Determination of Highest Sea Water Level at Drainage Channel Outlet of Third Ring Road in Tripoli, Libya

Abstract

The Third Ring Road (TRR) is one of the strategic projects that the Housing and Infrastructure Board (HIB) started its completion works at the end of 2023 for the purpose of reducing traffic congestion inside the city of Tripoli and to connect the southern regions of Tripoli to the center of the city. The road is designed to start from nearly the beginning of the existing second ring road and to end near the coast at an intersection with the coastal road. To drain the storm water collected from the road surface, a concrete box channel was designed along the whole of the road to convey and drain the collected water into the sea through an open outlet. Since the sea water level is fluctuating up and down on a daily basis due to astronomical tide or frequently due to wave and storm effects or gradually rising on an annual basis due to climate change effect, the invert level of the outlet should be higher than the highest level that the sea surface could reach to avoid the condition of outlet submergence. In this study, the highest sea water level has been determined under the aforementioned effects within a return period of 50 years. A numerical wave propagation model was used to determine the rise due to wave setup in the vicinity of the outlet location. A simplified analytical method was used to determine the rise during storms due to low atmospheric pressure and wind shearing stress on the sea water surface. The average of highest astronomical tide was obtained from Admiralty Tide Tables, while the rise due to climate change was obtained from a recent study on the Mediterranean basin. The results showed that the outlet is not expected to encounter a submergence condition.