# Calculation Option Attributes

Calculation Options contain the information described in the following table.

Attribute | Description |
---|---|

General | |

Label | Specify a name for the calculation option. |

Notes | Enter descriptive text to be associated with the current calculation profile. |

Calculation Options | |

Calculation Type | Identifies the numerical solver to be used . The solvers include: Explicit (SWMM) Implicit (Dynamic Wave) GVF-convex (gradually varied flow with convex routing) GVF-rational (gradually varied flow with ration method hydrology) The solver selected will affect the properties in the grid below as some are only available for specific solvers while others pertain to all solvers. While it is possible to select any solver from any product, SewerCAD will only run scenario with the GVF-convex solver and StormCAD will only run scenarios with the GVF-rational solver. Note that if a catchment is using the EPA SWMM runoff method and not using the same default infiltration method specified in the SWMM calc options then neither hydrology or network will calculate. If the user is not using the EPA SWMM runoff method, then any combination of other runof methods can be used. |

Time Analysis Type | If the user selects GVF-convex as the solver type, then this property determines whether a steady or extended period simulation is to be run. If Steady State is selected, most of the time related properties below are not available and the only additional property in this category is Calculation Type. |

Include Conduit Flow Travel Time in Design | If True, flow travel time in conduit will be included in time of concentration and larger time of concentration will cause smaller discharge value, which may cause smaller designed conduit size. |

Simulation Start Date | Select the calendar date on which the simulation begins. |

Simulation Start Time | Select the clock time at which the simulation begins. |

Duration Type | Choose between User Defined Duration (e.g. 48 hours) or End Date/End Time (e.g. 2/28/2014 12:00:00 AM). Default = User Defined. |

Duration | If duration type is set to User Defined, set the duration (default = 24 hrs). |

End Date | If Duration Type is set to End Date/End Time, specify the end date (default = same as start date). |

End Time | If Duration Type is set to End Date/End Time, specify the end time (default = same as start time). |

Minimum Tc | This is the minimum time of concentration. If a computed time of concentration on a catchment is less than this value, this value is used instead. |

Include Conduit Flow Travel Time in Design | If True, travel time in conduits will be included in time of concentration. Larger time of concentration values will cause smaller discharge values, which may cause smaller designed conduit sizes. |

Hydrologic Routing Time Step | When the GVF-convex solver is selected, this is where the user specifies the increment for the convex routing of flows in gravity subnetworks. This should be an even increment of the hydraulic time step. This is also the time step for the pressure subnetworks, although intermediate time steps may be inserted by the pressure solver based on pump switches. Default = 0.1 hr |

Hydraulic Time Step | When the GVF-convex solver is selected, this is where the user specifies the increment between which hydraulic properties (e.g. velocity, depth) are calculated using gradually varied flow methods based on flows from the convex routing. Default = 1 hr. |

Reporting Time Step | For the GVF-convex solver, the user can control the amount of results that are reported. The default is "All". However with this solver, the user can specify a large Constant time step or can only save results for some specific time steps if Varied is selected. |

Report Start Time | For the explicit solver, time at which reports will begin to be saved. |

Report Start Date | For the explicit solver, date at which reports will begin to be saved. |

Calculation Type | For a GVF-convex steady state simulation, this property establishes whether an analysis (simulation) or a design (pipe and invert sizing) run is to be made. Default = Analysis. |

Output Increment | Allows user to set the Output Increment you want to use to display the output hydrographs of a network analysis. |

Calculation Time Step | Lets you specify the computational time step in hydrodynamic calculations. See Troubleshooting DynamicWave Model Calculations for more information. |

Receding Limb Multiplier | Helps define the shape of the modified rational hydrograph. The receding limb of all modified rational hydrographs are taken to occur over a duration obtained by multiplying this value by the Tc. Refer to local design policy and practices to determine the appropriate value of Tc. The default value is 1.0. |

Calculation Options (Implicit) | |

Y Iteration Tolerance | In the implicit numerical scheme, Newton iteration converge criteria for depth/elevation. It is strongly recommended to use the default value. |

LPI Coefficient | Coefficient for advanced LPI supercritical-subcritical mix flow computation algorithm. It is strongly recommended to use the default value. The default value is 1.0. When the model is unstable or when the calculated results do not reflect some significant backwater effects, the user can try increasing the LPI value as high as 15. |

NR Weighting Coefficient | Implicit numerical scheme Newton iteration weighting factor. A Larger value tends to increase stability, but at the cost of performance. We suggest using the default value or values between 0.6 and 0.85, but values between 0.1 and 1.0 are valid. Use 0.98 - 1.0 in very difficult cases. See Troubleshooting DynamicWave Model Calculations for more information. |

NR Iterations | Allowed maximum Newton iterations in one time step during the numerical solution process. This attribute value is used to prevent the numerical solver from unlimited iterations under situations when the solver is unable to reach convergence. |

Relaxation Weighting Coefficient | Implicit numerical scheme relaxation factor for network computations. The range of valid values is between 0.5 and 0.9. |

Computation Distance | Implicit numerical scheme computational distance interval. The model will automatically insert additional computational sections based on this value, a small value increases stability while large value increases performance. Computational distance is the lesser of one half the pipe length or default distance See Troubleshooting DynamicWave Model Calculations for more information. |

Start Type | By default the engine assumes a dry condition to start the simulation; i.e., all inflows are zero and all depths are zero in all elements at the beginning. For situations in which the user wants a non-zero starting flow or the catchments’ hydrology calculations to give none-zero flows, the model provides two options to start the simulation: select Warm Up Time for a warm-up start or Transition Start for a transitional start. In a warm-up start, the model estimates initial depths based on non-zero inflows and uses a user-specified warm-up time (entered in the Warm Up Time field) to approach steady state conditions prior to starting the actual simulation. In a transition start, the model initiates the simulation from zero flows and immediately reaches the actual none-zero flows in the first time step and continued the simulation. See Troubleshooting DynamicWave Model Calculations for more information. Note that if the model is a looped network then the warm-up start will be disabled, because of the difficulty in estimating the non-zero initial conditions for complex looped networks. |

Warm Up Time | Lets you enter a warm-up time for warm-up starts. This field is available only when the user selects Warm Up Time as the Start Type. |

Virtual Flow Depth | This is an option used in the implicit solver to overcome the calculation instabilities when the conduit is in dry (zero flow) or when the flow is very small. Under very small flow conditions the implicit numerical solver for St. Venant equations tends to be unstable so the model adds a small artificial "virtual flow" to maintain the stability. The virtual flow can be specified using this virtual depth calculation option value. The model determines the virtual flow based on the virtual depth for each link. The default value of 0.04 ft has been tested and works well for a wide range of conditions. Generally speaking a larger value will further increase stability while a smaller value may increase accuracy for small flows for the same cases. The Y-Iteration tolerance for the Newton iteration may be also reduced together with lowing virtual flow depth. |

Calculation Options (Explicit) | |

Routing Time Step | Specify the computational time step in routing calculations. |

Allow Ponding at Gravity Structures | Select whether or not to allow excess water to collect at gravity structures and be re-introduced into the system as conditions permit. Select True to allow ponding at gravity structures in your model. In order for ponding to actually occur at a particular node, you must enter a non-zero value for the node’s Ponded Area attribute. |

Routing Method | Select which method to use to route flows through the conveyance system. Select Uniform Flow , Kinematic Wave , or Dynamic Wave. |

Skip Steady State Periods? | This set of options tells SWMM
solver how to identify and treat periods of time when system hydraulics is not
changing.
If the Skip Steady Periods is set True, the system is considered to be in a steady flow period if: 1) The percent difference between total system inflow and total system outflow is below the System Flow Tolerance (%). 2) The percent differences between the current lateral inflow and that from the previous time step for all points in the conveyance system are below the Lateral Flow Tolerance (%). Checking the Skip Steady Flow Periods box will make SWMM keep using the most recently computed conveyance system flows (instead of computing a new flow solution) whenever the above criteria are met. Using this feature can help speed up simulation run times at the expense of reduced accuracy. |

System Flow Tolerance | When the Skip Steady State Periods is selected as True, this option determines if the flow is still in steady state when the flow change in percent is below the tolerance. |

Lateral Flow Tolerance | When the Skip Steady State Periods is selected as True, this option determines if the lateral inflow is still in steady state when the local inflow change in percent is below the tolerance. |

Minimum Conduit Slope | The minimum value allowed for a conduit’s slope. If zero (the default) then no minimum is imposed, although the explicit solver uses a lower limit on elevation drop of 0.001 ft (0.00035 m) when computing a conduit slope. |

Use Bentley Transition Equation | Turn on a stability enhancement to improve stability when flow changes from gravity to surcharge states. |

Solver Compatibility | Choose the calculation mode of the SWMM engine to run during a simulation. Choose BENTLEY to include extensions to the SWMM engine, and EPA to exclude them. See SWMM Compatibility Mode for further information. |

Calculation Options (SWMM Hydrology) | |

Default Infiltration Method | Lets you determine how to model infiltration of rainfall into the upper soil zone of subcatchments. Select Horton, Horton (Modified), Green-Ampt, or SCS CN. If you change this attribute, you will have to re-enter values for the infiltration parameters in each subcatchment. |

SWWMM Hydrologic Increment | Lets you specify the computational time step in SWMM hydrology runoff calculations. |

Dry Step (hours) | Enter the time step length used for runoff computations (consisting essentially of pollutant buildup) during periods when there is no rainfall and no ponded water. This must be greater or equal to the Hydrologic Routing Time Step. |

Antecedent Dry Period | The number of days with no rainfall prior to the start of the simulation. This value is used to compute an initial buildup of pollutant load on the subcatchment surfaces. |

Start Sweeping On | Enter the day of the year (month/day) when street sweeping operations begin. The default is January 1. |

End Sweeping On | Enter the day of the year (month/day) when street sweeping operations end. The default is December 31. |

Inlets | |

Active Components for Combination Inlets on Grade | Select the active openings for combination inlets on grade. |

Active Components for Combination Inlets In Sag | Select the active openings for combination inlets in sag. |

Neglect Gutter Cross Slope For Side Flow? | If True, when grate width is less than gutter width, gutter cross slope is used to determine side flow. |

Neglect Side Flow? | If True, only frontal views wuill be included in the inlet calculations. |

Calculation Options (Convex/Pressure) | |

Peak Flow Ratio | Used when selecting a representative flow rate from the hydrograph to be routed when calculating the C parameter used to perform the convex routing calculations. |

Steady State Hydrograph Equivalent | Specify how the software should handle hydrographs during a steady state analysis. |

Extreme Flow Setup | Select an Extreme Flow Setup for the current calculation. |

Pattern Setup | Pattern setups allow the user to match unit sanitary (dry weather) loads with appropriate loading patterns. Specify a default Pattern Setup to associate with each Calculation Option. Each scenario can use a different Pattern Setup, thus allowing the user to model different loading alternatives for different extended period simulations. |

Minimum Convex C for Adverse Conduits | The convex coefficient for large negative sloped pipe (channel) can be too small and this can result in unrealistic flow attenuation through the pipe. By using a minimum convex C option you can improve the results; a value of between 0.3 and 0.5 is suggested. |

Calculation Options (SWMM Dynamic) | |

Max Trials per Time Step | This is the maximum number of trials that SWMM uses at each time step to reach convergence when updating hydraulic heads at the conveyance system's nodes. The default value is 8. |

Head Convergence Tolerance | When the difference in computed head at each node between successive trials is below this value the flow solution for the current time step is assumed to have converged. The default tolerance is 0.005 ft (0.0015 m). |

Inertial Terms | Define how the inertial terms in the St. Venant momentum equation will be handled: Keep --Maintains these terms at their full value under all conditions. Dampen --Reduces the terms as flow comes closer to being critical and ignores them when flow is supercritical. Ignore --Drops the terms altogether from the momentum equation, producing what is essentially a Diffusion Wave solution. |

Use Variable Time Step? | Select whether or not to use a variable time step. The variable step is computed for each time period to prevent an excessive change in water depth at each node. Select True to use a variable time step. a safety factor (between 10 and 200%) that will be applied against the variable time step as automatically derived to preserve the Courant stability criterion. |

Time Step Multiplier (%) | Enter a safety factor (between 10 and 200%) to be applied against the variable time step as automatically derived to preserve the Courant stability criterion. This field is available only if you select True in the Use Variable Time Step? field. |

Define Super Critical Flow | Select the basis used to determine when supercritical flow occurs in a conduit. |

Minimum Surface Area (Acres) | Enter the minimum surface area to be used at nodes when computing changes in water depth. If you enter 0, then the default value of 12.566 ft 2 (i.e., the area of a 4-ft diameter manhole) is used. |

Time Step For Conduit Lengthening | Enter the time step, in seconds, used to artificially lengthen conduits so that they meet the Courant stability criterion under full-flow conditions (i.e., the travel time of a wave will not be smaller than the specified conduit lengthening time step). As this value is decreased, fewer conduits will require lengthening. A value of 0 means that no conduits will be lengthened. |

Minimum Variable Time Step | This is the smallest time step allowed when variable time steps are used. The default value is 0.5 seconds. Smaller steps may be warranted, but they can lead to longer simulation runs without much improvement in solution quality. |

Number of Threads | This selects the number of parallel computing threads to use on machines equipped with multi-core processors. |

Gravity Hydraulics | |

Minimum Time of Concentration | User defined lower limit for the amount of time it takes for water to travel from the farthest point in the watershed to an inlet. |

Maximum Network Transversals | Maximum number of iterations that will be performed when solving GVF equations. |

Flow Convergence Test | This value is taken as the maximum relative change in discharge occurring at the system outfall between two successive network solutions. In rational hydrology, system discharge is a function of travel time and hydraulics through the system. Therefore, it is necessary to iterate until the system balances, or a maximum number of trials has occurred. |

Tractive Stress (Global Minimum) | The global minimum allowable tractive stress in the conduit. Value is compared with calculated tractive stress in conduit to determine if adequate scouring is occurring. Tractive stress calculations are available for Implicit (DW), Explicit (SWMM), and GVF-Convex solvers. |

Flow Profile Method | Allows you to choose between a backwater and capacity analysis flow option method. Default is backwater. |

Number of Flow Profile Steps | The gradually varied flow option divides each pipe into internal segments prior to calculation of the hydraulic grade. The default value of option steps is five, and it is recommended that the value entered here be at least five for accuracy. Increasing this number will increase the accuracy of the hydraulic grade calculation, but will increase the calculation time. |

Hydraulic Grade Convergence Test | The value entered here is taken as the maximum absolute change between two successive iterations of hydraulic grade at any junction or inlet in the system. For a given discharge, the upstream propagation of headlosses through pipes will continue until two successive calculations change by an absolute difference of less than this test value. Default is 0.001 ft. The Hydraulic Grade Convergence Test value is used in the standard step gradually varied flow profiling algorithm. The calculations is assumed to converge to the solution when the two successive depth iterations are within this absolute test value. |

Average Velocity Method | This section allows you to pick the method used to calculate the average travel time velocity. The following four options are available: Actual Uniform Flow Velocity (default) Full Flow Velocity Simple Average Velocity Weighted Average Velocity |

Minimum Structure Headloss | This section allows you to specify a minimum structure headloss. If the system calculates a structure headloss that is lower than this value, the value specified in the Minimum Headloss field will be used. This option applies to all structure headloss methods except for the Absolute Method. Absolute headlosses will not be overridden, even if they are less than the value specified in this option. |

Governing Upstream Pipe Selection Method | Select the method for selecting the upstream pipe when computing the headloss for a structure using the Generic Headloss Method. |

Structure Loss Mode | Choose either Hydraulic Grade (default)or Energy Grade as the basis for the hydraulic calculations. |

Report Hydrologic Time Step? | If True, hydrographs will be reported in the hydrologic increment. |

Save Detailed Headloss Data? | If True, the detailed headloss data will be saved after computation. If False, the detailed headloss data (the AASHTO results for manholes) used in the computations will not be saved, resulting in a smaller results file. |

Gravity Friction Method | Select the global friction method for gravity elements. The choices include Manning's, Darcy-Weisbach, Hazen-Williams or Kutter's. Default is Manning's. |

Darcy Friction Factor Method | The friction factor method used to compute Darcy-Weisbach friction losses. |

Liquid Label | Label which describes the type of liquid used in the simulation. |

Liquid Kinematic Viscosity | Ratio of the liquid’s dynamic, or absolute, viscosity to its mass density. Default is water at 20C. |

Use Explicit Depth and Slope Equations? | If true then explicit depth and slope equations will be used. Default is False. The GVF hydraulics solver computes the water profile by backwater calculations in which the control depths (normal depth and critical depth) and critical slope play important roles. The solver normally calculates the normal depth, critical depth and critical slope by iterative methods. For very large models, or models that have a long run duration with a very small hydraulic time step, the iterative methods can result in slow computation performance. In order to improve the performance a method of using highly accurate explicit equations can be used by enabling this option. This method uses simple polynomial fitting equations to the theoretical normal depth, critical depth and critical slope equations for circular pipes and can provides reliable and robust solutions with much improved (as much as 50% faster) computation performance. The technical details can be found in Jin & Walski, Efficient Equations for Circular Partly-full Pipe Hydraulics, Proc. EWRI 2011 conference. |

Ignore Travel Time in Carrier pipes? | Ignore the travel time in carrier pipes (pipes with no subcatchment connected to their upstream node) when computing system time at the node immediately downstream of the carrier pipe in rational method hydrology. Default is False. |

Consecutive Supercritical Transition Method |
For GVF solvers (GVF-Convex and GVF-Rational), when two supercritical conduits are linked through a node (manhole/inlet), the profile transition can possibly have two situations, the high velocity of incoming supercritical flow abruptly expands at the manhole entrance resulting in a side depression followed by shockwaves shortly downstream because of the flow impact on side walls. The shortwave impact can be either small enough to maintain supercritical flow in the downstream conduit or too large so that a hydraulic jump occurs. This calculation option provides two transition methods to account for the two possible conditions - either critical depth transition for hydraulic jump or normal depth transition for maintaining supercritical flow. The conservative (and default) method is to use critical depth that will result in higher profile at the node. |

Correct for Partial Area Effects? | If False (default), the software will always adopt the largest system time from all incoming flows. If True, when two or more rational flows enter a single node, the software will adopt the system time that produces the largest rational flow. A larger ‘partial area’ flow will be carried downstream until the ‘total area’ flows exceed it. |

Headloss - AASHTO | |

Bend Angle vs. Bend Loss Curve | Opens the Bend Angle vs Bend Loss Curve dialog, allowing you to modify the default curve. |

Expansion, Ke | Adjustment coefficient used in AASHTO equation to account for expansion of the flow on the exit from incoming pipe. |

Contraction, Kc | Adjustment coefficient used in the AASHTO equation to account for contraction of the flow on the entrance in the outfall pipe. |

Shaping Adjustment, Cs | Adjustment coefficient used in the AASHTO equation for junction headloss calculation to account for partial diameter inlet shaping (equivalent to Half and Full in HEC-22). If inlet shaping is used then the headloss is decreased by this factor (50% default). |

Non-Piped Flow Adjustment, Cn | If non-piped flow accounts for 10% or more of the total structure outflow, a correction factor is applied to the total loss. By default, this value is a 30% increase in headloss (a factor of 1.3) as documented in the AASHTO manual, but can be changed by the user. |

HEC-22 Energy Losses | |

Elevations Considered Equal Within | The maximum elevation distance that pipes entering a node can be separated by and still be considered to be at the same elevation. |

Consider Non-Piped Plunging Flow | If this value is set to True, plunging correction factor for non-piped flow will be applied during the calculation. |

HEC-22 Energy Losses (Second Edition) | |

Flat Unsubmerged Factor | Benching correction factor used in the HEC-22 Method for a flat unsubmerged transition structure. |

Flat Submerged Factor | Benching correction factor used in the HEC-22 Method for a flat unsubmerged transition structure. |

Depressed Unsubmerged Factor | Benching correction factor used in the HEC-22 Method for a depressed unsubmerged transition structure. |

Depressed Submerged Factor | Benching correction factor used in the HEC-22 Method for a depressed submerged transition structure. |

Half Bench Unsubmerged Factor | Benching correction factor used in the HEC-22 Method for a half bench unsubmerged transition structure. |

Half Bench Submerged Factor | Benching correction factor used in the HEC-22 Method for a half bench submerged transition structure. |

Full Bench Unsubmerged Factor | Benching correction factor used in the HEC-22 Method for a full bench unsubmerged transition structure. |

Full Bench Submerged Factor | Benching correction factor used in the HEC-22 Method for a full bench submerged transition structure. |

Improved Bench Unsubmerged Factor | Benching correction factor used in the HEC-22 Method for an unsubmerged and bench type transition structure. |

Improved Bench Submerged Factor | Benching correction factor used in the HEC-22 Method for a submerged and bench type transition structure. |

HEC-22 Energy Losses (Third Edition) | |

Flat Unsubmerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a flat unsubmerged transition structure. |

Flat Submerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a flat unsubmerged transition structure. |

Depressed Unsubmerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a depressed unsubmerged transition structure. |

Depressed Submerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a depressed submerged transition structure. |

Half Bench Unsubmerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a half bench unsubmerged transition structure. |

Half Bench Submerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a half bench submerged transition structure. |

Full Bench Unsubmerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a full bench unsubmerged transition structure. |

Full Bench Submerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a full bench submerged transition structure. |

Improved Bench Unsubmerged Coefficient | Benching correction coefficient used in the HEC-22 Method for an unsubmerged and bench type transition structure. |

Improved Bench Submerged Coefficient | Benching correction coefficient used in the HEC-22 Method for a submerged and bench type transition structure. |

Pressure Hydraulics | |

Liquid Specific Gravity | Ratio of the specific weight of the liquid to the specific weight of water. |

Wet Well Increment | Unless a wet well is set to Fixed Level, this is the increment that is used to attempt to balance the wet well level such that the total flow out is greater than the total flow in. |

Use Pumped Flows? | In a steady state run, in pressure subnetworks, the flow from the network is calculated using pressure equations, the characteristics of the system and number of pumps running. For that flow rate to be passed to the downstream gravity system, the user should set this property to "True" (default). In some cases, the user will not want to use that flow but would rather pass a loading to the downstream system based on upstream loads and appropriate extreme flow factors similar to the way flows are handled in the gravity system. To pass those flows on to the downstream gravity system, the user sets this property to "False". In general, using pumped flows (True) is used when the user wants to look at the peak flows when the pumps are running, while using the loadings (False) gives more of a true picture as one moves far downstream from the pressure system and the effects of pump cycling become diminished. |

Use Linear Interpolation for Multipoint Pumps? | If set to true, the engine will use linear interpolation to interpret the pump curve as opposed to quadratic interpolation. Default is False. |

Accuracy | Unitless number that defines the convergence criteria for the iterative solution of the network hydraulic equations. When the sum of the absolute flow changes between successive iterations in all links is divided by the sum of the absolute flows in all links, and is less than the Accuracy value, the solution is said to have converged. The default value is 0.001 and the minimum allowed value is 1.0e-5. |

Trials | Maximum number of iterations to be performed for each hydraulic solution. Default is 40. |

Use Controls During Steady State? | When this box is checked, controls will be active during Steady State analyses. |

Pressure Friction Method | Lets you select a default friction method for all pressure pipes in your model. Select Mannings, Hazen-Williams, Darcy-Weisbach, or Kutters. The Property Editor attributes for pressure pipes are updated with the default friction method selected here. |

Rational Method | |

Use Rational Method Frequency Factors | If True, the Rational Method equation includes the Frequency Factor term. |

Frequency Factors | Specify the Frequency Factor for varying Return Periods. |

Allow Runoff Coefficient to Exceed 1.0? | When a Frequency Factor multiplier is applied to an area with a high runoff coefficient the result can sometimes exceed a value of 1.0. Set this property to False to prevent a runoff coefficient greater than 1.0 from being used in calculations. |

Carryover Modeling Method | Choose how bypassed carryover flow is conserved as it moves downstream. This option provides two choices, AS CA (Traditional) and AS Flow (HEC-22) with first being the default selection. What this option does is to specify how to add the carryover rational flow (the flow received from a bypassing gutter) to a receiving inlet. If the first choice is selected the calculation uses the bypassed CA and the receiving inlet local surface intensity to calculation the carryover flow which is added as part of the surface rational inflow. This sometimes can result in significant difference between the carryover flow and the flow in the bypassing gutter. The use of the second choice (AS Flow) then can improve such use case; this will make the calculation to directly use the bypassing gutter's flow as the carryover flow into the inlet, accordingly the carryover CA is derived by the flow and local inlet intensity. The calculation now support a fully networked system (the system to have both surface and subsurface elements connected, a surface only system (there are no pipes at all), a hybrid system (some partially piped) and any combination of surface and subsurface systems. The basic principle to support surface or mixed systems is that surface systems (inlets and gutters) have hydraulic behaviour (inlet capture and bypass) that is independent of subsurface pipe system. Therefore identical inlet calculation results are expected with or without subsurface pipes. |

SWMM Interface Files | |

Rainfall File Mode | Rainfall files are binary files 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 SWMM 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 SWMM to save the rainfall interface file after the first run and then reusing this file in subsequent runs can save computation time. The following file modes are available: None -When this option is selected, no Rainfall File will be used or saved. Use -When this option is selected, the Rainfall File field will become available, allowing you to select the rainfall file to use. Save -When this option is selected, the Rainfall File field will become available, allowing you to specify the name and location for the rainfall file to be saved. |

Rainfall File | This field is only available when the Rainfall File Mode is set to Use or Save, and allows you to specify the rainfall file to be used or saved, respectively. |

Runoff File Mode | This option 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 SWMM use this interface file to supply runoff results without having to repeat the runoff calculations again. The following file modes are available: None -When this option is selected, no Runoff File will be used or saved. Use -When this option is selected, the Runoff File field will become available, allowing you to select the runoff file to use. Save -When this option is selected, the Runoff File field will become available, allowing you to specify the name and location for the runoff file to be saved. |

Runoff File | This field is only available when the Runoff File Mode is set to Use or Save, and allows you to specify the runoff file to be used or saved, respectively. |

RDII File Mode | 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 SWMM run when Unit Hydrographs and nodal RDII inflow data have been defined for the model, or it can be created outside of SWMM using some other source of RDII data (e.g., through measurements or output from a different computer program). None -When this option is selected, no RDII File will be used or saved. Use -When this option is selected, the RDII File field will become available, allowing you to select the RDII file to use. Save -When this option is selected, the RDII File field will become available, allowing you to specify the name and location for the RDII file to be saved. |

RDII File | This field is only available when the RDII File Mode is set to Use or Save, and allows you to specify the RDII file to be used or saved, respectively. |

Save Hot Start File? | Hot start files are binary files created by SWMM that contain hydraulic and water quality variables for the drainage system at the end of a run. These data consist of the water depth and concentration of each pollutant at each node of the system as well as the flow rate and concentration of each pollutant in each link. 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 either to the same or to another file. 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. When this field is set to True a hot start file will be generated from the end results of the run. |

Hot Start File to Save | This field is only available when the Save Hot Start File? option is set to True, and allows you to specify the hot start file to be saved. |

Use Hot Start File? | When this field is set to True you can specify a hot start file to initialize the SWMM calculation run. |

Hot Start File to Use | This field is only available when the Use Hot Start File? option is set to True, and allows you to specify the hot start file to be used. |

Use Inflow File? | If True you can specify an inflow file to load the SWMM network. |

Inflow File to Use | Specify the path to the inflow file to be used. |

Save Outflow File? | If True you can generate a SWMM outflow file. |

Outflow File to Save | Specify the path to the outflow file to be saved. |

Explicit Results Control | |

Catchment Results Type | Specify the degree of results to be generated for catchments. |

Nodes Results Type | Specify the degree of results to be generated for nodes. |

Links Results Type | Specify the degree of results to be generated for links. |

SWMM Pattern Mode | Choose how patterns are handled by the SWMM engine. |

Apply SWMM Control Set? | When this proprty is set to True, you can apply a SWMM control set to the calculation run. |

SWMM Control Set | Specify the SWMM control set to be applied to the calculation run. |

Inlets | |

Active Components for Combination Inlets on Grade | Select the active openings for combination inlets on grade. |

Active Components for Combination Inlets in Sag | Select the active openings for combination inlets in sag. |

Neglect Gutter Cross Slope for Side Flow? | If True, when grate width is less than gutter width, gutter cross slope is used to determine side flow. |

Neglect Side Flow? | If True, only frontal views will be included in the inlet calculations. |

Inlet Transition Depth | A depth that is used to transition hydraulic calculations between surcharge dynamic calculation and non-surcharged inlet calculation. See Inlet Transition Depth. |