Rules and Ranges the for Hydrology Options in InfoSWMM and InfoSWMM SA

Subcatchment Hydrological (Modeling) - Data Table

This table contains all subwatershed data that is used to estimate the amount of  runoff and pollutant yielding from Subwatersheds. For more information on each of the input (data fields) in this table, Subcatchment editor may be referred.  The following table is in invert colors and shows the whole first row of the DB Table on separate rows in the image.

Field	Description
Subcatchment ID	User determined ID.  It can only be changed with the Change ID command.
Raingage ID	Specify Raingage ID used to input rainfall data to Subcatchment.
Receiving Node ID	Node ID for node receiving rainfall hydrograph from Subcatchment.
Subcatchment Area	Area of Subcatchment
Subcatchment Impervious (%)	Percentage of the Subcatchment covered by impervious surfaces.
Subcatchment Width	Characteristic width of the Subcatchment (feet or meters).
Subcatchment Slope	(%) Slope of the Subcatchment.
Subcatchment Curb Length	Total length of curbs in the Subcatchment (any length units). Used only when pollutant buildup is normalized to curb length.
Snow Pack ID	Name of snow pack parameter set (if any) assigned to the Subcatchment.
Manning's N for Imperv. Portion	Manning's N for overland flow over the impervious portion of the Subcatchment.
Manning's N for Pervious Portion	Manning's N for overland flow over the pervious portion of the Subcatchment.
Depression Stor. for Imp. Portion	Depth of depression storage on the impervious portion of the Subcatchment (inches or millimeters)
Depression Stor. for Perv. Portion	Depth of depression storage on the pervious portion of the Subcatchment (inches or millimeters).
% of Imperv. Part w/o Dep. Stor.	Percent of the impervious area with no depression storage.
Runoff Routing Destination	Choice of internal routing of runoff between pervious and impervious areas: IMPERV -    runoff from pervious area flows to impervious area. PERV -   runoff from impervious flows to pervious area. OUTLET -   runoff from both areas flows directly to outlet.
% of Runoff Routed to Destination	Percent of runoff routed between subareas.
LENGTH	Characteristic length of the Subcatchment (feet or meters).
CNTRD_DIST	Distance from centroid of Subcatchment to outlet (feet or meters).
NRCS_CN	NRCS Curve Number
DCIA_LEVEL	Directly Connected Impervious Area Level for CUHP method Level 1 assumes that all roof gutters are disconnected from driveways, gutters and Stormwater conveyance elements. Level 2 is for developments that already use Level 1 and do not have any curbs and gutters, including concrete swale gutters.  All runoff from streets and parking areas is directed as sheet flow across grass surfaces.  Intermittent curbs with frequent opening to the grass surface qualifies as Level 2.
CIA_RATIO	Fraction of the impervious area that is directly connected to the drainage system.
RPA_RATIO	Fraction of the pervious area that receives runoff from pervious area and unconnected impervious area.
TC	Time of concentration (minutes).
WQCV	Water Quality Capture Volume (watershed inches or millimeters).
WQCV_TIME	The time it takes to fully drain the brim-full WQCV
Runoff Coefficient	SDMRH only.  (Note - There is a different Runoff Coefficient reported in HYDQUA.RPT.  It is the total runoff from the Subcatchment divided by the total rainfall over the Subcatchment.  It should always be between 0 and 1.)
Storage Coefficient	Snyder UH and Clark UH.  Represents storage effects of the watershed.
Empirical Coefficient	Snyder UH only.
Conveyance Factor	Espey UH only
Infiltration Model	Use this to use a different infiltration model than the default model set in Simulation Options.
Depression Storage	Average depth of depression storage across the Subcatchment.  Can be used in NRCS methods to indicate Initial Abstraction (Ia).
Storage Coefficient	Storage Coefficient for German Runoff
Reservoir Count	Reservoir Count for German Runoff

  

Rules and Ranges the for Hydrology Options

Innovyze Hydrology Type Data Ranges and Default
Hydrology Type	Data Type	User Unit	Internal Unit	Valid Internal Range	Default Internal Values
		rain-depth
Colorado  UH		in or mm
DCIA level	enumerator			1, 2, 3	1
hydraulic length	double	ft or m	ft	>= 1	50
centroid distance	double	ft or m	ft	>= 0	0
DCIA fraction	double			0 <= & <= 1	0.2
RPA fraction	double			0 <= & <= 1	0.75
time of concentration	double	minutes	seconds	>= 1	60
captured volume	double	rain-depth	ft	>= 0	0
Drainage time	double	hours	seconds	>= 0	12
NRCS/Delmarva
Curve Number	double			40 <= & <= 100	75
hydraulic length	double	ft or m	ft	>= 1	50
time of concentration	double	minutes	seconds	>= 1	60
depression storage	double	rain-depth	ft	>= 0	0
Snyder  UH
storage coefficient	double			0.1 <= & <= 8	2
empirical coefficient	double			0.1 <= & <= 1.0	0.5
hydraulic length	double	ft or m	ft	>= 1	50
centroid distance	double	ft or m	ft	>= 0	0
depression storage	double	rain-depth	ft	>= 0	0
Clark UH
storage coefficient	double			0.1 <= & <= 10	1
time of concentration	double	minutes	seconds	>= 1	60
depression storage	double	rain-depth	ft	>= 0	0
Santa Barbara
time of concentration	double	minutes	seconds	>= 1	60
depression storage	double	rain-depth	ft	>= 0	0
Espey  UH
hydraulic length	double	ft or m	ft	>= 1	50
conveyance factor	double			0.6 <= & <= 1.3	1
depression storage	double	rain-depth	ft	>= 0	0
Modified Rational
time of concentration	double	minutes	minutes	>= 1	5
runoff coefficient	double			0 <= & <= 1	0.5
storm duration	double	factor	factor	TC:  > 0	1
		hours	hours	Dur:  >= 0
San Diego Rational
runoff coefficient	double			0 <= & <= 1	0.5
time of concentration	double	minutes	minutes	>= 1	0.75
German Runoff
Storage constant	double	minutes	minutes	> 0	5
Reservoir count	integer			> 0	1

Extended Period Dynamic Simulation (Unsteady Flow) in InfoSewer SA

Extended Period Dynamic Simulation (Unsteady Flow)

InfoSewer SA tracks the movement of wastewater flowing through the network over an extended period of time under varying wastewater loading and operating conditions. The extended period simulation (EPS) model implemented in InfoSewer SA is a fully dynamic (unsteady) model and is predicated on solving a simplified form of the full 1D Saint-Venant equations neglecting local acceleration.

 

The Saint-Venant equations or full dynamic wave equations for open channel flow routing consist of the conservation of momentum equation and the equation of continuity. The momentum equation is:

The continuity (mass conservation) equation is:

                                                                                                

where

 

x          =          distance along the pipe (longitudinal direction of sewer)

 

A          =          flow cross sectional area normal to x

 

y          =          coordinate direction normal to x on a vertical plane

 

d          =          depth of flow of the cross section, measured along y direction

 

Q         =          discharge through A

 

V          =          cross sectional average velocity along x direction

 

S₀         =          pipe slope, equal to sin θ

 

θ          =          angle between sewer bottom and horizontal plane

 

S_f            =          friction slope

 

g             =          gravitational acceleration

 

t              =          time

 

β          =          Boussinesqmomentum flux correction coefficient for velocity distribution

 

These complete unsteady flow equations (momentum together with continuity) along with appropriate initial and boundary conditions are rather tedious and computationally expensive to solve, especially for large sewer collections systems. As a result, acceptable simplifications and improved solution methods have been proposed including non-inertial, kinematic wave and dynamic wave simplifications. Hydraulically, the dynamic wave approach is the most accurate model among the approximations. The Muskingum-Cunge explicit diffusion wave dynamic flow routing model, obtained by neglecting local acceleration term in the momentum equation, is the most commonly used dynamic wave model.

In InfoSewer SAH20Map SewerPro, unsteady open channel (free surface) flow is simulated using Muskingum-Cunge technique whereas pressurized flow in any pipe is modeled assuming the pipe is flowing full and the energy equation is applied to the entire pipe section.

Muskingum-Cunge:       

where

                       

Here c is the dynamic wave celerity and B is the top width at normal depth for discharge Q. This highly efficient and accurate flow routing algorithm is used by InfoSewer SA to track the spatial and temporal variation of flows throughout the collection system.

In this method (a.k.a., one sweep explicit solution method), the network flow dynamic equations are formulated by using an explicit finite difference scheme such that the flow depth, discharge, or velocity at a given location and the current time can be solved explicitly from the known information at the previous locations at the same time level, as well as known information at the previous time level. Thus, the solution is obtained segment by segment, pipe by pipe, over a given time interval for the entire sewer network before progressing to the next interval for another sweep of individual solutions of the network flow equations for the entire network. A variable time step approach (based on the Courant number  is used to minimize numerical dispersion and ensure robustness and stability of the numerical scheme. Complex flow attenuation calculations can be explicitly carried out to more accurately simulate the movement and transformation of sanitary sewer flows in the collection system.

An excellent review and comparison between simulated and observed hydrographs of the various numerical methods for solving unsteady flow in simple and compound channels was presented by Chatila (Chatila 2003). In terms of overall performance, the Muskingum unsteady solution scheme compared favorably and proved to be a simple and reliable method avoiding complicated mathematical and numerical computations for the cases considered.

Flooding at manholes and wet-wells in InfoSewer is not modeled during an extended period dynamic simulation. Instead, the flows at the flooded structures are conserved and are not lost by the occurrence of flooding at the manholes. In actual flooding situations, flows may be diverted away from the flooded structures and out of the sewer collection system. However, a surcharged pipe or manhole is generally an indication of poor hydraulic performance of the sewer system. InfoSewer SA Pro assumes that the downstream pipes of flooded manholes are flowing full.

Sanitary sewer systems are typically designed to flow less than full and have an upper pressure limit of 4 to 6 psi. Sewer systems operating under pressurized flow condition may run the risk of violating local, state, and federal health codes. The USEPA regulations would also be in violation if raw sewage were discharged into the ground, potentially affecting groundwater. For these reasons, pressurized flows in sanitary sewers not designed to sustain pressures can be dangerous and in some cases can present an unlawful activity.

Surcharge

Sewer pipes can flow full with water under pressure, which is often known as surcharge flow. Surcharge flow occurs in under-designed pipes (or under extreme flows) when the flow rate Q exceeds the full pipe capacity Qf .

Flow conditions are unstable at the transition between open-channel (free surface) flow and full pipe flow. A wave or surge can induce full flow in the pipe in the unstable range. Surcharge in sewer pipes is modeled in InfoSewer SA using energy and continuity principles. The energy equation between sections 1 and 2 in a pipe can be written as:

Here z denotes the invert elevation; d represents the water depth; and H_L designates the head loss between sections 1 and 2. The energy equation is used to determine the difference in hydraulic grade line elevation (which is added at the upstream manholes) needed to pass downstream flows under the surcharge condition.

The procedure for analyzing surcharge in sewer pipes is illustrated using the figure below as a reference.

 

Assuming that pipe 4 (between manholes 4 and 5) is under-designed, Q4 will exceed its full flow capacity and the hydraulic grade line at manhole 4 will increase based on energy consideration to allow Q4 to pass through pipe 4 (note that water always flows from higher to lower energy) as continuity must be satisfied. This forces the hydraulic grade line at manhole 3 to increase in order for Q3 to pass through pipe 3. The procedure continues upstream until the slope of the energy grade line needed to transport the flow allows open-channel flow condition to occur in the pipe. The projected hydraulic grade line will then intersect the uniform water surface flow to complete the backwater curve.

The energy equation is also used to model the flow in siphons, which can occur in adverse pipes. InfoSewer assumes that the siphon flows full, with a continuous liquid column throughout it.  This image shows how an adverse sloped link InfoSewer looks

Flow Attenuation

When a flow hydrograph is injected and propagates downstream in sewer pipes the bulk of the water will normally travel slower than its induced disturbance or wave. That is, if the water is injected with a tracer then the tracer lags behind the disturbance. The speed of the disturbance depends on parameters such as depth, width and flow velocity. This disturbance will tend to flatten, or spread out, the peak flow in the downstream direction along the sewer pipes.

Flow attenuation in a sewer system is defined as the process of reducing the peak flow rate by redistributing the same volume of flow over a longer period of time as a result of friction (resistance), internal storage and diffusion along the sewer pipes. InfoSewer SA  uses the distributed Muskingum-Cunge flow routing method based on diffusion analogy, which is capable of accurately predicting hydrograph attenuation or peak flow damping effects (peak subsidence). The method is attractive since the routing parameters can be directly calculated as a function of pipe and flow properties, is applicable for a wide range of flow conditions, and does not require calibration or any iterative scheme. The Muskingum coefficients are derived from the pipe diameter, length, discharge, dynamic wave celerity, and slope of the flow. The magnitude of attenuation depends on parameters such as the peak discharge, the curvature of the hydrograph, and the width of flow. An example of flow attenuation process as a hydrograph is routed through a sewer system is illustrated in the figure below.

Hydrograph Aggregation/Flow Accumulation

Proper aggregation of multiple hydrographs with distinct time steps is essential in a sewer collection system as the flows are routed in both time and space. Aggregation normally occurs when laterals are merging around manholes and wet-wells. This can create offset of time-steps, which can affect accurate determination of flow peaks and volumes. InfoSewer SA utilizes a highly accurate dynamic hydrograph aggregation method that allows preservation of both flow peaks and flow volumes when multiple hydrographs with different time steps are added. The method is Lagrangian in nature and tracks the hydrograph ordinates as they are transported along the sewer pipes and mix together at manholes and wet-wells. A variable time step is used to minimize numerical dispersion, enhance stability, and maximize computational efficiency. See the User Guide for more information on Extended Period Simulations.

 

 

 

How to Force SWMM5 to use ONLY the Wet Well area for a Pump

Problem:  As SWMM5 is a link node network, the area of a Storage Node is both the area of the Wet Well and typically ½ the surface area of the connecting links.  There is no surface area for the Pump(s) downstream of the Wet Well (Storage) but the area of the upstream links will add to the surface area of the Wet Well.   One Answer:  You can eliminate this issue by adding a in a Dummy link to connect the upstream Gravity Main links to the Wet Well. The Dummy link has no surface area and sets the Outflow of the link to the Total Inflow of the Upstream Node to the Dummy link.   The Wet Well will then only have the surface area of the Wet Well.

An important difference between Capacity d/D and Surcharge d/D in InfoSWMM

An important difference between Capacity d/D and Surcharge d/D in InfoSWMM, Capacity is based on Area and Surcharge d/D is based on Depth

InfoSWMM is a comprehensive tool for the design and management of wastewater and stormwater systems. In InfoSWMM, the terms 'Capacity' and 'Surcharge' are used to describe different aspects of the system's performance under various flow conditions.

Capacity d/D:

The term 'Capacity d/D' in InfoSWMM refers to the ratio of the flow depth (d) to the diameter (D) of the pipe. However, when we talk about 'Capacity', it's crucial to understand that this is derived based on the area of flow within the pipe, not the depth. The 'd/D' ratio here gives us an understanding of how full the pipe is under normal flow conditions. The 'Area' here refers to the cross-sectional area of the flow within the pipe.

This ratio gives an idea of how much of the pipe's total potential flow area is being used. When the ratio is low, the pipe has plenty of additional capacity. When the ratio is close to or at 1, the pipe is at or near its total flow capacity, and any additional flow could result in surcharging.

Surcharge d/D:

'Surcharge d/D', on the other hand, refers to the situation where the flow depth (d) exceeds the pipe's diameter (D) - in other words when water rises above the crown of the pipe. Unlike 'Capacity', which is based on the area of flow, 'Surcharge' is directly concerned with the actual depth of the water above the pipe crown.

In this situation, the pipe is essentially functioning as a pressurized conduit, as it is completely filled with water and the water level in upstream manholes (or other structures) is higher than the crown of the pipe. This is a situation that typically needs to be avoided in gravity-fed systems, as it can lead to backups and overflows.

In conclusion, 'Capacity d/D' and 'Surcharge d/D' represent different operational conditions in a drainage system modeled by InfoSWMM. 'Capacity d/D' is an indicator of how much of the pipe's flow area is being used under normal conditions, while 'Surcharge d/D' is an indicator of conditions when the water level exceeds the top of the pipe, potentially leading to problematic conditions in the system.