Hydraulic Design in Kerb2019-03-01T14:22:42+00:00

All exposed impermeable surfaces and structures require efficient drainage to prevent flooding or settlement and to protect surfaces. Our design advice and calculations will help you to design a hydraulically efficient, sustainable and lightweight solution for surface water management.

For an optimum/best design each section of channel/ckd should be designed to work as close to their maximum capacity, as this aids silt transit with faster flows created within the channel body. It is also cost effective to have long sections of CKD delivering to the minimum of outlet points.


Durakerb standard kerb units provide a simple drainage/road/landscape feature where surface water can be contained and channelled at surface level to single or multiple outlets. The water management/function is therefore dependant on factors beyond our scope. Traditional methods of calculation should be used.

Effective & Simple Solution for Surface Drainage

Combined Kerb & Linear Surface Drainage is a simple concept and therefore provides an effective and simple solution for surface drainage. As a drainage system, there are basically two main elements of primary design to consider;

Collection (Surface Water)

Disposal to SW Connection/Attenuation.

In most instances the design requirements for a kerb edge feature will be set out in MHCW – Series 1100 with additional requirements in 500 series appendix 5/5.

The Duradrain CKD range is produced to match the traditional standard kerbs used extensively across the UK. The hydraulic function works hidden within the channel body, protected within the kerb-line of a project.

In getting flows to outlet, every section of ld/ckd must therefore transition seamlessly through typical kerb features such as drops in driveways, pedestrian crossings, bends, corners and intersections.

Installed usually within the boundary or within a surface structure, linear systems are not designed to be stand-along structures. They require full integration, front and back, into the surrounding structure or landscape.

Our hydraulic calculations predict the maximum potential output in litres/second at outlet/outlets for sections of ckd/channel of any length and level. This information is then presented compared with a project’s designed rate of output based on run-off from one or more serving catchments.

A project’s designed rate of output can be derived from the overall drainage strategy. Duradrain and Durachannel are surface water collection and delivery systems, so unlike attenuation systems designed on volume dropped over a storm, CKD and channel systems deliver collected flows continually so the designed rate of output is usually derived from a project’s predicted maximum rainfall intensity falling over 100% of one or more serving catchments.

50mm/hr Rainfall Intensity (Io) is usual for highways however local conditions, position of collection, climate change, levels and increased risk can determine a higher designed rate. For ref, see (HA37/17)

Io= 32.7(N -0.4)0.233 (T – 0.4)0.565 (2MIN-M5)/T

Io= Mean Rainfall Intensity mm/hr

The position of collection is generally determined by the levels on site and the position/access to connecting services. With CKD, the kerb lines are usually set at a low point and are ideal for containment and collection of surface water. Surface channels will also be best placed at the low points across a project.

For larger more complex designs, it is best to increase the length of each run so it delivers the required flow close to its working capacity to a minimum number of outlets. Catchments will usually increase and decrease relative to changes in run length so our calculations can be worked to provide a check, or specific to design, predict a maximum run length before an outlet is required.

Length, gradient and changes in direction can have an effect on the flows within the CKD/channel so for a fully proven system it is necessary to check each section of CKD to outlet/outlets to ensure flows are of a sufficient velocity to exceed any designed requirement.

Given drawings with proposed levels, we can supply full hydraulic calculations, run schedules and overlaid layouts where necessary.

Calculations Show the Maximum Created Outputs @ Outlet

By working back from the designed outputs for each catchment you can establish the optimum lengths and number of runs/outlets required for a project. Our calculations will tell you the maximum potential output/flow @ outlet for each section of channel/ckd cof any length and level compared against the designed required output for each serving catchment. Our flow calculations will determine maximum flows/outputs specific to site levels, position and varied project design.

One Directional Flows driven by gradient. (Restraint to Outlet)

One Directional Flows driven by gravity only. (Restraint to Outlet)

Two Directional Flows driven by gravity only. (Outlet to Outlet)

Hydraulic Design & Data: Duradrain

Duradrain 60000 Combined Kerb & Drainage SP Profile Standard Unit

Length = 500mm

Width = 215mm

Depth = 305mm

Profile = Full Batter/Splay

Designed Weir Height/Kerb-Show = 75-100mm

Usable Flow Area = 22,182mm²

Roughness Coefficient = 0.009

Duradrain 70000 Combined Kerb & Drainage HB Profile Standard Unit

Length = 500mm

Width = 215mm

Depth = 305mm

Profile = Half Batter

Designed Weir Height/Kerb-Show = 75-125mm

Usable Flow Area = 21,197mm²

Roughness Value = 0.009

Hydraulic Design & Data: Durachannel

Durachannel 50000 Linear Surface Drainage Channel Standard Unit

Length = 500mm

Width = 187mm

Depth = 260mm

Slot = Dual Pedestrian Slots 8mm

Colour = Black

Usable Flow Area = 18,246mm²

Roughness Coefficient = 0.01

A = Usable Channel (Open-Flow – mm2)

P = Wetted Perimeter (mm)

n = Roughness Value

S = Slope/Equivalent Head

R = A/P

V = 1/n x R^2/3 x S^1/2

V (Velocity) x A = Q – Flow @ Outlet (Unrestricted – Litres/sec)

HB – Duradrain – Hydraulic Flow Chart

It is the function of the ckd/channel to collect and then compound run-off hidden within the channel and deliver to outlet at a rate equivalent to or greater than the required output/flows.

It is good practice to allow for a reduction in flows in tight radii, junctions and angles. The choice of outlet can also have an effect on the flows within each section of CKD/Channel, we can advise as to the best method.

Once all sections are proved, an outlet can be chosen to best suit the designed outputs, size, direction and invert of any connecting carrier or connection. For optimum designs it is best to allow the flows to drop-out free of obstruction so we recommend using gully outlets where ever possible. The gully outlet for both CKD and Channel do not restrict the l/sec output and the velocity of flow is maintained so silt transit is optimum.

Duradrain CKD Gully units are designed to be installed above standard road gullies which have a large discharge capacity.

We can supply run schedules to follow the road, kerb and pavement design. To enable future maintenance we recommend each section should be installed with an access point at the head of the run to allow jetting/cleanout. We also recommend access points are placed at intervals of 40-50mtrs subject to site conditions and any ongoing maintenance strategy. Sealed end caps should be fitted at the head/start of any section of ckd.

If you require advice, have any questions  or want to take advantage of our free design service, please get in touch.

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