MIKE+ | Displaceable Covers for Manholes in MIKE+ 2026

Displaceable Covers for Manholes in the Nodes Editor

In MIKE+ 2026 another option to define node’s cover has been introduced in the Nodes editor. This feature allows users to define manholes as “Displaceable cover” type. 

Setting-up a node with a “Displaceable cover” allows for improved modeling of interaction between network hydraulics and surface, providing a more realistic representation of the manhole’s response to pressure build-up during surcharge, with or without surface inundation.

Concept Overview

Conventionally , manhole covers in hydraulic models are represented as either “sealed” (non-opening), “spilling” (in which surcharged flows  leave the hydraulic system, once a certain pressure threshold is exceeded), or most frequently as “normal” in which the numerical engine handles surcharges by storing volumes in a virtual basin above the manhole cover level. 

The new ”Displaceable cover” option provides for the simulation of surcharge mechanism more realistically. Starting (normally) from a full closure, a manhole cover moves progressively with growing internal pressure within the structure, giving place to partial flow before being completely removed. The “Displaceable cover” models this effect by controlling the opening percentage based on the node’s internal pressure. 

The opening percentage is actually a ratio between the actual opening area and the full cover area.  See Fig. 1.

Fig. 1 - Displacement Cover Concept

How to work with the Feature

In the Nodes Editor the user can choose the cover type for manholes. When the “Displaceable cover” is selected, a curve (tabulated function) must be specified defining the relation between the node pressure and opening percentage of the lid, in other words how much the cover opens at a specific pressure.

With dry surface, pressure is calculated as height of internal water column above the node’s ground level. In integrated 1D/2D Overland models with inundation on the surface, pressure is calculated as difference between the internal node’s water level and the surface water level.

The lid will start moving when the pressure force exceeds the forces that keep the lid in its original position: the lid’s own weight, the weight of any other material or objects placed on the lid, plus any attachment features, such as consolidated dirt, rust, bolts or welding.

Spilling (surcharging) flow through partially displaced lid is calculated as flow through orifice with area corresponding to the actual lid position and driven by the available pressure.

The flow area for a fully displaced lid is equivalent to the manhole area.  As lid sizes are typically smaller than manholes themselves, a fully displaced lid is not necessarily described as 100% displacement in cover displacement table, but with a number corresponding to the ratio between the lid and the manhole areas.

Setting-up the “Displaceable cover” type follows the same workflow as for any of the three cover types available so far in MIKE+. 

1. Go to Nodes editor and select the target manhole(s).

2. In the Cover tab look in the dropdown option and select “Displaceable cover” (Fig. 2).

3. In Curves and Relations create a manhole cover opening percentage/pressure relation (Fig. 3).  

Fig. 2 - Cover type options
 

By careful definition of the pressure/movement function, any movement scenario  can be specified, only limited by the practicalities of time discretization, i.e. the simulation time step. Modelling displaceable covers may require significant shortening of simulation time to preserve stability and provide insight into the details of lids’ movements and resulting rapid changes in flow conditions in the network.

Once when displaced to some new position, the lid does not move back to its original position with falling pressure: it remains in a new position until pressure grows again so high that the lid is displaced even further.

The manhole cover displacement can be recorded in the results file, to analyze the cover response through the simulation. Look at “Additional Items” under Network HD and check in the “Manhole cover displacement”.  See Fig. 4. 

Fig. 4 - HD Results Additional Items

Results and Output Analysis

The resulting time series of cover opening percentage shall be analyzed jointly with time series of surcharging discharge (or flow exchange between the network and surface in case of 1D/2D integrated models) and water levels in the manhole. These results provide insight into the surcharge event dynamics locally for individual manholes, but also provide a broader picture  on the system scale , of likely locations for blow-up surcharge .

The results can be presented as map results (see Fig. 5), plotted in time series (see Fig. 6) or added as additional items in Longitudinal profiles (see Fig. 7). 

Fig. 5 - Cover opening percentage map of a simple network.

Fig. 6 - Cover opening percentage time series plot.

Fig. 7 - Longitudinal Profile result presentation.

Conclusion  

The Displaceable Cover feature increases hydraulic modeling realism by including a configurable, user-defined behavior of manhole covers during surcharging conditions, thus complementing the existing tools for surface flooding and overflows.  

Its application will benefit all modelers interested in as accurate as possible description of stormwater networks behavior during extreme hydraulic loads.