Preliminary study of river- and beach processes in the Matina region of Costa Rica

Abstract

The starting point for this project are the severe erosion problems at the Pacuare Nature Reserve, situated on the Caribbean coast of Costa Rica. The Reserve’s installations are situated next to a lagoon which is separated from the open sea by a barrier beach. The lagoon is connected on the landward side to local river? and channel system. During periods of high rainfall, the lagoon is susceptible to break through to the open sea. After such breaches, high flow velocities and waves have caused significant land?loss and subsequently endangered the continued existence of the buildings at the Reserve. Since 1989, recorded breaches occurred in 1994, 2005 and 2009. It is believed that erosion of land is mainly caused by breaching events rather than continued coastal erosion by waves or currents. The breaching events may be caused by the increasing channelisation of river and drainage stretches and increasing water discharges by cultivated areas in former natural flood?plains. These interventions may be beneficial for some populated areas who are protected by channelised section and for the economy in certain regions as formerly unused land becomes productive (enabling banana plantations). However, the interventions increase the volume of water to be discharged in a confined space which reduces the capacity to discharge water safely towards open sea. The objective is to present recommendations for safely discharging water during extreme events towards the open sea, in which the ‘small scale’ breakthrough problem forms the criterion for damage for the reserve. The project consists of two areas of interest: river? and beach processes. The river processes were analysed and solutions were sought to safely discharge water using a computer model which models the real life processes. These solutions focus on the macro scale problem, and interfere in the water system as a whole. Analyzing the beach processes involved identifying the key processes in the stretch of coast between the Río Matina and Río Pacuare and modelling these processes in a computer model. Possible small scale solutions were then tested in the computer models and assessed on their effectiveness. These small scale solutions have to be interpreted as interventions the Reserve staff can implement themselves to help prevent the continued erosion during extreme events.