Sedimentation and Erosion


Sediments are material of varying size of mineral and organic origin. Erosion is the process of carrying away or displacement of sediment by the action of wind, water, gravity, or ice (Smith & Smith 1998). The process of deposition of sediment from a state of suspension or solution in a fluid is called sedimentation (

Natural sources of sediments transported to the sea include erosion of bedrock, soil and decomposition of plants and animals (UNEP & Gems Water Programme 2006). Natural sediment mobilization is an important process in the development and maintenance of coastal habitats, including wetlands, lagoons, estuaries, sea-grass beds, coral reefs, mangroves, dunes and sand barriers (UNEP/GPA 2006a). However, anthropogenic activities or those which are carried out by man, often change the processes of erosion and sedimentation as well as modifying the flow of rivers and the amount of sediments it can carry.

Most land-based activities that occur in sectors such as agriculture, forestry, urbanization, and mining contribute to these changes. Another significant cause of changes in sedimentation and erosion patterns is through hydrological modifications that may occur from construction of reservoirs, dams and causeways, dredging of water bodies and development of large-scale irrigation schemes (UNEP/GPA 2006a).



The effects of changes to erosion and sedimentation patterns will depend on whether the change results in an increase or decrease in sediment availability. Both effects have various physical and chemical consequences for water quality and aquatic ecosystem health (UNEP/GPA 2006a, UNEP & Gems Water Programme 2006). Sedimentation effects are usually local, but transboundary impacts may occur where major river systems form a common border and where littoral currents carry inputs across international boundaries ( Examples of this in the Wider Caribbean include the impacts of the Mississippi River in the Gulf of Mexico and the Orinoco, Amazon and Magdelena Rivers in South America.

A summary of some of these effects are: (UNEP & Gems Water Programme 2006, UNEP DEWA/GRID-Europe 2008,, Owens et al 2005, Ongley 1996, Boatman et al 1999);


From increased Sedimentation:

  • Smothering of marine communities and in severe cases, complete burial leading to suffocation of corals, mangrove stands and seagrass beds;
  • decreases in the amount of available sunlight which may in turn limit the production of algae and macrophytes, increase water temperatures and reduce growth of natural vegetation;
  • damage fish by irritating or scouring their gills and degrade fish habitats as gravel containing buried eggs becomes filled with fine particles, thus reducing available oxygen;
  • reduce the success of visual predators and may also harm some benthic macroinvertebrates;
  • fill watercourses, storm drains and reservoirs leading to costly dredging and an increased risk for flooding;
  • many toxic organic chemicals, heavy metals and nutrients are physically and/or chemically adsorbed by sediments, so that an increase of sediment loading to the marine environment  can also lead to increased deposition of these toxic substances that result in further negative impacts such as eutrophication;


Decreased Sedimentation:

  • if a decrease of sediment occurs it can lead to degradation of an ecosystem by starving it of the elements needed to sustain production since sediments often carry a variety of minerals, nutrients, and organic matter;
  • increased velocity of the water which may cause erosion downstream and in coastal zones and cause damage to coastal and marine ecosystems and human settlements;


Overall the degradation of coastal ecosystems and coral reefs from increases or decreases in sediment loads may lead to important losses in revenue caused by  impacts on the tourism and fishing industries and on coastal development.


Global versus Caribbean Studies on Sedimentation and Erosion

According to ( the average global estimate of annual sediment load to the world oceans varies from 15 to 30 billion tonnes. Worldwide, the storage of sediments in large reservoirs has according to Loicz (2005) decreased the global flux of sediment to coastal zones by some 30% over the past 50 years. In the future, these flows will continue to decrease, mainly because of continued construction of large dams (WCD 2000 & Loicz 2005). The Nile in Africa is one such example where the construction of the Aswan High Dam in 1964 has changed the total flow and sediment load. Currently 98% of the sediments are trapped behind the dam causing consequences like increased erosion along the coastline, salinization of cultivated land and a 95% decline in sardine yields (Loicz 2005).

Two thirds or 66% of the world’s total sediment transport to the sea take place in Southeastern Asian ( In comparison, the Wider Caribbean annual sediment loads are estimated at 1 Gt, or approximately 12% of global sediment input from rivers (UNEP/GPA 2006b). In a regional overview of land-based sources and activities affecting the marine, coastal, and associated freshwater environments in the Wider Caribbean Region, almost all the countries have included high levels of sediments in the coastal zone among the major environmental problems they face (UNEP 1999).

The main river systems influencing the Wider Caribbean Region includes the Amazon River (Brazil) with a mean sediment load of 1200 million tonnes per year (Luiz A et al 2004), the Magdalena River (Colombia) with a mean sediment load of 143 million tonnes/year (INVEMAR 2006), the Orinoco River (Venezuela) with a mean sediment load of 105 million tonnes/year (MINAMB 2006) and the Mississippi River (USA) with a  mean sediment load of 157 million tones/year (Turner  R E et al  2007).

The Amazon River accounts for approximately 1/5 of the world's total river flow, and it has the largest drainage basin in the world ( Even though most of the outflow of the Amazon is going eastward across the Atlantic, an important quantity flows northward around the coast of the continent into the Eastern Caribbean (Caribbean Sea Ecosystem Assessment Team 2007). Together with the waters of the Orinoco River, the Amazon water creates plumes of buoyant fresh water across wide stretches of the southern Caribbean sea (Müller Karger et al 1988, 1989).

The Magdalena River is the largest river discharging directly into the Caribbean Sea and it discharges more sediment for each square kilometer of its catchment area than any of the other large rivers along the Caribbean and Atlantic coasts of South America (the rate is 560 t km-2 year-1) (Caribbean Sea Ecosystem Assessment Team 2007). The sediment load from the Magdalena River has had a strong impact on coastal ecosystems and during the past 50 years the Magdalena River has come under increasing environmental stress (Caribbean Sea Ecosystem Assessment Team 2007). This stress was brought by the economic development of Colombia which caused an escalating population density within the drainage basin.  Increasing deforestation, mining and poor agricultural practices have all contributed to an increased rate of upland erosion and water pollution.

Increased sediment loads in Barbacoas Bay(Colombia) has impacted the El Rosario Islands, a 68 km2 coral-reef ecosystem as well as the largest coral reef on the Colombian Caribbean coast, a system covering 135 km2 between the San Bernardo and Fuerte Islands, north and south from the Morrosquillo Gulf. In El Rosario Islands, 58% of the coral reef cover has died and between the San Bernardo and Fuerte Islands live coral decreased by 25% between 1995 and 2000 (Caribbean Sea Ecosystem Assessment Team 2007). According to the Caribbean Sea Ecosystem Assessment Team (2007), the decline in fisheries catches from 63 700 t in 1978 to 7 850 t in 1998, is another indication of the environmental degradation caused by reduced water quality.

Along the rivers of the Orinoco Basin there is dredged waste on the riverbank which is a major environmental concern since it inhibits drainage into the river (UNEP et al 2006b). The seasonal change of outflow from the Orinoco River influences the concentrations of sediments in the north Venezuelan coastal waters (Gomez 1996).


 Figure 1; Mississippi river sediment plume

sedimentation-fig1.pngThe Mississippi River is one of the world's major river systems in size, habitat diversity, and biological productivity and is the largest river draining in the Gulf of Mexico. Most of the river and its floodplain have been extensively modified by humans and much of the watershed is intensively cultivated (USGS 2003). According to UNESCO 2005 sedimentation on the Mississippi River and its major tributaries, like the Missouri, Ohio, and Illinois Rivers, has long been an issue of serious concern. The Mississippi River brings enough sediment to extend the coast of Louisiana 91 m each year


Predictions of estimated erosion, sediment and nutrient transport and delivery at river mouths of over 400 watersheds in the Meso-american Reef for potential land use in 2025, adapted from the UNEP (2007) scenarios, show that increases in sediment delivery of up to 13% are possible compared with the current situation. In addition soil erosion in the tropics may be 20% higher on cleared forested land in comparison to lands with forest (MA 2005). The topography of the islands of the Caribbean, with a combination of short steep slopes terminating in sensitive wetlands and marine environments make them susceptible to damage from even slight increases in erosion (DPNR/DEP & USDA/NRCS1998). In most countries of the Wider Caribbean Region forested land is declining with the highest rate in Central America (FAO 2006) and during the past four decades the largest increase of arable land in the world took place in Latin America and the Caribbean. Predictions for 2030 indicate a continuation of this increase (FAO 2003). The national deforestation rate of Nicaragua is according to Allen (2001) greater than 150 000 ha/year and in Costa Rica 18 500 ha/year.

Recently it has been estimated that 70% of Caribbean beaches are eroding at rates of between 0.25 and 9 metres per year (UNEP/GPA 2003). Erosion is manifested in the whole Caribbean region, and causes are related to a higher frequency and intensity of tropical storms, sea level rise, the deficit in the sand inputs, and tectonic phenomena. Antrophogenic causes include sand mining, destruction and occupation of dunes by tourist facilities, construction of marinas, incorrect location of coastal protection infrastructure, and the damage to coral reefs and seagrass beds, important sources of production of marine carbonated sand. According to UNEP/GPA (2003), all tourist areas of the Caribbean show direct relationship between erosion and human activities which demonstrates the unsustainable character of tourist development. Sand mining and beach erosion are issues of great concern in countries such as St. Kitts and Nevis, Saint Lucia, and St. Vincent and the Grenadines among others (UNEP 1999).

Growing coastal populations and the growth of coastal tourism in the Wider Caribbean Region are two additional factors contributing to increased sedimentation. In the past 15 years, the number of tourist accommodations more than doubled, and numbers continue to increase rapidly in many countries (

Another factor that may contribute to increased erosion and sedimentation is climate change. The latest report on this subject suggests that it is likely the frequency of heavy precipitation events will increase, meaning greater likelihood of erosion and sediment runoff. According to the IPCC (2007) climate change impacts will increase both the level and temperature of the sea. The effect of this will be increased damage from storm surges, increased erosion on small islands and impacts on coastal ecosystems such as mangroves, salt marshes and coral reefs.

A recent watershed-based runoff analysis, done by the World Resource Institute in 2004, over more than 3 000 watersheds of 35 countries in the Wider Caribbean Region shows that one-third of all Caribbean coral reefs are threatened by sedimentation, with 20% classified as a high threat (Figure 2 ).


Figure 2; one-third of all Caribbean coral reefs are threatened by sedimentation, with 20% classified as a high threat (The World Resource Institute in 2004).


According to UNEP et al (2006a), suspended solids were assessed as having severe impacts on the Caribbean Small Islands as there is an increase of suspended solids and turbidity. There are also transboundary impacts of sediment transport from continental land masses. Sedimentation is a primary problem affecting the US Virgin Islands and dirt roads, farmlands, construction sites, urban encroachments, and other disturbed soils are the primary non-point sources of sediment threatening the island’s water resources. According to UNEP et al (2006a), sedimentation is one of the major influences on the conditions of the reefs In Antigua & Barbuda. High turbidity of inshore water and elevated algal cover on reefs are linked to the impacts of coastal development, with sedimentation being a major influence on the conditions of reefs (Smith et al 2000).

In Jamaica and Haiti, deforestation is considered to be the most significant cause of erosion and there have even been associated desertification (UNEP et al 2004). Bauxite mining is particularly important for the economy of Jamaican and, to a lesser extent, of the Dominican Republic and Haiti. This activity also releases large quantities of particulate matter that can be deposited in marine areas. In Cuba and the Dominican Republic mining and processing of ores for the production of nickel oxide is carried out in close proximity to the coast. However, there is limited information on the final disposal of these mine wastes (UNEP/GPA 2006b).


Laws, Regulations, and Policy Responses on Sedimentation and Erosion

The most important regional legal framework in the Wider Caribbean Region for the protection of the Caribbean Sea from pollution is the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region (Cartagena Convention). The Convention entered into force in 1986 and is a legally binding, regional multilateral environmental agreement for the protection and development of the Wider Caribbean Region. The Cartagena Convention deals with sedimentation through the Protocol Concerning Pollution from Land-Based Sources and Activities (LBS Protocol).

The LBS Protocol sets forward general obligations and a legal framework for regional co-operation, provides a list of priority source categories, activities and associated pollutants of concern and promotes the establishment of pollution standards and schedules for implementation. Sediments are primary pollutants of concern (Annex I), and effluent limitations in domestic wastewaters for total suspended solids (Annex III) are set to 30 mg/l for Class I Waters (particularly sensitive to impacts from pollution) and to 150 mg/l for Class II Waters (less sensitive to impacts from pollution).

Annex IV of the LBS Protocol refers to Agricultural Non-point Sources of Pollution and states that the Parties should develop plans for the prevention, reduction and control of agricultural non-point sources of pollution including runoff of storm water containing sediments.


International conventions and a number of international relevant action plans including:

  • The United Nations Convention to Combat Desertification is a Convention to combat desertification (land degradation) and mitigate the effects of drought through national action programs that incorporate long-term strategies supported by international cooperation and partnership arrangements. It was adopted in Paris on 17 June 1994 and entered into force in December 1996. Read more at
  • The Global Programme of Action for the Protection of the Marine Environment from Land-based Activities (GPA). The GPA is designed to be a source of conceptual and practical guidance to be drawn upon by national and/or regional authorities for devising and implementing sustained action to prevent, reduce, control and/or eliminate marine degradation from land-based activities. Read more at
  • Agenda 21 is another global action plan dealing with land based sources of pollution including sedimentation. The agenda sets out actions that nations, communities and international organisations can take to contribute to the goal of global sustainability in the twenty-first century. Chapter 17 of Agenda 21 covers marine and coastal management. Read more at
  • The Johannesburg Plan of Implementation, agreed at the World Summit on Sustainable Development affirmed UN commitment to 'full implementation' of Agenda 21, alongside achievement of the Millennium Development Goals and other international agreements. Read more at,, and
  • The United Nations Programme of Action on the Sustainable Development of Small Island Developing States, referred to as the Barbados Program of Action (BPOA), is a policy document that both addresses the economic, environmental, and social developmental vulnerabilities facing islands and outlines a strategy that seeks to mitigate those vulnerabilities. Read more at, and
  • The Mauritius Strategy (International Meeting for the 10-year Review of the Barbados Programme of Action). Read more at
  • The Millennium Development Goals (MDGs) are eight goals to be achieved by 2015 that respond to the world's main development challenges. Read more at
  • The International Coral Reef Initiative (ICRI) with the purpose to ensure the long-term survival, productivity, and recovery of coral reefs and related ecosystems by fostering and maintaining their resiliency through awareness, conservation and management. Read more at



What is the Caribbean Environment Programme (CEP) doing?


  • In collaboration with Earth University in Costa Rica, the CEP has supported activities under the project “Best Management Practices in Agriculture”. These include pilot projects in Guatemala, Costa Rica and Saint Lucia demonstrating best practices in organic farming techniques and dairy farming, sustainable farming practices including proper fertilization and the use of environmentally friendly techniques and alternatives in pest control. Document links.
  • The CEP in collaboration with the UNEP GPA facilitates the development and implementation of National Programmes of Action (NPAs) for the prevention of pollution from land based sources and activities.
  • Regional practical workshops on Modeling Non-Point Sources of Marin Pollution and Sediment Discharges using Geographical Information Systems (GIS) were conducted in Panama in February 2008 and Cuba July 2008.
  • With financing provided by the Global Environment Facility (GEF), a project entitled "Reducing Pesticide Runoff to the Caribbean Sea" is currently on-going in Colombia, Costa Rica and Nicaragua. Links – should be to project web site.
  • The Integrating Watersheds and Coastal Areas Management (IWCAM) Project in the Small Developing States (SIDS) of the Caribbean was approved by the Global Environment Facility (GEF) in May 2004. The project is five (5) years in duration and it commenced in the last quarter of 2005. The overall objective of this Project is to strengthen the commitment and capacity of the participating countries to implement an integrated approach to the management of watersheds and coastal areas. The 13 Caribbean SIDS participating in this project are Antigua & Barbuda, The Bahamas, Barbados, Cuba, Dominica, Dominican Republic, Grenada, Haiti, Jamaica, Saint Kitts & Nevis, Saint Lucia, Saint Vincent & the Grenadines and Trinidad and Tobago. The main issues to be addressed under the IWCAM Project are: Diminishing freshwater supplies, degraded freshwater and coastal water quality, Inappropriate land use, and hygiene and sanitation. Additional information on the Project may be found on the Project website:
  • The CEP has published a set of guidelines for sediment control practices in the insular Caribbean. All islands in the region should make an effort to apply these guidelines to reduce erosion and sedimentation, as well as to improve watershed management.


Link to Guideline: UNEP/CEP (1994b). Guidelines for Sediment Control Practices in the Insular Caribbean. CEP Technical Report 32. UNEP Caribbean Environment Programme, Kingston, Jamaica)


What can you do?


  • Sweep sidewalks and driveways instead of hosing them off. Washing these areas results in sediment and other pollutants running off into streams, rivers and lakes.
  • Practice landscaping to reduce surface run-off from your yard. A few examples include; eliminating bare surfaces; preserving existing trees, and planting trees and shrubs to help prevent erosion and promote infiltration of water into the soil; installing gravel trenches along driveways or patios to collect water allowing it to filter into the ground; avoiding cutting the grass within 3-7 meters from the edge of a stream or river which will create a buffer zone that will help minimize erosion and naturally filter stormwater runoff that may contain sediment.
  • Wash your car at a commercial car wash or on a surface that absorbs water, such as grass or gravel.
  • Join environmental groups that protect the environment.
  • Promote environmental education. Help educate people in your community that increased erosion and sedimentation in the Caribbean Sea may harm marine life and their habitats. Get your community groups involved.





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