Storm Water module in MiTS 3 has 2 modes, Design and Analysis. These 2 modes of analysis can be switched by clicking their respective button, Design/Analysis mode in the Analysis section.
General Input #
Inflow Source #
In MiTS 3, the user was given the option to choose the project’s Inflow Source, Tabular Flow or Graphic Catchment. Choosing the Tabular Flow will require the user to input the data into User Defined Hydrograph after clicking the Tabular button.
Meanwhile, the Graphic Catchment is the old behaviour of designing catchment for the drainage system. The user may either design the catchment directly in MiTS or import it from the drawing.
Design Mode #
Input #
Design mode is the type of analysis from the previous version, MiTS 2. The project will be analysed as a preliminary design based on the design standard, which is the iteration of the drain sizes and IL (if iterate == Yes). This Design mode does not utilize routing and is based on a straightforward, static manning equation. As a result, it is incapable of recognizing time-varying inputs and will always provide a constant output for variables like flow, velocity and water depth.
To analyse the output, the Analysis Type should be Design in the Storm Design Option Dialog box. Click the Execute button to open this box and choose the Inflow Source; CatchmentHydrology or UserDefined.
Output #
Sample Project File HERE
As the Design mode is the default analysis mode in MiTS 2, the output is similar to what was analysed in MiTS 2: Excel Report, KeyPlan, Long Section, QS, Textual Report and Sump Detail. There are another 2 Output, Summary and Graph which will be enable for Analysis mode output.
Analysis Mode #
Input #
In the event that users change to the Analysis mode, the project will be analysed in a time series format. This means that the analysis of the drain and storage system will generate a series of flow, discharge and water depth every n seconds. As this Analysis mode is a simulation of the stormwater in a real-life situation, all drain ILs and dimensions are based on the user’s judgement, which means no iteration from MiTS. (User may use Design mode first to get the best possible drain IL and dimension from iteration)
Similarly to Design mode, in the Storm Design Option Dialog, the user must choose Analysis as Analysis Type when executing the analysis and select the right Inflow Source. For Analysis mode, the user must input additional data for;
- Storm Events
- Hydrology
- Hydraulics
- Storage
These four input must be completed to proceed with the analysis. If the Inflow Source is UserDefined, the user only has to input a., c. and d.. Other than the Storm Design Option Dialog, these options can also be found in the Project Settings > Storm Design > Expand Routing (Analysis Type == Analysis) > Analysis Events/Hydrology/Hydraulics
Storm Events #
Click the ‘…‘ button to open the Storm Event Dialog and configure them. Double-click on the default data to adjust them.
Hydrology #
There are multiple Catchment Routing Methods that the user can choose; RationalSteady, RationalHydrograph, TimeArea and EPASWMM. RationalHydrograph and EPASWMM routing method will require additional input;
RationalSteady routing method is a straightforward approach (static analysis) used to estimate peak stormwater runoff by multiplying the runoff coefficient (which reflects how much rain turns into runoff), the rainfall intensity (the rate of rainfall) and the area of the land. It provides a quick way to calculate how much runoff will be generated from a given area during a storm, which helps in designing effective drainage systems to manage and mitigate potential flooding.
RationalHydrograph routing method extends the RationalSteady routing method by estimating the runoff hydrograph, which is a graphical representation of the flow rate over time during a storm event. Instead of just calculating a single peak flow rate, it provides a more detailed view of how runoff changes over time. It involves creating a hydrograph that starts with an initial rise in runoff, reaches a peak and the declines as the stormwater recedes. It is ideal for simple projects like on-site detention (OSD) and small ponds. For complex systems or high-risk areas, the TimeArea routing method or computer models is more suitable.
TimeArea routing method assumes that the outflow hydrograph for any storm results from separate subcatchment translation and storage effects. It describes the pure translation of direct runoff through the drainage network using channel travel time, resulting in an outflow hydrograph that excludes storage effects.
EPASWMM routing method utilises the infiltration method from EPASWMM. The user must choose the runoff infiltration method between HORTON, MODIFIED_HORTON, GREEN_AMPT, MODIFIED_GREEN_AMPT and CURVE_NUMEBR.
| Infiltration Method | Description |
| HORTON | This method models infiltration as decreasing exponentially from a maximum to a minimum rate during extended rainfall. Inputs needed are the maximum and minimum infiltration rates, a decay coefficient and the time for saturated soil to dry. |
| MODIFIED_HORTON | This modified Horton Method used cumulative infiltration above the minimum rate as its state variable, rather than time, leading to more accurate estimates at low rainfall intensities. It requires the same input parameters as the traditional Horton Method. |
| GREEN_AMPT | This infiltration model assumes a sharp wetting front divides the soil into unsaturated below and saturated above. Required inputs are the initial moisture deficit, the soil’s hydraulic conductivity and the suction head at the wetting front. The recovery rate of moisture deficit during dry periods is empirically linked to hydraulic conductivity. |
| MODIFIED_GREEN_AMPT | This method adjusts the Green-Ampt procedure by not depleting the moisture deficit in the topsoil layer during initial low rainfall periods. This modification yields more realistic infiltration results for storms with prolonged low-intensity rainfall. |
| CURVE_NUMBER | This approach, based on the NRCS (SCS) Curve Number method, estimates runoff by determining soil infiltration capacity from the Curve Number. During rainfall, this capacity decreases with cumulative rainfall. Required inputs are the Curve Number and the time for fully saturated soil to dry. |
Hydraulics #
The hydraulics parameters that the user must define are Flow Proportioning, Intensity Calculation, Flow Routing Method and Routing Steps.
| Parameters | Options | Description |
| Flow Proportioning | Split | Designated the drain flow to the beginning of the node, the end of the node, or divide them equally |
| BeginningNode | ||
| EndNode | ||
| Intensity Calculation | StormDuration | Based on the actual storm duration |
| IndividualDrain | Based on individual drain designed rainfall intensity | |
| Flow Routing Method | STEADY | – Simplest routing method (effectively no routing) – Assumes flow is uniform and steady within each time step – Directly translates inflow hydrographs from upstream to downstream without delay or shape change – Uses normal flow equation to link flow rate with flow area or depth – Cannot account for channel storage, backwater effects, entrance/exit losses, flow reversal, or pressurised flow – Suitable only for dendritic networks with single (or two for dividers) outflow links per node – Best for preliminary, long-term continuous simulations; insensitive to time step |
| KINWAVE (Kinematic Wave) | – Solves the continuity equation and a simplified momentum equation for each conduit – Assumes the water surface slope equals the conduit slope – Maximum flow is the full normal flow value; excess flow can be lost or ponded at the inlet node and reintroduced as capacity allows – Allows flow and area to vary spatially and temporally, leading to attenuated and delayed outflow hydrographs – Cannot account for backwater effects, entrance/exit losses, flow reversal, or pressurised flow – Limited to dendritic network layouts – Maintains numerical stability with moderately large time steps (1 to 5 minutes) – Effective and efficient for long-term simulations if significant effects are not expected | |
| XKINWAVE (Extended Kinematic Wave) | – Builds on the basic Kinematic Wave approach – Handles more complex flow scenarios – Models spatial and temporal variations in flow and storage – Offers improved numerical stability and performance – Suitable for detailed analysis when full dynamic wave modelling is too complex or intensive | |
| DYNWAVE (Dynamic Wave) | – Solves the complete one-dimensional Saint Venant flow equations for accuracy – Includes continuity and momentum equations for conduits and volume continuity at nodes – Can model pressurised flow when conduits are full, with flows exceeding normal values – Handles flooding by ponding excess flow at nodes or losing it from the system – Accounts for channel storage, backwater, entrance/exit losses, flow reversal, and pressurised flow – Suitable for any network layout, including those with diversions and loops – Ideals for systems with significant backwater effects and flow regulation via weirs and orifices – Required small time steps (around 30 seconds or less) for numerical stability, with SWMM adjusting time steps as needed | |
| Routing Steps | The time step of level pool routing |
Storage #
There is only one parameter to be inputted which is the storage slice. It is the depth step used to slice the storage for the depth vs area.
Output #
CatchmentHydrology Project File HERE
UserDefined Project File HERE
The only difference between Design mode and Analysis mode output is the Summary and Graph report. The Summary report is where the user can see the Error(s) and Warning(s) within the simulation and the Graph report is a time series graph (e.g.: Flow vs Time).
Some errors that the user might encounter in when using the Analysis mode are as below:
| Error Code | Description |
| Code 113, invalid roughness for Conduit n | Drain’s n roughness (Manning) is either 0 or negative (Inflow Source: UserDefined) |
| Code 115, adverse slope for Conduit n | Under Steady and Kinematic Wave routing, all drains must have positive slopes. Adverse slopes are permitted under the Dynamic Wave routing |
| Code 131, the following links form cyclic loops in the drainage system | The Steady and Kinematic Wave flow routing methods cannot be applied to systems where a cyclic loop exists |
| Code 133, Node n has more than one outlet link | Under Steady or Kinematic Wave flow routing, a junction node can have only a single outlet link |
| Code 139, Regulator n is the outlet of a non-storage node | Under Steady or Kinematic Wave flow routing, orifices, weirs and outlet links can only be used as outflow links from storage nodes |
| Code 141, Outfall n has more than 1 inlet link or an outlet link | An outfall node is only permitted to have one link attached to it |
| Code 145, Drainage systems has no acceptable outlet nodes | Under Dynamic Wave flow routing, there must be at least one node designated as an outfall |
| Code 173, Time Series n has its data out of sequence | The time values of a time series must be entered in sequential order |
| Code 227, Transect n has no manning’s N | When the drain n Manning Coefficient is 0 (Inflow Source: CatchmentHydrology) |
CatchmentHydrology #
By analysing the project using CatchmentHydrology, the user can choose the suitable routing method based on the project requirement. Each routing method generates its inflow hydrograph.
RationalSteady
A static inflow us used during the analysis, meaning the water flow rate does not change over time, reflecting a constant discharge resulting in a steady flow hydrograph, a simple, flat-line graph.
RationalHydrograph
The hydrograph generated shows the flow rate of water over time, with the peak flow calculated using the Rational method formula, Q = CiA/360 producing a simplified hydrograph shape.
TimeArea
“Work is in progress”
EPASWMM
“Work is in progress”
UserDefined #
UserDefined which required the user to create a time-series hydrograph plots flow rate against time, providing a detailed view of how discharge in the drainage system varies over a given period.
