Hydraulics Complete Research

Junction Loss Experiments

The study had two objectives. The first was to evaluate the Roger Kilgore's proposed procedure, which required conducting some of the same types of tests that were run in the previous study. But the new tests included a wider range of parameters, such as greater plunge height ratios and steeper pipe slopes. Previous research was limited in that it was applicable to storm drain systems located only in relatively flat areas; the research would not hold up for systems in hilly and mountainous regions of the country, where steep pipe slopes are the norm.

Juction Loss setup with the 3D PIV system in place.

The second and more challenging objective was to characterize the energy level in an access hole. If that can be accomplished, then the familiar culvert hydraulics analyses can be applied to the access hole that serves as the tail box where inflow pipes enter and to the head box for outflow pipes, where the water exits. Researchers have attempted numerous analyses of PIV data and three-dimensional (3-D) numerical model data, with uneven results. Characterizing energy in the access hole is highly problematic because the flow is so chaotic, and arbitrary assumptions had to be made to obtain results that fall between intuitive limits. Researchers at the FHWA lab now have investigated the more organized flow in the contracted area of the outflow pipe, using the contraction ratio as an indirect measure of the contraction loss in the flow from the access hole to the outflow pipe to back-calculate the energy loss in the access hole.

Bottomless Culvert Experiments

The "bottomless culvert," or natural-bottom culvert, is essentially a three-sided structure with the stream bed forming the bottom. This natural bottom arrangement is becoming more popular since it facilitates fish passage through the structures.  The hydraulic performance of these structures had never been specifically studied.

These images show the scour around the sidewalls and throughout the culvert. The image on the left was the experiment before testing (with leveled sand). The image on the right shows how the fluid moves the sand while passing through the system.

In partnership with the Maryland State Highway Administration, the laboratory evaluated three bottomless culvert configurations; two arch types and a rectangular type.  Examined were scour effects at entrance (abutment and contraction), exit, and downstream.  Then the use of riprap as a countermeasure against the scour was analyzed. 

Using the data collected, the laboratory developed an equation for estimating scour in these culvert configurations. A report containing the results of the study is being prepared and will be made available here.

Effects of Inlet Geometry on Flow Capacity of Single and Multiple Barrel Box Culverts (South Dakota DOT)

Full description.

Each year, the South Dakota Department of Transportation (SDDOT) designs and builds many cast-in-place (CIP), or field cast, and precast box culvert structures that allow drainage to pass under roadways. The CIP boxes typically have 30-degree-flared wingwalls, and the precast have straight wingwalls with 10.16-centimeter (cm) (4-inch) bevels on the inside edges of the wingwalls and top slab. Previous research conducted on a limited number of single barrel box culverts indicated that further research was necessary to determine (1) the effects of multiple barrel structures, (2) loss coefficients of unsubmerged outlets, and (3) the effects of 30.48-cm (12-inch) corner fillets versus 15.24-cm (6-inch) corner fillets. In order to optimize the design of both types of box culverts, it was also necessary to determine the effects of span-to-rise ratios, skewed end conditions, and optimum edge conditions on typical box culvert installations.

Juction Loss setup with the 3D PIV system in place.	A drawing of one style of inlet models used.