Hydropower Dams Can Harm Coastal Areas Far Downstream
By Paula Ezcurra and Octavio Aburto
Thousands of hydroelectric dams are under construction around the world, mainly in developing countries. These enormous structures are one of the world's largest sources of renewable energy, but they also cause environmental problems.
Hydropower dams degrade water quality along rivers. Water that flows downstream from the dams is depleted of oxygen, which harms many aquatic animals. The reservoirs above dams are susceptible to harmful algal blooms, and can leach toxic metals such as mercury from submerged soil.
We wanted to know whether dams also impact river systems farther away, at the coastlines where rivers flow into the sea. So we performed a natural experiment comparing four rivers along Mexico's Pacific coast — two that are dammed and two that remain free-flowing. We found that damming rivers has measurable negative ecologic and economic effects on coastal regions more than 60 miles downstream.
Feeding or Starving Coastlines
We studied four river outflows along the Pacific Coast of Mexico in the states of Sinaloa and Nayarit. Two of these were from the San Pedro and Acaponeta rivers, which are relatively unrestricted, with over 75% of their flow unobstructed.
The other two outflows came from the nearby Santiago and Fuerte rivers, which have over 95% of their flow retained in reservoirs. In addition to restricting water flow, these reservoirs trap sediments — over 1 million tons per year along the two rivers combined.
In unobstructed rivers, sediment flows downstream and is eventually deposited along the coast, helping to stabilize the shoreline and sometimes even to build it up. We found that this was happening along the free-flowing Acaponeta and San Pedro rivers.
However, because the sediment from the dammed Santiago and Fuerte rivers is no longer carried downstream, wave action takes over at the coast. At the mouths of these two rivers, we found that waves were eroding up to 33 hectares of combined land — equivalent to about 62 football fields — each year, with widespread ecologic and economic effects on the surrounding regions.
The dammed Fuerto and Santiago Rivers show greater erosion where they reach the Pacific coast than the free-flowing San Pedro and Acaponeta rivers. Images at right show coastline changes during the two periods: blue indicates land accretion, red indicates erosion.
Ezcurra et al., 2019., CC BY-NC
The Ecology of Healthy Coasts
Our field research clearly showed that coastal instability resulting from sediment loss at the mouths of the dammed rivers was harming ecosystems along the shore. For example, we found that coastal regions downstream of free-flowing rivers had significantly more plant diversity. Many of these plants were found only in coastal areas, and therefore had high conservation value.
Coastal erosion due to lack of sediment input from the rivers also reduces critical nursery habitat, such as mangrove forest, where many commercially important fish species spend their juvenile stage. We found that fishing activity at the mouth of the free-flowing San Pedro River was much higher than around the mouth of the dammed Fuerte River. This loss of fishing potential comes at a cost of around $1.3 million every year.
Reduced sediment flow also deprives coastal estuaries of nutrients. Lucrative shrimp and oyster fisheries in the region we studied rely heavily on nutrient inputs from rivers. In the San Pedro River region, these fisheries generate around $5.8 million yearly; near the dammed rivers, they have been all but abandoned.
Coastal mangrove wetlands also protect shorelines from hurricanes and tropical storms, and serve as recreational areas and conservation habitat for wildlife. Knowing this, we calculated that the loss of these ecosystem services around the dammed rivers totals $3.9 million annually.
Vegetation profile of sandbars of the free-flowing San Pedro River (A) and dammed Santiago River (B), where receding black mangrove forest is being eroded away into the advancing coastline
Ezcurra et al., 2019, CC BY-NC
Still another valuable function that mangrove wetlands perform is storing "blue carbon" in plant tissue and soils, reducing the effects of climate change. But when coastlines recede and mangroves are destroyed, this carbon is released. We calculated that mangrove loss in our study region represented a loss of around $130,000 in annual carbon trading potential for this region.
Adding up all of the ecological services that coastal ecosystems provide, we estimate that the economic consequences of shoreline loss around the Santiago and Fuerte rivers related to hydroelectric damming totaled well over $10 million yearly.
Letting More Sediment Flow
Because sediments are so essential to areas around river mouths, reducing sediment trapping behind dams could mitigate some harmful impacts on coastal areas. There are several ways to do this — notably, sediment bypassing, or diverting a portion of the sediments flowing from upriver around dams and allowing it to rejoin the river downstream.
This strategy can be included in new construction or incorporated into existing dams. In addition to reducing dams' environmental impacts, it also increases dams' service lives by reducing the rate at which their reservoirs fill up with silt.
To date, environmental impact assessments of large inland dams have often failed to properly analyze the impacts that these dams will have downriver on coastlines, estuaries, deltas and lagoons. Our study shows how important it is to fully account for dams' environmental and economic impacts along coasts and basins.
Mexico may be at a juncture in its approach to hydropower. The Mexican government recently contracted with Hydro-Quebec, the world's largest hydroelectric power producer, to revamp existing dams across the country. And a recent study by a Mexican nongovernment organization, SuMar-Voces por la Naturaleza, reported that a long-disputed proposal to build a new hydroelectric dam at Las Cruces is neither financially feasible nor needed to meet energy demand for the region, prompting national groups to call for the final cancellation of the project.
We believe that Mexico and all nations working to develop efficient, low-impact energy sources should take a holistic approach to future dam-related projects, so they can weigh their potentially harmful consequences. The coastal effects that we documented should be part of those reviews.
Paula Ezcurra is a digital communications specialist with the Gulf of California Marine Program, University of California San Diego.
Octavio Aburto is an assistant professor of marine biology with the the Scripps Institute of Oceanography, University of California San Diego.
Disclosure statement: Octavio Aburto receives funding from the David and Lucile Packard Foundation, UC MEXUS and the Leona M. and Harry B. Helmsley Charitable Trust. Paula Ezcurra does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond her academic appointment.
Reposted with permission from our media associate The Conversation.
Typhoon Molave is expected to make landfall in Vietnam on Wednesday with 90 mph winds and heavy rainfall that could lead to flooding and landslides, according to the U.S. Embassy and U.S. Consulate in Ho Chi Minh City. To prepare for the powerful storm that already tore through the Philippines, Vietnam is making plans to evacuate nearly 1.3 million people along the central coast, as Reuters reported.
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A stretch of coastline in the Philippine capital, Manila has received backlash from environmentalists. The heavily polluted Manila Bay area, which had been slated for cleanup, has become the site of a controversial 500-meter (1,600-foot) stretch of white sand beach.
Sand Makeup Crucial for Ecosystems<p>While UNEP/GRID-Geneva generally supports finding <a href="https://www.dw.com/en/not-enough-sand-for-construction-industry-despite-abundance/a-49342942" target="_blank" rel="noopener noreferrer">alternative sources of sand</a> so as not to disrupt ecosystems in rivers and oceans when extracting them, Vander Velpen stressed it was vital to use sand which closely matches the makeup of the native sand to protect beach fauna.</p><p>"If you change the core characteristics of the native sand, the original sand, you need to do an environmental impact assessment (EIA) to find out how it's going to impact the ecosystem and nearby ecosystems," he told DW.</p><p>But according to Torres, such an assessment was not done in Manila.</p>
Beautification Stunt Instead of Proper Cleanup?<p>Manila Bay's waters are heavily polluted by oil and trash from nearby residential areas and ports. A huge "No swimming" sign warns visitors to stay away from the ocean.</p><p>Philippines' <a href="https://denr.gov.ph/index.php/priority-programs/manila-bay-clean-up/25-priority-programs/1825-frequently-ask-questions-faqs-on-the-dolomite-and-the-beach-nourishment-project" target="_blank">Department of Environment and Natural Resources (DENR)</a> has denied dolomite sand poses any risk to human health and the ecosystem.</p><p>However, scientists of the University of the Philippines have come forward disputing the DENR's claims. A <a href="https://biology.science.upd.edu.ph/index.php/ib-statement-regarding-dolomite-in-manila-bay/" target="_blank" rel="noopener noreferrer">statement by the Institute of Biology</a> said that using crushed dolomite did not address any of the rehabilitation phases and instead was "even more detrimental to the existing biodiversity as well as the communities in the area," pointing to the case of water birds. "The dumping of dolomite in Manila Bay has effectively covered part of the intertidal area used by the birds thereby reducing their habitat."</p><p>At peak migration season, Manila Bay is home to 90 aquatic bird species, including species of international conservation concern that are facing a very high extinction risk in the wild. </p><p>Authorities should focus on protecting and conserving biodiversity, the Institute of Biology added. "Rehabilitating mangroves is an example of a nature-based solution that is cheaper and more cost-effective than the dolomite dumping project," the scientists said.</p><p>Moreover, <a href="http://www.msi.upd.edu.ph/" target="_blank" rel="noopener noreferrer">the Marine Science Institute</a> has warned that prolonged inhalation of finer dust particles of dolomite could "cause chronic health effects," leading to discomfort in the chest, shortness of breath and coughing.</p><p>They also warned dolomite sand grains would erode during storms and be carried out to sea, essentially being washed away.</p>
Rehabilitation vs. Reclamation<p>Environmentalists say covering up the beach doesn't address the real issues of the bay. Torres and others believe the best way to clean up Manila Bay is not to add anything, but rather remove trash and pollution.</p><p>"There have been studies saying much of the waste comes from already collected waste — so these are open dump sites along the coast that get washed up because of the rain," Torres said.</p><p>She criticized the authorities for continuing to push reclamation projects she says are at odds with each other. These projects will affect large areas of mangrove forests, she said, and experts warn that this, in turn, exacerbates coastal erosion.</p><p>"If you've removed the areas that helped trap the sand, like mangrove forests, then the likelihood increases that you will have to nourish a beach. Same as building right up to the waterfront," said Vander Velpen of UNEP/GRID-Geneva.</p>
Plenty of Sand in the Sea?<p>The question of Manila's contentious white beach echoes larger questions about sand mining worldwide. <a href="https://unepgrid.ch/storage/app/media/documents/Sand_and_sustainability_UNEP_2019.pdf" target="_blank">Global sand consumption has tripled</a> over the past two decades, UNEP/GRID-Geneva has found. A huge chunk of it is now taken up by construction.</p><p>"Many operate on the assumption that natural sand is endless in its supply," said Vander Velpen.</p><p>Sand scarcity is a concern shared by Stefan Schimmels of <a href="https://www.fzk.uni-hannover.de/fzk_start.html?&L=1" target="_blank">Forschungszentrum Küste</a> who's done extensive research on shore nourishment to stop coastal erosion. And as climate change and rising sea levels are threatening coasts, demand for sand will grow even more.</p><p>A large study, the <a href="http://www.stencil-project.de/wp-content/uploads/2019/10/STENCIL_SWOT_Analyse_191026.pdf" target="_blank">Strategies and Tools for Environment-Friendly Shore Nourishments as Climate Change Impact Low-Regret Measures (STENCIL project)</a>, focused on the German island of Sylt, a popular vacation spot.</p><p>About 1 million cubic meter of sand per year is used to maintain the coastal area of Sylt, STENCIL project head Schimmels said. That's about 100 million 10-liter buckets of sand.</p><p>When sand was extracted off the coast of Sylt, underwater craters were formed. "You can still detect these craters even decades later," Schimmels told DW.</p><p>"Also when you add a couple of meters sand onto the beach — you essentially bury all things that do creep and fly," he said. "How quickly will they recover?" Schimmels said more research was needed as there was still too little known about long-term effects on the environment. </p>
Criticism Piling Up<p>As for Manila's artificial white sand, it looks like some might have already been blown away by a recent storm. DENR claims it wasn't washed away, but said that grayish sand, stones and other material had simply piled up over the dolomite sand. People in Manila have tweeted photos showing how the storm has ravaged the beach. </p>
<div id="adc0b" class="rm-shortcode" data-rm-shortcode-id="98f9390db6bb81cb421aaf0bb9d9a6fb"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1318816633280851969" data-partner="rebelmouse"><div style="margin:1em 0">Exactly one month after giving excited netizen a glimpse of Manila Bay white sands, look what happened now after ju… https://t.co/X0Z9i0bPB0</div> — M*A*S*H (@M*A*S*H)<a href="https://twitter.com/Magtira_Matibay/statuses/1318816633280851969">1603265362.0</a></blockquote></div><p>Authorities have been called tone-deaf for spending around 389 million pesos ($8 million) on a beach nourishment project in the middle of a raging pandemic.</p><p>An image of cake iced with the words "It really hurts - that's [worth] 389 million pesos?" has since gone viral.</p>
<div class="rm-shortcode" data-rm-shortcode-id="4387aad52ea316e4db7330052318ca2f"><div class="fb-post" data-href="https://www.facebook.com/theweekendpatisserie/posts/144564207350008"></div></div><p>"It's just a waste of precious resources," Torres said. </p><p>The environmental activist now also worries that she might be labeled a terrorist for speaking out under the <a href="https://www.dw.com/en/philippine-anti-terrorism-law-triggers-fear-of-massive-rights-abuses/a-53732140" target="_blank" rel="noopener noreferrer">Philippines' controversial new anti-terrorism law</a>. She says she could be arrested for inciting fear when talking about environmental dangers.</p>
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