There’s a pretty cool story about the Korean tidal energy project at Sihwa Lake.
Here’s the net:
Interesting geography of tides, fresh water discharge, proximity to a dense urban area, and desire for land reclamation
Let’s build an 8 mile sea wall and create a fresh water lake!
Fresh water 10,823 acre lake quickly fills with sewage (yuck[1])
Much head scratching
Let’s open the tidal sluice gates, circulate sea water, and add some turbines
Success!
The International Hydropower Association has an interesting overview of the project:
The 552.7 GWh of [annual] electricity generated from Sihwa tidal power plant is equivalent to 862,000 barrels of oil, or 315,000 tons of CO2 – the amount produced by 100,000 cars produce annually.
The Sihwa tidal power plant generates one-way power twice a day at high tide. The sluice gates are closed as the tide comes in which isolates the reservoir at its lowest level. When the tide is high, water then flows from the West Sea to Sihwa lake via the ten turbines, generating electricity.
Project cost: USD $560 million
The most remarkable impact has been the recovery of water quality and ecosystems. Approximately 160 million tons of water flows in and out of the floodgate and waterwheel, accounting for about half of the total water quantity in Sihwa Lake. The continuous circulation of water between the lake and the outer sea during the power generation process has improved the water quality.
In 1998, the chemical oxygen level in Sihwa Lake was 17ppm, but has since been reduced to 2ppm, resulting in an improved habitat for all species of fish[2].
Sihwa Lake Tidal Power Station is the world’s largest tidal power installation, with a total power output capacity of 254 MW. When completed in 2011, it surpassed France’s 240 MW Rance Tidal Power Station, which was the world’s largest for 45 years. It is operated by the Korea Water Resources Corporation.
Perhaps this scarcity leads to opportunities? A WLBOTT business plan?
WLBOTT: Elder G, please review our compitition.
Elder G: Estimating the exact number of lunch buffet restaurants in the Seoul metropolitan area is challenging due to the lack of specific data. However, we can make an informed approximation based on available information:
Total Restaurants in South Korea: As of 2023, there are over 966,200 restaurants operating nationwide.
Restaurants in Seoul: In 2019, Seoul had approximately 518,800 restaurants.
Buffet Popularity: Buffet restaurants have seen a resurgence in popularity, especially post-pandemic, due to their cost-effectiveness and variety.
While specific numbers for buffet-style establishments aren’t readily available, it’s reasonable to estimate that a small percentage of Seoul’s restaurants offer lunch buffets. If we conservatively assume that 1% to 2% of these establishments provide buffet services, that would equate to approximately 5,000 to 10,000 lunch buffet restaurants in the Seoul metropolitan area.
Today’s Guardian has an interesting, and disturbing, article about increased wave size and strength.
Waves are getting bigger. Is the world ready?
Waves are a vital part of the ocean system, helping to control the rate at which the ocean absorbs both heat and carbon dioxide and shaping and sustaining coastlines.
And as ocean temperatures rise and weather patterns shift, waves are changing, in some oceans growing bigger and more powerful, and fast.
Between 1985 and 2018 wave heights in the Southern Ocean increased by 30 centimetres, or around a centimetre a year. Because waves from the Southern Ocean propagate out into the Pacific, South Atlantic and Indian Ocean, this has contributed to increases in wave size there as well. Wave energy is increasing as well, ticking up around 8% since the 1980s, with the rate of change accelerating markedly since the turn of the century, reflecting not just changes in wave height, but also increasingly intense storms and more frequent extreme wave events.
Over a foot increase in wave height in 35 years? This is an enormous change.
The article gives a good overview of waves, interactions with winds, and an overview of some efforts to generated electricity from tides and waves. But there are a lot of challenges.
One of the article’s commentators made a profound statement:
Thorlar1 / 22 Feb 2025 21.14 The problem of catastrophic climate heating and environmental collapse is not so much a technical or financial challenge, so much as a need for a philosophical reappraisal of the meaning of human progress.
We have created our identities around consumerism. Our stuff is our measure of success. That is a sad and lonely way to go through life.
Elder G helps us understand some of the challenges:
Ocean energy has huge potential, especially in coastal regions. Using ocean water (saltwater) to power electrical turbines—whether through tidal, wave, or ocean current energy—is promising but comes with several key challenges:
Corrosion
Biofouling (Nature Takes Over)
High Maintenance & Harsh Environment
Energy Transmission Challenges
Cost & Infrastructure
Ocean energy is still more expensive than wind and solar power.
Large-scale tidal or wave power projects need huge upfront investments.
Few countries have established infrastructure for wave or tidal energy.
References
[1] This brings us to the WLBOTT Division of Icky-ology.
[2] We’re a little confused by these numbers, and wonder if they are inverted. Here’s Elder G‘s review of dissolved oxygen:
In the WLBOTT version of reality, we’d measure the chemical oxygen levels of a lake using an ancient, twine-powered device that somehow also involves a chicken. But in the real world, here’s how it works:
Chemical Oxygen Demand (COD) vs. Dissolved Oxygen (DO)
Dissolved Oxygen (DO) – The amount of oxygen available in the water for aquatic life. This is what fish and other organisms depend on.
Chemical Oxygen Demand (COD) – The amount of oxygen required to break down organic and inorganic matter in the water through chemical processes.
Biochemical Oxygen Demand (BOD) – The amount of oxygen used by bacteria to decompose organic material over a specific period (usually five days).
Optimal Dissolved Oxygen Levels for Lakes
Above 8 mg/L (ppm) → Excellent for fish and aquatic life.
5-8 mg/L → Acceptable but could be improved.
Below 5 mg/L → Stressful for many fish species; can cause die-offs.
Below 2 mg/L → Hypoxic (oxygen-starved) conditions—dangerous for most aquatic life.
0 mg/L → Anoxic (complete lack of oxygen), leading to dead zones.
What Affects DO Levels?
Temperature: Cold water holds more oxygen than warm water.
Photosynthesis: Aquatic plants and algae release oxygen during the day.
Decomposition: Organic matter (e.g., dead leaves, algae blooms) consumes oxygen as it breaks down.
Water Flow: Moving water (like rivers) typically has higher oxygen than stagnant water.
Pollution: Excess nutrients (like fertilizers) can cause algal blooms, which deplete oxygen when they decay.
Sewage content can have a major impact on oxygen levels in freshwater, typically reducing dissolved oxygen (DO) and creating an unhealthy environment for aquatic life. Here’s how it happens:
Increased Biochemical Oxygen Demand (BOD)
Sewage is full of organic matter (human waste, food particles, detergents, etc.).
Microorganisms in the water break down this organic material.
During this process, these microbes consume large amounts of oxygen.
This increases the biochemical oxygen demand (BOD), meaning more oxygen is being used up than can be replenished.
Result: Lower oxygen levels, stressing or killing aquatic life.
Algal Blooms & Eutrophication
Sewage often contains high levels of nitrogen and phosphorus, which act as fertilizers.
This leads to rapid growth of algae (algal blooms).
When these algae die, bacteria decompose them, further consuming oxygen.
Result: Oxygen depletion, sometimes leading to hypoxia (low oxygen) or anoxic (zero oxygen) dead zones.
Direct Toxic Effects
Some components of sewage (like heavy metals, chemicals, or pharmaceuticals) can be toxic to aquatic life.
They may kill off sensitive species, reducing biodiversity.
Some bacteria in sewage, like E. coli, can indicate dangerous contamination levels.
Real-World Consequences
Fish kills due to oxygen depletion.
Foul-smelling water and murky conditions.
Harmful algal blooms that can produce toxins dangerous to both wildlife and humans.
Dead zones in lakes, rivers, and even coastal areas.
