Upstream B1 Student 39;s Book Answers

[Martez Fields]

Massiveengineered structures such as dams have an effect on the natural environment. Because the application of scientific knowledge to satisfy human needs requires natural resources, engineering solutions inevitably impact the natural environment. The priorities of engineering projects are ultimately chosen by the priorities of the public, and thus, engineering projects change along with people. Because society is now more aware of the importance of environmental conservation, the design and modification of these structures take into consideration care for the ecosystems in which they operate and on which they depend.

When we build dams on rivers, we get the benefits of hydroelectric power generation. We also have discovered that blocking the river and lowering the water flow impacts the surrounding ecosystems. Realizing this has led to environmental stewardship practices such as enabling fish to bypass dams, improving water quality and implementing additional river flows to benefit downstream aquatic habitat.

Let's review some basic salmon biology. Once they are hatched, what stages do salmon go through to become adults? How many stages do you go through as a human? Let's look at the handout to understand the stages of a salmon's life. (As a class, review the Salmon Life Cycle Handout in detail.)

Figure 1. To aid fish migration at hydroelectric dams, engineers design into dams juvenile bypass systems, fish transport facilities, and adult fish ladders.copyrightCopyright U.S. Army Corps of Engineers

Figure 2. Fish ladders are a series of steps and pools that provide a gradual upward climb over dams, providing passageways for returning adult fish that are swimming upstream.copyrightCopyright U.S. Army Corps of Engineers

In our ongoing hypothetical situation, citizens in and around Thirsty County are concerned about the salmon population in the Birdseye River. They have asked Splash Engineering to present a variety of dam designs that will be safe to the fish population and not hinder seasonal salmon migration up and down Birdseye River.

Upstream fish passage can be aided using fish ladders or elevators (see Figure 2), or by trapping and hauling the fish upstream by barge or truck. Downstream fish passage is aided by diverting fish from turbine intakes using screens or racks or even underwater lights, sounds and bubbles, and by maintaining a minimum spill flow past the turbine. Let's discuss these designs and how they help the fish survive passing by the dam.

As the engineers for Splash Engineering, you can incorporate into your Thirsty County dam designs these sorts of devices and structures that protect and help the migrating salmon in Birdseye River. Let's brainstorm to think about how we could protect fish swimming both upstream and downstream.

(To conclude, either lead an informal discussion or assign student teams to come up with their own proposed plan of fish mitigation solutions for the Birdseye River dam in Thirsty County that include a labeled drawing and short presentation; see details in the Assessment section. If conducting the associated activity Fish-Friendly Engineering, do this after the activity is completed.)

Six species of anadromous salmon find habitat in the Columbia River Basin (chinook, coho, chum, sockeye, pink and steelhead), plus anadromous shad, smelt and lamprey. Anadromous fish migrate from salt water to breed in fresh water, which is different than catadromous fish that live in fresh water and migrate to marine waters to breed.

As described on the Salmon Life Cycle Handout, the six stages of the salmon life cycle are egg, alevin, fry or parr, smolt, juvenile and adult. The salmon life cycle begins when they hatch in fresh water rivers and tributaries where they remain to grow for a year or two (see Figure 3). Then they migrate from fresh-water rivers to the salty ocean where they live for two to five years. As mature adults, they return to their birthplaces to spawn. Exhausted after the upstream swim, the adults die shortly after spawning, their bodies adding nutrients to the stream where the eggs hatch.

Many factors can impact the health of salmon populations, including overharvesting; the harming of water habitat from farming, cattle grazing, mining, logging, road construction and industrial pollution; and the existence of a network of tributary and mainstream dams. The presence of dams affects the habitat and migration of anadromous salmon species because they impede fish migrations to and from the ocean by their physical presence and by creating reservoirs. Compared to rivers, the reservoirs behind dams are places of slower water velocities and altered river temperatures. Slowed water movement increases the time it takes fish to migrate and increases the likelihood of being caught by predators. Warmer water temperatures alter the fish habitat and can change fish behavior. Dams also lower salmon survival because they are treacherous for juvenile salmon to navigate en route to the ocean, and reduce (or eliminate) access to fresh water habitat (preventing adult fish from returning to spawn).

To address these issues, many dams now have facilities to help fish migrate past the dams. In addition, many dams are now operated to improve passage and reservoir conditions for fish. For example, during the juvenile fish migration season, late March until fall, river flows are increased to mimic seasonal high flows, and additional water is spilled to aid migration.

Juvenile fish can migrate past dams by several routes: through the turbines (not safe!), over a dam spillway, through a screened juvenile fish bypass system, or via transport by barge or truck. Juvenile fish bypass systems use submerged screens (or cage-like racks) positioned in front of dam turbines to keep fish away from the dangerous powerhouse turbines. Sometimes underwater sound, light and bubbles are used as "behavioral barriers" to divert fish away from turbine intakes. Once at the screens, the young fish are directed into channel openings that route them back to the river below the dam (which is called "bypassing"), over a spillway, through ice or trash sluiceways, or to holding areas for loading on specially equipped barges or trucks for transport downriver. During barge transport, river water circulates through the boats so the fish can imprint the chemicals and smells of the water during the trip downriver through dams and locks. Juvenile bypass systems safely guide millions of spring/summer salmon away from the turbines and help them navigate rivers containing many dams and reservoirs.

Most juvenile salmon tend to stay in the upper 10 to 20 feet of the water column as they migrate downstream to the ocean, so it is harder for them to find a way past a dam if they must dive to 50 to 60 feet to find a spillway opening or a bypass channel. Engineers design new technologies that provide more surface-oriented, less stressful passage routes for the young fish. Some new designs are similar to waterslides.

Sending juvenile fish over dam spillways is one safe way to help fish past the dams, but so much spilling water causes more bubbles of gas (nitrogen) to be trapped in the water, which can be harmful to fish at high levels. Engineers design spillway flow deflectors to produce a more horizontal spill flow that minimizes this problem, causing less change to fish habitat.

To help adult fish gain access to fresh water habitat above dams, adult fishways include fish ladders and fish elevators. Since 1938, fish ladders have been effectively integrated into the design of many Columbia River Basin dams. These ladders look like a series of steps and pools and provide a gradual upward climb up the vertical height of the dams for returning adult fish (see Figure 2). Essentially, fish ladders mimic a series of low, natural waterfalls, which is something that salmon are able to navigate. To guide the adult fish to the downstream ladder entrances, engineers simulate "attraction" flow conditions like those that would be found at the base of natural waterfalls. Fish elevators or fish lifts are mechanical ways to raise fish up from the bottom of a dam to the top part of the reservoir so they can continue to swim upstream.

Engineers and biologists continue to evaluate and monitor the success of fish passage and survival at hydropower dams. Some of their studies involve inserting very small tags containing radio antennas and/or computer chips into fish body cavities to enable them to track the fish during their lifetimes. Sometimes engineers place sensors in the stream flow to collect data on how many fish go through the various passage routes.

Let's review the six stages of the salmon life cycle. What are they? (Answer: Egg, alevin, fry or parr, smolt, juvenile and adult.) At which stage are salmon when they swim downstream past dams? And at which stage are they when swimming upstream? (Answers: Smolts and adults, respectively.) Why do the adult salmon swim upstream? (Answer: To return to their birthplaces to spawn.) What happens if the adult salmon cannot migrate upstream to where they hatched? (Answer: They will not lay eggs so that new salmon can be born, reducing the salmon population.)

How do dams lower salmon survival rates? (Possible answers: Dams are physical barriers to the seasonal fish navigation up and down rivers, some fish die in the turbines, reservoirs above dams are not the ideal habitat for salmon, some fish are lost or eaten while in the warmer and slower-moving reservoirs, salmon cannot get past the dams to return to their native rivers to reproduce, etc.)

What types of structures and solutions do engineers incorporate into the dams they design so they are less disruptive of the natural migration cycle of fish such as salmon? (Possible answers: Engineers incorporate fish ladders, fish elevators/lifts, juvenile fish bypass systems with submerged turbine intake screens and racks, underwater sound/light/bubble diversion devices to guide fish to safer routes over a dam, barge and truck transportation, ice or trash sluiceways, spilling additional water to flow past the turbines and the dam, increasing river flows to mimic seasonal river water levels, etc.)

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