Environmental Management of a Tropical Delta

Jaime Ordóñez, Luis A. Camacho, Leonel Vega, Gabriel Pinilla

Chair(s): Esther Stouthamer

Tuesday 30 june 2015

11:40 - 12:00h at Asia (level 0)

Themes: (T) Special session, (ST) Deltas from multiple pressures to integrated solutions

Parallel session: 5C. Special session: Deltas - from multiple pressures to integrated solutions.

The Delta of the Magdalena River, is located in the republic of Colombia. The western part of this large Delta was abandoned by the River in the Holocene period, and was reactivated by the Spanish colonists in 1650 with the construction of the Canal del Dique, by interconnecting a series of lagoons and salt marshes. This part of the Magdalena Delta, mostly fresh water today, still has the character of a low floodplain with a tendency for the penetration of saline waters, and also frequent invasions of fresh waters during flood stages of the River. Successive Canal improvements through the years, cut the Canal directly to the bay of Cartagena, (1934), increasing the discharge and generating an abundant sediment inflow which has created a large depositional delta and also a cloudy plume which are considered detrimental to the bay, requiring control. This article presents the results of an investigation by the National University of Colombia, to evaluate the natural functioning of the ecosystems related to the canal and its distributive drainage system, and to present different types of solutions to reduce the sediment entrance to the Bay while trying to keep the environmental quality of the ecosystem. CONCLUSIONS The very small amount of bed load derived towards the bay do not warrant the construction of a complicated structural control system to keep the sediments from entering the Canal. Moderate improvement of the dredging coupled with a simple sluice system at the end of the canal will suffice to maintain proper sediment management within the system, while maintaining in a natural way the flows in and out of the lagoons and wetlands. The Colombian government, however has decided to undertake a new study to introduce structural control in order to diminish the entrance of water to the Canal and thus reduce the sediment entrance, control flooding and manage water and sediment in the Delta through a complicated structural complex, keeping water and sediments in the channels without overflow, thus arresting the natural deposition on the delta surface. A rather risky system to operate by local authorities, while this new study is still in progress, the discussion of the natural functioning of the ecosystem is necessary to understand the risk of the different control alternatives being proposed.