Archive for the 'Sediment control' Category

Progress in Tela reef conservation in Honduras

Text and photos (c) 2013 Erkki “Eric” Siirila, copyright & all rights reserved. 

Some years ago the city of Tela in Honduras was only known for its beaches. No one was aware that underwater additional national heritage could be found. The coral reefs of the Tela Bay are this other treasure.

The Tela Bay in Honduras has coral reefs, the conservation of which needs attention. Photographer and copyright (c) 2013 Erkki Siirila.

The Tela Bay in Honduras has coral reefs, the conservation of which needs attention. Photographer and copyright (c) 2013 Erkki Siirila.

Francois Ligeard, The Chamber of Tourism of Tela, says: “The good news is that we can offer a new site for both the national and international tourist. We have to highlight the fact that this place is very beautiful. It has high cover of live coral. We notice that always when we dive on this reef. One easily gets emotional because every time we go the local reef we find something new and more beautiful.”

Dennis Sierra, The Prolansate Conservation Foundation, Tela, sees the “newly discovered” coral reefs in the following way: “The best news is that in Tela we have many people both in the civil society, local government and the business sector who are very interested in the conservation of the coral banks of the Tela Bay. The preservation needs have an acceptance at the community level. Also at the level of the central government there is a lot of interest in declaring a marine park in the Bay of Tela.”

Only fishing was done on the local Capiro Reef in the past. Nowadays, divers come here to see the angelfish and the many species of coral. For example, black coral is found here.

The coral bank of Capiro is the best known reef area in the Tela waters. Photo and copyright (c) 2013 Erkki Siirila.

The coral bank of Capiro is the best known reef area in the Tela waters. Photo and copyright (c) 2013 Erkki Siirila.

Dennis Sierra: “Logically we look toward the future generations. We need to implement conservation actions in the Bay area, if we want to leave this ecosystem as a heritage to our children. Tela has been favored by God. We have to remember that the natural richness we have in Tela contributes in a positive way to tourism opportunities here. Tela has its future in the resources of that Bay.”

Francois Ligeard: “The biggest challenge we face is to take care of the reef both for our generation and the future generations. We need to get the fishermen and other local people involved to be able to preserve this reef. We have been working already by installing permanent mooring buoys. In this way, we need not anchor the boats and we can stop the damage that has been caused to the reef by anchors in the past.”

The mangroves of the Bay may not be forgotten as reef conservation is promoted. The mangroves produce nutrition for marine life. In addition, among the roots, many species of coral reef fish live during their juvenile stage. The mangroves also protect the coast from the waves of the sea.

The seagrass beds in the Tela waters have functions similar to those of the mangroves. In addition, many reef fish migrate to the seagrass areas in order to eat.

When forests are preserved, there is only little erosion on land and less mud enters the sea via the rivers. This is crucial in reef conservation as the corals need clean and clear water. Related to the above, it is also necessary to develop the treatment of sewage and waste waters.

In the Tela Bay there are very healthy coral colonies. It is important to take care of the reefs, because climate change threatens them, through the elevated sea-water temperatures and through the acidification of the sea.

Coral reefs will be more resistant to global environmental changes, when at the local level there is no overfishing and when the other pressures are kept at the minimum level. In this way, the coral reefs of Tela will produce economic and environmental benefits to us also in the future.

The following Youtube video was shot and produced by the Coastal Challenges’ Editor. It tells the above story of the Tela coral reefs in Spanish. The original is in high definition; this lower-resolution Youtube version can be best seen be adjusting the image resolution under the Youtube window to 480 p.

Coral conservation in Honduras: building on local roots is important

“We have got one of the best coral reefs in the Caribbean”, says Nelbin Bustamante from the Prolansate Foundation and Amatela reef conservation group of the Town of Tela, Honduras.  More in detail, Mr. Bustamante summarises the good news of a recent underwater study on the Tela reefs in the following words: “The live coral cover on our reefs is nearly 70 per cent per square metre”. This high number was registered on the Capiro Reef just seven kilometres from the city centre.


An offshore reef near Tela, Honduras. Photographer and copyright (c) 2012 Erkki Siirila.

Nevertheless, all the evaluation results were not positive. Mr. Bustamante says: “It could also be observed that the number of herbivorous and commercial fishes had reduced. Their biomass had gone down.”

As regards the threats, two main threats were identified in the study. One was the loss of forest cover. The other one was the lack of wastewater treatment. The Tela wastewaters flow directly into the sea and coral reefs. In addition to soil, the runoff contains many chemicals including fertilizers. The nutrients in the runoff may facilitate algal growth on the reefs as, at the same time, the levels of herbivorous fishes consuming the algae are lower than normal. Overfishing is an additional threat which needs to be controlled in Tela.

In any case Tela is a good and encouraging example in a world where the coral reefs are threatened by high fishing pressure, global climate change and other side effects of the growth of human societies. Off Tela, fairly healthy coral reefs can still be found and new awareness is creating motivation to protect the reefs.

Mr. Marcello Dicunta Servellón, who operates a dive centre in Tela, is satisfied: “Healthy coral reefs represents incredible opportunities. One of the most obvious ones is recreational diving. A well-managed dive industry on healthy reefs can result in high economic growth for the community.”

A Spanish-speaking documentary (Corales para amar – Tela protege sus arrecifes) with the above-mentioned content can be watched on Youtube:

Revolutionary method: gypsum controls runoff

An interesting discovery is helping in Baltic Sea conservation efforts in Finland. It involves the use a gypsum, which is a chemical substance known to most of us.

The environmental challenge we are talking about is that phosphorus, an essential plant nutrient, is transported from the farming fields through runoff into the rivers and sea. In the sea water, elevated levels of phosphorus cause eutrophication.

Yara, a chemical company, has together with a few Finnish partners developed a gypsum-based technique to stabilize soil particles in the farming fields. The method reduces soil (and nutrient) erosion caused by surface runoff.

The results achieved indicate that a high percentage of the phosphorus stays in the soil when the new technique is used. Consequently, harmful nutrient inputs into the waterways and sea are highly reduced. The new method also helps the farmer as more phosphorus is available for the agricultural plants. Furthermore, there is less need for costly, additional phosphorus fertilizers.

In spite of not being visible in this image, eutrophication caused by excessive nutrients is a problem on the Baltic coast of Finland. Photo (c) 2010 Erkki Siirila.

The method involves spreading of a gypsum-based product on the farming field after harvest or before planting. The product, which is basically gypsum (calcium sulphate), infiltrates with water into soil. According Yara, this well-known chemical compound in its slightly developed form improves “particle aggregation and dissolved phosphorus retention”. In addition, “better soil structure means that the earth resists rain and melting snow better and therefore prevents erosion and phosphorus leakage”.

Gypsum is useful to the farmer also because it improves the plants’ ability to utilise the phosphorus reserves of the soil. In addition, farmers can continue their agricultural activities as before. For the gypsum treatment to be effective, it would need to be repeated once in three to four years.

Gypsum treatment of the soil could be important news for many countries. Soil,sediment and nutrient runoff is degrading forestry and agricultural areas around the world. This runoff is also killing shallow marine ecosystems. Could gypsum help save the world’s endangered coral reefs?

A brochure on the gypsum-based method to control agricultural runoff into the sea can be found here:

Mangroves and environmental impacts

Like the previous Coastal Challenges’ article, this summary of mangroves and environmental impacts is based on How to assess environmental impacts on tropical islands and coastal areas: South Pacific Regional Environment Programme (SPREP) training manual. The manual was edited by Richard A. Carpenter and James E. Maragos.  This handbook was prepared by Environment and Policy Institute, East-West Center, in 1989, and sponsored by Asian Development Bank.

The Carpenter and Maragos manual presents useful tips and background material for the management of mangrove communities in the tropics.  (The three most important marine ecosystems in the tropical coastal zones are the coral reefs, mangroves and seagrass beds.) The information on mangroves is summarised in a slightly edited form below: 

Sustainable uses and values of mangroves: Mangroves maintain nearshore fisheries and are an important area for fish & shellfish production in the sea. Mangrove communities also protect the coast from storms; especially low-lying areas benefit.  By trapping of nutrients and sediments from drainage, mangroves protect coral reefs, sea grass meadows and coastal waters in general. In addition, wood and other forest products are obtained from mangrove areas.

Sensitivity to environmental changes: Changes in tidal flushing patterns damage mangroves.  Oil spills can be extremely harmful to mangrove communities.  Mangroves are also sensitive to salinity changes.  Furthermore, excessive harvesting can weaken the natural production and regeneration capacity of the mangrove ecosystem.

Development hazards: Environmental impacts which change the topography and water flow in the mangrove areas can be considered development hazards (for example damming, dredging, bulk-heading and impoundment). Activities which result in excessive sediment production may also damage the mangroves. Freshwater discharges, freshwater diversions and groundwater pumping are other examples of possible development-related threats. Naturally, clear-cutting, deforestation and land reclamation may seriously damage or destroy a mangrove area.

Mitigation: Natural characteristics of water movement need to be maintained. Harvesting limits need to be set and enforced. Buffer zones are a useful tool in mangrove management.

Mangrove management is an important component of coastal zone management when we get prepared for global climate change and sea-level rise. Youtube provides access to a Wetlands International video highlighting these issues. The link to the video is here:

Seagrass meadows and environmental impacts

The key reference used for the previous Coastal Challenges’ article on coral reefs was How to assess environmental impacts on tropical islands and coastal areas: South Pacific Regional Environment Programme (SPREP) training manual. The manual edited by Richard A. Carpenter and James E. Maragos was prepared by Environment and Policy Institute, East-West Center, in 1989. Asian Development Bank sponsored the venture.

The manual (not widely available in these days) presents useful conclusions  for the management of environmental impacts in seagrass meadows everywhere in the tropics.  (Together with mangroves and coral reefs, seagrass beds are the most important marine ecosystems of the tropical coastal zones. In addition, seagrass meadows are key components of shallow-water nature in temperate waters.)

The information presented by Carpenter and Maragos is summarised in a slightly edited form below: 

Sustainable uses and values of seagrass meadows: The biological productivity is high; especially the fish and shellfish production is important. Seagrass beds are nursery areas for reef and mangrove species.  These underwater meadows have useful functions in beach sand replenishment and act as a beach stabilisation area. Seagrass beds are also part of important synergistic interactions with onshore mangroves and offshore coral reefs. In addition, they are feeding areas of sea turtles and dugongs / manatees.

Sensitivity to environmental changes: Chemical pollution, changes in currents (leading to scouring or stagnation), changes in sedimentation patterns (leading to accumulation or burial), changes in longshore sand movements (disrupting the long-term balance of coastal sediment movements), dredging on offshore reefs (leading to lack of protection offered by the reef and resulting in changes in sediment movements), and cutting of onshore mangroves (resulting in loose sediments and lack of physical/runoff protection on the landward side of the seagrass beds).

Development hazards: Dredging, filling and construction of coastal structures commonly put the near-by seagrass beds at risk. Also oil and chemical spills can harm the seagrass meadows.  In addition, damming and blocking the natural water flow and sediment movements may  harm the seagrass communities.

Mitigation: The effects of projects on sediment and water movements need to be understood in advance. Damage to adjacent reefs and mangroves need to be avoided in projects leading to environmental impacts. In causeway construction, culverts and bridge openings help maintain the natural water circulation and sedimentation patterns thus protecting the seagrass meadows. Locating nonwater dependent facilities onshore is part of sound seagrass management.

The following Youtube video by is an excellent summary of  the global importance of seagrass meadows:

Sediment control strategies for the coastal zone

Guidelines for Sediment Control Practices In The Insular Caribbean is one of the most practical and useful coastal management handbooks ever written. The report was published by CEP (the Caribbean Environment Programme) of UNEP in 1995. Fifteen year have passed and the publication is as useful as ever.
On land, the loss of fertile soil during rains is a big problem in agricultural areas of developing countries: farmers would need a steady income to survive and the growing population would need more and more food. Survival is difficult also in forest areas where logging or other human activities have destroyed the rain forests: the thin layer of fertile soil is quickly lost during the rainy season and this hampers reforestation. The globally important Amazon rainforests in Brazil are an example.
Don Anderson, the author of the CEP report, summarises the background to the guidelines in the following words: “Among the impacts of greatest concern in the insular Caribbean today are accelerated soil erosion and the delivery of eroded material to sites where it is not wanted.”

Erosion control on land supports the conservation of underwater ecosystems. Good ecosystem health will benefit these young fishermen in the Eastern Caribbean. Photo (c) 2010 Erkki Siirila.

Sensitive areas receiving sediment runoff from land include coral reefs, mangrove swamps, seagrass beds and fishing areas.  Receiving areas may also include recreational beaches, water reservoirs, navigable harbours and other zones crucial to maintenance of tourism and other economic activities.
Coral reefs are especially vulnerable to excessive sediment inputs. Sediment runoff from land was considered as the number one reef killer in the world before global climate change and coral bleaching got that position a few years ago. Coral polyps need to use extra energy to get rid of the sediment particles, the polyps get stressed and may finally die.  Sediments in the water also result in turbidity which reduces the amount of light in the depths. As a result, photosynthesis of the symbiotic algae in the coral tissues may stop and the coral starve. The lack of light is another cause of reef bleaching – the elevated mean water temperatures are not the only cause. Finally, in areas where excessive sediments have lead to loss of suitable substrata, juvenile corals have a poor survival rate.

Coral colonies were buried under mud in Saint Lucia, when heavy rains led to unprecedented runoff from land. A few days later a high percentage of the coral surface was bleached resulting in partial mortality of these Caribbean reefs. Underwater image (c) 2010 Erkki Siirila.

The CEP guidelines summarise the  Caribbean coastal erosion in the following manner: “Where land has been disturbed by human activity, the rate of erosion usually increases.  This accelerated erosion is typically many times the natural rate”.
Direct raindrop impacts result in splash erosion. Sheet erosion takes place when water flows over the soil surface. Rill erosion occurs when surface runoff leads to small eroding channels. Enlarging and joining rills lead to gully erosion. The most rapid erosion is caused by mass wasting processes, which are induced by gravity alone.
The CEP guidelines stress the need for sediment reduction programmes.  The report divides the technical work in three action areas:
  • watershed planning and management
  • stream corridor management, and
  • site-specific erosion and sediment control practices
As regards the institional considerations, the guidelines tell us that the most important challenges are these:
  • identify a lead agency
  • identify the responsibilities and limits of jurisdiction of each agency, and
  • ensure that key responsibilities are not overlooked and that there is no duplication of work
In addition, the educational and training efforts are considered critical for success. The public in general needs to understand key erosion-related issues while those in charge of the technical work need special training.

Well-functioning sediment control practices are needed on the Caribbean island of Roatan in Honduras. Coral reefs surround the island. Reef degradation due to soil runoff is visible underwater in the area where the picture was taken. Photo (c) 2010 Erkki Siirila.

The best management practices suggested in the CEP guidelines cover the following issues. This list helps us understand the wide scope of sediment control needs in coastal areas:
  • development practices: clearing only essential areas, minimising road disturbances
  • surface stabilisation: seeding, mulching and matting
  • runoff diversion: perimetre dikes and swales
  • runoff conveyance: lined channels, temporary slope drains, check dams
  • outlet protection
  • sediment traps and barriers: sediment fences, brush barriers, sediment basins, sediment traps
  • stream protection: buffer strips
The CEP Technical Report No. 32 can be downloaded from the following web address (due to server issues, downloading is not always possible):