The slope-tapered inlet incorporates the efficient flow characteristics of side-tapered inlets with a concentration of more of the total available culvert fall at the throat control section. This type of improvement is similar in operation to the flared inlet for pipes. Maintain control at the throat for the design discharge in order to realize significant cost savings in the culvert barrel. In order to keep a proper seal, Teflon tape is needed around the male threads. The male end is twisted inside the female until it is snug. As a female, it accepts the male pipe, which is threaded on the outside. The IPS standard dates back to the early 19th century and was originally used for sizing wrought iron pipe.

Such inlets have two possible control sections as shown in : the face and the throat as shown in Figure 2. Simply, FIP is pipe that is threaded on the inside.

Side-tapered inlets involve a widening of the face area of the culvert by tapering the sidewalls. Other inlet improvement types are not feasible for multiple barrel box culverts because of the need to taper or flare the sidewalls of the barrels. This type inlet improvement is desirable when designing a multiple barrel box culvert. In terms of design and construction, top-tapered transition inlet is effective, economical, and simple to construct. This method is arbitrary, and care should be exercised when the culvert is operating in inlet control. The transition length should be a minimum of 20 feet (6 m) as shown in Figure 1, below. The designer may reduce the barrel depth in transition from the original depth to a minimum of 1.0 feet (0.3 m) greater than the uniform depth of flow. If the box culvert is operating under inlet control, the barrel of the culvert is more hydraulically efficient than the entrance geometry. Top-Tapered Culvert InletĪ simple transition of depth in a rectangular box culvert may improve the hydraulic efficiency. The recommended types of improved inlets are top-tapered inlets, side-tapered inlets, and slope-tapered inlets. Guidelines for design can be found in FHWA publication, Hydraulic Design of Highway Culverts, HDS-5. Improved inlets are usually costly to construct when compared with standard inlets.Ĭareful consideration should be given before selecting and using an improved inlet design.The flow reduction at the throat may cause the culvert to flow as outlet control, which would negate any advantages of the improved inlet.Heavy debris loads could pass through the inlet entrance and become lodged further in the culvert due to the restriction at the throat.Available design procedures cannot accommodate an improved inlet when the face of the inlet is skewed to the flow entering the inlet.

Inklet definition