The United States Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) is a tool that simulates how rainwater and groundwater move over and under the ground in urban and suburban areas. It can model processes such as rainfall turning into runoff, water evaporating, soaking into the ground, and connecting with underground water. These processes are studied in areas like streets, grassy spaces, rain gardens, ditches, and pipes.

SWMM divides areas into smaller sections called subcatchments. These sections are split into parts where water cannot soak into the ground (impervious) and parts where it can (pervious). Some areas also have spaces that temporarily hold water (depression storage). This helps predict how much water runs off and how much pollution is carried away from each section. Low Impact Development (LID) and other water management practices can be modeled to reduce runoff from both impervious and pervious areas.

The model also tracks how water moves through systems like pipes, open channels, storage tanks, ponds, pumps, and other structures. It calculates the amount of water, its depth, and its quality in each pipe or channel during a simulation. Water quality factors, such as pollutants, can be modeled as they build up on surfaces and then wash into the water system. These pollutants may break down over time or be removed through treatment systems, LID practices, or other methods.

SWMM is widely used by the EPA and other organizations in North America, as well as by consultants and universities worldwide. Updates and new features are available on the EPA website. In 2015, the EPA released the SWMM 5.1 Hydrology Manual (Volume I). In 2016, it released the SWMM 5.1 Hydraulic Manual (Volume II) and the SWMM 5.1 Water Quality Manual (Volume III), including LID modules, along with corrections (Errata).

Program description

The EPA Storm Water Management Model (SWMM) is a tool that simulates how rainwater flows and is managed in urban areas. It helps predict the amount and quality of water that runs off surfaces during short events or over long periods. The model divides an area into smaller sections called subcatchments, where rainfall is collected and runoff and pollution are calculated. The model then tracks how this runoff moves through pipes, channels, storage tanks, pumps, and other structures. During a simulation, the model calculates the amount of water, its depth, and its quality in each part of the system at different times.

SWMM considers several processes that affect how rainwater moves in urban areas. These include:

• changing rainfall amounts over time
• water evaporating from surfaces
• snow building up and melting
• rainfall being held by small depressions on surfaces
• water soaking into dry soil
• water moving deeper into the ground
• water moving between groundwater and drainage systems
• managing water flowing over land in complex ways
• capturing rainwater using special designs like green spaces and permeable surfaces.

SWMM also has tools to model how water moves through drainage systems. These tools can:

• handle large and complex networks
• use different shapes for pipes and channels
• model special structures like storage tanks and pumps
• include water from various sources, such as rain, groundwater, and sewers
• use different methods to calculate water movement
• model situations like water backing up or flooding
• use rules to control how pumps and other structures operate.

The model divides study areas into smaller, similar sections to account for differences in how water behaves. Water can flow between these sections or into drainage systems.

Since it was created, SWMM has been used in thousands of studies worldwide. Common uses include:

• designing drainage systems to prevent flooding
• planning storage areas to manage floodwater and pollution
• mapping flood-prone areas using river models
• creating plans to reduce sewer overflows
• studying how water entering sewers affects overflows
• calculating pollution from rainwater for environmental planning
• testing how special designs reduce pollution in urban and rural areas
• analyzing water flow and quality in sewer and storm systems
• planning large-scale sewer and water systems
• evaluating systems to meet environmental regulations
• predicting flood levels and volumes using 1D and 2D models.

SWMM is free software available to the public. It includes code written in C and Delphi for its interface. This code can be edited and used by students and professionals to add new features or outputs.

History

SWMM was first created between 1969 and 1971. Since then, it has had four major updates. These updates were: (1) Version 2 from 1973 to 1975, (2) Version 3 from 1979 to 1981, (3) Version 4 from 1985 to 1988, and (4) Version 5 from 2001 to 2004. A list of these updates and changes after 2004 is shown in Table 1. The most recent version, Version 5.2.3, was completely rewritten using the programming language C instead of Fortran. It can run on Windows XP, Windows Vista, Windows 7, Windows 8, and Windows 10. It can also be run on Unix with some changes. The code for SWMM5 is open source and freely available on the EPA website.

EPA SWMM 5 includes tools for editing data about watersheds, running simulations for water flow, water movement, real-time control, and water quality, and viewing results in different formats. These formats include maps that show drainage areas with colors, graphs that show changes over time, tables, line graphs, scatter plots, and statistical summaries.

The most recent rewrite of EPA SWMM was done by the Water Supply and Water Resources Division of the U.S. Environmental Protection Agency's National Risk Management Research Laboratory. This work was helped by the consulting firm CDM Inc under a Cooperative Research and Development Agreement (CRADA). SWMM 5 is used as the main tool for calculations in many modeling programs. Some parts of SWMM5 are also used in other modeling programs. The names of these programs are listed in the Vendor section. A list of updates to SWMM 5 from the original version (5.0.001) to the current version (5.2.3) is available on the EPA website. SWMM 5 was approved by FEMA in May 2005. The approved versions for use in NFIP modeling include SWMM 5 Version 5.0.005 and later. SWMM 5 is used as the main tool for calculations in many modeling programs (see the SWMM 5 Platform Section of this article). Some parts of SWMM5 are also used in other modeling programs (see the SWMM 5 Vendor Section of this article).

SWMM conceptual model

SWMM views a drainage system as a series of water and material movements between several main parts of the environment. These parts and the SWMM objects they include are as follows:

The atmosphere part, from which rain and snow fall, and pollutants land on the land surface part. SWMM uses Rain Gage objects to show rainfall data for the system. Rain Gage objects can use data over time, files from outside sources, or rainfall records from NOAA. These objects can use precipitation data from thousands of years. The SWMM-CAT Addon to SWMM5 allows climate change effects to be modeled by adjusting temperature, evaporation, or rainfall.

The land surface part is shown by one or more subcatchment objects. This part receives rain or snow from the atmosphere part, sends water into the groundwater part through soil absorption, and also sends surface runoff and pollutants to the transport part. Low impact development (LID) controls are included in subcatchments and help store, absorb, or release water through evaporation.

The groundwater part receives water from the land surface part and sends some of this water to the transport part. This part is modeled using aquifer objects. The connection to the transport part can be a fixed boundary or a changing water level in channels. Links in the transport part now also include water loss through seepage and evaporation.

The transport part includes a network of movement elements (channels, pipes, pumps, and regulators) and storage or treatment units that move water to outfalls or treatment facilities. Water entering this part can come from surface runoff, groundwater flow, normal wastewater flow, or user-defined water flow data. The parts of the transport section are modeled with Node and Link objects.

Not all parts must be included in a specific SWMM model. For example, a model could focus only on the transport part, using pre-defined water flow data as inputs. If kinematic wave routing is used, the nodes in the model do not need to include an outfall.

Model parameters

The model settings for subcatchments include surface roughness, depression storage, slope, and flow path length. For infiltration, the Horton method uses maximum and minimum rates along with a decay constant. The Green-Ampt method includes hydraulic conductivity, initial moisture deficit, and suction head. The Curve Number method uses the NRCS (SCS) Curve number. All methods consider the time needed for saturated soil to fully drain. For conduits, Manning’s roughness is used. For water quality, the model includes buildup and washoff function coefficients, first-order decay coefficients, and removal equations. A study area can be split into many subcatchments, each of which drains to one specific point. Study areas can be as small as part of a single lot or as large as thousands of acres. SWMM uses rainfall data recorded hourly or more often as input. It can be used to simulate single events or run continuously for many years.

Hydrology and hydraulics capabilities

SWMM 5 models different water movement processes that create surface and underground water flow in urban areas. These processes include:

• Changing rainfall patterns for any number of rain measurement points, used for both planned and ongoing rainfall events
• Evaporation of water from open surfaces in watersheds and ponds
• Snow accumulation, removal, and melting
• Rainfall absorbed by small depressions in both paved and unpaved areas
• Water soaking into dry soil layers
• Water moving deeper into groundwater layers
• Water movement between groundwater and drainage pipes or ditches
• Complex calculation of water flowing over land surfaces across watersheds.

To show how these processes vary across areas, SWMM divides a study region into smaller, similar sections called subcatchments. Each section has its own mix of paved and unpaved areas. Water can move between these sections or through drainage systems.

SWMM also models how water moves through drainage systems, including pipes, channels, storage tanks, and control structures. It can:

• Model drainage systems of any size
• Use many types of pipe and channel shapes, including natural ones
• Model special features like storage tanks, outlets, pumps, and barriers
• Include water flow and quality inputs from rain, groundwater, and user-defined sources
• Use different methods to calculate water movement, such as steady flow or dynamic wave calculations
• Model different water flow situations, like flooding, pressure, and reverse flow
• Use user-defined rules to control pumps and other system components.

Infiltration is the process of rainwater soaking into the ground in areas with soil that allows water to pass through. SWMM 5 uses four methods to model infiltration:

This method assumes infiltration decreases quickly at first and then slows over time during long rain events. It needs inputs like maximum and minimum infiltration rates, a rate-decay factor, and the time it takes dry soil to recover after rain.

This method is a modified version of the Horton method. It uses total infiltration instead of time to calculate infiltration more accurately during light rain. It uses the same inputs as the traditional Horton method.

This method assumes a clear boundary in soil between dry and wet areas. It needs inputs like initial soil dryness, soil water movement ability, and water pressure at the boundary. Soil recovery during dry periods is related to water movement ability.

This method uses the NRCS (SCS) curve number system to estimate infiltration. It calculates infiltration based on soil type and how much rain has fallen. Inputs include a curve number and the time it takes dry soil to recover after rain.

SWMM allows infiltration recovery rates to change monthly to account for seasonal factors like evaporation and groundwater levels. This monthly adjustment is part of the project's evaporation data.

SWMM also models how pollutants in runoff water are created and transported. It can model:

• Accumulation of pollutants on different land types during dry weather
• Pollutants washed away from land during rain events
• Pollutants from rain and dry weather deposition
• Reduction of pollutants from street cleaning
• Reduction of pollutants from green infrastructure and other controls
• Pollutants entering the system from sewers or user-defined sources
• Movement of pollutants through the drainage system
• Reduction of pollutants through treatment in storage units or natural processes in pipes and channels.

Rain measurement points in SWMM 5 provide rainfall data for areas in a study region. Rainfall data can be user-defined or from external files. Supported formats include standard and user-defined types. Key rain gage properties include:

• Type of rainfall data (e.g., intensity, volume)
• Time interval for measurements (e.g., hourly, 15-minute)
• Source of data (user input or external file)
• Name of the data source.

Key subcatchment parameters include:

• Assigned rain gage
• Outlet location and routing fraction
• Land use types
• Surface area of the area
• Percentage of paved and unpaved areas
• Slope of the land
• Width of overland flow paths
• Roughness values (Manning’s n) for both paved and unpaved areas
• Water storage in depressions on both paved and unpaved areas
• Percentage of paved areas with no depression storage
• Infiltration-related parameters
• Snow accumulation data
• Groundwater-related parameters
• Green infrastructure parameters for each control used.

Routing options

Steady-flow routing is the simplest method. It assumes that water flow does not change during each time step. This method moves the inflow graph from the beginning of a channel to the end without any delay or changes in shape. The normal flow equation connects flow rate to the area of the channel (or water depth).

This method cannot consider storage in the channel, backwater effects, losses at channel entrances or exits, reversed flow, or pressurized flow. It works only with networks where each node has one outgoing path, except for dividers, which may have two. This method is not affected by the size of the time step and is best for early analysis with long-term simulations.

Kinematic wave routing solves the continuity equation and a simplified version of the momentum equation in each channel. This requires that the slope of the water surface matches the slope of the channel. The maximum flow through a channel is the full normal flow value. Any flow exceeding this at an inlet node is either lost or stored above the node until space becomes available.

Kinematic wave routing allows flow and area to change both in space and time within a channel. This can cause delayed and reduced outflow graphs as water moves through the channel. However, it cannot consider backwater effects, losses at channel entrances or exits, reversed flow, or pressurized flow. It also works only with dendritic network layouts. It usually stays numerically stable with time steps of 1 to 5 minutes. If backwater effects and similar issues are not important, this method can be accurate and efficient for long-term simulations.

Dynamic wave routing solves the full one-dimensional Saint Venant equations, which include the continuity and momentum equations for channels and a volume continuity equation at nodes. This method can represent pressurized flow when a closed channel becomes full, allowing flows to exceed the normal maximum. Flooding happens when water depth at a node exceeds the maximum available depth, and extra flow is either lost or stored above the node until space becomes available.

Dynamic wave routing can account for storage in the channel, backwater effects, losses at channel entrances or exits, reversed flow, and pressurized flow. Because it connects water levels at nodes with flow in channels, it works with any network layout, even those with loops or multiple downstream paths. It is preferred for systems with significant backwater effects or flow control using weirs and orifices. However, it requires very small time steps, often less than a minute, to stay numerically stable.

Integrated hydrology/hydraulics

SWMM 5 made an important improvement by combining the movement of underground water in cities and suburbs with the calculations of how water flows through drainage systems. This change is better than older versions of SWMM because it allows modelers to create a more accurate picture of how water moves in real-world environments, such as open channels and shallow underground water areas. The SWMM 5 computer system calculates how water runs off the surface, moves underground, and uses current weather data during either wet or dry periods. Then, it calculates how water moves through pipes, channels, control systems, and boundaries using either fixed or changing time steps within the weather period. Versions of SWMM 5 after 5.1.007 let users adjust rainfall, temperature, and evaporation using monthly changes to simulate climate effects.

An example of this improvement is how SWMM 5 grouped different types of pipes and channels from SWMM 4 into one unified set of closed pipes and open channels (Figure 2). It also grouped different types of system points.

SWMM has tools to model how water moves through drainage systems, including pipes, channels, storage tanks, and structures that direct water flow. These tools can:

• Work with drainage systems of any size.
• Use many different shapes for pipes and open channels.
• Simulate special parts like storage tanks, pumps, weirs, and orifices.
• Include water from rain, groundwater, and user-defined sources.
• Use two methods to track water movement: one for faster calculations and one for detailed analysis.
• Simulate different water flow situations, such as flooding, reverse flow, and water pooling on the surface.
• Set rules for how pumps and weirs operate.
• Track water moving from the surface to underground layers.
• Track water moving between underground layers and the drainage system.
• Track water moving over land in complex ways.
• Reduce runoff using green infrastructure like rain gardens.

Low-impact development components

The low-impact development (LID) function was introduced in SWMM 5.0.019/20/21/22 and SWMM 5.1+. It is part of the subcatchment and helps improve how water overflows, infiltrates, and evaporates in systems like rain barrels, swales, permeable paving, green roofs, rain gardens, bioretention areas, and infiltration trenches. The term low-impact development (LID) is used in Canada and the United States to describe a planning and engineering method for managing stormwater runoff. In recent years, many U.S. states have adopted LID concepts and standards to reduce stormwater pollution in new construction projects. LID includes many methods, but it generally aims to reduce or stop concentrated stormwater flows from leaving a site. To achieve this, LID suggests that when impervious surfaces (like concrete) are used, they should be interrupted by pervious areas that allow stormwater to soak into the ground.

In SWMM 5, several sub-processes within each LID can be defined, such as surface, pavement, soil, storage, drainmat, and drain. Each type of LID has limits on the sub-processes allowed by SWMM 5. SWMM 5 includes a report feature that provides details like surface depth, soil moisture, storage depth, surface inflow, evaporation, surface infiltration, soil percolation, storage infiltration, surface outflow, and LID continuity errors in the rpt file or an external report file. Multiple LID systems can exist within a single subcatchment, and no issues have been reported with complex LID networks or continuity problems that might require smaller time steps for analysis. The types of LID compartments in SWMM 5 include storage, underdrain, surface, pavement, and soil. For example, a bio-retention cell includes storage, underdrain, and surface compartments. An infiltration trench LID includes storage, underdrain, and surface compartments. A porous pavement LID includes storage, underdrain, and pavement compartments. A rain barrel has only storage and underdrain compartments, while a vegetative swale LID has a single surface compartment. Each LID type uses different layers, called compartments, in SWMM 5.

Equations in SWMM 5 can be solved numerically at each runoff time step to determine how inflow to an LID unit is converted into runoff, subsurface storage, subsurface drainage, and infiltration into surrounding soil. In addition to street planters and green roofs, the bio-retention model can represent rain gardens by removing the storage layer and porous pavement systems by replacing the soil layer with a pavement layer.

The surface layer of an LID receives direct rainfall and runoff from other areas. Water is lost through infiltration into the soil layer below, evapotranspiration (ET) of water stored in depressions or vegetation, and surface runoff. The soil layer contains a special soil mix that supports plant growth. It receives infiltration from the surface layer and loses water through ET and percolation into the storage layer below. The storage layer consists of coarse gravel or crushed stone. It receives percolation from the soil layer and loses water through infiltration into natural soil or outflow through a perforated underdrain pipe.

Since July 2013, the EPA's National Stormwater Calculator has been a Windows desktop tool that estimates annual rainfall and runoff from a specific site in the United States. These estimates depend on local soil conditions, land cover, and historical rainfall data. The Calculator uses national databases for soil, topography, rainfall, and evaporation information. Users provide details about their site's land cover and select LID controls to use. SWMM 5.1.013 includes the following types of green infrastructure as LID controls:

• StreetPlanter: These are depressions with vegetation in an engineered soil mix above a gravel drainage bed. They store, infiltrate, and evaporate rainfall and runoff from surrounding areas. Street planters are concrete boxes filled with soil that supports plants, with gravel below. The planter walls extend 3 to 12 inches above the soil bed to allow water to collect temporarily. Soil depth ranges from 6 to 24 inches, and gravel depth is 6 to 18 inches. The capture ratio is the area of the planter compared to the impervious area it drains.

• Raingarden: These are shallow depressions filled with engineered soil that supports plants. They capture roof runoff from homes. Soil depth ranges from 6 to 18 inches. The capture ratio is the area of the rain garden compared to the impervious area it drains.

• GreenRoof: These are bio-retention systems on rooftops with a soil layer above a drainage mat. They temporarily store rainwater and prevent ponding on the roof. The soil layer is 3 to 6 inches thick.

• InfilTrench: These are narrow ditches filled with gravel that intercept runoff from impervious areas. They provide storage and allow infiltration into the soil below.

• PermPave or Permeable Pavement: These are areas filled with gravel and covered with porous concrete or asphalt. They allow water to pass through into the gravel below for infiltration. Pavement layers are 4 to 6 inches thick, and gravel storage layers are 6 to 18 inches thick. The capture ratio is the percentage of treated area replaced with permeable pavement.

• Cistern: Rain barrels or cisterns collect roof runoff during storms and store it for later use or infiltration. Systems are based on a fixed number of cisterns per 1,000 square feet of rooftop area. Water is removed at a constant rate and used or infiltrated on-site.

• VegSwale: These are grass-covered channels or depressions with sloping sides. They slow runoff and allow more time for water to infiltrate the soil below.

SWMM5 components

The main parts of SWMM 5.0.001 to 5.1.022 include rain gages, watersheds, LID controls or BMP features like wet and dry ponds, nodes, links, pollutants, land uses, time patterns, curves, time series, controls, transects, aquifers, unit hydrographs, snowmelt, and shapes (Table 3). Other related parts include types of nodes and link shapes. These parts help simulate the major parts of the water cycle, the movement of water through drainage, sewer, or stormwater systems, and the buildup and washoff of water quality substances. A watershed simulation begins with a record of rainfall over time. SWMM 5 includes many types of open and closed pipes and channels: dummy, circular, filled circular, rectangular closed, rectangular open, trapezoidal, triangular, parabolic, power function, rectangular triangle, rectangle round, modified baskethandle, horizontal ellipse, vertical ellipse, arch, eggshaped, horseshoe, gothic, catenary, semielliptical, baskethandle, semicircular, irregular, custom, and force main.

The major parts or hydrology and hydraulic components in SWMM 5 are:

• GAGE (rain gage)
• SUBCATCH (subcatchment)
• NODE (conveyance system node)
• LINK (conveyance system link)
• POLLUT (pollutant)
• LANDUSE (land use category)
• TIMEPATTERN (dry weather flow time pattern)
• CURVE (generic table of values)
• TSERIES (generic time series of values)
• CONTROL (conveyance system control rules)
• TRANSECT (irregular channel cross-section)
• AQUIFER (groundwater aquifer)
• UNITHYD (RDII unit hydrograph)
• SNOWMELT (snowmelt parameter set)
• SHAPE (custom conduit shape)
• LID (LID treatment units)

These major parts are named in the SWMM 5 input file and C code of the simulation engine: gage, subcatch, node, link, pollute, landuse, timepattern, curve, tseries, control, transect, aquifer, unithyd, snowmelt, shape, and lid. Types of nodes include junction, outfall, storage, and divider. Storage nodes can use either a table showing depth and area or a formula connecting area and depth. Possible node inflows include: external_inflow, dry_weather_inflow, wet_weather_inflow, groundwater_inflow, rdii_inflow, flow_inflow, concen_inflow, and mass_inflow. Dry weather inflows can use patterns like monthly_pattern, daily_pattern, hourly_pattern, and weekend_pattern.

The SWMM 5 structure allows users to select which major hydrology and hydraulic parts are used during the simulation:

• Rainfall/runoff with infiltration options: horton, modified horton, green ampt, and curve number
• RDII
• Water Quality
• Groundwater
• Snowmelt
• Flow Routing with Routing Options: Steady State, Kinematic Wave, and Dynamic Wave

SWMM 3 and 4 to 5 converter

The SWMM 3 and SWMM 4 converter can change up to two files from older SWMM 3 and 4 versions into SWMM 5 at the same time. Usually, users convert a Runoff and Transport file to SWMM 5 or a Runoff and Extran file to SWMM 5. If a SWMM 4 file includes a Runoff, Transport, and Extran network together, it must be converted in separate steps. After conversion, the two sets of data must be copied and pasted together to create one SWMM 5 data set. The x,y coordinate file is only needed if the SWMM 4 Extran input data does not already include x, y coordinates on the D1 line. The command File => Define Ini File can be used to set the location of the ini file. The ini file stores the input data files and directories for the conversion project.

SWMM 3 and SWMM 3.5 files use a fixed format, while SWMM 4 files use a free format. The converter automatically detects which SWMM version is being used. Converted files can be combined using a text editor to merge the created inp files.

SWMM-CAT Climate Change AddOn

The Storm Water Management Model Climate Adjustment Tool (SWMM-CAT) is a new feature added to SWMM5 in December 2014. It is a software tool that helps users include future climate change predictions in the Storm Water Management Model (SWMM). SWMM was recently updated to use monthly adjustment factors for time series data, which can show how future climate changes might affect weather patterns. SWMM-CAT provides adjustments based on global climate models from the World Climate Research Programme (WCRP) Coupled Model Intercomparison Project Phase 3 (CMIP3) archive (Figure 4). This tool adds location-specific climate change adjustments to an SWMM project file. Adjustments can be applied monthly to air temperature, evaporation rates, and precipitation, as well as to the 24-hour design storm at different recurrence intervals. These adjustments come from global climate models in the CMIP3 archive. Adjusted data from this archive was created and converted into changes compared to historical values by the USEPA's CREAT project.

To choose a set of adjustments for SWMM5, follow these steps:

1) Enter the latitude and longitude of the location, or its 5-digit zip code if available. SWMM-CAT will show climate change results from the CMIP3 models closest to the location.

2) Choose whether to use climate change projections for a near-term or far-term time period. The displayed results will update to match your selection.

3) Pick a climate change outcome to save to SWMM. Three options are available, each based on different global climate models from the CMIP3 project. The Hot/Dry outcome represents a model with high temperature increases and low rainfall changes. The Warm/Wet outcome represents a model with lower temperature increases and higher rainfall changes. The Median outcome represents a model with temperature and rainfall changes closest to the average of all models.

4) Click the "Save Adjustments to SWMM" link to open a dialog box. This box lets you select an existing SWMM project file to save the adjustments to. It also lets you choose which type of adjustments (monthly temperature, evaporation, rainfall, or 24-hour design storm) to save. The tool automatically converts temperature and evaporation units based on the unit system (US or SI) detected in the SWMM file.

EPA stormwater calculator based on SWMM5

Other tools that help create data for the EPA SWMM 5 model include: SUSTAIN, BASINS, SSOAP, and the EPA’s National Stormwater Calculator (SWC). The SWC is a desktop application that estimates how much rainwater falls each year and how often water runs off the ground at a specific location in the United States, including Puerto Rico. These estimates are based on local soil types, land cover, and historical rainfall records (Figure 5).

SWMM platforms

The SWMM5 engine is used by many different programs, including some that are sold by companies. Some of these programs include:

• h3O by Aqualyze
• SewerGEMS by Bentley
• StormNET by BOSS
• PCSWMM by CHI
• MIKE URBAN by DHI
• InfoSWMM by Innovyze
• xpswmm by XP Software
• GeoSWMM by Utilian