Stormwater Management Model (SWMM) Information for watershed water quality, hydrology and hydraulics modelers (Note this Blog is not associated with the EPA). You will find Blog Posts and Twitter Embeds on the Subjects of SWMM5, InfoSWMM, InfoSewer, SWMMLive, InfoSWMM SUSTAIN, SWMM4 and SWMM in general.
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Flow Routing in InfoSWMM and Innovyze SWMM Products
Flow routing within a conduit link in InfoSWMM H2OMap SWMM InfoSWMM SA is governed by the conservation of mass and momentum equations for gradually varied, unsteady flow (i.e., the Saint Venant flow equations). The InfoSWMM H2OMap SWMM InfoSWMM SA user has a choice on the level of sophistication used to solve these equations:
Steady Flow Routing
Kinematic Wave Routing
Dynamic Wave Routing
Steady Flow Routing
Steady Flow routing represents the simplest type of routing possible (actually no routing) by assuming that within each computational time step flow is uniform and steady. Thus it simply translates inflow hydrographs at the upstream end of the conduit to the downstream end, with no delay or change in shape. The Manning equation is used to relate flow rate to flow area (or depth).
This type of routing cannot account for channel storage, backwater effects, entrance/exit losses, flow reversal or pressurized flow. It can only be used with dendritic conveyance networks, where each node has only a single outflow link (unless the node is a divider in which case two outflow links are required). This form of routing is insensitive to the time step employed and is really only appropriate for preliminary analysis using long-term continuous simulations.
Kinematic Wave Routing
This routing method solves the continuity equation along with a simplified form of the momentum equation in each conduit. The latter requires that the slope of the water surface equal the slope of the conduit.
The maximum flow that can be conveyed through a conduit is the full-flow Manning equation value. Any flow in excess of this entering the inlet node is either lost from the system or can pond atop the inlet node and be re-introduced into the conduit as capacity becomes available.
Kinematic wave routing allows flow and area to vary both spatially and temporally within a conduit. This can result in attenuated and delayed outflow hydrographs as inflow is routed through the channel. However this form of routing cannot account for backwater effects, entrance/exit losses, flow reversal, or pressurized flow, and is also restricted to dendritic network layouts. It can usually maintain numerical stability with moderately large time steps, on the order of 5 to 15 minutes. If the aforementioned effects are not expected to be significant then this alternative can be an accurate and efficient routing method, especially for long-term simulations.
Dynamic Wave Routing
Dynamic Wave routing solves the complete one-dimensional Saint Venant flow equations and therefore produces the most theoretically accurate results. These equations consist of the continuity and momentum equations for conduits and a volume continuity equation at nodes.
With this form of routing it is possible to represent pressurized flow when a closed conduit becomes full, such that flows can exceed the full-flow Manning equation value. Flooding occurs when the water depth at a node exceeds the maximum available depth, and the excess flow is either lost from the system or can pond atop the node and re-enter the drainage system.
Dynamic wave routing can account for channel storage, backwater, entrance/exit losses, flow reversal, and pressurized flow. Because it couples together the solution for both water levels at nodes and flow in conduits it can be applied to any general network layout, even those containing multiple downstream diversions and loops. It is the method of choice for systems subjected to significant backwater effects due to downstream flow restrictions and with flow regulation via weirs and orifices. This generality comes at a price of having to use much smaller time steps, on the order of a minute or less (InfoSWMM will automatically reduce the user-defined maximum time step as needed to maintain numerical stability).
Normally in flow routing, when the flow into a junction exceeds the capacity of the system to transport it further downstream, the excess volume overflows the system and is lost. An option exists to have instead the excess volume be stored atop the junction, in a ponded fashion, and be reintroduced into the system as capacity permits. Under Steady and Kinematic Wave flow routing, the ponded water is stored simply as an excess volume. For Dynamic Wave routing, which is influenced by the water depths maintained at nodes, the excess volume is assumed to pond over the node with a constant surface area. This amount of surface area is an input parameter supplied for the junction.
Alternatively, the user may wish to represent the surface overflow system explicitly. In open channel systems this can include road overflows at bridges or culvert crossings as well as additional floodplain storage areas. In closed conduit systems, surface overflows may be conveyed down streets, alleys, or other surface routes to the next available stormwater inlet or open channel. Overflows may also be impounded in surface depressions such as parking lots, back yards or other areas.
World-Renowned Urban Drainage Modeling Authority Robert Dickinson Joined Innovyze in January, 2008Broomfield, Colorado USA, January 16, 2008/altered 20142008/2014 Robert E. Dickinson, one of the world’s leading experts in wastewater and urban drainage modeling, has joined Innovyze as Product Sector Leader. Dickinson, who comes to the company from CDM now CDMSmith, will be charged with maintaining, enhancing and supporting Innovyze's flagship SWMM5-based product line (InfoSWMM and H2OMAP SWMM as well as the GIS based InfoSewer and H2OMap Sewer), which are some of the industry’s leading wastewater and urban drainage systems design and modeling software. He will also be responsible for coordinating vital collaborative research and technology transfer with key universities and government organizations as well as developing business strategies that advance Innovye’s overall growth objectives in wastewater and stormwater systems management and heighten its initiatives in both U.S. and i…
Engine Error NumberDescription ERROR 101: memory allocation error. ERROR 103: cannot solve KW equations for Link ERROR 105: cannot open ODE solver. ERROR 107: cannot compute a valid time step. ERROR 108: ambiguous outlet ID name for Subcatchment
These warning and error messages were added in SWMM 184.108.40.206 to 5.0.016 to trap questionable raingage, link and node data. Correcting these errors does make a better model . The list shown below has the major new warnings and errors and help on interpreting the messages. WARNING01: wet weather time step reduced to recording interval for RainGage Explanation: The user selected hydrology time step is automatically reduced by the engine to match the rain gage interval. The smallest rainfall interval among all of the gages will be used during the simulation. WARNING 02: maximum depth increased for Node Explanation: The rim elevation of a node has to be at least equal to the crown elevation of the highest connecting link to the node. The maximum depth of the node is increased to match the highest crown elevation. WARNING03: negative offset ignored forLink Explanation:Negative Offsets are set to offsets of 0.0 WARNING 04: minimum elevation drop used forConduit Explanation: If the elevation acro…