Per capita sanitary flow

[MitchHeineman]

A sanitary sewer model can be easier to develop and understand if wastewater rates are specified using per capita values and population instead of directly specified flowrates. This can currently be achieved by creating a DWF pattern that identifies a per capita rate (e.g., 75E-6 mgd representing 75 gallons per capita per day) and specifying associated population equivalents instead of flow rates at model load points (e.g., 2000 people). A better paradigm would let the user choose whether to represent sanitary flows as absolute rates or via per capita values.

[In related veins, SWMM should allow dry weather flow specification using some of the methods found in similar software, such as allowing DWF to be associated with subcatchments rather than junctions and allowing multiple diurnal patterns to contribute to a single load point. Although I don't want to see unnecessary code bloat ;) ]

[dickinsonre]

I heartedly agree. I do have a blog with a workaround to use population and per capita flow but the real thing in a future SWMM5 would be better. https://www.linkedin.com/pulse/how-use-population-node-dwf-swmm5-infoswmm-instead-mean-dickinson/

[dickinsonre]

In addition - In SWMM5, the ability to assign multiple Dry Weather Flows (DWFs) to a single node would offer significant modeling benefits, both in terms of accuracy and workflow efficiency. Here are the key reasons why this enhancement would be valuable:

1. More Accurate Representation of Complex Inflows:
   Real-world catchments often receive a combination of different baseline flows: domestic wastewater, commercial or industrial contributions, infiltration/inflow (I/I), and possibly groundwater seepage. Currently, to represent these multiple sources, modelers must combine them into a single aggregated DWF or create additional “dummy” nodes linked to the main node. By allowing multiple DWF inputs directly at a single node, each flow source can be represented distinctly, preserving each category's unique patterns and diurnal variations without resorting to artificial node configurations.

2. Simplified Modeling Structures:
   Without the capability for multiple DWF rows, the workaround of using dummy nodes and dummy links adds complexity and clutter to the model network. These extra elements make the model harder to visualize, maintain, and troubleshoot. If SWMM5 were to support multiple DWF entries per node, the user could specify all base flows at their actual location in the network. This reduces the number of unnecessary nodes and links, leading to a cleaner, more direct representation of the system.

3. Improved Calibration and Sensitivity Analyses:
   With multiple DWF inputs, adjusting and calibrating individual base flow components becomes easier. For instance, if infiltration and domestic load need to be calibrated separately, each can have its own DWF record with distinct patterns and baseline assumptions. This granular control streamlines sensitivity testing and calibration, as you can directly tweak one flow category without affecting the others.

4. Enhanced Scenario Management:
   Planning and scenario analysis often require changing certain baseline conditions while leaving others intact. With multiple DWFs at a single node, scenarios like "reduce infiltration by 20%" or "increase commercial flow due to new development" can be implemented by adjusting just the relevant DWF input line. This targeted approach is more straightforward than recalculating and redistributing flows through a dummy-node configuration.

5. Consistency with Other Modeling Software:
   Many modern modeling tools support assigning multiple base flow components directly to the same element. Adding this capability to SWMM5—especially within user interfaces like InfoSWMM—would bring it closer in line with industry expectations and best practices.

In summary, allowing multiple DWF rows at a single node would significantly simplify model setups, improve calibration processes, make scenario testing more efficient, and provide a more faithful representation of complex, real-world baseline flow conditions. The current method of using dummy nodes and links is a workaround that works, but it introduces unnecessary complexity that could be elegantly eliminated by native support for multiple DWF inputs.