This means that bridge and road designs must take into account the maximum probable hydrometeorological event that could occur under a trough, a tropical wave, a storm, or a hurricane.”.
SANTO DOMINGO– Since Hurricane David in 1979, hydrometeorological events have caused damage to approximately 300 bridges across the country. Osiris de León, a geological engineer, believes that, consequently, the Dominican Republic needs to redefine its bridge construction criteria.
“In three fundamental aspects: The bridge foundations must not be susceptible to erosion, the bridge deck must always be higher, at the highest level the river can reach with the maximum probable flood; and the bridge approaches must not be made of sand, clay, or fine gravel, they must be built with large blocks of rock of at least one cubic meter each that are not susceptible to erosion by flooding,” the expert recommends.
De León understands that rainfall data from the various events that the Dominican nation has experienced helps to establish the maximum amount of rain that can fall and the maximum that a river or stream can flow through where a bridge is to be built.
“The design of a bridge must respond to two important variables: the amount of water that can pass through the cross-section of that river or stream and the characteristics of the materials in its channel, because gravel, sand and clay are materials susceptible to erosion, rock is not; consequently, when designing a bridge in an area where the riverbed consists of gravel, sand, or clay, it is advisable that the foundations of that bridge be supported on piles in such a way that with the maximum probable flood the concavation does not expose its foundations,” suggests de León.
He elaborates that many of the bridges that fail in the Dominican Republic do so due to erosion of their approaches, "which are the connections between the deck and the road, so they make the deck too short, remaining within the riverbed to save 4 or 5 meters on each side, when they could make longer decks that extend beyond the riverbed and thus reduce the possibility of traffic disruptions during floods.".
"Because from Hurricane David to the present, the hydrometeorological events we have experienced have caused the failure of some 300 bridges. When George struck, all the bridges in the southern part of the country, from Azua to Barahona, including San Juan de la Maguana, were washed away. When Tropical Storm Jeanne hit, the bridge deck over the Chavón River was swept away. When Tropical Storms Olga and Noel hit, the bridges in San Cristóbal, Bonao, and Maimón collapsed. All of this indicates that we need to redefine the construction criteria for bridges," the geologist emphasizes.
He explains that the Dominican Republic is a tropical island territory that experiences torrential rains every year between May and November, with a very heterogeneous pattern with areas of high and low rainfall where nearly three thousand millimeters of rain can fall per square meter, and in others where only 300 and 400 millimeters of rain fall per square meter.
"That means that bridge and road designs must consider the maximum probable hydrometeorological event that can occur under a trough, a tropical wave, a storm or a hurricane.".
Osiris de León believes the country is repeating history because it hasn't taken into account that bridge designs should consider the worst-case scenario, not the normal one, especially in a tropical region like ours where hurricanes can strike at any time. "Therefore, building codes must prioritize storm and hurricane situations as their primary consideration.".
Pontoon Bridge
Osiris de León believes that the Pontón bridge in La Vega should have been demolished the same day that the Ministry of Public Works and Communications (MOPC) identified that there was a settlement of its foundation, because when a bridge is supported on clay as in this case, if the load of the bridge that is transmitted to the footing is greater than the load that the soil resists, the soil settles or takes pressure.
“But it could also be an effect of erosion from rain or it could be an effect of dissolution by something we call colloidal suspension, the clay enters into colloidal suspension in the presence of water and it goes away, that's why we see the river dirty when it rains, because it carries clay that in turn enters into colloidal suspension, it simulates that it dissolved, then it loses volume and when that happens the structure that is on top ends up failing.”.
Miches Pier
He explains that when designing a port structure, one must also consider the maximum hurricane capacity that could affect the area. “Consider a Category 5 hurricane, and based on that, consider the abnormal swells that occur along the coastline and how these swells would impact the structure.”.
