Considerations for Surface Runoff

The design of highways and streets requires a delicate balance between the physical demands of a project and the realities of everyday constraints. From feasibility studies to planning, design, procurement, construction supervision and post-construction assessments, there are many different facets that must be evaluated to ensure optimal efficiency and safety, while minimizing costs and environmental impacts. During the planning and design of highways, it is important to account for the increased surface runoff that results along these impervious surfaces. This is compounded when considering the safety of motorists passage along these routes. So what are some options you might want to consider for surface runoff? There are several, but may I suggest a steel slotted drain solution? Slotted Drain is a unique pipe which removes sheet flow without multiple grades or water channeling devices.


Slotted Drain is used effectively to intercept storm water runoff from wide, flat areas such as parking lots, municipal streets, highway medians, and airport taxiways.  In these installations, the slotted drain is placed transverse to the direction of storm water flow.  The open grate intercepts all the flow uniformly along the entire length of the drain.  Slotted Drain is designed to supply at least 0.025 CFS of flow per lineal foot of pipe.   These results are published in the Federal Highway Administration Report No. FHWA-RD-79-106.

Unlike typical parking lots that require grades to be sloped in four directions for each storm collection grate, a parking lot with slotted drain requires only one transverse and one longitudinal slope for the entire drainage area. That translates to a lower-cost installation for the contractor and owner; and less stake-out for the engineer. Because of Slotted Drain’s efficiency in removing surface water, fewer collectors and fewer laterals under the roadway are needed. Not only is Slotted Drain an efficient way to collect storm water sheet flow, it also is aesthetically pleasing when compared to traditional drop inlets and pre-cast drain troughs.


For over 50 years, Contech Engineered Solutions has been manufacturing Slotted Drain™ for heavy highway and aircraft loading applications.  Slotted Drain is included in the Standard Specification for Construction of Road and Bridges on Federal Highway Projects under section 707.10 Slotted Drain Pipe.

Slotted Drain is fabricated from corrugated steel pipe.  The pipe is cut along a longitudinal axis in the crown of the pipe.  A reinforced, hot-dip galvanized, steel grate is welded in place to create a continuous 1 ¾ inch-wide slot opening in the crown of the pipe. The slot collects runoff and channels it to the pipe invert below. This drains to an outlet.  The drain pipe can be made from galvanized, Aluminized Type 2, (ALT2)  or polymer-coated corrugated steel pipe.  Slotted Drain is available in 10” diameter through 36” diameter pipe.  Standard stock grate heights are 2 ½ inch and 6 inch.  Variable height grates can be made to meet specific project conditions.  Grate heights as tall as 36” have been supplied on projects. If you have questions on the advantages that can be obtained from this unique, surface runoff solution, feel free to reach out to me or your local Contech sales engineer!


Steel Slotted Drain on Interstate 94 Installing Slotted Drain along a Major Highway