Question

Why are dams opposed

Answer 1

Dams are opposed due to various reasons:
1) It requires huge acres of land in order to construct it.
2) it takes lots of years to construct it.
3) Promises made for the people are not fulfilled and they will face consequences.
4) Low lying land areas will be submerged under the dam and the vegetation rots leading to spread of diseases.
5) During rainy season the water may overflow and damage the crops in the surrounding areas.

Answer 2

There are different reasons in different places, but here are the typical challenges for siting hydroelectric dams:

Displacing existing people: Reservoirs are big. The Site C dam in BC reservoir, if it ever fills, will cover 93 square kilometers for only a GW of capacity. Often there are people living on that land, growing crops on that land or who fish or hunt in that land. Sometimes they are indigenous, sometimes they are settlers. But they all have to move. The life they had changes substantially. And as hydro dams are built in remote areas, these are not people who have a habit of changing apartments every year, or moving to a new city every couple of years following work. Often they have been on the land for generations or centuries. That’s hard for them.
Sacred or historic sites: In addition to the people, sites which they consider sacred or sites of great historic value are lost beneath reservoirs as well. North American indigenous often have a very strong connection to the burial grounds of their ancestors and consider them sacred.
Loss of mineral access: Hydroelectric reservoirs cover a lot of area, as mentioned, and that land surface has other uses both on the surface and below the surface. Mineral deposits become much more expensive to extract if they are under tons of water.
CO2 emissions: Reservoirs that cover large amounts of biomass have a greenhouse gas problem. Anaerobic decomposition of vegetation causes emissions of potent greenhouse gases, 50%-75% methane and 25%-50% CO2 as well as a few irrelevant trace gases. Far northern, far southern and desert biome reservoirs typically have much lower emissions than most tropical and temperate forest reservoirs. Site C Dam won’t be producing carbon neutral electricity for about 30 years. Over a 100 year lifespan it looks good, but not in the short term. Their official policy is that it’s better than wind energy, but only by a hair and the risks and costs of hydro megaprojects don’t make the numbers entirely credible.
Mercury and heavy metal buildup: Many reservoirs become accumulators for heavy metals from upstream watersheds, especially if the waters flow through areas with high mineral extraction. The James Bay Dam in northern Canada had this problem and it required substantial remediation.
Dead reservoirs and remediation: Related to the anaerobic decomposition, these are artificial lakes with no ecosystems. They don’t have natural flow through of water and easy ability of spawning fish to move upstream and silt to move downstream. As a result they become oxygen-free zones without intervention. Most reservoirs require ongoing fertilization in order to keep them somewhat alive. Similarly, they have to be stocked with fish to be useful recreational facilities at significant expense. These are substantial, ongoing, expensive interventions which displace the existing natural processes.
Loss of spawning grounds: Many species of fish swim upstream to spawn in shallow gravel headwaters, salmon being the obvious marker fish. Dams block that spawning. Fish ladders and fish cannons are only somewhat effective in overcoming this problem. This is mostly resolved with large scale stocking programs.
Loss of canoeing, rafting and kayaking recreation: Block a river and you block a potential recreation path.
Changing water cycle: Global warming and climate change are fundamentally altering cycles and degrees of drought and deluge around the world. Many hydroelectric facilities are underperforming against design and expectations due to regional drought. Others are suffering near collapse under water levels outside of forecast. Predicting the amount of electricity that will actually be gained from hydroelectric facilities has become much harder, and is much harder than predicting electricity from wind or solar. Forecasts need to be looked at carefully to ensure that the error bars are understood, especially with assets built where the global warming benefits don’t start accruing for 30 years.
Remoteness: All of the locations anywhere near large electricity requirements have already been dammed or deemed unfit for damming. All of the remaining places are either much more remote and expensive to exploit or come with massive downsides that prevent them from being built outside of China with its Three Gorges project or the ill-considered Amazon dams of Brazil