Cross-sections, dimensions, and slope design

Drainage channels are available as linear elements in several cross-sectional shapes. Box channels with a U-shaped cross-section and a surface-mounted grating or slotted cover are widely used. Alternatively, there are slotted channels with a closed channel profile, where water enters only through a narrow slot at the surface (aesthetically unobtrusive, but more difficult to clean). Channels with gratings allow for a higher inflow rate and are easier to clean, while slotted channels are more visually discreet (often found in pedestrian zones and squares). The choice of the appropriate channel cover depends on the hydraulic performance, the theoretically expected rainfall, and the desired design.

Channel elements are manufactured in standard lengths to facilitate installation. Common lengths are 0.5 m and 1.0 m. Odd lengths can be achieved using adapter pieces. Some manufacturers also offer 1.5 m or 2.0 m long elements, but due to weight considerations (and to better accommodate uneven surfaces), 0.5 m and 1 m elements have proven most effective. It is crucial that the connections are tight and form-fitting.

The width of the channel cross-section is specified by the nominal size NW (nominal diameter), which is the clear internal dimension in millimeters. Common nominal sizes are NW 100, 150, 200, and 300. Larger widths such as NW 400 or 500 are less common and usually only required for very high flow rates (in practice, NW > 300 is rarely encountered). The flow cross-section of a channel body of certain nominal sizes must be at least equal to that of a pipe with a circular cross-section whose internal diameter (nominal diameter DN) corresponds numerically to this nominal size.

The internal height of the channel determines the storage volume and thus the hydraulic capacity. The ratio of clear height h to clear width b must not be less than 1 (h/b ≥ 1). Typical standard channels (DN 100–300) have a height of approximately 150–300 mm. For larger nominal sizes (DN 400–500), heights of up to approximately 600 mm can be achieved. Shallow channels (for parking decks, multi-story buildings) require a height of 50–100 mm (DN 100) or 75–130 mm (DN 200). Crucially, all channel elements must be able to be connected seamlessly, i.e., without any step or reduction in cross-section at the joints. Manufacturers achieve this through precise manufacturing and special connections (tongue-and-groove systems, sealing lips, etc.). A good connection system also prevents the elements from tilting or shifting under traffic loads.

Almost all modern drainage channels feature factory-formed tongue-and-groove or folded joints at the ends. When joined, these interlock, securing the elements against horizontal and vertical displacement. Often, sealing profiles (e.g., rubber lips) are integrated, or a sealant is applied to the joint on-site to create a watertight seal, particularly important for channels requiring liquid tightness (e.g., at gas stations). Some manufacturers offer system solutions, such as pre-formed sealing strips, to ensure a tight and secure connection.

A critical aspect of linear drainage is the gradient along the channel, ensuring that the collected water flows quickly to the drains. There are three basic concepts: Channels without a gradient: The required longitudinal gradient is achieved through the natural slope of the terrain. Channels with a gradient: The required longitudinal gradient is achieved through the inherent gradient in the base of the individual channel elements. Channel elements are available with gradients of 0.5%, 0.6%, or 1.0%. Channels with a stepped gradient: The required longitudinal gradient is achieved by installing channel elements of varying heights and connecting elements with a steeper gradient.

Water is directed from the surface to the channel via the cross slope of the surface. In road construction, the guidelines (RAS-Ew, now REwS) stipulate that the cross slope should be at least ≥ 2.5%. If the minimum cross slope cannot be achieved, a slope of 2.0% (or 3% for paved surfaces) is required to reliably direct surface water to the edge (channel). Channels can be laid along surfaces sloping on one side (sloping on one side) or along the low point axis of two surfaces sloping in opposite directions (roof-shaped or funnel-shaped). In the latter case, water flows from two sides to the central channel. When planning linear drainage, the terrain must therefore be carefully considered: the location of the low points, the connection height to the sewer, and the arrangement of the outlets (lateral or below the channel).

The edge of the channel elements requires special attention. With conventional channels, this area is particularly prone to breakage due to lateral loads during installation or subsequent traffic loads. Therefore, channels in the more heavily loaded area are equipped with special edge protection. This is often referred to as a frame or surround and is usually firmly integrated into the channel body using anchoring elements. The edge protection also ensures a precise and stable fit for the grating. In combination with the grating and the subsequent paving, the edge protection contributes to the visual appearance of channel systems. Therefore, it should be as narrow as possible. The smooth lateral connection surface also provides an optimal joint for the adjacent paving. Depending on the design and the expected load, the edge protection can be made of galvanized steel, stainless steel, cast iron, polypropylene (PP), or fiberglass-reinforced plastic (FRP). Permissible material thicknesses for edges and bearing surfaces of gratings are regulated in the EN 1433 standard. Recesses within the edge protection allow for the use of grating locking systems and anti-displacement devices. Gutter systems without edge protection are designed for lower load classes. Here, the cover is simply placed on top and secured by integrated clips or crossbars on the underside.

Drainage channels are classified according to EN 1433 into load classes A 15 to F 900 (see section Planning). Each channel body should be permanently marked with the class, the nominal size, a manufacturer's mark, and the CE marking. In Germany, the DIN mark and a quality mark according to DIN 19580 were previously required; today, the CE marking (with reference to EN 1433) is the primary mark, supplemented by national Ü marks if necessary. The class assignment is verified by tests in the installed state (channel in the concrete base). A testing machine loads the channel and cover with the standard force (e.g., 125 kN for class B 125, 400 kN for D 400, etc.). The class is only confirmed if no fractures or impermissible deformations occur. Strict adherence to the specified testing procedure and execution is ensured through internal and external monitoring according to DIN 19585, and product monitoring by a corresponding product protection association or an accredited testing laboratory.