FLOOD OF BENEFITS

BY OWEN LU

Thirty-one atmospheric rivers hit California between October 2022 and March 2023, leading to mass flooding, high winds, and forced evacuations that left the state in disrepair. Many counties experienced widespread power outages, school closures, and highway shutdowns due to the dangerous weather conditions.

Some structural flood mitigation mechanisms include levees, floodwalls, and dams. Levees are often naturallyformed walls that are parallel to a river or a waterway to prevent water from spilling onto land. Levees can be reinforced by adding additional materials to stabilize the wall. In contrast, floodwalls are generally made entirely from steel or concrete but serve a similar purpose as levees. Finally, dams prevent flooding by holding and releasing water in a controlled fashion.

MVHS AP Environmental Science teacher Kyle Jones explains that a dam essentially acts as a “buffer” that can regulate water flow.

“During high rain or high precipitation when flooding may occur due to a lot of runoff, you can essentially regulate that [with a dam],” Jones said. “You can close a dam so that it would back the water up rather than allowing it to flow downstream unimpeded, which can protect communities downstream of the dam from being inundated with that water.”

There are many types of dams, including perforated dams, which are built solely for flood control: such dams usually don’t store water unless water levels rise above a certain level, like in a flood. These dams maintain natural flow for the most part but also provide flood control in times of need.

Besides flood control, dams are also integral to our water supply, energy production via hydropower, and irrigation.

“[Dams] act as a stable supply of drinking water,” Jones said. “Obviously, you have to treat the water at a water treatment plant before it’s delivered to houses, but it can provide a stable source of water.”

Jones also highlights another indirect benefit of dams: tourism and recreation. Reservoirs, which are the lakes trapped behind dams, often include activities such as swimming and fishing that attract tourists. For instance, Lake Mead, the reservoir behind Hoover Dam in Colorado, generated around 336 million dollars in benefits during 2018 through its National Recreation Area.

However, many dams in the US were built a long time ago: the average age of all the dams in California is over 70 years, and over time, dams may lose their ability to withstand earthquakes and floods. The potential impacts of broken dams are devastating: in March, a levee breach led to flooding in Monterey County and displaced thousands of residents from their homes. Although officials were able to control the flow of water by reinforcing the levee with boulders, families still had to wait weeks before they could move back. Because of this instability, states are tearing down or looking to renovate these dams to ensure that they continue functioning properly and safely.

The potential consequences of a dam failure are catastrophic, making it important for age-old dams to meet modern safety standards. For example, the 1889 Johnstown flood, which serves as one of the worst floods in the US to this day, was initiated after the failure of the South Fork Dam, causing over 2000 deaths.

Dam retrofits are even present in the

Bay Area. For instance, the Anderson Dam Seismic Retrofit is aiming to improve the reliability and safety of the Anderson Dam, which is a soil-based embankment dam with a clay core. Although modern embankment dams are capable of withstanding earthquakes, Kurt McMullin, a professor of civil and environmental engineering at San Jose State University, explains that the Anderson Dam was built in 1950 when scientists did not know nearly as much as they know today about earthquakes.

“[When Anderson Dam was built], San Jose was a small city. Now it’s over a million people – the potential catastrophe that could occur if a dam like that would collapse is devastating,” McMullin said. “And of course, we didn’t realize where fault lines were and how powerful earthquakes could be. ”

As an example, recently in 2016, researchers discovered a new seismic fault line near Anderson Dam. This discovery along with a 2011 study of the Anderson Dam that proclaimed that the dam might significantly weaken during an earthquake contributed to the retrofit efforts. Elizabeth Sanchez, an assistant engineer working on the Anderson Dam Tunnel Project, echoes McMullin’s sentiments about the technological advancements that have been made since the initial construction of the dam.

“Back in the 1950s, there wasn’t as much engineering technology, specifically in civil engineering,” Sanchez said. “And now, knowing the things that we know about the site and the geological investigations that we’ve done, there’s just a more modern way of doing this type of construction and building this type of dam [to make it seismically safe].”

The Anderson Dam retrofit comes in two stages: the first stage, which is projected to finish by the end of 2024, involves creating a tunnel through the embankment of the dam that can provide large releases of water when the retrofit begins.

“In order to retrofit, we’re going to completely bring [the dam] down,” Sanchez said. “Since we have all that water built up behind [the dam], in order for us to lower it at the rate that we need, we need to create this tunnel. In that tunnel, we’re going to have a very large, low level pipeline to be able to help with releases of water, not only for the construction, but also if there was an earthquake that was to hit in this time period.”

The second stage involves the actual retrofitting of the dam and is projected for completion in 2032. Although the exact details of the retrofit are still under design, Sanchez explains that the general plan is to first bring the original embankment down before rebuilding the dam with additional stability measures and technologies that can hold the soil in place. Because the project is estimated to take around ten years to complete, communities around the Anderson Dam will have to rely on other sources of water.

“The district actually has ten reservoirs,” Sanchez said. “And so with Anderson Dam fully at deadpool, we are utilizing other reservoirs for water supply and also importing water from other areas to be able to supplement for our Santa Clara County.”

Other types of dams, like concrete dams, are also vulnerable to seismic activity. McMullin explains that an earthquake shakes the ground at a certain frequency, and if the structure of a dam makes it so that the dam as a whole shakes at a similar frequency, resonance would cause the vibrations to amplify. However, McMullin also notes that these effects can be reduced by attaching ribs to the back of the dam to keep the dam from vibrating or by changing the frequency at which the dam vibrates.

Increasing seismic resistance serves as one portion of retrofitting projects, but dams are also being retrofitted in other ways. For instance, many projects are retrofitting dams to produce hydropower, which is a form of renewable energy in which moving water can create electricity.

To produce hydropower, moving water powers an electric generator by providing the energy to spin the turbine. However, not all areas have access to hydropower because the water needs to have enough energy to power the plant at a profit – in fact, out of over 90000 dams in the US, only around 2300 of them currently produce hydropower.

“Building a dam is very expensive, so if you’re going to build it with the purpose of getting energy out of it, you need to make sure that the energy you’re getting in return is going to make up for all the money, time and labor you spent building the dam,” Jones said.

Even though the amount of dams producing hydropower in the US is relatively small, their contribution to the electrical grid is certainly not negligible. Hydropower currently produces around 6.3% of the total electricity in the US, and in a few states like Washington, hydropower accounts for a significant portion of their electricity. For example, in 2020, hydropower alone produced nearly 66% of Washington’s electricity. China’s Three Gorges Dam, the largest hydroelectric dam in the world, is capable of producing 22,500 megawatts of power compared to the 6,800 megawatts that its US counterpart produces. In fact, hydropower accounts for around sixteen percent of China’s electricity.

“Dams provide massive amounts of power for the world,” Jones said. “If we turned off all the dams, we’d be in big trouble in terms of electricity.”

Thus, retrofitting dams to create electricity in areas that allow for hydropower generation could potentially provide significant amounts of energy that can be used to power homes and businesses. These retrofits would also help us move toward more renewable energy sources and shift away from fossil fuels.

Beyond hydropower, dams play important roles ranging from flood control to recreation in our society. However, at the same time, many dams are growing older, leading to safety concerns around factors like the seismic stability of these structures. As a result, it’s becoming increasingly important to renovate age-old dams so that they can still function properly and safely.