Boy this is a tough one, and one of the most polarizing subjects that is played out at not only the small local town level but at the international level as well. There can be supporters of a small local dam or weir in a town as well as the opponents of the dam, just as much as there can be one country supporting and building a dam on a river that the neighbouring country downstream is an opponent of.I think the one thing we need to talk about first is the variety of water control structures because they can vary significantly and many people are opposed to some and not others, some are opposed to all, etc, so you should probably look at the differences between three of them in our FAQ section “what is the difference between a dam, a weir and a barrage?” There’s no doubt all have effects, but the extent of effects differ highly, especially for the giant projects like Hoover Dam or the Three Gorges Dam in China.
The question is, are these big dams with their big detrimental effects worth it because they provide big benefits like huge power generation potential and a water supply for entire regions? Are they better than small water control structures with small detrimental effects? Or are small structures just the same thing really, just death by a thousand cuts, instead of one big cut?
All the big projects are dams by design, they are almost always installed for water supply and power production purposes, and they flood vast areas, and they store huge amounts of water at great depths such that the heads they create are very high, they sometimes store several years worth of river flow behind them and they usually release water based on power supply requirements ie to supply a constant amount of electricity to the grid or to supply water to vast geographic areas, not to maintain seasonal river flows as they existed before, or not even to maintain constant water heights behind the dams. Water heights behind these big project dams can fluctuate significantly because they draw more water to produce power or to supply for consumption at times than there is water flow in the river to replenish it.
While these projects have big effects they also allow humans to populate and liver places in numbers that we otherwise wouldn’t be capable of. For instance the Hoover dam provides a reliable water supply to Nevada, California and Arizona, as well as power.
While I can understand the reasons for installing these large facilities, which we’ll talk about below, I consider these larger facilities less desirable than small local hydro project development. On the one hand there just seems to be something wrong with altering nature on such a grand scale and completely ignoring the limits of nature where you live. If you want to live in the Nevada Desert or California, that’s fine, but try and do it within the limits of that environment. On the other hand, on a more detailed technical level, I have a problem with storing 2 years worth of water, or consuming more than the river can supply, or causing large fluctuations in water levels. This is why I’m biased to smaller local run of river micro hydro, if the resource exists locally.
These small sites may only store a days or few days of water, and don’t manage water flows, but just use whatever naturally occurring flows exist. To me that just seems better. And where fish migration is an issue, it can be dealt with much more easily.
And this last point, is something to consider, the benefits and the costs of local micro hydro are both felt locally mainly, rather than the costs of huge hydro being felt in one geographic region and the benefits going to those in another far off region.
While not all hydro is the same as we’ve discussed above, let’s look at the Pros and Cons of hydro in general.
PROS (Good)
- Each year over 100,000 lives are lost in floods, and flood control is a major reason for building water control structures, even in Canada, to protect human lives and property.
- Water control structures improve and / or make navigation possible on certain waterways.
- Water control structures provide water supplies for drinking water and irrigating fields.
- Water control structures provide a non polluting, inexpensive, renewable, 7 days a week, 24 hours a day, source of electricity.
- Water reservoirs created by water control structures are enjoyed for recreation, tourism, boating and fisheries.
CONS (Evil)
- Dams can break and if they do can cause serious flooding and damage.
- Dams are expensive to build.
- The silt that usually flows down and out rivers is blocked by the dam, changing sedimentation patterns.
- Ends flooding that would help clean out the silt in rivers.
- Disrupts natural seasonal changes in the river by regulating river flows, and can change ecosystems.
- Large dams can cause loss of agricultural lands and displace human populations.