In SWMM 5 (Storm Water Management Model), surcharging refers to a condition where water levels rise above the highest point, or crown, of the conduits (pipes) in the drainage network. This situation usually occurs when the system's capacity is exceeded due to high levels of stormwater or wastewater inflow.
The SWMM 5 report file (RPT file) includes a Node Surcharge Summary Table, which provides crucial details about the duration and extent of these surcharging events.
Node Surcharging:
A node is a point in the network where pipes connect. Surcharging can occur at a node in the following conditions:
If the node cannot store additional water (i.e., it cannot 'pond') and the water depth at the node exceeds the crown elevation of the highest pipe connected to that node.
If the node can store additional water (it can 'pond'), surcharging occurs when the water depth exceeds the crown elevation of the highest pipe connected to the node but remains below the full depth of the node.
Essentially, surcharging happens when the system cannot accommodate the excess water, leading to water levels rising above the pipe's topmost part but not yet reaching the full depth of the node.
Node Flooding:
Node flooding is a more extreme event that occurs when the water surface level reaches or surpasses the rim elevation of the node. This situation means that the water is spilling out of the system, potentially leading to surface flooding.
Node Surcharge Summary Table (Figure 1)
This table in the RPT file presents a summary of the surcharging events at each node, including the duration of surcharging.
Definition of Surcharging at a Node (Figure 2)
This figure would typically show a diagram or explanation illustrating the conditions under which a node is considered to be surcharging, visually demonstrating the situations described above.
Definition of the Height above Crown and Depth below Rim (Figure 3)
This figure would likely provide definitions or illustrations explaining the 'Height above Crown' and 'Depth below Rim' columns in the Node Surcharge Summary Table. 'Height above Crown' refers to how much higher the water level is compared to the crown of the highest pipe, while 'Depth below Rim' refers to the difference between the water level and the full depth of the node.
These details allow engineers to understand the behavior of the drainage system under various flow conditions and inform necessary adjustments or improvements to manage stormwater effectively.
