Submersible Bridge

A bridge type designed low so that its deck is submerged during floods; it normally serves as a passage and leisure space and is closed when water levels rise.

Submersible Bridge

Overview

A submersible bridge (Korean: 잠수교; Hanja: 潛水橋) is a bridge whose deck is designed at a height similar to or slightly above the normal water level of a river, so that the deck is submerged during floods. Normally, it functions as a passage for vehicles and pedestrians and further as a leisure and cultural space for local residents, but when river levels exceed a certain threshold due to heavy rainfall, passage is fully controlled. Because construction and maintenance costs are low and it does not significantly obstruct river flow, it is widely used as a secondary bridge over urban small streams and large rivers.

Definition and Structural Principle

Unlike ordinary bridges, a submersible bridge does not place its deck above the flood water level (design flood level). Instead, the deck is placed low so that when a flood occurs, water naturally overflows and flows over the deck. For this reason, piers and the deck are designed to withstand pressure from flowing water, collisions with floating debris, and scour (erosion of the riverbed around piers), and deck finishes and railings use materials resistant to repeated inundation. When the deck is submerged, the bridge itself acts as a kind of 'spillway' (餘水路), providing an additional river cross-section.

Design and Safety Standards

In submersible bridge design, design-frequency flood discharge, flow velocity, inflow of floating debris (driftwood and waste), and scour depth are treated as key variables. It is common to install water-level gauges and automatic warning systems and establish operating rules so that when a certain water level is reached (e.g., 30–50 cm below the deck), barriers lower and warning lights and announcements operate. After inundation, sediment and sludge are removed, and pavement, railings, and lighting are checked for damage before passage resumes.

Advantages and Disadvantages

Advantages are low construction cost, short construction period, and no interference with the river's flood conveyance capacity. In addition, it directly connects the riverside and the city center, offering excellent accessibility, and thanks to its distinctive landscape close to water, it shows high utility as a space for walking, cycling, and festivals. On the other hand, disadvantages include suspension of passage every flood season, risk of safety accidents during inundation, and maintenance costs due to repeated inundation as well as risks such as vehicle breakdowns and burial accidents.

Representative Cases in Korea

The most widely known example is Jamsu Bridge (formerly Banpo Bridge), located beneath Banpo Bridge over the Han River in Seoul. Completed in the early 1980s, this bridge is closed to traffic when the Han River water level rises, and since the late 2000s it has been reevaluated as a space centered on pedestrians and cyclists. The fountain facility installed on the side of the bridge and the night lighting have become representative scenery of the Han River, and cultural events such as film screenings and flea markets held on the bridge are regularly held. In addition, secondary river-crossing bridges in small and medium-sized local cities and submersible bridges for connecting farmland are distributed throughout the country.

Global Cases

Submersible bridges have long been used in Europe and Japan as well. In lowland rivers of the Netherlands and Germany, low bridges that prioritize flood conveyance are common, and on small rivers in Japan there are many bridges in the form of 'submersible bridges' (水沒橋) on agricultural and community roads. Recently, smart operation cases that provide real-time guidance on whether passage is possible in connection with flood forecast information are increasing.

Operation and Control

The core of a submersible bridge is the decision-making system for 'when to close and when to open'. Observation data on water level and rainfall is linked with local government disaster safety systems, and the method of simultaneously notifying the start and lifting of control through text messages, electronic displays, and navigation is becoming standardized. During inundation, physical barriers (automatic barriers, bollards) and manpower control are used together to prevent entry under any circumstances.

Recent Trends

In 2024–2025, as the frequency and intensity of localized heavy rainfall increase due to climate change, the operating standards for submersible bridges are becoming stricter. Local governments including the Seoul Metropolitan Government are combining water-level sensors, CCTV, and AI-based water-level prediction to advance control timing and accumulating inundation history data to refine maintenance cycles. At the same time, the cultural and tourism value of submersible bridges is being highlighted, and programs linked to expanded pedestrian-only sections, improved night landscape lighting, and riverside festivals are increasing. Meanwhile, to prevent safety accidents during flood season, intelligent blocking facilities that prevent unauthorized entry and construction methods to strengthen the durability of structures are being introduced together.