Component: Inlets, outlets and controls



Hydraulic control is essential for the adequate functioning of any SuDS component. As SuDS promote the use of small, cost effective landscape features, on the surface and close to source, the control and conveyance of low flows and velocities are essential.


Inlets, outlets and other control structures are key elements of well designed SuDS. Inlet and outlet features allow water to flow into and out of features and also limit the rate at which water flows along and out of the system.


There are many different designs and variations, including landscaped pipes, perforated pipes, weirs, orifices, vortex control devices and spillways. Each inlet or outlet structure should be designed to add interest to the urban landscape, but also consider the implications of maintenance, as regular inspections and cleaning may be required.


Advantages & disadvantages 



  • Simple structures

  • Can be designed to suit individual sites

  • Can provide accurate flow control from one SuDS feature to another

  • Can block and require regular maintenance

  • Poorly designed inlets and outlets can look ugly


Where component can be used 

Residential: Yes

Commercial/industrial: Yes

High density: Yes

Retrofit: Yes

Contaminated sites: Yes

Sites above vulnerable groundwater: Yes



Design criteria


  • Upstream SuDS which promote slow water velocities encourage an efficient design by reducing the need for erosion control features and vertical headwalls

  • For shallow systems, where there is a limited depth of water storage, simple orifice controls are often the most suitable form of control.

  • Submerged outflow conditions are most suitable when water is discharged to a watercourse.


Landscape and Urban Design

  • Scale and form to suit surrounding landscape character

  • Aesthetically pleasing design is preferable.

  • Minimal embodied carbon (e.g. minimal use of concrete) is preferable in the design



  • Ease of access & maintenance are preferable design considerations in order to allow for regular inspections

  • Surface control structures are less costly to maintain than underground features.



  • Regular inspections

  • Removal of litter/debris 

  • Check the prime flow controls are discharging and working correctly.


 Read more on:

SuDS Component Inlet


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