Abstract
Culverts, as an essential part of drainage networks worldwide, provide an efficient solution for flowing waters to cross man-made barriers including roads. Existing structures can be many years old and changes in rainfall patterns due to global warming might not have been considered in their original design. While correctly designed culverts can effectively drain water during high-intensity rainfall events, poorly designed or outdated structures could cause upstream flooding resulting in costly damage and losses. Hydraulic improvements to prepare existing culverts for greater discharge rates could be a favorable alternative to rebuilding every failing structure. Modern design guidelines calculate the performance for inlet and outlet controlled flows on the basis of established hydraulic theories. After calculating the headwater levels for both flow controls, the inferior one is then chosen, based on the assumption that the culvert will operate in its least efficient state. Flow improvements could be made by enforcing the better performing option. Outlet control can be ensured by raising the tailwater levels as high as the outlet thereby utilizing the entire cross-sectional area of the culvert. It was found that, in some cases, an enforced outlet control enables culverts to perform better than operation under inlet control. However, only smooth and short culverts with high losses at the inlet were identified as benefiting from this approach and many existing structures could be improved by better inlet designs.
Highlights
Culverts play an important role at the intersection of the stormwater drainage system and transport infrastructure
Our experiments and calculations show that some culvert configurations perform better under outlet control than under inlet control at higher flow rates
The headwater levels are typically higher under outlet control than under inlet control
Summary
Culverts play an important role at the intersection of the stormwater drainage system and transport infrastructure They are typically designed using historical rainfall data to estimate discharge rates. Guidelines support designers and engineers in choosing adequate pipe sizes but there is little advice on when to use low friction materials, certain wingwall angles or steep slopes, leaving designers and planners with little information regarding the potential benefits. This has led to the common use of culverts with square inlet corners or with high friction losses inside the barrel, both designs that have low hydraulic efficiency. One of the most comprehensive guidelines today is the Hydraulic Design Series Number
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