Guest editorial: All power generation has an impact

The Kenai Peninsula hosts a couple hydroelectric generation facilities and a couple others were proposed in the past. With the ever-increasing costs of electricity, there are renewed activities looking into the feasibility of additional hydroelectric plants on the peninsula.

Unfortunately, there is a lot of rhetoric about these proposals that is misleading at best. A term being erroneously attached to the proposals and studies is “low impact.” However, hydroelectric power generation can hardly be called “low impact” when streams are completely dewatered or the entire biotic community is completely changed.

In order to generate electricity with water power, one needs a large volume of water that can be released on demand (whenever there is a demand for electricity). Also, in order to generate as much power as possible, the water needs a substantial “head.” That translates to mean the water source is dammed up as high as possible and allowed to generate power as the water is selectively released. The greater the height of the “head,” the greater the force the water exerts on the turbine impellers. That benefit of increased water height is why some of our well-known dams, like Hoover Dam or Grand Coolee, can generate so much electricity.

Besides aesthetic considerations, there are a number of very well-known impacts that dams always exert on a stream. Perhaps the first thing to understand is that any dam instantaneously changes the stream from a moving body of water into a lakelike reservoir. Virtually all stream species of algae, diatoms, insects, crustaceans, fish and associated animal life will be displaced by lake-associated species. All areas that were once valuable spawning sites for resident and anadromous fish will be filled with silt and sediments when the flow ceases. No further spawning will occur there. This stream disruption will continue as far upstream as the water is allowed to back up.

As a point of reference, the Kenai River gets backed up for almost 15 miles by the twice-daily tidal changes of 20 to 30 feet. Thus a lot of river or stream can be impacted by a relatively “low impact” dam.

Downstream of the impoundment there are other issues. Hydroelectric dams release water for power generation on a schedule that fits human power needs, not the stream needs. Most power is actually needed during daylight or normal working hours so more water is released during the day. Depending upon the size of the receiving stream, daily variations in water releases can raise or lower stream levels by a foot or more. Small streams can go from bank full conditions to drought levels on a daily basis. This unnatural fluctuation eliminates a great many stream organisms. While some stream invertebrates will remain in the now altered stream, the species assemblage will be unlike the original inhabitants and total biomass within the stream will be heavily reduced downstream of the dam. The invertebrate losses will then cause a heavy reduction in the fish populations that relied on them for food.

Since the stream below an impoundment has its flow closely regulated, there are no more floods. At first blush that may seem to be a good thing. However, streams benefit from periodic flooding and high waters. These events clear out fine particles deposited in the stream and re-sort the gravels into like-sized sections. Salmon look for these uniform-sized gravel beds to use for spawning.

Another seemingly subtle change caused by dams and impoundments is the temperature of the waters being released. Water coming from the bottom of a reservoir will be colder than the normal stream temperature and water released from the surface of the reservoir tends to be much warmer than normal stream water. Generally, the winter water outflow is warmer than normal and the summer water outflow is cooler than normal. Some large dams can produce detectable thermal changes in the outflow streams for dozens and dozens of miles downstream. The concern here is that we know many aquatic organisms depend upon temperature changes to signal times for migration, emergence, reproduction, etc. Thus, subtle changes in water temperatures on a seasonal and daily basis can disrupt the life cycles of the remaining organisms.

These are just a few of the changes a dam can exert upon a stream. If we are going to consider hydroelectric power generation on the Kenai Peninsula we will have to consider the tradeoffs and decide what we value most highly. These will be some difficult decisions. Remember, there is no “free lunch,” and there is no “low-impact” way to generate power.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus.