts monthly adjustment factors for climate-related variables that could represent the potential impact of future climate changes. Typical applications of SWMM:. SWMM allows engineers and planners to represent combinations of green infrastructure practices as low impact development LID controls to determine their effectiveness in managing runoff.